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Space Time explores the outer reaches of space, the craziness of astrophysics, the possibilities of sci-fi, and anything else you can think of beyond Planet Earth.
2015
We've run, jumped, and stomped all over the world of Super Mario, but, where in the universe is Super Mario EXACTLY? It's virtual so it obviously DOESN'T exist, but if it did, could Super Mario world be in our solar system? And what do the planet's dynamics reveal about Mario's crazy jumping ability? Join Gabe as he takes us on a rick-roaring tour of our known universe as we search for the answer in this week's SpaceTime!
Aliens! Could humans really be alone in this expansive universe? And if we're not, how come we've never made contact with other intelligent life? Everyone's thought about it; especially members of the scientific community. Join Gabe as he presents some of the most popular theories that scientists use to rationalize their support or skepticism of the existence of aliens. We may never know the answer to this age old question, but a little scientific thinking never hurt anybody!
The universe is HUGE. But, there is only so much of the universe we can ACTUALLY see, and if we wanted to measure that FINITE space, how would we do it? A gigantic ruler? One really long car ride? Or maybe it's something even more spectacular, something that involves not only the observable universe as it is NOW, but how it was when it was first BORN?
Mars One. The Mars Rover. Bruno Mars. Mars Bars. It's pretty clear we're OBSESSED with the idea of Mars, especially in regard to it being a potential colony for earthlings. But is that really the best option? Is there a better place for us to colonize in our solar system? Well, how about Venus? Sure the surface temperature is over 450 degrees Celsius, with crazy pressure, but there might be a smart way around that, making Venus a better option for long term colonization than Mars!
Killing all the life on Earth is easy. But what about destroying the planet itself? That is DEFINITELY going to happen!! But HOW? Could it be Nukes? A Giant Asteroid? A Collision with another planet? And what’s more, will anyone be around to actually watch the world reach its ultimate demise?
DO A BARREL ROLL! Or at least, try…? The iconic move from Star Fox seems so easy, just press a button and BOOM. The ship rolls. But HOW? Barrel rolls in atmosphere are easy to execute with the use of ailerons, but in space, it's a different issue altogether. With no atmosphere (and no thrusters), how does one Barrel Roll like Star Fox in space?
HAS SPACE ALWAYS BEEN BLACK? As long as we've been around, YES. But the universe gets much more exciting, AND much BRIGHTER, as we start winding our clocks back to the early days of the universe. Near the beginning of the universe, when space was rapidly expanding, that dark night sky we know so well as actually…ORANGE! But why? Did the lights just go out, or did something more spectacular happen?
Is Link in Majora's Mask actually being overseen by a Black Hole (with teeth)? It's easy to take things at face value in video games. But when we take a deeper dive into the physics in The Legend of Zelda: Majora's Mask, it seems that the "MOON" might be one of those things that isn't quite what it seems. Given its size and the way it affects Termina, it actually appears that the moon is really a BLACK HOLE! Is that seriously the only possibility? What is the evidence that supports this theory?
Listen, we know you've thought about it, and we're here to give you THE DEFINITIVE ANSWER to one of the greatest science questions of all time. How long would it take to get to the MOON by farting?
EVER WANTED TO WEIGH A FART? Well, it isn't easy, but walk through the math, physics, and science behind farts and how to measure them!
Last time we talked about what curvature means, looked at geodesics, great circles on spheres, and tried to understand the notion of "straightness". This week on Spacetime, we take a detour into how geometry works in spacetime. Get excited, because this episode is even more mind-bending than the last!
We all know tides have something to do with gravity from the Moon and Sun, but if gravity affects the motion of all objects equally, then how come oceans have large tides while other bodies of water don't? It's because your mental picture of the tides is probably WRONG!!! Join Gabe on this week’s episode of PBS Space Time as he sets the record straight on tidal force, gravitational differential and what role the moon actually plays in tides. Why don't lakes have tides? Watch the episode to find out!
Lots of people believe the Universe is infinite, but there's a good possibility that might not be the case. Which means that there would be an actual edge of the Universe. What happens at that edge? Is there a restaurant? Join Matt on this week’s episode of Space Time as he explores the greatest expanses of our Universe. So what do you find when you reach the edge? More Universe? Bubble Universes? Back where you started?! Check out this episode of Space Time to find out!
2015
We've run, jumped, and stomped all over the world of Super Mario, but, where in the universe is Super Mario EXACTLY? It's virtual so it obviously DOESN'T exist, but if it did, could Super Mario world be in our solar system? And what do the planet's dynamics reveal about Mario's crazy jumping ability? Join Gabe as he takes us on a rick-roaring tour of our known universe as we search for the answer in this week's SpaceTime!
2021
Since the very beginning of quantum mechanics, a debate has raged about how to interpret its bizarre predictions. And at the heart and origin of that debate is the quantum jump or quantum leap - the seemingly miraculous and instantaneous transitions of quantum systems that have always defied observation or prediction. At least, until now.
2025
Dark matter has eluded us for many decades. Even our most advanced particle colliders and sophisticated underground detectors have come up short. But it may be that we can finally solve this mystery with a much simpler experiment, involving a ray of light, a good clock, and the planet Mars.
Today we’re going to delve into a couple of the most famous paradoxes of special relativity: the Twin Paradox, The Ladder Paradox (aka the Barn-Pole Paradox), and a paradox suggested by our very own viewers, which asks whether a spaceship could wrap around the universe & destroy itself. We’ll explore these paradoxes and see why, against our intuition, the universe really does work in this seemingly nonsensical way. But the point of this episode is to go much further - we’re going to try to break the universe by pushing these paradoxes beyond the limit.
Dark Matter Particles: Gateway to The Dark Universe
There’s a deep connection between gravity and time - gravitational fields seem to slow the pace of time in what we call gravitational time dilation. And today we’ll explore the origin of this effect. And ultimately, we’ll use what we learn to understand how curvature in time - this gradient of time dilation - can be thought of as the true source of the force of gravity.
It was pretty impressive when LIGO detected gravitational waves from colliding black holes. Well we’ve just taken that to the next level with a galaxy-spanning gravitational wave detector that may have detected a foundational element of space itself - the gravitational wave background.
We know that gravity must cause clocks to run slow on the basis of logical consistency. And we know that gravity DOES cause clocks to run slow based on many brilliant experiments. But I never explained WHY or HOW gravity causes the flow of time to slow down. And I’m not going to explain it now - because in a sense it’s not true. Gravity does NOT warp the flow of time. It’s the other way around - the warping of time causes gravity.
We know that gravity exerts its pull on light, and we have an explanation for why. Actually, we have multiple explanations that all predict the same thing. And at first glance, these explanations seem to describe completely different causes. So what is the true connection between light and gravity, or is truth, in fact, entirely relative?
I have good news and bad news. Bad news first: two years ago we reported on the Crisis in Cosmology. Since then, it’s only gotten worse. And actually, the good news is also that the crisis in cosmology has actually gotten worse, which means we may be onto something! The most exciting thing for any scientist is when something they thought they knew turns out to be wrong. So it’s no wonder that many cosmologists are starting to get excited by what has become known as the Hubble tension, or the crisis in cosmology. The “crisis” is the fact that we have two extremely careful, increasingly precise measurements of how fast the universe is expanding which should agree with each other, and yet they don’t.
“A moving arrow is at rest.” This is obviously a nonsensical contradiction. But Zeno, a Greek philosopher famous for his metaphysical trolling, devised a paradox whose conclusion is just this. Here’s how it goes: if you look at an arrow flying through the air at any instantaneous snapshot in time, the arrow doesn’t travel any distance. If time is composed of an infinite number of these snapshots, and the arrow doesn’t move in any of them, then the arrow is at rest during the entirety of its flight. The moving arrow is at rest.
When a theory makes a prediction that disagrees with an experimental test, sometimes it means we should throw the theory away. But what if that theory has otherwise produced the most successful predictions in all of physics? Then, that little glitch may be pointing the way to layers of physics deeper than we've yet imagined. Well, FermiLabs Muon G-2 experiment has been chasing the most promising glitch of all, and they've just announced their results
It may be that for every star in the universe there are billions of microscopic black holes streaming through the solar system, the planet, even our bodies every second. Sounds horrible - but hey, at least we’d have explained dark matter.
That Einstein guy was a real bummer for our hopes of a star-hopping, science-fiction-y future. His whole “nothing travels faster than light” rule seems to ensure that exploration of even the local part of our galaxy will be an excruciating slow. But Einstein also gave us a glimmer of hope. He showed us that space and time can be warped - and so the warp drive was conceived. Just recently, a couple of papers contend that these are not pure science fiction.
There’s one rule on Space Time: It’s never Aliens. But every rule has an exception and this rule is no exception because: It’s never aliens, until it is. So is it aliens yet? And on today’s Space Time we’re going to examine all the best case scenarios for life beyond Earth.
Quantum mechanics forbids us from measuring the universe beyond a certain level of precision. But that doesn’t stop us from trying. And in some cases succeeding, by squeezing the Heisenberg uncertainty principle to its breaking point.
It’s fair to say that black holes may be the scariest objects in the universe. Happily for us, the nearest is probably many light-years away. Unless of course, Planck relics are a thing - in which case they might be literally everywhere.
While recent news about the Chinese Long March 5 Rocket made a lot of people very nervous because a 22-ton rocket was going to fall out of the sky, this sort of thing happens all the time. Boosters, dead satellites, and sometimes even old space stations get dropped out of the sky fairly often. While the litter seems a little inconsiderate, this is probably far safer than the alternative. The accumulation of space junk poses a huge risk to all human operations in space especially if we cross the threshold into the chain reaction of exponentially growing collisions known as the Kessler Syndrome.
How many times can I half the distance between my hands? Assume perfect coordination and the ability to localize my palms to the quantum level. 15 halvings gets them to within a cell’s width. 33 to within a single atom, 50 and they’re a proton’s width apart. Half the distance 115 times and they’re a single Planck-length apart - 1.6x10^-35 meters. Surely we can keep going - .8, .4, .2 x10^-35 m? Bizarrely, those distances might not even exist in any meaningful way.
Entropy is surely one of the most perplexing concepts in physics. It’s variously described as a measure of a system’s disorder - or as the amount of useful work that you can get from it - or as the information hidden by the system. Despite the seeming ambiguity in its definition, many physicists hold entropy to be behind one of the most fundamental laws of physics.
Quantum mechanics has a lot of weird stuff - but there’s thing that everyone agrees that no one understands. I’m talking about quantum spin. Let’s find out how chasing this elusive little behavior of the electron led us to some of the deepest insights into the nature of the quantum world.
Many Worlds interpretation of quantum mechanics proposes that every time a quantum event gets decided, the universe splits so that every possible outcome really does occur. But where exactly are those worlds, and can we ever see them?
How far can you follow a compass needle? As far as the north magnetic pole where the needle starts spinning wildly? Compass needles align with magnetic field lines; and on the precise spot of magnetic north, those field lines are vertical. So just tilt your compass 90 degrees and you can continue your journey: either down to the molten iron dynamo surrounding Earth's core; or up. But up to where? The answer: to everywhere. And today that's exactly where we're going to go.
A new white dwarf has been discovered (poetically named: ZTF J1901+1458) that’s doing some stuff that no white dwarf should ever be able to do. In fact, it has multiple properties that are so extreme that it almost certainly did NOT form in the way that we thought all white dwarfs formed. This one peculiar point of faint light may change our understanding of not just white dwarfs, but of all cosmology.
In the Many Worlds interpretation of quantum mechanics, the universal wavefunction is the reality, encompassing all possible histories and futures and all exist. But we are only sensitive to a slice of the wavefunction corresponding to our “world”, and due to the superposition principle our world can happily do its thing unperturbed by other parts of the wavefunction - other “ripples,” or worlds. And while it may seem like it would be physically impossible to have any connection between worlds, it may turn out to be entirely possible to communicate between them.
