New model 'permits time travel'

[Dover]

New model 'permits time travel'

By Julianna Kettlewell
BBC News science reporter



If you went back in time and met your teenage parents, you could not split them up and prevent your birth - even if you wanted to, a new quantum model has stated.

Researchers speculate that time travel can occur within a kind of feedback loop where backwards movement is possible, but only in a way that is "complementary" to the present.

In other words, you can pop back in time and have a look around, but you cannot do anything that will alter the present you left behind.

The new model, which uses the laws of quantum mechanics, gets rid of the famous paradox surrounding time travel.

Paradox explained

Although the laws of physics seem to permit temporal gymnastics, the concept is laden with uncomfortable contradictions.

The main headache stems from the idea that if you went back in time you could, theoretically, do something to change the present; and that possibility messes up the whole theory of time travel.

Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious.

So either time travel is not possible, or something is actually acting to prevent any backward movement from changing the present.

..cont'd

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

[mcscajun]

1. Oh good. I can stop having those headaches now...

...the ones I get whenever I consider temporal mechanics.

:)

[Dufaeth]

2. Hmph.

"Clearly, the present never is changed by mischievous time-travelers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious."

This article lost my interest right there. That is an illogical statement, because if people were removed from existence they would disappear from every aspect and we wouldn't notice them "fade" away anyway.

[Massacure]

5. Have you seen the Terminator?

Wouldn't this be similar to that movie? Theoretically the future is already based on the fact that you tried to alter the past. Therefore, you cannot alter anything further as you already have...

[Jon_da_brockman]

3. Obvious?

Come on, EVERYONE knows that you can not have a paradox, cause it would have already happened.

DUH!!!!

[bemildred]

4. There is no paradox. It's just like self-modifying code.

It goes back and changes itself.
(It is very tricky to understand though.)

[Celebration]

6. The first Superman movie

Does anyone remember it? Chirstopher Reeve and Margot Kidder. Lois Lane died I think. Superman had the power to change the outcome by going back in time and changing the events. He had been warned A LOT not to do that-- the consequences would be terrible-- I forget how the warning was conveyed. He did it anyway. There were no consequences in the movie. It always bugged me about that movie. Of course in real life the two costars didn't have stellar "luck." I don't even remember anyone discussing that odd part of the movie at the time, or later.

[hecate77]

7. If someone went back and changed the past, you would never know it

Sorry, but if someone went back and did change the past, you would not see people disappear off the street. You would always live in a consistent present with a consistent set of memories. That it might change dramatically from one moment to another would not be part of your awareness (as measured in some super frame that was independant of the changes - assuming such even existed).

Thus a change in the past could not be measured in the present. You would never know that anything had changed. Your past would change to reflect the new past, including all memories and records.

That doesn't mean that what you are suggesting isn't true (that the past cannot be changed), but just that the lack of noticing changes is not proof of it. (from your statement - Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious.)

[bmbmd]

8. it's like unravelling a sweater

that someone keeps on knitting and knitting and knitting and knitting and knitting.......

[trotsky]

9. This model also assumes only one timeline.

From what I've heard, some physicists think that every possible quantum event ends up splitting into two universes, one where it happened and one where it didn't. You could indeed go back in time, kill your grandfather, and thus put yourself into a timeline where you never existed. However, you DO exist, because there is an alternate timeline where you did not kill your grandfather.

[jokerman93]

10. Nonsense

The Vulcan High Command has determined that time travel is impossible.

J

[anarch]

11. I myself am able to travel through time...

but only in the one direction.

[bemildred]

12. Yeah, the speed control really is lacking too, and no brakes. nt