Time travel?

[mosimo]

:idea: Okay lets start a discussion here.

Time travel plausible or crazy?

Lets see how much life we can give this discussion.

[MrD]

We have more chance of coming across a time traveller as the barriers between countries come down and it is not so unusual now to come across people radically different from our own culture and community. How do you know you haven't already met one?

[mosimo]

If a person from the future came back in time to our present day one of three things could have or could happen. The future could have a high respect of the past and therefore would only travel back to study it and not to disturb it in any way and therefore no one would know that they were even from the future.

The time traveler could travel back in time and performing technical advances and that sort of stuff entirely change the future. In that case we would already know if it were possible because it would have made big news.

Thirdly the traveler could have traveled back in time and after declaring himself a time traveler people would think him crazy having him killed as demon possessed.

Nevertheless is time travel scientifically plausible?

[Literary_Cat]

Not possible. Time always goes at the same speed in one direction. This is not negotiable.

[mosimo]

There have been experiments done in which speed has caused an atomic clock to go slower. Therefore time can be slowed down. Those same experiments have brought up the hypothesis that the speed of time and the speed of light are the same. Therefore if matter could travel faster then the speed of light the matter would travel back in time hypothetically speaking. Therefore if matter could travel back in time could not it also go the other way?

[mosimo]

Refute me. Come on!

[bluevictim]

Nevertheless is time travel scientifically plausible?
Not possible. Time always goes at the same speed in one direction. This is not negotiable.There are a number of respected scientists interested in the possibility of time travel, so I wouldn't blithely rule it out. A number of paradoxes do come up. What if someone travels back in time and kills his parents? If time travel is possible, why hasn't someone from the future come back in time to tell us? Maybe some kind of time travel is possible, but not in the way we imagine it in movies. Maybe it's possible only to go into the future (faster than usual), or it's possible only to go to places in the past that are far enough away so as to avoid contradictions.


There have been experiments done in which speed has caused an atomic clock to go slower. Therefore time can be slowed down. Those same experiments have brought up the hypothesis that the speed of time and the speed of light are the same. Therefore if matter could travel faster then the speed of light the matter would travel back in time hypothetically speaking. Therefore if matter could travel back in time could not it also go the other way?The experiments that you mention relate to pretty standard special relativity. Your account is close, but a little off. The idea is that the length of time intervals between events depends on the speed of the reference frame in which it is measured. So, if there are two observers with clocks, and observer A is going faster than observer B, observer B will see that it took longer than five minutes for the clock of observer A to go from noon to 12:05pm, whereas, of course, it took exactly five minutes for observer A. Thus, to observer B, the time "slowed down" for observer A. As you said, in the framework of special relativity, traveling back in time would require going faster than the speed of light.

However, if there is the right kind of "curvature" (aka gravity) in the universe, it might be possible to go back in time without going faster than the speed of light. The effects of "curvature" fall under the domain of general relativity, which is the framework used for studying things like black holes.

If you ever have kids and one of them when he's eight years old accidentally sets fire to the living room rug... go easy on him. :)

[falloutLXIV]

time travel? not possible, at least not now. maybe in another 30,000 years, but not now and definately not soon. that is all i have to say.

[travel-exchange]

time travel is craziest thing time always travel forward never backward,It is also good to move forward then looking backward that cant be changed

[soundofmusic]

Stephen Hawking now believes it possible. Einstein thought it possible. It seems that the difficulty is not time travel itself; but finding the energy power to move a body through time. Of course, we've all heard stories of the "Philadelphia Experiment"; and what of Astral projection...a bit of a segway, of course

[Lokasenna]

Stephen Hawking now believes it possible. Einstein thought it possible. It seems that the difficulty is not time travel itself; but finding the energy power to move a body through time. Of course, we've all heard stories of the "Philadelphia Experiment"; and what of Astral projection...a bit of a segway, of course

I seem to remember Hawking did qualify that comment by saying that the traveling object would have to be crushed into a particle small enough to pass through the holes in the quantum foam, the very material of reality itself. I doubt anyone would be in the mood for tourism after that!

[Paulclem]

Perhaps it's only possible through reincarnation.

[homeswap]

time travel is craziest thing time always travel forward never backward,It is also good to move forward then looking backward that cant be changed

I totally concur with you. I the art of travelling it is a golden rule to travel light.
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[kev67]

It's sort of possible going into the future. You just have to travel at near light speed to say Alpha Centauri, then turn around and come back. You would have effectively travelled eight years into the future, because Alpha Centauri is four light-years away. Going back into the past is not so easy.

[free]

I don't know if it is possible or not, but I enjoy reading books about it.

[YesNo]

It should be theoretically possible to slow down relative to someone else so you can reach their future while you are younger than you would be if you just waited in their frame of reference with them. That would be a time travel into the future.

