General Relavitiy, P-branes, and time travel.

[QuantumTheory]

OK, I made another post on this, being too sure of myself that I knew this the answers. This is the wrong thing to do on a forum when everyone else knows more than you

So, I'll try to make it more reasonable this time.

Doesn't general relativity allow the *theortical* possibility of time travel? I'm not saying it's practical, in fact, some people say the paradoxes (grandfather's paradox, etc) prove that you can not go back into time, or change the past, etc.

I was just surprised when everyone responded and was so sure it wasn't even theortically possible. Now, don't quote me on this, but I've read several laymans books, (" A brief history of time" by stephen hawking was one) since I don't understand the complicated calculus/physics behind the textbooks. Now, I'm pretty sure he said it's theorticall possible, right?

I've always been fasinated by time travel, I know it's probably just a dream, but I know we have so much more to find about the world, so I'm trying to be optimistic here. I mean, look how far we've come in 50 years...
Now space tourism is emerging!


OK, here's why I think the laws of physics may allow it:
Don't some theorties support it? I thought general relativity did? I forgot exactly how (It's been awhile since I've read those books, (^^;;) but I was pretty sure GR was a theory that instead of gravity being an unknown force, gravity was a force that bends spacetime. Therefore, a nearby object in space (a large body, planet, etc) and when a smaller object comes, it will circle around the other planets gravitational field. This is why planets orbit, right?

Also, I heard of something in quantum physics like B-Branes or something, that may allow it to be pratical.

I just want to know why everyone here disapproves of it even being a theortical possibility (which I realize is different than being practicail), since I've read about it qutie a bit, and have gotten quite difference answers, but would like some honest answers from a scientific community.

Thank you :)

 

[Aether]

So, I'll try to make it more reasonable this time.

Here's what would be more reasonable: go to www.arxiv.org and find a scientific paper that teaches something about any scientific topic whatsoever that you are interested in, put in some effort to learn something concrete about the subject, and then come back for a chat about it.

Papers at www.arxiv.org aren't always as solid as papers published in a peer reviewed journal, or a textbook, but they are easily accessible.

 

[Tarheel]

Here's some stuff I found...

Last year Mallett published a paper in Physics Letters describing how a circulating laser beam creates a vortex in space within its circle. The bent laser light actually causes space to whirl around like a twister within the circle.

Mallett deduced that, if he adds a second laser beam shining in the opposite direction and increases its intensity enough, he can warp time into a loop. Unfortunately, once again the energy required is out of reach.

Then he saw an answer. His equations show the slower the light moves within the laser circle, the more space and time distort. Bingo. He can get the needed energy from slow-moving light. The whole crazy notion suddenly became maybe, just maybe, feasible.

In February 1999, Lene Hua and a team at Rowland Institute for Science succeeded slowing light to 38 miles per hour-a galloping zebra goes faster. Mallett plans to use their results in his experiment.

http://www.wonderquest.com/TimeTravel.htm

Light, which normally travels the 240,000 miles from the Moon to Earth in less than two seconds(186,282 miles a second), has been slowed to the speed of a minivan in rush-hour traffic -- 38 miles an hour.

http://www.news.harvard.edu/gazette/1999/02.18/light.html
Interesting...

 

[Ivan Seeking]

My best understanding is that there are solutions to the equations of General Relativity that appear to allow for time travel, however, practical considerations as well as deeper complications may render time travel impossible. At this time there is no consensus among physicists what the correct answer to all of this may be, but the nay crowd seems to have a larger population than the yay crowd. My opinion is that without a unified theory this is all speculation at best. For all that we know, we may not have even identified all of variables needed for such a theory.

If any Mentors wish to correct or modify [add to] this statement, please go ahead. If any of our physics gurus wish to comment, please send me a PM. I am closing this to prevent inappropriate speculation.

Finally, if you want to learn physics, go to school. If you want to explore these issues as a hobby, don't expect to understand them.

Edit: Oh yes, as I understand things, Mallet used linearized equations for a non-linear field. In other words, he screwed up and used the wrong equations. That's why his time machine - really a "time-telephone" - won't work.