---
title: 'Brian Greene Answers Quantum Physics Questions'
source: 'https://youtube.com/watch?v=7bbZysDRSp0'
video_id: '7bbZysDRSp0'
date: 2026-08-04
duration_sec: 1517
---

# Brian Greene Answers Quantum Physics Questions

> Source: [Brian Greene Answers Quantum Physics Questions](https://youtube.com/watch?v=7bbZysDRSp0)

## Summary

In this video, physicist Brian Greene answers a series of questions about quantum physics, covering topics such as quantum mechanics, wormholes, the multiverse, time travel, teleportation, the nature of reality, black holes, quantum computers, entanglement, and the fate of the universe. He provides accessible explanations and addresses common misconceptions.

### Key Points

- **Understanding Quantum Physics** [00:31] — We understand the core ideas of quantum physics, but it requires reorienting our thinking about how the universe behaves.
- **Wormholes Explained** [01:16] — Wormholes are hypothetical warps in space that could connect distant locations, but we don't know if they exist.
- **Quantum Tunneling** [02:11] — Particles like electrons can pass through barriers via quantum tunneling, but for macroscopic objects like humans, the probability is exponentially small.
- **Multiverse Theory** [03:21] — The Big Bang may not have been a one-time event; mathematics suggests a multiverse of expanding universes, possibly testable via bubble collisions.
- **Time Travel to the Future** [05:18] — Travel to the future is possible via time dilation near light speed, but travel to the past remains uncertain and likely impossible.
- **Quantum Teleportation** [06:35] — Quantum teleportation works for particles via entanglement, but not for macroscopic objects like humans.
- **What is Reality Made Of?** [07:17] — Reality is made of fundamental particles (quarks, electrons) and possibly even smaller constituents of space itself.
- **Quantum Weirdness** [08:38] — Quantum mechanics is weird from the start, but it works; it describes superpositions and entanglement, and it underlies all of reality.
- **Black Hole Evaporation** [09:37] — Stephen Hawking showed that black holes radiate particles and eventually evaporate, but what happens at the end is unknown.
- **Electron in Two Places** [10:48] — An electron can be in a superposition of two paths, but it's still one electron, not two.
- **Block Universe Theory** [11:34] — The block universe idea suggests all of time exists simultaneously, which can be comforting as nothing ever truly dies.
- **String Theory Status** [12:16] — String theory is not dead; it's the best-developed framework for unifying quantum mechanics and gravity, though not yet tested.
- **Beginning of Time** [13:17] — Time may have a beginning at the Big Bang, similar to how 'north' begins at the North Pole, but other ideas exist.
- **Quantum Computers** [15:08] — Quantum computers use superposition for parallel calculations, offering exponential speed-up for specific problems like factoring.
- **Quantum Entanglement** [16:35] — Entangled particles have correlated behaviors even when far apart, a phenomenon we still don't fully understand.
- **Schrodinger's Cat** [17:29] — Schrodinger's cat illustrates how quantum weirdness can be amplified to macroscopic scales, but it's a thought experiment.
- **Does Observation Create Reality?** [19:06] — Observation/measurement can influence quantum systems, but exactly how remains a mystery.
- **Why Atoms Don't Collapse** [20:05] — Quantum mechanics explains that atoms have a lowest energy state, preventing electrons from spiraling into the nucleus.
- **Laws for Super Big Things** [21:13] — General relativity governs the very large, quantum mechanics the very small, but we haven't found a new set of laws for super big things.
- **Why Does Anything Exist?** [22:37] — Physicists don't have a definitive answer; a state of absolute nothingness may be unstable and quantum mechanically fall apart.
- **Fate of the Universe** [23:34] — The universe may expand forever, with matter disintegrating into a cold, quiet bath of particles.

### Conclusion

Brian Greene provides accessible explanations of complex quantum physics concepts, emphasizing that while we understand much, many deep questions remain unanswered.

