# If time travel is possible does it allow for violation of the no clone theorem

1. Oct 2, 2011

### bert444

If time travel is possible does it allow for violatation of the no clone theorem?

thanks

2. Oct 3, 2011

### mathman

In logic a false hypothesis implies anything you want.

3. Oct 3, 2011

### bert444

what do you mean by that

My questions is that does time travel allow for a perfect clone of something

As opposed to an imperfect clone?

thanks

4. Oct 3, 2011

### xts

Mathman explained it perfectly well, but maybe not clearly enough: as you make false assumption, you may deduct any conclusion of this. Pure logic.

Your assumption is false, so it makes no sense to hunt its implications.

5. Oct 3, 2011

### bert444

When you say false hypothesis do you mean assuming that time travel is possible. Also when I say time travel I mean backwards time travel. Sorry for being a little annoying

6. Oct 3, 2011

### xts

Time travel forward is perfectly possible. You do it every day. Yesterday you was at Oct.2nd, today you are at Oct.3rd, tomorrow - at Oct.4th. You perform time travel. But travel backward is impossible, so it makes no sense to discuss implications of 'what if it would be'. It makes as much sense as discussing 'what if grass is pink, rather than green'. Grass is green and where physic rules obey cannot be pink. Where they don't obey - everything is possibles: gnomes, angels, travel in time and even meaningful self contradictory sentences.

7. Oct 4, 2011

### Demystifier

The no-clone theorem is a consequence of linearity of QM. The question is: Is QM linear if time travel is possible? Unfortunately, the concept of time travel is somewhat vague, so it is desirable to replace that notion with something better defined, such as CLOSED TIMELIKE CURVE (CTC). This leads to the final question:

Is QM linear in the presence of CTC?

Some physicists, such as Deutch, argue that it isn't. Others, including myself, argue that it is. For more details see e.g.
http://xxx.lanl.gov/abs/1006.0338
and references therein.

8. Oct 4, 2011

### f95toli

We don't know that for sure. There are plenty of 'exotic' suggestions (published in peer-reviewed journals) for situations which would perhaps in principle allow something to travel backwards in time. No one knows for sure.
Whether or not these suggestions are practical or not is besides the point for a question like this.

9. Oct 4, 2011

### Chronos

The system of laws by which the universe operates are internally self-consistent. Were this not true, science would be irrelevant.

10. Oct 5, 2011

### yoron

Assume a ctc.

As you follow it, are you then at two places 'simultaneously'? To prove such a statement we need the eye of a God as it seems to me?
==

Also, isn't this a question about 'frames of reference'?

11. Oct 6, 2011

### Demystifier

No. Think of it as a circle on which the angle variable is interpreted as the time variable. No two points on the circle have the same value of angle (between 0 and 2 pi).

12. Oct 6, 2011

### yoron

Yes, that was my thought too. So where would a clone be? You have the theoretical possibility though to send information about a state without disturbing it, but practically it seems impossible to do as it involves so incredibly much information. But assuming that you could you would have now have a 'perfect' clone, possibly? Depends on if thoughts is a direct relation to the body/brain of course. You might want to argue that if the clone didn't have the exact same 'thought' (and memories) as it materialized it can't be a 'perfect' clone. Then again, if it's about 'dead materials'? one microgram of something might be possible some day :) Who knows?
==

Although it does not involve 'teleporting', it's a procedure inside our constant.

13. Oct 7, 2011

### Demystifier

Yoron, perhaps you misunderstood the meaning of the no-cloning theorem in quantum mechanics.

If you know how someone prepared an electron in a certain quantum state, then you can repeat that procedure again and you will prepare another electron in an exactly the same state. The no-cloning theorem does not forbid this.

However, if there is an electron in a certain state but you don't know how it was prepared, then, as far as you know, it can be in ANY state. Can you prepare another electron in the same state now? You can certainly do it by accident, but the question is: Is there a procedure which would do it with 100% certainty?

Well, to do it with 100% certainty, you must first probe the original electron to find out what its state is. But the problem is that such a probation of the electron affects its original state. As a consequence, your attempt to make a copy changes the original. You can make a copy, but with the price of changing the original. That's the content of the no-cloning theorem.

14. Oct 7, 2011

### thenewmans

I am in no way the person to answer this thing. And I don’t know about cloning. But what I know about Bell’s theorem sure makes me think that time travel is very much a possibility. Besides, I recall several physicists, including Feynman, that speculate a positron is an electron going backwards through time. When someone says time travel or some other crazy idea, it’s easy to think he’s throwing all the rules of physics out the window. That’s a mistake.

In a way, Bells theorem says that either (1) locality or (2) counterfactual definiteness is false. One of them must go. I like to interpret that as either FTL travel is possible or time travel is possible. I think most choose to sacrifice locality. I prefer to sacrifice #2.

On cloning, my guess is this. If a positron truly is an electron travelling backwards through time, then 2 copies of an electron can travel through the same point in time. But since it’s turned around in time twice (emitting and absorbing gamma rays), I doubt the 2 copies look anything alike.

15. Oct 7, 2011

### yoron

Yeah, maybe I'm missing something here, it depends on what you mean by 'measuring' I guess?

Assume you want to port state A to some other place. You get two entangled objects, B1 and B2. One you keep, the other you deliver somehow to the place where you want to replicate state A. You can't measure on state A directly as that will interfere with its state, changing it. So what you do is to measure on the relation state A has to state B1, for example the way state B1:s spin has to state A, around some axis. Knowing the relation you haven't measured state A directly. but you have a relation that will be just as true for your friend 'over there' that you sent the entangled B2 too. The only thing he will need is a new 'photon' State C that he then put in the exact same relation to B2 that your B1 have to state A.

But it is indeed measuring involved, although on the relation between those particles state. And what you should end up with is two exactly correlated photons both in State A. But it is a tricky one. Check up Charles Bennet (1993) IBM if you're interested of it.

In principle, if we mean no measurements at all for this cloning to take place then it would be a freak of nature if it ever happened. If we by it mean not changing what we want to port? Then maybe?
==

As for time travel, imagine all 'gravity' as clocks. it actually will be as 'clocks' for any of us measuring any other 'frame of reference'. Do you expect any of those 'clocks' you measure to go 'backward'? What would happen if you ever moved to that 'clock'? Would you expect it to go 'backward' joining its 'frame of reference'?
=

You can take that a step further by consider the inside of a event horizon. Gravity is expected to obey 'c', that is propagate at 'c'. What do you expect happens to those 'clocks' as they pass the event horizon? We do expect gravity to exist inside a event horizon too.

Last edited: Oct 7, 2011
16. Oct 11, 2011

### RehNavah

While I agree with what many of you are saying I must point out something that, from what I have read, all of you might have forgotten about. That being the infinite reality theory. The basic concept of it being that there is a reality, whether it is ours or not is yet to be seen, where not only time travel in any direction but also where is does and doesn not violate the clone theorem. I know this seems like a vague argument but I thought it might be another interesting way to discuss this topic as well as the direction you have already gone.