# The Naked Scientists Forum

### Author Topic: If time travel is at all possible...  (Read 9913 times)

#### Pure Neutronium

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##### If time travel is at all possible...
« on: 09/08/2009 09:37:48 »
...is it reasonable to assume time-travelers must now be amongst us?

#### WiredScientist

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##### If time travel is at all possible...
« Reply #1 on: 09/08/2009 09:59:47 »
We have create time machine since 2001, or 2000. Since the scientist make the mini black hole on SPEARS, the particle accelerator.

In interdimensional means, time travel are possible through Astral plane. Just google it, astral plane/astral projection. Im too lazy to explain it here, it will be miles of typos [xx(]

#### BenV

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##### If time travel is at all possible...
« Reply #2 on: 09/08/2009 10:09:32 »
We have create time machine since 2001, or 2000. Since the scientist make the mini black hole on SPEARS, the particle accelerator.

Prove it.

Quote
In interdimensional means, time travel are possible through Astral plane. Just google it, astral plane/astral projection. Im too lazy to explain it here, it will be miles of typos [xx(]
Also, it's not really appropriate for a science forum.

#### Chemistry4me

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##### If time travel is at all possible...
« Reply #3 on: 09/08/2009 10:11:15 »
This should be interesting...

#### graham.d

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##### If time travel is at all possible...
« Reply #4 on: 09/08/2009 10:11:47 »
In the spirit you ask the question I would suppose the answer would be "maybe". There are a lot of assumptions though. Time travel (at least back in time) is not possible as far as we know and would either lead to logical paradoxes or need some concept of multiple parallel universes. Some recent ideas suggest that going back in time maybe be possible, but only a very small amount and that, even then, it would take an unreasonably huge amount of energy. Then you have the mundane problem that if you maintain your spacial position (relative to something) and go back in time, would you be on the earth or somewhere floating in space.

I guess, even if these problems were soluble, how many people in the distant future would have access to the equipment and the interest in going back in time, and would they be interested in this period? It might be unlikely just on the basis of statistics.

#### neilep

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##### If time travel is at all possible...
« Reply #5 on: 09/08/2009 11:13:58 »
Isn't there a theory that states that you can not go back in time earlier than the time you activate the time machine ?  ie: You activate the machine Sunday Aug 9th but you can not travel back to Saturday August 8th ?...only in the future can you travel back to Sunday Aug 9th !!?

#### graham.d

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##### If time travel is at all possible...
« Reply #6 on: 09/08/2009 11:35:17 »
I seem to remember that concept appearing in a sci-fi book but I can't think what reason there would be for such a restriction. I mean there are plenty of huge reasons why backward time travel is unlikely, but this seems a bit artificial. I think the reason may have had something to do with going back in time to a point where the time machine had not been invented but then publicising "your" time machine invention. But I don't think this is any more of a paradox than numerous others that can occur.

#### neilep

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##### If time travel is at all possible...
« Reply #7 on: 09/08/2009 11:46:09 »
Could it be something to do with ' how do you get back ?'...unless you can travel with your time machine how can you activate it in the past (before it was invented) to bring you back ?

#### graham.d

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##### If time travel is at all possible...
« Reply #8 on: 09/08/2009 12:03:14 »
I assumed that the machine was portable and travelled back with you. But if it is a sort of "transporter" with a send and receive station or a fixed installation that just moved its contents through time, then you could be right. Maybe that is the reason for the idea.

#### LeeE

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##### If time travel is at all possible...
« Reply #9 on: 09/08/2009 12:07:12 »
Going back in time within our time 'stream' doesn't necessarily have to result in paradoxes as it could simply be viewed as a 're-winding' of the sequence of all events that occurred from the point where you return to, up to the point where you started going back.  Everything thus remains consistent.

What most people think of with respect to time travel requires the journey back to be made outside our time stream, so that locally, the time traveling person's stream either just halts or continues going forward whilst, most importantly, without un-winding their history.

#### graham.d

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##### If time travel is at all possible...
« Reply #10 on: 09/08/2009 12:36:55 »
But if no paradox then you have parallel universes don't you? If you go back in time and kill your father before you were conceived, then either there is a paradox or, the future is from that point on, a different one from whence you came. Given there seems no limit to the extent whereby the future could be changed, it means that there must exist many co-existent universes. The concept of going back a very small amount of time (if time quanta ruly exist) may be possible, but this is not the spirit of the enquiry.

#### lyner

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##### If time travel is at all possible...
« Reply #11 on: 09/08/2009 16:00:32 »
But there are plenty of paths,worth considering. which could involve backwards time travel without killing your grandfather or other paradoxes.

#### DoctorBeaver

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##### If time travel is at all possible...
« Reply #12 on: 09/08/2009 16:16:11 »
There is no need for paradoxes nor alternative universes. The past has happened & is immutable. If you did go back, you didn't kill your grandad. Even if you went back with that intention, something had stopped you. Where's the problem?

