Kristopher on November 21, 2011, 07:30:11 pm
Yes ... it sounds a bit odd.

Indulge me please.

Watch this video from 10:18 to 26:00   ... the meat is at about 22:40 to 24:00.

Now ... let us give the alien and the man at the gas station a tanglenet link.  At 10 Billion light years distance, if the alien bicycles away from the earth, he can communicate with the other end 200 years in the past. If he bicycles toward the earth, he can communicate 200 years into the future.

Use two sets for tanglenets, connections A and B, and two aliens, and connect the two aliens' sets with a local tanglenet. One alien bikes toward earth, and the other bikes away from earth. Signals from A get sent automatically to B on the aliens' end, and vice versa.

Earth end point A can talk to Earth end point B 400 years in the future ... and B can talk to A at 400 years in the past.


Now, instead of having aliens 10 billion LYs away moving at bicycle speeds as your far end, substitute two automated space ships much closer ... say in the distant Oort cloud. And have them pass each other at a significant fraction of C, instead of at bicycle speeds.

Even a signal timewise distance of only a day or so would be incredibly valuable.


Kristopher on November 21, 2011, 08:17:47 pm
Hmm. Use thousands of small ships in a really big elliptical orbit.  Have two sets orbiting in opposite directions. Each one has connections to all of the others going in the opposite direction, but will only send data to the one passing closest.

Time gain is smaller, but a lot of the pairs have a usable time gain, and you can daisy-chain your signal as many times as you need to to get the time length you want.

If each one has enough bandwidth, you can re-daisy chain repeatedly to get a signal sent from the time in the future when the system is shut down, to the time in the past when the system was started up.

Finding a way to prioritize use will be a problem ... you may think your day ahead stock quotes are more important that the battered signal concerning 1000km wide Asteroid DA1950 striking the Earth in circa 2800 AD ...
« Last Edit: November 21, 2011, 08:19:50 pm by Kristopher »

SandySandfort on November 22, 2011, 11:47:02 am
Why do so many people believe that instantaneous communication involved time-traveling information? Yes, given certain assumptions about how the universe works, that might be a reasonable conclusion. Other assumptions, however, result in different conclusions.

When EFT eventually goes to the stars, it will involve instantaneous teleportation. I already have the rationale for that, and it does not require nor imply time travel.

Kristopher on November 22, 2011, 01:38:56 pm
It is not a matter of what people believe.

If you have instantaneous entanglement communication outside of your event light-speed cone, these anomalies will happen. Which is why a lot of physicists really hate the notion of using entanglement to communicate. It takes causality and chucks it out a multistory window.

They don't want to admit that causality, as we think of it, is incompatible with a stochastic quantum-mechanical universe.

sam on November 22, 2011, 02:33:53 pm
Why do so many people believe that instantaneous communication involved time-traveling information?

Instantantaneous with respect to which rest frame?

For it to be instantaneous, and not allow time travelling information, it has to be instantaneous with respect to one, and only one, rest frame.

Name that rest frame and tell us why it is special.

Simultaneity is, as Einsteing pointed out in "On the Electrodynamics of moving bodies", not well defined.  If you have a method of communication that is instantaneous, you have to define simultaneity for everyone.   If it is merely simultaneous with respect to the rest frame of the people communicating, you can send information backwards in time.
« Last Edit: November 22, 2011, 05:17:07 pm by sam »

SandySandfort on November 22, 2011, 08:37:31 pm
It is not a matter of what people believe.

If you have instantaneous entanglement communication outside of your event light-speed cone...

Sure, if we assume it must go through this brane or doesn't use a worm hole or other mechanism that side-steps this universe. As I said, different assumptions result in different outcomes.

mellyrn on November 23, 2011, 06:12:27 am
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As I said, different assumptions result in different outcomes.

So they do.  One that's long bugged me involves the "identical twin paradox", where one twin stays on Earth and the other rockets away at a large fraction of c and returns, and the Earthbound twin is 50 years older while the rocketeer twin is only 5 years older, kind of thing.  That's what we see if we assume the Earth is the reference frame.  But from the rocketeer's frame of reference, it's the Earth and his twin that go shooting away at a large fraction of c, so why does time pass so "slowly" for rocket-twin and so "rapidly" for Earther-twin?  If there's some reason why the frame of reference here must be Earth-centered, then it's not all "just" relative speed.

There seem to be two chief time concepts.  One I've seen called the "god clock" -- an absolute reference, which we seem to have more or less instinctively.  Time "flying" when we're having fun, dragging when we're not -- that's in comparison with our sort of gut-level "neutral" notion of the passage of time.  Then there's Einsteinian-relativity time, where duration depends on how fast a given clock is traveling (which implies that, for a photon, the act of leaving a ten-billion-l.y.-distant star and arriving in a human telescope are simultaneous events -- along with being in each angstrom of space in between, so that for a photon, that whole distance is no larger or longer than itself).  Apparently Einsteinian time applies cosmologically, and conventional, god-clockery time in earthly traffic court as well as quantum dynamics; or so it was once described to me in reference to a physicist who reconciled relativity and quantum dynamics by eliminating the concept of time altogether. . . .

