sorry michael0916! Never mind, sleep gives you cancer. 
Saltire writes:
I’m trying to be careful about how I say this… Einstein said that gravity is the curvature of space around massive objects. He did not say that space has a natural curvature, often associated with the SciFi pseudo-theory of using worm holes to move between points in the universe, as you are referring to. This is a very distinct point. In fact, everything that I’ve read from or about Einstein, he clearly did not believe that space had some sort of inherent wrap-around feature.
Actually, time dialation occurs at all velocities. It’s just more noticeable at greater velocities.
Not exactly true. You would only be able to traverse backwards in time a fixed delta. If you stepped into the future end of the wormhole at exactly the moment after it appeared, you would travel back to the start time + a small delta. If you wait 10 minutes from the appearance of the future wormhole to enter, you would travel back to the start time + a small delta + 10 minutes.
This remains to be seen, however there may be tremendous inertial and tidal forces that one may have to overcome within a wormhole of succicient size to traverse.
Kip S. Thorne
The Feynman Professor of Theoretical Physics
California Institute of Technology
The theory of wormholes goes back at least as far as the 60’s and has been a part of theoretical physics long before Carl Sagan wrote “Contact”.
Another method of time travel proposed by Frank Tipler uses the gravity of a massive spinning cylinder to travel backwards in time. This has the similar constraint of wormholes that you can only go back to a point just after the moment when the cylinder began rotating. Assuming that the cylinder spins forever, there’s no upper limit on how far into the future you can travel. Aside from the minor technical issues that you need a nearly infinite mass cylinder that is nearly infinite in length and you have to get the cylinder spinning at nearly light speed, the Tipler Cylinder is actually considered a more viable method of time travel than wormholes.
JoeyBlades is right on all counts, in case anyone would believe my somewhat slipshod post over his. But allow me to clarify a bit.
Thorne’s wormholes would not have large tides or inertial effects in the center of the tube. Thorne’s theories say they would be perfectly survivable, as long as you didn’t run into the sides.
The ‘Contact’ anecdote wasn’t meant to imply that wormholes were a new idea in the '80s. Just that Thorne and his team were the first to use newer ideas to invent a scenario in which a wormhole could be created and kept stable without using a black hole or other super-massive object.
I’ve got a book by a physicist named Jim al-Kahlili (sp?) from which I could pull some references. If anyone wants them, I’ll pull them out next time I’m in the same room with that book. The book is fairly recent, and could almost be inspired by Cecil’s 1989 column. It goes into great depth to answer the same question in much the same way (but with less wit).
It’s from heraldry. The proper heraldic term for things like the “Cross of St. Patrick.” Look it up.
About 20 years ago, someone told me about a popular sentiment: If time travel were possible, we could go back to April 14, 1865, to Washington, D.C., to keep President Abraham Lincoln from being assassinated. The person pointed out, however, that, even if such a thing were possible, the time paradox interferes: If we actually kept Lincoln from being shot, it wouldn’t have happened and we couldn’t have thought to do it.
This is exactly the kind of broken causality loop that makes most physicists think time travel is impossible. They believe that better cosmological theories will come along that will better explain spacetime itself and outlaw time travel as a side effect.
It’s from heraldry. The proper heraldic term for things like the “Cross of St. Patrick.” Look it up.
It would be nice if that pseudo gedanken experiment actually proved anything, however I could simply propose a non-linear view of time where events don’t develop, they merely are.
In that case, we would simply find that we inhabited a world in which Lincoln was not assassinated. (It wouldn’t necessarily be very different over here).
Your theory mentions some radical ideas - wormholes, blackholes etc. I have something a little more simple that you might consider.
Take “time” as “the passage of time (on the clock)”. Therefore the simplest way to ‘gain’ time is to cross the International Time Line. Obviously this is easily done once, but the gain of a day is negligible in this respect ( being away from those things which might make the gain of a day useful). However if one were to travel in the correct direction ( gaining a day ) and at a speed which permitted one to cross the Int Time Line at a frequency greater than once a day then one would actually be ‘Gaining’ time. This gain only occurs because time is moving ahead at the normal pace for the rest of the world, while the time traveller is now travelling back in time. (e.g. spend 23hrs, then go back 1 day = go back 1 hour). So what would the result be? It’s hard to imagine that the result would be anything other than a return to everything normal having just spent a week travelling around the world at supersonic speed.
tonerce,
You’re yankin’ our chains…
Sorry for reviving such an old thread… but I recently read the Time Travel column and I wanted to say a few things. Plus I wanted to make sure I didn’t repeat anything by starting a new thread.
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I agree with the original post. Time does not exist. It is merely a concept we humans have invented to explain how something is no longer in the place it used to be. As far as the universe is concerned, the Earth is in a certain position around the sun, and it never was or ever will be in any other position. It’s hard to explain this idea without mentioning words like “used to” which relate to the concept of time, but oh well. At least try to imagine it. I’ve tried endlessly to explain this to people but nobody wants to believe it, probably because their whole world would then be based on something that doesn’t exist, thus causing them to probably lose their sanity. “You can’t handle the truth!” could never be more appropriate.
