Time Travel

[NWO Sentryman]

I was wondering about time travel:

I i went back in time and killed Hitler, why would i go back in time in the first place?:confused:

If i went back in time to meet Jesus, how would that affect christianity?:confused:

If i went back in time with a very advanced computer and gave it to Richard Nixon, would that mean sawtooth snap?:boggled:

[Toke]

It would depend on which trouserleg of time you returned to.

[In My Spare Time]

That would require time travel backward to be possible. I don't think there's much indication that it is.

[Fnord]

Look, all I remember is going back in time to prevent Amos Weatherby from marrying his wife Abigail in 1807, in order to later prevent the birth of a certain bully who put me in a coma, thus forcing me to miss the senior prom. Little did I know that events would precipitate that would (a) lead to the Great Depression instead of the Great Enlightenment, and (b) bring about proving the principle behind the atomic bomb instead of proving the principle of the "time-bomb" on July 16, 1945.

Besides, the timestream re-converged in such a way that a drunk driver put me in traction, thus forcing me to miss the senior prom...

[lumos]

Do you think you could go back in time and find Jesus? Do you think all that stuff really happened?

But, if you could go back in time, you'd create an alternate timeline with nearly every trip so that the future you travel back to would not be the original future you left. So if you killed Hitler and then went back to your own time, you'd go back to an "alternate universe" or "alternate reality" and never be able to return to the original timeline.

Then again, you could go back to the original moment you popped into the past to kill Hitler and kill your previous self the moment you previously arrived to prevent you from killing Hitler and the new alternate future you returned to would be very similar, potentially, to the original future you left. That is, of course, if you didn't spread a horrible pandemic in the past when you zapped into it briefly.

I don't believe time travel into the past as you speak of it is possible.

[Fnord]

... if you could go back in time, you'd create an alternate timeline with nearly every trip so that the future you travel back to would not be the original future you left. So if you killed Hitler and then went back to your own time, you'd go back to an "alternate universe" or "alternate reality" and never be able to return to the original timeline.
.
I once wrote a short story that addressed the speculation of just such a scenario, except that as soon as the protagonist returned to the same time/space coordinates, he found that without the Hitler War Machine, Stalin ran roughshod over most of Europe and plunged the world into a war from which it never fully recovered. It seems that the Stalinists saw the potential of the Nazi Atomic Bomb project, and accelerated its schedule, thus producing the bomb first, and inflicting it not on just one or two cities, but on dozens of cities around the world, leaving little more than radioactive rain and a dying world behind.

The teacher gave the story a "B" for, commenting only, "Better than average use of a literary trope."

[thaiboxerken]

I like the Star Trek explanation as employed in the new movie. I guess it's Back to the Futurish as well.

[Piscivore]

Build a city out of Legos. Take it apart, and build a whole new different city out of the exact same Legos, using each and every Lego brick. Now take one of the little Lego people from the new city and try to have it visit the first city.

[The_Fire]

Isn't this what's normally called the Grandfather Paradox (http://en.wikipedia.org/wiki/Grandfather_paradox)?

[Policenaut]

Before you consider traveling through time please take this guys advice:

owlz8Emd17U

[godless dave]

I was wondering about time travel:

I i went back in time and killed Hitler, why would i go back in time in the first place?:confused:

If i went back in time to meet Jesus, how would that affect christianity?:confused:

If i went back in time with a very advanced computer and gave it to Richard Nixon, would that mean sawtooth snap?:boggled:

Causality, as far as we can tell, is directional. As soon as you traveled backwards in time, you would be out of the chain of events that "caused" you to go back in time. The "cause" of Hitler's death would be you appearing suddenly in Austria in the 1920s (or whenever you were shooting for) and killing him. It doesn't matter that the future cause of you going back in time will no longer happen.

[Asm]

Anyone seen Primer (2004)? Very fun and confusing.

http://www.imdb.com/title/tt0390384/)

[Gord_in_Toronto]

Besides which the Time Police would prevent you.

The_End_of_Eternity

or possibly not.

[godless dave]

"Days of Cain" was another sci-fi novel to use this trope. In that one, there was a time travel enforcement agency to prevent this kind of thing from happening. So Hitler, having seen several people try to assassinate him only to be mysteriously prevented at the last minute, concluded he was invincible and had a cosmic destiny, which only emboldened him further.

[dudalb]

Let's Nor Forget H Beam Piper's "Paratime" series.

[Fnord]

"Days of Cain" was another sci-fi novel to use this trope. In that one, there was a time travel enforcement agency to prevent this kind of thing from happening. So Hitler, having seen several people try to assassinate him only to be mysteriously prevented at the last minute, concluded he was invincible and had a cosmic destiny, which only emboldened him further.
.
Kinda makes one wonder about all those other Über-confident, egomaniacal dictators ... Stalin ... Caligula ... Mao ... Hussein ... Pilate ... Nero ... Rev. Jim Jones ... Kim Jong Il ...

What if all of those man-made catastrophies (911, Titanic, Three-Mile Island, Jonestown, the 1969 World Series, et cetera) were actually condoned by the Time Police in order to prevent even worse disasters from happening?

And what's that "WOOOOOOO" sound I keep hearing?

;)

[shadron]

One of several interpretations of time would have you accidentally forking off a whole new universe at the point where you re-entered the time stream with your anomaly. Those lucky/poor people would never know that you saved/condemned them from/to a horrible fate. See James Hogan's Thrice Upon a Time.

I i went back in time and killed Hitler, why would i go back in time in the first place?:confused:

I read a short story once where the time traveller from the future travelled back to the Nuremburg Rally in 1938 with the mission of assassinating Hitler. He found he had a hell of a time finding a parking space among all the other time travelling machines in the area.

[Fnord]

... I read a short story once where the time traveller from the future travelled back to the Nuremburg Rally in 1938 with the mission of assassinating Hitler. He found he had a hell of a time finding a parking space among all the other time travelling machines in the area.

Well, that would explain some of the violence ... the pro-nazi time travellers duking it out with the anti-nazi time travellers. Of course, they'd "have to" use only those weapons appropriate to local and current technology, or risk an anachronistic anomaly in the timestream.

You can't prove it didn't happen that way!

(WTF? There's that "WOOOOO" sound again!)

