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

Apparently people are missing to possibility that travelling back in time requires a time machine at both ends of the travel. If this were so, it would not be possible to travel further back in time than the point at which the time machine was built, but it might solve the problem of drift caused by the tremendous speed at which our solar system and it's constituent parts travel relative to other objects.

Isaac Asimov wrote a short story using exactly that premise. Two scientists used time travel to travel through space and observe a distant star up close.

Good point!

That's interesting, I didn't think anyone else had thought about my problem, especially in literature. I can imagine people saying things like , "I'm just 'popping' back in time to see my late father".

This was a pretty weird novel overall. It mostly involved the protagonist meeting insane numbers of his past and future selves, and of course living everything over several times from different viewpoints, and doing various other strange things like convincing his other selves to sleep with him on the grounds that it was technically masturbation....

The Time Ships by Stephen Baxter is another good book for the consequences of Time Travel. There is one point, before alternate dimension theory is explained to the hero, when he kills a monkey in the far past, and then worries about having wiped out the entire German race. It is an official sequel to H.G. Wells The Time Machine. Does get a bit convoluted at the end though.

Here's My question then...not reguarding the travel itself, but the atoms in your own body. Going along with the whole conservation of matter thing, if you went back in time, then the atoms that make up your body would already be in use, right? So couldn't traveling back in time slowly dissolve you (if not just all at once)?
Again, with traveling forward int time, if you travel forward to see yourself, wouldn't you kill one of you? I know that our bodies change day by day (as far as chemical makeup and whathaveyou) but wouldn't you still be running that risk?

Maybe this is a valid point, maybe it's not...

There doesn't appear to be any quality in subatomic matter that affixes it to a particular point in time, nor do they know who they are.

If you took an atom and sent it back in time and placed it next to itself, nothing unusual would happen.

What you do when you see yourself is another matter.

Hmmm...but I think B.C is saying that there might be a limit to the total number of particles that can exist at any given point in time.

Particles are being created and destroyed constantly. I see no reason why there would be an "upper limit" on the number of particles within our universe.
On a different note the statement "Time is an illusion, lunchtime doubly so." does seem to agree with 'A Brief History of Time' which states that time is simply an effect of the universe's inevitable increase of entropy. I'm not quite sure how lunchtime is twice as illusory, unless of course you're a very messy eater.

A very interesting subject. Most people are generally divided between (a) worrying about paradoxes (go back, kill your earlier self, meaning you (later self) can't go back, and so on) and (b) getting round this by assuming the time traveller causes an alternative universe to be sprouted.

As an alternative theory, suppose no new universes sprout, but paradoxes are avoided through not having free will. You could (perhaps) go back in time, but you wouldn't kill your earlier self, or ancestors, or 'modify' history. The results of changing history would have already happened in the past, and our knowledge of the past is actually proof that you couldn't do things like kill your ancestors.

For example, suppose you want to go back in time and kill your grandmother. You can't do this without knowing where she was at some particular time, and so you try to get information from her. She tells you "I vividly remember being in the post office in Gorbledon at 11 o'clock AM on 23 March 1928. I was a little girl, and it was the first time I ever heard a gunshot or saw somebody die. I was very scared." You then go there in your time machine, and shoot a little girl in the post office, go back to your present and find yourself and your grandmother still alive, and nothing different at all.

You see, you are alive, and this means that it is impossible that any of your ancestors died young, so it is futile to try to go back and kill them. The results of what you are planning have already happened.

This raises some interesting possibilities. Suppose humans from (say) 100000 AD, finally having discovered TT, but never having contacted aliens, decide to go back and investigate 20th century UFO sightings, and find nothing. Well, these humans, in amazingly hi-tech vessels, and the result of millennia of human self-reengineering, are the aliens they were trying to find! (I say this as an "explanation" for the stereotype UFO sighting, but this posting is in no way a true statement of my own thoughts about aliens etc.)

Equally, if somebody ever goes into the future, and finds it to be horrible, there is nothing they can do. If they tell everyone, in the hope that the knowledge of that future will improve things, then perhaps everyone will become apathetic, knowing that things are going to be horrible, so what's the point? Thus the act of telling everyone makes the future happen. But of course, if the discoverer does nothing, that future happens anyway. Of course, this applies to good futures too.

