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The Grandfather, Grandson Paradox

What am I on about? Read on for enlightenment...

The Grandfather, Grandson paradox is an example which was thought up to explain the problems associated with time travel. You see it poses a problem which in effect cannot really be solved because we don't have a spare TARDIS (DR Who's time machine) sitting around and thus no way to find out what would happen. The problem goes like this:

Lets suppose I got bored one day and decided to build myself a time machine and just for a laugh went back in time and prevented my grandfather and grandmother from ever meeting. This would have an effect on future time since if they never met my mother (or father) would never be born and therefore neither would I.

The resulting problem called a paradox is that if I was never born I could not go back and prevent my grandfather meeting my grandmother, they would then meet and I would be born in which case I would go back and they wouldn't meet and I wouldn't be born and... you see what I mean!

Another example of this is done on a pool table. First you hit a ball which then precedes to go down a pocket, OK big deal but this pocket is magic...

It sends the ball back in time a few seconds and it comes out of a pocket on the other side of the table and rolls into the ball you just hit preventing it from going into the pocket. if it didn't go down the pocket it couldn't come out the other side and in that case it did go down the pocket.

On the off chance you understood that lot you will understand that time travel is going to have some problems, there are going to be events which stop themselves from happening and in doing so allow themselves to happen.

If this does not confuse you are either a quantum physicist or you didn't understand the problem. If you are both a quantum physicist and you didn't get confused then you probably know about the proposed solutions:

One of these is that you can go back in time but your grandparents will meet irrespective of what you do, if you try to kill them the bullets will miss because they are not allowed to hit.

The second one is that both events will happen, you will both be born and not be born, you will both kill your grandparents and not kill them. This believe it or not is probably the most accepted solution although I don't agree with it.

Or...

Then there is my solution, this is blindingly obvious but no one seems to have noticed it. Time in my view follows a law, a very simple law which we all know and understand :

• You cannot change your past.

Well, I did say it was blindingly obvious... but how does it solve the paradoxes? The answer to this is quite simple, If say you go back in time and stop you grandparents from meeting this WILL happen, one of your parents will NOT be born and you will NOT be born.

But does this not mean that you will not go back in time? Yes this is correct, you will not go back in time but you see all this happens in the future, it does not effect the past. Once you are in the past that's it, no matter what you do cannot change that fact, so even if you kill your grandparents it will have no effect on you (except getting you put in prison). You can go back in time and kill yourself as a child and you will still exist although in the future you will have never existed except as a child.

What about the pool balls?

The answer is much the same, when the ball goes down the pocket it reappears out the other side and hits itself as it heads towards the pocket and knocks itself off course. The ball has already came out of the other pocket and this cannot be changed but it can be prevented from going into the pocket. The end result is that you have an extra ball which appears from nowhere and knocks your shot off course.

The paradox in both cases is prevented by a simple law, If you go back in time you can do what you want but you will still be there, there is nothing you can do to the future that will change the fact that you are in the past.

And if you think that was confusing, just wait till the Butterflies get involved...

No, I have not been smoking illegal chemical substances of drinking too much Cafferys (or Sherry, or Vodka, or Poteen...). The butterfly is a reference to the "butterfly effect" which is found in Chaos theory. What this basically means is that if you change one variable by even the smallest amount possible it will have a gigantic effect later on. It is called the butterfly effect because the example given by whether forecasters is that a butterfly flapping it's wings can cause a hurricane. You may think this is impossible but actually this is the way chaos theory works (it's not called Chaos for nothing!).

So, what has this to do with time travel? Actually lots, you see time itself is a chaotic system, if you make the slightest change to the past it will have a very large change in the future. Just look at how things happen in our world, many events are caused by just a single person, there may be many other people involved but ultimately it all has to start with one person.

Technology is the same, it goes along paths caused by different inventions. Go back in time and change any of these or change the path of any person and the future would be completely different. what's more you don't even need to interfere with anyone or anything important to change the future, just trip someone up in the street and you have set the changes in motion.

The delay caused by tripping someone up could cause them to do things differently that day, the difference may be very small but that change will effect everyone else that person comes into contact with and everyone they come into contact with. A fraction of a second can cause or prevent major accidents saving or destroying lives. By making the slightest change in the past you can have a massive effect on the future. If you went back in time to you grandfathers time for just moments when you return to the future you may not recognise it. The person you were when you left will be completely different and may not even exist.

This is perhaps the biggest danger with time travel, you may go back to make a slight change but you will never be able to predict what effect this change will have.

But, is this true?

Good question, proving this is sort of difficult as I don't have any time machines (at least none free) so the only way I think this theory can be tested is in a good old computer simulation.

And there's more...

You see, I don't think time travel is possible.

There are some theories that say you can travel in time when going through a worm hole but I'm not quite so sure.

An idea for a suggested time machine is that you create two ends of a worm hole using two pairs of metal plates charged up with unimaginaly large amounts of energy. This creates the worm hole but to travel in time you put one set of plates on a spaceship and fly off at as close to the speed of light as you possibly can.

Flying at close to the speed of light does decidly odd things, you suffer from what is known as time dilation. the best description of this I can give is that the rate at which you age changes, the rate of time slows down so you age at a slower rate, on the outside of the spaceship years can pass but for you this will seem like minutes.

It is this property that is used in the time machine, the idea is that one end of the time machine is subject to time dilation and the other is not, so you wait a few minutes then jump in at one end and come at the other end out a year or so later, you then do the opposite and travel backwards in time by a year.

It is this which in my view is wrong, because while your rate of aging may change due to time dilation your position in time will not. You can jump to and fro along the worm hole all you like but you never actually travel backwards or forwards in time. When you first jump in you travel through the wormhole but you appear where the spaceship is a few minutes later not a year later, when you travel back again you arrive after you left, not at the same time or before.

The only other way to supposedly travel backwards in time is to travel faster then light which is impossible if you have any mass. The trouble is the backwards travel will only occur if you do have mass. On the other hand if you do manage to do it my bet is that you will not go backwards in time but you will instead form a singularity - the central part of a black hole .

Now, any more suggestions...

23rd May 97

Disclaimer: In case you haven't noticed I'm not a trained Physicist, just an enthusiastic amateur.

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