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

In response to the grandfather paradox...
If you go back and time and kill your grandfather, perhaps BECAUSE you had time traveled and done this, YOU, the current you who went into the past is safe from harm. However, if you were to go back into the present, you would find that nobody knows who you are, and there's no record of your existance, because in fact you were never born.

Surely killing your Grandfather would have more far reaching implications than there being no record of your existance. Every person no matter how insignificant their life may seem has an impact on the future, you go back and kill your Grandfather what else are you changing?

Talk about your far-reaching complications, if one built a time machine that went back six months, you would probably not change your position in space. You would therefore appear at least 190 million miles from the Earth. Now where was my grandfather 100 years ago?

aha! true enough, Fordstowel

but surely if you could build a time machine without ending the universe etc. etc. would it be too complicated to move back in time *relative* to, say, a rock outside... no matter how far back you move, you would be the same distance from that rock, in the same direction in the 3 spacial dimensions

but

what if someone moves the rock as you travel back in time? u'd follow the rock i assume... then if the rock is broken in to 2 peices... would you split up and half of u follow half of the rock while the opther half follows the other half of the rock? i doubt it... probably when calibrating which object to follow, you would have to designate which atom to follow... but atoms, like rocks can be split, so which (for example) neutron to follow? well im not majorly familiar with sub-sub-atomic particles (like those little loop things that make neutrons and protons etc.... i saw them on the discovery channel one time... anyhoo) but you would have to pick what to follow all the way down to Planck's constant (i forget the number, but its very small) and that alone would take alot of work... let alone travelling in time...

so maybe its just a good idea to move backwards in time, not move in space, then use thrusters or whatever to come back to the earth, which will have moved ALOT! not only the earth moving, but the solar system and Sol and even the galaxy moving so much that the cumulative effect is so great that u move so much that in moving backwards a year in time moved you AU's or even parsecs in space... or rather, everything else moved and u just stayed put

one more thought on time travel
as you move back in time, let's say that the effect is similar to that in the movie "the time machine" where it takes, i dunno, picking a number at random, 1 second that you experience for every year of travel backwards... what if you wnt to travel to 300,000 years after the big bang, when things start to calm down and physics is what we know it today... thats roughly 14.7 billion years ago, which means 14.7 billion seconds of travel, thats about 450 years! yowza! thats a long wait, so time still goes by for you normally inside your little capsule, would time not stop for you? or go backwards for you as well? so that by the time your readdy to kill grandaddy you are just a few molecules floating around inside his.... inside him, and that travelling back was pointless, it made the hole universe (including you and the machine) go backwards, like a movie on rewind

heres one last thing before i give it a rest
im sure this issue was talked about before, but not in length
you all know the "butterfly effect" a butterfly's wing beats in japan, and a thunderstorm, because of that, beats down on ontario... all the cause and effect paradoxa are staggering, its like in the "simpsons" episode where homer's time travelling toaster takes him back to the time of the dinosaurs and every little thing he does then has huge effects on his own time, that would seriously happen in real life, assuming that time can be changed. I personally think it cant be changed, like in hitch hikers guide, all the changes you want to make in time have already happened, and like the history book example in the article or some ones conversation (i forget now)

now ill just inhale and let you all pick my theories apart! enjoy im 14 years old and i want y'all to know that im really interseted in this kinda stuff, i have all sorts of books on the subject, anyway email me: [email protected] if you have something important to say NO SPAM

I suggest two things. The first being, if you view time as a dimension through which you can travel, and you travel along it, your position on the other three dimensions does not change.

I don't see how you can attach yourself to, say, a rock, and still travel along time. If you were to stay attached to anything, perhaps because of gravity, it would more likely be in position to a greater source, such as the sun.

Even in three dimensional space, we are only ever moving through two dimensions at a time. Sometimes only one. (Not counting time, though standing still is traveling through the one dimension of time.)

Second, the problem that exists with time travel as exhibited, but not addressed, in H.G. Wells' 'Time Machine', is hard to counter. From the vantage of his device, the scientist could 'see' time moving at accelerated rates as he traveled. This makes it clear that if you pass through time, you are still rooted in a three-dimensional world as well.

We all pass through time, just only forward, and all at the same rate. (Let's just ignore the effects of time-relativity as we are discussing local travel.)

Passing through time faster, or backward, you still exist at every point through which you travel. The result is you appear to be an extremely slow moving mannequin to the 'normal-time' observer, but you never disappear, and you are both seen and vulnerable at every point. You can be shot, crushed, burned, etc. because your physical structure has not changed.

Let us say that you built a 3-D rooted machine that travels only through time, and you want to watch the pyramids being built. You take it to what you believe is a safe distance from your favorite, and through it into rapid rewind. Every person who had ever passed through that area would have had to see you sitting, rock solid, at every point in the past.

We in the future would certainly know that you had been there by now. You'd have become a historic curiousity. And, you would still have to worry about the sandstorms, shifting depths of sand, other unknown buildings and excavations, and tribes of superstitious bedoins passing by who might consider you either an evil omen, or an interesting collectible.

Lots of dangers. Perhaps someone has worked it out, tried moving a few hours, and realized the dangers. That might stop each successful inventor in his or her tracks.

You have some good points. Indeed, it *would* be pointless to go back in time, unless you have an atemporal bubble around you. That is, you are in a shell of time that's going at what seems to be a normal rate, and the rest of the universe is blurring past. It's something like the wind and your car: you don't feel the wind since it's hitting your car instead of you. Get on a motorcycle, though, and you realize that it's powerful.

So the first step would be to create a bubble of time that wouldn't change with the rest of the universe. It would have to have an internal source of time. This has a couple of inherent problems.

- Gravity and speed distort time. We know of nothing else that alters time. So are you going to attach your time vehicle to a giant rock to keep normal time? Or are you not going to bother with the rate of time (sic) in your vehicle? You couldn't tell the difference anyway, I suppose. But how are you going to keep your time distinct?

- You're in a space of time that's going at one rate. The rest of the universe is going at another rate. What happens at the interface of times? Would it, like water, create vortices? Could these turn into temporal whirlpools and tornados? What effects would that have? That could tear the world to pieces, not only temporally but physically.

I'd rather not try time travel. It's too risky.

~gareis

In my opinion, these theories visualize a time machine in an entirely incorrect fashion. You all imagine a time machine to be like a car, moving from point A to point B by traveling through all the spaces in between, and also being able to travel to any point which is connected to the current point by a direct line. I think a time machine would more resemble a doorway, where you always entered at "this" side of the machine and always exited at "the other" side. This neatly solves both the problem of where one ends up in space and the problem of appearing to everyone throughout history. For the first, you'll just end up wherever the other end of the time machine happens to be at the time you exit it. Simple as that. And as for appearing to everyone in between, since you're going directly from one point in spacetime to another, no one at other points in spacetime will see you.

The only problem with this theory is that since you can only travel to places that already have one end of a time machine, you can't travel to before the time machine was created. So we can't see the pyrimids being built, or even kill our own grandfathers. What a shame.

The only problem with this theory, is you don't present any reason why time machines CAN'T go both ways.