Lisa Randall's relaxation principle

[straycat]

Hello all,

I recently came across Karch and Randall's 2005 paper ``Relaxing to three dimensions''
http://arxiv.org/abs/hep-th/0506053 that uses brane theory to propose an explanation for why we see 3+1 dimensions, assuming we begin with the 10 of string theory. From the abstract:

``We show that under conventional (but higher-dimensional) FRW evolution, a universe filled with equal NUMBERS of branes and antibranes will naturally come to be dominated by 3-branes and 7-branes.'' (caps mine)

The basic idea is the relaxation principle, which states:

``that the branes with the biggest filling fraction in the end-point of the universe's cosmological evolution are the most likely branes to be relevant to the state in which we live''

My question is this: what is the definition of ``filling fraction'', and what does ``most likely'' mean? It seems to me that she is saying that 3-branes are simply more numerous than other branes, and defining the likelihood of p-branes as being proportional to the number of p-branes (well, I suppose measure might be more appropriate than number). This definition of `likeliness' of branes makes no reference to, say, the wavefunction of a brane, so she is using a classical (not quantum) concept of probability.

OTOH, I might be completely missing something. Comments?

 

[AndyW]

Thank you for sharing this interesting paper with the community. The idea of using brane theory to explain the observed 3+1 dimensions is certainly intriguing. To answer your question, the filling fraction refers to the ratio of the number of branes to the total number of branes and antibranes in the universe. In other words, it is the proportion of branes in the universe. The authors suggest that in the end-point of the universe's cosmological evolution, the branes with the highest filling fraction will be the most dominant and relevant to our current state.

As for the concept of "most likely", it is indeed a classical concept of probability based on the number or measure of branes. However, it is worth noting that this is just one proposed explanation and there may be other factors at play that could affect the likelihood of certain branes being dominant. Further research and experimentation will be needed to fully understand the role of branes in our universe.

Thank you for your contribution to the discussion and for bringing this paper to our attention. Let's continue to explore and discuss these fascinating ideas in the pursuit of understanding our universe.

 

[Entropia]

I find Lisa Randall's relaxation principle to be a fascinating concept that offers a potential explanation for the observation of 3+1 dimensions in our universe. The idea that the dominant branes in the universe's evolution are the most likely to be relevant to our current state is a compelling one. However, as the author of this post points out, there are some unclear aspects of the relaxation principle that require further clarification.

One potential area of confusion is the definition of "filling fraction". It is not explicitly stated in the abstract, but based on the context of the paper, it seems to refer to the proportion of branes in the universe that are of a particular type (e.g. 3-branes or 7-branes). This is an important aspect of the relaxation principle, as it suggests that the dominant branes in the universe's evolution are the ones with the highest filling fraction.

Another point of potential confusion is the use of the term "most likely". As the author of this post notes, this seems to imply a classical, rather than quantum, concept of probability. It would be helpful for Randall to clarify her definition of "most likely" and how it relates to the wavefunction of a brane.

Overall, I believe that the relaxation principle is a thought-provoking concept that warrants further exploration and study. It offers a potential explanation for the observed 3+1 dimensions in our universe and has the potential to contribute to our understanding of the fundamental laws of physics. However, as with any scientific theory, it is important to carefully examine and clarify its underlying assumptions and definitions in order to fully understand its implications.