My pet theory: all atoms decay back to hydrogen given enough time, gravity pulls them together, stars form, the universe is one big loop that self resets :)
I went to a talk of his on CCC ages ago, and it was such a fascinating combination of geometry, causality, and asymptotics. I have absolutely no clue whether it's reasonable physically, but independent of that, it's just a really elegant fusion of topics in a fun to think about way. Worth a read for anyone who just appreciates elegant new ways of combining mathematical structures.
I've also seen this talk, at the behest of some spaced out friends of mine, an amazing experience and I still think about the universe through the lens of that talk!
My understanding of this idea is that once the universe reaches a state of maximum entropy (this is the “heath death” of the universe, where everything is a uniform, undifferentiated cloud of photons, then time stops being meaningful because there can be no change from moment to moment. In a sense, time _is_ the change from low to high entropy - if you don’t have any entropy gradient, you can’t have any time either.
I've always rejected the idea that time is entropy change.
First, in many local processes entropy moves from high to low (e.g. life). Nobody says that time is moving backwards for living things. It only increases if you consider the system it is embedded in as well. So this idea that entropy is time is something that only applies to the entire universe?
It's true that we don't see eggs unbreaking, or broken coffee cups flying off the floor and reassembling. This increase in entropy seems to give an "arrow" of time, but to my mind this view (ironically) confuses cause with effect.
If you have any causal system (cause preceding effects) then you will always see this type of entropic increase, by simple statistics. There are just many, many more ways for things to be scrambled and high entropy than ordered and low entropy.
So yes, entropy does tend to increase over time, but that's an effect of being in a causal system, not the system itself. At least, that's my view.
Could you expand on your comment that life has entropy moving from high to low? Doesn't aging increase the entropy in our biological system? I have always thought that we are at our most structured in the early phases of conception with entropy increasing constantly as we age.
Life is essentially a process of creating order (lower entropy) building complex cells and so on using energy and matter from its environment.
Perfectly true that entropy gets us in the end as we age, as the system breaks down and cannot sustain itself any longer. Although if we could fix those systems, there's no reason in principle we couldn't halt aging entirely.
I took it as capital-L Life is moving from high to low. As evolution continues Life seems to evolve ever higher -> lower/more-ordered organisms (as more complex organisms depend on the systems created by simpler organisms prior to themselves).
I am slightly blending the concept of entropy and complexity. But "ordered complexity" is how I imagine it.
I don’t think entropy ever moves from high to low overall, it only ever distills some local low out of an higher entropy area, and in doing so, the overall entropy increases.
It works a bit like air conditioning: yeah, you can make one room cold, but only by making more heat outside the room. The overall temperature of the system increases.
This sounds sort of like the "if a tree falls in a forest and no one hears it, did it make a sound".
if time passes and there's no observable difference, did it pass? I guess it makes no meaningful difference, but it's not really answering the underlying question of if some variable is advancing or not.
If nobody logs in to a multiplayer game, does the game world still exist?
Sure there are files sitting on a server somewhere waiting to be read when the first user logs in, there may even be a physics engine polling abstract data structures for updates, but the game world doesn't render without players present with their computers bringing all this data into a coherent structure.
Also, for an extra existential kick, realize that it renders /independently/ in the GPU/CPU/RAM of each player's computer.
I remember the book "Now - Physics of Time" by Richard Muller (a Berkley physics professor) touching on the subject of entropy linked to time, but I never got to finish the book and sadly I can't provide more insight.
And potentially leads to things like Boltzmann Brains, given enough time! Quantum fluctuations can still create wildly improbable things, even if only briefly.
If everything is massless, everything travels at the speed of light, and nothing experiences any time (photons travel null geodesics with zero spacetime interval).
This is required to make Penrose's end state Conformal i.e. scale invariant, so that it can arbitrarily Cycle to a small scale to make a new Bing Bang Cosmology (CCC).
Neutron decay is one of those things that I forgot between college physics classes and today and it was sort of surprising to rediscover it.
We also know that electrons eventually decay but it's something like 10^26 years, which is long enough to say that probably not many electrons in the solar system have decayed since the universe was born but the universe is really stupidly big, so it absolute numbers that could still be a lot of dead electrons. Maybe a solar system's worth.
Surprisingly there is no wikipedia page for this. Just rando articles.
Electrons do not decay, because there is nothing they could decay into. You need a lighter particle of the same charge due to charge conservation, and there is none.
About ten years ago a research team concluded that electrons last for at least 10^28 years. Which is just a lower bound, and did not establish an upper. Rereading it now, it does seem that proving they decay is an attempt at a new branch of physics. So they might decay or they might not.
Can you link that paper? Or name at least one of the authors? Not to mention that checking for a lower bound means nothing for a potential upper bound.
It's ridiculous to cite an unnamed paper while being unable to procure a single source on the internet and then proclaim it's equally likely that they might or might not decay. With everything we know about physics there is absolutely no way imaginable that they might decay.
Well... black holes don't evaporate into hydrogen, but into light and various light particles. The hydrogen left over at the heat death will necessarily be too diffuse due to the expansion of the universe. It can't light up again like that. Perhaps the computer in The Last Question was hallucinating at the end.
A) We don’t know if all derivatives are >= 0. e.g. if the jerk rate is < 0, then you’d expect contraction eventually. Similarly, if the derivative of the jerk rate is < 0 & so on. So even accelerating expansion could eventually lead to contraction.
B) We don’t have a lot of very highly compelling evidence that the universe is actually accelerating (at least nowhere like we do for the Big Bang). For example, alternate models have proposed that our apparent perception of the expansion is simply as a result of the effect of non-uniform gravity throughout the universe & that the vaccuum of space between galaxies has even less time dilation and that’s what make it look like things are expanding.
In other words, I’d put the model of a permanently expanding universe as less likely to actually match reality.
The Big Bang happened at the "north pole" of spacetime. Eventually all matter and energy will reach the "south pole" and recombine. The Big Crunch theory will never die!
The big bang happened at the center of the universe and every point of space is the center of the universe at all times. You could argue that the center of spacetime is definitionally the Big Bang since that’s when time is believed to have started to exist in the first place but we don’t have a good grasp of how to define the center of a 4D physical structure where one dimension is time which doesn’t seem to really act like the other dimensions.
Maybe we should siphon off hydrogen and helium from the Sun for storage elsewhere in the Solar System to reduce the burn rate to prolong the usable lifetime of its fuel? And build a Dyson sphere. ;D
You've been watching too many bleak, post-apocalyptic, fatalist celebrations of losers. I'm talking about adding millions to billions of years of extra good life in the giant dome with plenty of temperature difference to keep entropy down for longer.
