Time travel

[FlyingLemons]

I noticed an interesting discussion occurring in the "If you could visit any decade in the 20th Century" thread in Misc, and I felt that perhaps it might be good to start up a discussion here. And it's a current hot topic in the world of Trek too, for obvious reasons.

I've always been fascinated by the idea of time travel, and specifically all the different varieties that modern physics has thrown up. There's the Chronology Protection Conjecture, where the universe very specifically intervenes to stop any form of time travel, the Novikov Consistency Principle, where if you intervene in the past to change events time just alters itself to render that change inert, and also the many-worlds idea that all the changes have their own separate universe.

I always remember a Stephen Baxter/Arthur C. Clark story called The Light of Other Days where a method of looking back in time was developed by plucking wormholes from the quantum foam and expanding them to look at past events. These were unalterable, and indeed it caused people a lot of pain to watch things like the loss of loved ones playing out all over again. It also altered the way people looked at things like religion and privacy as well. Indeed, time travel or related phenomena would probably change every single aspect of our society.

I'm not entirely sure what really to ask, but I'm just curious to see what people think of theories of time travel, whether they believe it can actually be done, and indeed if there's already time travellers swanning around the place...

 

[Zachary Smith]

My personal opinion, based on nothing but intuition, is that if one were somehow able to go back to the past and make a change, the universe would continue forward from THAT reality and the "future" the traveler came from would have ceased to exist. One universe, one time-line moving past to future.

I can think of no reason why nature would have any "opinion" as to how the future should unfold--it is merely a continuing sequence of Cause and Effect. It seems that there would have to be some "Awareness" that would be offended by changes in the time-line for there to be an intervention that would "un-do" or otherwise prevent an alteration. I also find it inconceivable that one can somehow create an entire alternate universe simply by turning left instead of right in the past. Where does the mass and energy come from? Where does the universe exist physically relative to the original? Etc etc etc.

As far as whether time travel is possible--yes. It is OBVIOUSLY possible. We travel into the future at 1 second/per second and, to SOME extent the rate of travel can be influenced (gravitational fields and at relativistic speeds). OBVIOUSLY time-travel is possible. The question is whether it is possible to or whether we can learn to control the direction and rate. As far as those questions go, who knows?

 

[ProtoAvatar]

Is time travel into the past possible?

According to the Chronology Protection Conjecture, it isn't.
But this Conjecture is far from being proven. Many physicists support Chronology Protection because it preserves causality and avoids paradoxes.
Indeed, in certain conditions, time travel into the past may be possible (according to what humanity knows now) - worm holes, flying around a spinning singularity.

Let's assume information can travel into the past. What will happen?

The Novikov Consistency Principle says - nothing. A time traveller (or information sent into the past) won't change anything, because the events of the past will modify themselves so as to prevent any such changes.
This is only possible if there exists a previously undiscovered physical law that supersedes all other laws - ironically, including causality - and that nullifies any changes one attempts to make to the past.

Perhaps a hybrid between the Chronology Protection Conjecture and the Novikov Consistency Principle is in effect. Only travellers and information that can't change the past can actually reach the past - due to quantum mechanical principles.
Or it is possible only to view history, not experience it.

Another theory is that one can travel into the past and change it, creating a new timeline that exists alongside the old one.

All the possibilities I analysed up to this point avoid paradoxes.

One hypothesis predicts that only the new timeline (created by time travel) continues to exist - and paradoxes be damned! (you'll find a lot of them here).
If this view is correct, then we are nothing but flies who live for a day - until a time traveller changes the past and we cease to exists or we "exist" in a completly different form - one second we're rich, the next one we're beggers, the third one we don't exist. And we would never know any of this - we think we lived full lives and have the memories and status in the world to prove it - all of which is ephermal and easily changed by temporal intervention.

Personally, I beleive information, at least, can be sent into the past. What happens then?

Let's say a new timeline appears and the old one disappears.
But, in this case, where did the information that changed the past come from? From nowhere? In this case, the information disappears and the old timeline reappears.
But, if the old timeline exists again, then that information also exists. And if the information exists, then the new timeline appears again and the old timeline vanishes.
And so forth.
Essentially, I'm saying that both timelines exist, but consecutively not simultaneously.

