Cosmology 101 pop question

A

arfa brane

call me arf
Valued Senior Member
The entropy of the universe is increasing with time because:

1) The amount of information in the universe is increasing with time
2) The number of interactions between particles increases as they get more spatial degrees of freedom with time
3) Shit happens
 
But 2 implies 1, right?

Otherwise an explanation for increasing complexity (of information)--the number of different types of star, evolution of lifeforms, increasing nuclear particle densities (since it was all hydrogen and helium pretty much to start with)--and so on.
 
Various forms of more ordered energy , e.g. nuclear and gravitational potential energy, are being converted to heat energy, which is more disordered. These are irreversible processes. So entropy goes up with time.
 
arfa brane said:
But 2 implies 1, right?
Click to expand...

But is all that information stable? More directly, something about the idea that the other implies the one requires a manner of uniformity about the information, but something about that presupposed uniformity, or perhaps the implicit presupposition itself, is erroneous.

Increasing complexity, maybe, but I feel like I'm missing something about durability.
 
Well, here's the thing about information increasing in complexity:

According to the Standard Model, information can't be created or destroyed, it has to be conserved like energy is.
But that comes with the caveat that the information is a function of quantum interactions; as if, when quantum fields appeared the amount of information was fixed and remains unchanging (in the global sense).

And it's understood that information can change from one form to another; classically it can be copied and erased, but that's impossible in the quantum context. Things got strange a long time ago.
And here we are . . .

What it all means, apparently, is that classically, information is not 'stable'--nothing is--and the only truly invariant thing in the universe is probability.
 
Last edited:
exchemist said:
Various forms of more ordered energy , e.g. nuclear and gravitational potential energy, are being converted to heat energy, which is more disordered. These are irreversible processes. So entropy goes up with time.
Click to expand...
About irreversibility:
Time-reversible physical processes are a requirement for QM. Without so-called T-symmetry it all falls apart--there is no closure, anything is possible because probabilities are not conserved. No predictions are possible in such a universe.

Just sayin'
 
Some stuff about the nature of information and why what most people would believe is a purely human concept, has become important in physical theories:
The central role that the concept of information is gaining in physics raises some intriguing questions that deserve close scrutiny.

The concept of information is, in a sense, a human-centered concept. After all, information theory was created to address engineering problems related to communication technology. We humans are the ones who care about information.

Why should Nature care about information? Does nature care about information? These are perhaps naive questions. But we find it perplexing that a concept developed to address purely human needs turns out to be essential to understand the fabric of Nature at its deepest level.
Click to expand...
--https://www.intechopen.com/chapters/78758

And I would caution that the word "information" does have slightly different meanings, depending on the, ah, context. In physics, information in some system is equivalent to a description of the system. How many descriptions can there be? Is there a shortest description, and so on.
Does the description of a system have to be written down or is this just an "in principle" thing?
 
A passing comment about information theory and computation.

A physical theory 'explains and predicts' interactions between physical systems. A theory can't be proven, but a mathematical theorem can be.
Using mathematical induction you can prove that an algorithm is correct (this means you can prove that it will halt, without error); you can also prove that an algorithm is efficient (that it will run in 'polynomial time', not 'exponential time').

Note it's called Bell's theorem, not Bell's theory . . .
 
So, attempting to debunk the premises I posted in the OP:

1) according to QM, information cannot increase or decrease (globally)
2) when particles collapse together under gravitational interaction they have fewer d.o.f. (but gravitational entropy increases)
3) Yeah, apparently
 
So now a next question in the pop quiz, about stability and protons--the hadrons that don't decay spontaneously.

And the next multichoice question is--hydrogen was one of (and the most of) the light elements to 'condense' from the primordial quark-gluon soup, this is because:

1) protons are more stable than alpha particles or nuclei with more than one proton.
2) The entropy of the universe prior to the condensation of hadronic matter was very low.
3) Lorentz symmetry didn't apply prior to the emergence of free hadrons.
4) The speed of light didn't apply because there was no vacuum.

p.s. some caution is advised when considering which if any of the above tentative answers apply to the question. Just sayin'
 
I wonder if the question above needs to also consider that normal matter survived the initial emergence of hadronic matter and antimatter, for reasons that remain somewhat obscure, but are assumed to be (I think) because of an inherent asymmetry in certain 'sectors' of the SM.

I'll stop raving now
 
arfa brane said:
And the next multichoice question is--hydrogen was one of (and the most of) the light elements to 'condense' from the primordial quark-gluon soup, this is because:

1) protons are more stable than alpha particles or nuclei with more than one proton.
Click to expand...
True.
2) The entropy of the universe prior to the condensation of hadronic matter was very low.
Click to expand...
True.
3) Lorentz symmetry didn't apply prior to the emergence of free hadrons.
Click to expand...
Probably false.
4) The speed of light didn't apply because there was no vacuum.
Click to expand...
? Light has a speed, whether it is propagating in a vacuum or in a medium. Even in a medium, the speed of light in the vacuum between the particles of the medium is the same as in a "pure" vacuum.
 
James R said:
True.

True.

Probably false.

? Light has a speed, whether it is propagating in a vacuum or in a medium. Even in a medium, the speed of light in the vacuum between the particles of the medium is the same as in a "pure" vacuum.
Click to expand...
Is that last statement right? My understanding is the phase velocity is slowed down, due to coupling with the electrons in the medium, but the front velocity (I think) is still c. There's a bit about it here:https://en.wikipedia.org/wiki/Speed_of_light
 
exchemist:

Phase and group velocities are only different when you have a superposition of more than one frequency of waves.

Necessarily, a photon - described as a localised wavefunction - is a "wave packet" made of many different frequencies. I don't think the photon picture is the best way to think about how light propagates through a medium. However, I suppose that in that picture different frequencies "couple" to particles of the medium more or less strongly, which causes some frequencies to be "delayed" more than others as they propagate through the medium. In that case, the group velocity of the photon ends up slowed, while we might say that the phase velocities of the component waves all still travel at the vacuum speed, c.

I'm not completely confident I have described this accurately, though...
 
James R said:
exchemist:

Phase and group velocities are only different when you have a superposition of more than one frequency of waves.

Necessarily, a photon - described as a localised wavefunction - is a "wave packet" made of many different frequencies. I don't think the photon picture is the best way to think about how light propagates through a medium. However, I suppose that in that picture different frequencies "couple" to particles of the medium more or less strongly, which causes some frequencies to be "delayed" more than others as they propagate through the medium. In that case, the group velocity of the photon ends up slowed, while we might say that the phase velocities of the component waves all still travel at the vacuum speed, c.

I'm not completely confident I have described this accurately, though...
Click to expand...
Good point about the velocities and wave packets.
 
You must log in or register to reply here.
Back
Top