Here's my problem with time travel.

yes you are correct in both. [quote]You have a water molecule in your body . A year from now that very same molecule is in the ocean. If go a year into the future will that molecule not be in two different places at the same time ??[/quote] this problem is widely known as paradox. paradox always happens what ever you do in past by time travel. Perhaps you would have heard grandfather paradox.If not [url=http://en.wikipedia.org/wiki/Grandfather_paradox]Do check it out.[/url]

Intervene Thanks for posting. so is time travel a real possibility then ?

I agree with what Intervene posted about the grandfather paradox. Take a closer look at the parallel universe section because this is how the problem is "solved". Lots of physicists today suggest that evidence supports a "multi-verse" existing and in such you can time travel because you are jumping between universes, so not changing the history from your own universe but joining one of the infinite other universes that exist.

So you are not travelling through time you are just going to a universe where ."you" already existed. So what meganism would you use acces this universe ??

Yeah sort of. You could travel into a time in that universe where you haven't been born yet and say accidentally change the events that led to your grandparents not meeting and so your parents don't meet etc etc and you then aren't born. In that universe "you" technically never existed but you do because you as such aren't from that specific universe. Some people say that wormholes could allow you to travel into these other universes. I'm not 100% sure on this because I don't have a doctorate in physics or anything lol but I get the idea from some books that I've read that seem to suggest that wormholes are probably the most likely way of travelling between universes.

It's an interesting topic. At the end of the day all of it is just in theory though. However the paradox you're talking about is not a paradox at all if everything happens at the same time. So if this is true then your body molecules are existing at any possible position on the time line (or lines if multiuniverses exist) at the same moment anyway. So actually there is no "timeline" then.

timetravel for me, works like that: You live in universe A in 2100. Somehow timetravel is possible (you would need almost infinite energy, like a black hole kind of energy). You travel 50 years back. Thanks for the black hole energy, you emerge in a new dimension, that is exactly like universe A 50 years back. We will called it, universe B. In universe B, you decide to kill your father (shame on you), so you cant be born. But that, doesnt effect universe A. In universe A your father still live, and the only record of you in universe A, it's that you left (or disapear ) the universe A in 2100. Everything you do or not do, will only effect universe B. Let's now imagine that you dont kill your father, better, you dont interfeer with your famely at all. So it will be high possibility that a person like you, who comes from universe A, will be born in universe B. He can even replicate the experimente in 50 years, so he can travel 50 years back in universe C. But it will never be you. Becouse John from Universe A is not John from universe B, and C. So John from universe A can live pacefuly with John from universe B, both in universe B. (So everytime you travelback in time, you create alternate universe)

[i]http://cdn2.sbnation.com/imported_assets/1223629/stone-cold-laughing.gif[/i]

According to Stephen Hawking, time travel into the past is impossible because it "violates a fundamental rule that cause comes before effect." (Source: http://www.foxnews.com/scitech/2010/05/03/time-travel-possible-says-stephen-hawking/). This makes sense to me. If there is anyone that could be considered an "authority" on time travel, it would be Stephen Hawking. As far as time travel into the future, that is in fact possible and has already happened. Our satellites do it every day, albeit by extremely tiny fractions of seconds. There is a cosmonaut who spent so much time up in space orbiting the Earth that time passed slow enough for him relative to everyone else on Earth that he effectively "traveled into the future" by about .02 seconds. It's not much, but it's something. (Source: http://www.huffingtonpost.co.uk/2013/10/23/sergei-krikalev-time-travel_n_4147793.html)

This was quite the conversation. Allow me to re-read these comments a few times so I can hopefully add something constructive :).

Apparently, in a well known bet, Stephen Hawking was unsuccessful at disproving Kip Thorne's theories on wormholes and owed Kip a year's subscription to Penthouse magazine.

1. Why would it be in two places at the same time?.. I presume your meaning is that, [if you don't go anywhen], a year from when you are, you would expect the molecule to be in the ocean, for example. That would be reasonable. However, if you Sci-fi Time-travel a year into the future, your molecule will go with you - so, a year into the future, the molecule will not be in the ocean as you would have predicted it to be, while in your past - it will be in you: and not in any other place, at the same time. For that reason, you could say, from one perspective, that you would have/will have changed what you could call the molecule's destiny - along with your own. Or, from another perspective, you could as equally say that you will have, "changed", absolutely not one thing, at all - as it was *always* the molecule's destiny to Time-travel along with you, one year into the future; and be, then, not in the ocean - but, in you.. There is no paradox. 2. Yes.