Time flows in One Direction

[mistermack]

Many concepts in physics only require time to be plugged into a formula as a duration, a perfectly scalar number with no direction implied.

Indeed. Running the hypothetical clock backwards led to the postulates which ultimately discredited the steady state universe theory, which was quite a big deal at the time.

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

The crucial word there is hypothetical.
The way I look at it is that time reversing is actually possible, but ALMOST infinitely unlikely.
If you imagine the size of the Universe, and the number of objects and particles in it, all moving about at random, then time is a record of all of the incidents that happen.
Once things become bigger than single particle size, it's pretty much impossible for time to go backwards.
A single gas particle might possibly go backwards, exactly as it had moved forwards, even though it's movement is random. Sometime or other, that might happen.
But in a flask full of billions of particles, what are the chances of ALL of them, by sheer chance, reversing in the exact same way that they just moved? It's still possible, but the odds are absolutely astronomic.

Then, if you expand that unlikelihood from a flask to a gas cloud bigger than the Milky Way, then you get an idea of how unlikely time is to reverse, even though it's still theoretically possible.

Another way of looking at it is to imagine a domino standing on end, that falls over.
It gets pulled down by gravity, hits the surface that it was standing on, and it's energy of falling gets dissipated as vibrations in the surface, plus noise vibrations in the air, etc etc.
It's actually theoretically possible that all of that energy could reverse the way it came, particle on particle, and the domino could be pushed back upright by the same energy that pulled it down.
But the odds are so incredibly huge against that happening, that nobody will ever see it.
Each vibration has billions of options, at every micro-second. And only one will lead to time reversal.
And that applies to every particle involved in the incident.

[pErvinalia]

That only applies if you grant that the flow of time is a real phenomenon. If you view macro events in time as just individual points in space-time that are determined by the laws of physics, then there's no reason to think they can't be accessed in any order.

[mistermack]

That only applies if you grant that the flow of time is a real phenomenon. If you view macro events in time as just individual points in space-time that are determined by the laws of physics, then there's no reason to think they can't be accessed in any order.

If every event that ever happened exists, like a frame in a film, then that could happen.
But, as you are just a pinpoint, in one of those frames, there is no way for you to jump out of it, and to jump into another frame. And if you could, and you did, you would have altered the entire film.

The reason is that each frame is the RESULT of the previous one. Change one frame, and you change the entire film after that frame, in a random way. So if you went back and killed Adolf Hitler, you might have never been born.

[pErvinalia]

But your kind of mixing up the concepts of free will and determinism. If the universe is deterministic, then you wouldn't actually have the free will to kill Hitler outside of that determinism. Your actions have already been written since the very first action. The real question then becomes: is the (macro) universe deterministic? So far it seems it is, but there are hypotheses of how quantum effects can "leak" into our cosmic inflation. Also, I don't think General Relativity is known to cover behind the event horizon of black holes. Some other sort of physics might be going on there..

[mistermack]

But your kind of mixing up the concepts of free will and determinism. If the universe is deterministic, then you wouldn't actually have the free will to kill Hitler outside of that determinism. Your actions have already been written since the very first action. The real question then becomes: is the (macro) universe deterministic? So far it seems it is, but there are hypotheses of how quantum effects can "leak" into our cosmic inflation. Also, I don't think General Relativity is known to cover behind the event horizon of black holes. Some other sort of physics might be going on there..

I don't think it's much to do with free will. If the Universe is as you suggested, that every event actually exists, in space and time, then you can have as much will as you like, but there is no means of actually jumping to a different time frame.
If you picture the analogy of a film, consisting of frames, then time is the passing of those frames.
You couldn't travel IN time, from one frame to another, backwards, nor could you travel forwards in time, other than the way that we do now, by living in each frame as it happens.

To do that, you would have to access other dimensions. There would have to be another reality, that you could somehow enter, with another version of time, that would allow you to move from one frame to another "outside" of time.

However, as we observe that one event causes another and causality has never been observed to not happen, then the pre-determined universe, where the future and past actually exist, in some version of space and time, don't seem very likely.
It could come about, I suppose, by a process where everything has already happened, and been recorded in space and time, and we are just re-running it. But for that to be the case, it would have had to happen first, just like it appears to be happening now. So there would be no essential difference.

