h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I think its more fun to do it here

Hmm. I may be young and nieve but I was thinking that the possiblity of aliens is nearly definate (i'm judging this from the size and age of the universe). If this is the case then surely if time travel was possible aliens would have achived this by now (in probability) since an alien species could have been around for millions of years (for all we know).

I personally beleive that this is likely simply due to the millions of galaxys in the universe. We can't simply be the only intelligent species in the whole universe.

Oh well. I'll let everyone rip my theory apart

No arguments here, I'd agree that intelligent life *somewhere* else was a near-certainty. But it doesn't count as evidence either way: if time travel were possible, and has therefore already been done, how would we know about it?

Ah good point I didn't explain that part. I mean that if the universe would come to an end due to the grandfather paradox (if that is what happens.) then surely it would have come to an end by now if it had been invented.
I've confused myself now. I'm sure i'm not making any sence. Heh.

The grandfather paradox should not end the world, as why should one lapse in time create that much trouble when black holes, wormholes and massive suns etc... create massive disturbances in time. I mean if aliens hav created time travel and come back here, that means that ; 1) time is not a constant as we thought 2) there 'time' is simply different to ours 3) we are not in the present but are in the past. Thus, under these parametrs the Grandfather paradox is quite conceivable.

Hi. Intervention Time! this post is to try and clear up some points i've had a good time reading.
1. time is not constant it is relitive.
2. as time is relitive we occupie past, present and future simultaneuosly relitive to some point in the universe.
A sees us in the past
B sees us in the present
C sees us in the future.
i'll discuss some other time.
3. all this talk about the universe spliting. ok. but the universe likes to keep things simple as possible. so spliting occours but the split universe will at a later point rejoin the universe.
a split will only happen when there is no way for the universe to resolve things

example
split rejoin
-----\---------------/------------> the universe
\-------------/
split universe

forgive the art work
this rejoining enables the universe to keep track of time with in itself. or time to keep track of the universe
so any time travel will happen up and down the universe.
of course to confuse you all orther universes exist in our own!?

the picture is ment to look like this. ignore the dots.

.......--------\---------------/----------->
..................\-------------/

Hi
If your talking about multi-universes,(Hugh Everett) then you must accept there will be an infinite amount of them.
Therefore everyting was/is/going to be poosible.

But in a single linear universe, if time travel (backwards) was possible, where are all the "future tourists"?

Stephen Hawking postulates that time machines cannot exist in his Chronology protection conjecture. Which states that the laws of physics are such as to prevent time travel ("closed timelike curves") on all but sub-microscopic scales.

How about the free will question? You were born, you exist, therefore you will never travel back in time, and have never killed your grandfather... Nor will you ever want to, because you exist. I'm no physicist though... does this idea hold water?

The idea of time travel would (could?) suggest that every event is preordained (even your "free will"), nothing is random, any and every event is accurately predictable with enough information and information processing capacities (computer industry, we're looking at you!). So, if this is true, you can predict the future accurately: "Hey, I'm never going to have the desire and ability to travel in time and negate my own existence!" And if this is the case, we can make it into a nice slogan to put on a T-shirt for an icebreaker in social situations!

I am thinkin to myself. Is it possible to travel in time? I hope it is. But If I did I do not know what I'd do with that device.
It would be fun, but I can't imagine the results would possibly outweigh the possibilities for outlandish catastrophie.
Better to just get into a tanning booth. Far less harmful to you and a lot less energy to do, aswell.

OK guys Ive heard enough how about this theory.
You go back in time, in the exact moment you go back in time the whole reality down to the moment you went back to dissapears, now you are on the past but it became your present. You can kill your "grandfather" but you will still live, you will stay in a world where your grandfather is dead but you will complete your life there, there is no way to go to the age you were born because it dissapeared.

This is easier to imagine like this, you go back in time and stop Hitler from beginning WWII, then you will stay in that decade and will live the rest of your life thereseeing the new future unravel. If time travel is possible this would be a pretty good explanation of why we havent seen anyone from the future.

btw I forgot to add. some guy said that all the universes would be the same because no outside factor would influence them. well i think you're forgetting the chaos theory here, there is nothing controlled. there is no outside factor that changes dropping 5 drops of water off the same spot at the same time on the same funnel but each one will take a different route.

I'm partial to the belief that if you went back to kill your grandfather, something would stop you. Like someone said, kill the wrong person, or get hit by a bus. I think the universe would prevent it, which is what allows you to (almost) do it in the first place.

Or, here's a hypothetical: Suppose going back in time works, in our single universe. You go back, pull the trigger, grandad dies. Then, your grandmother (seeing as she is young and hasn't given birth to your father yet) moves on, finally from the brutal murder of her boyfriend. She has a kid. This new life, created by your own meddling, lives a life, gets a wife, has a kid. Is this kid an alternate you? Different genes, same underlying consciousness/soul/ka/whatever? Would the alternate you go back and kill your poor grandmother's other boyfriend?

I see two possibilities, both precluding the Grandfather Paradox from ever happening:

1) You travel back in time and kill someone you think is your grandfather. Your information is incorrect, and you kill a drifter dying from tuberculosis, or you kill his identical twin who disappeared mysteriously years ago and you were never told of him, or you fail to kill him as he miraculously survives a gunshot which would normally be fatal. You always wondered how he got those scars...

or

2) The matter which you are composed of exists in the past already in a different form, and you switch places (and states with it) meaning you become water in a river somewhere, along with plant matter elsewhere, and so on and so forth, while all the matter back in time becomes you in the present. This process would be unnoticeable, and would result in absolutely no change. The experiment would likely be called a failure. Even carbon dating would not measure the change correctly, as decay would also reverse or accelerate in all involved matter.

No grandfather paradox exists:

1. Time travel to the past is logically possible.

2. Time travel to the past does not break the laws of physics.

3. But you cannot kill your grandfather because you cannot change the past.