I am Brian Greene, Theoretical Physicist & co-founder of World Science U. My obsessions: Space, Time, Quantum, Einstein, the Cosmos. AMA!

I was blown away by the Many Worlds interpretation of quantum mechanics. If we assume that it's true, and we also assume that I haven't completely misunderstood quantum experiments, would it be possible that there is a parallel universe where every single experiment ever conducted that normally gives results that agree with quantum mechanics, gave results consistent with Newtonian physics, thus never giving rise to quantum theory?

Yeah--that's one of the difficulties with making the Many Worlds approach to quantum mechanics work. If it is true, we would be 100% certain that there would be worlds in which the inhabitants would witness outcomes that would NOT provide support for the predictions of quantum mechanics itself.

Those who develop these ideas want to prove that such worlds are RARE in some well defined sense of the term. But as you've already pointed out, that's pretty challenging to do.

Professor,

Given the latest developments in quantum mechanics, even the crazyiest ones like the holographic universe, I'd like to know your personal opinion:

Do we have free will? Can we measure it?

Tough question of course. But as I don't think there's free will, I'm compelled to answer it.

Clearly, there's much about reality we don't understand. But based on the current laws of physics, there's just no room for human intervention, no room for what we usually call "free will". We are all collections of particles that fully play by the rules of physics. There's no place that we can step in and change the course of how those particles -- you and I -- evolve. The SENSATION of free will is real, of course. But that's all it is--a sensation.

So would you say you're a hard determinist?

Yes. But I'm open to being proved wrong. I'm excited by the possibility that in the future, physics will teach us that there's another way to think about reality.

(Note: Quantum mechanics IS a deterministic theory. What it determines, though, are probabilities.)

What is your opinion about compatibilism -- the thesis that determinism and free will are compatible?

I think they are compatible so long as one properly interprets the phrase "free will". If free will is the sensation we have of making choices, making decisions, deciding what to do, then sure--that sensation is definitely real, even in a deterministic universe.

I have a good high school education, and a college degree from a good university, but I never formally studied any physics (basic or advanced) at any educational level. I've picked up a lot along the way, but if I wanted to get an adult introduction to physics (as a preparation to taking more advanced courses), how do you think I should start?

Thanks for the question--and apologies if this sounds like a shameless plug. But the project I am just about to launch, World Science U, is meant in part to fill this need. The idea is to create next-generation online science courses which make the abstract ideas of science visual, interactive, and exciting. We are starting with two pilot courses on Einstein's special relativity--one is purely conceptual and the other is mathematical. All are filled with animations that show how time slows and space compresses, and so on. In time, we will add other courses in math, physics and the other sciences too, biology, chemistry, astronomy. You should check it out.

I'm super excited about World Science U, by the way. Thanks for sharing the knowledge!

Nothing more exciting to me than making the wondrous ideas of physics and science more generally as widely available as possible.

so who else is planned to teach? is it all being taught by you?

We're talking to a handful of top-notch educators/researchers--and the level of enthusiasm for the project has been gratifying. Scientists WANT the world to learn science, and we know full well that we've not done anywhere near what we could to make the experience as easy, effective, enjoyable and exciting as it might be.

when will the other courses be announced?

The site will go live next week and new courses will be announced in the coming months. You can get a sneak peek for our approach by going to worldscienceu.com.

Will you give out any sort of diplomas for people who participate in World Science U? Or is it just for informational purposes?

For now there will be certificates of completion and certificates of achievement. In the future, we'll see.

You may want to check out Leonard Susskind's 'The Theoretical Minimum.' He has several lectures on YouTube as well as a book by the same name.

Definitely. Lenny is a great physicist and wonderful expositor.

Dr Greene, in The Elegant Universe, you say that an electron will go through all possible paths in the double slit experiment. One path is "a long journey to the Andromeda galaxy before turning back and passing through the left slit on its way to the screen." If the electron is detected any time in our lifetime, wouldn't it not have enough time to take that path?

Screenshot of section:http://imgur.com/sAR06wB

Yup, right you are. But here's the amazing thing: If you do indeed interact with that electron before it hits the detector screen, you will gain information about its trajectory, and by so doing you will SPOIL the double slit interference pattern. The universe is sharp: if you try to access information you "shouldn't" have, the experiment will show traces of your meddling. The interference pattern won't form.

Hello Dr. Greene and thanks for doing this AMA. I don’t have a question, I just want to tell you that in 2002 I was in a very rough place in my life and had entered a recovery program that encouraged me to find a belief in a power greater than myself. I’d been raised Catholic and had come to disagree with the teachings of the church but I had begun to think that maybe I should go back to Catholicism just to have some kind of higher power to believe in.

