PBS Space Time Season 2022, Episode 17: Is Interstellar Travel Impossible?

How To Simulate The Universe With DFT

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.

21 min

How To Build The Universe in a Computer

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.

14 min

How Does Gravity Escape A Black Hole?

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?

19 min

Is The Wave Function The Building Block of Reality?

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.

21 min

Are Cosmic Strings Cracks in the Universe?

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.

16 min

Is the Proxima System Our Best Hope For Another Earth?

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.

22 min

What If Charge is NOT Fundamental?

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.

16 min

Where Is The Center of The Universe?

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?

20 min

Could The Universe Be Inside A Black Hole?

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.

14 min

Does the Universe Create Itself?

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.

19 min

How the Higgs Mechanism Give Things Mass

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.

19 min

Space DOES NOT Expand Everywhere

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?

18 min

What If the Galactic Habitable Zone LIMITS Intelligent Life?

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?

16 min

The Evolution of the Modern Milky Way Galaxy

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.

21 min

What If Physics IS NOT Describing Reality?

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.

19 min

Have We SOLVED The Black Hole Information Paradox with Wormholes?

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.

15 min

Could We Decode Alien Physics?

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.

20 min

What If We Live in a Superdeterministic Universe?

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.

19 min

How Many States Of Matter Are There?

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.

15 min

What Happens Inside a Proton?

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.

21 min

What If Dark Energy is a New Quantum Field?

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?

17 min

What Makes The Strong Force Strong?

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.

22 min

Could the Higgs Boson Lead Us to Dark Matter?

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.

15 min

Science of the James Webb Telescope Explained!

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?

19 min

Why Is 1/137 One of the Greatest Unsolved Problems In Physics?

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.

16 min

The REAL Possibility of Mapping Alien Planets!

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.

22 min

The Equation That Explains (Nearly) Everything!

17 min

Why Did Quantum Entanglement Win the Nobel Prize in Physics?

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

21 min

What If Humanity Is Among The First Spacefaring Civilizations?

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.

21 min

Are there Undiscovered Elements Beyond The Periodic Table?

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?

21 min

How To See Black Holes By Catching Neutrinos

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.

19 min

How Are Quasiparticles Different From Particles?

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.

17 min

How Can Matter Be BOTH Liquid AND Gas?

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.

22 min