The universe is going to end. But of all the possible ends of the universe vacuum decay would have to be the most thorough - because it could totally rewrite the laws of physics. Today I hope to help you understand exactly how terrified you should be.
How do you see the unseeable - how do you explore the inescapable? Our cleverest astronomers have figured out ways to catch light that skims the very edge of black holes. Let’s find out what they learned.
We’ve traveled to lots of weird places on this show - from the interiors of black holes to the time before the big bang. But today I want to take you on a journey to what has got to be the weirdest place in the modern universe - a place where matter exists in states I bet you’ve never heard of. Today we take a journey to the center of the neutron star.
Today I’m going to explain why you’re not falling through your chair right now using one simple fact, and one object. The fact is that all electrons are the same as each other, and the object is a structurally critical item of my clothing. There’s a chance this episode could get very weird.
What happens if you cut a bar magnetic in half? We get two magnets, each with their own North and South poles. But what happens if you keep on cutting, into fourths and eighths and sixteenths and so on? Will we ever get to a single pole? I’ll spoil the answer for you: we don’t know! But the idea of magnetic monopoles remains one of physics’ most tantalizing maybes.
Paradoxically, the most promising prospects for moving matter around faster than light may be to put a metaphorical brick wall in its way. New efforts in quantum tunneling - both theory and experiment - show that superluminal motion may be possible, while still managing to avoid the paradox of superluminal signaling.Paradoxically, the most promising prospects for moving matter around faster than light may be to put a metaphorical brick wall in its way. New efforts in quantum tunneling - both theory and experiment - show that superluminal motion may be possible, while still managing to avoid the paradox of superluminal signaling.
The people behind the greatest leaps in physics - Einstein, Newton, Heisenberg, all had the uncanny ability to see the fundamentals - see the deepest, underlying facts about the world, and from simple statements about reality they built up their incredible theories. Well what if we all had a recipe book for doing exactly this. Well, one might be just around the corner and it’s called Constructor Theory.
It’s about time we discussed an obscure concept in physics that may be more fundamental than energy and entropy and perhaps time itself. That’s right - the time has come for Action.
What if there is no such thing as dark matter? What if our understanding of gravity is just wrong? New work is taking another shot at that Einstein guy. Let’s see if we’ve finally scored a hit with Modified Newtonian Dynamics aka MOND.
Black holes are a paradox. They are paradoxical because they simultaneously must exist but can’t, and so they break physics as we know it. Many physicists will tell you that the best way to fix broken physics is with string. String theory, in fact. And in the black holes of string theory - fuzzballs - are perhaps even weirder than the regular type.
The possibility that a black hole could actually impact Earth may seem straight out of science fiction, but the reality is that microscopic primordial black holes could actually hit Earth. If one did, it wouldn't just impact like an asteroid, it'd pass straight through the entire Earth and exit the other side. Perhaps craziest of all, this may have already happened!
On our search for alien lifeforms we scan for primitive biosignatures, and wait and hope for their errant signals to happen by the Earth. But that may not be the best way. Any energy-hungry civilization more advanced than our own may leave an indisputable technological mark on the galaxy. And yes, we’re very actively searching for those also. Time to update you on the hunt for galactic empires.
The universe is expanding and that expansion is accelerating under the power of dark energy and eventually all matter and energy will be dispersed over such unthinkable distances that nothing can stop space from blowing up infinitely. Unless of course cosmologists blundered and dark energy doesn't even exist. Then it's back to the drawing board.
According to quantum physics, the universe should have collapsed on itself in the instant after the Big Bang due to all particles being 100 million billion times heavier. Recent observations of the universe existing suggest that this may not have happened. Even more recent experiments at the Large Hardron Collider have failed to find out why. In particular, why the Higgs boson is light enough to allow the universe to exist. This is part of something known as the hierarchy problem, and some consider it to be the most important unsolved problem in physics.
They say fusion is 50 years away, no matter when you ask. Then why are billions suddenly being pumped into fusion startups? Yes to train LLMs, but there's a reason the technobrats are bullish on fusion in particular. The fact is, the technological challenges have been chipped away and in many cases solved over the past decades, and there's really no one deal-breaker difficulty remaining. One of the final challenges is deciding on the physical vessel to contain our mini artificial stars--and we have some pretty sci-fi options that are nearly ready to go.
How did the universe begin? How can something come from nothing? One way to “solve” this most difficult of philosophical conundrums is to avoid it altogether. Maybe the universe didn’t begin. Maybe the Big Bang was just one in an endless cycle.
Did you know that many of us have up to 4% neanderthal DNA? And that 100% of your DNA may come from outer space? No joke. The biochemistry that defined the coding system of your DNA may have happened off-world, and perhaps even long before Earth existed.
Giant space rocks are definitely going to hit the Earth again. We actually do know how to deflect them, but only if we find them and correctly assess their risk. But the solar system is a chaotic place. How is it even possible to tell if a space rock will one day collide with the Earth?
Planet Earth is the jewel of the solar system—the shimmery blue oceans, the verdant green forests, the wispy whimsical cloud formations. Saturn is the only competitor for most gorgeous planet with that giant ring system. Hmm… what if we could put the jewel of the Earth in its own ring? Then no contest. Well, there’s an extremely good chance that Earth once DID have a ring system. At least, that’s the proposal by a recent study that has evidence that a mysterious burst in meteor activity nearly half a billion years ago was actually caused by that ancient ring system collapsing onto the Earth. And, you know, if we had a ring once maybe we can have one again.
At one-one-thousandth of a second after the Big Bang, the great annihilation event should have wiped out all matter, leaving a universe of only radiation. Why still don't know why any matter survived. Well, a new finding from the LHC brings us one step closer to understanding why there's something rather than nothing.
The vacuum of space is a chaotic sea of quantum fluctuations. Some have said that this vacuum energy can be harvested to build our future starship engines, or manipulated to build warp drives. It can't. But it is technically possible to move real energy through the quantum vacuum without it passing through intervening space. Quantum energy teleportation may be as close as we get to transporter beams. But how close is that?
Around 2 billion years ago, life had plateaued in complexity, ruined the atmosphere, and was on the verge of self-annihilation. But then something strange and potentially extremely lucky happened that enabled endless new evolutionary paths. The first eukaryote cell was born. This may also explain why there are no aliens.
The biggest news in cosmology in recent years is that the mysterious universe-accelerating entity we call dark energy may be fading away. The evidence for this is now strong enough that enormous effort is going into confirming this result. So what’s it going to take, and when are we going to know?
Big things are made of smaller things, and those smaller things are made of smaller things still. That’s reductionism in a nutshell, and digging our way to the smallest layer has been one of the primary goals of physics for ever. But what if, just before we reach the bottom, we find out that reductionism fails?
Did God have any choice in creating the world? So asked Albert Einstein. He was being poetic. What he really meant, was whether the universe could have been any other way. Could it have had different laws of physics, driven by different fundamental constants. Or is this one vast and complex universe the inevitable result of an inevitable and unique underlying principle, perhaps expressible as a supremely elegant Theory of Everything. It certainly seems that Einstein thought this should be the case … that God had no choice in whether or how to create the world. It seems like a pretty arm-chair philosophical and perhaps unanswerable question, but the modern “problem” of naturalness may lead to an answer.
The molecular basis of all life is mysteriously asymmetric, only using molecules on one side of what should be the equivalent mirrored pairs. The universe has a similar mirror asymmetry, and it may be that our very DNA inherited its twist from the underlying handedness of reality.
The multiverse pops out of quite a few theories in physics, and has been proposed as a solution to certain vexing problems. But it’s also been argued that the very idea of a multiverse is just bad science. That it’s unfalsifiable and a dead-end to inquiry and as bad a violation of Occam’s razor as you could imagine. But the multiverse might also exist. Can something that exists be bad science?
In 1987, Steven Weinberg wrote a cute little paper entitled “Anthropic Bound on the Cosmological Constant”. I say cute little paper because it feels minor in comparison to, say, electroweak unification theory that won him the Nobel Prize. Weinberg was foundational in establishing the standard model of particle physics, and represented an enormous leap in understanding how this universe works. But his little 1987 paper, though more obscure, may tell us something about how the multiverse works, and can even be thought of as evidence for the existence of an enormous number of other universes.
One of the most important reasons we go to space is to know our own planet better. Today I'm going to tell you about an orbiting facility that literally watches Earth's biosphere breath and grow and die with incredible resolution. I'll talk about its profound existential and economic importance, and about why it's in danger of being lost.
To observe the quantum nature of gravity and of spacetime itself, we need a particle collider the size of the solar system. Or we could just physics smarter and build one on a lab bench. Here’s how.
Recent findings have brought us closer than we’ve ever been to confirming life beyond the Earth. As we wait for confirmation or otherwise, let’s think about what this will tell us about life everywhere, and also about our own imminent destruction.
Does quantum mechanics allow the future to retroactively influence the past, as in the infamous delayed choice quantum eraser experiment? How about we get an actual quantum physicist--who many of you already know--to show us how to do this experiment at home, and hopefully set this matter to rest.
Antimatter drives sound like science fiction, but they may not be as far as you think. There’s a version that could, just maybe, launch within your lifetime.
Physics is this close to understanding the entire universe. And what lives in this gap? Many physicists think it’s the elusive graviton—the quantum particle of gravity—whose discovery will finally allow us to stitch together our two great theories of nature into a single master theory. But what is the graviton, and does it even exist?
There are lots of reasons to search for planets around other stars—exoplanets. A big one is to find other places in the universe that might harbor life. We only know of one such planet so far: Earth. And so we get particularly excited when we find Earth-mass planets at the right distance from their star to sustain liquid water—also critical for life as we know it. We’ve found lots of those “habitable” worlds. But we also don’t know what factors are really critical to the initial development of life. Maybe star type? We get even more excited if that Earth-mass at the right distance from a Sun-type star. We’ve found a few of those too, and we can infer that there are lots more.
2025 is … was the international year of quantum science and technology. Yes because quantum tech is increasingly important, but especially because quantum mechanics was invented 100 years ago this year. In 1925, our strangest true theory went from being a peculiar set of ideas to describe some funny results from experiments, to a full-blown theoretical framework that overturned how we think reality really works. So today, as the centenary year approaches its end I want to take you on a little journey through what may be the most paradigm-destroying several months in scientific history.
2016
We know that mass is energy… but what is energy? And where did matter and time even come from? Matt begins to dive into these intricate topics by first examining what inertial mass is, how it relates to gravitational mass, and what it all means for mass as a fundamental property.
The Kepler telescope recently noticed a strange partial eclipse that some have speculated could be a Dyson Sphere. Are Dyson Sphere's possible? Are they practical? What other alternatives to futuristic energy capture do we have to choose from? Why not a kugelblitz - a swarm of black hole powered engines?
We’ll soon be capable of building self-replicating robots. This will not only change humanity’s future but reshape the galaxy as we know it.
Albert Einstein strongly disagreed with Niels Bohr when it came to Bohr’s interpretation of quantum mechanics. Quantum entanglement settled the argument once and for all.
The Hubble Telescope found more evidence of vast plumes of water bursting through the icy surface of Jupiter’s moon Europa. What does this tell us about the potential for life on Europa?
The Drake Equation tells us the likelihood that there are other advanced technological civilizations waiting for us among the stars. In this episode of Space Time we challenge you to use the Drake Equation to help us determine how near or far these alien races may be. Links to reference material below.
Primordial black holes may be lurking throughout our universe. How large are they, how many are out there and what would happen if they moved through our solar system?
Elon Musk’s SpaceX program proposes that 100 people could be sent to colonize Mars within 10 years. What might that colony look like?
Is our universe a definitive single reality or is it merely one within an infinitely branching multiverse?
Are aliens watching Earth TV? We'd like to credit the SKA Organization for the image used in the thumbnail.
