How Do Thermodynamics and Branes Influence the Universe's Origin?

[alex_j]

[I'm creating this thread to hold a discussion of some questions raised by alex_j in a thread where they were off topic. -- bcrowell]

Could someone elaborate on the relationship between the big bang and thermodynamics? (anthropic principle)

How does the state of entropy of a brane relate to that of the universe at the time of it's creation (assuming we exist within a brane)?

How "main-stream" is Boltzmann's universe and what are the general thoughts on fluctuations at high levels of entropy leading to lower levels?

How valid is the statement that the laws of entropy only apply to closed systems and what are the general views about branes being closed or open systems?** questions arise out of:
1. Dr. Leonard Susskind, Stanford University
2. Dr. Sean Carroll, California Institute of Technology
3. Dr. Roger Penrose @ George Mason University

 

[Chalnoth]

Could someone elaborate on the relationship between the big bang and thermodynamics? (anthropic principle)

These are two extremely different topics, so I don't quite know why you're lumping them together here.

As for thermodynamics and the big bang, well, we know that early in our universe, the entropy of the universe was unbelievably low. Right now it is many, many orders of magnitude higher. It remains an open question as to precisely how that early, low-entropy state came about.

How "main-stream" is Boltzmann's universe and what are the general thoughts on fluctuations at high levels of entropy leading to lower levels?

The Boltzmann brain issue is basically a proof that you cannot simply consider a universe to be a state which periodically fluctuates out of equilibrium in a standard thermodynamic way. Any alternative theory for producing the low-entropy early universe is required to pass the Boltzmann brain test (that is, it must strongly favor real observers over Boltzmann brains). If it doesn't pass this test, it cannot describe our reality.

How valid is the statement that the laws of entropy only apply to closed systems and what are the general views about branes being closed or open systems?

The laws of entropy absolutely apply to open systems, you just have to take into account what goes on at the boundary.

 

[Tanelorn]

Chalnoth, I get confused by high, higher, very high, low, lower and extremely low levels of, well, anything really, especially entropy! eg. I often forget that heat death occurs when there is high entropy because that is also when the available energy density is low or zero.

Do you know if there may be a chart showing relative entropy vs time from 10-43 to 10+1500 years? perhaps also showing the energy density?

Thanks
Chris

 

[bcrowell]

Do you know if there may be a chart showing relative entropy vs time from 10-43 to 10+1500 years? perhaps also showing the energy density?

There have been various attempts to estimate the entropy of the observable universe, but this is highly speculative. It is not really established what should be the general definition of entropy in the context of cosmology. Here is a sample of this kind of work:
http://arxiv.org/abs/0801.1847

 

[sardar]

Thermodynamics and branes are two concepts that are often discussed in the context of the origin and evolution of the universe. The big bang theory, which is the most widely accepted explanation for the origin of the universe, is based on the laws of thermodynamics. According to this theory, the universe began as a hot, dense and highly ordered state, and has been expanding and cooling ever since. This process of expansion and cooling is governed by the laws of thermodynamics, which describe how energy and matter behave in a closed system.

The anthropic principle is a controversial idea that suggests that the laws of the universe are fine-tuned for the existence of life. This idea is often used to explain the apparent fine-tuning of physical constants and the initial conditions of the universe. However, the relationship between the anthropic principle and thermodynamics is still a topic of debate among scientists.

In terms of branes, they are theoretical objects that are postulated by certain theories in physics, such as string theory and M-theory. These theories suggest that our universe may exist within a higher-dimensional space, known as a brane, and that the laws of physics that we observe are a result of interactions between different branes. In this context, the state of entropy of a brane may be related to the overall entropy of the universe at the time of its creation. However, the exact nature of this relationship is still not fully understood.

Boltzmann's universe is a concept that suggests that our universe is just one of many possible universes that exist in a larger multiverse. This idea is based on the concept of fluctuations at high levels of entropy leading to lower levels, which is known as the Boltzmann brain paradox. While this idea is not widely accepted in the scientific community, it continues to be a topic of research and debate.

The laws of thermodynamics are generally considered to apply to closed systems, which are systems that do not exchange matter or energy with their surroundings. However, the concept of branes as closed or open systems is still a topic of discussion and further research is needed to fully understand their nature.

In summary, the relationship between thermodynamics and branes is a complex and ongoing topic of research in the scientific community. While there are various theories and ideas that attempt to explain this relationship, more research and evidence is needed to fully understand the origin and evolution of the universe and the role of thermodynamics and branes in it.