 

[think]

As the past and future illusions are real when we let them we know the now that is ever textured and fictional frictions of surface and submarines that can make more of the ever lived life tenses and tones altered by blinking in and out of bubbling morphisms in tandem to the view that makes not much of a difference yet is different still.

"A casual stroll through the lunatic asylum shows that faith does not prove anything" - Friedrich Nietzsche

I believe faith is possible and that Friedrich was a lier but still a good quote who believes the mad men of societies casting ., speaking of proving something not that it really matters the proof is a blue green shade that shadows the lights even after they go out.

but why is it so beautiful why why why ., why not let it be beautiful ., so what.

 

[Asbo Zaprudder]

I also find it inconceivable that one can somehow create an entire alternate universe simply by turning left instead of right in the past.

I've often wondered what happens if the probability of an event is an irrational number (it cannot be expressed by the division one integer by another integer). Would this not imply that the number of possible universes participating in the event is an uncountable infinity (that is, greater than Aleph-null: the countable infinity of natural numbers)? It makes me doubt the hypothesis, but who am I to tell the multiverse how to behave.

 

[Ronald Held]

No one can definitively say whether time travel can occur, and whether you get a close consistent time loop or spawn of another timeline.

 

[FlyingLemons]

I'm not so sure about the ideas of time travel myself. The idea is fascinating, although the position of a few people I've talked to seems to be that it's probably not possible. The sum over paths approach of quantum mechanics would suggest that there is something to the many-worlds idea, but at the same time a lot of niggling problems come up with the maths involved.

I guess the only way to actually find out is to find a cosmic string and try it, but well, I don't think anyone has one lying around...

 

[Zulu Romeo]

I noticed an interesting discussion occurring in the "If you could visit any decade in the 20th Century" thread in Misc, and I felt that perhaps it might be good to start up a discussion here.

Yeah, sorry about that - I guess we just got carried away there.

To reiterate, in the other thread it was suggested that creating a time loop was impossible from an energy point of view, as an object (let's say, Admiral Kirk's reading glasses) directly caught in the loop would cease to exist through being infintely old and thus losing all its energy as it entered and re-entered the loop several times. I suggested, however, that an object can still be valid if sent back through time, so long as it doesn't itself become reused in the time loop e.g. it dies in the past. However, it is highly likely through chaos theory that any object entering the timeline where it "shouldn't" be will create its own ripples through the space-time continuum, altering every thermodynamic variable in the Universe by its very unwanted presence, and that somehow the space-time continuum will "course-correct" itself by destroying the object and preventing any potential paradox (the "upset digestive tract" model).

Or at least that's what I think the whole discussion was about - feel free to elaborate and correct me if I was wrong.

In that thread I was trying to describe the "time HAS told" theory that travelling into the past creates: that the actions of the time traveller are supposed to happen in the normal timeline (i.e. there is only one reality and one timeline, and it's all unfolded as it should). This theory carries a heavy sense of dramatic irony in terms of the traveller's intention to change things - the traveller is unaware that his very being there and his actions are the very things he is trying to change in the first place.

Spoiler: another certain JJ Abrams project running since 2004

It's the sort of theory the creators of LOST are trying to explain in the current series.

Come to think of it, if this scenario was true, in order to preserve the timeline, time travel must be made possible to allow the traveller to go back in time in the first place. Whether the traveller's actions are intended or not... that's what is supposed to happen (even if the traveller doesn't know it yet). By destroying the time travel capabilities, the paradox is created. Still, it's fascinating.

 

[What's his face]

Wait...
If there are infinite universes.... and every possible outcome is real, then in one of these universes... someone or something has accidentally (or on purpose) done something (make a bomb, etc) that could destroy all of the universes. But if that is the case, then how are we here?