2017
Find out how scientists are mapping the black holes throughout the Milky Way and beyond as well as the answer to the Escape the Kugelblitz Challenge Question. Were you able to save humanity?
Because you demanded it … we break down the EM Drive!
Isaac Newton’s Universal Law of Gravitation tells us that there is a singularity to be found within a black hole, but scientists and mathematicians have found a number of issues with Newton’s equations. They don’t always accurately represent reality. Einstein’s General Theory of Relativity is a more complete theory of gravity. So does using the General Theory of Relativity eliminate the singularity? No. Not only does it concur with Newton’s Universal Law of Gravitation but it also reveals a second singularity, not at the center of the black hole but at the event horizon.
When Quasars were first discovered the amount of light pouring out of such a tiny dot in space seemed impossible. A hysterical flurry of hypothesizing followed: swarms of neutron stars, alien civilizations harnessing their entire galaxy’s power, bright, fast-moving objects being ejected by our own galaxy’s core. But by the 1980’s we were converging on the most awesome explanation. It goes a little like this: Take a black hole of millions to billions times the mass of the sun. Where from? It turns out every decent-sized galaxy has one at its core. Now drive gas into the galactic core. One way this can happen is when galaxies merge and grow. That gas descends into the waiting black hole’s gravitational well and gains incredible speed on the way. It is swept up in a raging whirlpool around the black hole that we call an accretion disk, where its energy of motion is turned into heat. The heat-glow of the accretion disk is so bright that we can see quasars to the ends of the universe.
In this episode we dive deeper into the relationship between space and time and explore how we can geometrically map the causality of the universe and increase our understanding of how time and distance relate to one another.
Fomalhaut is a massive young star surrounded by a ring of dust debris that can tell us a great deal about the formation of our own solar system.
Can humanity survive on one of the seven earth-like Trappist-1 planets? Last week, seven earth-like planets were discovered orbiting a Red Dwarf star 39 light years away. Each one could be capable of supporting life.
You’ve discovered a habitable exoplanet, but so has an an evil interplanetary mining corporation. Can you get to the planet before they strip it bare and leave it unsuitable for life? You’re going to need a ship, the Lorentz Transformation and the Wait Equation. Hang on, it’s going to be a bumpy ride.
In this episode of the Space Time Journal Club Matt discusses how two independent research teams created their own Time Crystals, a form of matter that breaks time translational symmetry and could be used in quantum computers.
Find out how traveling faster than light and traveling back in time are the same thing.
Find out how time and space switch roles when we move beyond the event horizon of the black hole.
Find out about China’s current telescope on the moon and what the future plans are for mounting larger telescopes on the lunar surface.
In 1991 a single atomic nucleus slammed into our atmosphere with the intensity of a macroscopic object. It’s been named The Oh My God Particle.
Was an incredible drop in entropy responsible for the Big Bang? If that’s the case, this would lead us to conclude that a great many other things are possible, including the likelihood that you are a Boltzmann Brain.
Neil deGrasse Tyson sits down with Matt to discuss Ancestor Simulations. And check out Matt and Neil discussing how sure we are about our map of the universe
The first total solar eclipse in over 40 years is about to hit the United States.
What will become of humanity after spend a few hundred years on Mars? What will happen after a few thousand? Evolution has, and still is, shaping humanity in rather drastic ways. How long will humans stop being human and become Martian?
Soon after the Big Bang, the first generation of monstrously large stars ignited, lit up the universe, and then died. The resulting swarms of supernova explosions enriched the universe with the first heavy elements and LOTs of black holes. They shaped everything that came after. These were the stars of Population III, and they are one of the most enduring mysteries in astrophysics.
If you study a map of the Cosmic Microwave Background, or CMB, you may notice a large, deep blue splotch on the lower right. This area, creatively named the Cold Spot. Is this feature a statistical fluke, the signature of vast supervoids, or even the imprint of another universe?
Paul Dirac’s insights into the nature of Quantum Mechanics laid the foundation for Quantum Field Theory and predicted the existence of anti-matter.
Quantum mechanics is perhaps the most unintuitive theory ever devised. And yet it’s also the most successful, in terms of sheer predictive power. Simply by following the math of quantum mechanics, incredible discoveries have been made. Its wild success tells us that the mathematical description provided by quantum mechanics reflects deep truths about reality. And by far the most successful, most predictive formulation of quantum mechanics is quantum field theory. It is our best description we have of the fundamental workings of reality. And the first part of quantum field theory that was derived – quantum electrodynamics – is the most precise, most accurate of all.
How to predict the path of a quantum particle. Part 3 in our Quantum Field Theory Series.
How do you calculate infinite quantum outcomes? Feynman Diagrams.
Anti-Satellite weaponry, giant X-ray lasers and kinetic impact missiles nicknamed the “Rods from God.” Find out about the history of the real star wars that have been waged over the past 50 years.
Unlock the secrets of Feynman Diagrams. Part 5 in our Quantum Field Theory series. And if you're submitting an answer to our challenge question email your answer by August 2nd to pbsspsacetime@gmail.com with the subject line "Feynman Diagram Challenge."
Why does the universe seem to be moving in one particular direction?
Could it be that all the electrons in the universe are simply one, single electron moving back and forth through time?
Earth has its share of monster storms, but even our most powerful hurricanes are a breeze compared to the great, planet-sized tempests of the gas giants.
What does life look like from space?
Black holes are very well known but... What is a White Hole?
LIGO may have just detected gravitational waves from the collision of two Neutron Stars.
The mysteries of our universe seem limitless. However to unlock them, we’re going to need some incredible technologies to peer deeper and more sharply into space time.
The laws of physics are the same everywhere in the universe. At least we astrophysicists hope so. After all, it’s hard to unravel the complexities of distant parts of the universe if we don’t know the basic rules. But what if this is wrong? There is a hint of evidence that the fundamental constants that govern our universe may evolve over time, and even from one location to another.
So what happens when two Super Massive Black Holes collide? We may be about to find out, because astronomers have spotted a pair of them in a close binary orbit for the very first time.
Can we ever achieve absolute cold?
It turns out that "nothing" is one of the most interesting somethings in all of physics.
For years, astronomers have been unable to find up to half of the matter in the universe. We may just have solved this problem. Fingers crossed.
If vacuum energy really does have the enormous value predicted by quantum field theory then our gently expanding, geometrically flat universe shouldn’t exist. This is the vacuum catastrophe.
Let’s talk about the mysterious zero-point energy and what it really can, and really can’t do.
Let’s take a moment to remember the selfless sacrifices made by some amazing robotic explorers. And be sure to learn more about your personal DNA story by going to 23andMe.com/spacetime and taking advantage of their special holiday offer.
The future of science is you.
Sometimes intuitive, large-scale phenomena can give us incredible insights into the extremely unintuitive world of quantum mechanics.
We were recently visited by a traveler from outside our solar system. This is the first time we’ve ever seen an object that came to us from interstellar space. It's name is 'Oumuamua.
Find out about the last time and the next time the Earth will be hit by a Gamma-ray Burst.
2022
If you used every particle in the observable universe to do a full quantum simulation, how big would that simulation be? At best a large molecule. That’s how insanely information dense the quantum wavefunction really is. And yet we routinely simulate systems with thousands, even millions of particles. How? By cheating. Using the ultimate compression algorithm: Density Functional Theory (DFT). Let’s learn how to cheat the universe.
We routinely simulate the universe on all of its scales, from planets to large fractions of the cosmos. Today we’re going to see how it’s possible to build a universe in a computer - and see whether there’s a limit to what we can simulate.
Fact: in a black hole, all of the mass is concentrated at the singularity at the very center. Fact: every black hole singularity is surrounded by an event horizon. Nothing can escape from within the event horizon unless it can travel faster than light. Fact: gravity travels at the speed of light. So how does a black hole manage to communicate its gravitational force to the outside universe? How does gravity escape a black hole?
Objective Collapse Theories offer a explanation of quantum mechanics that is at once brand new and based in classical mechanics. In the world of quantum mechanics, it’s no big deal for particles to be in multiple different states at the same time, or to teleport between locations, or to influence each other faster than light. But somehow, none of this strangeness makes its way to the familiar scale of human beings - even though our world is made entirely of quantum-weird building blocks. The explanations of this transition range from the mystical influence of the conscious mind to the grandiose proposition of multiple realities. But Objective Collapse Theories feels as down to earth as the classical world that we’re trying to explain. Let’s see if it makes any sense.
Reality has cracks in it. Universe-spanning filaments of ancient Big Bang energy, formed from topological defects in the quantum fields, aka cosmic strings. They have subatomic thickness but prodigious mass and they lash through space at a close to the speed of light. They could be the most bizarre undiscovered entities that actually exist.
At just four light years away, Proxima Centauri is our closest solar neighbor. The recent discovery of the new exoplanet Proxima D, has reopened the discussion of whether the proxima system is our best chance at reaching another Earth. How did we discover Proxima D? How do we know what the conditions are on planets so far away? Watch the episode to learn more.
If you've studied any physics you know that like charges repel and opposite charges attract. But why? It's as though this thing - electric charge - is as fundamental a property of an object as its mass. It just sort of ... is. Well it turns out if you dig deep enough, the fundamental-ness of charge unravels, and in many things, including mass itself, are unraveled with it.
Today we’re going to ask a simple-seeming question that will lead to so pretty wacky places. The question is this: If the universe has a center, where is it?
What is inside a black hole? Inevitable crushing doom? Gateways to other universes? Weird, multidimensional libraries? If you’ve ever wanted to know then you might be in luck - Some physicists have argued that you’re inside one right now.
Imagine you’re leading a game of 20 questions and you forget the thing you chose half way through. You have to keep answering yesses and nos and hope that you think of something that’s consistent with all your previous questions before the game is done. Well it could be that’s what the entire universe is doing. I hope it thinks of something good before we run out of questions.
Fermilab physicists really care about the mass of the W boson. They spent nearly a decade recording collisions in the Tevatron collider and another decade analysing the data. This culminated in the April 7 announcement that this obscure particle’s mass seems to be heavier than expected. So why do we care? Because understanding why this particle even has mass was one of the most important breakthroughs in our understanding of the subatomic world. And because measuring its precise mass either doubles down on our current understanding or reveals a path to an even deeper knowledge. The FermiLab discrepancy is a tantalizing hint of the latter.
Space is big, and it’s getting bigger. But where does all that new space actually come from? And is it popping into existence all around you right now? Is that why the remote control is always further away than I thought?
Our solar system is a tiny bubble of habitability suspended in a vast universe that mostly wants to kill us. In fact, a good fraction of our own galaxy turns out to be utterly uninhabitable, even for sun—like stellar systems. Is this why .. most of us .. haven’t seen aliens?
When we scan the heavens with giant telescopes we see galactic cannibalism everywhere. We see moments that appear frozen on the human timescale, but are really snapshots of the incredibly violent process of galaxy formation. This is how all galaxies are made. We can piece together a pretty good understanding of this process from countless snapshots. Looking into the distance means looking into the past, so it’s possible to stitch together a Frankenstein flip book of galaxy evolution.
Neils Bohr said, “It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we can say about Nature.” Well it turns out that if we pay attention to this subtle difference, some of the most mysterious aspects of nature make a lot more sense.
Black holes are very real, but are also a theoretical nightmare. It turns out that in order to make sense of their paradoxical nature, every black hole has to be thought of as a multitude of imaginary black holes, all connected by wormholes. And you thought the universe couldn’t get any weirder.
Space is pretty deadly. But is it so deadly that we’re effectively imprisoned in our solar system forever? Many have said so, but a few have actually figured it out.
How hard can it really be to decode alien physics and engineering? It’s gotta map to our own physics - I mean, we live in the same universe. We start by noticing that the alien technology seems to use good ol’ fashioned electronics, even if it is insanely complex. We know this because the particle carried by the alien circuitry looks like the electron. We decide this through a process of elimination.
