# Oscillating Unvierse Theory and the 2nd law of Thermodynamics

I have read two contraditory explanations of why the 2nd Law of Thermodynamics would prohibit an oscillating universe ad infinitum.

The first one, from a Paul Davies Books states that the second law of thermodynamics only would permit the oscillations to become larger each time. While this would lead to an infinite future, it also points to a finite past.

Another explanation used a bouncing ball as an analogy and stated that the bounces would get smaller each time.

Which is correct?

Thanks,
Glenn

Ambitwistor
I know that in Tolman's original oscillating universe, the cycles get longer and longer. It doesn't necessarily follow that the universe then gets bigger each cycle, but I wouldn't be surprised. I haven't read the papers, though, so I don't know.

It's worth noting that Tolman's model was in the context of classical general relativity, and in quantum gravity, all bets are off; we can't extrapolate the effects of a collapse on a future expansion.

It's also worth noting that people have worked on oscillating models that try to avoid the entropy problems of Tolman's, e.g.:

http://arXiv.org/pdf/gr-qc/9510041
http://arXiv.org/abs/astro-ph/0204479

I have heard a few different takes on this myself. However, it seems to me that the law of entropy cannot be applied to the Oscilating Universe model at all. I have two reasons for this opinion;

1)Entropy is the tendency of energy to distribute itself more and more evenly throughout the universe. This means that where there is more energy (in the form of a particle of matter, for example) that energy will tend to radiate away (through particle decay) and spread out into places where there is less. That is, places within the universe. But the energy cannot leave the universe, because that would constitute anihilation, which would violate conservation. By all the observational evidence we have, energy cannot be created or destroyed. So the same energy that went into this Big Bang will also be present in the next.

2) By all the Oscilating Universe models I have seen, the basic laws of physics are randomised at the moment of the Big Crunch. If this is true, then even if entropy did mean the whole system loses energy, it would only mean that for this current oscilation. In the previous oscilation, the law of entropy may not have existed, or it may have been the opposite of what it is now, or any number of possibilities. One geuss is as good as another, once you cross the singularity-boundary between cosmoses (cosmi?).

Ambitwistor
Originally posted by LURCH
1)Entropy is the tendency of energy to distribute itself more and more evenly throughout the universe.

That isn't the definition of entropy.

By all the observational evidence we have, energy cannot be created or destroyed. So the same energy that went into this Big Bang will also be present in the next.

Conservation of energy doesn't say anything directly about what happens to the entropy.

2) By all the Oscilating Universe models I have seen, the basic laws of physics are randomised at the moment of the Big Crunch.

The idea has been proposed, but I've never heard of any concrete oscillating universe model in which the laws of physics were actually different.

The kernel of truth in your argument is that we don't know what happens at a singularity, or whether there even is one

Staff Emeritus
Gold Member
The 2nd law is a description of a phenomenon within this universe. I don't see how it can be applied to anything before or outside of this universe.

Originally posted by Ambitwistor

Conservation of energy doesn't say anything directly about what happens to the entropy.

I think it does if we try to apply entropy to an entire cosmological model. If the system being studied is "the universe", then energy lost from that system is energy that ceases to exist within the universe. This amounts to the annihilation of the energy in question.

For energy to be lost from a particular system to the universe is one thing, but for energy to be lost from the universe, that energy ceases to exist. This violates conservation.

Originally posted by LURCH
I think it does if we try to apply entropy to an entire cosmological model. If the system being studied is "the universe", then energy lost from that system is energy that ceases to exist within the universe. This amounts to the annihilation of the energy in question.

For energy to be lost from a particular system to the universe is one thing, but for energy to be lost from the universe, that energy ceases to exist. This violates conservation.
Your second paragraph is dead-on. That is why Guth's "first" model failed and why there are currently about 23 different Inflation models, none successful yet, in my humble opinion.

Labguy

Ambitwistor
LURCH, you said a lot about energy conservation, but what are you trying to say about entropy?

Ambitwistor
Originally posted by Labguy
Your second paragraph is dead-on. That is why Guth's "first" model failed [...]

Guth's original inflation model didn't fail because energy was not conserved, or was being "lost from the universe", or anything like that.

Originally posted by Ambitwistor
Guth's original inflation model didn't fail because energy was not conserved, or was being "lost from the universe", or anything like that.
Ok, it failed for something(s) else.. I used to know a lot about entropy, but that was back when my mind was in a more ordered state. It seems to be getting more and more random as time goes by...

Guylab

Originally posted by Ambitwistor
LURCH, you said a lot about energy conservation, but what are you trying to say about entropy?

That entropy involves the loss of energy from a system. If I understand you correctly, you're saying it doesn't? If entropy is not the redistribution of energy from places of higher concentration to places of lower concentration, then I've greatly missunderstood the whole concept. Can entropy take place without this movement of energy?