(brain explodes)

Also, if there are infinite universes and every possible outcome actually happens somewhere, then if I imagine myself traveling to an alternate universe and looking through my alternate self's bedroom window and looking at my alternate self, that means that in a small number of these universes, this has actually happened. But if that's the case, why is it that when I look out my bedroom window, there is not alternate version of me looking back?

(brain explodes again)

 

[Zulu Romeo]

Wait...
If there are infinite universes.... and every possible outcome is real, then in one of these universes... someone or something has accidentally (or on purpose) done something (make a bomb, etc) that could destroy all of the universes. But if that is the case, then how are we here?

(brain explodes)

The bomb worked, and each and every Uinverse was replaced by something else more bizarre and inexplicable?

One could also theorise that this has not only happened, but is happening right now and will happen again.

 

[FlyingLemons]

Wait...
If there are infinite universes.... and every possible outcome is real, then in one of these universes... someone or something has accidentally (or on purpose) done something (make a bomb, etc) that could destroy all of the universes. But if that is the case, then how are we here?

(brain explodes)

Also, if there are infinite universes and every possible outcome actually happens somewhere, then if I imagine myself traveling to an alternate universe and looking through my alternate self's bedroom window and looking at my alternate self, that means that in a small number of these universes, this has actually happened. But if that's the case, why is it that when I look out my bedroom window, there is not alternate version of me looking back?

(brain explodes again)

Well, there's the theory that the universe is "open", i.e. that it's infinitely vast and extends for ever, and within this open universe are infinite copies of the Earth with every single possible event being played out on it. In theory, it is actually possible to find yourself in a part of the universe with another you. If this is true, and there is another me out there, quite what I'd say to other me I don't know.

Indeed, it's best not to contemplate how I exist in other universes, because invariably I end up very confused thinking of all the possible people I could have turned into...

 

[PurpleBuddha]

Wait...
If there are infinite universes.... and every possible outcome is real, then in one of these universes... someone or something has accidentally (or on purpose) done something (make a bomb, etc) that could destroy all of the universes. But if that is the case, then how are we here?

(brain explodes)

Also, if there are infinite universes and every possible outcome actually happens somewhere, then if I imagine myself traveling to an alternate universe and looking through my alternate self's bedroom window and looking at my alternate self, that means that in a small number of these universes, this has actually happened. But if that's the case, why is it that when I look out my bedroom window, there is not alternate version of me looking back?

(brain explodes again)

Maybe it is not possible to built a bomb that can destroy an infinite number of universes.

Maybe it is not possible to travel from one to another.

And maybe the idea that every thing that that could possibly occur, does occur, is simply false. There are sets of infinity. Say there are an infinite number of choices you could make that could play out in other universes. It is possible that only a very small set of these choice do play out, and possible further that there really is only one of you, in this universe. This would in no way have to limit the possible universes out there to finite number.

Edit: Or, in other words, infinity minus one is still infinity.

 

[Kaziarl]

What if people are looking at the timeline wrong? I mean what have we been "taught?" And I say taught loosely since it is mostly a fictional idea.

Most people think of the timeline as a stream. It has a source, it (maybe) has an end, and we're traveling from one to the other. Now, under special circumstances we can go back up the stream, or find a way to go down the stream a little faster then the current takes us.

Here's my thought though, and the idea comes from what I saw in a Voyager episode.

Now, in Year of Hell, they still referred to it as a time stream, but I saw the way the weapon worked a little differently.

I saw what seemed more like a pond. You throw a rock in a pond, and it sends ripples across the entire pond. The farther edges feel less of an effect, and the spot where the pebble hits is changed the most.

When the rock hits, it also sends several droplets of water into the air, and they hit the water creating more ripples.

Now, we see this in Year of Hell when the Krenim Time Ship takes out a planet, and it makes large and small changes to the neighboring planets. But we also see the other trait that you get from a pond, and not from a river. At the end, the surface calms down and returns to normal.

Now, I'll admit, i'm not a scientist. I don't have degree's and books, but that seems to me like it explains most of the problems with time travel. It could even explain the Grandfather Paradox.

