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

Time travel is impossible. Because time isn't something tangible. Unlike say distance which is very very real. This can be proven because where ever I want to go is not right here, where it should be but somewhere over there, which is difficult to get to.

The Idea of Time travel comes from an Idea, the Idea that Time is a dimension. Its not. Time is a way of explaining the movement of things in the other three dimensions. Here arises an interesting thing, its is actually the product of other dimensions. Unlike say width which was no bearing on height, or length.

Now from this above definition of time, we can move on to do a few thought experiments. First how can you stop time? First you would have to stop everything moving. Every particle, every atom, everything all the way down to the resonating quark's and the spinning electrons. This naturally brings about all sorts of interesting questions, all of which show this as impossible, because by its very nature if time did stop we'd never know about it, because we would have stopped as well.

Now onto time travelling, well that would mean the objects moving in 3 Dimensions would have to undo what they have already done. Its not the same as making everything go backwards as thats would mean time was still going forward only things were going backwards. It would mean the reversal of entropy, thermodynamics, red tape, and balding. All of which are generally accepted as impossible. Our universe can be described by our laws of physics, if any of those changed then it couldn't really be called our universe, as well as the fact we'd probably all implode into minature signularitys.

The fact is that once a moment has passed, a second, a nanosecond, a picosecond or even an attosecond has passed, that time will never pass again.

I recently heard an interview with Professor Paul Davies http://aca.mq.edu.au/pdavies.html in which he stated that time travel was possible and that we actually do it now.
To explain:
The example he gave was that when we travel forward at speed (a car or train) we're actually travelling forward in time - albeit in tiny increments. Not sure if I understand but his book "About Time" might give you more information - I am still struggling with his book "The Mind of God"
He did say that he doubted that backwards travel was possible - so when you say that "time travel is impossible" it seems that you may be half right and the interview was liberally sprinkled with references to worm holes

All very interesting ..... fascinating man!!! Might have to steel myself and have a look at more of his books

He's most probably thinking of relativistic tricks to do with time.

Like the old twin sisters thing,

The thing is the faster you go the slower time goes, this isn't really noticable until you get up to a decent percentage of light speed, so moving in a train or car is virtually the same as not moving at all compared to the speed of light. However because you are going faster time is going slower but its such a small difference.
They did an exeriment with a pair of atomic clocks exactly aligned then left one on earth and one in a concorde, flew around as fast as it could then came back, and there was a very small difference in the clocks time.

Your not really travelling in time. Unless you want to start arguing over semantics, in which we are all travelling in time a second at a time.

Now lets see if you go off in a spaceship travelling at the speed of light fly around and come back. For you only 5 years passed but for earth 10 years passed. If you consider your time frame to be the primary reference then you've travelled 5 years into the future. Of course if you consider earths time frame as the primary reference then ten years has passed whilst you were off on your spaceship, and you just seem a lot younger for being 10 years older. Have you really travelled in time? not really you've just slowed down whilst travelling at lightspeed. What if you accelerated earth to lightspeed for 10 years and you stayed exactly still, you'd age faster than earth so would that be travelling back in time? This really comes down to such less than precise things as semantics and reference frames.

Relativity is nice because it brings about all sorts of funs tricks, One of the most important things is the idea of reference frames. If you are in a car going 70 own a motorway and a car overtakes you at 80 then from your frame of reference the car is only going 10 mph.
When your on a train you can equally consider the train standing still and the tracks moving beneath you because both situations are mathematically the same.

Next time I start talking about time travel I'll make sure I actually define it first otherwise I get some wiseass professor springing relativity on me ;P

As for wormholes, thats all in the airy fairy land of imagination physics, no ones ever seen one no ones ever created destroyed one let alone travelled down one. The problem with things like wormholes, if you want them to exist what says you don't make them exist with your own mathematics and equations.
In the same way the CPU industry always keeps up with moores law, they make it the target to reach and so they reach it.

The thing I always find about astrophysics, and theoretical physics is that people are willing to accept the hypothesis's too easily, by definition the fields are all about unproven idea's, or semi-proven idea's, which puts them on par with the existance of god. Whilst religion is all about faith, sciece is not. It probably doesn't help that these theorys are then writen up into popular science books that present these as being legitimate science. It only takes a sci-fi writer to take a few idea's put them into a film or book or tv series, and it reinforces the idea in everyones mind.

Ahh yes, but isn't it wonderful when the sci-fi writers spark an idea in the minds of the scientists (all hail Arthur C Clarke and Isaac Asimov etc) Unfortunately their aren't many of their ilk about these days - they are too busy writing fantasy for money.

All that relativity stuff makes my head hurt - but I love it I went recently to see the play "Copenhagen" which was all about Bohr and Heisenberg's meeting in 1941 - all fictionalised of course but based on extensive research - great play!! I almost understand Heisenberg's Uncertainty Principle now - but I'm not sure If it's on near you - don't miss it!! Real thinking theatre.

"The thing I always find about astrophysics, and theoretical physics is that people are willing to accept the hypothesis's too easily, by definition the fields are all about unproven idea's, or semi-proven idea's, which puts them on par with the existance of god."

Not even close, the existance of god has no basis in fact or observation, but only in belief.

The hypothisis's in physics and science in general are put forth to explain certain known facts and/or observations.

" It probably doesn't help that these theorys are then writen up into popular science books that present these as being legitimate science."

Again, not even close, it is very legitimate science. The theories in physics and science in general are well-substantiated explanation of some observation and/or known fact in the world as we know it. Or as the dictionary puts it ie; An organized system of accepted knowledge that applies in a variety of circumstances to explain a set of phenomena.


Tim

I absolutely agree with you. I know that time travel has the potential for success of a chocolate parasol. The fact that you have to bend the space-time fabric over itself will cause it to rip and create an interdimensional rift that will suck up all matter. If that doesn't happen the stars and planets will more than likely overlap and destroy eachother at different periods of time. This will change the history of the universe and whole galaxies could be forgotten about because they were ceased from existence.
The rifts will leak out into an external void which will erase all memory of the universe and force it to restart.
And if you think that after opening a wormhole to go from one section of space to another, that it could be repaired, then think again. How will you repair it? Cosmic sewing kit? Interdimensional superglue.
Even if you can fix it, you will change that amount of space. An object could weigh half what it truly weighs over there as it is stronger, though you may think this is irrelevant, that could mean it has not enough gravity to orbit a star (if it's a planet). But if it's a star then other planets may not orbit it.
In short, I'm sorry if you are a fan of doctor who and I've spoiled your day, but grow up. It is amazing how stupid science fiction shows can prompt universities into trying to make warp cores or TARDISes.

An interesting post .... though this thread hasn't been active for a long time.

I'm not sure whether you will get a reply from your protagonist.

Welcome to h2g2 BTW.