Time travel

[Adrian Brezhnev]

I have just done a search and was surprised to find that this does not appear to have been discussed in detail in this forum before, apart from in the Time travel plots thread from two years ago.

This week's New Scientist has a cover story entitled "Time Travel. At last, an idea we can test".

http://www.arxiv.org/abs/gr-qc/0603045

It's a response to a recently published paper my Heinrich Pä, catchily titled "Closed timelike curves in asymmetrically warped brane universes"- by brane universe, he is referring to widely regarded current theory that the four dimensions that we are used to are actually a membrane (or "brane) adrift in a higher dimentional space-time... which is 10 or 11 dimensional, depending on who you ask.

All of the particles and forces in our universe are trapped in our brane like flies on fly paper, and that's why we have no knowledge of any dimensions other than the four we experience.

If you can imagine that our brane universe was bent back on itself, like the four-dimensiolan version of a pancake folded in two, you can see that we could leave the brane at one point, travelling a small distance, and re-entering at a point far away from where you started.

And in doing so, negating any need to mess around with rotating blackholes or wormhole tunnels- both of which have always seemed to me to be rather dangerous places to visit.

Anyway, I've always believed that time travel is not impossible, but is something that the human race may never manage to knowingly achieve.

Any thoughts?

[Purple Tentacle]

Sounds like the same ideas written by Kurt Vonnegaut in Slaughterhouse 5, that aliens can see time from beginning to end like a mountain range, and can journey just as easily to any point, but cannot, and do not see the point of changing anything, because it has already happened, and already will happen, and besides you can re-visit any point in time anyway.

[hencole]

I don't believe time travel is possible in the way most people percieve time travel to operate. I'm not sure I even believe in time in the classical sense. I read the article and to me the ideas they were trying to convey as being time travel were nothing of the sort. Sure bits of matter could be shifted around by entering a higher dimension, but it is of little practical use and not classical time travel. I  think the use of branes in desribing the universe seems one of the most plausible ways of describing a lot of the unexplained stuff that goes on in the universe, but as 3 dimensional beings we are doomed to wonder our 'flatland' oblivious and unable to see the bigger picture.

[Almost Yearly]

At the moment we set fire to irreplaceable stuff we've dug up in order to propel ourselves through three dimensions in costly little boxes. When they break down we sit on the hard shoulder dreaming of theoretical subatomic particles with our bent branes.

[Frinky]

This was all much more fun when it was De Loreans and snogging your teenage mum.

[Santa's Boyfriend]

So what's your theory on the reality of temporal paradoxes?  Surely time travel will never happen (or at least nobody will ever go back before this point in time) because a temporal paradox would be inevitable were we to do so?  After all I would imagine that there's no such thing as small or insignificant when we're talking about changing a timeline because of the inevitable cause and effect multiplied millions of times over.  And I can't imagine what would happen to the universe if these causes and effects were enough to stop the time traveller from travelling back in time in exactly the same way.


It really makes my brain hurt.  Am I making too many assumptions on the nature of time travel?


"Time Travellers do it in DeLoreans"

[Jemble Fred]

Surely time travel will never happen (or at least nobody will ever go back before this point in time) because a temporal paradox would be inevitable were we to do so?  

For all we know, isn't it equally reasonable to presume that it's happening every two minutes, and we just happen to be stuck in one particular universe where things happened as they did?

For some reason, I spent a long time recently daydreaming about life if the Romans had never invaded, or indeed Rome had been crushed by Hannibal. Basically trying to work out whether we'd still be quite so great without the English Language. Whether we'd have had an Empire if we were all still relatively pedigree 'Celts' on this island and so on. But as one big change over two thousand years ago would have rendered absolutely everything completely different, and the combinations of DNA that make us all what we are wouldn't exist, I gave up.

[hencole]

So what's your theory on the reality of temporal paradoxes?  Surely time travel will never happen (or at least nobody will ever go back before this point in time) because a temporal paradox would be inevitable were we to do so?  

Thats fisher price time travel with toy cars. Hawkins and others are going over to the 'History isn't even written until you observe it' train of thought on this.
Think of where we our and where w have come from as an infinite number of states that are only observed as one state. It's possible that everything that ever could happen and has happened. That way you don't have such problems as it's largely irrelevent. It does make human time travel somewhat unlikely though. You're better of taking drugs to get where ever it is you want to get too.

[Alberon]

With the mulitple worlds theory of Time Travel you can get round the Grandfather Paradox, by simply having you splitting off into a parallel universe to the one you left the instant you arrive in the past (thereby changing it).

While it might be theoretically possible to fold one part of the brane to touch the other, what level of energy would have to be expended to cause it? Is it actually possible to warp a brane like that from the inside?

Some recent theories suggest time actually existed before the Big Bang. If that is the case and it isn't purely local to this brane then folding the brane back on itself will not allow travel into the past.

