Fascinating Time-Travel Paradox

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I love this time-travel paradox

Suppose you get visited by a man claiming to be the future you. he tells you the plans to build a time machine, and tells you that you must build it, and use it to tell your younger self about the invention (like he is doing now)

You then grow up, and use the man's plans to build a time machine, and visit your younger self.

Where did the actual "idea" of the time machine come from?? Who or what generated that idea, and set those series of events into motion? :surprised

I have heard that time travel BACK in time is permitted by physics so that makes this scenario is possible.

Anton
 

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  • #2
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AFAIK, time travel is "permitted in physics" in that if you were to travel faster than light, you could stop and look back and see what you were doing a few seconds ago because the light would need time to catch up to you. However, this obviously does not allow you to go back and change anything. What you have done cannot be undone. According to relativity, this is not possible.

Such theoretical concepts are far beyond me, so I usually don't meddle in this kind of stuff, but I'm sure others will comment and correct any flaws in reasoning I may have made.

Interesting idea, though.
 
  • #3
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Where in the world do you people get the idea that physics even suggests time travel is possible?
 
  • #4
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But I suddenly have a notion that what if the universe is parallel?And quantum mechanics allow possibilities and one thing have many states mixing together. I mean there can be a time machine which would carry you to another "universe"-state in which you are indeed dead to prevent that contradiction you kill your younger self. But that's good scientific novel material rather than a physics theory.
 
  • #5
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KingNothing said:
Where in the world do you people get the idea that physics even suggests time travel is possible?
Probably from General Relativity. As far as I know, there isn't a thing in the laws of physics that expressly prohibits it. However it may be very improbable.
 
  • #6
Averagesupernova
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What you describe is probably the ONLY time travel permitted. The act of time travel reinforces itself in the scenario. How you would actually get into this loop is perplexing though. I believe Hawing has described something like this. Travel back in time to kill yourself and you will NEVER succeed. The fact that you exist at all to travel back guarantees you will NOT be able to do so. Something will always happen. Time machine break down, get hit by a bus on the way, crazy things of this nature are guaranteed to happen. Otherwise, you would not exist to travel back in time. The loop you described reinforces itself. Going back to kill someone who has caused you grief cannot succeed because once you change history you no longer have a reason to go back. Your plans will always be foiled by physics.
 
  • #7
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I always get a kick out of the time travel movies. Some people go back in time, talk to about 50 people, get in fights, steal cars, etc, and then caution one another 'be careful not to change anything.'

I tend to subscribe more to a version of Chaozen's parallel universes theory, i.e., an infinite number of possible universes for any given moment in time. Go back in time and kill yourself - No problem. You're now stranded on an alternate 'worldline' in which 'you' (think of him like the evil Captain Kirk :devil: ) die at an early age. Meanwhile, the old universe (worldline) keeps clicking along normally, although short one mad scientist and one time machine.
 
  • #8
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No offense you guys, but if this is going to turn into a Sci-Fi discussion, it should go in the general Discussion board. And grogs, if you are trying to describe that even small actions make huge differences, I believe that's called the butterfly effect. Yes, the movie applies to the theory very well.
 
  • #9
cronxeh
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Actually there is a law in physics that prohibits this. There are even probabilities and formulas. Until you figure out which law it is, I will remain in the skeptical group.
 
  • #10
Integral
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KingNothing said:
No offense you guys, but if this is going to turn into a Sci-Fi discussion, it should go in the general Discussion board. And grogs, if you are trying to describe that even small actions make huge differences, I believe that's called the butterfly effect. Yes, the movie applies to the theory very well.
BINGO! My Thoughts exactly!
 
  • #11
matthyaouw
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If I ever invent a time machine, i will come back and visit myself right now!

...............................

Damn!

Try it. You never know, it might work.
 
  • #12
Gonzolo
fomenkoa said:
I have heard that time travel BACK in time is permitted by physics so that makes this scenario is possible.

Anton
"Permitted" is a bit of a strong word here. There is consensus on travelling to the past.

Travel to future however, is part of elementary special relativity, and is measurable with particles. The obstacle is having to go near light speed to make it observable.
 
  • #13
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Gonzolo said:
Travel to future however, is part of elementary special relativity, and is measurable with particles. The obstacle is having to go near light speed to make it observable.
How can future time travel b e part of elementary special relativity, when it seems quite impossible. Can't you observe the future, and then decide to change it? For example, you see youself eating cereal tomorrow, but when tomorrow comes you decide to eat oranges instead
Anton
 
  • #14
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fomenkoa said:
How can future time travel b e part of elementary special relativity, when it seems quite impossible. Can't you observe the future, and then decide to change it? For example, you see youself eating cereal tomorrow, but when tomorrow comes you decide to eat oranges instead
Anton
Don't know. Don't care. Just as long as I can get the horse track results :biggrin:
 
  • #15
BobG
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fomenkoa said:
I love this time-travel paradox

Suppose you get visited by a man claiming to be the future you. he tells you the plans to build a time machine, and tells you that you must build it, and use it to tell your younger self about the invention (like he is doing now)

You then grow up, and use the man's plans to build a time machine, and visit your younger self.