Then one day I got an email from my college’s alumni association announcing that you were giving a lecture on string theory and it was open to the public, so I decided to go instead of going to a meeting. That night I heard you talk about the possibility of the universe being made up of all these tiny vibrating strings, and how one reason the big bang theory can’t be proven is because, if I remember your analogy correctly, if you think of the universe as a film strip on a projector and you take that film off and look at each frame, the film breaks down and disintegrates before you can see the origin of the universe. In that moment, I understood what it meant to feel like there are powers way greater than myself in the universe, and that there are things going on all around us that I have absolutely no control over. It was the spiritual awakening I needed and was looking for. It helped me tremendously at a time when I really needed it. I’ve always wanted to tell you that. Thank you for everything you do.

Thank you for telling me. Much appreciated.

Does your head still hurt when you think about quantum mechanics?

Always.

If you study quantum mechanics and your head doesn't hurt, make sure someone takes your pulse. You may no longer be with us.

Would you rather fight 1 horse-sized multiverse or 100 multiverse-sized horses?

In this universe, I'd go with the horse-sized multiverse. But ask the the Brian Greene in one of the other universes and he may feel differently.

Hi Brian, big fan of your books and especially of your way of teaching science, to which I look up to when I try to teach science to my son. However, this two-part question is not about science or physics, it is about veganism. The first question is how do you approach veganism, from an emotional view in which you are displeased with animal suffering or from a rational point of view in which the consumption of animal-derived products is not a necessity for the majority of the population? The second question is somewhat related, how often does veganism come up with fellow physicists/scientists and how do they tackle the issue, emotionally or rationally?

For me, it's pretty simple: I am totally grossed out by the idea of eating an animal. Started when I was 9 yrs old and my mom cooked spare ribs. I was a city kid and to me meat was just another thing that you bought at the supermarket. Had no idea meat was from animals. But when I saw those ribs, tasted that flesh--I was done with meat. (My mom still thinks that if she'd only used her other recipe....)

But I'm not an activist about being vegan. It's just what I do. I don't try to convince anyone else to do the same. (Except my kids who routinely act out for their friends the death throes of a chicken being slaughtered. Doesn't make me popular with the parents).

Greetings Dr Greene.

If you could pin point something that the educational system is doing wrong when it comes to getting young students intersted in science and math. And what can be done about it?

I think we teach the details of science without providing a parallel focus on the big, amazing ideas which those details allow us to understand. It's like teaching music by having the student only learn scales and never hear Beethoven. That's not to say that some teachers are fantastic. But overall, this is the big problem.

Hola, Dr. Greene. I've been a great fan of yours since I was a little girl!

What's your take on Boltzmann Brains?

Avoid them at all cost.

(For those who dont' know the term--a Boltzmann Brain is a brain that spontaneously forms, on its own, from the random coming together of matter, a random fluctuation that generates a mind.)

Once Boltzmann Brains afflict your theory, you are in a difficult spot--hard to trust anything once our theory tells us that all our thoughts might be taking place in a brain that just formed. All our memories would be of things that didn't happen, just thoughts that formed with the brain itself. Can't even trust our memory of experimentally verifying the very laws of physics which we used to draw our conclusions. It's a mess.

Dr. Greene... being from Europe, I'm appaled at the level of support in the US for Creationism and other "movements", which are trying to sideline scientific reasearch and development. Is it really that big a deal or are "they" just riding a media hype?

Here's my view: There is no way for science to rule out a god, so when (some) scientists claim that religion is nonsense, we are doing ourselves a huge disservice. We garner applause from those who already hold the same perspective and disdain from those who don't. That kind of talk changes very few minds.

On the other hand, science can, and should, and does, and must argue forcefully that as a description of the natural world, science is our most powerful tool. Science is the future of a living, breathing, thriving culture.

So we need to make sure that everyone keeps straight the relevant domains. Religion--teach it in classes on theology, practice it in sacred halls. Science--teach it in the science class, practice it as a means of understanding and controlling nature.

Don't bring religion into the science class.

So, is it a big deal? Yes, but we're on it.

I am a little confused about the hypothesis that we may live in a holographic universe. If a 3 dimensional image is projected from 2 dimensional information how do we account for the layers that we know exist in the 3rd dimension? For example, how could 2D information form all the layers in the human body. Is it because matter is mostly empty space and therefore layers in the 3rd dimension wouldn't necessarily "block" the appearance of all the layers? Thanks so much! I really enjoyed your recent lecture at the Air and Space Museum!

