PBS Space Time Season 2025: Episode Guide & Ratings

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.

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.