Is time travel possible?

Posted: June 13, 2011 in Misc
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When I watched Dr Who recently I wondered is Time travel possible??

I think it’s a very intriguing question as I love science fiction and stuff to do with time travel.  The “back to the Future” trilogy and “the time machine” are my favourite films to do with time travel. And so with my scientific background it got me thinking…..

Can we construct a time machine and travel throught time?

Well, I think we first need to look at Quantam theory and Einstein’s theory of relativity and see if time travel is theoretically possible within the laws of physics?. It’s very complicated so please bear with me.

I’m assuming that most of you have not got a degree in physics so I am going to try to make it as simple as possible.

So here’s the science bit!!!! (Skip if you want)

We will begin with quantam theory….

If we can look at an event that begins with a photon and an electron, and ends with a photon and an electron. We can say that what has taken place is a photon is absorbed by an electron,  the electron continues on a bit, and a new photon comes out. This process is called the scattering of light. When calculations are made for scattering, we must include some peculiar possibilities. For example, the electron could emit a photon before absorbing one. Even more strange is the possibility that the electron emits a photon, then travels backwards in time to absorb a photon, and then proceeds forwards in time again. The path of such a ‘backwards-moving’ electron can be so long as to appear real in an actual physical experiment in  the laboratory. The backwards-moving electron when viewed with time moving forwards appears the same as an ordinary electron, except it’s attracted to normal electrons – we say it has a ‘positive’ charge. For this reason it’s called a ‘positron’. The positron is a sister particle to the electron, and is an example of an ‘anti-particle’. This phenomenon is general.

Every particle in Nature has an amplitude to move backwards in time, and therefore has an anti-particle. When a particle and its antiparticle collide, they annihilate each other and form other particles. So time travel is not only possible, it is a perfectly normal phenomenon.

Now lets look at the Einstein’s theory of relativity….

Black holes, according to relativity theory, warp spacetime with their enormously powerful gravitation field. The effect of this gravitational field is that if an astronaut were to cross the event horizon of a black hole, time would slow down on board his spacecraft as he approached the singularity and eventually come to a stop. Similarly time slows down in proportion to speed, the faster our astronaut travels the slower time runs. The closer the astronaut travels to the speed of light the more time slows, until at the speed of light, time would stop. Both these effects of time being affected by speed and gravity illustrates that time is not a fixed  constant, but is affected by gravitational fields and relative speed in the same manner as the other three dimensions of space. The solutions to particular equations of the Special Theory of Relativity can be expressed mathematically in any direction of time without running into any problems. This means that there is nothing in relativity that rules out time travel and that it is theoretically possible.

Ok great its possible but if time travel is theoretically possible then it should have already happened and at some time in the future a clever scientist has already invented a time machine that can travel through time in any direction, just like the fictional time machine created by H. G. Wells.

So where is our intrepid time traveller?

To my knowledge, correct me if I am wrong, I believe history shows no record of a time traveller ever visiting us from the future, and so therefore I have to conclude it’s never going to happen. This appears at first glance to be a good solid argument against the possibility of time travel. But It may be that time travellers from the future have visited us, but have not revealed themselves in order to avoid changing the future. The fact that we have no record of having been visited by time travellers does not exclude its possibility.

Alternatively, time travel may be possible, but only into the future, the past already having been determined.

Finally, time travel into the past may be possible, but only into a different (alternative) universe, thus avoiding a paradox.

What do I mean by a Paradox? Let me try to explain.

The most commonly posed paradox is known as the ‘grand parent’ paradox. This states that if you could travel back in time you could murder your grand parents and thus prevent your existence, thus rendering it impossible for you to have gone back in time and killed them… no need to draw you a picture. Even more to the point perhaps, suppose you could travel back in time and kill the person responsible for time travel before they discover it! Then you wouldn’t have been able to travel back in time to kill him….. Catch 22. But this only reveals the tip of the iceberg.

Let’s examine a theoretical time travel situation in more detail in order to highlight some of the problems involved.

Ok lets imagine that today you travel back in time to say August 2001 and warn the authorities that the World Trade Centre in New York is going to be attacked on September 11th. Firstly will they believe you and lock you up for being a nutter. But suppose they do believe you and take the necessary action and as time unfolds the disaster is eventually averted.  But you are still in 2001 at this point and the disaster has been prevented, and you now wish to return to the time you came from. Here comes the Big Question – can you return to where you came from? Where you came from the attack had taken place, therefore where you came from no longer exists! If you do return to your original time, the World Trade Centre will still be standing (because you prevented the attack), so it cannot be where you came from. You will have changed the course of history, not just for yourself, but for the entire world. The question is, will the World Trade Centre still be standing when you return to your starting time? This is a major point of contention. According to one theory it both will and it won’t! This is because your actions will have created an alternative possibility and in the process an ‘alternative’ universe, where we now have one universe with the World Trade Centre intact, and one with it destroyed, and we will all exist in both.

The theory is firmly rooted in quantum theory that states that ALL alternative outcomes are possible. However, there is no evidence at this stage that the strange  phenomenon found in quantum theory can be applied to the larger world.

Yet another theory suggests that alternative universes will not be created because events will conspire against you that prevent you (as in this scenario) from warning the authorities and changing history. This ‘theory’ it isn’t really a theory as such, more an expression of a desire, because it is believed to be impossible (and very bad manners from the point of view of historians) to change history. The theory has no explanation as to how this ‘prevention’ could actually come about and has no solid theoretical basis. The same arguments can be applied to travel into the future. Suppose I travel 24 hours into the future and happen to meet myself crossing the street. (can you meet and interact with yourself?) . I push him in front of a car and he is killed instantly and then I return.

On my return, when tomorrow comes, I receive a visit from ‘me’ from my past. I of course knew he is gong to push me in front of a car and so I move out the way and push him into the path of the car and kill him instead. Can I do that? That isn’t what happened in my future, it was the ‘me’ in the future that died. Even if I don’t manage to kill ‘him’ in time and still die by the car, which one of us exactly is it that is still alive? We have created a nonsense scenario. Now this may sound like nonsense, and perhaps it is, but if the future really does exist then it does raise the prospect of meeting and interacting with yourself.

If we accept the idea that the future does exist, because time is just another dimension as discussed in the previous section, then these paradoxes would be unavoidable. If however, we take the view that only the dimension of time itself exists, and not the events  within it, then this would suggest that time travel is impossible. Why? Because if future events do not exist, then it would be impossible to travel into the future to witness them, there would be no ‘future’ to visit.

We either have to accept that if time travel is possible we will, by our actions , create all sorts of paradoxes, or accept that we will create alternative universes. The paradox problem will not go away. As for alternate universes, the mind boggles!.

So in answer to the question, is time travel possible??? Well, No I don’t think so because of the paradoxes created if you are able to interact with the surroundings. But if you are just an observer in a box and can’t interact with your surroundings then I think it may be theoretically possible.

But that’s just my opinion, what do you think?

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