[quarky]

Imagine all the gypsies we'd have if you went back and killed Hitler. Where would they live?

[Fnord]

Imagine all the gypsies we'd have if you went back and killed Hitler. Where would they live?

Romany?

[Dr. Lao]

I'd go back in time and kill Rich Little.

I'd get a Nobel Prize for that.

[Fnord]

Don't you mean Little Richard?

[Kuko 4000]

By going back in time and killing Hitler, besides erasing yourself from the chain that lead to your current "state" wouldn't you also erase everyone else from their current "states" as well. Not sure how people would feel about that, zzzipp, and we're all gone :boggled: but at least Hitler is dead. Now who's the bad guy?

[BTMO]

I have... actually built a time machine.

It allows one to travel slowly into the future....

For an *enormous* amount of money, I will let you ride it.

[lumos]

I have... actually built a time machine.

It allows one to travel slowly into the future....

For an *enormous* amount of money, I will let you ride it.

I bought one at Target the other day. It says "Casio" on it.

[Fnord]

Mine said "La-Z-Boy" on the label. It came with a Universal Remote, so that I can control All That Is Important without leaving the comfort of my time machine. Although it's odd that the faster or more often I use the remote, the quicker time seems to pass. Is this a factor of subjective or objective time? Or does relativity come into play?

[Gord_in_Toronto]

Mine said "La-Z-Boy" on the label. It came with a Universal Remote, so that I can control All That Is Important without leaving the comfort of my time machine. Although it's odd that the faster or more often I use the remote, the quicker time seems to pass. Is this a factor of subjective or objective time? Or does relativity come into play?

Try moving your "La-Z-Boy" into a church service and see whether its tears a rip in the time continuum.
:covereyes

[JollyRoger]

how about going exactly one light year out into space and constructing a Giant mirror that is aimed at Earth, and on Earth you take a super powerful telescope and look at the mirror, in theory you would be able to see what happed two years ago.

A theoretical window into the past

[Fnord]

Try moving your "La-Z-Boy" into a church service and see whether its tears a rip in the time continuum.
:covereyes
.

No ... I think I read somewhere that there is a special property about churches that makes time move more slowly. It could be the Powerpoint software they use to display graphics for the sermon, since I've noticed the same effect at several departmental meetings at work.

[Gord_in_Toronto]

.

No ... I think I read somewhere that there is a special property about churches that makes time move more slowly. It could be the Powerpoint software they use to display graphics for the sermon, since I've noticed the same effect at several departmental meetings at work.

As I just make up; based on similar experience:
"If you have something to say, say it. If you have nothing to say, make a PowerPoint presentation."
;)

[quarky]

So many time-traveler wannabes site removing Hitler as the pinnacle of fantasy achievment.

Yet, the Brits offed a higher % of Irish in their genocide than the Germans did with the Jews.

And the early Americans did heavier genocide on the Indians than Hitler did on the Jews.
Jews are actually doing quite well, globally.

Meanwhile, the Negro race is in danger of being removed from the picture.
Negroes are doomed. It should be of major concern.
Africa is ****ed.

Yet, no Hitler exists for our knee-jerk repulsion of this on-going genocide.
Hitler is too convienent, imho.

One could go back in time, and stop Hitler.
Yet, someone else would try to kill all the Jews.

[Cavemonster]

how about going exactly one light year out into space and constructing a Giant mirror that is aimed at Earth, and on Earth you take a super powerful telescope and look at the mirror, in theory you would be able to see what happed two years ago.

A theoretical window into the past

You can get a similar effect much cheaper using a video camera and waiting two years to watch it.

[Ashles]

There is already a device that can slow down time to a crawl, so that half an hour can feel like three days.

It is called an episode of Last of the Sumer Wine.

[leafman91]

If you went back in time and killed Hitler then you could theoretically get back to your own timeline. Sure, killing Hitler would create an alternate reality, but that isn't to say the existing reality would be destroyed in the process. All you would need is to find a loophole in the laws of time and space and you are back to the reality you know and love.Hitler, of course would still be alive.

This is assuming that time is a measure of cause and effect. Otherwise crossing the international dateline would really be dragging you back in time (365 times around the world, and look! You're back in June 2008!)
:D:D:D:D:D:D:D:D:D:D:D:DD:D:D:D:D:D

That line of smileys is the gateway to the past :)

[JcR]

So where exactly are all these "events in time" stored?
On some kind of cosmic hard drive I presume.

[Professor Yaffle]

x8w95xIdH4o

[reason1]

I traveled in time today: I closed my eyes and then opened them to find myself 9 hours in the future. How could this happen?.

[Moon-Spinner]

If I could time travel, I would go back in time to visit myself as a teenager, and slap some sense into me!!! :rolleyes:

[Moon-Spinner]

Before you consider traveling through time please take this guys advice:

owlz8Emd17U

This is very interesting, as I have thought about this possibly being a problem with time travel too, but this is the first time I've seen/heard/read about this subject. I'm sure there are pockets of physicists that have discussed this, but in popular culture it never comes up. It's nice to know that my musings may have had some merit.

With that problem aside, I thought that the Time Traveler in "The Time Machine" was awfully lucky to have gone 800,000 years into the future, and not have the ground underneath him eroded away (or a large tree growing on the spot where his time machine was). There are still so many problems with traveling through time while sitting in one spot.

Anyway, I guess I should just sit back and enjoy all those time travel movies, and not be seeing all the problems with the "Science" behind it (but it's so dang hard not to sometimes - LOL)

[Nursefoxfire]

Anytime (pun intended) I hear about someone wanting to theoretically travel back in time to assassinate Hitler, I think of all the modern-day leaders who're committing atrocities and genocide (several African leaders come to mind) and wonder, "Why can't you just assassinate some of THEM, instead? It would certainly be easier than constructing a time machine!"

[Doc Daneeka]

I'm sure that this will result in heated argument, which is not what I am aiming for. Nor do I wish to derail the thread. It's perhaps still worth pointing out:

These scenarios are only paradoxical if you assume that we have free will.

[leafman91]

Well said. I was just about to post a very harsh reply to that comment involving her (him?) standing by with a bucket and mop while...never mind.

