The post are starting to repeat themselves.
DaddyMack -
Actually, observation dictates this - there is no reason according to maths why time cannot run backwards. The fact that time is never observed to run backwards presents a very real dilemma in theoretical physics.
the earth is moving at 1000 miles per minute due to orbiting around the sun. the sun is orbiting around the center of the galaxy. where was the earth one week ago? a time machine would have to compensate for all of these velocity vectors.
NOW is the position and vector of every particle in the universe. the past does not exist there is nothing to go back to. the universe cannot be rewound. travel into the future via hybernation or relativistic velocities is possible but there would be no coming back.
Dal Timgar
Mathematics says is should be possible.
I think you missed the notion of space-time.
“Time” is a system of measure. How do you “travel” through a measurement!?!!
The concepts of “past” and “future” are simply human creations to refer to memories and projections. Useful for mutual communication… Don’t make the mistake that creating a word for a human-fabricated concept causes it to become anything.
Empirically speaking, throwing out theories on the subject (just theories after all), observation certainly proves that the science-FICTION idea of “time travel” (into the past at least) isn’t possible.
Randy
PS: If you want to travel into the “future”, simply kill yourself. Then you won’t exist either! (Hmm… Maybe I should start a cult… Everyone who wants to join me in the future, buy life insurance to benefit me and drink this…)
Thought of something else–the Law of Conservation of Mass prevents such!
The science-fiction idea of time travel suggests you can remove mass from existance which we know is NOT possible. This was an accepted law before Einsteins theory was developed actually…
Randy
PS: Fictionally it would make a great weapon though… “Time travel” the earth a moment ealier or later and the doubled mass would throw us out of orbit! Hehe… Time travel… Haha…
No - the idea is simply about moving mass through space. We know that is possible. It’s moving it in a particular space-time orientation that is the issue.
Sorry everyone. It’s actualy called a Tipler Cylinder not a Kepler. Proposed by physicist Frank Tipler.
Whoops.
Oh god, not Tipler again.
That man couldn’t calculate his way out of a paper bag.
First, we need to agree what we are going to call “time travel”. In this post, by time travel I understand being able to travel on a closed loop in space-time. I.e. take a sheet of paper and let one direction on that sheet be space and the other time. If you were to plot your history with a pen, that would be a line that advances mostly in the direction of time. By “time travel” I understand the question: can I cook up an scenario where that line of my history comes back to intersect itself?
Now for the answers. The “time travel” question is a question about the possibility of specific geometries for space-time. General relativity relates the geometry of space-time with the distribution of matter-energy, so it looks like a good place to ask this question. However, General Relativity by itself can’t answer it, because it is not a theory of the matter that exists or can be created in our Universe.
Let me try to clarify this. General Relativity is a theory that relates the matter and energy with the bending of space and time. The classical analogy is to think of stars and planets (and elephants and apples) as marbles on a sheet. By the very presence of the marbles, the sheet bends, and that bending is felt by the rest of the marbles.
General Relativity is expressed by Einstein equations, which morally read:
Geometry of space-time <—> Distribution of matter and energy.
Normally, we think about this equation in the direction matter–>geometry, i.e. given a star this big and rotating this fast, how does it affect the geometry. However, you can turn things around, and ask, if I want the geometry of space-time to have such and such properties, what distribution of matter do I need to cook up?
In particular, you can construct geometries that do allow for “time travel”, and a number of them have appeared in the literature (Goedel universes, Gott time machine…), but the price you have to pay is typically that the matter that would create them has weird properties.
Of course, the next question is whether that matter exists in our Universe or could be created by some technology yet to be discovered. The short answer is that we don’t quite know, but at least in the examples we have the answer seems to be no. A commonly held view is that once you take into account Quantum Mechanics, it will provide a universal mechanism preventing the
existence of “time travel”. However, we don’t yet understand our best current candidate for a theory of quantum gravity, superstring theory, to the point of showing that it rules out time travel.
For what is worth, from a physical point of view, I find the idea of time travel repugnant, and I hope we will eventually understand that it is not possible. Not that it wouldn’t be cool.