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| Time Travel, again
Posted: 9/10/2007 11:53:57 AM | How so? Einstein stated that the speed of light is the same in all inertial frames. Not sure how that can be, but all of the discussions of special relativity use that fact. No matter how fast you are traveling, you will always measure the velocity of light as c. In the train's inertial frame, the train's velocity is zero, the velocity of light is c. Therefore YOUR velocity is zero and you are free to behave and experience normally. Even accelerate to the speed of light!
But by riding the train going the speed of light you have already accelerated to light speed and therefore all movement of your body, inside and out, is dedicated to moving at light speed in the direction the train is travelling.
I'm not saying it's possible to actually do this, btw. | |
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| Time Travel, again
Posted: 9/10/2007 1:36:23 PM | "we overtake the light carrying the story of our history and therefore 'rewind' our ability to observe it. Special relativity allows us to observe our history but not to interact with it."
I don't know though. If your in a jet going mach 3 you don't hear sounds before they happen. You probly don't hear anything from outside the plane since the sound waves would not be able to catch up to your ears.
If you were zooming around the earth in orbit at the speed of light its not like you would see whats going on, on the ground. Everything would probly be a red shifted dot. You would time travel forward though as your time in the ship would slow down while the world was at its normal pace. When you landed you would be farther in the future time wise than what you aged while in the ship.
Going back in time though...I suspect time just doesn't work that way to be possible. | |
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| Time Travel, again
Posted: 9/10/2007 3:19:32 PM |
I don't know though. If your in a jet going mach 3 you don't hear sounds before they happen.
Um...that's because you have two problems here. I'm not counting the fact that the sonic boom might drown out anything else.
First, you have to STOP, or at least slow down, so that the light/sound from the events you're trying to observe can actually reach you.
Second, you're not thinking of the past, you're thinking of NOW. That sonic boom is created now, and you're getting ahead of it. Whether you wish to see; or hear, past events, you can use a tape measure analogy. At some point in time, light reflects off things, allowing one to see what is happening at that time. That light is the zero on your tape measure. Extend the tape measure. As time passes, light continues to reflect off events, all of it moving away at the speed of light. Note that the oldest events, your "zero", are farthest away. I'll assume you're trying this alone [if at all], so lock the tape measure. The present is the highest measurement - the part which JUST came out. You wish to observe the past. To do that, you must see the oldest light. The only way to do that is to outrun it. Start walking. Note that, as you walk you are passing older and older light. You can't see it because it can't reach your eye at your current speed. When you drop below light speed, you can start to observe the light. Where you stop determines how old the image is that you see. If you want to see "zero", you have to at least get that far. If you want to see what happened at 15, you stop at 15. If you want to see your own departure, you must backtrack or wait for that light to catch up. This experiment would work best with three people and a long reel tape. One person acts as light/time, marching on, one acts as the "present", anchoring the tape, and one is the superluminal traveller, starting at the present, outrunning light, then backtracking as need be.
If you were zooming around the earth in orbit at the speed of light its not like you would see whats going on, on the ground. Everything would probly be a red shifted dot.
Actually, you would travel away from the Earth if you want to accomplish anything. In orbit, half of what you see would be blue-shifted, half would be red-shifted, depending whether it's ahead or behind you. Your goal is to get AHEAD of the light (or sound). Orbit puts you at 90 degrees to what you wish to see, and you won't get ahead of anything by travelling at a right angle.
You would time travel forward though as your time ...