Where did the actual "idea" of the time machine come from?? Who or what generated that idea, and set those series of events into motion? :surprised

I have heard that time travel BACK in time is permitted by physics so that makes this scenario is possible.

Anton
There's a very good Isaac Asimov story about a group responsible for managing time travel (who gets to travel through time, what changes should be made, etc), including how these guys ensure their time machine gets invented, in the first place. It's called "End of Eternity".

But what if someone from your older self's future looked back and realized the damage caused by time travel and decided to come back and try to prevent you from telling yourself how to invent the time machine in the first place? In other words, they were intentionally trying to create a situation in which 'their' present didn't exist. Or is that plot line too similar to Terminator?
 
  • #16
Moonbear
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Well, gee, it's all so simple really. It's that big time sphere that encircles the 4 corners of the time cube. Just be careful not to get off on a tangent while traveling, or you could fall right off the end of the universe! :rofl:
 
  • #17
Gokul43201
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Time travel is permitted so long as you relinquish the ability to interact with the outside world - meaning that you can never know you've time traveled. Interaction would violate causality.
 
  • #18
Evo
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It wouldn't matter if you were aware you were time traveling or not, just your presence is going to throw things off. You are right that no interaction could be allowed, that means you could not go near people.

For instance, you decide to buy a pack of gum and walk up to the cashier. A woman gets in line behind you. Your presence has delayed her by 83 seconds. (she would not have had to wait if you had not been there). She gets into her car and is killed when a drunk runs a red light. Before you showed up, she would have not been in a wreck and eventually given birth to the person that finds the cure to cancer. Now that child is never born.

Another scenario, you're driving a car. The man in the car behind you has to stop for a red light. The light turns green, he continues, nothing happens, he goes on to live for years. Before you appeared, he made the light (your presence caused him to miss it), he was killed a few moments later in a car wreck. Because of you he is alive, he ends up becoming a mass murderer.

Because you are there, people are continually affected by your presence. You don't have to knowingly do anything in order to cause drastic changes to the future.
 
  • #19
Chi Meson
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I'm running on somewhat dated material here, but I bielive the work of Kip Thorne has provided a model for time-travel using the spaces described as "quantum foam." These are the micro-nano-scopic spaces between the "virtual particles" that fill up normal "space." These foam holes do not exist in the spacetime of our everyday world. If these foam holes could be expanded (which requires a huge negative energy density) then a portal could be created BUT...

... this portal would allow time travel back only to the moment of the creation of the portal.

This theory is improbable but, last I heard, Kip Thorne is not a crackpot. Anyone heard an update on this idea?
 
  • #20
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Evo you seem quite pessemistic about it, is it not also possible that your presence may have indirectly saved the lives of millions of people and eventually caused the invention of the cure to AIDES and periodically prevented a nuclear holocaust?

but onto more theory, if by some slim chance your going back in time some how creates the exact same results as when you were originally there, then your still in the past, but it's the same past you've already experienced and you are now stuck in an indefinite loop of reoccuring time.
 
  • #21
Averagesupernova
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Smurf said:
Evo you seem quite pessemistic about it, is it not also possible that your presence may have indirectly saved the lives of millions of people and eventually caused the invention of the cure to AIDES and periodically prevented a nuclear holocaust?

but onto more theory, if by some slim chance your going back in time some how creates the exact same results as when you were originally there, then your still in the past, but it's the same past you've already experienced and you are now stuck in an indefinite loop of reoccuring time.

No. You as a person are not stuck in a loop. If this were the case then more and more of you would continue to show up. An infinite number of you would show up in the time line. The closed loop is simply a representation of not really being able to determine which is cause and which is effect. If the older you did not travel back to the future, then what would happen is this person would grow old and die in the past.

Someone mentioned something about being impossible to know you have time traveled. I have said this many times. If I go back and change the past so something I don't like doesn't happen then I have no reason to go back. OR, I may have just simply created an alternate time line and don't remember anything except what is actually in the new time line. I jumped over and I have no memory of any previous alternate time lines. Granted, they may be the same up to a point, but I don't remember things that did not happen in my current time line.

I still stand by the theory that says for time travel to be possible and a person consciously know it you have to get a cause/effect loop going. And that is stretching it.
 
