Big Bang Theory Violates First Law of Thermodynamics

[arfa brane]

Don't confuse with time translation invariance as per Noether's theorem.

So translation and reversal shouldn't be confused. Right.

But the symmetries are of time, whether it's translated or reversed, and to me, if time-translation doesn't change the laws of physics it kind of follows that time-reversal doesn't either. Even though they lead to different conclusions or theories.

 

[Q-reeus]

Or kind of not. Here is a Wikipedia short-list table showing what quantity is conserved if a given symmetry holds:
https://en.wikipedia.org/wiki/Time_translation_symmetry
So now you can study Kramers degeneracy . What fun this all is.

 

[arfa brane]

Or kind of not.

Translation is kind of not reversal, or time is kind of not . . . time?

 

[Q-reeus]

Translation is kind of not reversal, or time is kind of not . . . time?

The first part. Time is afaik always time - but don't quote me on it!

 

[exchemist]

Or kind of not. Here is a Wikipedia short-list table showing what quantity is conserved if a given symmetry holds:
https://en.wikipedia.org/wiki/Time_translation_symmetry
So now you can study Kramers degeneracy . What fun this all is.

Indeed.

As I understand it (but tell me if this is wrong), time translation invariance simply means that if a relation involving time holds today, then it also holds next year, or in the c.15th. That is obviously not at all the same as saying that a physical process is reversible.

 

[arfa brane]

Apparently (according to those physics dudes) time translation is a continuous symmetry (with a Lie group), and time reversal is a discrete symmetry (and part of CPT symmetry).

Time reversal does not conserve energy. But it makes sense that at any "point" of time there is a t, -t symmetry which holds for any translation (t + s, -t +s). The difficulty for humans is understanding how time can be both continuous and discrete. Or Something.

 

[Q-reeus]

Apparently (according to those physics dudes) time translation is a continuous symmetry (with a Lie group), and time reversal is a discrete symmetry (and part of CPT symmetry).

Agreed.

Time reversal does not conserve energy.

??? I refer you back to that Wikipedia table again. If the system violates time translational symmetry, as many cosmologists believe applies to our universe, THEN time reversal will see a violation of energy conservation, of opposite sign to the forward running system. But not owing to time reversal per se. Check out the first system considered here:
http://www.physics.usu.edu/torre/6010_Fall_2016/Lectures/04.pdf
Total energy E is a parametric function of both velocity and position - guaranteeing it is conserved on time reversal. Adding in dissipation wrecks that neat result but only because the total energy is no longer just mechanical. Then, time translation symmetry holds overall but time reversal symmetry fails owing to 2nd Law considerations - friction.
Of course it holds if one simply runs the movie backwards, which however implies negative friction owing to fantastically improbable perfectly synchronized reverse motions of all particles and radiation, which is never seen.

[There are let's say hypothetical situations where violation of time reversal symmetry implies the possibility of energy conservation violation, apart from any time translation symmetry considerations. For example a non-reciprocal reactance. It was an active study for at least two decades beginning with paradoxical predictions for certain microwave ferrite devices. In the end, it was concluded after many practical tests and inconclusive theory papers, that 'nature prefers conservation of energy'.]

But it makes sense that at any "point" of time there is a t, -t symmetry which holds for any translation (t + s, -t +s).

Time symmetry is fundamentally about the sense of time flow, the sign of rate-of-change. Instead of your 'discretized time' I'd think (t-dt, t+dt) is an appropriate differential interval to evaluate. Anyway both senses of time reversal are covered here:
http://philsci-archive.pitt.edu/15033/1/Roberts2018-TimeReversal.pdf

The difficulty for humans is understanding how time can be both continuous and discrete. Or Something.

Nothing in your #86 implies discretized time. Which is however dealt with in various tomes because it's necessary to properly evaluate digital systems e.g. digital filters. Not my specialty!

 

[arfa brane]

I think one needs to be careful when discussing time, about whether you mean the kind of time familiar to engineers, say in the field of communications, or whether you mean the kind that has symmetries and that theoretical physicists use.

For instance, it should occur to a freshman calculus student that integrating from -dt to dt implies that the direction of time isn't important to the mathematics (of real numbers).

 

[Write4U]

I think one needs to be careful when discussing time, about whether you mean the kind of time familiar to engineers, say in the field of communications, or whether you mean the kind that has symmetries and that theoretical physicists use.