Perhaps there has been time travel. Perhaps in the future someone will figure out a way to transfer your soul, but not your body, to the past. As merely a soul you could move places and see things. But they didn't count on certain souls being visible or on certain people (or animals) being able to see souls wandering around. People would think these souls are ghosts. These "ghosts" might not always be able to (or want to) return home. These ghosts might become angry or lonely after a while of wandering the world without true interaction. After time some of these ghosts might learn to actually interact with the physical world. Hence, you would have poltergueists. This theory would explain the mystery of ghosts and the paradox of time travel except that there still is an issue. Since some ghosts do seem to learn to interact with the world, these time travellers have influenced and changed the past and therefore buggered up the future. I imagine that this sort of time travel would be rare, hard to do, and/or expensive. Normally it would be used for documentation or recovery of the past events. Certain souls might abuse it.

A very likely result of time travel is that it almost always destroys itself or the universe/dimension it was in through some sort of paradox. Look at your own experience. If you had created a time machine, what would you do with it? Probably go back in time to save yourself some previous pain in your past. The act of doing so would change your entire life from that point on. Most likely, you would never invent your time machine because everything was changed. Results of such a change would likely either be that the new timeline happens OR the universe refuses the change OR the universe simply gives up and explodes/implodes OR you don't actually change our universe but you do change a different one and always come back home to the same timeline. That last one would be a neat (if still dangerous) side effect. You could "time travel" (in this case it would be more aptly named universe/dimension jumping) to anytime feeling safe with the knowledge that you wouldn't actually be changing anything in our universe. You could use it to document history or to live in a time you feel better suited in. You could likely travel to future timelines of our universe to predict our future. Simply the act of doing so and especially telling people might change, destroy, or nullify that event, though. But think of all the damage (or at least differences) you would cause to other universes. Perhaps aliens are us from our same timeline just many many years from now.

I posted those in a different forum and then as a guide entry and now again. I know some of my points are already brought up in this forum but I believe this post adds something new (definitely with the theory on ghosts).

I do like someone's post about how no matter what you might do in the past, you would never make a change because it's all already happened. If you go back in time planning to do something you know never happened, even if you think you can't possibly fail, you will fail and/or you'll do something that has already happened. You will screw it up somehow.

Post about matter displacement (the pocket of air effect) is a neat concept too.

Another post I saw listed the movement and rotation of the earth as a problem. If time travel ever became possible it would either have to be in space but calculating to make sure no matter is in the way such as comets or the earth OR on earth but calculating precisely when and where the earth will be so you don't end up embedded in rock or flying through space OR between time travel portals built at certain locations wherever (this also involves transporting matter I'm pretty sure) OR travelling backwards in time and transporting your matter as well to a planned point in time and space OR (last one) transporting back something that doesn't conflict with matter (such as a soul). A straight old back to the future style time travel is definitely highly improbable unless you calculate accurately.