You're confused? You are not alone. We are confused too. The holographic principle--that we may be, in a very specific sense, holograms is among the strangest ideas we've been led to by recent research.

The idea is this: ALL the information necessary to describe (or reconstruct fully) an ordinary 3d object like a baseball can be fully stored on a 2d surface. If you looked at that information the baseball would not appear as it ordinarily does--the information is highly encoded. But the amazing thing is that ALL the information can be stored there, even though the surface only has 2 dimensions.

In that sense, all the usual coming and goings in our 3d world is equivalent to information zipping this way and that on the 2d surface--kind of how a hologram is a 2d piece of plastic that encodes a 3d image.

Crazy sounding idea--but that's where some of the math has taken us.

It's hard to read this and not immediately think, "so The Matrix is real?"

It does sound Matrix-like. But the vital point is this:

We don't come up with these ideas by staring at a blank page and trying to come up with an interesting script. We don't let our minds go wild, come up with nutty ideas, and then try to shoehorn them into physics. Instead, we let the math guide us. That doesn't mean that the mathematical ideas are all correct in the sense that they all describe reality. That is a question, ultimately, that only experiment can answer. But the math has already proven itself a powerful guide.

So, all of the data is being compressed. We're just zip files on a big, expanding computer.

Far more compressed than that. The amount of storage on a surface bounding a region of space puts to shame every hard drive ever manufactured.

So is that amount of storage infinite for any given area?

Not infinite. Instead, there is a wonderful little formula that tells that the amount of information is equal to the AREA of the surface divided by 4 (when expressed in natural units).

Similarly information of a 2D object can be stored on 1D line ? 1D to a point ? It would be great if you can explain how it is possible to store complete information of a 3D object on a 2D surface because I tend to think that dimensionality reduction might result in loss of data.

PS: Big fan, Columbia alum here :-)

No loss of data: Instead, there is LESS information in any volume than you'd think. Not talking air heads here--but if you consider the MAXIMUM information possible in any 3d volume, it is proportional to the AREA of the surface bounding that volume.

What would you say to a student who loves physics but is hesitant to study it due to job uncertainty (particularly compared to something like engineering)?

You have to do what fires you up. And if physics is it, go for it. But that's a question only you (or the student) can answer.

I've had many students speak to me about their love of physics but how they did not want to do the math, or get into the details. The only loved the ideas. That's cool. That's fine. But that's not what it takes to be a physicist. You have to love the ideas and also the work itself.

what is your take on the format of frontiers of science course you teach at columbia university? is it useful for freshman to be forced through a generic science course that's akin to those in high school or is it simply necessary?

The great works of science need to be placed right next to great works of literature and music and art. The great works of science need to as central to a full education as anything else our species has produced.

How best to do that? Tougher question. Personally, I'm not a great fan of any kind of required courses...

So Big Crunch or Big Freeze?

Also do you think it is plausible that dark energy diminishes over time?

Big Freeze. Forecast for the far future of the cosmos is cold, dark, dilute. As far as we can tell.

Hi, Brian! Do you think that math is a sort of objective truth that is discovered, rather than made up? Also, you're one of my favorite [vegan] scientists!

Depends when you ask me. If I've just completed an exciting calculation, often feels like the math was there to be discovered. But when I take a step back and really consider math itself, seems more like a language we make up.

Is the universe fundamentally mathematical? Surely seems so. But I could imagine that one day we encounter an alien civilization and they say "So, show us what you've found to explain the universe" and we open our math-filled texts. To which they chuckle "Oh, math. We tried that. Only takes you so far. Here's how to REALLY understand reality..."

Now, what would they show us? That is, what would they show us that in some deep way would not be EQUIVALENT to math? I don't know. Hard to imagine. But that could easily be a failure of creativity, or a limitation of our human brain.

Hi Brian, Im a big fan! Thank you for taking your time and doing this AMA. Im a 16 year old Israeli high school student and I usually get good grades, but a couple weeks ago I messed up on my geometry test, my math teacher came up to me and said - "math is like drawing some people can't draw and some people are just born bad at math". that comment really got me depressed, it's hard for me to believe some people are "just born bad at math" and i'd like to ask you as a person who's career is math based - what's your opinion on the matter, are some people born bad at math?

Some people have a natural talent for math, others find it harder. But I can tell you from decades of experience -- it is all about hard work. Ideas that can seem impenetrable CAN be mastered if you take your time and press on step by step.

