Qauntum theory says time travel possible!

[child of Thor]

http://news.bbc.co.uk/1/hi/sci/tech/4097258.stm

"If we don't know your father is alive right now - if there is only a 90% chance that he is alive right now, then there is a chance that you can go back and kill him.
"But if you know he is alive, there is no chance you can kill him."

In other words, even if you take a trip back in time with the specific intention of killing your father, so long as you know he is happily sitting in his chair when you leave him in the present, you can be sure that something will prevent you from murdering him in the past. It is as if it has already happened.

"You go back to kill your father, but you'd arrive after he'd left the room, you wouldn't find him, or you'd change your mind," said Professor Greenberger.

"You wouldn't be able to kill him because the very fact that he is alive today is going to conspire against you so that you'll never end up taking that path leads you to killing him."


what the heck?

[DeathByTheSword]

nice...but sounds a little bit like the grandpa paradox...if you go back to kill your grandpa when he was a child you wouldnt exist and so you couldnt come back to kill him so it never happened...it is essentially the same...but here is states you can go back but what ever will happen or you want to happen your grandpa doesnt get killed...

[Starchild]

So time travel is possible but because we know the present, we can only choose paths in the past that lead to the present as we know it. Makes sense. You can go back in time but you can't kill your father because, obviously, your father was never killed in the past.

You can swim in the river of time but you can't change the flow.

[DeathByTheSword]

Originally posted by Starchild
So time travel is possible but because we know the present, we can only choose paths in the past that lead to the present as we know it. Makes sense. You can go back in time but you can't kill your father because, obviously, your father was never killed in the past.

You can swim in the river of time but you can't change the flow.

well isnt it then like: you do change it at the moment in the past...but that results in the flow we know today...

this would make looking at the building of the pyrimedis and stuff fun

[OzzyKP]

But wouldn't anything you do in the past change things in some minor way?

Chaos theory and all.

[DeathByTheSword]

yes but this saids it was ment to be changed

[OzzyKP]

My brain is melting.

[Flandrien]

Originally posted by Starchild
You can swim in the river of time but you can't change the flow.

But you can choose the flow.
If you kill your (grand)father, you choose the flow where your (grand)father does not exist.
In other words, you do not change future, but end up in a different flow of future yourself.

[child of Thor]

Originally posted by Starchild
So time travel is possible but because we know the present, we can only choose paths in the past that lead to the present as we know it. Makes sense. You can go back in time but you can't kill your father because, obviously, your father was never killed in the past.

You can swim in the river of time but you can't change the flow.

It was the bit about if your not 100% about a particular thing in the present then you would have a chance to change it in the past.

So if say i never met my father, but thought he 'might' be alive(like i heard a family rumour he was last heard of x years ago and seemed fine), then by going back in time i'd have a chance of killing him as opposed to me seeing him on the porch and then trying to go back and kill him........

I dont like it.

Or i could be suffering from brain-drain as i tried to get my head around it the first time? and have missed something

[reds4ever]

It all still sounds a bit 'woolly' to me.

[child of Thor]

Yeah -like why isn't our world full of timetravellers who cant change anything?

[Japher]

Well, their mere existence in the past would cause some sort of ripple effect, and since we can't cognitively choose to change things we know already happened time travel can't exist because we chose it not to exist based on those things we already know to be true...

BS

[OzzyKP]

I think though what the theory is suggesting is that we can't change something in the past because it has already been changed, and we are living in that timeline. Perhaps our world IS full of time travelers, and the things we learn about in history class are all the result of time traveler meddling.

Of course that still creates a paradox. If a time traveler changed the past and created our world as it is today, then the original timeline that time traveler came from would be altered. And if they could do it, so could we.

[Japher]

Have you ever seen "Sliders"?

That, or it could all be relative to the viewer. While we accept the change as something that always has been perhapse the time traveler perceives it as something new.

So, per the OP, while we think that the father was always murdered at that time the person performing the act did not. Them wanting to go back and kill their father was caused by the father not already having died.

So, yes, a paradox if we assume that only one time line can exist. However, string theory suggests many dimensions, and the most excellent television show "Sliders" suggests that the number is infinite.