Imagine a world based on the portal concept. Say from the year 3000 on, time travel (they would double as matter transportation portals) 1000 time travel portals existed around the world. Living in the year 3450 you could travel to any of those 1000 portals at any point in time after the year 3000. It would become the major transportation tool for most anything. They could send a robot to each consecutive year reporting back each time whether or not the world and/or universe is still there. If the last # it reports back is 7874 then we'll know something goes wrong in that year. We could test it by trying to send another robot to the other portals in 7875. We would end up with more portals every year I bet. Portals on other planets. Eventually we could probably determine the end of the universe itself just like in the "restaurant at the end of the universe". Well, the end of the universe for as far out as we could place portals that is. I imagine that would get pretty far because we could probably discover some way of traveling the speed of light (or greater) eventually without portals on the other side. So when this robot discovers this technology it would send that info back in time to an appropiate year where we could use that info effectively and off our probes would go. Our probes would travel to distant planets rotating around faraway suns and plant down more portals. So, say it's the year 3450. We send a probe out a 100 light years away and assuming we will travel at light speed, the probe will reach there 100 years later. You don't have to wait though because that portal name is planned and should be there around 3550 and when you get there you can still go back to 3450. All portals would be tested first by robots. With all these rules in place. First imagine if the human race (and the space time continium) could survive this. Then, imagine if the portals were reliable. You would have an infinite and place to be in only limited by your own life. Even the limits of your own life could be stretched by any techologies made up until the end of the universe itself. Perhaps death itself could be cheated by the end. All life would be in the same time. All technology would become one super technology that would test all the extremes of physics. Thinking of it, wouldn't accidental deaths, assassinations and murders be totally eliminated? If you died because of accidentally falling off a cliff then someone that knows you would be able to came back tell you or save you. If someone killed you intenionally then cops could go back in time just enough to stop the killer. But for as many benefits this can bring, imagine all the problems. Traffic. With a universe like this, eventually there would be too many humans (especially on earth, the homeworld, everyone's favorite must see tourist attraction). Could take a long time but eventually the universe would fill up. But the problem is, the term "a long time" doesn't apply to this. With anyone, traveling, anywhere, anytime, living almost forever. The number two can only be squared so many times without subtraction until we would reach a population that could only be labled "too many". Human kind would be the ultimate bacterial virus that everyone keeps saying we are. Have to go. Perhaps I'll write more tomorrow.

Here's another one for ya.
The technology for time travel will most likely always be very limited either by choice or by technology. ex: If it takes 20000 nuclear bombs going off at once in space to create the reaction needed to send someone back in time, then I doubt people will want that sort of thing happening a lot. That's also a tech limitation because of the production needed to make 20000 nukes. It probably won't involve nukes but will involve very expensive and dangerous technologies. Many people will fear that we'll create a black hole or that kind of thing.
-Destroy

I've heard a couple of time travel theories that haven't already been posted here...
1) First of all you find yourself a wormhole, showing the place you want to travel to on the other side of it (this eliminates the possibility of the Earth's movement getting in the way as the other end of the wormhole would move with it)
2) Somehow you need to polarise both sides of it, enabling you to drag one end around with you (I have no idea how this would be done, cos I don't have the book I saw this in with me - sorry)
3) Attach one end of the wormhole to a spacecraft and fly it a couple of times around the solar systam to create a time difference.
4) As the wormhole still shows a specific point in space, no matter where it is, once a sufficient time difference has been made you can step through it and - voila!
In theory this sounds OK, cos it also mean's that you can't go into the past - you can only travel from your current point in time onwards - though if anyone would like to poke a few holes in it, be my guest - I'll have to find the book I saw it in and correct any mistakes I've made.

Ah, the elusive time travel dilemma. Depending on the theory you wish to use, new weird and wacky problems arise.

If you follow the theory behind 12 Monkeys, where any time travel is caught in a sort of "time loop," then you must embrace the fact that the only way this is true is if predestination exists.

Unfortunately, this means that you are a slave to the time line, and that your role in life has already been set, and there's nothing you can do about it. pretty depressing, if you ask me. And then there's always the problem of the first time the loop was created, unless the loop has always been there, and the whole time line has already been made, and cannot be changed.

On the other hand, if you don't believe in this theory, and that you can actually alter history (past, present, or future), you run into the following problem:

If you stop something in the past from happening, then in your present, there is no need to change the past... therefore, the jump back in time never happens. Now, what happens to reality if this ever occurs is anyone's guess. Possible theories include:

a) the timeline automatically resets itself, overriding the time change.

b) the timeline deviates and follows through to create an alternate present (and future) that replaces the original one.

c) the same as pointer b) except that the timeline deviation creates a new "parallel" timeline.

d) the timeline self destructs.

Of course, there also exists the theory that all of this is pure bunk and that time travel is pure science fiction. For now, this is the most plausible of them all, until proven otherwise, at any rate.

In theory travalling backwards in time is very straight forward. However, in practice it is less so.First you need to exceed the universal speed limit. After this the space-time continuum (excuse the spelling) is said to loop back on itself. However, there is no guarantee that you could control where you went to, or even get back.
Traveling forwards I think could only be achieve through stasis fields which scientists are currently investigating.
But Dr Who type time travel is still well into the future or maybe you know better.