For instance, it should occur to a freshman calculus student that integrating from -dt to dt implies that the direction of time isn't important to the mathematics (of real numbers).

I am really confounded by the notion that time is reversible.
Time Reversal Bryan W. Roberts May 30, 2018 1. Introduction:

Time reversal is a wonderfully strange concept. It sounds like science fiction at first blush, and yet plays a substantial role in the foundations of physics. For example, time reversal is often use to describe the ‘arrow of time’, by allowing one to say how evolving to the future is different from evolving to the past.

How can one evolve backwards in time? Seems to me that the proper term here should be "devolve" back in time. One thing that time reversal ought to do is turn around the spatial order in which such states originally occurred.

The standard time reversal transformation does this by transforming the temporal parameter t as follows: t 7→ −t. This flips time around a particular initial moment t = 0. That may seem a bit arbitrary at first.

You bet it does! It is completely irrational. t7 = t0 . IOW, mathematics do not hold in spacetime?

However, most of the time, it isn’t philosophically or physically significant.

Everything is philosophically possible, it has nothing to do with reality itself. But not everything is physically possible. In spacetime, how can time not be physically (spatially) significant? Temporal change emerges along with spatial change. If it were possible to go both forward and backward in time there would exist a unsolvable paradoxical dichotomy.

The assumption here is that time is a independent temporal dimension which can be traversed forward and backward without affecting physical (spatial) change. To me that sounds completely irrational.

Science has finally agreed that we're dealing with "spacetime". Now the proposition is that we can travel back and forth in time as if time is not dependent on the existence of space and space is not dependent on time.

Even worse, the proposition now is that spacetime isn't really spacetime, but can both be separate spatial and temporal dimensions which can be traversed simultaneously in both directions as separate independent dimensions.

This is where I have a problem with the concept of travelling back in time only, without travelling back in space, no?

Can anyone show me how the dimension of time can be separated from being affected by what happens in space? You can travel forward and backward in space, but time is always an emergent (additive) property of spatial change. Reversing time cannot result in increase in complexity other than retracing the original change in thermodynamics, which is going back in time and space.

Prove to me that we can travel back in time without going back in spacetime.

Arbitrarily changing human symbolic numbers does not do it for me. It's mathematically dishonest and has no relationship to what happens in the real world.

 

[arfa brane]

It seems that the laws of physics are time-symmetric because time is a symmetry of nature, type of thing.

So conservation of energy is also one of these symmetries, and so on.
Which demands that antiparticles "go" backwards in time.

 

[Write4U]

It seems that the laws of physics are time-symmetric because time is a symmetry of nature, type of thing.

So conservation of energy is also one of these symmetries, and so on.
Which demands that antiparticles "go" backwards in time.

Why does time have anything to do with that? AFAIK the "symmetry of time with reality" is the continued durable existence of spacetime.
Time is an emergent result. It is only symmetrical to that which continues to exist, like spacetime.

Time itself has no symmetry. It is an emergent property of "duration" of existence and doesn't care in what form or pattern that existence takes on. Positive, neutral, negative, pro-xxx, anti-xxx, it's all the same.
If it exists, it goes forward in time or it ends existence. There is no anti-existence!

Particle/anti-Particle is a symmetry. They both live going forward in time.
Time itself is not symmetrical, it is always a result, a product of "duration" of something, anything, all things.
But Time itself has no existence. There is no duration of Time.

imo, even virtual particles, which must travel @ FTL and cannot exist in our time, go forward in time, by reason that even if they are "virtual" they do have occasional existence in our spacetime dimension. But even when they decay they do not go back in time, their constituent parts continue existence in simpler form and existence itself demands going continually (chronologically) forward in time, not always in the same form, but never backward.

When something travels backward in time, it eventually reaches a "beginning" and then cannot go past the beginning of it's own time and simply disappear from its own reality. It's existence ends.

Unless we want to equate thermo-dynamics as an expression of time, entropy itself always goes forward in time. Can there be "reverse entropy"?
What would be the natural creative benefit of possessing ability to go back in time?

imo, Time ends with end of existence. Before the existence of the universe there was no time, in our reality.
Before the Beginning , our SpaceTime did not exist yet as it does today, 14.5 billion years later (going forward from the beginning).