I think the slightly better idea would be to go back in time and stop whatever influence gave these people the ideas of bloodshed/tyranny. Assuming we still had our time machine. Do you reckon you could make one in the shape of a blue policebox? :)

[shawmutt]

Perhaps time travel is possible, but the travelers get caught in a paradox every time.

Or maybe the smoke monster gets them.

[leafman91]

Only if their age is one of Hurley's magic numbers :)

[Jimbo07]

So many time-traveler wannabes site removing Hitler as the pinnacle of fantasy achievment.


"Everybody's in favour of saving Hitler's brain, but try putting it in the body of a great white shark and... oooohh... suddenly you've gone too far!"

:D

[Jiddu]

Assuming we still had our time machine. Do you reckon you could make one in the shape of a blue policebox? :)

It'd probably be stolen too, and have a knackered chameleon circuit to boot.

Time travel paradoxes are very familiar to such science fiction writers. The question is, what does physicis to make of them? Do they imply that time travel is a non starter, or that reality is more complex than we suppose? This is where, as per usual, opinions start to diverge. There are some theoretical physicists, most notably David Deutsch, that maintain the way out of this is to assume that there are multiple realities, so that when you travel back into the past, the world you change is not the same one that you left, but a parallel imitation - a bit like Everett's Many Worlds in reverse.. This perhaps answers Hawking's main objection as to why reverse time travel is impossible by virtue of the fact that we haven't yet been overrun by people from the future.

Hawking also proffered Chronology Protection Conjecture which says Time Machines contravene the laws of physics. Basically, such scientists argue that nature will conspire to prevent the building of a time machine - one possibility is that runaway surges in quantum energy would generate massive gravitational fields and turn any time machine into pulp.

Arguably, the best hope for erstwhile time travellers still comes from the General Theory of Relativity. Kurt Gödel used this to produce equations indicating the possibility of time travel to the past. He demonstrated that a rotating universe, consistent with Einstein’s theory, would allow you travel back in time. Given that his model was unlike the real universe we inhabit and also that even if we did live in such a universe, time travel would be practically unachievable because you would need a unfeasibly powerful energy source which to cover astronomical distances, Gödel’s work was nonetheless firm evidence that time travel to the past is, at least in theory, possible - where the beginning is actually just a continuation of the end. In Godel’s universe there is not time and any physical event if possible including going back in time and killing your ancestor and still living.

Since then, innumerable other scientists have suggested other solutions of general relativity that permit time travel to the past. Most rely on the prediction of the hypothetical existence of 'closed time-like curves'. There are supposedly ways of distorting space-time to make it curved in such a way that shortcuts through space-time exist allowing you to effectively travel faster than light and journey back into the past.

Attempt to bring anything like that up in this space, and you're unlikely to 'woo' anyone to your cause.

Personally I find Penrose's notion of 'cosmic censorship' the most interesting.

Regarding the prospect of being overrun with Time Travel Tourists from the future, what was that film, I'm sure it stared Jeff Bridges, in which there was a bunch of people doing just that? - turning up at the scene of infamous events or to spectate on historical natural disasters? I think they arrived in the film to view a large meteorite strike.

[Cuddles]

Meanwhile, the Negro race is in danger of being removed from the picture.
Negroes are doomed. It should be of major concern.
Africa is ****ed.

Um, what?
http://en.wikipedia.org/wiki/Demographics_of_Africa
And this (http://en.wikipedia.org/wiki/File:Population_growth_rate_world.PNG) in particular.

One could go back in time, and stop Hitler.
Yet, someone else would try to kill all the Jews.

Bollocks.

[thought_fugitive]

Wanted: Somebody to go back in time with me. This is not a joke. P.O. Box 322 Oakview, CA 93022. You'll get paid after we get back. Must bring your own weapons. Safety not guaranteed. I have only done this once before.

[Marduk]

Regarding the prospect of being overrun with Time Travel Tourists from the future, what was that film, I'm sure it stared Jeff Bridges, in which there was a bunch of people doing just that? - turning up at the scene of infamous events or to spectate on historical natural disasters? I think they arrived in the film to view a large meteorite strike.

It starred Jeff Daniels not Bridges and was called Timescape,
http://en.wikipedia.org/wiki/Timescape_(1992_film)

one of my old favourites,

[leafman91]

Bollocks.

I say... Bollocks to your bollocks.

[Ashles]

Anytime (pun intended) I hear about someone wanting to theoretically travel back in time to assassinate Hitler, I think of all the modern-day leaders who're committing atrocities and genocide (several African leaders come to mind) and wonder, "Why can't you just assassinate some of THEM, instead? It would certainly be easier than constructing a time machine!"

Actually I think that is a really good point. We know full well of the existence of some absolutely vile people right now in the world. I don't see anybody rushing out to assasinate them.
I guess because many of them are in African countries the west doesn't really care about.


Incidentally the book Making History (http://www.amazon.co.uk/Making-History-Stephen-Fry/dp/0099464810) by Stephen Fry takes another look at the killing Hitler scenario, with interesting results (although as per usual the hero somehow retains all his knowledge of now non-existent past).

[Marduk]

Regarding the prospect of being overrun with Time Travel Tourists from the future, what was that film, I'm sure it stared Jeff Bridges, in which there was a bunch of people doing just that? - turning up at the scene of infamous events or to spectate on historical natural disasters? I think they arrived in the film to view a large meteorite strike.
incidentally there was another more recent movie that dealt with the subject of time travelling tourists coming back to watch natural (and unnatural) disasters that you might want to look up
http://en.wikipedia.org/wiki/Thrill_Seekers_(film)
It was called "time shifters" when it was released in the U.S.

imo it borrowed heavily from Timescapes, same plot, same details, but much better special effects
;)

then of course there was "a sound of thunder" originally written by Ray Bradbury, which featured tourists going back in time to hunt dinosaurs
http://www.imdb.com/title/tt0318081/

[leafman91]

Actually I think that is a really good point. We know full well of the existence of some absolutely vile people right now in the world. I don't see anybody rushing out to assasinate them.
I guess because many of them are in African countries the west doesn't really care about.

Or maybe because the sudden removal of head chief would create a power vacuum that would most likely result in civil war. Perhaps why the CIA or MI5 haven't attempted already.

