Friday, November 24, 2006

The New Physics

In the comments thread on Bee's blog

Bee:
"I used the word 'unverified' with the meaning it's not verified through experimental facts that it is actually realized in nature."

Lumo:
"This is a nonsensical assertion. AdS/CFT is a statement about the character of mathematics that describes quantum gravity, and if you agree that it is an essentially proven one, then it follows that it is realized in Nature much like 2+2=4 is realized in Nature."

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What is AdS/CFT you ask?
Wikipedia on AdS/CFT
"In physics, the AdS/CFT correspondence (anti-De-Sitter space/conformal field theory correspondence), sometimes called the Maldacena duality, is the conjectured equivalence between a string theory defined on one space, and a quantum field theory without gravity defined on the conformal boundary of this space, whose dimension is lower by at least one. The name suggests that the first space is the product of anti de Sitter space (AdS) with some closed manifold like sphere, orbifold, or noncommutative space, and that the quantum field theory is a conformal field theory (CFT). However, the conjectured equivalence is more general, and is therefore sometimes termed gauge / gravity duality."

and

"The most known example and the first one to be studied is the duality between Type IIB supergravity on AdS5 * S5 (a product space of a five-dimensional Anti de Sitter space and a five-sphere) on one hand, and N=4 supersymmetric Yang-Mills theory on the four-dimensional boundary of the Anti de Sitter space (either a flat four-dimensional spacetime R3,1 or a three-sphere with time S3* R).[6] This is known as the AdS/CFT correspondence, a name often used for Gauge / gravity duality in general."

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The reader should note:
1. AdS/CFT is a conjecture; a very well-founded one perhaps, but still a conjecture.
2. Even if proven, it does not mean it is realized in nature. In particular that we live in a 5-dimensional AdS spacetime is yet to be established. :)
3. Even if AdS/CFT is established, its relevance to ultra-high energy heavy atomic nuclei collisions is yet to be established.

This is the new style of physics. In theology, non-existence would be a permanent imperfection that mars The Perfect God, and therefore God must exist. In the new physics, the same holds with Superstring Theory.

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4 comments:

Bee said...

Thanks. As you know, in principle I have asked myself very similar questions, that is, how tight the constraints of mathematical consistency are, and whether all mathematically possible theories are realized - somewhere, somehow, possibly in another part of the multiverse ;-) In a certain sense it is very sad when people mistake 'mathematically proven' for 'experimentally verified'. The point with 2+2=4 is imo completely vacuous. If you've defined the natural numbers, then that's just what they do. Now you explain me why our universe counts apples in N and not in Z_3 or so, where 2+2 = 1 ?

And while we're at it, I can give you THE equation that explains everything: A=B. You'll just have to figure out what A and B is ;-)

Have a nice weekend,

B.

Arun said...

Bee,
Happy you visited! A great weekend to you, too!

Strangely, I was thinking virtually the same thing, why our universe counts in N and not in Z_P where P is some large prime, and how would we know?

Savyasachi said...

Arun,

You should perhaps change the first sentence in the last paragraph to "This is the new style of String Theory".

There are enough examples of good physicists who do not do this. IMHO String Theory should make a clean break with Physics...

Arun said...

Savyasachi, yes.

Further info about this stuff:

Comment at Woit's blog