No big bang?

[Sorcerer]

I was reading this article http://m.phys.org/news/2015-02-big-quantum-equation-universe.html

 

I was wondering if this is correct what does this mean for the second law of thermodynamics?

 

If the law is followed and the universe is an infinite age then entropy must be at a maximum. Observation shows this isn't the case, how would this problem be reconciled?

[Asimov]

Sorcerer: Wow, they sure smm sure of themselves.

 

"It is satisfying to note that such straightforward corrections can potentially resolve so many issues at once," Das said.

 

OK, except for a few little details like maximum entropy and 2nd law of thermodynamics. Aren't there a few others? Infinite black holes? Infinite Star Wars sequels?

[Bill Angel]

Here is a quote from another article about this same work titled

 

"Big Bang, Deflated? Universe May Have Had No Beginning"

 

There are other problems brewing in physics namely, that the two most dominant theories, quantum mechanics and general relativity, can't be reconciled.

Quantum mechanics says that the behavior of tiny subatomic particles is fundamentally uncertain. This is at odds with Einstein's general relativity, which is deterministic, meaning that once all the natural laws are known, the future is completely predetermined by the past, Das said.

Das and his colleagues ...looked at an older way of visualizing quantum mechanics, called Bohmian mechanics. In it, a hidden variable governs the bizarre behavior of subatomic particles. Unlike other formulations of quantum mechanics, it provides a way to calculate the trajectory of a particle.

Using this old-fashioned form of quantum theory, the researchers calculated a small correction term that could be included in Einstein's theory of general relativity. Then, they figured out what would happen in deep time. The upshot? In the new formulation, there is no singularity, and the universe is infinitely old.

See http://www.livescience.com/49958-theory-no-big-bang.html

 

So the claim here is that these theoreticians have reconciled general relativity and quantum mechanics, but have done so by introducing hidden variables that allow the seemingly probabilistic bahavior of subatomic particles to now be considered deterministic.

[Strange]

Sorcerer: Wow, they sure smm sure of themselves.

 

No more than any other scientists presenting their work.

 

OK, except for a few little details like maximum entropy and 2nd law of thermodynamics. Aren't there a few others? Infinite black holes? Infinite Star Wars sequels?

 

I don't see the relevance of any of those "objections".

So the claim here is that these theoreticians have reconciled general relativity and quantum mechanics, but have done so by introducing hidden variables that allow the seemingly probabilistic bahavior of subatomic particles to now be considered deterministic.

 

My understanding is that they are simply using Bohmian trajectories as an easier way of trying to calculate the quantum effects in the early universe. They are not claiming there are hidden variables, just using it as a useful approximation.

 

Similar techniques are often used to try and approximate a theory of quantum gravity. For example, Hawking had to use (other) simplifications in order to derive the equations for Hawking radiation.

p.s. I'm sure this work has been discussed before but I can't find the thread now.

 

This paper gives some good context for the misleading (or basically grossly dishonest/ignorant) headlines: https://medium.com/starts-with-a-bang/the-two-big-bangs-1493194f5cd9#.2pk1j4l9a

"In fact, as far as the question of where space and time come from goes, there is still plenty of debate on all sides, and this recent paper that came out is simply another drop in the ocean of that debate: nothing more."

Another good commentary on this paper here: https://plus.google.com/+BrianKoberlein/posts/3wW3fNH7GMV

 

Unfortunately many articles confuse “no singularity” with “no big bang.”

While this is an interesting model, it should be noted that it’s very basic. More of a proof of concept than anything else. It should also be noted that replacing the big bang singularity with an eternal history isn’t a new idea. Many inflation models, for example, make similar predictions. But none of these ideas eliminate the big bang, which is an established scientific fact.

[Sorcerer]

Is it possible for the hypothetical Bose Einstein condensate to have remained at the same order, ie same value of entropy, for an infinite amount of time? Does that violate the 2nd law?

 

This begs the question however, why at some point did entropy increase?

 

Could it be reasoned that because it could, it had to at some point, and once it had, it was no longer stable enough to not continue increasing?

 

What value is given for entropy in a system that only contains a Bose Einstein condensate?

 

What meaning does assigning a time value to a system which is static, ie an entropy stable Bose Einstein condensate, even have? Surely where there is no change, time is a meaningless concept.