Though if you don't mind, it was a bit rude of you to bring the subject up, as the person who started the thread requested that as the thread was just for fun, the subject should be avoided.

[Leif Roar]

Wanted: Somebody to go back in time with me. This is not a joke. P.O. Box 322 Oakview, CA 93022. You'll get paid after we get back. Must bring your own weapons. Safety not guaranteed. I have only done this once before.

NB! Do not step on the butterflies.

[Fnord]

Build a city out of Legos. Take it apart, and build a whole new different city out of the exact same Legos, using each and every Lego brick. Now take one of the little Lego people from the new city and try to have it visit the first city.

It took a few readings of this post to perceive its meaning. Nicely put, Piscivore!

Essentially, this idea states that while all of the same elements of the first city would still be present in the second, there would be no first city for the second city citizen to visit, thus describing "Piscivore's Crosstime Corollary to the Law of Conservation of Energy and Matter."

Again, nicely put!

[Lensman]

It starred Jeff Daniels not Bridges and was called Timescape,
http://en.wikipedia.org/wiki/Timescape_(1992_film)

one of my old favourites,

incidentally there was another more recent movie that dealt with the subject of time travelling tourists coming back to watch natural (and unnatural) disasters that you might want to look up
http://en.wikipedia.org/wiki/Thrill_Seekers_(film)
It was called "time shifters" when it was released in the U.S.

imo it borrowed heavily from Timescapes, same plot, same details, but much better special effects
;)

<snip>

Both based on the novella "Grand Tour: Disasters in Time" by Henry Kuttner & C. L. Moore. Excellent story.

[Piscivore]

It took a few readings of this post to perceive its meaning. Nicely put, Piscivore!

Essentially, this idea states that while all of the same elements of the first city would still be present in the second, there would be no first city for the second city citizen to visit, thus describing "Piscivore's Crosstime Corollary to the Law of Conservation of Energy and Matter."

Again, nicely put!

Thank you. :)

[William Parcher]

I was given my grandfather's wrist watch after he passed away at an old age. It's a good mechanical watch that he wore daily for most of his life and he had his name engraved on the back.

If I was a time traveller, I could go back to visit him wearing his watch on my wrist. What can be said about comparing the watches? They aren't simply similar or even identical... they are the same watch. Besides additional scratches and dirt, both watches contain the same molecules of iron and gold. How could they sit side-by-side in any world?

[Piscivore]

I was given my grandfather's wrist watch after he passed away at an old age. It's a good mechanical watch that he wore daily for most of his life and he had his name engraved on the back.

If I was a time traveller, I could go back to visit him wearing his watch on my wrist. What can be said about comparing the watches? They aren't simply similar or even identical... they are the same watch. Besides additional scratches and dirt, both watches contain the same molecules of iron and gold. How could they sit side-by-side in any world?

Exactly my point- and the same applies to the molecules that make up you. Some of what you are would be in your grandfather, his neighbors, the flora and fauna, the soil, the air, even in the sun- but all of what comprises "you" would be accounted for already someplace in the past. Time travel starts off with the assumption that the traveller is somehow separate and distinct from the "past", and that's just not so.

[Toke]

My high school math teacher insisted that be all had a bit of ceasars dying breath in our lungs. (the "e tu bruto" bit).
He could prove it.

[Fnord]

Time-travel makes for good SciFi Channel programming, but all the speculation in the world changes not the one essential fact - there is no evidence above the quantum level that retrograde time-travel is possible.

[Cuddles]

Besides additional scratches and dirt, both watches contain the same molecules of iron and gold. How could they sit side-by-side in any world?

What's the problem? Why couldn't they sit side by side? Remember, once you get down to the atomic, or even molecular, level, all similar particles are identical. You can't take two electrons (just for example, it's the same for any other particle) and say that this is one electron and this is a different electron, all you can say is that they're both electrons. In fact, one of Feynman's rather neat ideas is that there is actually only one electron in the entire universe, travelling backwards and forwards in time. Now, that's not a particularly nice theory as far as Occam's razor is concerned, and it was never meant to be anything more than a mathematical abstraction, but the fact remains that we have no way to prove that it's not actually true.

So given that it's possible that every single particle making up that watch could already be sitting next to countless billions of time-travelled versions of itself, it seems a bit silly to complain about the watch as a whole doing the same.

There are plenty of legitimate reasons to think time travel probably isn't possible, but personal incredulity at some of the consequences isn't one of them.

[Piscivore]

What's the problem? Why couldn't they sit side by side? Remember, once you get down to the atomic, or even molecular, level, all similar particles are identical. You can't take two electrons (just for example, it's the same for any other particle) and say that this is one electron and this is a different electron, all you can say is that they're both electrons. In fact, one of Feynman's rather neat ideas is that there is actually only one electron in the entire universe, travelling backwards and forwards in time. Now, that's not a particularly nice theory as far as Occam's razor is concerned, and it was never meant to be anything more than a mathematical abstraction, but the fact remains that we have no way to prove that it's not actually true.

So given that it's possible that every single particle making up that watch could already be sitting next to countless billions of time-travelled versions of itself, it seems a bit silly to complain about the watch as a whole doing the same.

To have even two atoms of hydrogen, for there to be only one time travelling electron it would have to spend the entire life of the universe in one atom, then at the end travel back all the way to the beginning again and exist simultaneously in the other atom, from beginning to end- wouldn't it?

Where does all the extra energy come from to keep moving this one electron backwards however gawd-awful many billions of times it would have to do so to exist simultaneously- and in multiplicity, for everything except hydrogen- in every single atom that ever existed?

[Ashles]

Or maybe because the sudden removal of head chief would create a power vacuum that would most likely result in civil war. Perhaps why the CIA or MI5 haven't attempted already.

Though if you don't mind, it was a bit rude of you to bring the subject up, as the person who started the thread requested that as the thread was just for fun, the subject should be avoided.
No they didn't say that, they said they wanted to avoid a heated argument. Which isn't happening.
As it happened I didn't see their post, but it really isn't up to you to elect yourself thread monitor.

[Cuddles]

To have even two atoms of hydrogen, for there to be only one time travelling electron it would have to spend the entire life of the universe in one atom, then at the end travel back all the way to the beginning again and exist simultaneously in the other atom, from beginning to end- wouldn't it?