Ambitwistor
Originally posted by LURCH
That entropy involves the loss of energy from a system. If I understand you correctly, you're saying it doesn't?

The total energy of a closed system will remain constant, but its entropy will tend to increase.

If entropy is not the redistribution of energy from places of higher concentration to places of lower concentration, then I've greatly missunderstood the whole concept. Can entropy take place without this movement of energy?

Entropy isn't something that "takes place". Do you mean, can entropy increase without movement of energy? Well, without local transport of energy from one part of a system to another, generally nothing happens: you have a static system. But I don't know what connection you want to make with entropy. I'm also not sure what you mean by "redistribution of energy from places of higher concentration to places of lower concentration". Do you mean that when a system equilibriates, it should end up with the same energy at all points of the system? If so, that's not the case.

prashantmg123
well i would only say that,if everrything in this universe is happening on the basis of alll physical laws,then it would be an almost perpetual motion body revealing all its death and birth time dependently...does any meaning to the NEGENTROPY? if it is then it would be a mirror effect of either birth or of death..wanaa have something to say on this?

Originally posted by Glenn
I have read two contraditory explanations of why the 2nd Law of Thermodynamics would prohibit an oscillating universe ad infinitum.

The first one, from a Paul Davies Books states that the second law of thermodynamics only would permit the oscillations to become larger each time. While this would lead to an infinite future, it also points to a finite past.

Another explanation used a bouncing ball as an analogy and stated that the bounces would get smaller each time.

Which is correct?

Thanks,
Glenn

Staff Emeritus
Gold Member
Entropy is a thermodynamic measurement of an isolated system. It is a measurement of the randomness, uncertainty, or disorder in that system. Energy is not lost as the system does what it does...the energy is converted to a less useful state. But overall energy is still conserved.

Nommos Prime (Dogon)
Exotic Transformation (Entropy)

Entropy (as it applies to physics); is the measure of the unavailability of a system’s (open OR closed) thermal energy for conversion into mechanical work. It can also be the measure of degradation or chaos of the Universe.
Entropy (as it applies to maths); is the measure of the rate of transfer of information in a message.

The classical laws of thermodynamics do not apply or work with all observable phenomena. They don’t. Eg. Hawking Radiation and Quantum Microstates (currently being discussed on another thread on this forum). It IS possible for energy to disappear from this Universe or to “cease to exist”. No replacement force is needed for the resultant loss of energy.

Gold Member

Originally posted by Nommos Prime (Dogon)
Entropy (as it applies to physics); is the measure of the unavailability of a system’s (open OR closed) thermal energy for conversion into mechanical work. It can also be the measure of degradation or chaos of the Universe.
Entropy (as it applies to maths); is the measure of the rate of transfer of information in a message.

The classical laws of thermodynamics do not apply or work with all observable phenomena. They don’t. Eg. Hawking Radiation and Quantum Microstates (currently being discussed on another thread on this forum). It IS possible for energy to disappear from this Universe or to “cease to exist”. No replacement force is needed for the resultant loss of energy.

The classical laws of thermo dynamics DO apply to all physical situations. I don't know where you got the idea that they don't apply to Hawking radiation, but that's absurd as Hawking radiation is the mechanism that allows black holes to comply with the laws of thermodynamics. Again it is absurd to say that quantum microstates don't obey the laws of thermodynamics as they allow you to look at statistical mechanics from a quantum point of view.

The conservation of energy, in it's corrected form (to allow for the HUP, mass-energy equivalance, etc.) is absolute and cannot be violated.

Ambitwistor

Although it isn't a "loss of energy", perhaps Nommos Prime (Dogon) is actually referring to the black hole information loss paradox, which is a problem for the quantum thermodynamics of black holes.

Originally posted by Ambitwistor
Although it isn't a "loss of energy", perhaps Nommos Prime (Dogon) is actually referring to the black hole information loss paradox, which is a problem for the quantum thermodynamics of black holes.

...even if he isn't, can you explain what this is as it sounds very interesting.

Ambitwistor

The information loss paradox is this: if the black hole starts out in a pure quantum state, after emitting thermal radiation it ends up in a mixed state (a statistical ensemble of pure states). But unitary time evolution of quantum mechanics forbids a pure state to evlove into a mixed state. See:

http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/info_loss.html

Gold Member
What is the state of play with the information paradox, does the appeal to string theory for answers about the microstates of a black hole resolve this paradox?

Ambitwistor
Originally posted by jcsd
What is the state of play with the information paradox, does the appeal to string theory for answers about the microstates of a black hole resolve this paradox?

As far as I know, a knowledge of the microstates in string theory still hasn't yet helped with the information loss paradox. I think string theorists like to appeal to the more general principle of holography, without the microscopic details being fully understood, e.g.:

http://arXiv.org/abs/hep-th/0002044