[hencole]

Here's a centrict theory for you that I came up with: You never die.

Think about it. How many of you have died? None

Why? The reason for this is that whenever you get to a point in your life where you might die (eg. crossing a dangerous road), your life splits to a universe in which you don't get run over.  As a result you are in fact imortal and will live forever. This even works for decapitation, so no highlander problems either.

The only downside is that for this to work everyone else you know will seem to eventually die.

[SetToStun]

Here's a centrict theory for you that I came up with: You never die.

Think about it. How many of you have died? None

Why? The reason for this is that whenever you get to a point in your life where you might die (eg. crossing a dangerous road), your life splits to a universe in which you don't get run over.  As a result you are in fact imortal and will live forever. This even works for decapitation, so no highlander problems either.

The only downside is that for this to work everyone else you know will seem to eventually die.

If that were the case, where are all the 999-year olds? Since everyone is immortal, some of them would be left in this version. This must be true because otherwise there wouldn't be any 100+ year olds around as they would have split off before me as well.

[Dark Sky]

SetToStun, I think the theory only applies to YOU, not to anyone else.

And a bloody good theory it is, too!  Bravo, hencole!

As for time travel...  Has anyone ever caused a huge media storm by saying that they're a time traveller from the future?

Could be some big bucks in that.

[Alberon]

I did read about a version of Schroedinger's Cat that revolves around this idea. It involves a gun, a random source (like a radioactive one in the Cat experiment) and you.

It's called the Quantum Suicide idea. Here's the page on it from Wiki

http://en.wikipedia.org/wiki/Quantum_suicide

The experiment essentially involves looking at the Schrödinger's cat experiment from the point of view of the cat.

In this experiment, a physicist sits in front of a gun which is triggered or not triggered depending on the decay of some radioactive atom. With each run of the experiment there is a 50-50 chance that the gun will be triggered and the physicist will die. If the Copenhagen interpretation is correct, then the gun will eventually be triggered and the physicist will die. If the many-worlds interpretation is correct then at each run of the experiment the physicist will be split into one world in which he lives and another world in which he dies. After many runs of the experiment, there will be many worlds. In the worlds where the physicist dies, he will cease to exist. However, from the point of view of the non-dead physicist, the experiment will continue running without his ceasing to exist, because at each branch, he will only be able to observe the result in the world in which he survives, and if many-worlds is correct, the physicist will notice that he never seems to die, presuming, of course, that there is no afterlife in which the physicist is conscious of his death.

Unfortunately, the physicist will be unable to report the results because, from the viewpoint of an outside observer, the probabilities will be the same whether many worlds or Copenhagen is correct.

A variation of this thought experiment suggests a controversial outcome known as quantum immortality, which is the argument that if the many-worlds interpretation of quantum mechanics is correct then a conscious observer can never cease to exist.

And here's the page on the even more disputed idea of Quantum Immortality

http://en.wikipedia.org/wiki/Quantum_immortality


I think the main problem of the Quantum Suicide idea is that death has to be absolutely instantaneous (ie at the speed of life). If the observer observes anything of an event that will cause his or her death, (like hearing the beginning of the gunshot) or observing the hole where his or her chest used to be, then the multi-worlds theory is not going to save them.

[Go With The Flow]

I don't get the "if you go back in time and change something, it will affect the future" theory. Surely if you go back in time and do something, that thing (in the past) would have happened anyway (ie it already has), and it would stay the same!

[swarfmonkey]

LOTS OF SCIENCE

hencole said it better.

[Smackhead Kangaroo]

You killing your own father prior to your conception cannot be necessary.

[opyty]

Can I just point out that if anybody goes back in time and kills my grandad, I'll be fucking livid. Do you hear ?

[Sherringford Hovis]

Has anyone ever caused a huge media storm by saying that they're a time traveller from the future?

Could be some big bucks in that.

Not quite a huge media storm, but John Titor caused a few ripples about six years ago. I was threatened with being fired from my job at the time as I spent so much time Googling sciencey stuff related to his claims.

I've sent off my $10 and am expecting to be collected any moment now...

[swarfmonkey]

Can I just point out that if anybody goes back in time and kills my grandad, I'll be fucking livid. Do you hear ?

Oh no, you won't!



Or will you?

[Frinky]

John Titor caused a few ripples about six years ago.

Apart from the fact that his time machine was made from 1950's surplus and was an absolutely textbook piece of budget propmaking for dummies, it was a good story.

I did my first year mini-dissertation on him, and how elements of his story were deliberately unbelievable in order to become actually quite believable, going on about "hyperreality" and post modernism and other such bollocks.

If only he'd built a better prop.


Edit: I actually proof-read my dissertation, unlike my posts.

