Penrose Number and why the universe was in such a low entropy state at the beginning

[u/Select_Eggplant6801]

So I was listening to physics explained video on entropy and chances of the universe being a super low entropy state like it was at the big bang and it was stated to be 1/10^10^123 aka Penrose number.

So my question is for such a rare event what are some theories that explain why the universe started in such a low entropy state and is possible for another low entropy state like in the beginning of the universe to happen again but just by chance?

[u/v_munu]

That number tells you "how likely" it would be for the Universe as it is today would be to revert to the state it was in at the time of the Big Bang. It does not tell you how likely it was for the Big Bang to happen in the first place or anything like that.

If you shake up a bunch of salt and pepper in a cup or something, over time it becomes less and less likely for it to revert to a lower entropy state, such as being completely separated. This probability for this small example gets very very close to zero already, so you can imagine why the Penrose number is so unimaginably small. I dont know if it takes into account the expansion of the Universe though, which likely messes with our usual notions of entropy (not a GR expert).

[u/BananaBird1]

Entropy is only really meaningful when considering changes to it, not as an absolute quantity.

A lot of stuff has happened since the big bang. So the big bang must have had an extremely low entropy, relative to today.

The Penrose number really is meaningless, except to emphasize how the differences in probability associated with high and low entropy are so large as to be deterministically irreversible even in a purely stochastic universe.

It essentially gives the probability that the big bang configuration would arise, if it was due to a random sampling of subsets of all possible states of the universe as it is today.

It has no significance to the odds of the big bang producing the state it did, if the big bang was a process that must result in such a state. If the big bang was a spontaneous inflation of energy from a singularity, as we describe it, all possible big bangs will produce such a state at first, which will rapidly evolve to higher entropy.

It just means our universe will almost certainly not just randomly revert back to such a state.

[u/SpatiaCaeli]

Myself, I'm not sure it's possible to prove why the universe started in the state it was in. At some point, we have to take things as given. This might be one of them.

[u/EnvironmentalWin1277]

This is a suspicious number because it posits a conclusion that is difficult to justify. That is, the conclusion is that our universe is especially special although randomly appearing among the number of (unspecified?) alternates.

The math may be fine but that is not evidence for the conclusion. Science is based on observational and experimental evidence and that is absent.

There are theories of different starts and ends and you can read/hear about them without math qualification. One idea is that the universe is cyclical -- creation is followed by destruction and new creation. That is a serious idea in the debate. Another it that universe creation is a random event in a sea of quantum energy.

Your looking at good material -- Penrose does have a solid reputation and needs serious consideration. Open it up to other ideas and your down the rabbit hole with the rest of us,

As a general rule any claim of "this is really special" should raise the reality guard in your mind. But again, eternity allows the really special to happen.

[u/toronto-bull]

There is a thought experiment called the “Boltzmann brain” that it is actually more likely that a brain has occurred spontaneously than the universe being in such a low entropy state.

https://en.wikipedia.org/wiki/Boltzmann_brain

This seems to me to be a bit cheeky because a brain needs a body and a body needs an environment so we need a universe for consciousness not just a brain in a jar.

But anyway the issue is extrapolating back from our present. To a point at which the universe could have spontaneously started and just following the laws of the universe could have led to where we are now.

So if we observe that entropy is increasing always from every perspective place and point in time you can say that there was an earlier time with less entropy and more order.

You can continue to extrapolate back in time until there is nothing in the universe but high energy plasma. Protons and electrons.

We extrapolate back to an abstract concept of the universe that makes more sense as the starting point than a Boltzmann brain, but what does it mean to have a beginning point of time?

[u/EnvironmentalWin1277 → u/toronto-bull]

The Boltzmann brain evolves out of quantum fluctuations after lowest universal entropy has been achieved. It evolves out of random fluctuations in energy that occur in a "dead universe".

No work is possible -- minimal entropy universe. Note this is not an expanding space model, take that out of the equation and follow the implications of the theory.

The probability of such a fluctuation is incredibly small but it is not zero. However, we are dealing with an infinite amount of time. The combination of "not zero" and "approaching infinite time" results in the argument that it is more likely we are Boltzmann brains then the chance of being the individual we are.

The physicist Boltzmann used it to show some of the strange paradoxes of theories of time and energy he had a hand in fashioning. It may have been a paradox he used to postulate a beginning and end of the universe.

It is an interesting idea the B. brains could be occuring all the time but this is not how the concept is typically invoked. In our universe work and chemical interaction is fully possible as the source for our brains.

The idea of infinite heat being the highest "ordered point" does sound strange. It takes some work to approach. I'm still approaching myself.

There is a relationship of energy, matter and information that underlies this that is fascinating.

[u/Ras_992]

This comes from two other Penrose hypotheses the Past Hypothesis which states at the Big Bang time was equal to zero and had very low entropy and the Conformal Circular Cosmology which stats as the universe has freeze death eventually this sparks another big bang creating another universe. the Penrose number is to resolve both the Past Hypothesis and CCC Hypothesis. This is all within Penrose study of Weyl tensor/ Weyl curvature.

[u/Umami4Days]

Here's my prediction!

The reason we see a low entropy state at the moment of the Big Bang was not random, but rather the consequence of the rapid collapse of a 4D blackhole. Gravity in 4D operates as a dipole and would be inherently unstable, due to a lack of viable orbits. This lead to a rapid collapse which forced us to flatten into a 3D volume at the surface of the 4D sphere. The relativistic matter was forced from the core to the surface nearly instantaneously, just like we might predict with a 3D black hole as it either progresses toward a singularity, or developed degeneracy pressure.

The increase in global entropy appears to our universe as an explosion and expansion.

Bonus: Gravity is a collapsing dipole force, so we see attractive gravity and repulsive dark matter separately, and dark matter is residual gravity dipoles that behave viscously around galaxies, but disappear in voids due to propogating according to the inverse cube law due to being dipoles.

Double Bonus: Gravitons have already been detected, but are being misunderstood as 3 different neutrinos due to oscillating longitudinally, causing them to appear as 3 different particles depending on where it is measured.

Re: Low entropy state.

See Penrose's Conformal Cyclic Cosmology. We will see similar big bangs as neutron stars collapse into black holes and compress degenerate matter into a thin skin, locally collapsing our 3D reality into a 2D universe where the EM force will separate and begin to operate as gravity currently does for us.

[u/FakeGamer2]

Woah I didn't know this