Edited October 30, 2015 by Sorcerer

[studiot]

It is important to realise that the second law does not say entropy always increases.

 

It says entropy never decreases, which is not the same.

 

It is possible to offer theoretical systems where entropy does not change, but other thermodynamic variables do.

[Sorcerer]

It is important to realise that the second law does not say entropy always increases.

 

It says entropy never decreases, which is not the same.

 

It is possible to offer theoretical systems where entropy does not change, but other thermodynamic variables do.

Such as?

[Strange]

Surely where there is no change, time is a meaningless concept.

 

Of course not. Space-time can continue to exist, even if nothing changes along the time dimension.

 

The idea that time is defined by change is bizarre but quite common. It seems to be based on the idea that we can use change to measure time.

[studiot]

 

Such as?

 

 

Since the question was so pleasantly asked for I will tell you.

 

Consider a sealed cylinder of ideal gas containing a frictionless adiabatic piston, dividing it into two chambers, A and B.

 

If the piston is mechanically displaced and then released. the entropy change is zero as (say) chamber A is compressed and chamber B expanded.

Edited October 30, 2015 by studiot

[Sorcerer]

 

Since the question was so pleasantly asked for I will tell you.

 

Consider a sealed cylinder of ideal gas containing a frictionless adiabatic piston, dividing it into two chambers, A and B.

 

If the piston is mechanically displaced and then released. the entropy change is zero as (say) chamber A is compressed and chamber B expanded.

Sorry if my query sounded rude, I was in a rush.

 

Isn't a frictionless piston an impossibility?

 

Also this doesn't really relate to a universe since it is the entire system, in this case isn't there some external force acting on the piston doing work, and that work would result in an increase in entropy.

 

Also if we subdivide the cylinder into two chambers and not consider both at once doesn't the entropy of each change, and it's only when considering the sum of the two that there isn't change.

 

I guess what I want to know is how can a Bose Einstein condensate change over time while not increasing in entropy?

 

How much addition of entropy to a system which is a Bose Einstein condensate tolerate before it is no longer a stable form. Could destabilizing result in the big bang.

[studiot]

 

Isn't a frictionless piston an impossibility?

 

 

 

Does that make a difference to a theoretical system or the laws themselves?

Where do any of the laws of thermodynamics declare zero friction impossible?

Even if we have never observed it can we not treat zero friction by the time honoured method of asymptotic approach?

 

 

Also this doesn't really relate to a universe since it is the entire system, in this case isn't there some external force acting on the piston doing work, and that work would result in an increase in entropy.

 

Also if we subdivide the cylinder into two chambers and not consider both at once doesn't the entropy of each change, and it's only when considering the sum of the two that there isn't change.

 

 

 

I don't follow how your next two lines are compatible.

Don't they contradict each other as underlined?

 

 

Also this doesn't really relate to a universe since it is the entire system

 

The same laws of thermodynamics are supposed to apply to all systems.

I merely said one can propose a system where entropy does not increase.

 

In the case of the universe we have a few dilemmas to resolve.

 

We do not know if the uiverse is finite or infinite.

If it is infinite, does it not possess infinite entropy?

If so how can entropy increase?

 

If it is finite then what is beyond the finite?

Could not some agent there move the piston?

 

After all, what started the Big Bang if there was one?

 

So you see there are quite a few (apparently) conflicting principles to reconcile.

 

As a matter of interest, what is your prognosis for the future history of my piston-in-cylinder system, once activated?

[Sorcerer]

 

Does that make a difference to a theoretical system or the laws themselves?

Where do any of the laws of thermodynamics declare zero friction impossible?

Even if we have never observed it can we not treat zero friction by the time honoured method of asymptotic approach?

 

As a matter of interest, what is your prognosis for the future history of my piston-in-cylinder system, once activated?

I was hoping more for an explanation which would apply to the assumed quantum fluid in the article I linked in the first post. An explanation relating directly to how there was time in that state without entropy increase. I assume that time requires change, and that Bose Einstein condensates consisting of only gravitons are completely uniform crystals. What process in which time exists could occur?

 

The piston example is fine, but fails in analogy by having multiple parts and having something external to it which put a force on the piston.

 

I would say that because of the pressure difference between the two chambers that the piston would move back to the middle,it would perhaps bounce like a pendulum taking time to settle. It would take longer because of no friction but eventually would settle exactly at equilibrium.