Loading episode...
PBS Space Time
Season 2025 • Episode 21 • We Were WRONG About the Quantum Eraser!
Select Server:
PBS Space Time Season 2025, Episode 21: We Were WRONG About the Quantum Eraser!
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. Watch PBS Space Time Season 2025, Episode 21 We Were WRONG About the Quantum Eraser! in HD free online. Enjoy high-quality streaming of PBS Space Time Season 2025, Episode 21 and share your thoughts in the comments below!
Comments
No comments yet. Be the first to comment.
Episodes
25 episodes
How Many Black Holes Are In The Solar System?
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.
21 min
Does Timescapes DISPROVE Dark Energy?
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.
16 min
The Crisis in Physics: Why the Higgs Boson Should NOT Exist!
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.
19 min
The Final Barrier to (Nearly) Infinite Energy
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.
22 min
Will The Big Bang Happen AGAIN (and Again)?
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.
18 min
Your DNA Is (Almost Certainly) From Outer Space
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.
18 min
How Astrophysics Can (LITERALLY) Save the World
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?
20 min
NEW EVIDENCE: Earth Had Rings (and Might Regain Them)
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.
19 min
Why Didn’t Antimatter Destroy The Universe? | LHC Breakthrough
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.
18 min
Quantum Energy Teleportation is REAL!
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?
20 min
Is There A Simple Solution To The Fermi Paradox?
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.
21 min
Is Our Model of Dark Energy WRONG? | New 4.2σ Results
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?
22 min
The Crisis In Physics: Are We Missing 17 Layers of Reality?
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?
21 min
Are The Fundamental Constants Finely Tuned? | The Naturalness Problem
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.
20 min
How Did SPACE Shape Your DNA?
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.
20 min
Why The Multiverse Could Be Real
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?
20 min
Is There Evidence For a Vast Multiverse?
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.
19 min
The Most Important Satellite You’ve (Probably) Never Heard Of
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.
15 min
At What Point Does Spacetime Become Quantum?
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.
21 min
Why Life on Mars Will DOOM Humanity
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.
21 min
We Were WRONG About the Quantum Eraser!
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.
25 min
Why Antimatter Engines Could Launch In Your Lifetime
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.
22 min
The Gravity Particle Should Exist. So Where Is It?
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?
23 min
The Biggest Planet Discovery in History Is About to Begin! (Next Year)
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.
23 min
Heisenberg Made a Discovery in 1925. We Still Can't Explain It
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.
27 min