#### graham.d

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##### If time travel is at all possible...
« Reply #13 on: 09/08/2009 19:40:27 »
You would be suggesting a complex set of criteria that would prevent you from doing anything that would alter the future in any way you could subsequently recognise. And, what is more, these protection systems must have been put in place in advance of your possible return and at every possible time that you may return to. This would be unlikely to the extent of being impossible. I know Dr Who manages it but then he does not have real physics to contend with :-)

#### DoctorBeaver

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##### If time travel is at all possible...
« Reply #14 on: 09/08/2009 20:02:03 »
graham - not at all. There is no need for anything to have "been put in place". What happened in the past has happened. It is cast in stone. Nothing can alter it. The very fact that a time traveller is alive and able to travel back in time is enough to show that he didn't manage to kill his grandfather.

#### graham.d

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##### If time travel is at all possible...
« Reply #15 on: 09/08/2009 23:43:47 »
Yes, but you are saying that, no matter how much he tried, he could not kill his grandfather. Now whilst you may think that it is just about possible that there could be events that prevent him from doing this no matter how much he tried, it seems unlikely that all such future changing events (perhaps much less dramatic than murder) from any arbitrary number of time travellers could be so restricted.

#### DoctorBeaver

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##### If time travel is at all possible...
« Reply #16 on: 10/08/2009 08:57:08 »
You say it seems unlikely, but if he is alive to travel back then that is what happened. I don't see that there can be any argument about it.

#### lyner

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##### If time travel is at all possible...
« Reply #17 on: 10/08/2009 10:44:09 »
You are using the term "what's happened" but, if this guy goes back, for him there's an element of "what's going to happen"  AND "what's happened", too, about the same event.. If he's desperately looking for ways to kill his grandfather, whilst back in 1943, he's thinking that he has good old freewill. But he clearly hasn't, because circumstances are channeling his actions away from certain paths and towards others.

There's a memorable short story in the Spectrum series (Kingsly Amis) called "By his own bootstraps" (or somesuch). In the story, a guy meets himself on the way through the adventure and it all hangs together very well - he is 'channeled' into certain choices, whilst behaving quite normlly.

I don't actually have a particular problem with this because I don't think you need to treat time as a steadily increasing quantity any more than distance. I have an idea that the only reason that we appreciate time with an 'arrow' is so that we can cope with the complexity of things. 'Experiencing' things one at a time makes life much easier.

#### DoctorBeaver

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##### If time travel is at all possible...
« Reply #18 on: 10/08/2009 11:02:54 »
You are using the term "what's happened" but, if this guy goes back, for him there's an element of "what's going to happen"  AND "what's happened", too, about the same event.

No there isn't. Although he is now experiencing it as part of his present, it is really a part of the past. If we accept that was has happened is now immutable then it is obvious that nothing can be done to alter it. Paradoxes then become irrelevant as they cannot exist.

#### graham.d

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##### If time travel is at all possible...
« Reply #19 on: 10/08/2009 12:25:46 »
Think about this mathematically and in extrema if you like. Assuming there is no restrictions on who or how many people can travel back in time and to when they can travel back, then extrapolate this to everyone at every conceivable time. This gives an infinite number of possible events that could be changed at an arbitrary large number of occasions in history. The only way to avoid such events being tampered with would be if such time travel were prevented by nature, otherwise I would say that the result of going back in time would be accompanied by an infinite set of caveats to prevent an individual having any free will whatever. I would therefore conclude that the likelyhood of such a system is confined to the less plausible end of science fiction. The parallel universe system is, at least, logically self consistant, although there are some difficulties regarding the physics.

What you are saying is logical to a point. If I had a time machine I could never go back and meet myself in the past because I have no memory of having met my future self, which would be a paradox. But the mechanism by which nature should prevent such actions, when taken to every possible case, is simply that it cannot be possible to go back in time. The reason being that a paradox results. To say that you can go back in time but that nature somehow intervenes to avoid specific paradoxical situations seems, at least to me, impossible.

#### LeeE

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##### If time travel is at all possible...
« Reply #20 on: 10/08/2009 19:08:13 »
I think that just about all of the paradoxes that seem to accompany going back in time are due to requiring simultaneous movement in both directions i.e. the time frame for the time traveler continues moving forwards, or stops, while he is traveling backwards in time.  Of course you're going to end up with paradoxes concerning where you are if you're trying to move in two opposing directions at the same time.

In the scenario where events are sequentially unrolled, you end up back in the past but the future no longer exists.  Because nothing is isolated in the universe, such a rolling back would require the entire universe to be rolled back.  When the time pointer then starts moving forward again, events may indeed occur differently but because the previous future has been rolled back and no longer exists there would be no paradox.

This type of time reversal isn't much use for time travel as we want it to work though.