You cannot go back past the beginning. You can only go forward in time from the beginning.

The OP question cannot really be answered.
The BB did not violate thermodynamics.
Before the BB and the beginning of spacetime, thermodynamics did not yet exist.
Thermodynamics and their attendant laws were created during the BB.
What was before the BB is "unknown". Can't go back in time past the beginning of time....

 

[Q-reeus]

Write4U - your last two shock-horror-can't-be posts are illogical reactions to having badly misunderstood what Bryan Roberts was actually saying in what you quoted in #89. Time has no meaning apart from its operation on a physical system. Mathematically reversing time has nothing to do with 'actual time travel to the past', or 'separating time from spacetime'. It allows classification of physical processes/interactions into time-reversible vs time-irreversible ones. Examples were given earlier and I WONT repeat here. Give it a rest.

Where has the OP gone? Bad manners to just abandon early on ones own thread.

 

[Write4U]

Mathematically reversing time has nothing to do with 'actual time travel to the past', or 'separating time from spacetime'. It allows classification of physical processes/interactions into time-reversible vs time-irreversible ones.

That was my point. I was addressing the mathematics of reversing time. Bryan Roberts was speaking theoretically as it pertains to human symbolisms, which have nothing to do with "actual time travel" or "separating time from spacetime", the normal functional properties of spacetime.

I was giving my opinion of this segue in regard to the OP question......

p.s. I do understand the concept of "repetition" in time.

A time crystal or space-time crystal is a state of matter that repeats in time, as well as in space. Normal three-dimensional crystals have a repeating pattern in space, but remain unchanged as time passes. Time crystals repeat themselves in time as well, leading the crystal to change from moment to moment.

https://en.wikipedia.org/wiki/Time_crystal#

Can I have an answer to this;
Do time crystals travel back time or do they just repeat themselves going forward in time? Kinda like fractals?

 

[Q-reeus]

That was my point. I was addressing the mathematics of reversing time. Bryan Roberts was speaking theoretically as it pertains to human symbolisms, which have nothing to do with "actual time travel" or "separating time from spacetime", the normal functional properties of spacetime.

I was giving my opinion of this segue in regard to the OP question......

p.s. I do understand the concept of "repetition" in time. https://en.wikipedia.org/wiki/Time_crystal#

Can I have an answer to this;
Do time crystals travel back time or do they just repeat themselves going forward in time? Kinda like fractals?

Having no familiarity with 'time crystal physics', I will nevertheless venture that 'backward time travel' does not occur there. Anymore than for a regular harmonic oscillator.

 

[Q-reeus]

It seems that the laws of physics are time-symmetric because time is a symmetry of nature, type of thing.

So conservation of energy is also one of these symmetries, and so on.
Which demands that antiparticles "go" backwards in time.

I've covered this several times in earlier threads, but once more:
Back in the 1940's Wheeler-Feynman developed the notion of antiparticles as ordinary particles traveling backwards in time. There remain adherents but most physicists reject it.
The fatal issue imo is inertial/gravitational mass. Given the yet to be detected graviton is its own antiparticle, logically the sign of gravitational mass does not change on time reversal.
Hence two antiparticles should gravitationally attract, which manifestly does not correspond with a time-reversed movie of particle-particle gravitation.
Similarly, suppose antiparticles did anti-gravitate. An initial equal mix of particles/antiparticles should weigh exactly zero, but after annihilating to radiation, the gravitational mass is not zero but double that for the ordinary particle aggregate initial mass. Happy with that sort of thing?

 

[arfa brane]

The fatal issue imo is inertial/gravitational mass. Given the yet to be detected graviton is its own antiparticle, logically the sign of gravitational mass does not change on time reversal.

What about the detection of classical gravitational waves? What if anything, does that say about t-symmetry (the translation or reversal of intervals of time)?

Hence two antiparticles should gravitationally attract, which manifestly does not correspond with a time-reversed movie of particle-particle gravitation.
Similarly, suppose antiparticles did anti-gravitate. An initial equal mix of particles/antiparticles should weigh exactly zero, but after annihilating to radiation, the gravitational mass is not zero but double that for the ordinary particle aggregate initial mass. Happy with that sort of thing?

