MzNeko

Nothing happens, because the milkman slipped one in on ol' Gramps - you shoulda shot your Grandmother!

Speechless

I'm not the only one who watches Futurama then?

tronvillain

If we are going to go with the "alternate timeline theory", it seems more likely that one would be created at the moment you arrive rather than at the moment you kill your grandfather. Another possibility is of course that it is impossible to cause a grandfather paradox - whatever you do in the past will turn out to have been what happened all along. Yet another possibility is that you can kill your grandfather without creating an alternate timeline, but it will make you an object without apparent causal explanation, leaving you with the rather disturbing question "Did I actually come from the future or did I simply pop into existence with memories of the future?" Finally, there is the possibility that time simply loops until the paradox is resolved by random variation in events.

jj

Someone else would become your grandfather.

Then what would you do?

On an even less serious note, does anyone else know the song "Alma Turl" by Mike Cross?

I think that song sums up the real answer, yes indeed I do.

(edited because I felt like it)

Godless Dave

I'm no astrophysicist, but I read a hell of a lot of SF. My completely uninformed opinion is "causality" only needs to be conserved in one direction. If you go back in time to kill your grandfather it doesn't matter that the future you will never exist. The contemporary you began its existence as soon as your time machine materialized in your target time. When you gun down the old geezer you prevent the (now) future you from ever being born, but you still exist and even have your memories of events that are no longer going to happen. If you time travel back to the "present" you came from you'll find a different reality.

xeren

Actually, it would be impossible to kill your grandfather before he conceived your father. Think about it: You merely EXISTING, is testament to the fact that your grandfather succeeded in impregnating your grandmother. So the polling answer that "your gun would jam or a meteor would hit you" sounds ridiculous, but it is in fact the most plausible, as something must have happened to not allow you to kill you grandfather, or you just plain wouldn't have existed in the first place to go back and kill him.

Darkblade

I voted for five, but I agree with Godless Dave on some level, in that it must have been that way at some time, unless I am to believe in infinite regress or the Many Worlds Theory.

Ronin

Not to be a showoff or anything...but I just *actually* did go back in time and murdered my grandfathers and I'm

managalar

Everett interpetation of Quantum Mechanics...

http://www.hedweb.com/everett/everett.htm


I've seen single particle interference in the lab. Trying visualize a particle which can interfear with other particles (like waves on the water) is kind of tricky (unless you get the wave motion from the quantum irregularities in space its self ie. virtual particles or quantum foam or whatever the buzzword is). BUT, its even harder to imagine each particle (or photon) interfering with nothing and still getting the wave pattern, and that's what happens.

If our particle has a 50-50 chance of going through one of 2 slits, we'll get a nice interference pattern. If we know what slit it goes through, there will be a shadow pattern behind the slits, and no interference.

Many Worlds makes this problem simple, everything that can happen does, and while its not detected (wave function collapsed in the jargon) every way it could be is connected...This is what quantum computers take advantage of, this is how they work. Current quantum storage devices are comprised of only a few qubits, but a 100 qubit quantum storage device could store more distinct intergers than there are atoms in our universe, and a qubit can be something as simple as a single atom.

I'd have to say there is pretty decent evidence that the grandfather paradox isn't a paradox. You may figure out some way to travel back in time (though I would bet you'd have to be transfered as information and re-constructed, beam me back scottie) but I suspect you'll never make it back to your 'own' time....

Mageth

My answer: "I don't know."

My best guesses are either the many-worlds solution or something along the lines of what xeren said (and what tron mentioned, as well, when he said "whatever you do in the past will turn out to have been what happened all along." In other words, there can be no paradoxes - what happened in the past, happened in the past.