Five-Year-Olds Can Learn Calculus https://plus.google.com/109794669788083578017/posts/bsLnjfAJThP

When yours truly was five, I was counting on my fingers, to be sure.

Hi Brian! First off, I think I speak for everyone when I say thank you for making incredibly complex topics accessible to a general audience; your books inspired me to have a huge interest in cosmology. I saw your talk last week at the Air and Space Museum in Washington, DC but didn’t get a chance to ask my question there, so hopefully this time is better.

My Question:

Where do you think the laws of physics came from? Why do they exist and why does the universe seem to follow these laws?

Most direct answer: I don't know. No one does. Did those laws exist prior to the universe? Do they come into existence with the universe? And if so, what governed the process of their creation? Or perhaps, is the very notion of time that underlies the question just not applicable? Might it be that the laws JUST ARE. PERIOD.

The sign of a tough question: All I can do is elaborate on the question itself.

Hi Brian, I'm a big fan and thanks for doing this AMA! If you could grab a beer and talk shop with any physicist throughout history, who would it be and why?

Let's see--Newton would be up there at the very top. I'd jump right in and explain quantum mechanics and general relativity, and watch the great man's jaw drop to the floor.

What, currently, do you have in your pockets?

Electrons, quarks, gluons...and strangely, what looks like an old peanut (?)

Does all motion really stop when we hit absolute zero? Can it ever actually get that cold? One of the predictions of quantum mechanics is that you can't ever measure the exact position or momentum of a particle with perfect certainty -correct. If the particle completely stops then we will KNOW its exact position and momentum.

Isn't getting down to absolute zero has essentially the same problem with getting up to the speed of light? Always closer but never over.

Yes, great point. And in your question is the seed of the answer. If absolute zero really did mean all motion stops, then we'd know position and velocity as you say. But the Uncertainty Principle says that can't happen. So....it must be that at absolute zero all motion does not stop. There is a residual amount of "quantum motion" or "quantum jitter" that you can't eliminate.

Brian - Loved The Elegant Universe and the Nova special you did on it. Is there anything new in the field of String theory? Is it still a valid theory or has it gotten more complex.

Many thanks.

There is much new in string theory. A question I just answered on the possibility that we are, in a sense, holograms is one of the strangest new developments. But what we lack is any connection to experiment or observation. And that is the only way to know if these ideas are correct.

Do you think it would ever be possible to use entangled particles to create some kind of morse code that could be used for communications over large distances? If you know how one of the particles will react when you do something specific to the other, could you use that information to create such a code and communicate instantaneously over large distances (light-years)?

No. Quantum entanglement is a startling subject. The quantum notion that a measurement you do here, say in NY, can immediately impact the results of other measurements being done far away, say in California, is stunning. So stunning that Einstein called the possibility "spooky" -- a derogatory description showing Einstein's belief in a more conventional classical reality. But the "non local" effects of quantum theory (as they are called) are now experimentally confirmed. That's amazing.

However, to your question: You can't send information with these spooky quantum effects. That's how these effects still respect the dictum of special relativity that nothing goes faster than light. "Nothing" here means -- in the quantum interpretation -- no information. So spooky quantum effects just barely co-exist with special relativity.

Thank you for being open about your diet choices. This may sound silly, but when people try to argue that I’ll damage my brain I point to you! I know it probably seems silly, but thanks for being out there.

As long as no one throws tofu at your head, you'll be just fine.

even that probably won't hurt you that much.

Just back from dinner and, indeed, it was tofu. Tough tofu. If this piece hit your head, I'd worry for your brain.

Hi Professor!

What will be the next major breakthrough in physics?

Also, what book do you recommend regarding physics for someone who already knows about the subject?

If I knew the answer to that, I wouldn't be doing this AMA. I'd be working on it! My guess: Next major breakthrough will be in understanding the "ingredients" that make up space and time themselves.

Since the past, present, and future all exist simultaneously, can we say the future is pre-determined? and the past is still in this universe?

Einstein said it best:

"To we convinced physicists, the distinction between past, present and future is only an illusion, however persistent."

Hi Dr. Greene, thank you for your time.

You have been a big part of bringing String Theory to the populace, and making it somewhat understandable to laypeople. I know scientifically it's a "theory" and that's the way science works, but are you yourself completely convinced that it represents the best version of "the way things work" that we are capable of reaching (at least, with our current level of knowledge)? Are there any other theories that are currently being posited which you think are equally possible, or at least have a fighting chance?

Also, I can't wait to check out worldscienceu.com.