One can go to the past through one's memories or by reading about the past.

There is the quantum eraser experiment that might seem like time travel, but probably isn't. Assuming a realist interpretation of our universe, one could claim that observing the present forces the past to change a wave into a particle in the past. However, one could easily avoid that chicken-egg problem with idealism. Actually, I don't know how "easy" that is. One does have to accept idealism which might be hard to do.

[PeterL]

It is quite and thoroughly possible, and I enjoy writing about it.

[YesNo]

Ronald Mallett's Time Traveler was an interesting description of his process of trying to go back in time to find his father. He did mention the following limitation of his method based on many worlds and relativity (page 173):


My time machine could only carry a time traveler back to the moment the machine was turned on, and not one second before.

Although he made some physical discoveries using lasers (I don't remember what exactly), I don't think he actually sent anything back in time.

[PeterL]

Ronald Mallett's Time Traveler was an interesting description of his process of trying to go back in time to find his father. He did mention the following limitation of his method based on many worlds and relativity (page 173):


My time machine could only carry a time traveler back to the moment the machine was turned on, and not one second before.

Although he made some physical discoveries using lasers (I don't remember what exactly), I don't think he actually sent anything back in time.

The claim that a time machine can't go back before the time when it was built is fairly common, but it is not required by any physical laws, and logically it is not necessary, so I greatly doubt that limitation exists.

[free]

It is quite and thoroughly possible, and I enjoy writing about it.

How very nice! I have been writing a story which involves time travel into the past, but I don't know which method to use. I want something original. Can you give me some advice, please?

[kev67]

There was an article in the paper a couple of days ago about a quantum transmitter. Basically, some very clever scientists had managed to transfer information from one place to another about two or three metres away using quantum effects. It is quite an unreliable method of transmission at the moment, but the article was postulating that the technology might one day be the basis of teleportation devices. Less exotically, it the technology might be used to make computer communication more secure. If I understand correctly, quantum effects are not limited by light speed. If one subparticle collapses into one of two fixed states, its partnering subparticle instantly collapses into the other state, no matter how far away. Therefore, if you had one device observing the Earth from far distant space, it could record what was happening on Earth many years ago, and transmit it instantly back to Earth. Thing is, you'd need to teleport the device out there, and it would have to be a gigantic telescope. It still does not get you into the past, but it enables you to observe the past.

Edit: a problem is that the telescope/transmitter device could not get to its far distant spot at faster than light speed, so it could not see further back into Earth's history than when it blasted off.

[PeterL]

How very nice! I have been writing a story which involves time travel into the past, but I don't know which method to use. I want something original. Can you give me some advice, please?

The method isn't important, but the effect is . That is, can a traveller into the past change things, and, if he can change things, are they changed in a single space-time, universally, or does the change cause the universe to bifurcate? What one can do with each is different. I favor an amended version of the Unitersal Wave Theory, AKA the Many Worlds Interpretation of Quantum Theory.

[YesNo]

We take it for granted, and so don't bother developing any skills we might have in this regard, but we all can travel both forward and backward into time already.

The forward travel comes with paying more attention to our premonitions. And the backward travel comes from memory. They are not reliable. I wouldn't want the world to be deterministic, but they are not useless abilities. Premonitions can help us avoid problems we will face in the future. Memories can help us resolve issues that are bothering us now, perhaps mainly in our subconscious habits, that happened in the past.

[free]

The method isn't important, but the effect is . That is, can a traveller into the past change things, and, if he can change things, are they changed in a single space-time, universally, or does the change cause the universe to bifurcate? What one can do with each is different. I favor an amended version of the Unitersal Wave Theory, AKA the Many Worlds Interpretation of Quantum Theory.

Thanks, PeterL. My story is a product of imagination. It doesn't revolve around the laws of physics. It is inspired by a mediaeval poet (not much known internationally) about whom I read some old archive records. I've got stuck at the point of which time travel way to use.

[PeterL]

Thanks, PeterL. My story is a product of imagination. It doesn't revolve around the laws of physics. It is inspired by a mediaeval poet (not much known internationally) about whom I read some old archive records. I've got stuck at the point of which time travel way to use.

If you are using magic, then just have the traveller stand in the right place and say when and where he wants to go. Or he could quote the poet'slines that are relevant. Don't get tangled up in the process of travelling, worry more about what happens as a result of travelling. Fair poetry would be a good method.
"Backwar oh backward turn time in its course.

[free]

If you are using magic, then just have the traveller stand in the right place and say when and where he wants to go. Or he could quote the poet'slines that are relevant. Don't get tangled up in the process of travelling, worry more about what happens as a result of travelling. Fair poetry would be a good method.
"Backwar oh backward turn time in its course.