Yes. Well, probably not the entire lifetime of the universe, since all atoms will interact with something else given an infinite time, and if we're correct that protons can decay then all atoms will eventually decay given enough time. But close enough.

Where does all the extra energy come from to keep moving this one electron backwards however gawd-awful many billions of times it would have to do so to exist simultaneously- and in multiplicity, for everything except hydrogen- in every single atom that ever existed?

No extra energy is needed. It's not magically jumping from the end of the universe back to the start, the idea is simply that anti-matter is regular matter going back in time. The simplest example is pair production. From our point of view, it appears that you have a photon floating around that causes an electron and positron to appear:
http://forums.randi.org/imagehosting/108294a4dea7c1bf41.gif (http://forums.randi.org/vbimghost.php?do=displayimg&imgid=16841)

However, this is exactly equivalent to having an electron travelling backwards in time and interacting with a photon, causing it to travel forwards in time:
http://forums.randi.org/imagehosting/108294a4dea841a8ec.gif (http://forums.randi.org/vbimghost.php?do=displayimg&imgid=16842)

Both viewpoints obey conservation of both energy and momentum, and are exactly equivalent mathematically.

[quarky]

Um, what?
http://en.wikipedia.org/wiki/Demographics_of_Africa
And this (http://en.wikipedia.org/wiki/File:Population_growth_rate_world.PNG) in particular.



Bollocks.

Blacks constitute 14% of the global population. Despite the high population bloom in Africa, it is the most threatened by disease and famine.

I can't really argue the point about how unique Hitler was, or if his time-traveling killer would have saved the Jews from the attempted genocide.
It does seem that genocide mostly threatens people that are easily identifiable as a particular group.

[Piscivore]

Yes. Well, probably not the entire lifetime of the universe, since all atoms will interact with something else given an infinite time, and if we're correct that protons can decay then all atoms will eventually decay given enough time. But close enough.



No extra energy is needed. It's not magically jumping from the end of the universe back to the start, the idea is simply that anti-matter is regular matter going back in time. The simplest example is pair production. From our point of view, it appears that you have a photon floating around that causes an electron and positron to appear:
http://forums.randi.org/imagehosting/108294a4dea7c1bf41.gif (http://forums.randi.org/vbimghost.php?do=displayimg&imgid=16841)

However, this is exactly equivalent to having an electron travelling backwards in time and interacting with a photon, causing it to travel forwards in time:
http://forums.randi.org/imagehosting/108294a4dea841a8ec.gif (http://forums.randi.org/vbimghost.php?do=displayimg&imgid=16842)

Both viewpoints obey conservation of both energy and momentum, and are exactly equivalent mathematically.

What would cause them to travel backwards in the first place?

[Cuddles]

What would cause them to travel backwards in the first place?

The interaction with the photon.

[Piscivore]

The interaction with the photon.

The interaction with the photon causes it to travel back in time and interact with the photon?

[shadron]

What would cause them to travel backwards in the first place?

The only current scientific explanation that I've heard is the fact that while we are free in the three spatial dimensions but locked into uniform motion on the time dimension, inside a black hole the reverse is true: the spatial dimensions are constrained to a single point, while the time dimension is navigable. What this might mean for a being crushed into a singularity is difficult to understand, especially since we can't get in touch with him.

[Toke]

http://www.viruscomix.com/page417.html

[Soapy Sam]

Maybe the time events are coded in knots in the strings in all the teeny weeny curly- wurly bijou dimensionettes?

[JollyRoger]

You can get a similar effect much cheaper using a video camera and waiting two years to watch it.

OK then lets take it one step closer to woohoo and send a radio signal the same way, you could tell your self "hay don't do that" and really screw up the time line

[Cuddles]

The interaction with the photon causes it to travel back in time and interact with the photon?

What?

It's really not as complicated as you're making it out to be. First, remember that time and space are not independent things. Just as a particle can bounce off another and travel in a different direction in space, it can do the same and travel in a different direction in time. That's really all there is to it.

What caused the electron to travel backwards in time was an interaction with another particle. What caused it to travel forwards in time again was another interaction with another particle. What caused it to travel backwards in time again was yet another interaction with yet another particle. The problem you seem to have with the cause of it travelling backwards in time is exactly the same as the problem you don't have with the cause of it travelling to the left.

The only current scientific explanation that I've heard is the fact that while we are free in the three spatial dimensions but locked into uniform motion on the time dimension

Given that science doesn't say that we are locked in uniform motion in any dimension, that was not a scientific explanation.

[Piscivore]

What?

It's really not as complicated as you're making it out to be. First, remember that time and space are not independent things. Just as a particle can bounce off another and travel in a different direction in space, it can do the same and travel in a different direction in time. That's really all there is to it.

What caused the electron to travel backwards in time was an interaction with another particle. What caused it to travel forwards in time again was another interaction with another particle. What caused it to travel backwards in time again was yet another interaction with yet another particle. The problem you seem to have with the cause of it travelling backwards in time is exactly the same as the problem you don't have with the cause of it travelling to the left.
I don't have a problem with it, I just want to make sure I understand what you are saying.

[jredf]

I've actually thought long and hard about this and was even going to write a story about it. Time for some outrageous claims that are hard to believe but true.
If time travel is possible, then there are some rules it has to follow.
#1 You can't travel back to the past unless you've already done it.
It's a little mind blowing, but only if you think of yourself as being in a linear existence. If you didn't already exist as yourself from the future some time in the past, then you aren't going to go. Ever. The past can't be changed, because it's already happened.
#2 You can still save someone in the past who died. Whoah, wait a minute. You just said the past can't be changed, so saving someone who is known to be dead is impossible. Not true. You can save them, but after you do you have to make it look like they died the way everyone thinks they do. And guess, what? You're going to get away with it because you've already done it. So, in effect, they never died. Atleast they won't die the way history records it.
#3 You cannot change the future. What? Yeah right. It hasn't happened yet, right? Wrong. The future HAS already happened. Again, linear thinking. The future is a label we put on time ahead of us, which has already happened to someone else, making it their past. Time is set, my friend. Whatever is going to happen is going to and has already happened.
#4 People who travel through time are for a certain period of time indestructable and unkillable. Scenario: Lets say you turn on your machine to travel somewhere and out walks a janitor from the future. You already know that we can't change the future, so no matter what anyone does, at some point in the future they are going to travel back to step out of your machine. Until that time, they cannot be killed or destroyed. You can send them anywhere, to do anything, and though they might not succeed at the mission, you know they will live. They may hate your guts in a great and mighty way, but they will be alive to do so. Such a person would be most dangerous, because they would probably walk through and start shooting and you'd never know why until it was either explained to you, or you'd never know because at that time, you were a causalty.
Thanks for listening kids.