## Transcript

- From Doktor J: "Boy, are you quantum gravity? I have no idea what you're referring to Hi, I'm Brian Greene, physicist, professor, author,
to answer your questions from the internet. [upbeat music] @peleenmziry: "Do people actually understand quantum physics
We understand the core ideas, that we would think should happen in the universe
So we have to reorient our thinking but it is something that those of us So yeah, we do understand a lot about quantum physics.
"Has some grizzled professor," like me, to explain wormholes ever made anyone go 'aha!'? Still seems like an incomprehensible magic to me."
I can draw a line connecting them, So imagine this is in space. and this is our Milky Way Galaxy.
It can warp so that these two locations that were very far apart are now very close together. you now see that the orange between the two locations,
We don't know if wormholes are real. but if they do exist, from one location to another.
From Do0ozy: "If I ran into a wall over and over again, to eventually pass through the wall? I would need to run into the wall to pass through?"
Now look, we don't do quantum mechanical experiments with macroscopic beings like a human body, but we do a version of you running into a wall
with a particle like an electron or a neutron or a proton that we fire at a barrier over and over and over again. we do find it passes through a barrier
If you scale this up, yeah, in principle, could undertake the same experiment.
You'd have to hit this barrier enormous number of times, exponentially large in the age of our current universe. the probability that you will pass through the barrier is.
AssusReamus: "Is our universe the only universe?" because it's the only one that we can observe But there's mathematics suggesting
that the Big Bang may not have been a one-time event. giving rise to many expanding universes that all populate a grand multiverse.
where the individual bubbles are universes like our own, many of these universes.
they say, "You're talking nonsense. They have a point, this is an important criticism, Number one, in principle, this may be a testable idea.
If two of these bubble universes were to collide, could leave an imprint We've not yet seen it at all,
this would be circumstantial evidence The second point I would make is a theoretical statement. For instance, the Big Bang idea has been tested
It has confirmed the predictions, which is wonderful. But if the math then says there should be other universes, because we have confirmed the parts
of the mathematics available to our observations. We don't, but we are willing to consider it suggests that this really may be true.
@Joonies_Girll: "Do we have any updates on time travel? what was happening on planet Earth a million years from now, for how in principle you could do that.
Say you go six months, You will be one year older, of course, your clock was ticking slow
So when you step out of that spaceship, it may be 2 years or 5 years or 10 years or 100,000 years, all dependent on how close to the speed of light
But many of us are more interested And that's the one where we just don't know. using exotic things like wormholes
or interesting kinds of motions around cosmic strings, we don't have an answer. And so we suspect that travel to the past is not possible,
but as of today, nobody has definitively ruled it out. Why is teleportation not possible?" It's not possible for macroscopic objects like you and me,
routinely teleport individual particles You set up two entangled particles that in some sense
You bring in whatever you want to teleport And through the magic of entanglement, This person can manipulate that particle
and extract an exact copy of the original. from one location to another. @sinonghostriley: "What is reality made of actually?
Way back in the early days, people though it was earth, air, fire, and water In the early years of the 20th century,
that matter is made of fundamental constituents, And as we examine atoms with ever greater precision, that make up atoms.
that are in orbital clouds around a nucleus And the neutrons and protons themselves we know are made of yet smaller particles known as quarks
They are the bulk of matter as we know it. atoms making up the fabric of space itself.
I think there will be fundamental constituents of space What those ingredients actually are, but my guess is that that is
where our understanding will lead us. "When does quantum mechanics get weird?" Quantum mechanics tells us
of different mutually incompatible states of being. It tells us that distant objects can be weirdly connected It's weird from the beginning and yet it works.
in terms of billiard balls bouncing around according to ideas and laws that he was able to intuit. the micro world doesn't behave that way.
called quantum physics. we can extract them from quantum physics. it's quantum mechanical through and through,
and quantum mechanics suppresses the weird stuff making the world appear to play But fundamentally, everything is quantum mechanical
"If nothing can escape a black hole, Stephen Hawking determined way back in roughly 1974
as the mathematics Particles in a sense can leak out of a black hole quantum mechanically.
And as particles slowly radiate from a large black hole, which means the intensity of the radiation until at the very end there's a gigantic burst of radiation,
which in essence is the death throes of a black hole. will take about 10 to the 68 years that the black hole will shrink down
But what happens then? Nobody knows. "If an electron can be two places at the same time, how do we know those are not two different electrons?"
We fire a single electron into an experimental context in which the results that we find can only be explained the electron took two different pathways
Since we only put one electron into the experiment when we find in the intermediate stage that the electron it's only one electron that's doing that, not two.
"I just learned about the block universe theory, It's funny that you're having an existential crisis.
To me, the block universe idea is very comforting from an existential standpoint. The idea is rather than thinking of the past as being gone
we imagine that all of time is out there within this block that has all of time and all of space. From that standpoint, we always exist
because the block itself containing all events, So in that sense, nothing ever dies. always occupies that position in the block.
From @miniapeur: "Is string theory dead?" you might get the impression that string theory is dead. string theory has been making enormous strides
and understanding the nature of space and time. that we can test in the laboratory, Physics is trying to understand a coherent description
