h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

But your argument doesn't preclude being able to invent a machine which moves you *forward* in time...

Of course you can invent a machine which moves you forward in time. It's called a "near-light-speed space ship." Or, for that matter, a "space station orbiting closely around a black hole." Going forward in time faster than usual is easy. It's going into the past which is a challenge.

So, you build the machine big enough to send everything forward in time *except* you...

Hopefully you all have not melted your brains and are still active in this discussion. A few points of thought:

1. How would you know there has not been any travellers from the future? If I travelled back there would be no way I would tell anybody not even back in time about it, just can't trust humans Would do there wat I want (or research..) and just come back

3.The multiverse exist, but is alot more complex that just parallel universes - it's called M-Theory.

4.You have free will, I can shoot the bloke at work whenever I want, but there are consequenses (obviously :D). Also remember that you are not alone in this universe, so there are loads of free-wills contesting for attention... The universe is much more complex than just the two possibilities of free will or not, you can have a free will while the other possibilities are still possible, almost like comparing the consept and possibilities of free will to multiple universes, all existing together.

2. Time Travel IS possible, just not propable. Timetravel is more complex than just zipping back in a little machine. If you take that time is the 4th dimension as mentioned by Einstein, then if you travel back in time you are moving along the 4d axis. The problem is then that in space 3d you are standing still while the earth and the solar system, actually the whole galaxy is moving, so even by just travelling back a few minutes you might end up anywhere in the galaxy (since the whole shebang is moving at great velocities)

So an effective time machine also have to be able to jump in space as well as in time. I think that is more difficult than time travel itself....

Fibonaccidragon the timetraveller ~-/\-/\---

A question that I have been carrying for a while, this seems the right place to put it down :

When a proton and an anti-proton bump into each other and "disappear" to the observer, leaving only the energy of the collision, isn't it actually a proton bumping into something (?) and bouncing back along the time dimension axis, then looking like an anti-proton to someone whose is (like we are) traveling in time in the opposite direction, but actually being a proton going backward in time ?

No, because in the case of a head-on collision, if the proton was "bouncing", the anti-proton going "back in time" would be superimposed on top of it rather than expressing itself in completely the opposite direction. In shallow-angle collisions I can see where you're coming from (or your anti-self is going to, delete as appropriate... )

Ok, here are my thoughts, one can take them or leave them...

On the possibility of time travel: I believe that it is possible, on the grounds of Einstein's Theory of Relativity. This theory manages to combine three space with one dimension of time to create a space-time continuum. Since space and time are equivalent, and one can move forwards, backwards, left, right, up and down in space, it follows that one could also do the same in time. However, since we cannot comprehend time travel (just think of all the paradoxes and problems it creates, if it were possible, it would not do this) it follows that humans are not capable of backwards time travel. Obviously, forward time travel is possible.

On multiverses and higher dimensions: Over the past year, I've become convinced that mulitverses and higher dimensions exist. It fits M- and string-theory rather well, and it provides a lot of answers. It negates the need for "luck" or "fate" since all possible outcomes DO occur. If we were able to travel to higher dimensions, it would make backwards time not only possible, but unavoidable (I believe, I wouldn't know how to explain that). It would also allow us to slip from one time stream to another, in between worlds. (Since multiverses are parallel in higher dimensions). Once again, our human limitations do not allow us to comprehend this, so somehow, we are not physically capable of doing this, though the possiblity exists.

On the particle-antiparticle theory: This was an actual quasi-theory of Dick Feynman who borrowed it from his mentor John Wheeler. He thought that an electron and a positron meeting and annihlating each other could be thought of as an electron that was moving forward in time, but then a photon or some other burst of energy causes it to move backwards in time. The world line for this event would look the same as the world line for a positron-electron meeting. This could also lead to the possiblity that there is only one electron in the entire universe (or multiverse, as the case may be), and it is simply moving forward and backward through time and space (since space and time are equivalent anyway).

Anyway, those are my thoughts, yeah, I kind of rambled on, but geez, what else do you get from a Physics major?

Neutrino

Peet : I don't see how the physical angle with which the particule and anti-particule seem to meet matters, as the bouncing motion I am mentionning happens on the time-axis, not on any of the 3 physical space axis...

And a slight angle might be the result on the whole trajectory of the intercepting object (photon ?).

Neutrino : you just made my day by adding a little structure to an idea I got a long time ago (back at school, actually), and never really dared mentionning, fearing it was really silly...

Cheers !
(or maybe "! sreehC", depending in which direction you are currently going...)