[Neville Chamberlain]

So, does all thids time travel gubbins and Prof. Hencole's theories of disappearing into a different world when you're about to die mean there's an entire entire universe of bitter and twisted - not to mention dead (in this world at least) - geriatrics? Dead babies? Dead junkies? Dead traffic accident victims? That is, presuming they all disappear off to separate worlds reserved for dead people of their kind. Or maybe not. Is it a continuation of the world in which we live, except that old people are older, young people are, well, older and things. Imagine a world full of 800 year olds. Blimey.

Oh, I dunno. Carry on, you lot.

(Yes, I habve had a lounchtime drink)

[Santa's Boyfriend]

John Titor caused a few ripples about six years ago.

Apart from the fact that his time machine was made from 1950's surplus and was an absolutely textbook piece of budget propmaking for dummies, it was a good story.

Mind you, if he had predicted that Lordi would win the Eurovision Song Contest in 2006 it would be hard to dispute his time travelling credentials.

[Eight Taiwanese Teenagers]

And here's the page on the even more disputed idea of Quantum Immortality

http://en.wikipedia.org/wiki/Quantum_immortality

That's absolutely fascinating!

[SetToStun]

SetToStun, I think the theory only applies to YOU, not to anyone else.

But unless the entire multiverse exists just for me - all worlds in it and all possible timelines - it applies to everyone. In which case, if I'm immortal, eventually I'll end up as a million year old man sooner or later (well, in a pecisely defined time, I suppose), which means the same is true of everyone. I would elaborate more, but I fear it will make my brain hurt.

As for time travel...  Has anyone ever caused a huge media storm by saying that they're a time traveller from the future?

Could be some big bucks in that.

I've got a feeling that this has been done - a quick search found nothing relevant, but then I'm rubbish at Google. I'll try again in a mo.

EDIT: This is exactly what happens when you go to lunch, come back and only think you've refreshed the page before replying. Bollocks. Now, if only there were some way of going back five minutes and not posting a load of stuff other people have already posted much better than me. Let that be a lesson to you all.

[hencole]

And here's the page on the even more disputed idea of Quantum Immortality

http://en.wikipedia.org/wiki/Quantum_immortality

That's absolutely fascinating!

Balls. They nicked my idea. Luckily I'll be the one left laughing when they all die and I piss all over their graves.

[hencole]

SetToStun, I think the theory only applies to YOU, not to anyone else.

But unless the entire multiverse exists just for me - all worlds in it and all possible timelines - it applies to everyone. In which case, if I'm immortal, eventually I'll end up as a million year old man sooner or later (well, in a pecisely defined time, I suppose), which means the same is true of everyone. I would elaborate more, but I fear it will make my brain hurt.

Or you take the view that the universe only exists for you, in which case everyone else is imaginary so they don't escape into other universes, or they  escape like you into other universes to continue their lives. Because of the infinite no. of universes that people are escaping into, the chances of being in the same one as someone else demishes with time to the extent you will most likely not share it with other long lived escaped individuals.

[SetToStun]

Or you take the view that the universe only exists for you, in which case everyone else is imaginary so they don't escape into other universes, or they  escape like you into other universes to continue their lives. Because of the infinite no. of universes that people are escaping into, the chances of being in the same one as someone else demishes with time to the extent you will most likely not share it with other long lived escaped individuals.

The people are only in my imagination" line is something I could never be comfortable with - because if that's true I really hate myself and express it through my imagination. Which would be very sucky. Also, I just barely scraped a score of 6 on the EQ test linked to from here ages ago - I'm a border-line sociopath, apparently, so actively trying to see people as not real would be a bad thing, I would say.

And if people are real then I'm surrounded by them, all having their own timelines and all cheating death constantly. Which means that, even by random distribution, there should be a proper mix of all possible ages here. Either that or everyone who's apparently older than me is actually the same age and just looks older, or never did anything or was anywhere that caused them to branch. And my Dad lived through the Blitz, so that seems unlikely.

It's either random distribution - so where are all the super-wrinklies? - or it's all mine.

[Lu tze]

Can I just point out that if anybody goes back in time and kills my grandad, I'll be fucking livid. Do you hear ?

Oh no, you won't!



Or will you?

He did. But as the event is/was on a different time line it isn't noticeable on this time line.
So should he be held accountable for what he did/does on other time lines just in case?
In an infinite universe of infinite time lines we are all guilty of an infinite number of transgressions and good deeds, perhaps it alls cancels out and keeps the universe in equilibrium but should an un-cancelled or un-cancellable event occur we will indeed all disappear in a puff of logic.
Anyway, back to having my head up my arse.

[opyty]

In an infinite universe of infinite time lines we are all guilty of an infinite number of transgressions

Including being guilty of horribly misusing the term 'infinite' ?
An infinite set of events doesn't necessarily contain every possible event infinitely often or indeed even once.
Anyway, back to having my head up my arse.

[Claude the Racecar Driving Rockstar Super Sleuth]

I wonder if any scientist has had the nerve to test out the quantum suicide theory.