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shlosmem
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If the universe was very hot right after the Big Bang how come the entropy of the universe was lower at that point than now? Isn't heat a reason for higher entropy?
shlosmem said:If the universe was very hot right after the Big Bang how come the entropy of the universe was lower at that point than now? Isn't heat a reason for higher entropy?
No. They're not.Vanadium 50 said:Temperature and entropy are not the same thing.
Where are you getting all this from? Empty space does not even have a well-defined heat capacity.jartsa said:Does this maybe kind of answer the question?
Let's look at the sun's formation. Some gas and dust in space compressed by gravity to form the sun. In one way the compressed particlesjartsa said:What happens when you keep the thermal energy constant and increase heat capacity? Well one thing is that temperature decreases. Other thing is that entropy increases.
This argument is faulty. Eventually the Sun runs out of stuff to burn and cools down. The correct argument in gravitational clustering is to not ignore the entropy of the radiation that is emitted in the process.shlosmem said:On the other hand the high temperature means more potential states , so in total we can say that the sun state has more entropy then the dust state and the second law is not broken.
In an idealized scenario where a single hole evaporates, after the last burst of outgoing radiation from the evaporation leaves, there is empty space inside where the hole used to be, yes. But in any real scenario, you won't have just one hole evaporating. There will already be radiation present coming from elsewhere, either from other holes evaporating or from the CMB if nothing else. So the end result for the universe as a whole would be a universe filled with nothing but radiation.kimbyd said:Those black holes will then evaporate over a long period of time, leading to empty space
This argument is uninformative. What exactly is faulty?Orodruin said:This argument is faulty.
You would have known if you continued reading. The rise in temperature is insufficient to lead to an increase in entropy unless you also consider the radiation emitted.shlosmem said:This argument is uninformative. What exactly is faulty?
Orodruin said:You would have known if you continued reading. The rise in temperature is insufficient to lead to an increase in entropy unless you also consider the radiation emitted.
shlosmem said:If the universe was very hot right after the Big Bang how come the entropy of the universe was lower at that point than now? Isn't heat a reason for higher entropy?
I'm sorry, but you are entirely missing the point. The point is not a question of how to define the Sun's entropy. The point is that the material that the Sun consists of is not a closed system. Over the billions of years that the Sun has formed and radiated, its entropy has actually decreased, which is fine as it is not a closed system. The "missing" entropy has been carried away by radiation over billions of years.shlosmem said:A. The radiation is a small faction of the entire sun's mass on any given moment , so it probably should be neglected in any practical measure of the sun's entropy.
B. How is even relevant. Are you suggesting that the low entropy of the hot universe after the bb is duo to the lack of radiation?
Well I thought I kind of understood how entropy, temperature and heat capacity work. Maybe I don't.PeterDonis said:Where are you getting all this from? Empty space does not even have a well-defined heat capacity.
shlosmem said:Let's look at the sun's formation. Some gas and dust in space compressed by gravity to form the sun. In one way the compressed particles
have less movement freedom so the system has less potential states which means lower entropy. On the other hand the high temperature means more potential states , so in total we can say that the sun state has more entropy then the dust state and the second law is not broken.
If we're talking about classical black holes, there is no way to define their temperature or their entropy. Making sense of those concepts at all for black holes requires some kind of quantum gravity theory or approximation thereof.jartsa said:Let's consider an universe with two black hokes, and nothing else.
If we're talking about classical black holes, this is false; the universe just contains one black hole instead of two. There is still no way to define either temperature or entropy.jartsa said:After the black holes have merged the universe contains cooler stuff and more entropy.
No, they don't. Evaporation is a constant temperature process. The average kinetic energy of the particles does not change. The reason the ice cube at 0 C evaporates (the correct name for the process is actually "sublimation") in empty space is that the vapor pressure is zero.jartsa said:after the evaporation the particles
have less kinetic energy
To put this into a bit more perspective, John Baez has a (now over 20 year old) writeup with the qualitative argumentation.Orodruin said:I'm sorry, but you are entirely missing the point. The point is not a question of how to define the Sun's entropy. The point is that the material that the Sun consists of is not a closed system. Over the billions of years that the Sun has formed and radiated, its entropy has actually decreased, which is fine as it is not a closed system. The "missing" entropy has been carried away by radiation over billions of years.
shlosmem said:If the universe was very hot right after the Big Bang how come the entropy of the universe was lower at that point than now? Isn't heat a reason for higher entropy?
That almost seems to suggest that there would be no structure formation without black holes ...JimJCW said:Ethan Siegel’s 2017 article,
might be interesting. The last paragraph of the article:
If there were no such things as black holes, the entropy of the Universe would have been almost constant for the past 13.8 billion years! That primal state actually had a considerable amount of entropy; it's just that black holes have so much more, and are so easy to make from a cosmic perspective.
PAllen said:That almost seems to suggest that there would be no structure formation without black holes ...
Point 1 - 2nd law states that entropy of a system can remain constant, or increase with time. If we treat the universe as a thermodynamic system. then its entropy is either the same or greater than that at the big bang.shlosmem said:If the universe was very hot right after the Big Bang how come the entropy of the universe was lower at that point than now? Isn't heat a reason for higher entropy?
Entropy is a measure of the disorder or randomness in a system. In physics, it is often used to describe the amount of energy that is unavailable for work in a system.
After the Big Bang, the universe was in a state of extremely low entropy. As the universe expanded and cooled, entropy increased and continues to increase as the universe expands.
Entropy plays a crucial role in the formation of galaxies and stars. As matter clumps together due to gravitational forces, entropy increases, leading to the formation of stars and galaxies.
It is currently believed that there is no maximum entropy in the universe. As the universe continues to expand, entropy will also continue to increase, potentially leading to a state of maximum entropy in the distant future.
The concept of entropy is closely related to the arrow of time. As entropy increases, the universe moves towards a state of maximum disorder, which is often seen as the direction of time. This is known as the "arrow of time" or the "thermodynamic arrow of time."