One little thing that a few people seem to be confused about... Time is not a line. Time is not a square, or a circle, or a cube. Time is an entirely different dimension from length, width, and depth. It therefore cannot be defined in three-dimensional terms. We don't have a word for what Time is, it's just kinda there. (think a God-like perception of the universe, but that's another forum....)

So, that would mean that in order to achieve Time travel, one would have remove oneself from the four dimensions we humans live in (mathematically, the x, y, and z axis, and Time), to go to say the fifth dimension. After that, Time travel isn't all that difficult... (after all, if one can leap from dimension to dimension, it isn't that hard to push oneself into one time or another). They'd be able to move around in time just like we can walk forward or backward or jump around... etc, etc. (for the best comparison, I have so mention the book "Flatland" that my tenth grade theoretical geometry teacher was always advocating... I've yet to read it, but I promise myself I will one day).

As for paradoxes (and predestination paradoxes), I don't like these, especially the predestination ones, but they do actually make sense. The circle thing that someone (I don't remember who after reading though all of this) was talking about could never happen: everything that has happened and that will ever happen is set in stone. It has to be, because Time just is and it doesn't change. It changes for us (because we only experience it in one way), but for anything in the fifth dimension and above, Time is kinda like that annoying little dimension that gets in the way (sort of like height for us short people). Therefore, history cannot be changed, no matter how hard we try. Things have already happened the way they were supposed to, and even if we (to use the example) went back in time to try to assassinate Hitler, we'd fail, and we know that because he obviously already had his way with Europe sixty years ago. (another book reference: "In the Garden Of Iden" and "Sky Coyote" by Kage Baker. The way time is manipulated in these books is essentially what I'm talking about).

Lastly... about the actual practice of Time travel... I don't think it's particularly possible. Personally, I'd never want to see everything that ever happened all at the same time... the beginning, the end, and everything in between. It'd blow my mind, and I'd probably end up spontaneously combusting or soemthing. And why'd one really want to after all if they knew they couldn't change anything...? Ah, well, I'm expert... just someone who took her theo geo class a bit too seriously...

~Amy †

Waah that was big
Anyway, your ghost thing. I believe John Wyndam once wrote a short story using that very theorem, only all the time travellers are tourists, and so many turn up at once that those living in the past (and seeing these ghosts) get fed up and start putting up large signs telling them to naff off home. It can get very annoying having several tens of see through tourists watching you take a bath.

Whoops, I just realized that that last line should read "NOT an expert"...

Somebody mentioned Twelve Monkeys earlier, and the theory therein that even if you travel back in time, you still cannot change the future. As far as I can see, there's a bit of a mistake in the film: Bruce Willis records messages on an answerphone, which are subsequently listened to in the future. Surely this is changing the future? Duh.

The way I see it (this theory has risen out of my belief in God, and that he is outside time, but I don't want to turn this forum into ANOTHER theological discussion because I'm sick of them ), Time is not all-enclosing. What I mean, is, we live inside a three-dimensional physical world and a one-dimensional timeline. Because our physical and mental bodies are built for one-dimensional time, as well as three-dimensional space, we cannot inhabit anything outside our normal timeline any more than we can inhabit a two-dimensional world. (and I think that God is outside (and created) our 3D world and 1D timeline, and so isn't constricted to it, but that's beside the point) So my point is... what was my point? I ought to get my memory upgraded.
Sorry, I've lost my train of thought again. Ho-hum.

You really need to have a firmer grasp on some of the issues at hand here.
I have been doing 'A' - levels and degrees and stuff for a while now and have come to understand some basics principles.
When you travel faster your mass starts to increase. The greater that you mass becomes the more energy that needs to be inputed to accelerate you further. Once you mass starts to reach infinite proportions you need infinite amounts of energy to produce the continued acceleration. Also due to Lorentz's time dialation theory as you go faster time passes slower. Theoretically when you reach the speed of light time does not pass at all, you cease to exist, game over.
As for escaping from a black hole. It ain't happening. Go read up on black holes.
Not sure what the scientists are up to. It ain't happening in our life times though.

p.s impossible to reach absolute zero.