[pErvinalia]

I'm not talking about time travel. There's no necessity for anyone to be able to just "visit" some point and time in space, for the concept to be valid. Causality is an interesting thing. Hume had a crack at debunking it. Dunno how seriously his philosophising on the subject is taken these days..

[mistermack]

What we can observe, and have worked out in physics, is that each event influences the next.
And every particle in the universe is linked by gravity to every other.

For example, an atom in your finger, is linked to every particle in the Sun by gravity.
With a time delay of about 8 minutes. One hydrogen atom in the Sun won't have much effect on your finger, but it is linked. And each link has a minute effect.

It's the sum of all of those links, which keeps the Earth circling round the Sun. So causality is vital to everything. And it's phenomenally complicated, if every massive particle in the Universe is connected to every other.
It's that sort of amount of incidents that would have to run backwards, for time to reverse. Not just collisions of particles against particles, but the gravitational link of every particle in the Universe, to every other.

[Hermit]

The problem with causation is how you can differentiate it from mere correlation. It has a name: The problem of induction. Hume was not the first, and certainly not the only one to point it out, though he is probably the most famous one. Sextus Empiricus wrote about it 15 centuries before Hume and Bertand Russell a couple of centuries after.

Induction is probably the main reason for our survival. Or at least without assuming causality we would not be where we are today. Without it we'd have no reason to believe that just because we succeeded in creating a fire by twirling a stick against a piece of wood once we'd get the same result the next time. Our pattern recognition ability (event B follows event A) is central to our evolution, and that of other animals. It is a simple concept: Observe events -> recognise repeated sequences among them -> induce a general law from the individual observations that share a common feature or process. It just works. Until it doesn't. For instance: Every swan we have ever clapped eyes on is white. The next swan we'll see will be white. [img=http://www.wildlifeextra.com/resources/ ... O@body.jpg]Oops[/img] So, how can we tell if we are looking at causality rather than mere correlation? Is there a criterion we could use to tell one from the other? Hume says "no", and I have not seen a convincing argument to the contrary yet.

My favourite story of induction of causality gone wrong is Russel's turkey. The turkey was fed every morning at nine. This was obviously not your average turkey. It was smart. It tried to figure out what caused it to be fed. It could not be the rain, for it was fed on sunny days as well. So rain was eliminated as the cause. It could not be the appearance of the man, because sometimes he did not appear, and a woman or a child appeared with the food instead. It could not be the heat on the day because it was fed in winter as well. And so on. Eventually, there remained only one constant: Without fail, as soon as the church bell had struck nine, food was given to it. Ergo, the church bell striking nine causes food being supplied.

One morning the church bell did its thing, someone came out to the cage, but instead of bringing food that person brought along a hatchet and chopped the turkey's head off. Happy Thanksgiving Day.

[JimC]

[Sean Hayden]

[mistermack]

The problem with causation is how you can differentiate it from mere correlation. It has a name: The problem of induction.

That's not a problem of causation. It's a problem of our understanding of causation. It's a different thing.
Just like philosophy is a different thing from physics.

It's like watching a helium balloon rising, and saying that there's a problem with gravity.
We might get it wrong, but gravity keeps working anyway.

[Hermit]

The problem with causation is how you can differentiate it from mere correlation. It has a name: The problem of induction.

That's not a problem of causation. It's a problem of our understanding of causation. It's a different thing.
Just like philosophy is a different thing from physics.

It's like watching a helium balloon rising, and saying that there's a problem with gravity.
We might get it wrong, but gravity keeps working anyway.

You have NFI what you're talking about.

[mistermack]

The problem with causation is how you can differentiate it from mere correlation. It has a name: The problem of induction.

That's not a problem of causation. It's a problem of our understanding of causation. It's a different thing.
Just like philosophy is a different thing from physics.

It's like watching a helium balloon rising, and saying that there's a problem with gravity.
We might get it wrong, but gravity keeps working anyway.

You have NFI what you're talking about.

That's the typical dumb-cunt response.

I'm amazed !!

Does a dumb-cunt response mean that the responder is a dumb cunt?
No, that conclusion might be natural to make, but it could be wrong.

[Brian Peacock]

...
And every particle in the universe is linked by gravity to every other.

For example, an atom in your finger, is linked to every particle in the Sun by gravity.
With a time delay of about 8 minutes. One hydrogen atom in the Sun won't have much effect on your finger, but it is linked. And each link has a minute effect...

What is the nature of this link called gravity?

[pErvinalia]

It's distortion of space-time.