So again: Why aren't all processes moving exactly opposite to their present direction? — EugeneW

Well, I will offer the most obvious and probably the most boring and non-progressive point in regards to the fluidity of the thread, 'Because it can't do that.' The Universe has no mechanism currently identified in physics, within which such action is demonstrable or possible. Heat and light radiate outwards,
'Them's da rools!'

Heat and light radiate outwards — universeness

Yes. But... Why they don't radiate inwards? Why isn't the beginning of time situated at the end? I think I'm drifting off from reality a bit now Stephen, but still... I asked this on a physics site, but the question was closed for being a duplicate of a question about the Loschmidt paradox I didn't agree though.

We all know it. Time is unidirectional. — EugeneW

We actually don't. The very start of the post rules out C theory, which rejects temporal directionality. C theorists only agree with temporal order, and would tell you that the timelines (1) ABC and (2) CBA are identical in virtue of the fact that the betweenness relations (C-properties) of these timelines are sortally equivalent. Meanwhile, both the A-theorist and B-theorist would find there to be distinction between (1) and (2) through either A-properties or B-properties.

But neither of these are a default position that lacks a burden of proof, so the A and B theorist must be the ones motivating the A-properties or B-properties. And I'm not so sure any of the strategies used are adequate. Phenomenal or intuitive arguments used in an A-theoretic fashion can be perfectly rationalized by indexical accounts, and the issue I perceive is that the accounts B theorists use to undermine A theory are not sufficient (but necessary!) for B theory. In other words, undermining temporal dynamicity on its own is necessary for both B theory and C theory, but only sufficient for C theory.

Because of this, while I may not strongly commit to a C theoretic understanding of time I think it is a highly plausible one and one of our best explanations. So I would warn from presupposing it away in a discussion about time, and I'd definitely invite its insight.

For further reading, I recommend Matt Farr's paper On the adirectionality of time. It is excellent.

Yes. But... Why they don't radiate inwards? Why isn't the beginning of time situated at the end? I think I'm drifting off from reality a bit now Stephen, but still... I asked this on a physics site, but the question was closed for being a duplicate of a question about the Loschmidt paradox I didn't agree though — EugeneW

I had never heard of the 'Loschmidt paradox,' where do you come across this stuff?
I had a quick read using your link, its interesting that it was provoked by Boltzmann musings.
I wouldn't worry too much about 'drifting off from reality a bit.' If you can achieve such trips for free and they are good trips then you are a lucky sod. If they are not good trips then you need to work hard at manipulating them better. Take control of them more often and dictate their dierction. I do quite well with my attempts at 'lucid dreaming.'

There are many systems that 'oscillate' or 'reverse,' water-ice-water, solid-liquid-gas-liquid-solid, components available in the Universe - assembly-human-alive-dies-dissassembly-components available in the universe......
But heat radiate outwards - heat radiates inwards, just doesn't happen.
Can your personal conception of the attributes of God be reversed?

Forgot one of the most important ones. mass-energy-mass-energy
<-------------time

Can your personal conception of the attributes of God be reversed? — universeness

Imagine, just for the sake of argument, gods brought about the universe with all particles having initial conditions, momenta, energies, and positions, in an expanding space. Why didn't he arrange it to begin at infinity, ending at the singularity?

But how can space be infinite if it is expanding, It has no need to expand if it is already infinite.
If God arranged it, then why is it expanding?

Why didn't he arrange it to begin at infinity, ending at the singularity? — EugeneW

Before cosmologists discovered that the expansion rate was accelerating, the big crunch was a front runner. I think however you are positing something akin to the fable of Merlin, who knew the future because his existence was in time-reversal from 'future to present.' I think that's why they presented him as a magical 'wizard' in the story. Would you like to live a reversed life from death point to fetus?

The classical approach is that the inflation happens in an infinite space, i.e, eternal inflation. In isolated pockets of this infinite eternally inflating space, inflation is halted and arrested. That pocket is our universe. Then in time, space starts inflating again and becomes one again with the inflating space it's embedded in.

There are problems with this view. How can space expand? What happens to the photons that emerged in all isolated pockets (universes)?