Not too long ago I was at home listening to a radio program about science when the host described me as a "staunch believer in string theory." I almost hit the roof. I don't believe in string theory. I don't believe in anything that doesn't have experimental support, observational evidence. So, similar to your description I would say this:

I think that string theory represents the most compelling approach we currently have for melding quantum theory with Einstein's general relativity. And that's a big deal. The failure to unite these two theories has been a large gap in our understanding for decades. But the union of which I speak is on paper. We don't yet know if the theory is correct. And indeed, there are other approaches (eg loop quantum gravity).

I don't work on those other approaches because they seem less promising to me. But nature is what decides what's right and what's wrong. And as of today, the jury is still out....

Dr. Greene,

You are quite possibly the only person I have ever considered to be my role model - your passion, dedication, intellect, and demeanor are truly inspiring. Thank you for all the work you do. (and for answering my question regarding World Science U on facebook the other day)

What's on your plate right now? Research? World Science U? A new book? Any appearances in the Midwest *crosses fingers *?

All of the above except, sadly, for an appearance in the Midwest.

Will World Science U have an outlet or page for live discussions among people exploring the courses?

Yes.

Hi Dr. Greene, what are some interesting concepts in theoretical physics that you think could be "confirmed" by observations in the near future (maybe 5-15 years)?

I'd say gravitational waves are one big one. Einstein's general relativity tells us that the fabric of space can warp and curve. It can also ripple, sort of like what happens if you throw a pebble into a pond. And if a ripple of space-time were to roll by Earth, it would (gently) stretch things one way and then the other. The stretching would likely be on the scale of atomic distances, making it, well, hard to measure. But there are some powerful gravitational wave detectors now in operation with the hope that we will see something some time soon.

Hey professor Greene! I was wondering if you could shed a bit of light on quantum measurements, and how they affect the multiverse. More particularly the evidence behind quantum measurements creating new universe's. Cheers, Ian

Wish I could. There are a number of proposals for solving the quantum measurement problem, but very unclear which if any is correct.

Thank you for taking the time to answer our numerous questions. What do you think is the next big step for researchers in string theory? What lies in the future of this famous yet not well understood theory?

Understanding the foundations of space and time. Are space and time fundamental or emergent? If emergent, as many think, are they made of finer constituents? What are the "atoms" of space and time. And what is the best way to formulate physical law without invoking the notions of space and time?

Is SUSY almost dead? Or will the higher energy at the LHC pull out a win? Go on the record!

The LHC will not be able to rule out SUSY. The LHC can make it difficult for SUSY to solve certain puzzles (like the hierarchy problem), but it can't rule SUSY out as a potential component of physical law.

Perhaps worth noting: I'd be THRILLED if we could rule out SUSY or String theory. Why? I'm focused on progress, not proving one particular theory relevant to reality. We go around once (I think) and don't want to spend my time and energy on wrong ideas. Great progress comes from confirming ideas, of course, but also from ruling out other ideas.

White or wheat toast? Also, aside from Special Relativity, what scientific breakthrough of the 20th century most impresses you?

Quantum mechanics.

The reality quantum theory paints is so spectacularly distinct from what anyone thought and so monumentally unexpected.

That's not to say that the woo-woo applications that are sometimes ascribed to it have any relevance or value. And it is not to say that we don't understand quantum mechanics really well. But if you asked a physicist in the 1800s whether anything like quantum mechanics would have any chance of describing reality, I think they'd look at you like you were nuts. And yet, by 1927, we learned that quantum theory is how the world works.

Do you think we'll ever know what led up to the big bang?

I do. We don't yet. But there's no known fundamental reason why we can't make significant progress on this deepest of all questions.

In fact, I'd say that it is this very question that, at some level, drives many theoretical physicists to do what they do. Certainly, the urge to understand the origin of the universe has been a driver for me.

Hi Brian,

What are the (ultimate) limits of understanding the world through physics? Are there any?

Well, any limits we encounter will likely reflect limits of the human mind. Look, dogs are smart but they don't understand quantum physics. (I think.) Chimps are smart but they don't understand general relativity. (I think). Our DNA differs from the chimps by some small number like 1.2%. And with that little difference we've been able to go farther. But who is to say that that difference gives us enough grey muscle to answer the deepest questions of reality? Definitely there's a chance we hit the wall. So far, though, we are going strong.

What are your favorite television series?

I love the old Twilight Zone series, was a great fan of Six Feet Under, and only recently started watching Breaking Bad (up to season 5 now....don't tell me now it ends).