Today we’re going to try to save reality - or at least realism. However this rescue effort has a price; one that you may not be willing to pay. Your very soul, or at least your free will, is on the line.
Let’s talk about states of matter. You know your states of matter don’t you? We have solids, liquids and gasses, and plasmas, quark-gluon plasmas, nuclear matter, bose-einstein condensates, neutronium, time crystals, and sand. Come to think of it, maybe I don’t know my states of matter. Or what a state of matter even is. Let’s see if we can figure it out.
If we ever want to simulate a universe, we should probably learn to simulate even a single atomic nucleus. But it’s taken some of the most incredible ingenuity of the past half-century to figure out how that out. All so that today I can teach you how to simulate a very very small universe.
What is Quintessence? Well we know that something is up with the way the universe is expanding - there’s some kind of anti-gravitational effect that’s causing the expansion to accelerate. We don’t know what it is - just that it competes against the inward-pulling effect of gravity. And it’s winning - it looks like the universe will expand forever, at an ever-increasing rate. We call this mysterious influence dark energy, but while we’ve talked a lot about how it behaves, we’ve never really explored what it is. So, what is dark energy, really?
Original Title: Why Isn’t The Nucleus Ripped Apart? Quantum mechanics gets weirder as you go to smaller sizes and higher energies. It’s strange enough for atoms, but positively bizarre when we get to the atomic nucleus. And today we’re going nuclear, as we dive into the weird world of quantum chromodynamics and the strong force.
The discovery of the Higgs boson ten years ago in the Large Hadron Collider was the culmination of decades of work and the collaboration of 1000s of brilliant and passionate people. It was the final piece needed to confirm the standard model of particle physics as it now stands. There are still many outstanding questions - for example, it seems like nothing in the standard model can explain what dark matter is. So the discovery of the Higgs wasn’t the end of particle physics - but it may be the way forward. Many physicists think that the secret to finding the elusive dark matter particle will come by studying the Higgs. In fact, the first tantalizing evidence is already in.
You’ve probably heard about the James Webb Space Telescope and seen some cool pictures. But why should astronomers have all the fun? How do we get to use this new toy ourselves?
The Fine Structure Constant is one the strangest numbers in all of physics. It’s the job of physicists to worry about numbers, but there’s one number that physicists have stressed about more than any other. That number is 0.00729735256 - approximately 1/137. This is the fine structure constant, and it appears everywhere in our equations of quantum physics, and we’re still trying to figure out why.
I’m going to tell you about the craziest proposal for an astrophysics mission that has a good chance of actually happening. A train of spacecraft sailing the sun’s light to a magical point out there in space where the Sun’s own gravity turns it into a gigantic lens. What could such a solar-system-sized telescope do? Pretty much anything. But definitely map the surfaces of alien worlds.
The Nobel prize in physics is typically awarded to scientists who make sense of nature; those whose discoveries render the universe more comprehensible. But the 2022 Nobel has been awarded to three physicists who revealed that the universe is even stranger than we thought thanks to Quantum Entanglement
Half of the universe is filled with expansionist alien civilizations, and it’s only a matter of time before they’ll reach us. OK, that sounded a little sensationalist. But it’s also the conclusion of a recent astrophysics paper. Let’s see how they figure this, and whether we should take it seriously.
Adamantium, bolognium, dilithium. Element Zero, Kryptonite. Mythril, Netherite, Orichalcum, Unobtanium. We love the idea of fictional elements with miraculous properties that science has yet to discover. But is it really possible that new elements exist beyond the periodic table?
Neutrinos are one of the most bizarre of known particles. Black holes are probably the most bizarre of astrophysical objects. Makes sense we should use one to study the other, no? Well, today we’re doing just that.
The device you’re watching this video on is best understood by thinking about positive and negative charges moving around a circuit of diodes and transistors. But the only elementary particle actually flowing in the circuit is the negatively charged electron. And yet those flowing positive charges are there, in the form of a particle you may never have heard of.
Supercritical Fluids are one the strangest states of matter and yet they are found everywhere from Decaf Coffee, to dry cleaning, to the atmosphere of Jupiter. When we think of an exotic state of matter we tend to think of the really weird things that matter can do in extreme circumstances - like how at very high temperatures we get the plasma that the sun is made of, or at extreme densities we get the nuclear matter of neutron stars. But there’s one state of matter - supercritical fluid - that’s not solid, liquid or gas, but is also not confined to extreme or rare environments. In fact, there are planets in our solar system completely covered with oceans of the stuff, and you’ve often been the beneficiary of its powers without even knowing it.
2019
Astronomers are the worst at naming things. Dark energy AND dark matter? Who can remember which is which. But perhaps one astronomer has just fixed it, with a theory that says perhaps actually they are they same stuff.
The foundations of quantum theory rests on its symmetries. For example, it should be impossible to distinguish our universe from one that is that is the perfect mirror opposite in charge, handedness, and the direction of time. But one by one these symmetries were found to be broken, threatening to break all of physics along with them.
The search for a single number: the hubble constant, which is the rate of expansion of our universe, has consumed astronomers for generations. Finally, two powerful and independent methods have refined its measurement to unprecedented precision. The only problem is that they don’t agree. This calls into question some of our most basic assumptions about the universe.
Exotic matter – matter with negative mass - has long been the pipedream of science fiction writers, futurists, and certain rather. . . optimistic researchers. It’s the key to faster than light travel because it’s the only stuff that can curve space in the right way to hold open wormholes and construct warp fields. And if you can travel faster than light you can also travel backwards in time. We’ve been over those already. And we also recently covered a very new use for negative mass: as “dark fluid”, a proposed explanation for both dark matter and dark energy. That episode really got me thinking about the subtleties of negative mass and how it should really behave gravitationally. Turns out it’s complicated, and to answer it we really have to question the very definition of mass.
Invisible to the naked eye, our night sky is scattered with the 100s of billions of galaxies the fill the known universe. Like the stars, these galaxies form constellations – hidden patterns that echo the reverberations of matter and light in an epoch long before galaxies ever formed. These are the baryon acoustic oscillations, and they may hold the key to understanding the nature of dark energy.
Hook up an old antenna to your TV and scan between channels. The static buzz you hear is mostly due to the ambient radio produced by our noisy pre-galactic civilization. But around one percent of that buzz is something very different – it’s the cosmic microwave background radiation – the remnant of the heat-glow released when the hot, dense early universe became transparent for the first time. It sound likes random static, but that buzz contains an incredible wealth of hidden information. It holds the secrets of the universe’s fiery beginning.
Bad ideas come and go in physics. But there’s one bit of nonsense that is perhaps more persistent than all others: the perpetual motion machine. No working perpetual motion machine has ever been experiment verified. All break the laws of thermodynamics. In fact, we classify based on WHICH law of thermodynamics they break. We have perpetual motion machines of the first kind - they violate energy conservation - they pump more energy out than they need to keep running. This includes most of the historical devices. Then there are machines of the second kind - they’re a bit more subtle in their wrongness because break the second law of thermodynamics - extracting energy by reversing entropy. Many modern “free-energy” devices fall into this category. Now the best modern designs are by you - answers to our recent challenge question, which we’ll get to at the end. But first let’s take a look at examples of what other people came up with - this’ll be a fun little journey through some ...
The Future of Space Tourism with Richard Branson The private space-race has been on for a while now. The attention has been on Space-X and Blue Origin with their reusable rockets. But there’s one private space program that’s been doing things a little differently. Richard Branson’s Virgin Galactic isn’t building rockets at all – it’s building spaceships. And I got to sit down and talk to him about it.
The power of Dark Energy may be increasing as the universe ages. Subtle clues are emerging that the accepted model for the nature of dark energy and dark matter may not be all that. We saw the first such clue recently in our recent episode on the Crisis in Cosmology. Today we’re doing a Space Time Journal Club to reveal another clue. We’re looking at a new paper in Nature Astronomy, “Cosmological constraints from the Hubble diagram of quasars at high redshifts” by Risaliti and Lusso. It hints that the cosmological constant may not be so constant after all. In fact it may be increasing. If this is true, then our prediction for the future of our universe looks VERY different, and may involve the entire universe tearing itself to shreds at the subatomic level in the Big Rip.
Of all the unlikely ends of the universe, the Big Rip has to be the most spectacular. Galaxies ripped to shreds, dogs and cat first living together, then tragically separated by the infinitely accelerating expansion of space on subatomic scales. Good thing it's not going to happen. Or is it?
Have you ever asked “what is beyond the edge of the universe?” And have you ever been told that an infinite universe that has no edge? You were told wrong. In a sense. We can define a boundary to an infinite universe, at least mathematically. And it turns out that boundary may be as real or even more real than the universe it contains.
We live in a universe with 3 dimensions of space and one of time. Up, down, left, right, forward, back, past, future. 3+1 dimensions. Or so our primitive Pleistocene-evolved brains find it useful to believe. And we cling to this intuition, even as physics shows us that this view of reality may be only a very narrow perception. One of the most startling possibilities is that our 3+1 dimensional universe may better described as resulting from a spacetime one dimension lower – like a hologram projected from a surface infinitely far away.
We’ve been failing to detect dark matter for decades. Finally, the latest failure to detect dark matter may have actually proved its existence. One of these is true: either most of the matter in the universe is invisible and formed of something not explained by modern particle physics OR our understanding of gravity is completely broken. The debate over which is true has raged for decades, but may finally have been resolved in an unlikely way: the proof that dark matter exists, and really is an exotic, unknown substance, may have come from the discovery of two galaxies that appear to have no dark matter at all. Today on Space Time Journal Club we’ll look at the papers that reveal this discovery.
How do you take a picture of a black hole and what can we learn from it? Our first ever actual bona fide photo of a black hole, made by the Event Horizon Telescope and revealed to the world in a press conference on April 10th. Since then it’s got plenty of coverage, because … I mean look at it. It’s a freaking black hole. It’s black, it’s holey, it’s everything we hoped it would be. Now that the giddiness has subsided and I personally have stopped spending hours on end staring at a black spot, we can take a breath and actually look at the real science here and discuss exactly how a picture like this could be taken and what we can learn from it.
Quantum computing is cool, but you know what would be extra awesome - a quantum internet. In fact if we want the first we’ll need the latter. And the first step to the quantum internet is quantum cryptography.
We live in the stelliferous era. Somewhere between 10 and 1000 billion trillion stars fill the observable universe with light. But there was a time before the first star ignited. A time we call the cosmic dark ages.
Carl Sagan’s famous words: “We are star stuff” refers to a mind-blowing idea – that most atomic nuclei in our bodies were created in the nuclear furnace and the explosive deaths of stars that lived in the ancient universe. In recent years it’s become clear that the truth is even more mind-blowing. Many heavy elements - includes most precious metals - were produced in an even more spectacular event: the collision of neutron stars. In fact, according to a recent study most of the Earth’s supply of these elements was created in a single neutron star merger that took place near our Sun’s birth nebula 80 million years ago before Earth formed.
Black holes are really only dangerous if you get too close. Ha, who am I kidding. It turns out they may be responsible for ending star formation across the entire universe.
Recently, the oldest quasar ever seen was discovered by the Gemini North telescope in Hawaii, the Magellan Telescopes at Las Campanas Observatory in Chile, as well as the Large Binocular Telescope in Arizona. In this first episode of the PBS DS mini-series, STELLAR, Matt travels to the top of Mauna Kea to visit the Gemini North telescope and see just how they found this ancient Quasar and it’s massive black hole.
Energy too cheap to meter - that was the promise of nuclear power in the 1950s, at least according to Lewis Strauss chairman of the Atomic Energy Commission. That promise has not come to pass - but with some incredible new technologies, perhaps it still could. The question is - should it?
