How flexible is the principle of causality?

[Mudhammam]

Not to split hairs here, and I don't want to act smarter than Wikipedia, but that sounds not like a well defined principle of causality at all. If you have two point masses approach each other, they repulse and fly on their way, what is then supposed to have caused what?

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I apologize if I sound naive (because I am), but wouldn't it have something to do with their gravitational pull which in some instances is known to have the opposite effect (anti-gravity)? Okay so what are the implications you're trying to get me to see?

So cue say 6 Billion years ago, again, with the same initial quantum state copenhagenously speaking - how different could the world have turned out due to quantum uncertainty? Is that your question?

Yeah.

[Alex K]

Not to split hairs here, and I don't want to act smarter than Wikipedia, but that sounds not like a well defined principle of causality at all. If you have two point masses approach each other, they repulse and fly on their way, what is then supposed to have caused what?

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I apologize if I sound naive (because I am), but wouldn't it have something to do with their gravitational pull which in some instances is known to have the opposite effect (anti-gravity)? Okay so what are the implications you're trying to show me?

I don't want to be so presumptuous as to try and show you the way, since I'm not the high priest of physics, but here's what I think (mainly gathered from what I've learned in classes):

It is well known that in simple Newtonian systems with a few masses, there is no discernible arrow of time. The extreme case is the two body problem, where you have two masses going round each other forever, and if you reverse the clock, it will behave exactly the same, and according to the same laws of physics (the laws of Newtonian physics are the same upon time reversal). Since there is no clear distinction between past and future, I would argue that causality is not really present.

Now if you go to a three body system, it can happen that you set it up as a little complicated three body "solar system" and let it run, and it will run and run, and suddenly after some time, one of the masses will be catapulted out of the system never to return again. Technically, the exact same thing can happen in reverse, with a mass coming flying in from infinity to integrate itself perfectly into a stable three body system. However, this is very unlikely and requires fine tuning of the initial condition. As an observer, you start getting a handle how to at least make a good guess in which direction the movie you watch is rolling, but not 100% certain.

I think it is here that we start to glimpse the effects of entropy, and what causality means: going from less likely to more likely configurations. Let's go the extreme case where you have 1000 gas particles, and you put them in the lower half of a flask. If you now let time run, they will spread throughout the vessel, never in billions of years to return to this state where they all are trapped in the lower half. It is now uniquely possible to tell in which direction time runs, but not because there is an arrow of time built into fundamental physics. It is only because you have as a boundary condition in time a unlikely configuration, which you can therefore associate with past.

So cue say 6 Billion years ago, again, with the same initial quantum state copenhagenously speaking - how different could the world have turned out due to quantum uncertainty? Is that your question?

Yeah.

There would probably be a star in the vicinity here because there was a lot of material nearby, maybe a double star sytem where jupiter has gathered enough mass to ignite, and some planets which bear no resemblance to the ones we know and love. Would there be life? maybe, maybe not.

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p.s.
Incidentally, we today know that the laws of fundamental physics are probably not completely invariant under reversal of time, because of the observation of CP-Violation and the CPT-Theorem. The latter tells you that under reasonable assumptions, the laws of nature remain the same if you reverse the flow of time, left and right, and the sign of all charges simultaneously. Since we know that the laws of nature are subtly different if you reverse all charges and left and right, it is probable that the same happens for the reversal of the direction of time T.

While this may have played an important role to define what is past and future in our world, these subtle effects are not what define the arrow of time in each moment. This is really the statistical mess I describe above.

[bennyboy]

I suppose this level of randomness would be something on the quantum level but sure, we could never really measure it.

Well, how do you measure temporal randomness? You can't. At best, you can make a very dangerous assumption: any particle at any time cannot have certain predictions made about it, or certain combinations of measurements made of it.

Therefore, if you imagine yourself traveling back in time before some past event, you can imagine the unpredictability of that event (even though it's set in stone now, having already passed). However, it's really non sequitur to then say that things could have turned out differently: there's no way, ever, under any circumstances, that we will get to replay a measurement of the same particle at the same space AND TIME, and see if it would have "rolled" a different outcome.

[Mudhammam]

Fascinating stuff, Alex and bennyboy. I'll have to let that mull around in my head for awhile. Bennyboy, you said:

However, it's really non sequitur to then say that things could have turned out differently: there's no way, ever, under any circumstances, that we will get to replay a measurement of the same particle at the same space AND TIME, and see if it would have "rolled" a different outcome.

