It's been said that if time travel were really possible then we'd probably expect that there would be time travellers amongst us in the present from any point in the future and we wouldn't know about it, so could the same thing be said about the ability to travel to parallel universes, if it were possible could people from an alternate universe be amongst us even now, exploring our universe examining any differences there might be?
Travelling to parallel realites?
- Thread starter Crewman47
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Some physicists - like Mitchio Kaku - say that we are separated from parallel realities (if they exist) - by a kind of probability space (to sort-of borrow a term from Douglas Adams)...and they would therefor be unreachable...
Or, at least, so *improbably* unreachable as to be effectively impossible to travel to...
They..are created by quantum probabilities...and evolve away from us in this probability space...sort of...
Or, at least, so *improbably* unreachable as to be effectively impossible to travel to...
They..are created by quantum probabilities...and evolve away from us in this probability space...sort of...
We haven't seen any time travelers because time travel into the past has not yet been invented in the chronology we occupy. Once it is invented, it WILL be possible to travel into the past but it will be an ALTERNATE past because it was not POSSIBLE to travel there until time travel into the past was invented. Alternate versions of ourselves will then be seeing time travelers (assuming they don't take steps to conceal their activities).
^I just read a short story from the 80's that explored that concept - "Mozart in Mirrorshades" by Bruce Sterling & Lewis Shiner...
http://www.uchronia.net/bib.cgi/label.html?id=stermozart
Here's an essay on it: http://www.jstor.org/pss/852603
In the story - people could travel back along the...pipeline...to "realtime" - the main timeline...and also from alternate history to alt history along it...
Cool story.
This article may be of interest.
http://www.newscientist.com/article/mg20527501.100-a-measure-for-the-multiverse.html
Even if we can't travel to other universes, we may be able to deduce the statistical likelihood of their properties from those of our own universe.
http://www.newscientist.com/article/mg20527501.100-a-measure-for-the-multiverse.html
Even if we can't travel to other universes, we may be able to deduce the statistical likelihood of their properties from those of our own universe.
Steven Baxter's The Time Ships----sequel to HG Wells' The Time Machine----also explores the notion that whenever one travels to the past, they inherently enter an alternate reality.
One of my favorites.
Well, the downside to traveling through time into an alternate past is that, once done, there is no way to access the original present/future. When you return to the "now" (or if you travel further ahead) you would be forced to travel along the time-line of the alternate past you entered when first went back in time. You'd be lost forever to your time-line of origin.
As such, time travelers going BACK in time would leave "our" time frame, never to return. So, from the point of view of observers in our reality, traveling BACK in time is essentially a one-way journey. From the perspective of the time-traveler though, he may return to a "now" virtually indistinguishable from the one he left, depending upon the impact he made in the "past". From the traveler's perspective, he could just pick up where he left off.
Yes, The Time Ships explores all that in depth. The more the Time Traveler journeys, the further events move from their original course. (Things really get strange once he reaches a timeline where other time machines exist.)
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Weird, cause I'm just making all this up as I go along. Never heard of that story before . . .
Sort of. Here's the idea:
A particle can exist in more than one quantum state at a time. So the larger ensemble of particles it interacts with (i.e. the universe) can also exist in a corresponding number of states. Schroedinger's Cat is both alive and dead, and the universe as a whole contains both realities.
However: the laws of physics can only work if every equation has a single solution; otherwise reality itself breaks down. If everything happens two or more ways at once, the paradoxes would be irresolvable. So the different outcomes have to be causally isolated. The different histories of the universe all exist at once, but are "unaware" of each other and have no effect on one another, because paradoxes, by definition, cannot occur. No information can pass from one quantum history (timeline) to another, ever.
What this means is that the fictional conceit of travelling into a parallel timeline is purely fictional. For one thing, that timeline isn't a physically separate space; it's another facet of your own reality. Your parallel self isn't a separate being you can meet and interact with, but another quantum facet of your own physical body. And for another thing, that facet of yourself is one you must perpetually be unaware of. You can't interact with it or with the history it occupies because it would create physical paradoxes if any information were exchanged between timelines.
As for travelling back in time to create a parallel timeline, physics argues that wouldn't happen either. Theorists who've applied quantum theory to the question of time travel have determined that if you go back into the past and interact with it, then you make it part of the same quantum system you belong to in your present, so that all the possible future paths the past might take "collapse" into the state that exists in the future you came from (at least from your own perspective). If you go back in time, the very fact of doing so will guarantee that the future you came from will be the one that occurs. Or at least, if your time travel did create an alternate timeline, you would be unable to perceive or experience it, because you'd still be quantum-bound to your own home timeline. Again, no information exchange is allowed. Your own timeline is the only one you can ever experience. (Classical physics reaches the same conclusion. All physical interactions must be self-consistent and free of paradox in order to operate; therefore, any observer can only measure a single outcome for a single event. Whatever happened a certain way in the past will always happen that way even if you go back and try to change it.)
That was a fascinating summary Christopher, thanks. I think I understood most of it! This bit intrigues me:
So if I wanted to:
I can go back in time, murder my father, and return to the present in time for his birthday party?
So if I wanted to:
I can go back in time, murder my father, and return to the present in time for his birthday party?
ProtoAvatar
Fleet Captain
The many-worlds interpretation.
Of course, it's only one of a number of quantum mechanical interpretations - none of which are proved.
And the Afshar experiment seems to refute this particular interpretation (and the copenhagen one).
The Novikov self-consistency principle and related works - all try, ultimately, to protect 'causality' at the cost of making highly improbable events certain or 'inventing' new physical laws in order to stop the time traveller from changing the past. In other words, these works break the laws of physics and probability in order to protect causality - two equivalent choices.
The best proof that time travel doesn't exist is that no time travellers appeared in our time. Then again, according to most theoretical models for time travel into the past, the time traveller can only go back until the moment the time machine he uses was built.
For a glance at how it might work-try The Coming of The Quantum Cats by Fred Pohl
Also, Cowboy Angels by Paul MacAuley, Silverberg's Up the Line, and Richard C. Meredith's Timeliner Trilogy(At The Narrow Passage/No Brother, No Friend/Vestiges of Time) as well as his novel Run, Come See Jerusalem! Also, Niven's All the Myriad Ways collection of short stories and essays tackles the many-worlds theory. A fun way to learn some of the theories, IMO.
Also, Cowboy Angels by Paul MacAuley, Silverberg's Up the Line, and Richard C. Meredith's Timeliner Trilogy(At The Narrow Passage/No Brother, No Friend/Vestiges of Time) as well as his novel Run, Come See Jerusalem! Also, Niven's All the Myriad Ways collection of short stories and essays tackles the many-worlds theory. A fun way to learn some of the theories, IMO.
And the more you drive, the less intelligent you are.