The infinite space I visualise is the (spatially) 4D bulk space our finite 3D space expands into. Why wasn't it set in motion from the other side of time (at infinity)? So an infinite space collapsing to a singularity and all particle motions, wavefunction and space metric evolutions, etc. Reversed. So all photons of the Hawking radiation that will be all that's left in our forward running universe
would reverse their momenta, meet at the black hole horizons, form black holes that eject matter (so they become white holes), and a universe crushing in towards the singularity that would be the end, instead of the begin as we perceive it.

But this is only for those who think that more than one universe is correct. Others like myself prefer to go with the idea that inflation/expansion is not 'into' anything as it is everything. I know issues like fine-tuning speak against this view but I for one await better or more convincing evidence for anything outside of this single Universe. Your position is every bit as valid as mine and you can add a lot more details in support of your viewpoint than I can for mine but overall, the search for the truth continues.

Others like myself prefer to go with the idea that inflation/expansion is not 'into' anything as it is everything — universeness

This idea has a bigger problem than fine-tuning (which I think is not a fundamental issue in context of a broader theory of elementary particles), which is how the metric of space can change over time. It's easy enough to write down a time dependent metric but the question how space grows is not answered by that. So why isn't everything moving backwards? It's a possibility and if it happened you couldn't reverse it back in time (which would be forward in time). Why doesn't an inverse second law of thermodynamics hold which means an entropy always decreasing...

I don't think I can offer you any more than I have already on this topic. I will leave it to those members who offer more detail than I can.
As always, thanks for the exchange of views EugeneW! :grin:

Why isn't the beginning of time situated at the end? — EugeneW

That is not a good question. Maybe it is. Maybe time IS going backwards, EugeneW; we just don't know it, for obvious reasons.

So using the second law of thermodynamics to explain why this won't happen is of no use. — EugeneW

You can't write off the second law in so cavalier a fashion, not legitimately at least. Entropy just reflects probability. Higher entropy is just more likely than lower entropy because there are so many more high entropy events than low entropy ones. There is no physical reason all the air in a room could not gather all at once into one corner. It doesn't happen because there are just so many more ways the atoms could be distributed evenly through the room. Time moves the direction it does because there is just one way an egg broken on the floor could regather into an egg but there are a billion gazillion trumpillion ways it could just sit there in a yellow puddle.

There are other ways of looking at it. Wikipedia has a good writeup of the Arrow of Time.

I understand the arrow of time, but I don't understand why the arrow doesn't point from future to past.

Time moves the direction it does because there is just one way an egg broken on the floor could regather into an egg but there are a billion gazillion trumpillion ways it could just sit there in a yellow puddle. — T Clark

But why doesn't it and all around it move backwards. Why isn't the law that entropy decreases?

I understand the arrow of time, but I don't understand why the arrow doesn't point from future to past. — EugeneW

But why doesn't it and all around it move backwards. Why isn't the law that entropy decreases? — EugeneW

For the same reason I'm more likely to be dealt a pair of twos than a royal straight flush. There's no reason time couldn't "flow backwards." It's just very, very, very, very....very, very, very....very unlikely.

But you could just as well argue the other way round. If entropy only decreased, it would be very unlikely for time to go forwards. If the initial state of the universe would lay in the very far future, at infinity maybe, the universe could have started from there with everything in opposite motion. I know a gas in a corner has a low probability of occurring spontaneously, but if the initial configuration is right then there is nothing that prevents time from going backwards. Its a complete mystery to me.

But you could just as well argue the other way round. If entropy only decreased, it would be very unlikely for time to go forwards. — EugeneW

I've given it my best shot, but I'll take one more swing. You're making this much more complicated than it really is. Entropy is the simplest thing in the world. Entropy isn't a force that directs events in a particular direction. It is just an expression of the fact that some events are more likely than others. Events that we identify as being in what we call the future are just more likely than those in what we call the past. Entropy is just another word for probability.

That's all I've got. Good luck.

As I already wrote, it's not the second law that I don't understand, or the arrow going forwards. I just ask why it doesn't go backwards. The fact that the forward direction has a higher probability isn't an explanation. Probabilities are no explanation. You simply say the second law of thermodynamics holds because it holds. That's circular. Saying time goes forward because it goes forward. Probabilities have nothing to do with this. But thanks anyway!

A good question. First, we have to understand what time is. Time is a concept. Imagine yourself at this moment. You are a combination of matter and energy at that snapshot with particular forces applying on them. One second later, you are the result of those forces. That is all time is. You have memory of the previous second, but the previous "second" isn't a real tangible time force unit, but simply an realization that the matter and force combination of now, is not what it was a second ago.

