Entropy of the last scattering surface and today's universe?

In summary, the conversation discusses the concept of entropy and how it relates to the universe's evolution. The main question is how the universe's increase in size and decrease in density since the time of last scattering can correlate to an increase in entropy. The response explains how the evolution from a gas cloud to a gravitationally bound system is not an isolated process and how the outgoing radiation plays a role in determining the overall entropy of the system. It is also mentioned that John Baez's discussion on this topic is worth reading.
  • #1
Astrotek
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Hi,
I am quite confused about followed question,
I think scientist think the last scattering surface was dense plasma at the temperature of 3000K. If the today's universe much cooler and less dense then "the last scattering surface" how can anyone says entropy increased by time? Isn't universe now have more order than a plasma phase?

Note: I am sorry If I couldn't make good sentences to explain my problem, it is almost 2 am and I just woken up and this question just bugs me a lot. I'll really appreciate if someone explains it.
 
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  • #2
The universe is much bigger now than it was at the time of last scattering.
 
  • #3
Astrotek said:
Hi,
I am quite confused about followed question,
I think scientist think the last scattering surface was dense plasma at the temperature of 3000K. If the today's universe much cooler and less dense then "the last scattering surface" how can anyone says entropy increased by time? Isn't universe now have more order than a plasma phase?
In what way do you think the universe now has more "order"?

If you are talking about gravitationally-bound systems such as planets and stars, then those systems have higher entropy than the diffuse gas clouds they collapsed from. While the precise details of how much entropy complicated systems have is unknown, we do know that the end point of matter contained within a black hole is the maximum-entropy configuration that amount of matter can have.

If you just mean the cooling of the plasma into a gas, that process is largely adiabatic (as in, entropy didn't change much).
 
  • #4
kimbyd said:
If you are talking about gravitationally-bound systems such as planets and stars, then those systems have higher entropy than the diffuse gas clouds they collapsed from.
This is actually not true. However, the point is that the evolution from a gas cloud to a gravitationally bound system is not an isolated one.

John Baez’s discussion on this is well worth a read.
 
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  • #5
Orodruin said:
John Baez’s discussion on this is well worth a read.

Well I got one more question now, but it was fun to read.

I am still thinking about other answers and I'd like to hear if there is any other thoughts on this subject.
 
  • #6
Orodruin said:
This is actually not true. However, the point is that the evolution from a gas cloud to a gravitationally bound system is not an isolated one.

John Baez’s discussion on this is well worth a read.
That's fair. It does make sense that you'd have to not only consider the configuration of the matter, but also of the outgoing radiation, which represents a large loss of heat for the system. That does bring things into clearer focus. Certainly the entropy of the observable universe is not decreased by this process regardless.
 
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1. What is the significance of the entropy of the last scattering surface in understanding the universe?

The entropy of the last scattering surface is a measure of the disorder or randomness in the early universe, specifically at the time of recombination when the universe transitioned from a hot, dense plasma to a neutral gas. This value is important because it provides insight into the initial conditions of the universe and the processes that led to the formation of galaxies and other structures.

2. How does the entropy of the last scattering surface affect the formation of large-scale structures in the universe?

The entropy of the last scattering surface plays a crucial role in the formation of large-scale structures such as galaxies, clusters, and filaments. As the universe expanded and cooled, regions with higher entropy or disorder were more likely to collapse under their own gravity and form these structures. This is known as the "gravitational instability" theory of structure formation.

3. What is the relationship between the entropy of the last scattering surface and the cosmic microwave background radiation?

The cosmic microwave background (CMB) radiation is the leftover thermal radiation from the early universe, which is currently observed as a nearly uniform glow in the microwave spectrum. The entropy of the last scattering surface is directly related to the temperature fluctuations in the CMB, as regions with higher entropy will have greater temperature variations. This allows us to study the distribution of matter in the early universe through the analysis of the CMB.

4. How has the entropy of the last scattering surface changed over time in the evolution of the universe?

The entropy of the last scattering surface has increased over time as the universe has expanded and cooled. This is due to the second law of thermodynamics, which states that entropy always increases in a closed system. As the universe continues to expand and dissipate energy, the overall entropy will continue to increase.

5. How does the entropy of the last scattering surface contribute to our understanding of the arrow of time in the universe?

The entropy of the last scattering surface is closely linked to the concept of the arrow of time, which refers to the unidirectional flow of time from the past to the future. The increase in entropy over time is a fundamental aspect of the arrow of time, and studying the entropy of the early universe can help us understand the origin and direction of this arrow. Additionally, the low entropy of the early universe is thought to be a key factor in explaining why the arrow of time appears to be pointing in one direction, rather than being reversible.

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