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Author Topic: Interstellar / planetary space communication  (Read 13387 times)
LB5KE
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Posts: 141




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« Reply #15 on: November 07, 2013, 03:08:13 PM »

Sure, at one point it seemed like heavier-than-air flight was impossible, but it's now possible. So does that mean that, in the same vein, time travel (which is a natural result of faster-than-light travel) might be one day possible, too? Well, maybe, but it would certainly create some paradoxes (like the grandfather paradox) which seem like they shouldn't be realizable.

Not only does it seems like you could communicate instantly (entaglement) but also backwords in time (double slit), it does create paradoxes, however the many worlds interpretation would solve all of those paradoxes. So the end result would be that while you could communicate instantly the information you sent would end up in a parallel world.
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KG6AF
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« Reply #16 on: November 07, 2013, 03:10:42 PM »

So the end result would be that while you could communicate instantly the information you sent would end up in a parallel world.

I've already seen that happen in some of these forum threads.
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KB1WTY
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« Reply #17 on: November 07, 2013, 05:36:05 PM »

...however the many worlds interpretation would solve all of those paradoxes. So the end result would be that while you could communicate instantly the information you sent would end up in a parallel world.

Ok, please clarify what you mean by a parallel world, because I feel like you're using it in a non-standard way as far as MWI goes. MWI predicts that universes keep branching. Once decoherence happens, they are cut off from each other. So, of course, you can't mean that the message goes into a universe that branched away from the current one at an earlier point (that would also be silly because then, in the receiving universe, a message would just come right out of nowhere!) So that leaves parallel world to mean a later evolution/branch of the current universe, but not the same one that "you" end up in. But that would mean that the sender of the message necessarily exists in all of those universes' pasts, and that's not really a parallel universe in the sense that it would allow you to avoid any side effects of killing your grandfather.

In any case, we're talking two different things here. FTL-related time travel is a relativistic effect, it has nothing especially to do with entanglement (except that it's sometimes implied that entanglement is one way that FTL would be possible, but I say to that there are *very* good reasons to believe the No-Communications Theorem), nothing to do with the double-slit experiment, and nothing to do which interpretation of QM you go with (there isn't even a known way of testing between MWI, the Copenhagen interpretation, de Broglie–Bohm, etc. If what you were saying were true, then you would have just discovered one. Incidentally, this would almost guarantee you the Nobel Prize.)

Rather, FTL time travel happens because of 2 main, experimentally verified effects of relativity: time dilation, and the constant speed of light in any inertial frame.
-Time dilation: we know that as an object accelerates close to that of light, time dilates. In other words, while a small amount of time passes on the near-light-speed object, a large amount of time passes in the relatively non-accelerating inertial frame.
-Constant speed of light: we also know that no matter how quickly you are moving, if you measure a beam of light in a vacuum, it will always be moving at exactly the speed of light. Even if you're moving at 99% the speed of light, the photons will seem, to you, to be moving at the speed of light relative to you, while a stationary observer will observe a very slight difference in the beam's speed and your speed (only 1%).

Ok, so let's put it together.

You are racing a photon in your spaceship. You and it are going 1 light year in distance. Your spaceship is capable of traveling at 99% the speed of light. You and the photon set off at the exact same moment. What happens?

From your point of view, the photon shoots ahead of you, since relative to you, it's moving at the speed of light. It necessarily must get to the finish line considerably before you, because you know it's flying away *much* faster than you. By the time you get to the finish line, you don't even smell its space dust. But, from the point of view of people watching from bleachers set up along the course, you do trail the photon, but not by much (to them, it's moving at the speed of light, but you're moving at 99% the speed of light, so not bad).

So when you finally get to the finish line and ask, "How much did that photon beat me by?" what are they going to say, that it got there just before you did, or waaay before? Well, this is where time dilation comes in. Even though you've been racing for, in your opinion, just a bit over a year (one light year at 99% the speed of light would take just over a year of your time to cover), to the people at the finish line, a century has passed! Therefore, they're going to say the light beam *did* get there well before you (only one year after the start of the race, and you showed up around 99 years later). I'm ignoring length contraction and the impossibility of defining simultaneousness in separated regions of space, both of which are necessary for a full picture, but this is enough to show why time travel is inherent in FTL: if you were going *faster* than the photon, the only way you'd agree with people at the finish line is if you traveled backwards in time and arrived before you left. Because, from your point of view, the photon still shot ahead of you (constant speed of light, remember), but to everyone else, you shot ahead of it. I don't see how MWI would change a thing in this thought experiment.
« Last Edit: November 07, 2013, 05:41:19 PM by KB1WTY » Logged
LB5KE
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« Reply #18 on: November 08, 2013, 05:12:52 AM »

There is so many worlds that i would wear out all the keyboards in the would trying to type the number in exponent. And since there are so many of them the person who meets his grandfather are  cut off from preventing his grandfather from going on a date (and then prevent the time traveler from being born) because that would happend anyway in a near infinite number of other universes.
(http://www.youtube.com/watch?v=e99vsYHIbsQ @ 08:00)

Regarding the space race with the photon. Lets say that the space traveler wants his photons to go faster than the speed of light (easier then a massive space ship) so he can tell his alien wife to have the dinner ready, he would have to bend the space in front of the photons using Miguel Alcubierre theory Alcubierre drive using negative energy.

Just as traveling back in time transferring information faster than light is something the universe has protected it self from by thowing the message in to another parallel universe. The MWI doesn't have to be the correct one describing the double slit experiment but i feel that it helps explain the seemingly random nature of the universe.

If you still feel i am MWI in a nonstandard way and that i am wrong, you are probably right.  Cheesy

 
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KO1D
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« Reply #19 on: November 08, 2013, 06:55:55 AM »

Does anyone realize that it would take 4.3 years for a signal to get to Alpha Centauri and another 4.3 years to receive an answer using our radio transmission techniques. That's 8.6 years round trip. Long wait to have a rag chew, unless a deep space transmission is developed that that uses warp technology (Star Trek).

73s

K2OWK

Sounds like some of the AM guys I listen to. Rubber band on the mic and then you listen to their broadcast  Cheesy By the time the signal reaches the receiving station should be time for an over HI HI!  Grin
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KB1WTY
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« Reply #20 on: November 08, 2013, 12:31:21 PM »

...the universe has protected it self from by thowing the message in to another parallel universe.

That's what I'm confused about in this scenario. From the point of view of the universe that had the message thrown into it, what would appear to happen? Does a message just appear out of nowhere? Wouldn't that violate conservation of energy to suddenly have message-encoding photons appear from nothing?
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LB5KE
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Posts: 141




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« Reply #21 on: November 08, 2013, 04:31:13 PM »

...the universe has protected it self from by thowing the message in to another parallel universe.

That's what I'm confused about in this scenario. From the point of view of the universe that had the message thrown into it, what would appear to happen? Does a message just appear out of nowhere? Wouldn't that violate conservation of energy to suddenly have message-encoding photons appear from nothing?

Yes it would. So the only way to handle this is to create a new parallel world containing the message. Just like the message it self was a quantum measurement that would have created a new world by itself.
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KD8HMB
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Posts: 138




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« Reply #22 on: December 01, 2013, 09:23:01 AM »

Does anyone realize that it would take 4.3 years for a signal to get to Alpha Centauri and another 4.3 years to receive an answer using our radio transmission techniques. That's 8.6 years round trip. Long wait to have a rag chew, unless a deep space transmission is developed that that uses warp technology (Star Trek).

73s

K2OWK

If the Alpha Centaurian was a typical contester, he would still send you a "59" signal report
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