# The Naked Scientists Forum

### Author Topic: Déjà vu  (Read 6251 times)

#### godcube

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##### Déjà vu
« on: 15/09/2010 18:55:59 »
Déjà vu

A number of years ago I played around with a couple of assumptions to see how these would affect things, the two assumptions were
1.   Nothing is random
2.   Nothing is infinite
Playing around with these assumptions I think can result in some interesting situations.

First consider dropping a glass of milk onto the floor. The glass would break and the milk would spill on the floor in a certain way. If we then repeat the process again with a new glass of milk keeping everything down to the tiniest components the same, the glass and the milk would break and spill in exactly the same way and the exact same pattern as before.

Now consider a perfectly bouncy ball bouncing around in a box, since there are only a finite number of arrangements (albeit a very large number considering all the factors involved), for example, where the ball could be inside the box, it’s speed and direction, the arrangement of the air molecules inside the box, the ball will eventually arrive at an exact same arrangement that it has taken before. Since nothing is random, once this happens the sequence would simply repeat itself again and again in a loop. This is because like the glass of milk breaking, the same exact arrangement would result in exactly the same result, and because the result is that everything ends up in exactly the same arrangements.

Taking this on a universal scale, it would imply that either the universe has a beginning and an end (for example if the ball was not perfectly bouncy it will eventually comes to a stop) or if the universe keeps progressing it will eventually repeat itself due to the limited permutations (though a very large number) it can take. Some could argue that this would break the assumption because the universe would repeat itself infinitely but I see it as more of a finite loop.

Taking things slightly further these assumptions would also permit moving time around to a certain degree because if you want to move to say 1945, you would only need to find a way to arrange the universe exactly as it was then (although this of course is very unlikely to be easy). Time travel however, would not be possible with this method since you would first need to arrange the universe as it was in 1945, but then you would need to create extra mass and energy to create your present self (the time traveler) as well, or else you would need to take mass and energy from elsewhere in the universe but that would result in the universe not being exactly the same as it was in 1945.

So since the universe would be repeating itself in a finite loop with these two assumptions we could all be living a Déjà vu moment right now, infact we could have been in this very moment several times previously.

Praphob Sussangkarn
godcube@gmail.com

#### Bored chemist

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##### Déjà vu
« Reply #1 on: 15/09/2010 20:30:29 »
"you would only need to find a way to arrange the universe exactly as it was then (although this of course is very unlikely to be easy). "
Not just difficult, but a breach of the uncertainty principle and, therefore, impossible.

#### Ron Hughes

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##### Déjà vu
« Reply #2 on: 15/09/2010 21:12:03 »
Does anyone ever wonder that we quote "HUP" almost on a daily basis and yet we have no way of proving it's validity. Why isn't it possible that IF we did know the position and momentum of ever particle in the Universe we could predict ever event? I sometimes wonder if maybe we have blown HUP out of proportion. Heisenberg was saying that in order to get information about a particle we must hit it with something and in so doing we change it's momentum and position.

#### Bored chemist

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##### Déjà vu
« Reply #3 on: 15/09/2010 22:08:11 »
The predictions made on the basis of QM are very good. That seems to be rather strong evidence of the uncertainty principle and also lots of other things.
It's not that we can't measure, for example, time and energy independently; it's that they don't exist independently.

#### imatfaal

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##### Déjà vu
« Reply #4 on: 15/09/2010 22:11:22 »
Ron,  Uncertainty principle comes from mathematical necessity.  The heisenberg microscope gedanken is just a way of explaining the principle not the basis for it.

#### Ron Hughes

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##### Déjà vu
« Reply #5 on: 15/09/2010 22:44:43 »
I don't vehemently disagree but disagree I do. I think it is the basis.

#### godcube

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##### Déjà vu
« Reply #6 on: 16/09/2010 05:07:01 »
I am not trying to say that

1. nothing is random
2. nothing is infinite

In both cases I don't think that we will ever know for sure one way or the other if these statements are true or false, but our best assumptions might change as the theories progress.

The piece however is more about what if these two statements are true and what would be the consequences.

#### JP

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##### Déjà vu
« Reply #7 on: 16/09/2010 05:36:57 »
I am not trying to say that

1. nothing is random
2. nothing is infinite

In both cases I don't think that we will ever know for sure one way or the other if these statements are true or false, but our best assumptions might change as the theories progress.

You can make a bunch of arbitrary assumptions and for some set of them, the universe will repeat itself eventually.  That doesn't mean those assumptions are realistic, though, but they can make interesting thought experiments.  The two points above aren't enough to get the universe to repeat.  You have to allow time to go on for long enough so that things within your finite universe are nearly-certain to repeat.

But if you do make more realistic assumptions, randomness can actually help you, since quantum mechanics could spit out Earth, ca. 1945 from randomness.  The problem is that such an event would take so long to occur that it could only happen if the universe was basically infinite and fairly stable in time--which are probably not good assumptions, either!

#### godcube

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##### Déjà vu
« Reply #8 on: 16/09/2010 05:50:54 »
JP

"But if you do make more realistic assumptions, randomness can actually help you, since quantum mechanics could spit out Earth, ca. 1945 from randomness"

This would not mean that the universe would repeat though. Since if randomness is involved you could have the exact same arrangements as before but you would end up with a different outcome. Also it might or might not spit out Earth ca. 1945 whereas if nothing is random or infinite it would eventually repeat itself as it progress.

#### JP

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##### Déjà vu
« Reply #9 on: 16/09/2010 06:24:35 »
JP

"But if you do make more realistic assumptions, randomness can actually help you, since quantum mechanics could spit out Earth, ca. 1945 from randomness"

This would not mean that the universe would repeat though. Since if randomness is involved you could have the exact same arrangements as before but you would end up with a different outcome. Also it might or might not spit out Earth ca. 1945 whereas if nothing is random or infinite it would eventually repeat itself as it progress.

