Thanks to SPS for the link.

http://calitreview.com/790

Susskind Quashes Hawking in Quarrel Over Quantum Quandary

CLR INTERVIEW: Leonard Susskind is the Felix Bloch Professor of theoretical physics at Stanford University. His new book, The Black Hole Wars, details his battles with Stephen Hawking over the true nature of black holes. The resulting theory postulates that every object in our world is actually a hologram being projected from the farthest edges of space. Below is Dr. Susskind's interview with the California Literary Review.

Would you give us an overview of what a black hole is?

A black hole is what you get if you compress so much mass into a region of space that it collapses, under its own weight, to an infinitely small, dense, point called the "singularity." Everything that gets too close to the black hole gets sucked in, and squashed beyond recognition. There is no escape from the singularity, even for a light ray. Someone falling into a black hole might try to send a message, on a beam of light, to the outside world: "Help, I'm being sucked in." But even the light ray gets pulled back to the singularity.

There is a certain radius—a particular distance from the dangerous singularity—that I like to call "the point-of-no-return." If you accidentally pass the point-of-no-return there is nothing you can do to escape; you and all your messages will get swept to the singularity and destroyed. The point-of-no-return is also called the horizon of the black hole.

Passing the horizon seems very innocent while it is happening. It's like being in a rowboat above Niagara Falls. If you accidentally pass the point where the current is moving faster than you can row, you are doomed. But there is no sign—DANGER! POINT OF NO RETURN—to warn you. Maybe on the river there are signs but not at the horizon of a black hole.

Stephen Hawking once said something about black holes that apparently upset you. What was it?

Stephen said that when a bit of information falls into a black hole it is permanently lost to the outside, despite the fact that he also proved that black holes evaporate and eventually disappear. That claim touched off a crisis in physics, a clash of basic principles like no other since Einstein was young.

The problem that upset me is that the most basic principle of physics—the principle that underpins everything including classical physics, thermodynamics, quantum mechanics, energy conservation, that physicists have believed for hundreds of years—is that information is never truly lost. It can be scrambled beyond recognition, but it is never completely erased.

Hawking's claim was outrageous, but he had very good reasons for it. So good that it took more than two decades to figure out why he was wrong. And the question led to a tremendous paradigm shift in the way we think about space, time, matter, and bits of information.

Why was this so important?

Well it's probably not important for curing cancer, or knocking down enemy missiles, or speeding up your computer. But it is important to the future of physics and cosmology. The universe is controlled by two fundamental laws: Einstein's gravity theory (the General Theory of Relativity) and Quantum Mechanics. Stephen argued very convincingly that the two (GTR and QM) were on a collision course. Gravity and Quantum Mechanics were just plain incompatible. One or the other would have to give, at least by Hawking's logic.
Stephen was wrong, but his astonishing question has changed the history of physics, and there is much more to come.

So, what do you believe happens to matter sucked into a black hole?

Remember that in a monumental contribution to physics, Hawking showed that black holes evaporate, like puddles of water on a hot day. It happens very slowly but the black hole does emit particles, and eventually disappears. The answer is that the evaporation products—the photons and other particles—carry away every bit of information, BUT in an extremely scrambled form. What we have learned is that black holes are not information-erasers but information-scramblers.

What was the final outcome of your competing theories?

The short answer is that Stephen was wrong and I was right. But that is a tremendous oversimplification and I would not like history to see it that way. Stephen asked an audacious, bold, and very brave question —do black holes erase information? Just realizing that there was a question took profound insight. It was enough to make anyone's reputation. The outcome was a whole new paradigm called the Holographic Principle. The Holographic Principle says something astonishing and completely beyond intuition. The world is a kind of hologram: an image projected from a distant mathematical film, far at the edges of the universe. To understand how we got from black holes to holograms you'll have to read my book, but here is a hint. The horizon of a black hole (a two dimensional surface like a film) somehow stores all the information that ever fell into the hole.

Where does biology fit into a theoretical physicist's thinking? Do the attempts at an elegant "Theory of Everything" include life's impulse to survive and replicate?

Physicists don't like to think that their science is anything like biology. Biology is messy, imprecise, and complicated. Physics is simple, crystal clear, and elegant, or so the argument goes. But physicists have been hit over the head with some "ugly" facts. There are powerful reasons to believe that the universe may also be a consequence of random mutation. It sounds crackpot, or at best, like fringe speculation, but by now the idea is very firmly established in the mainstream physics and cosmology literature. That's was what my book "The Cosmic Landscape" was all about.

According to String Theory the tiniest dimensions of space are curled up and twisted into an analog of the Double Helix. The Double Helix is a frame on which base-pairs can be arranged. And as you know, the pattern of base pairs determines the properties of a given biological entity.

Microscopic space (according to String Theory) is not a Double Helix, but something similar: a Calabi Yau manifold (don't ask). The analog of the base pairs of DNA are called "fluxes." The details don't matter. What does matter is that there exists an incredibly rich set of possibilities—you can call them blueprints—for the construction of a universe. And according to modern cosmological theory, the universe is filled with sub-universes of every allowable kind, formed from a process similar to random mutation.

If this is so then the question, "Why our universe is the way it is?" may have an "anthropic" component: we live in a very rare environment where the ordinary laws are such that life can exist. Where else would we live? Where else would it be possible to ask the question?

How about consciousness or awareness? Are there any physicists who see consciousness as a distinct but interwoven part of the universe?

I suppose there are. My own view is similar to Richard Feynman's when he was asked whether the conceptual puzzles of quantum mechanics confused him. He said that quantum mechanics was so puzzling that he wasn't even sure if there was a puzzle. There are other questions like that—questions that you can't even imagine what an answer could be like. "Why does mathematics work?" "Why does logic work?" "What is the purpose of the universe?" "What is the connection between mind and matter?" As I said, these seem like legitimate questions, but you can't imagine what answers would be like. My sense is that consciousness is one of those questions.

Incidentally, I don't mean to imply that these questions will never get answers; just right now I don't have a clue. But then again I am not a licensed cognitive scientist.

If I understand it correctly, you've recently written that our universe may just be one of an infinite number of universes, each with unique properties or laws of physics. Is this where you think our knowledge is headed and if so, do you find that discouraging or encouraging in terms of what we can ultimately know about the universe?


First of all I am not in the least bit alone in this view, nor am I the originator of it. It has been around for a long time. But since I wrote "The Cosmic Landscape," it has practically become the conventional view.

As to whether I find it discouraging or not—no—not at all. There are people who do, but I think they are victims of their own prejudices and hopes. The universe is far more interesting and challenging than we imagined. The next generation of physicists and cosmologists will have the fun and excitement of discovering the right mathematical formulation of a "multiverse." Finding observational (astronomical?) ways to confirm that we live in such a diverse world is another challenge. Only the old fogies who thought that physics was almost finished are disappointed. The only thing that I would find discouraging would be that we run out of questions.

Heard any good theoretical physics jokes lately?

Yup, and you'll find them in my book.