Can Black Holes Have Entropy?

In summary: This is a summary of the original thread:Black holes are famous because almost nothing can escape from them. Once an observer has crossed the event horizon, no more contact may be made with him or her. Thus it will forever be impossible to know what the interior of a black hole is like, because observers that go inside will never be able to communicate with us.Everyone knows that the entropy of a black hole is proportional to its area, and that there are only 3 parameters necessary to describe a black hole: its area, charge, and spin. All of the books I've read about the subject say that astronomical-scale black holes have very high entropy (the exception being very small black holes created in the lab).
  • #1
brcooke
7
0
Hi, I'm not a physicist so the answer to this question may be elementary but I can't figure it out for myself:

Black holes are famous because (almost) nothing can escape from them. Once an observer has crossed the event horizon, no more contact may be made with him or her. Thus it will forever be impossible to know what the interior of a black hole is like, because observers that go inside will never be able to communicate with us.

Everyone knows that the entropy of a black hole is proportional to its area, and that there are only 3 parameters necessary to describe a black hole: its area, charge, and spin (right?). All of the books I've read about the subject say that astronomical-scale black holes have very high entropy (the exception being very small black holes created in the lab).

Now, my understanding of entropy is that it is proportional to the logarithm of the number of microstates that could underlie a single macrostate. My question is: Since it is impossible to know anything about the interior of a black hole, and thus anything about the microstates within it, how can black holes have entropy at all? And contrary to the popular assumption that the entropy of black holes is very large, given how easy it is to define a black hole, shouldn't that indicate that their entropy is in fact very low?

Thanks for your help!

Brad.
 
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  • #3
No, I haven't, but I'm deep into the holographic principle as suggested. I will check that next. Thanks!
 
  • #4
I think that entropy of black hole is very high due to its capability of absorbing everything. Talking at macroscopic level, if we consider black hole as a system, then mass as well as heat in form of radiations are going into the system and not coming outside.
So, if we use the relation of entropy balance:
S in - S out + S gen = dS sys
S out=0 and S gen is positive
Thus Change in entropy of system(R.H.S) is positive.
Therefore we can say that the entropy of black holes is increasing continuously at a high rate meaning that it has very high entropy
 
  • #5

1. What is entropy and how does it relate to black holes?

Entropy is a measure of the disorder or randomness in a system. In the context of black holes, entropy is a measure of the amount of information that is lost when matter and energy are pulled into the black hole's singularity. This relates to the concept of the second law of thermodynamics, which states that the total entropy of an isolated system always increases over time.

2. How is the entropy of a black hole calculated?

The entropy of a black hole can be calculated using the famous formula developed by physicist Jacob Bekenstein: S = kA/4, where S is the entropy, k is the Boltzmann constant, and A is the surface area of the black hole's event horizon. This formula is known as the Bekenstein-Hawking formula.

3. Can the entropy of a black hole ever decrease?

According to the second law of thermodynamics, the entropy of an isolated system cannot decrease. This means that the entropy of a black hole can never decrease, even as it absorbs more matter and energy. The only way for the entropy of a black hole to decrease would be if it were to merge with another black hole, resulting in a larger total surface area and therefore a higher entropy.

4. How does the concept of entropy in black holes relate to the information paradox?

The information paradox is a theoretical problem that arises when considering the fate of information that falls into a black hole. According to the laws of physics, information cannot be destroyed, yet it seems that information is lost when it enters a black hole. The concept of entropy in black holes helps to explain this paradox, as the increase in entropy of the black hole can be seen as a way of preserving the lost information in a different form.

5. Is there any evidence for the existence of entropy in black holes?

Yes, there is strong evidence for the existence of entropy in black holes. The Bekenstein-Hawking formula has been tested and confirmed through various observations and experiments, providing evidence for the relationship between the entropy of a black hole and its event horizon. Additionally, the concept of black hole entropy is crucial in understanding the behavior and evolution of black holes in our universe.

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