I must be in a time warp myself, as I’ve already read this book…last year I think. Thus proving time travel IS possible. BTW, the book WAS about the multiverse, and discusses fairly shallowly the “many worlds interpretation of quantum mechanics”.
Cece did an article on the possibility of time travel using a fixed and a moble portable wormhold (the portable wormhold being accelerated to the speed of light away from the fixed, then brought back) which was theoretically possible, but practically impossible. I think thats where this debate stands…that ATM our science can’t disprove conclusively that time travel is NOT possible, but for all practical purposes its impossible to our current abilities. Not being a physisist I couldn’t say anything more than that.
The multiverse thing sure makes good sci-fi though (best I’ve read lately being the 1632/33 series)…
Whilst the Many Worlds interperetation sounds appealing for time travel, I agree that if you’re just “switching” into another Universe, you aren’t really time travelling.
I think it is possible to observe the past, but not interact with it. How can you, it already happened? You would not be able to hear it either, as the sound created at those moments has long been absorbed and changed into other forms of energy.
Time travel is very dangerous and uncomfortable to contemplate, and even if possible, will no doubt never be useful.
If the Many-worlds interpretation is correct, when you go back in time you create a new timeline- this is fine, but effectively means all time travellers into the past are never seen again, as they vanish into timelines of their own construction.
If there is only one universe, history becomes fluid- you might go back and change history, then another time traveller will change history o something else; the present will be an ever changing Kaleidoscope, with a different President or Prime Minister every day; you will go to sleep in a mansion, and wake up in a mobile home; your car will change fro a Buick to a Volksvagen while you are driving it.
Such a lack of continuity will invoke the Chronological Protection Conjecture; the universe will morph and mutate until it reaches a history where time travel has never been invented, ever, at any time in the past or future.
This is the only stable state for the universe, the one we are in now. The CPC has been proposed by many people, including Hawking, Azimov and Larry Niven… it convinces me.
Failing an effective CPC, the far future is a less desirable environment than today; little energy and matter to play with. Refugees from the far future will flood back, sometimes in multiple instances, increasing the mass of the present day universe until it collapse; the collapse will get closer to the present day, until it eventually happened yesterday and we will cease to exist.
That is why time travel will never be possible.
You’re just arguing over semantics though. I could argue that time travel should be defined as travel forward or backward though time like the name suggests. If you go back in time, then move forward into a different universe you’re still travelling though time, you just happen to moving into a different universe as well thats all.
So basically if only one universe exists, time travel is likely to be impossible. If many universes exist then time travel may be possible, but some people would say it isn’t really time travel.
IMO time travel should be defined as “travel forward or backward though time” (the former is not logically impossible AFAIK).
But you can’t “go back in time, then move forward into a different universe”. From the moment you leave the current time you can no longer exist in your own universe. “Time” only makes sense in relation to the universe you’re in. Before the universe there was no time. A different universe would not have the same time for you to travel in.
Jumping from one river to another is not “swimming upstream”, even if the spot you jump to is identical to a point upstream in your own river.
Or, as I would put it: “If only one universe exists, time travel is likely to be impossible. If many universes exist then something superficially resembling time travel may be possible, and some people would say it’s really time travel.”
This actually makes a lot of sense, as long as we confine it to travelling into the past. And so the upshot is:
Time travel (in either direction) may or may not be theoretically possible.
Due to CPC, we are living in a universe in which Time Travel into the past, whether or not possible, has never been and will never be actually done.
Jury is still out on whether Time Travel to the future will ever happen; however, since we have just ruled out returning from this little jaunt, it becomes rather uninteresting.
You ever watched a movie? Somehow I don’t think your observance of it has any affect on the original events. Same goes for watching a supernova.
I know the Schroedingers Cat argument, and yes, the bouncing of photons off of matter influences that matter. But, the mere act of your eyes absorbing those photons that have been bounced off of the matter should have no effect on the event in which you are witnessing.
In my opinion, the simplest resolution of the grandfather paradox is that, if it is possible to travel backward in time, no time traveler will ever do anything that creates a paradox.
The reasoning for this is as follows: it is reasonable to assume that a universe that is not internally consistent cannot possibly exist. If time travelers will ever create a paradox in our past, then that paradox already exists, so the universe contains an internal inconsistency. We know that our universe exists, therefore it cannot contain any internal inconsistencies, therefore no paradoxes were created in the past.
This implies that a time traveler, even knowing based on the historical record what he or she will do after traveling into the past, nonetheless must act in a manner consistent with the historical record. Unless, of course, the historical record is wrong, in which case the time traveler will of course do whatever he or she actually did in the past. Such a situation is alien to our normal experience, but so is time travel itself.
Actually, time travel – defined as a transition between two points in the space-time continuum without traversing the intervening space or time – is quite possible without wormholes or other theoretical processes. All one need do is construct a Tipler machine.
Much like making Cream of Tyrannosaurus Soup*, though, the “all you need do” is quite a bit more difficult than it may sound. What you need is something on the order of density of neutronium, drawn out into an indefinitely long cylinder and set to rotate at a speed in excess of 0.5 c surface speed. The region of warped space immediately surrounding this cylinder will enable transit from one point to another without covering the intervening distance.
This site has a brief summary of astronomer Frank Tipler’s theory and how to build one in six easy steps.
It should be noted that travel to a time before the Tipler machine was constructed and spun up to speed is impossible using it.
Poul Anderson’s novel *The Avatar uses the Tipler machine as a mode of making interstellar travel plausible.
Yes it has. I just read a short story about it. Lemme find it…
Of Scorned Women and Causel Loops by Robert Grossbach, found in the Seventeenth Annual Collection of The Year’s Best Science Fiction edited by Gardner Dozois.
The scientist (the psuedo-scorned woman in the title) explains it like this:
In general, the speed of light multiplied by the time interval [is the distance]. Nothing could travel back fast enough to cause a problem. The universe could protect itself from inconsistencies and non-causal events, it didn’t need other universes to help.
Which leads to interesting uses of moving time travel. Could I put a space ship right by Alpha Centauri (either in the future of past)? What about orbits of planets or moons?
No. you don’t affect the supernova, because that happened * before* your observation.
What you do by intercepting the photons of the light of the supernova by observing them is create a new timeline, one with your shadow in it spreading across the universe.
The light that you intercepted by observing it might have gone clear across the galaxy and been observed by an alien Tycho Brahe, who went on to develop scientific astronomy on his planet full of octopoid astrologers;
more likely it had little effect, but * you have made a measurable difference* to the universe, and effectively made a new timeline.
I don’t see it that way. You cannot influence past events by viewing light anywhere in the galaxy. What I meant by observing the past was to race to a point where the light is still expanding out into the universe and intercepting it. This is not time travel per se, this is just moving many times faster than the speed of light…easy
So, viewing of the light would not have any impact on what anyone on this planet saw years ago, or any other planet for that matter. Now, you could say that if you did race to intercept the light that bounced off of Earth from the beginning, you would be blocking it from expanding further out into the Universe, but that would not be changing the time line, it would simply be another point on this time line. No more than any other thing we as humans do that has an impact on the Universe.
Oh, sorry, I understand you now;
yes. In that sense it is possible to observe the past. In fact, it is not just possible, but obligatory.
Everything that we we is an image of something that happened in the past; the Hubble Deep Space Field galaxies are an extreme example of this.
Mind you, travelling faster than light has some peculiar effects on causality, if relativity is correct; for a discussion of which I refer you to this thread