[Ashles]

I've actually thought long and hard about this and was even going to write a story about it. Time for some outrageous claims that are hard to believe but true.
If time travel is possible, then there are some rules it has to follow.
#1 You can't travel back to the past unless you've already done it.
It's a little mind blowing, but only if you think of yourself as being in a linear existence. If you didn't already exist as yourself from the future some time in the past, then you aren't going to go. Ever. The past can't be changed, because it's already happened.

This doesn't adress any problems with time travel, you are simply saying if you create a sci-fi story where it all fits together, then it all fits together.

But this tells us nothing about time travel in reality other than a plot device.

#2 You can still save someone in the past who died. Whoah, wait a minute. You just said the past can't be changed, so saving someone who is known to be dead is impossible. Not true. You can save them, but after you do you have to make it look like they died the way everyone thinks they do. And guess, what? You're going to get away with it because you've already done it. So, in effect, they never died. Atleast they won't die the way history records it.
But any action you make alters history. If you fake their death that means you had to change other things, no matter how minor.

This affects history. So it falls subject to all the paradoxical issues usually raised.

#3 You cannot change the future. What? Yeah right. It hasn't happened yet, right? Wrong. The future HAS already happened. Again, linear thinking. The future is a label we put on time ahead of us, which has already happened to someone else, making it their past.
Time is set, my friend. Whatever is going to happen is going to and has already happened.


Again this only works in a sci-fi story or if you are a complete fatalist and assume everything you choose to do is inevitable (which is a seperate conversation).

And it contradicts your second rule (unless you believe the past can be changed yet the future can't - but you already defined the future as someone else's past so that doesn't work either)

#4 People who travel through time are for a certain period of time indestructable and unkillable. Scenario: Lets say you turn on your machine to travel somewhere and out walks a janitor from the future. You already know that we can't change the future, so no matter what anyone does, at some point in the future they are going to travel back to step out of your machine. Until that time, they cannot be killed or destroyed. You can send them anywhere, to do anything, and though they might not succeed at the mission, you know they will live. They may hate your guts in a great and mighty way, but they will be alive to do so. Such a person would be most dangerous, because they would probably walk through and start shooting and you'd never know why until it was either explained to you, or you'd never know because at that time, you were a causalty.

Again this means nothing outside of a sci-fi story. And it contradicts your own earlier rules.

I think you may need to make those 4 points 4 seperate sci-fi stories as they won't all work together.

And of course none of them are 'true' outside of a story.

[ServiceSoon]

All this talk about hypothetical alternate dimensions and alternate dimensions haven’t even been discovered.

[jredf]

I thought it was a damn good plot device. Oh well.
About the saving people, you wouldn't be changing anything. You might think you are, but you aren't, you're really just doing what's already happened. They are believed to be dead, but possibly alive.
I think that's what could explain so many Elvis sightings. Someone went back in time and molecularly changed a hog into a slobbering humanoid who appeared to od on the crapper. I'm just saying.

More seriously than above, aliens have craft that have been documented to take off at what, about 10,000 miles an hour? In the atmosphere? I wonder how fast they'd be in space. Ofcourse, normal people would probably just spontaneously combust at those speeds unless in some kind of stasis field. Surely that's fast enough to do some time traveling. That would explain why there are craft hovering near major disasters, not because they caused them but because they are documenting them for their alien History Channel documentary "Earth: How Many Times Can One Planet Almost Blow Itself Up?"

[shuttlt]

More seriously than above, aliens have craft that have been documented to take off at what, about 10,000 miles an hour? In the atmosphere? I wonder how fast they'd be in space. Ofcourse, normal people would probably just spontaneously combust at those speeds unless in some kind of stasis field. Surely that's fast enough to do some time traveling.

What, you mean faster than the speed of light? That's nearer to 671,000,000 than 10,000 miles per hour. That's 67,100 times faster. They should easily be able to make 88 miles per hour if they have a flux capacitor though.

[Kuko 4000]

More seriously than above, aliens have craft that have been documented to take off at what, about 10,000 miles an hour?


Welcome to the JREF forum jredf, I hope your stay will be inspiring!

[TjW]

Wanted: Somebody to go back in time with me. This is not a joke. P.O. Box 322 Oakview, CA 93022. You'll get paid after we get back. Must bring your own weapons. Safety not guaranteed. I have only done this once before.

If you're traveling in time, why can't I get paid up front?

[Ashles]

I thought it was a damn good plot device. Oh well.

It's a great plot device. And frankly has more internal logic than most time-travel stories.
(Just not enough to weork in reality.)

About the saving people, you wouldn't be changing anything. You might think you are, but you aren't, you're really just doing what's already happened. They are believed to be dead, but possibly alive.
I think that's what could explain so many Elvis sightings. Someone went back in time and molecularly changed a hog into a slobbering humanoid who appeared to od on the crapper. I'm just saying.

More seriously than above, aliens have craft that have been documented to take off at what, about 10,000 miles an hour? In the atmosphere? I wonder how fast they'd be in space. Ofcourse, normal people would probably just spontaneously combust at those speeds unless in some kind of stasis field. Surely that's fast enough to do some time traveling. That would explain why there are craft hovering near major disasters, not because they caused them but because they are documenting them for their alien History Channel documentary "Earth: How Many Times Can One Planet Almost Blow Itself Up?"

Ah okay you're joking. Sorry didn't realise - it's often hard to tell here, especially with new posters.

[Aepervius]

The S.F. novel I remember in time travel, was that each moment was a sphere, like pearl on a necklace. Going back only changed that time sphere, but going back to yours it as if there had never been any change whatsoever. That was a very good explanation on why nothing ever changed.

