Time travel is impossible because that would mean that the whole universe would have to be taken back to where it was before the present. Did you get that? The whole universe would have to be moved back to where it was to get back to where things were that were where they would have been. Also going back in time would mean people would have untaken dumps and uneaten food. Did you get that? The waste would have gone back into your body and then out of your mouth and became the food that you were about to eat. The idea of time travel is so far fetched in that people forget about the earth circling the sun and the sun moving around in the galaxy. Did you get that? The position of earth would have to go back a very long way to get to where it was when the time that you wanted to travel to would have been taking place at. That means somehow everything would have reversed path in the universe and thus gone back to where it was and then started back on the path it was going to take. I think people think that they can go back in time like you can go backwards on a video tape or other things that allow you to skip ahead or to rewind.
I heard someone say time travel is impossible since time is the invention of man and not found naturally. It is like we gave names to people in that people don't come with names in that people have to give babies names.
Time travel is impossible
You're doing it right now.
I thought our notion of time was just the measure of movement
No, Einstein demonstrated that time and space are intimately connected. Time dilatation with velocity also applies to distance. But, you will find that the rate of time at the top of a tower is different than at its bottom. There is no movement involved just the distance from the earth.
if one is infinite then the other must also be... no?
This is true but the question is, "Is The Universe Infinite?”.
The question of an infinite universe was fully explored in one paradox, Obler's Paradox. (see http://en.wikipedia.org/wiki/Olbers'_paradox ) What holds for stars, holds for galaxies and any glowing matter; even matter at or slightly greater than 3 degrees Kelvin. By the fact that the night sky is dark, the universe must be finite. So, while space and time are coupled, the universe is finite.
The real question that is the problem is the granularity of space-time. It is known that we can perceive time as what we can measure. Thus we time as we use clocks; the time from day to day; hunger and thirst; a big ben; or a Cesium Fountain ( good for 10^-15 sec). But, is there a limit to that precision? The answer is the Plank Length 1.616252(81)×10^-35. Therefore, space-time is related to our models of space-time itself. Currently theorists are into string theory. Hawking's book settles on M-theory or Brain theory; membranes, multiple ones are twisted in 11 dimensions. This model is typified by the mathematics of the Calabi-Yau manifold (there's a little picture of it here http://en.wikipedia.org/wiki/Calabi%E2%80%93Yau_manifold ) Where these membranes touch, once in a while, there is a big bang and a universes like ours is the result. So, while space and time are coupled, the universe is finite once again.
Please remember that these theories are formalizations of what we know to explain what we see. As new research is done all of the above can change. But, even with those changes, the model explains all of the data. Nothing is ignored for convenience. This is pure science as there is possibly little technology that will come from it. At the same time, the search for the famous Unified Theory, the continuous explanation of General Relativity and Quantum Mechanics, has not come forward. The research has taken place over two people’s life-times and will most likely take many more life-times. The Unified Theory has been delayed a bit.
Currently theorists are into string theory. Hawking's book settles on M-theory or Brain theory; membranes, multiple ones are twisted in 11 dimensions. [Post #15]
I presume you mean “M-theory or Brane theory”, unless someone is trying to tie string theory to brains and consciousness – a conjecture I’d be happy to entertain … and have speculated on …
The Unified Theory has been delayed a bit.
Any prognosis on when we might expect the definitive answer? Any thoughts on how close we are to realizing on those Dreams of a Final Theory? I see that Wikipedia notes the following about Dr. Hawking’s perspective on the topic (which he may have changed in his more recent hypothesizing and conjecturing):
Stephen Hawking was originally a believer in the Theory of Everything but, after considering Gödel's Theorem, concluded that one was not obtainable:
“Some people will be very disappointed if there is not an ultimate theory that can be formulated as a finite number of principles. I used to belong to that camp, but I have changed my mind.” — Gödel and the end of physics, July 20, 2002
Though I really do have to admit to some “perplexity” (at least) regarding that theorem. From what I’ve been able to understand of and follow in that theory (not a lot, unfortunately) the most that it says is that there is at least one theorem that cannot be proven in any formal system of logic: not sure that it necessarily follows that there is more than one … which, of course, may be sufficient to limit one's faith in such ...
ever increasing complexity and size (infinite)
Really, really large is not infinite.
I presume you mean “M-theory or Brane theory”
You presume correctly. My brain can't hold even a small one.