 

[Lookingglassman]

I dont believe in time travel because what ever happened in the past is gone forever. There is no "universal recorder" recording everything so if time travel is discovered we can just jump into the past.

 

[Asbo Zaprudder]

I'd like to know why time appears to limit you to travelling in one direction. Spatial dimensions generally don't have this limitation apart from when you're in the unfortunate position of having crossed the event horizon of a black hole, and you are falling toward the singularity. Equations in physics are time-symmetric -- time asymmetry is tacked on as an observation as in the second law of thermodynamics. We may observe time in one direction because our brains work by entropic processes, but we have no idea why there is such an arrow of time. Is it in fact an artifact of our physiology? That is, do we sense time passing even though all past and future spacetimes and possible events co-exist, and our experience is merely a path through one possible set of configurations?

It's also interesting to note that the solution to Maxwell's equations that describes the propagation of electromagnetic radiation exhibits both retarded waves (travelling outward and forward in time) and advanced waves (travelling outward and backward in time, which we would observe and interpret as inward and forward in time). The advanced wave solution is usually ignored in undergraduate courses. Feynman gave a very interesting discussion of how advanced waves influenced his thinking about quantum electrodynamics in his Nobel lecture back in 1965:

http://nobelprize.org/nobel_prizes/physics/laureates/1965/feynman-lecture.html

It has been speculated that waves could be used to communicate with the past -- the so-called "Feynman radio" -- and no, I have no idea how to construct one of those either to transmit or to receive. But, if it's allowed by the laws of physics to send information as the energy of EM radiation into the past, perhaps sending energy as mass might be permissible as well.

 

[Ronald Held]

There are several arrows of time, One is thermodynamic, another associated with the expansion of this Universe.

 

[Zachary Smith]

There are several arrows of time, One is thermodynamic, another associated with the expansion of this Universe.

I actually have an intuition that time is somehow related to the expansion of the universe. I suspect that the ENTIRE universe is expanding--not just space but everything it contains. This includes matter and all the objects it makes (you and me included). This expansion is imperceptible on the small scale because we are more or less expanding simultaneously. After all, if you were in a room and growing and everyone in the room AND the room itself were growing at about the same rate and you had no standard reference for scale, how would you ever perceive you were growing?

The reason that the expansion of space can be detected is because of gravity. Objects made of matter expand more slowly due to the gravitational fields they create. "Empty" space expands at a quicker rate than, say, a planet does. This is also demonstrated by experiments that indicate time "moves" more quickly in low gravity environment and is "slower" in a heavy gravity environment. I think if it were possible to place a measuring device in intergalactic space far from any strong gravity fields, you'd see it measuring the passage of time as faster than on Earth. This may have a related aspect to the idea that time passes more "slowly" at near relativistic speeds based on the idea that the inherent inertia of an object moving at such a velocity (approaching "infinite mass) creates an artificial "gravity field". Not a true gravity field, mind you, but inertia interferes with the expansion of an object and thus "pulls it out" of "normal" time.

It's a wacky idea, I know, but one I find intriguing on occasion. I can't feature how, even if this WERE true, that one could use it to travel BACKWARD in time--but if one were to do so, you might find yourself unexpectedly BIGGER than you would anticipate as the universe and everything in it was literally a smaller place in the "past". Of course, the further "back" you went in time, the LARGER you would be relative to your surroundings, so watch those ceilings, folks.

 

[Asbo Zaprudder]

There are several arrows of time, One is thermodynamic, another associated with the expansion of this Universe.

Perhaps if we interpret the Big Bang as the origin point with the lowest entropy value, the two arrows really boil own to the same thing. Of course, such speculation is nothing new.

 

[think]

if we were to put say "hallucinatory drugs" in the air? maybe we would all experience some kind of time travel or at least we could think we are traveling (through or) In time

and in time we would get used to this traveling through time, so, like we would do it all the time?

 

[Gepard]

if we were to put say "hallucinatory drugs" in the air? maybe we would all experience some kind of time travel or at least we could think we are traveling (through or) In time

and in time we would get used to this traveling through time, so, like we would do it all the time?

Are you okay?