When we finally have a quantum internet you’ll be able to simultaneously like and dislike this video. But we don’t. So I hope you like it. The world is widely regarded as being well and truly into the digital age, also called the information age. No longer are economies and industries solely characterised by the physical goods they produce, and in fact some of the largest companies in the world produce no physical goods at all: digital information is a commodity in its own right. As discussed in a previous episode, this worldwide digital economy is fundamentally reliant on certain cryptographic processes. Currently these processes work in the realm of classical cryptography, but one day soon this may not be enough and so quantum cryptographic methods and algorithms are being developed. However, it’s one thing to design a protocol, it’s something else entirely to build a system to support it. To understand what needs to be done we need to get to the foundations of quantum mech...
One of the fundamental questions humanity has always asked is how big is our Universe? For much of human history, people believed that Planet Earth was the very center of the entire universe. And Earth is pretty big. But compared the rest of the universe, we are infinitesimally small.
Every astronomy textbook tells us that soon after the Big Bang, there was a period of exponentially accelerating expansion called cosmic inflation. In a tiny fraction of a second, inflationary expansion multiplied the size of the universe by a larger factor than in the following 13 and a half billion years of regular expansion. This story seems like a bit of a … stretch. Is there really any mechanism that could cause something like this to happen? What what we’re covering today – the real physics of cosmic inflation.
How can you build a telescope that can see the entire night sky without moving its dish? Well in this special episode of Space Time we took a tour of the Arecibo Observatory with a VR 180 camera so you could explore the incredible ingenuity of Arecibo's giant spherical dish that allows it to reflect light from every spot on the sky in a symmetric way. We also talked to Dr. Abel Méndez about Exoplantes and Aliens!
We actually have a pretty good idea of what might have happened before the Big Bang. That is, as long as we define the Big Bang as the extremely hot, dense, rapidly expanding universe that is described by Einstein’s equations. That picture of the universe is very solid down to about a trillionth of a second after the supposed beginning of time. We can make good guesses down to about 10^-30th of a second. But before that?
Do you want to major in Astrophysics? Are you thinking about becoming (or ever just wondered how one becomes) an Astrophysicists? Do you want to know Matt O’Dowd’s origin story? Then buckle up and enjoy the ride and try your astrophysics skill in calculating bubble universes to try to win some free Space Time Swag from the Merch Store.
Earth’s magnetic field protects us from deadly space radiation. What if it were drastically weakened, as a precursor to flipping upside down? I mean, it has before … many, many times..
Humanity’s future is glorious. As we master space travel, we’ll hop from one lifeless world to the next. Life will blossom in our path and the galaxy with shimmer with beautiful Earth-like orbs. Hmmm… maybe. This won’t sound so far fetched if we prove we can do it at least once. If we successfully terraform Mars.
You know what a planet is, right? A big round thing that orbits a star. Uh, not so fast. The surprisingly vicious debate over the planetary status of Pluto has given us a fascinating glimpse into what a scientific definition really is. And perhaps the word planet is too vague to be used as a scientific definition at all.
The universe is big, but it’s peanuts compared to the eternally inflating multiverse. But just how many universes are there? What are they like? And most importantly, what can they tell us about … aliens?
Black holes are crazy enough on their own – but crash two together and you end up with a roiling blob of inescapable space that vibrates like a beaten drum. And the rich harmonics of those vibrations, seen through gravitational waves, could hold the secrets to the nature of the fabric of spacetime itself. Today on space time journal club we’ll explore the papers that claim to have detected black hole harmonics. We’ll also give you the latest updates on the most recent – in some cases quite bizarre - LIGO detections.
It’s time we talked about loop quantum gravity. What exactly is it? What are the loops? And can it really defeat string theory in our quest for a Theory of Everything?
Time travel stories are cool because both the past and future are somehow more interesting that the present and because everyone wants a redo. But so far it appears we’re doomed to live consumed by regret in the eternal, boring present. Time marches on, inexorably and only forward. Or so we thought until Einstein came along. His special and general theories of relativity changed the way we think about time forever, and believe it or not, their raw equations permit time travel. They even tell us how to do it. So let’s review the possibilities, and decide how possible they really are.
Why does it appear, that humanity is the lone intelligence in the universe? The answer might be that planet Earth is more unique than we've previously assumed. The rare earth hypothesis posits exactly this - that a range of factors made Earth exceptionally unusual and uniquely able to produce intelligent life.
Life exists in our universe. There we go - one hopefully uncontroversial statement. Therefore our universe is capable of producing and supporting life. How am I going? Two for two? Let’s try for three: therefore there are countless universes. Hmmm. Did I break my streak?
The moment you started observing reality, you hopelessly polluted any conclusions you might make about it. The anthropic principle guarantees that you are NOT seeing the universe in most typical state. But used correctly, this highly controversial idea can be extremely powerful. So, how do you correctly use the anthropic principle?
The universe is big, really, really big. Although according to a new paper, it may literally be infinitely smaller than we previously thought.
Since the dawn of humanity around 100 billion people have lived. How many will live in the future of our species? We might hope for a trillion times that if we colonize the galaxy. But a simple statistical argument tells us that the doom of our species is much, much closer.
What if every single black hole that formed in our universe sparked the big bang of a new universe? Cosmological natural selection proposes exactly this - but even better, it claims to be able to test the hypothesis.
2018
We can now map the interiors of stars by “listening” to their harmonies as they vibrate with seismic waves.
Learn about Horizon radiation and why it's essential for us to understand as we continue our journey towards the Unruh Effect and Hawking Radiation.
The Sun is slowly burning through its fuel. Hydrogen is fused into helium in the Sun’s core, producing energy that keeps it shining, and keeping the Earth warm and hospitable to life. But that fuel WILL run out, after which the Sun will swell into a red giant and flash-fry the Earth. But in fact that frying – well, slow-roasting – will begin much earlier. See, the Sun is getting brighter even now. This has complex, and for the most part terrible implications for life. The end of the world will come sooner than you think.
What happens when a star eats its planets? Find out on today’s Space Time Journal Club.
Energy is the most powerful and useful concept in all of physics, but what exactly is it?
What exactly will happen when the sun dies?
Do you have what it takes to calculate the awesome power of the trebuchet?
Will the future of space exploration be guided by public or private entities? Which is better?
It’s the most famous prediction of perhaps the most famous genius of our time ... Stephen Hawking's theory of Hawking Radiation
What do the first stars in the universe, dark matter, and superior siege engines have in common?
The Andromeda galaxy is heading straight toward our own Milky Way. The two galaxies will inevitably collide. Will that be the very last night sky our solar system witnesses?
Worried about black holes? Consider this: Every time you accelerate - you generate an event horizon behind you. The more you accelerate away from it the closer it gets. Don’t worry, it can never catch up to you, but the Unruh radiation it generates sure can.
Our universe is prone to increasing disorder and chaos. So how did it generate the extreme complexity we see in life? Actually, the laws of physics themselves may demand it.
Now that gravitational waves are definitely a thing, it’s time to think about some of the crazy things we can figure out with them. In some cases we’re going to need a gravitational wave observatory - in fact, we've already built one.
It’s been conjectured that the center of the Milky Way is swarming with tens of thousands of black holes. And now we’ve actually seen them.
If we, or any conscious being is around to witness the very distant future our galaxy, what will they see? How long will life persist as the stars begin to die?
The great advances in any science tend to come in sudden leaps. April 25th of 2018 marks the beginning of just such a leap for much of astronomy. In the early hours of the morning, the Gaia mission’s second data release dropped. Our understanding of our own galaxy will never be the same again.
Conservation laws are among the most important tools in physics. They feel as fundamental as you can get. And yet they’re wrong - or at least they’re only right sometimes. These laws are consequences of a much deeper, more fundamental principle: Noether’s theorem.
If you have perfect knowledge of every single particle in the universe, can you use the laws of physics to rewind all the way back to the Big Bang? Is the entire history of the universe perfectly knowable? Or has information somehow lost along the way?
We’ve established by now that black holes are weird. The result of absolute gravitational collapse of a massive body: a point of hypothetical infinite density surrounded by an event horizon. At that horizon time is frozen and the fabric of space itself cascades inwards at the speed of light. Nothing can travel faster than light, and so nothing can escape from below the event horizon- not matter, not light, not even information.
We’ve established by now that black holes are weird. The result of absolute gravitational collapse of a massive body: a point of hypothetical infinite density surrounded by an event horizon. At that horizon time is frozen and the fabric of space itself cascades inwards at the speed of light. Nothing can travel faster than light, and so nothing can escape from below the event horizon- not matter, not light, not even information.
The days of oil may be numbered, but there’s another natural resource that’s never been touched, Asteroids.
Since the discovery of the Higgs boson, physicists have searched and searched for any hint of new particles. That search has been fruitless. Until, perhaps, now. Today on Space Time Journal Club we’ll look at a paper that reports a compelling hint of a new particle outside the standard model: the sterile neutrino.
In simple terms a gauge theory is one that has mathematical parameters, or “degrees of freedom” that can be changed without affecting the predictions of the theory.
Entropy and the second law of thermodynamics has been credited with defining the arrow of time.
Can a demon defeat the 2nd Law of Thermodynamics?
Let’s talk about the best evidence we have that the theories of quantum physics truly represent the underlying workings of reality.
We live in an unusual age – the age when the stars still shine. We should count ourselves lucky – nearly all of future history will be dark. But events will still unfold in that long, cooling darkness, and civilizations may endure. So how will the universe and its far-future denizens spend eternity?
There is no greater hero in our search for life on mars than a little robot named Opportunity.
Black Holes should have no entropy, but they in fact hold most of the entropy in the universe. Let’s figure this out.
There’s quite a bit of stuff in the universe, to put it mildly.
Between them, general relativity and quantum mechanics seem to describe all of observable reality.
Physics seems to be telling us that it’s possible to simulate the entire universe on a computer smaller than the universe.
Physics seems to be telling us that it’s possible to simulate the entire universe on a computer smaller than the universe.
Why strings? What are they made of? How did physicists even come up with this bizarre idea? And what’s all this nonsense of extra dimensions?
The silence of the galaxy and the resulting Fermi Paradox has perplexed us for nearly 50 years. But our most recent surveys of the Milky Way finally allow us to draw scientific conclusions about the depressingly persistent absence of aliens.
Let me tell you a story about virtual particles. It may or may not be true.
Some see string theory as the one great hope for a theory of everything – that it will unite quantum mechanics and gravity and so unify all of physics into one glorious theory.
With the large hadron collider running out of places to look for clues to a deeper theory of physics, we need a bigger particle accelerator. We have one - the galaxy.
To repeat the space time maxim: it’s never aliens … until it is. So let’s talk about ‘oumuamua.
How did life on Earth get started? Did life on Earth originate on another planet? Either Mars, or in a distant solar system? Could Earth life have spread to have seeded life elsewhere? Let’s see what modern science has to say about the plausibility of panspermia.
When you look in mirror, and see what you think is a perfect reflection. You might be looking at universe whose laws are fundamentally different.
There’s this idea that beauty is a powerful guide to truth in the mathematics of physical theory. String theory is certainly beautiful in the eyes of many physicists. Beautiful enough to pursue even if it’s wrong?
2023
Einstein once asked whether “the moon exists only when I look at it?". It was rhetorical objection to the idea that measurement in quantum mechanics causes reality to become real. But there was a time when the moon didn’t exist, and then hours later suddenly did. At least, according to the latest simulations of its formation.
In his essay “The Unreasonable Effectiveness of Mathematics”, the physicist Eugine Wigner said that “the enormous usefulness of mathematics in the natural sciences is something bordering on the mysterious”. This statement was inspired by the observation that so many aspects of the physical world seem to be describable and predictable by mathematical equations to incredible precision especially as quantum phenomena. But quantum phenomena have no subjective qualities and have questionable physicality. They seem to be completely describable by only numbers, and their behavior precisely defined by equations. In a sense, the quantum world is made of math. So does that mean the universe is made of math too? If you believe the Mathematical Universe Hypothesis then yes. And so are you.
