Excercises in temporal logic

[Duda Jarek]

If we want to understand physics, first of all we have to understand, create a coherent picture of the nature of time.

So in this thread I would like to discuss about consequences of hypothetical assumption that there is a possibility to influence the past - does it have to lead to contradictions (time paradoxes)?

Observe that CPT conservation suggests that causality can go in both time directions... in general relativity we want more or less smooth 4D manifold - to minimize tensions from both time directions...

http://www.advancedphysics.org/forum/showthread.php?p=52348

 

First of all, let's assume some interpretation of quantum mechanics ... physics. Some people believes that physics isn't deterministic (because of wavefunction collapses), some in many-worlds interpretations (that such collapses splits worlds - creates alternative realities).

In many world interpretation - time travels doesn't seem to be forbidden - such travel would just create a new alternative timeline - there is no problem with time paradoxes.

 

For now I'll assume the most probably (and physical) for me looking point of view: full determinism - there is some 'wavefunction of the universe' which evolves in an unique way. It's like in the general relativity theory: there is some already created fourdimensional spacetime and we 'travel' through its time direction - so the future is already there (eternalism).

 

I'm afraid that full determinism/eternalism doesn't allow for perfect time traveling, like made because of that our spacetime would be bent so much that it would create stable 'wormholes' with endings in light cones of each other - such stable time-loop would allow for paradoxes physics couldn't handle with - like a machine which sends a beam to itself iff it doesn't do it. It's one of reasons I don't like Einstein's view:

http://www.thescienceforum.com/viewtopic.php?t=15841

 

But let's think about a possibility of a channel in which we could send information back in time on which we cannot fully rely - sometimes it's easier for physics to make it lie.

Observe that quantum mechanics gives physics large freedom in choosing effects below our recognition to stabilize such causal time-loops to avoid time paradoxes: like choosing what spin will be measured, or make some small influences on statistically looking behaviors ... or eventually make that this backtime channel would lie.

 

Assume that there are allowed causal time-loops, but they have to be stable.

So if there would be such 'device' to transmit information back in time and I for example would send to me a picture of the girl who will be my wife ... and just before sending it back in time I would change my mind - this timeline would never appeared - there would be completely different situation (without this knowledge).

So if I'd really get this picture from myself - I will have no choice but to really send it.

Like in (a good...) SF movie - they go back in time to repair something ... and finally it occurs that the situation is exactly as it was ...

 

How to use such 'device'?

Imagine we take some real random number generator - for example measuring spin of photon 45 degrees from its polarization.

Now the procedure is:

(1) make a choice according to this generator,

(2) if from future there is a message that it was a wrong choice - take a different one

(3) wait for results of this choice

(4) finally if it was wrong choice - send this information back in time to (2)

 

So if there was a satisfying choice - it has created stable time loop - so in fact the possibility of using this device made that our random number generator (quantum mechanics) has already chosen properly before the loop.

It can be imagined that each of choice starts a different timeline - in our language they are all entangled and physics will choose one of them in what we call future, such that there for example are no time paradoxes (like that on a string is allowed some discrete set of wavelengths).

 

What if there wasn't any satisfying choice? Would it create time paradox?

Not necessary - most probably the physics would destroy the weakest link of such loop - make that this 'device' had lied.

 

Observe that even without this real random number generator, such 'device' could work without actually being used: if for example there had to be a successful terrorist attack, there would be sent information to prevent it ... and finally in a stable timeline this attack would never happen (because of e.g. proper quantum choices below our recognition).

 

It's great exercise to imagine the world with such devices.

If it would allow to send message only some very small time back, we could use two such devices cyclically to increase this time as much as we want.

It would have great use in science - choose a random amino acid sequence/reaction parameters/... crypotokey ... and use above procedure to ask if they are somehow optimal.

One would say - we could get technologies from the future ... but I don't think it would be good choice for us in the future, because we are not prepared for most of them ... like artificial intelligence - for it 'we' in future would have to still want to send it, knowing the consequences.

I don't like a picture that only government/rich would have access it ... but if it could be cheap, it would quickly spread:

Imagine our world with commonly available such 'devices'...

 

If someone would make a wrong choice - he could send this information back to prevent it - so finally we wouldn't consciously make choices which results wouldn't satisfy us! ... like choosing a school/job/... politicians... there would be no random accidents ...

There would be also no hazard ... so what about economy? If some papers would have to drop ... they would drop to zero...

So economy would have to completely change - that finally all is worth as much as it is really worth ... there would no risk management ... finally it should be extremely stable.

The same with persons - no one would longer rely on illusionary values - we would have to work on our real values instead ... not depending on luck, frauds ...

 

We could concentrate on studying/working/having fun/... building our world without any worry...

Is such world without bad choices/risks perfect?

Could we in this way really send some information back in time?

That means it would make a stable timeline - that knowing this information, after a few years we would really like to send it ... reveling own future/destiny - taking away own free will ...

But people are not perfect ... one would from the beginning been told that he has to do in life exactly this and this ... but I believe if it's properly used - such timelines shouldn't be stable - never happen ... for example even saying someone about his real future would be considered a crime against his free will... in stable timeline never happen (it would be prevented).

... I want to believe that in mature society it would be marginal cases ... and the main use would be just existing of such possibility - creating timeline without 'bad' choices ...

?????

 

So in this picture we cannot send information back to change the past.

Possibility of sending information is already enough to make that to prevent time paradoxes, physics would have to to prevent making 'bad' choices: if we would make such choice - we would try to send this information creating a paradox. So using a proper choice of what we call uncertainty, physics should make that we make a 'good' choice.

 

What do You think about all of it?

Edited March 21, 2009 by Duda Jarek
Consecutive posts merged.

[Daecon]

The Universe has performed an illegal operation and will be shut down.

[Duda Jarek]

You are overestimating our possibilities

 

The universe just optimizes some fourdimensional action of some field and we are only a product of its internal reason-result relations ... somewhere in this spacetime ... it already knows all stupid things we will try to do and prepared for them such that we cannot do anything against its internal integrity ...

 

So maybe we could use its protectiveness ... make it choose for us such that we will be satisfied with the results - because if not we will try to make a time paradox!

 

This post is in fact about acceptance of CPT conservation ... against our 'evolving 3D' intuition...

There is nice picture to upgrade this intuition here:

http://arxiv.org/html/physics/9812021v2

The author suggests interesting view on the hypothetical picture that our universe will finally collapse and then there will be new big bang - evolution - collapse ... and so on ...

Namely look at such collapse from the perspective of CPT conservation - from singularity of relatively small entropy it slowly evolves ...

After this symmetry it's no longer collapse, but 'anti big bang' which creates universe built of antiparticles which evolves in opposite direction to our time arrow... which will finally (in maaany billions of years) crash with our reality...