That much is true. Ironically, you have to travel forward in time in order to observe your own past. | |
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| Time Travel, again
Posted: 9/10/2007 4:53:34 PM | "I haven't done it, but I think it would be fun to learn"
uh well duh you havnt done it,damn | |
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| Time Travel, again
Posted: 9/10/2007 6:57:46 PM |
But by riding the train going the speed of light you have already accelerated to light speed and therefore all movement of your body, inside and out, is dedicated to moving at light speed in the direction the train is travelling. As far as I know, astronauts traveling at 17,000 mph in a spacecraft don't make any effort to keep their bodies in motion, whether they are orbiting the earth or flying to the moon. As you sit browsing the web, you don't feel yourself flying through space at ~MACH 1.5. The point about relativity is that it is RELATIVE. As far as I understand special relativity, and quoting many texts on special relativity, the observed speed of light is ALWAYS c, regardless of the speed at which the observer is traveling. Therefore the speed of light measured by an observer on a train traveling at the speed of light is still c and everything on the train will appear normal to that observer. The train is only traveling at c RELATIVE to a static observer. As far as the observer on the train is concerned, the 'static' observer is the one traveling at velocity c. So far, this doesn't add up to me, but neither do many of the fanciful ideas about time travel. | |
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| Time Travel, again
Posted: 9/10/2007 8:31:50 PM | It's true that astronauts don't make an effort to go along with the motion of the spacecraft. That's because of inertia. Objects in motion will stay in motion if not acted upon by other forces in opposition to their movement. But those astronauts are subject to relativistic effects. It's often said they've "traveled forward in time" by some fraction of a second, but that's really a misleading way to think about it. What's happened is that their internal processes slowed as they orbited the Earth. They go quite fast by our standards of familiar means of travel but extremely slow compared to light, so the effect of their internal slowing (which would include their biochemical processes, their electrical conduction along nerves, everything) is so small as to not matter in any practical way.
Now, speed them up to nearly the speed of light as they orbit the Earth and it's a different story. In order to not break the speed of light, their processes would slow down much more. But yes, light would still seem to pass them by at C. Imagine the scenario. Light is passing them really really slowly by our observations. But, since their internal processes have slowed so much (which means the rate at which they take in and process information is slowed as well) the light appears to them to zip right on by at the usual rate.
To say that someone can ride along in something going the speed of light and still have a velocity of zero would lead to a continuous "reset" to zero velocity, meaning you could have a spacecraft going light speed, then another one inside going at light speed in this "new" frame of reference, and then another one in that, ad infinitum and there would be no limit to how fast you can go. But that's not the way it works.
Oh, and yes, the observed speed of light is always the same, but if you go the speed of light yourself there is no observing anything. | |
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| Time Travel, again
Posted: 9/10/2007 9:06:28 PM | | So, do you have some reference material to back up your claims, or are your comments just a best guess? | |
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| Time Travel, again
Posted: 9/10/2007 9:35:41 PM | My description comes from an accumulation of studying and thinking about it over time. I couldn't point to one book or paper that put things exactly the way I have just stated them, so no, I'm not going to give a reference. But all of what I say follows from the fundamental rule that nothing can surpass speed C. If you care to find a physicist to run this by, feel free. I went to Georgia Tech and, while I did not major in physics, I took a number of physics courses. And those I know who did major in physics agree. Btw, you can always come at if from the perspective that the astronauts' internal processes aren't slowing down, but that the processes of everyone on Earth have sped up. It's essentially the same thing, though. What you seem to be saying is that a thing that travels at the speed of light does not travel at the speed of light.
This helps in visualizing it.
http://video.google.com/videoplay?docid=6321903527820521732&q=speed+of+light+travel&total=140&start=0&num=10&so=0&type=search&plindex=3 | |
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| Time Travel, again
Posted: 9/10/2007 9:44:19 PM | | What I've stated isn't really an idea I developed "by myself". Now, if I were to speculate about how it worked at a deeper level, that's something I've never read (though it may have been addressed). I will give you my own idea (though again I'm going to bet it's not new). My guess is that there is some kind of action or transfer happening at the subatomic level that occurs at light speed, so, coupled with the light speed limit, if an atom moves, that internal process is slowed because if it were not, the speed limit would be broken. The implication is that all other processes (those occurring on scales larger than the subatomic) "build up" on top of these subatomic processes and that their rate is the result of the rate of subatomic processes. | |
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| Time Travel, again
Posted: 9/10/2007 9:48:02 PM |
astronauts traveling at 17,000 mph in a spacecraft
Is that really how fast astronauts travel? | |
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| Time Travel, again
Posted: 9/10/2007 10:00:24 PM | The speed they travel doesn't cause them harm. The acceleration could, though. If they were accelerated to that speed to quickly that would be a problem. In fact, astronauts have to meet a pretty strict health assessment in order to fly because the force of acceleration (and extended periods of weightlessness) is a problem for some people.