Life as we know it is carbon-based, but does it have to be this way? There’s another element on the periodic table that shares some of the key properties of carbon but is far more abundant on most planets. I’m talking about silicon. So is there silicon-based life out there?
Perhaps you’ve seen videos of how the planets of the solar system move through the universe in this cool helix. Not only are these misleading, but the Earth’s real motion - YOUR motion through the universe, is way more complicated and way more interesting.
Two protons next to each other in an atomic nucleus are repelling each other electromagnetically with enough force to lift a medium-sized labradoodle off the ground. Release this energy and you have, well, you have a nuclear explosion. Just as well there's an even stronger force than the electromagnetism holding our nuclei together. But it's not the strong force, as you might have imagined. At least not directly. Nuclei are held together by a quirk of nature, without which we would have no complex atoms, no chemistry, and certainly no labradoodles.
Physics progresses by breaking our intuitions, but we’re now at a point where further progress may require us to do away with the most intuitive and seemingly fundamental concepts of all—space and time.
Physics is the business of figuring out the structure of the world. So are our brains. But sometimes physics comes to conclusions that are in direct conflict with concepts fundamental to our minds, such as the realness of space and time. How do we tell who’s correct? Are time and space objective realities or human-invented concepts?
We tend to imagine there are connectings between things that we don’t understand. Quantum mechanics and consciousness, aliens and pyramids, black holes and dark matter, dark matter and dark energy, dark energy and black holes. Usually there’s no real relationship whatsoever, but this last pair—black holes and dark energy being the same thing—has received some recent hype in the press. Let’s see if it might actually be true.
There’s an absolute limit to our access to the universe beyond our own galaxy. There’s a limit to what we can ever hope to explore or send signals to, and a very different limit to what we can ever hope to witness. Today we’re going to explore the latter. We’re going to figure out the absolute limit of our future view of the universe, and of the universe’s ability to influence us. Next time we’ll turn it around and ask: how much of the external universe can WE potentially influence, and even explore?
We humans have always been explorers. The great civilizations that have arisen across the world are owed to our restless ancestors. These days, there’s not much of Earth left to explore. But if we look up, there’s a whole universe out there waiting for us. Future generations may one day explore the cosmos and even settle entire other galaxies. But there is a hard limit to how much of the universe we can expand into. So, how big can humanity get?
Astrophysicists have discovered a black hole that for millions of years has been blasting vast particle beams in opposite directions across the sky. And has recently swiveled to point its one of these jets directly at us. Is this an intergalactic death ray of an alien civilization that has suddenly noticed us? Absolutely not, and there’s no danger at all. But it’s a pretty cool phenomenon anyway, and something we’ve never seen before.
If I roll a pair of dice and you get to bet on one number, what do you choose? The smart choice is 7 because there are more ways for 2 dice to come up 7 than any other number. Well, it turns out that you can apply the same logic to predicting the behavior of the universe. Let’s see how some of our most powerful tools in physics are really a game of cosmic craps.
Whenever we open a new window on the universe, we discover things that no one expected. Our newfound ability to measure ripples in the fabric of spacetime—gravitational waves—is a very new window, and so far we’ve seen a lot of wild stuff. We’ve observed black holes colliding, and their oddly high masses challenges our understanding of black hole formation and growth. We’ve seen colliding neutron stars that have forced us to rewrite our ideas of how many of the elements of the periodic table get made. But what else might be hiding in the ripples’ of spacetime? Oh, I know: how about the gravitational wakes caused by planet-sized alien spacecraft accelerating to near light speed.
The weird rules of quantum mechanics lead to all sorts of bizarre phenomena on tiny scales— particles teleporting through walls or being in multiple places at once or simultaneously existing and not. Shame all this magical behavior doesn’t happen on scales large enough for us to see. Except that there is a way for us to see large-scale quantum weirdness, and that’s Bose-Einstein Condensates & Superfluids.
Interstellar travel is horrible-what with the cramped quarters of your spaceship and only the thin hull separating you from deathly cold and deadly cosmic rays. Much safer to stay on here Earth with our gloriously habitable biosphere, protective magnetic field, and endless energy from the Sun. But what if we could have the best of all worlds? No pun intended. What if we could turn our entire solar system into a spaceship and drive the Sun itself around the galaxy? Well, I don't know if we definitely can, but we might not not be able to.
The deaths of massive stars results in one of the most beautiful and violent events in the universe: the supernova. They are so luminous we can see them here on Earth and historical records show that we can even see them into the day. But supernovas release deadly and violent radiation that could destroy our atmosphere. So how far away do these supernova have to be for humanity to be safe? And when will the next supernova occur
The humble proton may seem simple enough, and they’re certainly common. People are made of cells, cells are made of molecules, molecules are made of atoms, atoms are made of electrons, protons, and neutrons. And protons are each made of three up or down quarks. Simple stuff, right? All except for that last part. Protons are actually made of many, many quarks that happen to look like three only when we look at them in a particular way. And even then, sometimes they’re made of 5 quarks - including the charm quark.
Quantum mechanics is our best theory of the fundamental nature of reality, but it's usually only distinguishable from familiar classical mechanics on the smallest scales. However, there are some fringe cases where its distinct features manifest on scales we can observe—in things like superfluids, or the interiors of collapsed stars. But it’s also possible that our entire galaxy is filled with a reverberating quantum mechanical wave that literally holds the galaxy together—and in fact explains all the dark matter that we see across the universe. And this isn’t even a fringe theory. It’s axionic dark matter.
One of the most fundamental physics facts is that the speed of light in a vacuum is constant for all observers. But can we really be sure that the speed of light wasn’t different in the past, or perhaps in other parts of the universe? In fact, variable speed of light theories have long been used to try to explain everything from dark energy to gravity itself. Let’s explore how constant this fundamental constant really is.
A few weeks ago a large team of gravitational wave astronomers announced something pretty wild. The moderately confident detection of pervasive ripples in the fabric of space time that presumably fills the cosmos, detected by watching for subtle connections between the signals from rapidly spinning cores of dead stars in our galactic neighborhood. In other words, the gravitational wave background has probably been detected using a pulsar timing array.
We have no idea what dark matter is, other than it’s some source of gravity that is completely invisible but exerts way more pull that all of the regular matter. More than all of the stars, all of the gas, all of the black holes…unless dark matter is black holes, then black holes are most of everything. Dark matter constitutes 80% or so of the mass in the universe, which means even our Milky Way galaxy is mostly a vast ball of dark matter that happens to have attracted a relative sprinkling of baryons—atoms in the form of gas, which lit up as starry glitter spinning in the middle of this invisible gravitational well.
We knew that the James Webb Space Telescope would find interesting stuff, especially about the mysterious early times. For example, there are hints that the galaxies we’re seeing are brighter and more regular than expected given the short amount of time they’d had to grow. Well, perhaps no one was expecting that we’d find a completely new type of star—one mostly made of and powered by dark matter and shining as bright as an entire galaxy. Which, by the way, might help us explain those pesky giant galaxies.
Spacetime on its smallest scales is a seething ocean of black holes and wormholes flickering into and out of existence—or so many physicists think has to be the case. But why should we take this spacetime foam seriously if we’ve never seen any evidence of it?
In order to see the faint light from objects in deepest space, astronomers go to the darkest places on the planet. In order to listen to their quite radio signals, they head as far from any radio-noisy humans as possible. But there’s nowhere on the earth, or even orbiting the Earth, that’s far enough to hear to the faint radio hum from the time before stars. In fact, we may need to build a giant radio telescope in the quietest place in the solar system—the far side of the moon.
Superconductive materials seem miraculous. Their resistanceless flow of electricity has been exploited in some powerful ways—from super-strong magnets used in MRIs, particle accelerators and fusion plants. And then there’s, their bizarre ability to levitate in magnetic fields. But the broader use of superconductors is limited because they need to be cooled to extremely low temperatures to work. But what if we could produce superconductivity at room temperature? It would change the world.
It’s hard to interpret the strange results of quantum mechanics, though many have tried. Interpretations range from the outlandish—like the multiple universes of Many Worlds, to the almost mundane, like the very mechanical Pilot Wave Theory. But perhaps we’re converging on an answer, because some are arguing that these two interpretations are really the same thing.
To understand where we came from—how earth, the solar system, the galaxy became what they are today—we need to understand the beginning of time. For example, how did the first galaxies pull themselves together from the dark universe-filling ocean of gas that followed the Big Bang? With the James Webb Space Telescope we’re starting to be able to find those first galaxies. It’s hard work because at those crazy distances all we see is tiny, faint and fuzzy blobs. If only we could see the individual stars in those galaxies we could learn so much more. Well, now using this one weird trick we can do exactly that. Or at least we have one lonely star at the end of the universe. But it won’t be lonely for long.
Whenever we open a new window on the universe we discover something new. Whether it's figuring out how to see to greater distances like with telescopes, or down to smaller size-scales like with microscopes, or perhaps expanding our vision to new wavelengths of light or via exotic means such as in neutrinos or gravitational waves. Well, the 2023 Nobel prize in physics has been awarded to three physicists for opening just such a new window—but it's not a window to a new size scale or a new mode of seeing—-it’s for a new window in time. It’s for attosecond physics—the billionth of a billionth of a second that represents the timescale of the insides of atoms. This year’s Nobel in physics is for a microscope in time.
The holy grail of theoretical physics is to come up with a quantum theory of gravity. But after a century of trying we really have no idea how close we are, or it it's even possible. But we shouldn't feel bad because it turns out that the universe is doing everything it its power to make this as difficult as possible. Or it's telling us that it isn't. Should we take the hint?
The mystery of what happens when we go from a superposition to a definite state is known as the Measurement Problem, and it’s arguably the most mysterious outstanding problem in physics. The different interpretations of quantum mechanics are really about solving the measurement problem. But Many Worlds offers one thing that the other interpretations do not: there’s no collapse of the wavefunction - which might be the key to solving the measurement problem?
2024
Two of the greatest mysteries in cosmology are the nature of dark energy and the apparent conflict in our measurements of the expansion rate of the early versus the modern universe that even dark energy can’t account for. Could both of these be explained by looking to a part of the universe that we’ve largely ignored so far? Could cosmic voids be driving the universe?
From hoverboards to flying cars to cloud cities, anti-gravity is a staple of science fiction and our dream of a less Earth-bound future. But in the real universe gravity appears to be a purely attractive force. Feels like its main MO is keeping us stuck to the surface of this lonely rock. But maybe if we science hard enough we can remove the fiction from science fiction. For the sake of our flying cars we should at least try. And for many years, physicists have wondered whether a certain well-known exotic material may experience gravitational repulsion from the Earth. That material is antimatter, and physicists at CERN have just completed a very long and very difficult experiment to answer a seemingly simple question: does antimatter fall down, or does it fall up?
This is what we astronomers call a blob, or a smudge, if you want to get really technical. It may not look like much from here, but what do you expect for something near the literal edge of the observable universe. If you were there when this light was emitted, you’d A. be at the beginning of time, and B. be looking at an entire galaxy containing an enormous black hole at its heart. It’s the most distant black hole we’ve semi-directly detected. That’s cool enough on its own, but as an added bonus this one smudge may have solved the mystery of the origin of the supermassive black holes in our universe.
It's not too often that a giant of physics threatens to overturn an idea held to be self-evident by generations of physicists. Well, that may be the fate of the famous Penrose Singularity Theorem if we're to believe a recent paper by Roy Kerr. Long story short, the terrible singularity at the heart of the black hole may be no more.
EMPs aren’t science fiction. Real militaries are experimenting on real EMP generators, and as Starfish Prime showed us, space nukes can send powerful EMPs to the surface. So what exactly is an EMP, and how dangerous are they?
In 1974 we sent the Arecibo radio message towards Messier 13, a globular cluster near the edge of the Milky Way, made up of a few hundred thousand stars. The message was mostly symbolic; we weren’t really expecting a reply. Yet surely other civilisations out there are doing the same thing. So, why haven’t we heard anything? What if the silence from the stars is a hint that we shouldn’t be so outgoing? What if aliens are deliberately keeping quiet for fear that they might be destroyed?
