You said:

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While it is true that there would be some time dilation simply by walking, we have not been able to measure this effect because it is so small.

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Since Survivor was talking about a hypothetical situation -- saying that if someone walked long enough, the effect of time dilation would be measurable -- I interpreted your response (coupled with your challenge to give an equation that demonstrated the effect) as being a denial of the truth of the hypothesis.

The equation that I gave showed the truth of the hypothesis: If someone walks for a long enough time, the time dilation will be measurable. That did not seem to be what you were saying.

Reading between the lines can be dangerous when someone never meant there to be anything between the lines. Anyway, I think I can see where your confusion came from, no hard feelings.

If you walk around the world enough times you can measure a time dilation effect. I don't believe I ever said differently, though apparently there was room for confusion in what I did say. What I interpreted Survivor as having said was that this effect is more significant than if you went around the world in a jet.

Time dilation, in my mind, is T'/T

Just like Christine saying that the dilation becoming undefined at c is correct in one sense and easily misinterpretable in another. I usually use 'undefined' for the case where both denomenator and numerator reach zero, and infinity for the case where only the denomenator approaches zero.

And I meant what I said about the distance traveled, for purposes of measuring the time dilation effect. The way we measure the effect is by starting with two clocks that share the same frame of reference, moving one of them, then moving it back and comparing it with the first.

However, my point about the movement of the Earth shouldn't be neglected. You can't use a reference FOR that is under several continously accelerating accelerations (which the surface of the Earth is under for reasons familiar to all of us). So in a sense...well, no, in every meaningful sense, you must compare two moving FORs, just one is moving more than the other relative to the reference FOR.

This is why, in practical terms, walking or flying planes doesn't make as much difference as how far you go. Now, in practical terms, it is a heck of a lot easier to get on a plane and fly several thousand miles than walking that same thousand miles. The point is that the practical difference, for operating on Earth, is how far you go, not your velocity relative to the surface of the Earth, which after all is not our reference FOR. It is impractical to use a supersonic jet when you can use a series of jets that don't even come close to being supersonic. Perhaps it isn't quite as impractical as walking (which could easily use up some poor scientist's entire working life )

I don't know whether the time dilation effect has ever been measured on a supersonic flight, I do know that it has been measured on non-supersonic flights...I'm almost positive that it hasn't been measured on the back of a walking scientist. But remember, 'walking speed' isn't 1.788 m/s (and why that instead of just 1 m/s?), it's that plus a whole bunch of other crazy speed. We aren't at the extremes of the defined curve.

That led me to do some google research, and led to some sites that might be interesting to anyone who is thinking of writing a time-travel story. Check out:

http://www.physicscentral.com/writers/writers-02-4.html

and

http://www.science-spirit.org/articles/Articledetail.cfm?article_ID=270

Also, this site from Nova has several interesting pages.

http://www.pbs.org/wgbh/nova/time/

That equation only works for determining apparent time dilation in another FOR, it can't be used to solve a twin paradox, because it is supposed to be commutative...both FORs see the other being slowed down. I tried adjusting the use a couple of different ways...but it just won't work for showing how much a moving clock actually slows down relative to a stationary one.

RE: Original post.

After reading the original post, I suspect that Christine’s questions presuppose that scientific explanations need to be correct in order to be effective verisimilitude devices in science fiction stories. I believe that is a faulty assumption, which also informs this debate about time dilation and what have you.

This entire debate seems to be irrelevant to the composition of a valid or effective SF story. What is more important? Effective story elements, or accurate science? Whether your science is highly accurate or ridiculous, it does not seem to matter when it comes to telling a good SF story. Edgar Rice Burroughs had his Carter hero mentally travel to Mars, a place nothing like the rovers Spirit and Opportunity reveal. And the flying ships were explained using the quaint 19th century notion of the ether. Bradbury’s “science” is just as bogus. On the other hand, Kim Stanley Robinson uses, I believe, fairly accurate terra-forming elements in his Martian stories. And, of course, time-travel stories are always plagued by paradox and impossibilities no matter how accurate you get the science.

We are storytellers first, and science enthusiasts second. Often the SF premise of a story is merely a device to explore a larger premise dealing with the human condition.

Also, there is a difference between creating verisimilitude in a story and offering scientific explanations, whether bogus or accurate.

One idea I find interesting is the idea of using time travel for archeology...or espionage! You wish you had bugged that street corner where that known agent talked with a half dozen unidentified persons? Send a little camera back in time, then collect it! Want to know what the paintings Botticelli burned were actually like (I bet he was planning on burning them anyway)? Whether Garner really shot the Kid? Who's really buried in Grant's tomb?

Basically, I believe that the actual travel through time is such an inherently flawed concept as to be somewhat ridiculous. I did enjoy Back to the Future, but that had little to do with the time travel. In fact, asherahpole, I would say that glossing over science is ESSENTIAL for a good scifi story, because when you try to go into too much detail the plausibility gets in the way of what might otherwise be a fun tale.

I think I've gotten all confusing, so let me try saying this a different way. There is the theory that time is a straight line, and whatever changes you might have done in the past have already happened so it doesn't matter. You can't kill Hitler before he conquers Europe because it didn't happen so it's impossible. Boy would I like a gun and a chance to prove that one wrong....it just doesn't make sense. Then there's the infinite universes theory, a little more plausible but usually implemented in a messy way, and at it's heart it, too, makes little sense.

Bottom line in this debate, however, goes something like this: Whatever you draw from science, it should work as a story premise. It should serve the story. The story should not serve the science.

I was reading a magazine dedicated to current theories in cosmology. Fascinating stuff, but I was struck by the lack of characters that plagued these cosmological "stories." Made it tough reading. As storytellers, we don't want to fall into that trap.

One of the attempts that came closest to success was a briefcase bomb that was about two meters away from the little dictator. With horseshoes and hand grenades (and bomds), close usually counts for something, but in this case someone tripped over the briefcase and kicked it under the table. It happened to be one of those conferance tables with two wide solid legs rather than four. The blast was deflected, killing some generals, but leaving Hitler basically unharmed.

That table leg was a simple physical fact, like the existance of a self-consistent solution for every possible wormhole transit into the past. You can't use the physics behind current theories of how time travel might be possible to force a paradox.

Does this mean it's impossible? I'm not sure...but that would seem to be the case. If the mathmatics of the universe dictate that you cannot force a logical impossibility to occur...then I would guess that it would remain a physical impossibility as well as a theoretical impossibility.

I personally would consider that "gun and a chance to prove that one wrong" a probable death sentance for no chance at all of proving anything but my own inability to force the universe to do things it doesn't want to do. That doesn't mean I would refuse, necessarily. I just wouldn't "love" the offer.

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Yeah, man! Good idea! Christine should go. Good idea, man!

Survivor on being told that someone has to go back and try killing Hitler in the past...after hearing Christine say she'd go.

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So let's try this scenario. I enter a room with a time machine in it, and I travel back in time 5 minutes to meet myself. There should therefore be 2 time machines and 2 me's in the room when I walked in. Were there? I figure I can beat those odds by not going back in time at all....then there should only be one of me so what's that other me doing there? She's an imposter! Kill her!

After all, time travel involves messing with quantum physics (anything that can go wrong, will, and anything can go wrong), high energy physics (Kaboom!), relativistic effects (c+me+past me=?), forces that bend space/time (*&^%!), or quite possibly any combination of the above.

At the very least, I would start my paradox attempts using...lab rats. And I'd be a very safe distance from the facility in which the experiment were being conducted.

I don't try to figure them out or prove them scientifically, and I think there are more readers like me than not.