There was another one where going backward actually created parallel branch of the universe , but you always returned to your own branch and no change whatsoever was done (although IIRC the protagonist at the end was "losing" substance by too many travel and was becoming ghost like). Again no paradox possible as you could never ever change your own branch.

[dlorde]

I thought it was a damn good plot device. Oh well.
I think you were pretty much right (given some basic assumptions). Ashles objections don't hold - if you fake someone's death in the past, you have to change all kinds of things, but as you said, no-one would notice, because if everyone thought that person had died, you clearly didn't leave obvious clues. If people did notice some discrepancy, you'd know before you went back. If you decided not to go back and fake the death because of the doubt about the veracity of this death, then clearly something else must have happened - perhaps the death was badly faked by someone else, or the death occurred but it appeared faked, etc.

Rule #3 - you can't change the future doesn't necessarily contradict rule #2 you can change the past - it depends on your viewpoint; a time-like loop is involved. If you travel back in time and do something, you can view it as changing the past, and therefore changing the future from that point in time, but you can equally view that action as being part of the past - the future from that point that might have happened had you not taken that action, never happens. Calling the action a 'change' to the past or future is misleading - the action was always going to happen. If the action had a noticeable effect, people (including you) might even remember it at the point you go back in time to do it...

Of course, as you said, this requires the basic assumption that all events are fixed in spacetime, which is a little controversial.

[Aepervius]

More seriously than above, aliens have craft that have been documented to take off at what, about 10,000 miles an hour? In the atmosphere? I wonder how fast they'd be in space. Ofcourse, normal people would probably just spontaneously combust at those speeds unless in some kind of stasis field. Surely that's fast enough to do some time traveling. That would explain why there are craft hovering near major disasters, not because they caused them but because they are documenting them for their alien History Channel documentary "Earth: How Many Times Can One Planet Almost Blow Itself Up?"


Just a nitpick, you can survive any speed whatsoever. The problem is not the speed , it is the acceleration. If you have an acceleration of 1 g over a few minutes, you will certainly reach speed of 3 km s-1 (10 meter s-2 * 300 seconds (5 minutes)=3 km s-1=~10800 km.h-1). 1 G is quite survivable as acceleration and your final speed would be ~10,000k m h-1. OTOH if it was an acceleration to get that speed within 1 second then that would be 300G, yeah, that would not be survivable (record was what , 120g?). You would still not combust, but be rather mushy at the end.

[Cainkane1]

I'd go back in time and eat from the tree of life and filch a few apples to take back home.

[Tumbleweed]

IF time travel to the past is possible, THEN time travelers from the future would be visiting us now. Unless we are considered so boring there is not much point in doing so

[Tumbleweed]

A nasty time traveler caused all those disasters and enabled Hitler

[Ashles]

1 G is quite survivable as acceleration


Indeed, I am surviving it right now. :)

[Ashles]

The S.F. novel I remember in time travel, was that each moment was a sphere, like pearl on a necklace. Going back only changed that time sphere, but going back to yours it as if there had never been any change whatsoever. That was a very good explanation on why nothing ever changed.

There was another one where going backward actually created parallel branch of the universe , but you always returned to your own branch and no change whatsoever was done (although IIRC the protagonist at the end was "losing" substance by too many travel and was becoming ghost like). Again no paradox possible as you could never ever change your own branch.


I've got a good Sci-Fi method myself, but I can't go into it as I'm using it in a book I'm writing at the moment.
But it does allow someone to kill their own grandfather which, I think we will all agree, is the ultimate aim of all time-travellers.

[Tumbleweed]

Time travel gone bad: pictures suddenly surface showing Marilyn Monroe taking a shower

[Ashles]

I think you were pretty much right (given some basic assumptions). Ashles objections don't hold - if you fake someone's death in the past, you have to change all kinds of things, but as you said, no-one would notice, because if everyone thought that person had died, you clearly didn't leave obvious clues. If people did notice some discrepancy, you'd know before you went back. If you decided not to go back and fake the death because of the doubt about the veracity of this death, then clearly something else must have happened - perhaps the death was badly faked by someone else, or the death occurred but it appeared faked, etc.


Your assuming the death is the only change. It wouldn't be. Just because people don't instantly notice the other changes (what did you have to alter to fake the death?), doesn't mean they won't have a knock on effect. Every single one will. Some will be minute, some will quickly become relatively large.

The effects of events over times would not be restricted to what people specifically notice. Any change will have effect - the longer the period, the greater the cumulative effects.

[big-E]

then of course there was "a sound of thunder" originally written by Ray Bradbury, which featured tourists going back in time to hunt dinosaurs
http://www.imdb.com/title/tt0318081/

A truly dreadful film - read the user comments. Shame, as it was a pretty good short story.

[Toke]

I've got a good Sci-Fi method myself, but I can't go into it as I'm using it in a book I'm writing at the moment.
But it does allow someone to kill their own grandfather which, I think we will all agree, is the ultimate aim of all time-travellers.

No, I liked both my grandfathers. :)

[Lithrael]

Your assuming the death is the only change. It wouldn't be. Just because people don't instantly notice the other changes (what did you have to alter to fake the death?), doesn't mean they won't have a knock on effect. Every single one will. Some will be minute, some will quickly become relatively large.

The effects of events over times would not be restricted to what people specifically notice. Any change will have effect - the longer the period, the greater the cumulative effects.

Well yes but all of that is included in the premise. All these things you have 'changed' in saving someone and covering up after yourself, all of them have already and always happened and the knock on effects of all these changes were already present and in effect at your future point of departure. It's been pointed out several times, this is the 'all events, past and future, are set in stone' version of a time travel plot premise. Which is to say even as you first watch some terrible death, so terrible that years later you will decide to go back in time and save this person - your future self is already RIGHT THERE offstage to the left, projecting a 3-D movie of this death for you to watch, having handed the saved person a one way ticket to Guam. If the guy in Guam ends up conquering it and beginning the New Guam Empire, then the New Guam Empire was already there in the future the time traveller left from, he just probably didn't know his interference was going to be its cause. All of the 'changed' events are not in fact changed, they always happened that way. The time traveller always came back and caused that bit of causality.