We don't have such a coherent description. but string theory is the best developed together into one consistent framework.
On that front, string theory is absolutely an enormously important development in the history of ideas. "If everything has a beginning, then when did time begin?
what was here before that beginning?" who does know the answer to that question. Let me just throw out a couple of them to you right now.
It could be that there is a beginning to time. You know, if you're walking on planet Earth "Hey, can you point me in the direction of further north?"
Yeah, point me in the direction of north. When you get to the North Pole and you say to someone there, "How do I go further north?",
"The concept of further north The North Pole is where north begins." that you can imagine going back a hundred years,
When you get to the Big Bang, it could be that the concept of going further back in time than the North Pole.
It could be that time itself simply began There are other ideas that people have developed In fact, there are some theories
is simply one expansion of space event has undergone this kind of rapid outward swelling,
other universes populating a grand multiverse. From Jerswar at the explain like I'm five subreddit: "What is the big deal with quantum computers?"
a particle can be in multiple places at the same time. A quantum computer leverages that multiplicity to carry out multiple calculations in essence in parallel,
on how fast the computer can in principle get to an answer. But there's a second part of quantum computation,
How do you find the answer among that multiplicity And so for a certain class of questions, a quantum computer can give rise to an exponential speed-up.
that works for other problems won't be applicable. And so my suspicion is that quantum computers will be a very niche-oriented kind of device
like simulating quantum systems or factoring numbers into their prime factors, that sits on your desk or on your lap
the kinds of things that we are familiar with. From @kero_sock: "What the [beep] is quantum entanglement?" we know that they can act independently of one another.
But in the quantum world, two things can be far apart, from a behavioral standpoint, Imagine you've got a particle whose spin, we call it,
And you can have two of these particles. a measurement on one of these particles The other particle, if they're quantum entangled,
and acquire a single definite reality. quantum entanglement bridges the gap between them and allows their behaviors to be tightly choreographed
in a way that we're still struggling to fully understand. What you do here quantum mechanically if the two objects are quantum entangled.
"Schrodinger's cat seems like a dumb concept." of Schrodinger's cat then,
Back in the 1930s you might have tried to argue that the weirdness of quantum mechanics
and we simply don't need to think about it Schrodinger's cat was introduced by Schrodinger And he basically said, look, if you have an electron,
of being here and being there, I'm willing to accept a particle in some mixture because it's in the microscopic world
We can amplify the weirdness All we need to do is set up a little gadget which has poison that will be released into this box
but it won't be released into the box And then if we put a cat in the box, the poison is in a 50/50 mixture of being released
which means the cat must be in a 50/50 mixture Quantum physics, he was saying, whereby it can infect the everyday reality
@ResonanceEnter1: "Does observation create reality?" There are physical systems where if there is no observation,
the system evolves and behaves one way. that interaction does change how the system behaves. if it sufficiently impinges on a particle like an electron,
that photon can coax a definite reality to emerge. that we have not yet fully understood is why is it that an observation or a measurement
on a quantum mechanical system? Somehow, intervention, environmental influence, but exactly how this happens,
still struggling to understand. El-Kabongg: "Why do atoms not run out of energy?" We've known since the 1800s that as electrons accelerate,
And if they radiate away energy, that electron should spiral into the nucleus and crash. The answer, according to quantum mechanics,
is that there is a lowest energy state that's available to a system like an atom, for the atom to achieve a lower-energy configuration.
on how close the electron can get We can actually calculate that lowest energy state
and then we can compare it to the energy states of atoms. It can come in chunks that can't be subdivided. From the Manuko subreddit:
At the normal level, we have relativity. Is there another set of laws for super big things?" but I would say for the super big,
That's Einstein's theory of gravity. when things are ever larger, for stars and black holes. We are the in between, the very small and the super big,
And so there are things in the world where quantum mechanics rears itself There are other things that we encounter
that have general relativity flexing its muscles, but we haven't found that there's a new set of laws Instead, our challenge
so the calculations that we human beings we want those calculations to make sense And that is a blending that we have been trying to do for,
From @ignorethatdoor: "Why does anything exist? so how did something come from nothing?"
All we physicists can do Energy, matter, a configuration And then from that point forward,
we analyze what happens to that something, that then come together to yield stars, galaxies, But if you push further back and ask,
nobody really has an answer yet for that. A state of absolute nothingness may be unstable.
may quantum mechanically fall apart We don't, but at least it's an interesting idea for how you could start with nothing and yield a something.
@troll_on_patrol: "What happens after the universe dies?" in this little stack under here, "Until the End of Time."
but one dominant possibility is that in the very far future, the universe will continue its spatial expansion. material objects will continue to disintegrate.
Even black holes disintegrate into a bath of particles. And so that suggests that in the very far future,
the universe will be nothing but a bath of particles ever quieter, ever colder cosmos. existed in the early universe,
Those particles come together for a brief period of time, and on this planet people as well. And then in the far future, it all disperses once again.
So everything that we know about, everything we care about, may just be a momentary aggregate of particles and then for effectively an eternity,
there's nothing but particles wafting through the void. All right, that's all for today. Thanks for joining us. This is Quantum Physics Support.