What current theory is there on time travel? I thought there were several.

lolwikipedia

I did see some grafitti the other day that was funny and on topic. It read,

"Interested in time travel? Meet me here last Thursday"

Maybe we're just not thinking with portals?

One piece of advice: don't go near the black hole. It won't send you back in time, it'll rip you in half when you get close enough.

Lol there was a time-travelers' convention at MIT in the 90s I think, when they were publicizing it they asked people to put adverts for it on acid-free paper in libraries everywhere. They gave the exact latitude and longitude. They said, "the great thing about a time-travelers' convention, is that you only need one!"

No one showed. Lol.

Don't worry too much about ‘the current theory’ of time travel. This wormhole/portal business is just the closest way that people have thought of to build a time machine using only physics that we know is real. But 100 (even 50, I think, but certainly 100) years ago nobody had thought of this method, and there may be a new idea in another 50 or 100 years or so. It would be different if there were a clear argument that any other way necessarily would violate known physics, but there is not.

Also, even with the wormhole method, it's always possible that some extraterrestrial civilisation has already built a network of portals that you can catch a ride on someday, to go wherever you wish. (But the wormhole method does not allow you to change history.)

man baseless supposition is awesome

The best proof that backward timetravelling is and will be impossible is that i (and supposedly we, mankind) never ran into a person from the future ...

I would prefer to assume that backwards time travel is entirely impossible. Otherwise, what happens if I travel back in time and kill the inventor of the time machine, before he invented it? Or what if I go back in time and kill one of my parents, before I was born?

Or what if I go back in time to 50 years before god was created?

Jamiet: en.wikipedia.org/wiki/Compossibility

Theory with 2 facts: you can change the past, the physical ability. And at the same time you cannot change the past, a logical statement and restriction since it occurrred already.

The link explains better.

This appears to be about possible worlds as they exist in God's mind. I don't believe in God.

Travelling into the future is, of course, very easy.

I do it all the time.

You beat me to the punch Jamie.

Here is an on topic comic from xkcd.com:

http://xkcd.com/630/

You can travel into the future today by going across the international date line

Backwards time travel could be possible even though we've encountered no time travelers. What if the time travelers disguise themselves, or no one believes them? Maybe there's some huge negative effect of backwards time travel, which prevents all but a few people from traveling back, who we haven't noticed. Maybe going back in time actually sends you to an alternate universe, identical to the original, except that time travelers appeared there. The fact that we haven't seen time travelers may be evidence against it, but it certainly doesn't disprove time travel.

The very act of traveling back would change the the past. Which would mean you would not go back in time the first place, or at least not precisely the same place and time. Which would mean you would not go back in time the first place or not the same place and time.

Changing the past wouldn't necessarily prevent you from going back in time. If I go to the past, look around without anyone seeing me, and then return, then nothing really changed that much in the past, at least nothing that would necessarily stop me from taking that trip.

That should be, going back in time wouldn't necessarily cause a paradox.

well.. if you think as time as a function.. so time would be described as the x axis and space as the Y then time always flows from left to right (or visa versa however you want to look at it) but if time flowed forward then backwards (like 1/(x^2)) that is NOT a function and therefore can only exist in theory and never in reality.. and that Einstien baby

also.. there is a universal LAW that states that matter can not be CREATED nor destryod.. so if you went back in time to a point where you already existed.. then there would be two of you.. and if there are two of you that means you copyd or created new atoms to create the new you which cant happen.. the closest we will ever get to time travel.. is teleportation which we are able to achieve via entangled particals. ( we were able to transport a few hydrogen atoms across a room during a lab experiment a while a go)

@ zuzak I was not saying it necessary would, but it might. But being there even for a picosecand, would change the universe at least in some small way. That might effect any traveling you do, or did in someway such as going back at secand later, or with a meter displacement etc. The butterfly affect.

Matter can be converted to energy or visa versa. Entanglement is not true transport but is closer to duplication.

