AdS/CFT (basic)

[s***@gmail.com]

Hi,

I was reading the news article about the "black holes at RHIC"
(http://www.bnl.gov/rhic/black_holes.htm), and I wanted to know a little
more about what this experiment involved.

So, after surfing for a while I discovered that it was related to
something called Ads/CFT correspondence

I tried to read the information on it here
(http://www.answers.com/topic/ads-cft?hl=anti&hl=de&hl=sitter&hl=space)

but unfortunately it would take me years to study/understand all the
math/physics terms/principles involved

Can someone here please explain to a lay person what Ads/CFT means?

Am I right, and was the "black holes at RHIC" really related to Ads/CFT?

If so, was this experiment meant to verify some aspect of string theory?

Thanks,
Guy Nussbaum

[Chris]

"Can someone here please explain to a lay person what Ads/CFT means?"
(in 100 words or less?)

AdS/CFT is a dictionary that relates a certain kind of string theory
(type IIB propagating in AdS_5 x S^5) to a certain kind of gauge theory
(N=4 SU(N) SYM). If you can calculate something in one theory, the
dictionary tells you how to convert that quantity into something in the
other theory. The dictionary is very useful because quantitites that
are easy to calculate in one theory are often very difficult to
calculate in the other. People were and are excited by AdS/CFT because
string theory and gauge theory are believed to be very useful ways of
thinking about the world in which we live.

"Am I right, and was the "black holes at RHIC" really related to
Ads/CFT?"

Horatiu Nastase thinks so, but an informal census reveals his work is
very controversial.
The RHIC experiment is an attempt to better understand QCD, the gauge
theory that describes the interactions between the quarks and gluons in
the nucleus of an atom. Although there is as yet no string theory dual
to QCD, there are generalized AdS/CFT correspondences which capture
some aspects of QCD. By using these toy models of QCD and calculating
on the string side of the correspondence, one may hope to gain a better
understanding of what is going on at RHIC. One of the more striking of
Nastase's predictions is that black holes are formed in the string side
of the correspondence. The dictionary then translates what that means
into gauge theory language -- for example Nastase is able to extract a
temperature of the quark-gluon plasma.

A somewhat less controversial attempt to use AdS/CFT was carried out by
Dam Son and collaborators. They try to understand the viscosity of the
quark-gluon plasma at RHIC. Lubos Motl has a nice discussion of their
attempts on his blog, and I believe there is a New Scientist article
about this work.

"If so, was this experiment meant to verify some aspect of string
theory?"

Hopefully the answer to this question is clear by now. The answer is
no. The RHIC
experiment is an attempt to understand QCD and more specifically the
quark-gluon plasma. Nastase's paper is an attempt to use string theory
to understand RHIC data. (But you can always take a larger view in
which you run these kinds of arguments backward.)

Hope that helps.

[Anthony Smales]

Post by s***@gmail.com
Can someone here please explain to a lay person what Ads/CFT means?

see URL:http://news.bbc.co.uk/2/hi/science/nature/4357613.stm


[Moderator's note: Quoted texted trimmed by moderator. -usc ]

[Urs Schreiber]

Post by Anthony Smales

Post by s***@gmail.com
Can someone here please explain to a lay person what Ads/CFT means?

see URL:http://news.bbc.co.uk/2/hi/science/nature/4357613.stm

With respect to this article I would like to emphasize a point that Chris
has already made in this thread:

AdS/CFT gives an interesting twist to the role that string theory might play
in physics, which is a little weird, in a sense and likely to be missed when
no attention is payed. The author of the above article seems to have missed
precisely this point.

At least the article makes it sound as if there were claims that the RHIC
fireball _is_ something like a black hole. That's not the case. The claim is
that the RHIC fireball is _dual_ to a black hole in the _dual_ theory.

So we have a gauge theory which we test by experiments like RHIC. The claim
is that this gauge theory can equivalently be reformulated in a strange way
as a very different-looking theory that describes strings and gravity in an
auxiliary higher dimensional space. From the gauge theory perspective these
strings and the space they live in are auxiliary fictitious entities. It
just so happens that we know that quantities in some gauge theories have the
same values as totally different quantities in a totally different theory
which is of a completely different nature. Like if you knew that every
telephone number in Suriname precisely corresponds to a license plate number
in Japan for some reason.

So the black hole that Nastase is talking about is a completely fictitious
one in a fictitious higher-dimensional space which however has properties
(telephone numbers) that can be translated into different properties
(license plate numbers) of a real object in a real collider.

Weird, eh? :-)

To me the moral is this: String theory is like a huge dictionary of
(effective) field theories. There is a multitude of ways to get all kinds of
field theories in certain scenarios and limits from string theory and relate
them to each other in various ways. AdS/CFT is one of them.

[brookg]

Post by Urs Schreiber
So the black hole that Nastase is talking
about is a completely fictitious
one in a fictitious higher-dimensional space
which however has properties
(telephone numbers) that can be translated
into different properties
(license plate numbers) of a real object in a real collider.
Weird, eh? :-)

Very :)

Does AdS provide some information that suggest something new about the
way in which nature operates?
Maybe something that CFT does not reveal?
or
is AdS just an abstraction which simplifies the calculation of results?
(telephone number --> license plate numbers)
If so, Is this the only way in which string theory is expected to be
useful?

[Urs Schreiber]

Post by brookg
Does AdS provide some information that suggest something new about the
way in which nature operates?

It might _suggest_ something, depending on what you find suggestive. There
is a theory of quantum gravity which in a dual way has to say something
about observable gauge theory. Decide for yourself if this makes it likely
that this theory of quantum gravity is unrelated to the gravity that we
observe.