There is nothing mechanistically from us recreating the first snapshot after one second. If something had the power to reorganize the matter and forces of the universe to what it was one second prior, then we would be "back in time". But really, we wouldn't. Because the reorganization happened at the second second if we're an outside observer.

A -> B -> A. From the inside observer, time travelled backwards, and none were aware of it. Did A still come before B, which then came before A again? Yes, but that is only because we are recording state changes. We cannot erase the state change. We can't reverse everything so that the state change was never made. Time is just that, states of change compared to a memory of a prior state.

But think about internally once again. If it is the case that time is merely the state of change from one moment to the next, then if reality reorganized itself to A -> B -> A, the second A would never be aware that B ever happened. They would be sitting there asking themselves, "Why does time always move forward?" or, "Why do the states of change never go back to the way they were prior?"

Basically, if time did move backwards, you would never know it, because backwards time is merely a change to a previous state. And in a change to a previous state, you saw time as moving forward. It is absolutely impossible to be aware of the state of the universe being reorganized to a previous state, unless you are an outside observer. As we are not outside observers of time, we have our answer. Time always moves forward, because it is impossible for us to be aware if a state returned to a previous set up.

Why isn't there a REWIND button? We can do it with TV remotes for movies, but it sorta looks funny if you know what I mean. That is to say, we can quite easily figure out time is running backwards.

That's at the macroscopic scale.

At the atomic/microscopic scale, there really is no way of knowing whether time's going forwards/backwards. Try this experiment: put a bunch of steel ball bearings (representing particles) in a box, shake the box and record a video of the balls moving randomly in all directions. Now, call two friends to your house. Play the video you recorded normally (forwards) to one friend and play the video in reverse (backwards) to the other friend. Ask both of them this question: Was the video played forwards/backwards? They won't be able to answer this question. Hmmmmm. :chin:

How do we explain this? Anyone...

Was the video played forwards/backwards? They won't be able to answer this question. Hmmmmm. :chin: — Agent Smith

Well, you have to show them more than that piece. What they don't see is the balls causing sounds an electromagnetic radiation, and heat. In fact, you will always be able to see if a process goes forward or backward. The question is though why not everything runs in reverse (and not a tiny patch, maybe artificially arranged. Though it's the question if a small patch can be said to go backwards. All or nothing.

Encopresis!

I see your point. Thanks for the contribution. I'm not sure if we'd not notice it. Forces stay the same if all particles and processes reverse direction. All particles and the spacetime they are in, as well as the developing wavefunctions could have started in a very (infinite) far future with all motions reversed. It would be strange though to first hear the thunder or see the lightning, after which the light and sound converges to the blitz.

Encopresis! — Agent Smith

Fecal incontinence? :grin:
It would turn to food. The apple would turn whole in my mouth and jump back in the tree. Counterintuitive but possible. If the futùre was the reversed begin it would happen.

:smile: Good day. I just learned that word, about 2 hours ago (technical term in medicine it is). You got it right! Kudos.

I managed to make some progress into the matter. Ball bearings are symmetrical (reflection + rotational). If we were all symmetrical spheres, it would be impossible to tell whether time is running forwards/backwards i.e. time would lack a direction. :chin:

I'm not sure if we'd not notice it. Forces stay the same if all particles and processes reverse direction. — EugeneW

Correct. If we are part of time that is being changed to a prior state, it is impossible to notice. The only way we would notice is if we continued forward, while everything else continued backwards.

we were all symmetrical spheres, it would be impossible to tell whether time is running forwards/backwards i.e. time would lack a direction — Agent Smith

Good day, my beloved! Kudos! Wouldn't we notice time if we are symmetrical spheres? Imagine a transparent box filled with bouncing solid metal spheres in interstellar spaces. We videotap the scene with a camera that shows every physical process in and around the box. Then we show the tap in two directions, forward and reverse. Is there a difference? Could it be we tapped a time-reversed scene in the first place? If we reverse the tap, shouldn't we include what happened before and after? Can parts of reality start running backwards in time? If time ran backwards could it start running forwards? ‍♀️

Probabilities have nothing to do with this. — EugeneW

You're wrong. Please don't go spreading your ignorance.