What is time?

[Qfwfq]

Is it a true statement to say that maximum entropy will not be reached until all molecular motion has stopped?

No.

 

To the contrary, at absolute zero you don't have the disorder of thermal agitation, yo have low entropy. A perfectly isolated physical system has maximum entropy when all energy is of purely thermal nature and all at the same temperature. From that point you couldn't use a thermal engine to change any of the energy into mechanical or other organized forms, you certainly couldn't lower the temperature at all, let alone to absolute zero.

[infamous]

No.

 

To the contrary, at absolute zero you don't have the disorder of thermal agitation, yo have low entropy. A perfectly isolated physical system has maximum entropy when all energy is of purely thermal nature and all at the same temperature. From that point you couldn't use a thermal engine to change any of the energy into mechanical or other organized forms, you certainly couldn't lower the temperature at all, let alone to absolute zero.

Yes I see Qfwfq; I continually misinterpretate the meaning of Entropy. So let me rephrase my comments; When the universe has reached it's final stage of evolution, and entropy is at it's maximum, thermally homogenious, will it then eventrually cool to absoulute zero? And if it is uniformly at absoulute zero, wouldn't this still be at a maximum state of entropy because in this closed system there would exist no place within it where a disparity of thermal agitation could exist?? Whether at 3 degrees Kelvin or at 0 degrees Kelvin, if it is thermally homogenious, wouldn't it still be at maximum entropy??

[Qfwfq]

When the universe has reached it's final stage of evolution, and entropy is at it's maximum, thermally homogenious, will it then eventrually cool to absoulute zero?

No, cooling would mean decreasing entropy. Cooling down to A0 would mean decreasing entropy to 0.

[infamous]

No, cooling would mean decreasing entropy. Cooling down to A0 would mean decreasing entropy to 0.

So your saying the universe will not cool to AO? Because entropy will only increase in a closed system.

[Qfwfq]

Not according to thermodynamics. The second principle is a statistical principle. To get around it you would have to do something smart to each individual vibrating particle.

[infamous]

No, cooling would mean decreasing entropy. Cooling down to A0 would mean decreasing entropy to 0.

Why do I see a paradox developing here. Shortly after the Big Bang the universe was incredibly hot after which it began to cool. The second law tells me that in a closed system entropy can only increase but, this explanation says that because the universe is cooling, entropy is decreasing. It's becoming clear to me that I'm missing something about the defination of entropy.

[Erasmus00]

Why do I see a paradox developing here. Shortly after the Big Bang the universe was incredibly hot after which it began to cool. The second law tells me that in a closed system entropy can only increase but, this explanation says that because the universe is cooling, entropy is decreasing. It's becoming clear to me that I'm missing something about the defination of entropy.

 

Take my answer with a grain of salt, as I know almost nothing about mixing cosmology with thermodynamics. Taking a guess, I think its tough to define the universe as a thermodynamically closed system, as it is constantly creating space, which has an essentially 0 energy density. The universe cools, I would guess, by sharing its heat with this new space.

-Will

[infamous]

The universe cools, I would guess, by sharing its heat with this new space.

-Will

OK, that makes sense, because the universe is expanding the total heat energy is spread out over a larger area resulting in a cooling effect. Very good, Erasmus00. This would also explain why it can never reach absolute zero for to do so it would have to expand by an infinite amount. Thanks, this clears up the question I had in mind.

[Qfwfq]

A hot material may cool by endothermic reaction taking place, a gas may cool by expansion. When the initial state isn't stable, these things may take place spontaneously. It doesn't mean going to a lower overall entropy. Have some very pure hot water in an excellent Dewar jar and let it reach equilibrium, then dump in some salt that you previously brought to the same temperature. What will happen?

 

When you say a system is at maximum entropy, I don't see there could be room for cooling to take place.

[Qfwfq]

As for the universe expanding:

 

A) As long as the universe is expanding, you couldn't very well say it has reached maximum entropy.

 

:eek2: As long as the universe is expanding, that is something that can serve as an operative definition of time measurement.

[infamous]

As for the universe expanding:

 

A) As long as the universe is expanding, you couldn't very well say it has reached maximum entropy.

Very good point, now this is making a lot more sense to me.

 

:eek2: As long as the universe is expanding, that is something that can serve as an operative definition of time measurement.

Yes, understandable. As long as expandsion is underway, time will still exist. And if I'm not mistken, most theorists believe that universal expansion may be unlimited, and I say "may be unlimited" because this question is still unanswered. So, as long as any feature of the universe is changing, these changes will manifest themselves as the passage of time however slight the change may be. When things stop changing time will cease.

[lindagarrette]

Very good point, now this is making a lot more sense to me.

 

Yes, understandable. As long as expandsion is underway, time will still exist. And if I'm not mistken, most theorists believe that universal expansion may be unlimited, and I say "may be unlimited" because this question is still unanswered. So, as long as any feature of the universe is changing, these changes will manifest themselves as the passage of time however slight the change may be. When things stop changing time will cease.

Doesn't make sense to me. As long as there is space, there has to be time.

[Qfwfq]

It's a very subtle epistemological point Linda.

[Jay-qu]

nice one Qfwfq! you would be suprised how little people know of that word and actually use it in the right context

[emessay]

In term of conscious universe, time is reflection of 'sleepless space' and space is reflection of 'sleepless time'. If there is no space-time, is it being meaningless or nothing ? When does both of space and time would being slept away ??

 

Do not forget we have sleeping time 8 hrs/24 hrs ~ 4.5 bya/13.7bya !!

I would be better slept away, let's God alone working before Planck time !!

When we wake up[conscious] in life reality, He[God] is gone. Where ??

[infamous]

Time is only the memory of passing events. Imagine how we would view our existence if we had no memory of past events, living in only the here and now, no past, no future. There is no future without recognizing the past.

[Qfwfq]

I partly agree, but:

Time is only the memory of passing events.

I'd say that time is only passing events while the memory of them is how we are aware of time and have a notion of it. There are animals that, while able to perceive their surroundings in order to find food and flee peril, appear to have no memory or ability to learn. They don't survive if they don't have the right instincts and a smarter animal can easily deceive them. To them, presumeably there's no such thing as time, to us there is.

 

Does time exist or not? A stone could even less have a notion of time but that doesn't mean it doesn't exist. :)