If so, does that mean that the big bang could actually be the end of the universe and we're just experiencing time in "reverse" toward an initial starting state that we perceive as the future?
In very informal terms, anywhere where there is very low entropy (higher order), any direction away from that will likely (to the point of certainty) be in a direction of higher entropy (lower order).
For instance, if you have a jar of red & blue marble, with high order (such as perfect alternating layers of red vs blue marbles) then any disturbances (such as shaking the jar, reaching in and moving a handful, …) will almost certainly reduce order.
And no practical amount of shaking the jar will ever return the marbles to a high order state again.
Even though any close up video of the marbles being jostled will reveal the same physical properties and behavior for the marbles, whether played forward or backward.
So at the individual marble level, laws are symmetric.
But at the jar of marbles level, one direction of time looks very different than the other.
We, and the particles that make us, and our environment, are the marbles whose configuration is more disordered the further in time we get from the Big Bang.
So we perceive the time direction away from the Big Bang as the future, toward the Big Bang as the past.
And the statistical “force” of increasing entropy provides the useful energy we use to survive, learn, create useful islands of order, in the greater sea of increasing disorder.
This can't be true. Take the case where there's only 2 marbles, it's likely that at some point that shaking them will return them to the original state. For higher numbers of marbles the probability becomes lower and lower, but is never 0.
(0.00..0..1 = 0 just as 0.99 repeating equals 1)
This sounds like a rather bold statement to make, as long as we're already speaking so metaphysically.
[0] https://stats.stackexchange.com/questions/142730/px-x-0-when...
Again, I'm not a physicist, but I think it's telling that the validity of continuum mechanics [0] depends on a model and multiple assumptions. I have no trouble agreeing with your original statement, "with enough marbles, the discrete distribution behaves like a continuous distribution," when speaking mathematically, but mathematics by its nature is an idealized model of the world - I'm not willing to accept that it's objectively representative of physical reality. The discussion we're having here is one of metaphysics, so it feels a bit like the height of hubris to use mathematics as the tool for describing objective reality, because metaphysically, we cannot say that mathematics is anything other than a tool we've constructed for approximating the model of the world as we understand it. Considering the subject of this post is about retrocausality, we're already throwing out some pretty wild ideas, so I think it's a bit hubristic to dismiss them by citing a branch of mathematics that assumes the existence of countably infinite sets [1].
[0] https://en.wikipedia.org/wiki/Continuum_mechanics#Validity
[1] https://en.wikipedia.org/wiki/Constructivism_(philosophy_of_...
Hence the disclaimer. I just think this stuff is fascinating. If you're interested, this is the article that originally got me thinking about these ideas as they relate to the flow of time: "Does Time Really Flow? New Clues Come From a Century-Old Approach to Math" [0]. It's effectively an appeal to intuitionist mathematics and a rejection of constructivism, where - simplified - every particle since the big bang can be assigned some "number" that describes its position on its world line, with a precision that is finite, but always increasing - and it's this increase in precision from which emerges the "flow" of time. If you ctrl+f the article for "continuum," you'll see some better constructed arguments for what I'm trying to argue, e.g.:
> Moreover, the continuum can’t be cleanly divided into two parts consisting of all numbers less than ½ and all those greater than or equal to ½. “If you try to cut the continuum in half, this number x is going to stick to the knife, and it won’t be on the left or on the right,” said Posy. “The continuum is viscous; it’s sticky.”
The impression I'm left with is that the difference between constructivist vs. intuitionist mathematics (which rejects the law of the excluded middle) has some parallels to the difference between eternalism (there is a past, present and future) vs. presentism (there is only the present).
As a layman, I just can't help but notice the same patterns come up again and again when looking at unresolved problems between classical and quantum mechanics, namely those that lie at the boundary between the continuous and discrete. FWIW, I asked ChatGPT for some unresolved mathematical problems that might relate to this, and it came up with: The Continuum Hypothesis, The Axiom of Choice, and The Riemann Hypothesis, all of which it admitted are possibly impossible to prove because they're effectively unfalsifiable. (I also showed it this entire thread, and it agreed with your critique of my arguments, but also that every argument in the thread is unfalsifiable - and then it pointed me to the Boltzmann Brain paradox).
[0] https://www.quantamagazine.org/does-time-really-flow-new-clu...
Mathematics still apply.
[0] https://en.wikipedia.org/wiki/Zeno%27s_paradoxes#In_modern_m...
[1] https://en.wikipedia.org/wiki/Philosophy_of_space_and_time#D...
Even if the point probability is 0 or approaching zero very fast, some event occurs with probability 1.
The probability that life would evolve on a blue planet that its anthropomorphic inhabitants will come to call Gaia or Earth, has as a star Sol, in this corner of the Milky Way, in this particular local group and so on is zero even if we limit ourselves to just the observable universe.
At the same time the probability that life will exist at some planet at some solar system at some galaxy at some local group and so on, is practically 1.
That is to say, depending on how you categorise and count said marbles, the reordering may occur.
While any individual marble will not be at its place with P=1. You can still end up in a situation where the marbles are ordered in layers.