  • #22
BobG
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Smurf said:
Evo you seem quite pessemistic about it, is it not also possible that your presence may have indirectly saved the lives of millions of people and eventually caused the invention of the cure to AIDES and periodically prevented a nuclear holocaust?
Impossible. I think the laws of sci-fi literature prohibit it. :rofl: Have you ever read a sci-fi story where a person's travels back into the past did some good for humanity? If you go back in time, it's going to take at least two sequels to set things back the way they're supposed to be. Inefficient, at best.
 
  • #23
Evo
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Chi Meson said:
... this portal would allow time travel back only to the moment of the creation of the portal.

This theory is improbable but, last I heard, Kip Thorne is not a crackpot. Anyone heard an update on this idea?
That is also what Ronald Mallett believes.

Here is a previous post of mine.

Why you haven't met someone from the future

However, putting Ronald's theory into practice presents plenty of problems. For example, the temperature of the ring would have to be close to absolute zero (-273°C), so humans would find it difficult to use. It would also be impossible to travel back to a time before the machine was switched on. This explains why people from the future haven't visited us - we are yet to build a time machine for them to exit from.

Ronald hopes that travellers from the future may be able to overcome these difficulties and use the rings of light that we construct today as portals to our time.

http://www.abc.net.au/science/slab/...les/default.htm [Broken]

This is an excerpt from a "layman's explanation" of Mallet's paper.

Nearly 50 years later, Mallett may be on the verge of building the world's first operative "time machine," though it will bear little relation to that of Wells, or to the DeLorean sports car of the movie Back to the Future, or the Tardis of Dr. Who or any of the other hundreds of time traveling mechanisms that have been imagined since Wells first took a crack at it.

Mallett's machine, as laid out in his May 2000 paper in Physics Letters entitled "Weak gravitational field of the electromagnetic radiation in a ring laser," is based on Einstein's formulation that light and matter are both forms of energy.

We know that matter can bend space-time and according to Einstein's theory, matter and light are both forms of energy. So why can't light bend space-time?

This fall, with UConn colleague Dr. Chandra Raychoudri, Mallett will begin work on building a "ring laser"--basically, a device that will create a circulating light beam, perhaps within a photonic crystal that will bend the light's trajectory and slow it down.

Then, a neutron particle will be sent into the space in the center of the beam. In short, the beam--perhaps two beams in one model, with the light traveling in opposite directions--is expected to twist the space-time inside the circle into a loop.

Think of a spoon stirring thick gravy in a pot and creating a vortex, only the vortex in this case is the fabric of space-time twisting, with past, present and future, circling one another so that the future precedes the past.
Then--and while this might not seem very exciting--a neutron, a small particle of matter--will be sent into the center of the beam. If its spin is affected, then it is being affected by warped space-time.

In a further experiment that Mallett has considered, two identical samples of a radioactive substance could be put into the center of the ring, one going in the direction of the beam. The other in the opposite direction. Since radioactivity decays at a measurable rate, it would be possible to measure, in effect, the time that both particles had experienced within the beam. If the time proves to be different, then time will have been measurably altered.

Eventually, says Mallett, "what would be neat is if you saw another neutron in there that you hadn't introduced yet." In essence, the same neutron "visiting itself from the future."

So you've moved a neutron. So what?

What Mallett will have shown--if it works--is that the fabric of time itself can be altered by light, and a thing can be moved into the past. If it works for a neutron, in theory, it would work for you and me.

http://www.walterzeichner.com/thezfiles/timetravel.html [Broken]

Mallett's paper "Weak gravitational field of the electromagnetic radiation in a ring laser"

http://temporology.bio.msu.ru/EREPORTS/mallett.pdf [Broken]
 
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  • #24
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Evo said:
It wouldn't matter if you were aware you were time traveling or not, just your presence is going to throw things off. You are right that no interaction could be allowed, that means you could not go near people.
.
Not only that, but even if you went back in time and moved a single MOLECULE of air, and then went back to your regular time, you would change the future immensely.

I believe that the "moved" molecule of air, would at first produce no significant change in the time-line, but eventually it would interact with other air particles which would eventually change winds, which would blow on objects causing them to fall etc, etc. The sci-fi scenario where time-travellers are warned to be "careful and not touch anything" is not only ridiculous because it is easy to make changes in the MACROscopic scale, but the MICROscopic scale as well (i.e moving the slightest particle)

Anton
 
  • #25
Gonzolo
fomenkoa said:
How can future time travel b e part of elementary special relativity, when it seems quite impossible. Can't you observe the future, and then decide to change it? For example, you see youself eating cereal tomorrow, but when tomorrow comes you decide to eat oranges instead
Anton
Once you've observed the future, you're there, there is no going back to the past and wait for tomorrow to happen again. By saying "then decide to change it" you have implied going back in time. According to standard curriculum physics, it's a one way route.
 
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