I agree in some sense...I mean this is undeniably true but... two things: isn't it kind of a cop out? And does that mean you're a fatalist? I mean, say for example the person who wins the lottery--only one winner is actually possible--but can you really say that only that person could have actually won? Does everything happen necessarily? That would seem to be the implication.

[bennyboy]

Fascinating stuff, Alex and bennyboy. I'll have to let that mull around in my head for awhile. Bennyboy, you said:

However, it's really non sequitur to then say that things could have turned out differently: there's no way, ever, under any circumstances, that we will get to replay a measurement of the same particle at the same space AND TIME, and see if it would have "rolled" a different outcome.

I agree in some sense...I mean this is undeniably true but... two things: isn't it kind of a cop out?

I'm an agnostic. Is that a cop out? I don't know-- personally, I think not knowing is the most legitimate position to take when there's something intrinsic to the human experience that prevents knowing.

And does that mean you're a fatalist?

No. I'm even worse than a fatalist. I'm an agnostic with leanings toward substance dualism, or to transcendent emergence. (by which I mean that once a sentient agent "ascends" out of the pseudo-random soup of particles in the universe, it can function freely DESPITE being completely rooted in deterministic processes. Crazy stuff, right? But the universe is no stranger to those kinds of paradoxes IMO.

I mean, say for example the person who wins the lottery--only one winner is actually possible--but can you really say that only that person could have actually won? Does everything happen necessarily? That would seem to be the implication.

Yes it does mean that. Given only one stream of time that we are aware of, and a completed event in that stream, then the simplest explanation is that things are exactly the way they were going to be.

[tor]

I as a physicist clarify that uncertainty principle doesn't give you proof of true randomness. All it does is show that we can't know the future 100% certain. But not knowing the outcome doesn't prove it's random.

I'm an agnostic with leanings toward substance dualism, or to transcendent emergence. (by which I mean that once a sentient agent "ascends" out of the pseudo-random soup of particles in the universe, it can function freely DESPITE being completely rooted in deterministic processes. Crazy stuff, right?

Not crazy just stupid and false.

[Alex K]

I as a physicist clarify that uncertainty principle doesn't give you proof of true randomness.

Can you just for fun clarify what you mean by true randomness? I as a physicist suspect that it is impossible to prove such a thing to begin with. You can show that there are no measurable correlations. When you do that, you will find some, but they should get weaker as you keep measuring. But proving true randomness, even in a scientific sense of proving... what would that entail in principle?

[bennyboy]

I as a physicist clarify that uncertainty principle doesn't give you proof of true randomness. All it does is show that we can't know the future 100% certain. But not knowing the outcome doesn't prove it's random.

Wow, it's almost like I just said that a couple posts ago. I as a guy with a computer clarify that the navigation buttons on this site work fine.

I'm an agnostic with leanings toward substance dualism, or to transcendent emergence. (by which I mean that once a sentient agent "ascends" out of the pseudo-random soup of particles in the universe, it can function freely DESPITE being completely rooted in deterministic processes. Crazy stuff, right?

Not crazy just stupid and false.

Pretty dismissive for a guy who's just parroted what I said yesterday. I'd be offended, but since I don't know if you could have turned out otherwise, I do not know whether it's right to blame you for being a prick.

[tor]

I as a physicist clarify that uncertainty principle doesn't give you proof of true randomness.

Can you just for fun clarify what you mean by true randomness? I as a physicist suspect that it is impossible to prove such a thing to begin with. You can show that there are no measurable correlations. When you do that, you will find some, but they should get weaker as you keep measuring.

True randomness is when distribution is uniform and statistically independent and is decided upon the action.

For instance if a computer will create 10 random numbers on the fly and give em to me or just give me 10 random numbers which were generated yesterday there would be no difference but in second option it is predetermined. So randomness can be either true(generated upon the action) or pre determined(looks random but is set in stone). We don't know which one can never know.

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I as a physicist clarify that uncertainty principle doesn't give you proof of true randomness. All it does is show that we can't know the future 100% certain. But not knowing the outcome doesn't prove it's random.

Wow, it's almost like I just said that a couple posts ago.

Not crazy just stupid and false.

Pretty dismissive for a guy who's just parroted what I said yesterday. I'd be offended, but since I don't know if you could have turned out otherwise, I do not know whether it's right to blame you for being a hostile prick.

We don't have free will so don't blame me. What did I say and what does it have to do with dualism which I think is bullshit?
Here is why it's bullshit btw.
http://www.youtube.com/watch?v=RS4PW35-Y00

[Alex K]

It sounds like I agree, but sorry if I'm a bit dense, what's "decided upon the action" supposed to mean?