The whole thing regarding entropy is concerned with a closed system. You can very much exchange energy to decrease entropy, but said exchange is a) leaky, and b) implies that the system is not isolated.
This was then used again when mentioning earth to argue that depending on the definition of "order" here:
> And no practical amount of shaking the jar will ever return the marbles to a high order state again.
It is entirely possible to reach a state of higher order if you don't require that individual marbles don't hold the same arrangement relative to adjacent marbles, meaning that any permutation of marbles with identical color is acceptable.
This happens because the event you are asking for is a very large subset.
This whole thread is silly, The 2nd law is about probabilities which are asymptotically 0, so small in practice that we could never do experiments to frequentist probability empirically, using "jars of marbles" with more than 100 marbles", let alone trillions of trillions of particles.
I realize that programmers are not always good scientists. Yet some claims are absurd in ways that I now believe this phenomenon necessitates rigorous study.
IIUC my professor right the probability is non zero but is practically impossible for a large number of incompressible spheres.
Exactly. It doesn’t take a very large jar to make a return to an original state practically impossible. But even for two marbles, shaking them to return them to their original locations costs a fair amount of organized energy.
And that is organized chemical energy in your muscles, which you are dissipating as disorganized heat energy due to your efforts, increasing the total disorganization.
And the marbles are microscopically wearing down, shedding compounds. The jar is also wearing down. Both becoming less organized.
So even with two marbles, overall entropy continues increasing.
We can locally reverse entropy, only at the cost of actually increasing entropy in total.
- Organizing your day takes effort and uses up useful organized energy.
- Computation uses up useful organized energy.
- Your cells, maintaining their metabolism, uses up useful organized energy.
No matter what we do, entropy still increases.
Everything we do takes advantage of the higher to lower entropy gradient.
We get relatively organized photons from the sun, a percentage get stored in wood of trees, so we can burn that for heat which can drive an engine or generate electricity, with the end result is doing some useful work.
And we don’t actually lose any energy, due to conservation of energy.
But we have now lost USABLE energy, because all our captured energy is now heat diffusely spreading out from our engine into the atmosphere where it becomes uncontrolled DISORGANIZED and therefore no longer usable.
So clear causes tend to occur in past of clear effects.
For large objects.
But again, if you watch videos of individual marbles bouncing around, forward or backward, you see just as clear chains of cause and effect in either direction.
Marbles in a jar are not arranged in a neat spacial grid, but in all kinds of configurations.
The chance of recovering any near perfect starting symmetry, depending on the size of a jar, might take decades or millions, or more years.
In the meantime, all that energy being used to shake the jar is generating huge amounts of heat entropy.
It is possible that that the original expansion, inflation, and even dark energy are also driven by thermodynamics, but we just don’t know that.
Im not saying you're wrong, but then there's Poincare's recurrence theorem. Entropy is funky. (Certainly not practical amounts anyway)
– The laws of physics are essentially time-symmetric, and they have no concept of causation or of a preferred direction of time. In principle, the future causes the past as much or as little as the past causes the future. Physics effectively only says they have to be consistent with each other, as related by the laws of physics.
– The apparent directionality of time that we perceive is suspected to be tied to the entropy gradient we are on. See the “past hypothesis” for example [0].
> Does this essentially mean that all states in time already exist and our consciousness is just traversing this 4D space in one direction on the time axis?
– I would say that all moments in time are equally real, including our consciousness at any given moment. There is no actual flow or “travelling”. The flow we perceive is merely an illusion caused by the fact that we only remember the past and not the future (which again may just be a consequence of the entropy gradient we are on). This is known as the “block universe”, or as “eternalism” [1]. The opposing view that only the current moment is real, and that the future differs from the past in its “realness”, is known as “presentism”.
– Note that any notion of “travelling” through time implies that you can draw a 2D diagram of where in time you are at each point in time, or which point in time is “real” at which point in time (in the sense that a moment in time isn’t real until time reaches that moment, but after that it is real and cannot be made unreal again), thus implying two dimensions of time. That doesn’t make any sense, and thus my personal conclusion is that the “presentism” view is nonsensical.
[0] https://en.wikipedia.org/wiki/Past_hypothesis
[1] https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time...
https://i.pinimg.com/originals/27/d7/8c/27d78c9c3ee93c13eda4...
Holographic universe is that the physics and information in a 3+1D space time could be encoded into a 2+1D universe (with it's own physics).
https://www.discovermagazine.com/the-sciences/from-here-to-e...
https://en.wikipedia.org/wiki/Tralfamadore#Slaughterhouse-Fi...
It's convenient to model our movement through space-time as occurring at the speed of light. Thus, the faster we move in space, the slower we move in time all the while the length of our space-time velocity vector is invariably c. We can then imagine 1 second of time being interchangeable with 299,792,458m.
https://en.wikipedia.org/wiki/The_Quincunx_of_Time
Also, the concept of causality itself is a kind of underlying theme in Hannu Rajaniemi's "The Causal Angel" (2014) (3rd of a series).
I often find them insightful, especially if I am reviewing them again years later.