Which incidentally, seems to be the version of time travel that "Lost" is using, so far. The other popular plot of time travel is the 'alternate reality' one, where each backwards time travel event creates a new version of reality. It has the subtypes 'many realities' where these events split off discrete independent realities: the old one still exists, minus the time traveler (funny enough the cartoon Dragon Ball Z uses this type of time travel correctly and consistently) and 'one reality' where these events rewrite the current reality into the new one (Back to the Future style).

[billydkid]

Before you consider traveling through time please take this guys advice:

owlz8Emd17U
Man, I'm sure happy I happened to watch this. You have no idea how close I was to making a really big mistake.

[billydkid]

IF time travel to the past is possible, THEN time travelers from the future would be visiting us now. Unless we are considered so boring there is not much point in doing so
Unless the future hasn't happened yet.

[big-E]

No, I liked both my grandfathers. :)

I never even got to meet either of mine! I wouldn't mind violating causality just to see what they were like...

[dlorde]

IF time travel to the past is possible, THEN time travelers from the future would be visiting us now. Unless we are considered so boring there is not much point in doing so
Who's to say they aren't ? They may be wandering around with period cameras just like any other tourist.

[Tumbleweed]

There should be axioms for time travel like " if you go into the past to make things better, they will only end up worse." For example:you go back because you wish you had married Vivacious Vivian instead of dull old Plain Jane. You come back to find Plain Jane gone, but Vivacious Vivian just took you for everything you had in a divorce. AFTER she slept with your best friend. So NOW you have you have to go back again and murder Vivacious Vivian or kill her parents, you think you got away with it but the Cold Case gang finally gets you, my axiom kicks in, and you end up on death row. I'd stick wth Plain Jane and forget about the time travel

[ZirconBlue]

I've got a good Sci-Fi method myself, but I can't go into it as I'm using it in a book I'm writing at the moment.
But it does allow someone to kill their own grandfather which, I think we will all agree, is the ultimate aim of all time-travellers.

I've never met either of my grandfathers, nor do I recall even seeing pictures of them. Perhaps in the future I will discover that will have, indeed, gone back in time and killed them.

Of course the real problem with time travel is grammar.

[Tumbleweed]

Well if people from the future are visiting us, can we catch one? Assuming they are viable not just watching a video of "2009- the important points". What if one of them got trapped here knowing what the future brings. He could of course end up being the richest man on Earth or pretty much just direct his life in any direction and be a smashing success because of prior knowledge. Beat Bill Gates to Windows for example without really even trying hard. "Cheating" would probably get old after awhile

[Tumbleweed]

Well if people from the future are visiting us, can we catch one? Assuming they are viable not just watching a video of "2009- the important points". What if one of them got trapped here knowing what the future brings. He could of course end up being the richest man on Earth or pretty much just direct his life in any direction and be a smashing success because of prior knowledge. Beat Bill Gates to Windows for example without really even trying hard. "Cheating" would probably get old after awhile
I think after I got bored at being a success at whatever at whim, I would come out of the closet and go the God route. You know, declare in the NY Times that I am from the future and if you don't believe it why am I right about EVERYTHING including my 5 day forecast and the exact rise and fall of the S&P 500 each and every day. I'd get a cult going like Warren Buffet has and take over the world and then--- but suppose the power trip would get old too. Uncertainty - its a good thing

[dlorde]

Jealous of a wealthy old man who has made his fortune from shrewd investments, you redouble your efforts on the time machine. Finally it is ready and you sacrifice your future to return to the past and make a fortune from shrewd investments. Years later, a wealthy old man, and dying of a disease for which the cure will not come soon enough, you hear about the guy who is trying to invent a time machine - it's you, young and healthy as you were when you invented it - but you know you can't stop yourself going back, and that you'll never live to see the future you left behind...

Polish it up, add a few twists, and there might be a story there :D

[Marduk]

More seriously than above, aliens have craft that have been documented to take off at what, about 10,000 miles an hour?

ok I'm going to have to point out the obvious oxymoron there, vis a vis "alien craft" and the word "documented".
:rolleyes:
The time travellers coming back to watch disasters theme has been done twice in hollywood already

;)

[big-E]

Of course the real problem with time travel is grammar.

Tut tut... the problem willan on-be with grammar

[Aitch]

But it does allow someone to kill their own grandfather which, I think we will all agree, is the ultimate aim of all time-travellers.

Apart from Philip J. Fry - who became his own grandfather (http://en.wikipedia.org/wiki/Roswell_That_Ends_Well). :eek:

[MortFurd]

Apart from Philip J. Fry - who became his own grandfather (http://en.wikipedia.org/wiki/Roswell_That_Ends_Well). :eek:
What a wimp.

This person (http://en.wikipedia.org/wiki/%E2%80%94All_You_Zombies%E2%80%94) got to be his own mother AND is own father - the first person to ever literally f*** himself. He also recruited himself into his job AND was responsible for his male self meeting up with his female self as well as paying for himself to be raised in an orphanage.

And if that wasn't complicated enough for you, listen to I'm my own grandpa. (http://en.wikipedia.org/wiki/I%27m_My_Own_Grandpa) No time travel, but the guy still gets to be his own grandfather.

[jredf]

I said documented because a jet in the UK Airforce was told to take one down the size of a football field and before he could fire it zoomed away at what they said was 10,000 miles an hour.

I was going to write a story about a time machine that broadcasts on a certain harmonic wavelength. When that wavelength is broadcast again, it picks up the wavelength itself and the person comes through. The problem is, every time they turn it on to broadcast, someone steps through from the future. A man shows up from a few years in the future and they can't figure out why he would even have access to the machine. He is just some blue collar guy with no ties to the military. So they hire him to do some wild jobs because they know he can't die till they send him through.

There are ways to fool this though like twins, facial reconstruction or, more to the point, make them look like someone that they are not. But at the end, they still have to go through the machine if they were witnessed arriving. Who-ever that is will do some traveling.

[jredf]

Also, if the aliens are from the future, then their History Channel Documentary broadcast commercials would probably go, "Tune in Flarkday at half past Bloomenfrubal, and witness the hilarity when Spaceman Bob makes a colossal mistake over Nevada, starting the humans building of mysterious Area 51. Good ol' Spaceman Bob, we'll miss your antics."