Space seems fundamental. To build a universe, surely you need something to build it on or in. Many, maybe most physicists now think that the fabric of space emerges from something deeper. And perhaps the most existentially disturbing such proposal is that our 3-D universe is just the inward projection of an infinitely distant boundary. A hologram, or sorts. Let’s see how that can actually work, and what the holographic principle really says about the “realness” of this universe.
There are four fundamental forces - the strong and weak nuclear forces, electromagnetism, and gravity. Except maybe gravity is no more fundamental than the force of a stretched elastic band. Maybe gravity is just an entropic byproduct—an emergent effect of the universe’s tendency to disorder. If you allow entropy to keep you in your seat for a bit, I’ll tell you all about it.
Of all the astronomical phenomena you can witness, the total solar eclipse has to be the most visceral--the most in-your-face reminder that our reality consists of giant balls of rock spinning around stars. It's also the eclipse and phenomena like it that set us on the path to understanding that reality in the first place.
The Moon has been one of the most important theoretical stepping stones to our understanding of the universe. We’ve long understood that it could also be our literal stepping stone: humanity’s first destination beyond our atmosphere.
Meet Alice and Bob, famous explorers of the abstract landscape of theoretical physics. Heroes of the gerdankenexperiment—the thought experiment—whose life mission is to find contradictions in the deepest layers of our theories. Today our intrepid pair are jumping into a black hole. Again. Why? Well, to determine the fundamental structure of spacetime and its connection to quantum entanglement of course.
In the far future we may have advanced propulsion technologies like matter-antimatter engines and compact fusion drives that allow humans to travel to other stars on timescales shorter than their own lives. But what if those technologies never materialize? Are we imprisoned by the vastness of space—doomed to remain in the solar system of our origin? Perhaps not. A possible path to a contemporary cosmic dream may just be to build a ship which can support human life for several generations; a so-called generation ship.
Black holes are inevitable predictions of general relativity—our best theory of space, time and gravity. But they clash in multiple ways with quantum mechanics, our equally successful description of the subatomic world. One such clash is the black hole information paradox—and a proposed solution—black hole complementarity—may forced us to radically rethink what it even means to say that something to exists.
Cern's Large Hadron Collider routinely collides particles at energies equivalent to a fraction of a second after the Big Bang. If this worries you, then the following fact will either put you at ease or scare the hell out of you. And that's that a particle with the energy of an LHC collision hits every square kilometer of the Earth every single second. And we only relatively recently figured out where these cosmic rays are coming from.
So you’ve decided to jump into a black hole. Good news: as long as the black hole is big enough you can sail through the event horizon without harm and get to experience the interior of the black hole before you’re annihilated by the central singularity. Or so we once thought. These days, quite a few physicists believe that the only way to avoid horrible contradictions in fundamental physics generated by black holes is for all them to be surrounded by screens of extreme energy that prevent anything from ever entering the event horizon. Sounds outlandish? Welcome to black holes. So let’s find out why many of our most brilliant physicists take these black hole firewalls deadly seriously.
Solar activity is still increasing in a sunspot cycle that is proving way more intense than scientists predicted. Just how much stronger is it going to get?
All particles belong to two large groups: fermions like protons and electrons make everything we consider "matter", while bosons like photons and gluons transmit the fundamental forces. And that about covers the universe: matter moving through space and time under the action of forces. But what if we could create particles in between these two possibilities. Physics says these neither matter nor force anyons can exist, and they may have some pretty incredible uses. They’re called anyons.
Warp drives may or may not be possible, but if they are then could a distant alien civilization’s warp fields produce gravitational waves that we could see here on Earth? According to a recent study.. Actually maybe, at least eventually. And we now know just what to look for and how to look for it.
Nobel laureate Roger Penrose is widely held to be one of the most brilliant living physicists for his wide-ranging work from black holes to cosmology. And then there’s his idea about how consciousness is caused by quantum processes. Most scientists have dismissed this as a cute eccentricity—a guy like Roger gets to have at least one crazy theory without being demoted from the supersmartypants club. The most common argument for this dismissal is that quantum effects can’t survive long enough in an environment as warm and chaotic as the brain. Well, a new study has revealed that Penrose’s prime candidate molecule for this quantum activity does indeed exhibit large scale quantum activity. So was Penrose right after all? Are you a quantum entity?
The primary characteristic that defines black holes is in the name. Black holes are black. The gravitational pull at the event horizon is so powerful that not even light can escape. In this case, black means absence of light. We also think of black as indicating absence of colour. But it turns out there is a way to make a coloured black hole—as long as by colour you mean quantum chromodynamic charge.
Scientists have been slowly extending the periodic table one element at a time, pushing to higher and higher masses, and have discovered some incredibly useful materials along the way. But the elements at the current end of the table are so unstable that they decay almost as soon as they’re created in our particle accelerators. Have we reached the end of the line of discoverable elements? There are new rows of the periodic table to unlock, and more stable versions of known heavy elements to synthesize—and while our accelerators are coming up short, astronomers have found a strange cosmic phenomenon that may populate the periodic table beyond our wildest dreams.
The holy grail of theoretical physics is to find the long-sought theory of quantum gravity. But what if this theory is as mythical as the grail of legend? What if gravity isn’t weirdly quantum at all, but rather … just a bit messy? Or random? So says the postquantum gravity hypothesis of Jonathan Oppenheim.
If we discover how to connect quantum mechanics with general relativity we’ll pretty much win physics. There are multiple theories that claim to do this, but it’s notoriously difficult to test them. They seem to require absurd experiments like a particle collider the size of a galaxy. Or we could try to physics smarter, instead of physicsing harder. Let’s talk about some ideas for quantum gravity experiments that can be done on a non-galaxy-sized lab bench, and in some cases already have been done.
If you track the motion of individual stars in the ultra-dense star cluster at the very center of the Milky Way you’ll see that they swing in sharp orbits around some vast but invisible mass—that’s the Sagittarius A* supermassive black hole. These are perilous orbits, and sometimes a star wanders just a little too close to that lurking monster, leading to its utter destruction in the spectacular phenomenon known as a tidal disruption event. We’ve never seen a TDE in the Milky Way, but we’ve seen them in distant galaxies—and we now know how to spot stellar destructions so extreme that they reveal properties of the black hole itself.
Here’s the story we like to tell about the beginning of the universe. Space is expanding evenly everywhere, but if you rewind that expansion you find that all of space was once compacted in an infinitesimal point of infinite density—the singularity at the beginning of time. The expansion of the universe from this point is called the Big Bang. We like to tell this story because it's the correct conclusion from the description of an expanding universe that followed Einstein's general theory of relativity back in the 19-teens. But since then we've learned so much more since then. Does our modern understanding of the universe still insist on a point-like Big Bang? Recent work actually gives us a way to avoid the beginning of time.
We know that the universe is getting bigger. And we know that the speed that the universe is getting bigger is also getting bigger. The standard assumption is that the acceleration rate is itself constant, which will surely result in ultimate heat death. But a recent survey of primordial sound waves frozen into the way galaxies are sprinkled through the universe reveals that this fate is now in question.
Neutron stars aren't dark matter--we figured that out a while ago. But new research is telling us that they may be dark matter factories. They may produce the exotic axion, one of the most popular dark matter candidates.
Imagine a world where humanity masters every planetary resource available to it—our first step on the famous Kardeshev scale of technological advancement. How distant is that step? Will we even become a true Type-1 civilization, and how can we get there?
There are cosmic events so powerful that they leave permanent marks on the fabric of the universe itself. Imagine two colossal black holes spiraling into each other, yes they send ripples in the fabric of spacetime—gravitational waves that we’ve only recently learned to sense. Ripples pass, leaving the pond … or the universe … unchanged when they’re gone. But ripples aren’t the only type of wave. There’s another type of wave that leaves a permanent mark—a memory etched in the fabric of the universe. They’re akin to gravitational tsunamis, and we’re on the verge of being able to detect them.
Every good nerd knows that E=mc^2. Every great nerd knows that, really, E^2=m^2c^4+p^2c^2 Want to know what that even means? Sure, I’ll tell you, but today I’d like to invite you to an even higher level of nerdom with extra bits to Einstein’s famous equation that will make even the greatest nerds quiver in their … space time merch if they turn out to be real.
Is there a limit to how much energy you can cram into, or pull out of one patch of space? Well, we thought so, but the James Webb Space Telescope has found a quasar that simultaneously breaks a century-old theoretical limit and may explain the conundrum of gigantic black holes in the early universe.
What does an electron really look like? I mean, if we zoom in all the way. Is it a sizeless speck of charge? Is it a multidimensional vortex of quantum strangeness? Is it the boundary of a tiny universe with universe-electrons of its own? Let’s find out.
What do you get if you take something that’s infinitely massive and combining with something else that’s negative infinitely massive? You get a single electron, at least that’s what it looks like in our most precise way of describing the quantum world.
2020
Why is there something rather than nothing? Well the answer may be found in the weakest particle in the universe: the neutrino. For over half a century Fermilab has been the premier particle accelerator facility of the United States and we got to visit with Don Lincoln to explore it’s science and its engineering. These days many of the super-powered geniuses of Fermilab are tackling the mysteries of the neutrino. Why? Because this elusive particle may hold powerful secrets: from the unification of the forces of nature to the biggest question of all: why is there something rather than nothing?
Black holes are awesome - but how about black holes being captured by the screaming vortex of a quasar, where they merge and grow like some monstrous version of a solar system. This insane hypothesis is getting closer to reality, according to the papers in today’s space time journal club.
The three body problem is famous for being impossible to solve. But actually it's been solved many times, and in ingenious ways. Some of those solutions are incredibly useful, and some are incredibly bizarre.
In particle physics we try to understand reality by looking for smaller and smaller building blocks. But what if that has been the wrong philosophy all along?
If the universe goes on forever, does that mean there are infinite versions of you out there?
What does the strong nuclear force, the fundamental symmetries of nature, and a laundry detergent have in common? They’re all important parts of the tale of the axion - a tale whose end may take us beyond the standard model and solve one of the most vexing mysteries in astrophysics.
It’s not surprising that the profound weirdness of the quantum world has inspired some outlandish explanations - nor that these have strayed into the realm of what we might call mysticism. One particularly pervasive notion is the idea that consciousness can directly influence quantum systems - and so influence reality. Today we’re going to see where this idea comes from, and whether quantum theory really supports it.
Why is it that we can see these multiple histories play out on the quantum scale, and why do lose sight of them on our macroscopic scale? Many physicists believe that the answer lies in a process known as quantum decoherence.
If we can’t ever peer into these other realities that are used to explain quantum mechanics, how do we know they exist? In order to understand what happens to those different branches, and to understand why we find ourselves in one of them, we need to embrace one of the interpretations of quantum mechanics.
In quantum world things are routinely in multiple states at once - what we call a “superposition” of states. But in the classical world of large scales, things are either this or that. The famous thought experiment is Schrodinger’s cat - in which a cat is in an opaque box with a vial of deadly poison that’s released on the radioactive decay of an atom. Quantum mechanics tells us that the atom’s wavefunction can be in a superposition of states - simultaneously decayed or not decayed. So is the cat’s wavefunction also in a superposition of both dead and alive.
If there’s one thing cooler than a black hole it’s a rotating black hole. Why? Because we can use them as futuristic power generators, galactic-scale bombs, and portals to other universes.
Normal maps are useless inside black holes. At the event horizon - the ultimate point of no return as you approach a black hole - time and space themselves change their character. We need new coordinate systems to trace paths into the black hole interior. But the maps we draw using those coordinates reveal something unexpected - they don’t simply end inside the black hole, but continue beyond. In these maps, black holes become wormholes, and new universes lie on the other side.
