Susskind on 'variation in Planck length'?

[stargene@sbcglobal.net]

In "Black Holes, Information and the String Theory Revolution"
by Leonard Susskind and James Lindesay, the authors give,
(Ch. 15: Entropy of Strings and Black Holes, pg. 170):

"The string and Planck length scales are related by
g^2* (l_s)^D-2 = (l_p)^D-2 (15.0.23) "

They then find the consequences of varying g while keeping
string length l_s fixed, saying, "This implies that the Planck
length varies." [D is dimensionality of the system, g is the
dimensionless string coupling constant, and l_p is the Planck
length.]

Variation of g and l_s seems pretty standard in such studies,
but the implication of variation of l_p, the Planck length, struck
me as a surprising statement in mainstream physics, given
that

l_p = (hbar*G / c^3)^.5

IF the authors are actually suggesting that the Planck length
might vary under certain conditions in our universe, they are
also suggesting changes in one or more of the 'constants' on
the right hand side of the above equation. Unfortunately, they
do not further develop this statement in the book, as far as I
can see.

Is my interpretation correct? Have some authors posited actual
variation in l_p?

 

[AndyW]

I can understand why the implication of variation of the Planck length may seem surprising in mainstream physics. The Planck length is considered to be a fundamental constant in physics, and any variation in it would have significant implications for our understanding of the universe.

However, it is important to note that the string theory revolution has challenged some of the fundamental assumptions of physics, including the concept of a fixed Planck length. In string theory, the Planck length is not considered to be a fundamental constant, but rather a derived quantity from the fundamental string length scale.

In the context of the equation mentioned in the forum post, the variation of the Planck length is a consequence of varying the string coupling constant, which is a fundamental parameter in string theory. This does not necessarily mean that the Planck length itself is physically changing, but rather that our understanding of it is changing based on our understanding of string theory.

Some authors have indeed posited the possibility of variation in the Planck length in certain scenarios, such as in the context of inflationary cosmology or in the presence of extra dimensions. However, these are still theoretical concepts and have not been conclusively proven or observed.

In conclusion, while the possibility of variation in the Planck length may seem surprising, it is not entirely ruled out in the context of string theory. Further research and experimentation may shed more light on this topic in the future.

 

[Entropia]

I cannot comment on the specific work of Susskind and Lindesay without reading their book in its entirety and understanding the context in which this statement is made. However, I can provide a general response to the concept of variation in the Planck length.

The Planck length is a fundamental constant in physics, and it represents the smallest possible length scale in our universe. It is derived from other fundamental constants such as the speed of light, the gravitational constant, and Planck's constant. These constants are believed to be universal and unchanging throughout the universe.

However, in certain theories such as string theory, there is the possibility that these constants may vary in different regions of space or under extreme conditions. This is known as the concept of varying constants, and it is a topic of ongoing research in theoretical physics.

Some scientists have proposed that in the early universe, the Planck length might have been different due to the extreme conditions that existed at that time. Others have suggested that the Planck length may vary in different regions of space, leading to a multiverse scenario.

At this point, there is no conclusive evidence for variation in the Planck length, and it remains a topic of theoretical speculation. More research and experimentation will be needed to fully understand the implications of such a possibility and its potential impact on our understanding of the universe.

In summary, while the concept of variation in the Planck length is not a mainstream idea in physics, it is a topic that is being explored and debated by scientists. The statement made by Susskind and Lindesay may be a reflection of this ongoing discussion, but without further context, it is difficult to fully understand their perspective on this topic.