Here's what can happen.
http://www.youtube.com/watch?v=52E3cet54bA
EDIT: Watching the earlier vid again, it looks like through the last half of it they pretty much DO describe it the way I did, so consider my thoughts "retread". | |
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| Time Travel, again
Posted: 9/10/2007 10:35:43 PM | And
"escape velocity" for the Earth is about 40,300 kilometers per hour, or about 25,000 miles per hour
That's amazing, I can't imagine the pressure. | |
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| Time Travel, again
Posted: 9/10/2007 10:38:33 PM | | I agree. It really is amazing. Then just imagine. Even that is excruciatingly slow compared to the speed of light. But speed itself doesn't cause pressure. You don't feel speed. You feel changes in speed (well, more accurately, changes in inertia, since you could maintain the same speed but change direction). | |
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| Time Travel, again
Posted: 9/10/2007 10:53:53 PM | | Heavy acceleration ages the body, breaks it down, correct? | |
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| Time Travel, again
Posted: 9/10/2007 11:00:56 PM | | It doesn't age it. It's just that any drastic changes in speed can be harmful. For instance, a car crash can kill a person. But let's idealize the situation and pretend the car doesn't get all crumpled up and the people inside don't hit their heads (or any other part of their bodies) on anything. If they went from, say, 150 mph to zero in a tenth of a second, their internal organs would get smashed inside their body because their momentum is still trying to make them go 150 mph. And you wouldn't have to come to a stop for the same thing to happen. If you just slowed down to, say, 10 mph you'd get much the same result. Same deal if you accelerated from 10 mph up to 150 mph in a tenth of a second. | |
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| Time Travel, again
Posted: 9/10/2007 11:23:31 PM | | Thanks for the video link. So Bertrand travels at half the speed of light, but sees Albert's light traveling at the speed of light. Given everything is relative (i.e., there is no absolute frame of reference), who is really traveling at what speed? Bertrand observes that he is traveling at zero speed relative to light and presumably light from his headlights would not overtake the light from Albert's headlights. So, why can't Bertrand accelerate to the speed of light relative to his current speed just as easily as Albert can accelerate to the speed of light relative to his, lesser, speed? | |
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| Time Travel, again
Posted: 9/10/2007 11:40:25 PM | | Yeah, it does get murky as to who is moving and who isn't, etc. I think the solution is that while there are no absolute frames of reference, there are local frames of reference. And measuring your speed relative to light will give you a misleading notion of how fast you're going. It will always be zero, as you say. But does that mean you never move and that nothing ever happens anywhere? No, you have to measure speed in relation to other things. | |
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| Time Travel, again
Posted: 9/11/2007 8:03:39 AM | A fundamental to the discussions of special relativity is the notion that you CANNOT detect the velocity of your inertial frame by any physical experiment. This is stated in almost every discussion I have read. The only murkiness is how light can apparently travel at different speeds, depending on the speed of the observer.
I still go back to the idea that much of the discussions on time travel are based on a misunderstanding of the fundamental premise, thereby failing to recognize that it is just an illusion. The Lorenz transform is the mathematical basis of relativity but as far as I can comprehend it, it merely describes how events in one frame of reference will be perceived by an observer in another frame of reference. It is about the perception of physics, not physics itself.
As far as me never moving, that seems to be the general idea of special relativity. There is absolutely no difference between Bertrand moving at half the speed of light with Albert not moving and the reverse of Bertrand not moving and Albert moving at half the speed of light. | |
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| Time Travel, again
Posted: 9/11/2007 12:49:22 PM | A fundamental to the discussions of special relativity is the notion that you CANNOT detect the velocity of your inertial frame by any physical experiment. This is stated in almost every discussion I have read. The only murkiness is how light can apparently travel at different speeds, depending on the speed of the observer.
But you can detect your velocity in relation to other objects (not light). The speed of light does not change depending on the speed of the observer. The speed of light through a medium never changes. What changes when the observer changes velocity is the rate of that observer's internal processes. This causes them to not detect the change in the velocity differential between them and light that others observers would detect.