Connie, an object rebounding on the time axis and no other would just seem to "vanish", as the anti-particle travelling "backwards" would be superimposed on the particle travelling "forwards"...

If it rebounds off a vector which exists in space-time, you could get the illusion of an anti-particle approaching it in "space".

But, that doesn't work for the special case of an exact head-on collision. There's no "space" element of a space-time vector that can cause a "rebound" at zero degrees. A bounce off such a vector would result in the antiparticle returning along the original path, not carrying on in a straight line.

This "special case" is only special because it is a point where the theory breaks down, which in my mind casts a little doubt on the theory.

Hmmm...I just had a thought about this whole time travel thingie. It might be a bit irrational or strange, but then again, the whole thing is strange...anyways, here I go.

I believe that time travel is possible in theory, but for humans, it is not, since we cannot comprehend such a concept without creating paradoxes and the like. What this means is that we are creatures bound to the three dimensions of space, and only one direction of time. What if there existed creatures who were the opposite of us? They would exist only in the dimensions of time, and not at all in space (in other words, they would be bodiless). They could move wherever they wanted in time, but are restricted to moving only "forward" in space (in the same way we are restricted to only moving forward in time). Perhaps these are angels? I don't know, like I said, it is purely conjecture, but I think it's interesting.

Neutrino

interesting...

In Bali, most gardens have a little wall just in front of the main gate, to ward off evil, because evil spirits are said to only be able to move in straight lines... I thought this was a way to justify putting the wall there so neighbours would not peek in, and maybe even to throw stones or darts, but with the new input from your theory, that "evil spirits only walking straight" thing kind of makes sense...

So they'd be free in one (or several) time dimension(s), they could go back and forth whenver, but bound to one direction, one speed... (more probably orbital than straight line, if you don't want them all to eave the Earth too early).

Perhaps this could be an explanation for the phenomena of ghosts as well...human souls, having left their body, cannot move around in space, only in time. However, since we are human and cannot comprehend time travel (as I explained above), they can only exist in forward-moving time, and hence, "haunt" the place where they formerly lived.

Of course, I don't take much of this seriously, I'm just speculating. I'm a scientist through and through, so no funny business for me. Ya gotta prove it first. But it's still fun to speculate...

Neutrino

I understand your objection to the "antiprotons are protons moving backwards in time" theory, Peet, but I think I can explain why it's spurious. Let's consider a minor addition to this theory whcih states that when world-lines of the forward-traveling proton and the backward-traveling proton get within a certain distance (say, the diameter of a proton), they "bounce" and emit a photon into the future. The importance of this addition is that the protons are no longer treated as point masses, and the Pauli exclusion principle is accounted for. So, with this variation, the spacial angle could never be zero; were it, the particles would have anihalted one another in the infinite past, which makes no sense.

Hmmm. PhysicsMan, I don't think I was ever considering them as point masses; if that were the case the chances of a collision would be infinitely small, so for all (im)practical purposes would never happen...

Neutrino, your "Ghosts travel in time but not in space" theory is flawed, for the reason mentioned a few posts back - the Earth is moving round the Sun, and the Sun is orbiting the gravitational centre of the galaxy. The galaxy is so large it's impossible for anywhere on the earth to have ever occupied the same point in space more than once; any given rock will have been following this orbital spiral since it firat coalesced. A ghost appearing in a room where it formerly lived must not only be able to travel in space, but quickly (and accurately! ) in order to keep up with its corporeal surroundings.

That's true, I never thought of that...but it was a neat theory while it lasted, right?

That's true, I never thought of that...but it was a neat theory while it lasted, right? And anyways, if you only exist in time, you would "be" at all spaces at the same time, so a ghost couldn't possibly only exist in time. Nor could they only exist in space, since they would have always existed. Perhaps it's a combination of the two that makes it all work out, but is still different from normal human space-time. Of course, that's just idle speculation, but whatever...

You're right about our body

The most far fetched scientific hypothesis is roughly said that you would have to abandon you body first, secondly, your thoughts should be replanted in the energy/vibrations/etc. of an particle/wave. Then someone/-thing should find a way of interacting this particle/wave to anything connected in another dimention/time, transfering 'you'. Next problem is reversing the process and take posession of a body if this is your intention.

All we have to do know is find out more about how we can do these things. We have to find out if and how we can seperate (if our mind is a product of our body, with all the hormones, neurons etc. making your thoughts), then how we can transfer it to what particle or wave etc.

Forward isn't necesary. It is hard to immagine what is there after time, still there are at least 6 or 7 more dimensions. New laws of physics means new posibilities, so you could go to another universe, time is just the beginning of time travel if you have the right technique.