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Old September 20 2012, 06:51 PM   #56
Crazy Eddie
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Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

gturner wrote: View Post
newtype_alpha wrote:
So when it arrives, it's clock indicates that perhaps a day has passed
No, nearly a year has indeed passed. From your point of view, EVERYONE ELSE seems to have slowed down.
I don't think that's how it works, at least according to Einstein and Hawking who talk about a starship traveller returning and meeting his great grandchildren.
I can't speak for Einstein or Hawking, but the MATH doesn't lie, and the underlying logic is pretty clear on this matter. If we're flying towards each other, we will both look at each other and we will be able to say the same three things: "You're moving towards me, you have more energy than me, and time is moving slower for you."

Now how could that be possible? "You're moving towards me" is simple enough: we're both moving towards each other, so we'd both be correct. But how could you have more kinetic energy than me AND I have more kinetic energy than you? That's the thing about relativity: kinetic energy is a relative value between the two of us, and in MY reference frame I have no kinetic energy and you have alot, while in your frame you have no energy and I have a lot. If we collide head on, however, the same amount of energy will be released regardless of whose frame you're using.

And the same is true of time. I see that your clock is running slower and you see that MY clock is running slower. But if we suddenly come to a stop right next to each other we see that our clocks are running at the same speed and apparently always have... but that jerk over there doing warp 7 in a school zone is picking his nose in ultra-slow motion (and he sees us very slowly giving him the finger and wonders "Wow, look at the time dilation on those too!")

You have to keep it in your head that velocity, energy and time can only be measured subjectively. In relativity, the only thing that doesn't change between any two frames is the speed of light.

Hawking discusses that as a method of prolonging your life so that you can watch the universe evolve over a human lifetime
And like most things Hawking says publicly, this is vastly oversimplified for the sake of people he considers to be simpletons.

What you're talking about, possibly, is that the 0.999c traveller would see light from the people he left behind as slowing down
Nope. The light still arrives at the same speed in all reference frames; if you're moving away from me at .99C, you still receive a photon from me at exactly the speed of light. That alone is the reason you observe time dilation at my position. I have a device that emits one pulse every second. You receive the first pulse, but by the time the second one fires you're just under 300,000km farther away from me. In your reference frame, the second pulse is ALSO coming at you at the speed of light, but it takes one second longer to reach you than the first one did. That means that from your point of view, my clock is running slow.

But guess what? You've got an atomic clock on your ship too. It's also emitting one pulse every second. You're moving away from ME at .99C, so from my point of view, and for the exact same reason, your clock is running a little bit slower than mine.

I don't know what Einstein or Hawking quotes you have in mind, but Einstein was pretty clear about the concept of curved spacetime. When you're traveling at relativistic velocities, you're in a reference frame this is LOCALLY flat, but is curved to outside observers. You should think of it like standing on a very tiny planet -- say, the size of a beach ball -- and you bend over and look at a person standing on the other side of the planet. You say to this person, "Hey dude, you're upside down." He looks at you and he says, "No, YOU'RE upside down." You're both correct, incidentally, because you're standing in a curved spacetime (General Relativity, I know, but the concept still applies). It works the same way in time dilation: I look at the starship and say "Your clock is running slow." The starship looks back at me, standing on Earth, and it will say the exact same thing about me, because velocity -- like time -- is relative, and in your own reference frame your OWN velocity is always zero.
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