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The thing with the clock in space being off when they returned. Did nobody ever think that the changes in gravitational forces would/could/should have some effect on a clock? Whether it’s mechanical or electrical, I’m sure that the g-forces of liftoff in a space shuttle and the lower gravitational pull of the earth would cause some sort of effect on the functionality of an electrical device. Are there any tests that show how maybe the rate of travel of electricity is affected under different gravitational forces? Although I suppose whatever device was used to measure the speed of electricity would also be affected by the g-forces, so it would be impossible to ever know for sure. If the electricity powering a clock moved slower, wouldn’t the “time” on the clock move slower too? I’m no EE, but this makes sense to me.
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Finally, the time paradox. There’s really no explanation needed here. Look back a few posts at the Abraham Lincoln thing and you’ll get the idea.
Just some things to ponder.
You’re right, c_goat, for reasons like that the clock experiment wouldn’t mean anything by itself. However, the fact that it produces results consistent with a mathematically derived theory is significant. The Special Theory of Relativity predicts that travel at high speeds will affect the readings of any device for measureing time, be that device a conventional clock, a tuning fork, a piezoelectric crystal, a person’s pulse, or anything else that you care to name, and that furthermore, it will affect all such devices in exactly the same manner. One could say that this just means that high speed affects all measuring devices, but it’s much simpler to say that it affects the thing that they’re all measuring, i.e., time.
As to your other point, yes, every point-moment (point in 4-space, specified by three spatial coodinates and one temporal) can be considered as a separate entity, but not as an independent entity. If, for example, we consider the point “Earth, 12:16:57 MDT August 18 2000”, we can note things like the direction a particular part of the planet is facing relative to the stars, and the position of particular objects, etc. If we then look at the point “Earth, 12:17:00 August 18 2000”, and note those same features, we’ll find that they’ve changed only a small amount, and in an approximately predicable way.
Well, I have to say this is an impressive amount of debate for a subject which appears to have been contrived, and the “other” side entirely debated by, the original poster.
Walk through the posts for a little bit, and you’ll notice a series of posts under various names: Smcdonald, skeldon947, SMAK D, Smick D–all of which have either posted only in this thread or are guests–and all of which are variations of one another.
They also all have a similar (poor) writing style, and also all espouse the same viewpoint: TT is impossible. A viewpoint which is, for the most art, not shared by anyone else.
Ladies and gentlemen, I think we’ve been had.
LL
Is time travel possible without paradox? I think some limited form of time travel cannot be ruled out as logically impossible (although I will not comment on its actual, physical impossibility).
If an elementary particle went back in time, it would not necessarily generate the deadly paradoxes that often rule out time travel in well know thought experiments (e.g. you go back and kill your parents before you are born). Suppose an effect on the quantum level that we observe today has a cause in our future.
(This was suggested in Huw Price’s Book “Time and Archimedes’ Point”.) As long as this quantum effect is incapable in priciple of destroying its own cause, paradox is avoided. Such a reverse time cause/effect link cannot therefore be ruled out. However, any present effect coming from our future that could potentially destroy its own cause would be paradoxical. So I am not suggesting that we could travel back in time and kill our own parents before we were born. This kind of time travel is impossible.
There is a name for this principle in the literature, although I cannot remember what it is called.
As to the issue of time’s flow: it is commonly believed that the “flow of time” is a confused metaphor. Time cannot be said to flow because it it did flow, it would make sense to ask “how fast does it flow?” Speed of flow of a river is measured by determining the change of the river over time. But against what are we to measure the change of time. Against time itself? This question is confused and meaningless. Of course time flows at one second per second – but what does that tell us? So time cannot be said to flow as a river does. If it does in fact flow, it does not do so in the same way that anything else flows. So until we can figure out what we mean by the “flow of time”, it doesn’t make much sense to talk about it.
The question of whether time flows does not seem to be related in any way to the issue of whether time travel is possible. What is the link? Also, the issue of time flow seems to me distinct from the issue of Einstein vs. Newton. Time flow would be a confused metaphor in both Einsteinian and Newtonian mechanics.
Interesting point, Daniel Shabossen, but that would require that the particle be unobservable, or at least, that it would take longer to observe it than the amount of time that it travelled. Otherwise, consider the following scenario: We have a device that, when activated, sends a particle back in time a half-hour. This device is hooked to another device that will detect the particle, if it’s present. Ordinarily, our device will transmit one particle every hour on the hour, but if the detector detects it, it overrides the sender, and causes it not to send a particle at the next scheduled hour. The particle, even though it’s a tiny, quantum mechanical effect, is still carrying the information to enable it to (in principle) prevent its own transmission.
Point well taken, Chronos. Or the particle sent back in time could be sent to a location that we could not even in principle determine. The particle sent back in time could be observed by us, but we would have no way of knowing that it was the same particle that we sent. The particle that we observe could be any other particle that went back in time. Otherwise, we could observe the particle and then later decide not to send it, therby generating a paradox.
It violates the principle I set out if we can send a message of any sort into the past.