It would repeat, eventually.  You'd have to spit out an earlier earth and then repeat all the random fluctuations that earth went through in time.  That would take a staggering number of tries, but what's a billion billion billion . . . billion tries for a universe that has no limit on time?

It would be even less likely to repeat the entire universe including all its random fluctuations, but if you have infinite time and a static universe, it will eventually happen.

It's an interesting thought experiment, but we're talking about time scales so long (even in your original case where there is no randomness), that the expansion and eventual fate of the universe come into play.

#### godcube

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##### Déjà vu
« Reply #10 on: 16/09/2010 07:05:04 »
does having just the "correct earth" means that the events would repeat? since the rest of the universe would be different? also to repeat would mean that in the next loop the "randomness" would have to try and spit out the different earths in the exact same order as before.

"but we're talking about time scales so long (even in your original case where there is no randomness), that the expansion and eventual fate of the universe come into play."

That is why I think that if the two assumptions are true, either the universe will have a beginning and an end(where it never repeats itself), but if the universe keeps progressing it will eventually repeat itself due to limited number of permutations it can take, and since there is no randomness once it takes up the same permutations it will progress exactly with the same result as before ending with it arriving at the same permutations again and again.

#### JP

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##### Déjà vu
« Reply #11 on: 16/09/2010 07:29:55 »
does having just the "correct earth" means that the events would repeat? since the rest of the universe would be different? also to repeat would mean that in the next loop the "randomness" would have to try and spit out the different earths in the exact same order as before.
Ah.... I get you.  You want to repeat the entire universe's history again, rather than starting from some point and repeating a portion of its history.  I'm not sure that's possible even with infinite time if there's randomness.  Every time you failed to repeat exactly the universe's history, you'd be adding to what you have to repeat the next time around, so it might be that things get more complicated so quickly that infinite time won't help.

Quote
"but we're talking about time scales so long (even in your original case where there is no randomness), that the expansion and eventual fate of the universe come into play."

That is why I think that if the two assumptions are true, either the universe will have a beginning and an end(where it never repeats itself), but if the universe keeps progressing it will eventually repeat itself due to limited number of permutations it can take, and since there is no randomness once it takes up the same permutations it will progress exactly with the same result as before ending with it arriving at the same permutations again and again.

That's probably true.  But again, those assumptions violate physics as we know it.

#### yor_on

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##### Déjà vu
« Reply #12 on: 21/09/2010 15:56:17 »
Why do you speak of a limited number of permutations?
Do you have a proof for them being finite?

Every causality chain we see, we see through its 'history', so in that motto all causality-chains can seem 'finite'. But there are no guarantees for it being true always, and it's very easy to prove that it's probability that argues for certain solutions to come into being, not 'blind determinism'.

I don't expect the universe to have a limited number of permutations, the only thing I expect it to have is 'patterns' as seen through its history. Those patterns may be limited though, although I'm not sure on that.

#### Don_1

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##### Déjà vu
« Reply #13 on: 21/09/2010 16:14:23 »
Haven't we discussed this before?

Awww, c'mon, somebody had to say it!

#### Geezer

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##### Déjà vu
« Reply #14 on: 21/09/2010 23:30:49 »

#### yor_on

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##### Déjà vu
« Reply #15 on: 22/09/2010 09:31:35 »
Ahw m'God, it's a closed ring, ehh, sort of?
Where do I get out?

#### Bored chemist

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##### Déjà vu
« Reply #16 on: 22/09/2010 20:16:25 »
Haven't we discussed this before?

Awww, c'mon, somebody had to say it!
We did
"you would only need to find a way to arrange the universe exactly as it was then (although this of course is very unlikely to be easy). "
Not just difficult, but a breach of the uncertainty principle and, therefore, impossible.

#### Don_1

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##### Déjà vu
« Reply #17 on: 23/09/2010 08:22:25 »
Haven't we discussed this before?

Awww, c'mon, somebody had to say it!

Hmmmm.......

#### yor_on

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##### Déjà vu
« Reply #18 on: 23/09/2010 12:49:30 »
Am I still here?

Sh****

#### Don_1

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##### Déjà vu
« Reply #19 on: 23/09/2010 13:45:19 »
Haven't we discussed this before?

Awww, c'mon, somebody had to say it!
We did
"you would only need to find a way to arrange the universe exactly as it was then (although this of course is very unlikely to be easy). "
Not just difficult, but a breach of the uncertainty principle and, therefore, impossible.

#### Geezer

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##### Déjà vu
« Reply #20 on: 23/09/2010 21:06:52 »

There was one about recursion, but it just seemed to go round and round.

#### Bored chemist

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##### Déjà vu
« Reply #21 on: 23/09/2010 21:12:09 »
Haven't we discussed this before?

Awww, c'mon, somebody had to say it!
We did
"you would only need to find a way to arrange the universe exactly as it was then (although this of course is very unlikely to be easy). "
Not just difficult, but a breach of the uncertainty principle and, therefore, impossible.

A path well trodden.

#### Don_1

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##### Déjà vu
« Reply #22 on: 24/09/2010 10:02:53 »
Last night, as I climbed into bed with the old bat wife, I said to her, "I had a strange feeling of Déjà vu last night."

She retorted "You're about to get it again, GO TO SLEEP!"

#### yor_on

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##### Déjà vu
« Reply #23 on: 25/09/2010 20:49:20 »
May thy dreams be wholesome, including or not including..
Bats?

Cricket Sir?
Absolutely cricket.

#### The Naked Scientists Forum

##### Déjà vu
« Reply #23 on: 25/09/2010 20:49:20 »