The idea is that it happens by chance, not by a character's intention. Time travel is not the main topic, just an episode in the story. Thanks.

[cacian]

time does not travel we do. :D
I don't believe that there is a movement of time assigned. time is constant that is why we are able to grow old gracefully.

[YesNo]

time does not travel we do. :D
I don't believe that there is a movement of time assigned. time is constant that is why we are able to grow old gracefully.

That's how I view it as well.

When we think of going back or forward into time, it makes me wonder just what is it we are going back or forward into and does it even exist. Here's a video summary by Jonathan Tallant on various views of time: https://www.youtube.com/watch?v=zw6hS_gy9MY

I prefer being a presentist, but I do need to squeeze in relativity in some way perhaps by including the mind of the observer in order to determine what exists from a particular frame of reference.

[YesNo]

I'm just trying to make sense of Presentism, Eternalism and time travel.

The problem with Presentism, Eternalism and relativity is presented by the following from Wikipedia: http://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)


Eternalism takes its inspiration from physics, especially the Rietdijk-Putnam argument, in which the relativity of simultaneity is used to show that each point in the universe can have a different set of events that are in its present moment. According to Presentism this is impossible because there is only one present moment that is instantaneous and encompasses the entire universe.

Is that all? I have no problem with accepting that the present moment for someone in a different frame of reference than I am in will be different. There isn't "one present moment". So the conflict with Presentism and relativity is resolved.

I wonder if Eternalism which maintains there is a block universe of space-time coordinates in which we are completely determined can wiggle around relativity any better than that?

In the Stanford Encyclopedia of Philosophy, Ned Markosian (http://plato.stanford.edu/entries/time/#TimTra) acknowledges that if time travel were possible, then there would be problems with causality. That makes sense to me. We might as well kiss determinism, or any fantasy about the causal closure of physics, good-bye if anyone gets a time machine to work.

His arguments for time travel though are amusing. He claims,


For one thing, many scientists and philosophers believe that the actual laws of physics are in fact compatible with time travel. And for another thing, as I mentioned at the beginning of this section, we often think about time travel stories; but when we do so, those thoughts do not have the characteristic, glitchy feeling that is normally associated with considering an impossible story.

Let me translate. Time travel makes sense because some anonymous people smarter than I am believe in it. (Although I think I could assume that there are people smarter than those smart people who don't believe in it.) And time travel makes sense because people have written entertaining stories involving time travel. (Although to me they all seem "glitchy".)

[PeterL]

I'm just trying to make sense of Presentism, Eternalism and time travel.

The problem with Presentism, Eternalism and relativity is presented by the following from Wikipedia: http://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)


Eternalism takes its inspiration from physics, especially the Rietdijk-Putnam argument, in which the relativity of simultaneity is used to show that each point in the universe can have a different set of events that are in its present moment. According to Presentism this is impossible because there is only one present moment that is instantaneous and encompasses the entire universe.

Is that all? I have no problem with accepting that the present moment for someone in a different frame of reference than I am in will be different. There isn't "one present moment". So the conflict with Presentism and relativity is resolved.

I think you have that right. Different frames can have different times.


I wonder if Eternalism which maintains there is a block universe of space-time coordinates in which we are completely determined can wiggle around relativity any better than that?

Both philosophy and physical theory and observation indicate that each space-time is determined. There can be only one chain of cause and effect, even if the chain is as wide as it is. The Many Worlds Interpretation and related views get around that for each space-time, because tthe universe bifurcates at each decision. This is sloppy and violates Occam's Razor, but it suggests way of handling it. In MWI the complete multiverse is determined, but no one can tell, because there isn't supposed to be communication among the various spact-times.


In the Stanford Encyclopedia of Philosophy, Ned Markosian (http://plato.stanford.edu/entries/time/#TimTra) acknowledges that if time travel were possible, then there would be problems with causality. That makes sense to me. We might as well kiss determinism, or any fantasy about the causal closure of physics, good-bye if anyone gets a time machine to work.

His arguments for time travel though are amusing. He claims,


For one thing, many scientists and philosophers believe that the actual laws of physics are in fact compatible with time travel. And for another thing, as I mentioned at the beginning of this section, we often think about time travel stories; but when we do so, those thoughts do not have the characteristic, glitchy feeling that is normally associated with considering an impossible story.

Let me translate. Time travel makes sense because some anonymous people smarter than I am believe in it. (Although I think I could assume that there are people smarter than those smart people who don't believe in it.) And time travel makes sense because people have written entertaining stories involving time travel. (Although to me they all seem "glitchy".)

Time travel makes perfect sense, and it fits well with what we know of the physical universe, and there are no problems with causality, but that's another story.