Personaly I like the multiverse ideal. Every option even at the quantium level creates a new universe.

Yes, parallel universe's seem to be an easier option to accept.

@saf d e a t h:re:conservation of matter.

Yes, however that conservation law only applies locally, you can change the amount of matter in a space by moving some into or out of it. You may similarily be able to change the amount of matter in a time by moving it in or out of that time.

Also moving, that's an english word, in physics it implicitally means something which is not stationary, ie it has a location in space which is changing as time changes. Therefore moving in time implies something which has a position in time which changes with time? Ok, well no since we do find particles which travel back in time there is some meaning to 'moving in time' but in physics it's not what people think about it...

Especially regarding conservation of matter/energy, in physics it is possible for two particles to spontaneously appear, move apart (in space) and the collide dissappearing again (this actually violates conservation of energy, but only for a short time; and heisenberg said it was ok.) Now it came be considered a closed time loop.

One particle moves forward in time turns around goes back in time and then turns back again. It doesn't repeat this cycle again and again, cause there is only two particles at any given point in time, always one moving forward in time and one moving backwards. (and none before and after the creation/destruction event)

I'm not sure if the turning around bit though... most particles don't seem to turn around in time... or turn around at all without good reason. hmm. I think that's right, look up vitrual particles or ask a better physcist.

but in conclusion, I don't know if conservation of matter is applicable to time travel considerations... in the very least it seems closed time loops are possible, (which doesn't mean you can go back in time, just that you can be a thing for which time is a closed loop.)

"The best proof that backward timetravelling is and will be impossible is that i (and supposedly we, mankind) never ran into a person from the future ..."

Maybe the future history books say life sucked in our era.

... But what about the superb owl?

Or maybe the rule about only travelling as far back as the creation of the time machine applies.

Too many blocks of text.
@jamiet99uk's very old comment.
That's called the grandfather paradox, where you kill yor grandfather so technically you don't exist, but you do.

@everyone: time traveling is suicide, suicide is illegal, and by the x=z theorem time travellng is illegal. And don't cheat in the lottery!

Lol at futurama

Let's say theoretically time travel is possible. I highly believe it is a bunch of bogus. When traveling in time would it not also affect the person traveling in time. (If this person traveled back 20 years he would be 20 years younger than he was when he traveled in time.) This would make time travel only available for a certain amount of time. This would also eliminate the grandfather paradox because, obviously, you wouldn't have been born yet.

One reason why I think time travel is a bunch of bogus is this point. When a person does travel in time wouldn't the rest of the universe's molecules have to dematerialize and reconstruct to configure what it would be in the past or present. This would in fact be impossible because a time machine could not stretch such limits or hold such capacity.

I don't know much about the time travel theory but that's just my opinion from my own simple observations.

but because the of the theory of relativity, the person in spaced aged more, so the effects of youth were reversed.

Someone correct me if I picked that up wrong, but since everyone is BSing off the top of their heads anyway, I'm in.

and in that case, going back in time is like replay. you don't even remember anything. which, just causes restarting the instantaneous universal frame.

Who knows? it could've just happened right now. or now. or 7 seconds ago. or 7 seconds in the future.

@redcrane: kinda...
@ZaZaMaRa: no, i think in a way, if time-travel is possible moving baackwards in time means the universe going back to an earlier configuration, just as moving forward in time results in the universe changing to a new configuration. so it don't think it is beyond the universe, at least acording to the laws of physics...

the only problem is the grandfather paradox, ie doing somethign which would prevent you from going back in time. It is not strictly forbidden by the laws of physics, which don't include causality, thouhg locality may imply some kind of causality... hmm.

@ag: the superb owl is a great idea.

Drifting through time passage.

to time travel, you must first answer some questions. does every chose cause a different parallel universe? is so, then the grandfather paradox cant happen, because a separate parallel universe would be created, where you do not exist. or does time flow like a river, never changing. in that case going back in time becomes impossible, but going forward is still possible.