In astronomy we talk about billions of years like it’s no big deal. But how can we be sure about timescales so far beyond the capacity for human intuition? Our discovery of what we now call deep time is very recent - as recent as our discovery of the true spatial vastness of our universe. And it came as scientists tried to measure the age of the Earth. What they found was as shocking and humbling as anything seen through the telescope.
The Milky Way galaxy is relatively calm by the destructive standards of the rest of the Universe, and compared to its own very violent past. But just recently we discovered that its violent past was much more recent than we thought - and could even happen again.
From Stargate to Interstellar, wormholes are our favorite method for traveling across fictional universes. But they are also a very serious field of study for some of our greatest minds over the last century. So what’s the holdup? When do we get to wormhole ourselves out of here?
The universe is precisely 13.8 billion year old - or so our best scientific methods tell us. But how do you learn the age of the universe when there’s no trace left of its beginnings?
As the 19th century came to a close, physicists were feeling pretty satisfied with the state of their science. The great edifice of physical theory seemed complete. A few minor experiments remained to verify everything. Little did those physicists know that one of those experiments would bring the entire structure crashing down paving the way for the physics revolution of the 20th century.
This is a map of the multiverse. Or in physics-ese, it’s the maximally extended Penrose diagram of a Kerr spacetime. And in english: when you solve Einstein’s equations of general relativity for a rotating black hole, the universe does not come to an abrupt halt at the bottom of the gravitational pit. Instead, a path can be traced out again but you do not end up in the universe that you started in. Like I said, it’s a map of the multiverse.
It’s been 120 years since Henry Cavendish measured the gravitational constant with a pair of lead balls suspended by a wire. The fundamental nature of gravity still eludes our best minds - but those secrets may be revealed by turning back to the Cavendish experiment. That steampunk contraption may even reveal the existence of extra dimensions of space.
With the global pandemic of Covid 19 still encompassing the word, we are generally not big fans of viruses right now. But we sure are thinking about them a lot. That’s right, even astrophysicists are pondering these bizarre little critters. In fact, astrovirology, although very new, is actually an emerging subfield of astrobiology. And that’s because it turns out viruses don’t just influence organisms - they’re incredibly important on a planetary scale. Perhaps an interplanetary scale.
Conformal Cyclic Cosmology is a story of the origin and the end of our universe from great mathematical physicist Sir Roger Penrose. It’s goes like this: the infinitely far future, when the universe has expanded exponentially to to an unthinkably large size, and every black hole and particle has decayed into faint radiation .... that infinite stretch of space and time is identically the SAME THING as the infinitesimal and instantaneous big bang of a new universe, and our universe is just one in an endless chain.
Black holes are about the worst subjects for direct study in the universe. But at this stage, it’s all we can do to convince ourselves of their existence. Actually studying the physics of real black holes is much, much harder. I mean, we could try to make one - but that’s way beyond our current tech level, and also potentially humanity-destroying. Well it turns out we don’t need to make real black holes to at least get started with the lab work. We can instead study analog black holes - and by analog, I don’t mean old fashioned clockwork black holes - I mean analogies. Physical systems that aren’t black holes but that behave in similar ways - and may reveal the real behaviours of real black holes.
Black hole singularities break physics - fortunately, the universe seems to conspire to protect itself from their causality-destroying madness. At least, so says the cosmic censorship hypothesis. Only problem is many physicists think it might be wrong, and that naked singularities may exist after all.
The most precious substance in our universe is not gold, nor oil. It’s not even printer ink. It’s antimatter. But it’s worth every penny of it’s very high cost, because it may hold the answer to the question of why anything exists in our universe at all.
When we detected the very first gravitational wave, a new window was opened to the mysteries of the universe. We knew we’d see things previously thought impossible. And we just did - an object on the boundary between neutron stars and black holes, which promises to reveal the secrets of both.
Our galaxy is full of dysfunctional stellar relationships. With more than half of all stars existing in binary orbits, it’s inevitable that many stellar remnants will end up in parasitic spirals with their partners. Today we’re going to look at the worst of these - from the novae produced by white dwarfs, to X-ray binaries created by neutron stars and black holes - and much weirder things besides.
If you wanna make an omelet you gotta break a few eggs. And by omelet I mean a theory of everything, and by eggs I mean a billion billion subatomic particles obliterated in the next generation of giant particle colliders.
Pin-pricks in the celestial sphere, through which shines the light of heaven? Or gods and heroes looking down from their constellations? Or lights kindled above middle earth by Varda Elbereth and brightened with the dew of the trees of Valinor? Science has long pondered the mysteries of the stars. This is how we finally figured them out.
The great physicist Hermann Weyl once said: "My work always tried to unite the true with the beautiful, but when I had to choose one or the other, I usually chose the beautiful." But is this actually good advice for doing physics?
One of the most bizarre proposals for life not as we know it doesn’t even use atoms. It proposes that fundamental kinks and defects in the fabric of the universe - cosmic strings beaded with magnetic monopoles - may evolve into complex structures, and even life, within stars. This idea was just published in Letters High Energy Physics Letters by physicists Luis Anchordoqui and Eugene Chudnovsky, and today on Space Time Journal Club we’re going to see how legit this actually is.
Your extensive posting history on r/birdswitharms and your old fanfiction-heavy livejournal are both one tiny math problem away from becoming public knowledge. That math problem is prime number factoring, and the new era of quantum computers may lay bare your indiscretions, as well as collapse the entire digital economy. Unless we get us some post-quantum cryptography post-haste. So, how close are we?
If you rank the most habitable places in our solar system Venus lands pretty low, with surface temperatures hot enough to melt lead and sulphuric acid rain. And yet it may have just jumped to the front of the pack. In fact, we may have detected the signature of alien life - Venusian life -for the first time.
Is all that exists just whatever exists right now? Is the past erased and the future a void yet to be filled? Well, the answer lies in between the past and the future - in the elusive, ever-moving eye-blink that we call the present.
Einstein’s special theory of relativity combines space and time into one dynamic, unified entity - spacetime. But if time is connected to space, could the universe be anything but deterministic? And does that mean that the future is predestined?
The Nobel prize in physics this year went to black holes. Generally speaking. Specifically, it was shared by the astronomers who revealed to us the Milky Way’s central black hole and by Roger Penrose, who proved that in general relativity, every black hole contains a place of infinite gravity - a singularity. But the true impact of Penrose’s singularity theorem would is much deeper - it leads us to the limits Einstein’s great theory and to the origin of the universe.
Our universe seems pretty complicated. We have a weird zoo of elementary particles, which interact through very different fundamental forces. But some extremely subtle clues in nature have led us to believe that the forces of nature were once unified, ruled by a single, grand symmetry. But how does one force separate into multiple? And how do the forces of nature arise from mathematical symmetries in the first place?
Physicists have a long history of sticking our noses where they don’t belong - and one of our favorite places to step beyond our expertise is the question of consciousness and free will. Sometimes our musings are insightful, sometimes incoherent, and usually at least somewhat naive. Which a fair description of this show, so of course Space Time needs to weigh in physics and free will..
Ever wish you could travel backward in time and do things differently? Good news: the laws of physics seem to say traveling backward in time is the same as traveling forwards. So why do we seem to be stuck in this inexorable flow towards the future? It's time to begin our journey towards really understanding time.
The laws of physics don’t specify an arrow of time - they don’t distinguish the past from the future. The equations we use to describe how things evolve forward in time also perfectly describe their evolution backwards in time. So the brain is a thing ruled by the laws of physics - why does the brain and the conscious experience that emerges from it, see the arrow of time so clearly? In other words why do we remember the past and not the future?
Good news everyone: it looks like the universe is going to end with a series of catastrophic explosions. The very, very long story short is that the universe ends in heat death, as it approaches maximum entropy, and its eternal exponential expansion drives it to effective utter emptiness and absolute cold. But new calculations have revealed we may be able to look forward to one last source of astrophysical cataclysms - a new type of supernova that can only happen at the end of the universe.
We often think of quantum mechanics as only affecting only the smallest scales of reality, with classical reality taking over at some intermediate level. But in his 1944 book, What is Life?, the quantum physicist Erwin Schrödinger suggested that “incredibly small groups of atoms, much too small to display exact statistical laws, do play a dominating role in the very orderly and lawful events within a living organism.” Schrodinger was a visionary - and perhaps very specifically in this case. Because it turns out we might need all the weirdness of quantum mechanics to explain birds.
2026
To progress to the next level in understanding reality, we need to combine quantum mechanics and Einstein’s general relativity. And to do that, most physicists believe we need a theory of quantum gravity .. which means we need gravitons. But it also seems like the laws of physics make it impossible to ever detect this quantum particle of gravity. Almost like the universe is set up to keep the final answer forever out of our reach. So, can we outsmart the universe, catch a graviton, and finally solve physics?
The universe thrums with quantum fields; and the particles of matter and force emerge as vibrational manifestations of the deep symmetries of these fields. The layers and reflections of those symmetries give us the wonderful richness of what we call the standard model of particle physics. Except there seems to be something missing: the sterile neutrino.
Physicists have long believed that detecting the particle of gravity—the graviton—was fundamentally impossible, with the universe itself seeming to block every direct attempt. This episode explores a new generation of clever experiments that may finally let us detect gravity’s particle, and why even succeeding wouldn’t quite mean what we think it does.
We've known that the universe is expanding since 1929, and that its expansion is accelerating since 1998. The culprit behind the acceleration is unknown, so we live with a stand-in term "dark energy". Our modern cosmological model assumes that dark energy has a constant density--always the same amount of the outward-shoving stuff per volume. But there's recent evidence to the contrary--which may be why our primary efforts to measure the expansion rate of the universe disagree with each other.
Some people worried that the large hadron collider would smash particles together so hard it would make black holes that would swallow the earth, open wormholes to other dimensions. It didn’t and won’t. But it may be making a different kind of portal. A portal to the dark sector. This isn’t the Rather, it’s a hypothetical family of elementary particles that exists in parallel to the familiar particles of the standard model, but are invisible to it. Invisible to us, and so could be the answer to the dark matter conundrum. And what is this portal? It’s the particle that the LHC was built to find in the first place - the Higgs boson.
Kurt Gödel discovered a solution to General Relativity that allows time travel without any exotic physics, revealing that the theory doesn’t actually guarantee a consistent chain of cause and effect . His “Gödel universe” shows that under certain conditions, the structure of spacetime itself can loop back on itself—blurring the line between past and future and exposing a deep limitation in our understanding of reality.
Is Earth’s core a solid or a liquid? Yes. The mysteries of our own planet’s interior have, in many ways, been harder to crack than those of the rest of the cosmos. We can send probes to the edge of the solar system, and the 42 billion light years to the cosmic horizon are largely transparent—a big enough telescope can see the most distant galaxy. But the 6400km to Earth’s center are both opaque to light and far beyond the reach of any conceivable drill. The best we can do for most of our planetary depths is to listen to the faint rumblings of distant earthquakes and then try to piece together how those seismic waves bounce around the interior.
The James Webb Space Telescope found galaxies that are too ancient-looking for our young universe. You may have heard that, but it keeps finding them, and our recent efforts to solve this conundrum point in wildly different directions. Have we found galaxies older than the universe, or did we just learn something incredible about how galaxies form?
For a while back there we might be able to avoid the black hole. They’d been lurking as shadows in our theories of gravity forever. Enough mass crammed into a small enough space would lead to a gravitational field at the surface from which not even light could escape from a surrounding surface that we call the event horizon. The event horizon generates paradoxes that worry physicists, and the singularity of infinite density within the black hole worries them even more. And so many brave physicists have fought for centuries to prove that these monsters don’t exist. They hoped nature would step in to save us from the theoretical horror of ultimate gravitational collapse. One of our final hopes is the Planck star—a ball of energy at the heart of the black hole like frozen shards of the Big Bang. Let’s hope they’re real, for physics’ sake.
Matthew O’Dowd
Self - Host
