first, don't necessarily denote time as linear....please visit the "infinity" thread....

anywho, it is in my thoughts that physical existence is linear.....metaphysical existence is circular....

thus, it could be possible to travel in time through some sort of metaphysical sense....as seems evident with QUOTE-UN-QUOTE past lives or seeing into the future (such as Nostradamus....or what have you).....even "deja-vu" would be an example of this.....

i do not believe in time travel, specifically when related to physical existence......if i'm not mistaken, scientists thought that "black holes" could prove to be a source of time travel....yet, just this year Stephen Hawking announced that his theory of time travel via the black hole now seems improbable, as the theory of black holes as they understood it (something with such a graviational force that nothing can escape it) proved to be false, and now they suspect that the black holes actually spit forth some matter out into space....

anywho....there's a couple of lil' problems you didn't think thoroughly through....for starters, you couldn't really go into the past....at least, not beyond the point prior to the time machine being built......

also, the only thhing that "exists" isn't now......you didn't clarify these terms.....you should have said, the only that exists when concerning linear time is now....but even then, thatz incorrect, as the past exists just the same.....although we are within the now, that doesn't mean yesterday didn't exist......and although there isn't a full 100% chance that tomorrow will come, it is still a high enough probability (99.9999999999%) that it will, so it exists just the same....

i believe it was Hume who mentioned some of this....i'm not 100% sure, but i think it was Hume.....he sort of touched on the theory of destiny, which he also spoke briefely about time (in a round about way)......he basically explained it as a sort of reverse-destiny...

take a choice...say, going to work.....you have the choice to go to work or not go to work....right?

wrong......granted free-will seeminly does exist (and i'm not quite sure whether Hume believed in free-will or not, but i think he did) it was in his theory that whatever choice you make you couldn't have done the other......if you go to work, then you go to work.....you never had the choice to not go to work, becasue you went to work.....if you didn't go to work, you didn't go to work....you never had the choice to go to work, because you didn't go to work...

i know it sounds rather confusing, but he explains it a lot better than i can.....anywho, to get to the point, he also touched somewhat on time....and the best analogy i can use, is when you're in a car...

you're in a car, going down the highway.....the past, is the road behind you, the present is where you're physically at at the present moment, and the future is the car in front of you......all three exist, yet you seem stationed in the present.....however, itz almost a trick....as you know that at some point in time you will be where the car is at in front of you, and then at some point in time that spot will be behind you.....all three do exist....