So, the speed of light through space doesn't change, but the speed of a traveler can. When the traveler's speed changes, so does the difference between their speed and the speed of light. However, because the speed of their internal processes changes as well, the ratio of the difference between their speed and the speed of light remains the same as compared to their internal processes. Let's say you're in a car traveling 30 mph. There are a line of other cars in the next lane over that are evenly spaced and going many times faster than you (all the same speed as one another). You then double your speed. The number of cars that pass you by in 10 seconds measured by your watch will decrease by half, right? Not if your watch were to slow to half its former pace. In that case, you'd see exactly the same number of cars passing you in 10 seconds measured by that watch. (Note so as to not confuse anyone... in reality you'd have to go MUCH faster than this for your watch to slow by half - we have never gotten anywhere near that speed.).
I still go back to the idea that much of the discussions on time travel are based on a misunderstanding of the fundamental premise, thereby failing to recognize that it is just an illusion.
Agreed. I believe the popular notion of time travel is false.
The Lorenz transform is the mathematical basis of relativity but as far as I can comprehend it, it merely describes how events in one frame of reference will be perceived by an observer in another frame of reference. It is about the perception of physics, not physics itself.
From the Britannica Concise Encyclopedia:
"Set of equations in relativity physics that relate the space and time coordinates of two systems moving at a constant speed relative to each other, developed in 1904 by Hendrik Antoon Lorentz. Required to describe phenomena approaching the speed of light, these transformations express the concepts that space and time are not absolute; that length, time, and mass depend on the observer's relative motion; and that the speed of light in a vacuum is constant and independent of the motion of the observer or the source."
The bold part gives it away. If the speed of light is constant and independent of the motion of an observer, how can it be seen by two observers (one stationary and one traveling in the direction the light is moving) to move away from each of them at the same speed? Light isn't going speed C for one and C + 17,000 mph for the other - light doesn't care about them or adjust its speed for them. For two observers to observe the same speed of light while themselves going different speeds, there has to be another difference in their conditions other than the difference in velocity. That difference is in their rates of observation.
As far as me never moving, that seems to be the general idea of special relativity. There is absolutely no difference between Bertrand moving at half the speed of light with Albert not moving and the reverse of Bertrand not moving and Albert moving at half the speed of light.
This does not mean that two objects in motion relative to one another will experience time the same way, though. If that were the case there'd be no need to correct the clocks in satellites, for instance. | |
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| Time Travel, again
Posted: 9/14/2007 9:00:24 PM | | Thanks for your patient responses, Guy. Still don't have it close to clear, but I'll keep working on it. | |
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| Time Travel, again
Posted: 11/12/2007 6:19:47 PM | | time travel can and will be possible some day, i feel it is being done in our future as we speak, others from a distant time, traveling back, watching the world, unable to intervene and themselves physically alter any events from taking place. there are many parallel planes in this universe we call home but as of yet, we have not mastered how to travel these planes as others have. you just cant see them but they are there, (the parallel planes i mean)..imagine in maybe a hundred years to be able to travel to and through different planes of existence | |
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| Time Travel, again
Posted: 7/1/2008 5:58:17 AM | If you're familiar with time dialation then it's not too difficult to imagine. As a craft approaches the speed of light (c), it behaves similar to the way it would within a powerful gravitational field. Time experienced by the occupants of this craft will "pass" more slowly relative to an object at rest. People at rest will experience normal time of perhaps 1 year, but for people on the craft it would seem as if less than a year passed by.
Note that I didn't use the actual equation, l'=l*sqr(1-v²/c²), to calculate the corresponding time. This is a quick conceptual example.
The magnitude of this phenomenon is more pronounced as one approaches c. If you were to go for a short ride in a craft traveling at .99c, you would emerge to find that perhaps thousands of years had passed for the stationary folks experiencing normal time. Your friends and family would probably all be long dead, but for you only a few days perhaps would've gone by. For all practical purposes, you just traveled into the future. The cool part is that the principle itself IS NOT science fiction. The only difficult part would be reaching and sustaining such a high velocity.
This is a great site to study the phenomenon more
http://www.thebigview.com/spacetime/timedilation.html | |
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| Time Travel, again
Posted: 7/1/2008 6:00:56 AM | | The real question should be, would you want to travel into the future at all? I'm not so sure that I'd want to see what everything will be like. Another interesting question, probably best for another thread, is whether or not the future can be changed if you could travel to it and saw something that you didn't like (i.e. Back to the Future II). | |
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