No, and my understanding is that gravity acts on particles or antiparticles the same, there is no negative mass or inertia in this universe. Also there's something I recall about CPT being an effective theory means that only baryon number and isospin are exact symmetries.

The universe is mostly ordinary matter because CP-symmetry was violated when matter and antimatter first condensed. The small remnant of positive matter survived because of a symmetry-breaking 'violation' of what had been, until then, an exact symmetry. Or Something Like That.

Ahem, but CPT says nothing about gravitational interactions or symmetries.

 

[Q-reeus]

What about the detection of classical gravitational waves? What if anything, does that say about t-symmetry (the translation or reversal of intervals of time)?

There is an issue there? The waves run in reverse and are absorbed by presumably a binary pair in the process of uncoalescing. The only anomaly I see is anti-gravitation of the masses.

No, and my understanding is that gravity acts on particles or antiparticles the same, there is no negative mass or inertia in this universe. Also there's something I recall about CPT being an effective theory means that only baryon number and isospin are exact symmetries.

Can't comment on last claim but agreed with first part.

The universe is mostly ordinary matter because CP-symmetry was violated when matter and antimatter first condensed. The small remnant of positive matter survived because of a symmetry-breaking 'violation' of what had been, until then, an exact symmetry. Or Something Like That.

Yes and I commented similarly earlier on here.

Ahem, but CPT says nothing about gravitational interactions or symmetries.

True. But time reversing a system does reveal that antiparticles are NOT ordinary particles traveling back in time. On reflection I should have thrown in ordinary charged particles, whose EM interactions (at least the electrostatic ones) do not correspond to their antiparticle duals in time reversed motions.
An earlier post quoted some authority to the effect one cannot distinguish forward or reverse run time by looking at just the fundamental interactions, which are time symmetric.
To me that is obviously false given the above examples. It might only hold for a system comprised of neutral particles having only short-range central contact forces operating, and gravitational interactions are negligible.

 

[arfa brane]

correction: CPT is a theorem, a consequence of quantum field theory. Since it's a theorem it can be proved.

And since the symmetries in CPT are the ones seen in nature, the theorem's existence appears to imply that nature is mathematical in a fundamental way.

One other comment about the cosmic CP-violation; it must have been equivalent to a violation of T-symmetry because CPT is exact.

 

[arfa brane]

My guess is that because a parity transformation is equivalent to a reflection, that's why Robert Adair titles his article A Flaw in a Universal Mirror.

For a clock with hands moving . . . clockwise (angle decreasing), the reflection is a clock with hands moving anticlockwise (angle increasing), mathematically a multiplication of the direction by -1. With a meson-antimeson pair aligned horizontally you get an exchange of position but not orientation (equivalently multiply the charges by -1). Do this with a current flowing in a wire loop though, and the symmetry is no longer exact. At least that's what I think he's trying to say.

Ed: should have said the meson-antimeson swap places, which does change the relative orientation, the orientation that's unchanged is of their spins.
And I was going to ask this: if P-symmetry is like a reflection, does the reflected or parity-reversed clock have hands moving backwards in time?; is a parity operation on a clock equivalent to sending it to the "-t domain"? It's easy enough to bring a clock back, just transform it twice, but where is it when you do it once?

My tentative answer is, it's a clock that's transformed in the P-mirror, which is what happens to a clock in an ordinary optical mirror. Time isn't transformed, parity or left and right, are exchanged; The P-symmetry 'mirror' fails to be like an optical mirror when a wire loop with a current flowing in it are transformed into their 'reflections'.

 

[arfa brane]

Banging on here. The introduction of another mirror, the C-mirror which exchanges charges, was thought to resolve the problem with parity and magnetic fields when a combined CP-mirror (actually a set of transformations acting on charge and parity) was applied.

The C-mirror does not have reflection symmetry like an optical mirror, but rather preserves orientations; acting on a meson-antimeson pair, or an electron-positron pair, say, the effect is the same as a parity change. The symmetry fails again with electrons flowing in a copper wire loop; positrons in a loop of anticopper wire are the "C-reflection".

This is why the CP combination was believed to resolve the failure, because the magnetic field direction is reversed by P, or by C, and together the double reversal leaves the magnetic field invariant (aka a symmetry).

But today it's called CPT-symmetry; the reason is not because CP and T are combined but because CP and T are equivalent.

Here's an online lecture about CPT and the Standard Model: