# Would universe repeat if restarted as of 100 years ago?

Discussion in 'Physics & Math' started by Dinosaur, Oct 23, 2005.

1. ### DinosaurRational SkepticValued Senior Member

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Obviously there is no way the universe could be rewound to 100 years ago and restarted with exactly the same initial conditions, so I would like to discuss the question ignoring this impossibility.

It is also obvious that Chaos Theory tells us that any finite deviation in initial conditions (no matter how small) would result in a very different universe in 100 years.

Since probability seems to rule at the quantum level (which has effects at the classical level), I would expect the restarted universe to be different even if the initial conditions of 100 years ago were duplicated exactly. Id est: At a very fundamental level, I do not believe in determinism.

I think my view is supported (not proved) by data relating to radioactive decay and other quantum level processes controlled by probabilistic laws. At least the data resulting from such processes indicate that probabilistic laws rule at the quantum level.

What are the views of others here? If you disagree, do you know of any evidence supporting your view?

3. ### kevinalmRegistered Senior Member

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Basically, your talking "butterfly effect", right? Maybe this example I heard some years ago might help. Line up 15 billiard balls on a pool table in a straight line. Hit the cue ball with a cue aiming to drive the final ball straight on along the line. How much control do you have in the actually direction of the final ball.

None at all. The difference in intial momentum caused by a random impact of a single air molecule (brownian motion) on the cue ball can swing the final ball from +90 degrees to -90 degrees.

5. ### RaphaelRegistered Senior Member

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Probability rules at the quantum level because one is unable to accurately measure both position and momentum or energy and time simultaneously.

If both position and momentum (and energy and time) were known for every event in the universe at 12:00 on Jan 1, 1900 (GMT) then all the events would play out identically if replicated precisely.

7. ### kevinalmRegistered Senior Member

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993
Hmm, I would say it depends on whether the ultimate physical reality is "classical" or quantum in nature. Is quantum mechanics a statistical way of modeling a chaotic deterministic system or is probability the reality? Interesting question. I am inclined toward the answer nobody really knows.

8. ### wesmorrisNerd Overlord - we(s):1 of NValued Senior Member

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I think the concept of relativity implies no. Every point in space-time is effectively its own reference frame, correct? While determinism may be applicable to that reference frame, the interaction of all the different points must be probabilistic. As such, I'm down with the chaos theory perspective that indeed it would not be the same.

9. ### Billy TUse Sugar Cane Alcohol car FuelValued Senior Member

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I think everone who has posted here, except wesmorris, is correct and just want to added that in addtion to the possibility of "hidden varriables" (which is constrained by Bell's inequality experiments results) the quantum entanglement has other strange possibilites:

Suppose that at present both members of an entangle pair have not been measured. -I.e. the present uinverse is now not known because no one has made an observation (not the standard "you can not measure eactly two non comuting varailables" idea). At some time in the future, one of the pair is measured. That causes our present universe to be better (in this one aspect, perhaps precisely defined.) So there is Chaos, QM uncertainity, and that future physical observation to prevent an exact replay of the last 100 years, but "relativity" has nothting to do with this - one can always state in the same frame conceptually.

Last edited by a moderator: Nov 4, 2005
10. ### Billy TUse Sugar Cane Alcohol car FuelValued Senior Member

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Given the "perfect measurability" false premiss, that is true, if you can rule out the existance of "free will." For years, I would have agreed that with this primiss the future is deterministic. I.e. La Place was correct, with this premiss, that the future is determined by the past, even if in pratice chaos and ignorgance make it unknowable.

I am not so sure anymore, that genuine free will, GFW, is inconsistent with deterministic physics ruling the universe. {Nothing to do with miracles, etc. but GFW may be possible. - See my relatively long post in the "Black Holes and Spooling Rope" thread - now a page down as I display pages. I present arguments why GFW (or at least a real time simulation for human perception) may have evolved in the more complex creatures.}

11. ### wesmorrisNerd Overlord - we(s):1 of NValued Senior Member

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Yeah pardon. I gotta stay off the crack. *sigh*

It made sense at the time, but looking back - not so much.