For a time traveler to be able to remember the future he came from he can't travel within the set of dimensions that contain our universe.  He would, therefore, need to entirely exit our set of dimensions and continue moving forward in a different spacetime set that was oriented so that his future end point in that set aligned with his target date in the past in our set.  When he then reached that point he would need to exit the set that he was traveling through and renter our set.

The problems to be overcome include a) finding and proving the existence other spacetime sets b) establishing their possible orientation and c) finding a mechanism and method of moving from one spacetime set to another.

This sort of time travel would seem to allow paradoxes but even then I'm not sure that they really are paradoxes, or at least simple absolute paradoxes.  For example, if a time traveler went back in time and killed their grandparent, so that their parent never existed, it's not a paradox for the time traveler because in his time line, the killing of his grandparent occurred after his parents' and his own birth.  For everyone else's time line, everything that subsequently happens is part of their future, including the presence of the time traveling killer, who is not now from the future but is part of the present.

All just speculation, of course, and it doesn't address all paradoxes, but I do think you have to be careful about what actually is a paradox and what is really just an unrecognised contradiction in terms.

#### graham.d

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##### If time travel is at all possible...
« Reply #21 on: 11/08/2009 13:24:14 »
Lee, what you descrobe is what I referred to as parallel universes. There is EITHER paradoxes OR sets (probably infinite sets) of parallel universes. A traveller who changes something in the past can only return to a universe where that change was made (by him) and not to the universe from which he started. This is logically correct but, although attractive from a Schrodinger cat point of view, I believe is not sustainable in many (if any) of the Quantum Theories that study such matters more deeply - I think there is a problem with the total energy. It would also be a pain if you trod on a blade of grass that somehow changed the world to something unrecognisable when you return to the future. This concept has been explored by many SciFi books.

#### Karen W.

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##### If time travel is at all possible...
« Reply #22 on: 11/08/2009 15:19:00 »
Could it be something to do with ' how do you get back ?'...unless you can travel with your time machine how can you activate it in the past (before it was invented) to bring you back ?
Wouldn't you have to make sure the time machine was equiped with all the knowledge to inform you as to how to replicate its use and design along with any future information they would have needed to get the materials and the knowledge that was used for that.. etc like the process would have to be detailed in every way every step  so that it could be replicated again in the time you land yourself in... quite complicated it seems to me... imformation like the processing of fuels etc the type of power used where to find fuel what it comes from how to process it same with plastics or anything really that the past had not encountered it would be complicated to say the least and depending on how far you were able to go back would be the extent of explanation and usage of tools materials supplies and information etc....

#### LeeE

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##### If time travel is at all possible...
« Reply #23 on: 11/08/2009 17:01:49 »
Lee, what you descrobe is what I referred to as parallel universes. There is EITHER paradoxes OR sets (probably infinite sets) of parallel universes. A traveller who changes something in the past can only return to a universe where that change was made (by him) and not to the universe from which he started. This is logically correct but, although attractive from a Schrodinger cat point of view, I believe is not sustainable in many (if any) of the Quantum Theories that study such matters more deeply - I think there is a problem with the total energy. It would also be a pain if you trod on a blade of grass that somehow changed the world to something unrecognisable when you return to the future. This concept has been explored by many SciFi books.

Yeah, I think there's an energy issue with bifurcating sets.  If a set splits so that there are now two parallel sets instead of just one, either energy is needed to form the new set or the energy of the original single set must be divided between the two resulting sets, leaving the original set with only half its original energy.  Note that I'm using the term 'energy' very loosely here, but the energy and mass present in the original set has to be duplicated in the bifurcated set, so the total energy and mass of the two sets would have appeared to have doubled from nowhere.  That is unless we posit a reservoir of unlimited energy/mass that can be drawn upon to power the bifurcation.

On the other hand though, if the total energy/mass of all sets is constant, and the energy/mass total for any particular system is halved every time a bifurcation occurs, then the energy/mass total for our 'current' set will be an incredibly tiny fraction of what it once was.  Such a reduction of a set's energy/mass total over time could parallel other time-related phenomenon in the universe though, like the Big-Bang and the expansion of the universe.

Another alternative is that the bifurcated sets are not wholly new additional sets but just different 'views' of the single original set, so the total energy/mass is common to all sets.  This would mean that everything in the one 'real' set would have to be able to occupy vast super-states of every possible outcome, with each specific 'view' only showing one specific state.

#### DoctorBeaver

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##### If time travel is at all possible...
« Reply #24 on: 12/08/2009 08:42:27 »
I'm a great believer in the simplest explanation being the most likely. The simplest explanation in this case being what I said. It takes but 1 premise - that if you travel back from time B to time A, then from time B's perspective A->B happened the way it did & cannot be altered. Bifurcation & conservation of energy are irrelevant.

#### The Naked Scientists Forum

##### If time travel is at all possible...
« Reply #24 on: 12/08/2009 08:42:27 »