I'm OK with tanglenet being "simultaneous" from the perspective of Sandfort's Demon.  I'm in no position to say whether such a thing is entirely compatible with today's physics (or whether today's physics is entirely without contradiction), or whether it would involve some amount of rewrite.  If the tanglenet did operate as per Kristopher's speculation, that would, I think, be such a huge variance from what we sort of naturally "feel" about time as to be worthy of being the defining element of very, very different stories -- it would be an assumption that would, or imo should, generate a very different literary outcome. :)

SandySandfort on November 23, 2011, 08:30:31 am
... One that's long bugged me involves the "identical twin paradox", where one twin stays on Earth and the other rockets away at a large fraction of c and returns, and the Earthbound twin is 50 years older while the rocketeer twin is only 5 years older, kind of thing.  That's what we see if we assume the Earth is the reference frame...

Einstein is driving down the road one day and gets pulled over by a cop. The cop sarcastically says, "Hey buddy, do you know how fast you were going?"

Einstein looks a bit perplexed, then asks the cop, "In what frame of reference, officer?"

sam on November 23, 2011, 03:09:23 pm
If you have instantaneous entanglement communication outside of your event light-speed cone...

Sure, if we assume it must go through this brane or doesn't use a worm hole or other mechanism that side-steps this universe

If you have a wormhole with one frame of simultaneity, and I have another wormhole with a different frame of simultaneity, then we can time travel information by going through both wormholes.

Time, you see, is ordered by this universe.  If you can side-step this universe to get from one place to another, you can side step this universe to get from one time to another.

You need ftl to have reasonable plots for mortals that travel between stars.  You don't need ftl for a story set in a single planetary system.  Ftl is as fantastic as dragons, indeed more fantastic, since dragons do not inherently violate physics.  A big talking lizard that spits fire like a gigantic bombardier beetle could have evolved on earth, and one day might.

Of course there are size limits on a big talking fire spitting flying lizard, but the pterodactyl demonstrates that flying lizards can still get plenty large enough to eat fair maidens.
« Last Edit: November 23, 2011, 03:12:29 pm by sam »

trench on December 06, 2011, 05:05:06 pm
One that's long bugged me involves the "identical twin paradox", where one twin stays on Earth and the other rockets away at a large fraction of c and returns, and the Earthbound twin is 50 years older while the rocketeer twin is only 5 years older, kind of thing.  That's what we see if we assume the Earth is the reference frame.  But from the rocketeer's frame of reference, it's the Earth and his twin that go shooting away at a large fraction of c, so why does time pass so "slowly" for rocket-twin and so "rapidly" for Earther-twin?  If there's some reason why the frame of reference here must be Earth-centered, then it's not all "just" relative speed.

The reason you can't look at it symmetrically is because it's not. The important thing to remember about relativity is that it predicts all inertial reference frames are equal. The space ship accelerates as it begins its trip, again when it turns around, and probably a third time when it comes home. Because these are non-inertial reference frames, you can't say that from the point of view of the traveler the Earth accelerates three times.

Another thing worth pointing out is that special relativity implies length contraction as well as time dilation. This means that the from the point of view of the traveler, the distance traveled is actually less than the distance he is observed to travel from the point of view of an observer on Earth.

mellyrn on December 07, 2011, 06:37:10 am
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Because these are non-inertial reference frames, you can't say that from the point of view of the traveler the Earth accelerates three times.

OK, that's interesting.  Still, what am I to make of a trip that goes out in a wide circle, so that there is only the (relative) acceleration at the start and (relative) deceleration at the end?

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special relativity implies length contraction as well as time dilation.

Does length contract to zero at speed c?  I'd understood (perhaps incorrectly) that mass increases with speed and becomes infinite at c, thus one reason why lightspeed is impossible for matter to attain; if length contracts to 0, that would be another barrier.  It would also mean that for the photon, the distant quasar and the human telescope (and everything in between) are in the "same" place.  ?

What happens to me if I take my little starcruiser out and identify a position at {x,y,z} and arrange to stay there "motionless" with respect to, say, the solar system, watching it zip away on its orbit around the Milky Way at 220 km/s?  I guess I'm asking, how close to motionless is it possible to get?

I do understand that there are heh heh challenges to establishing the abovementioned {x,y,z}, thus to establishing anything like absolute rest.  And that means that I am travelling at A% of c with respect to one entity, B% relative to another, and so on; I am travelling at as many different relative speeds as there are stellar entities.  Perhaps special relativity applies only to change in speed, aka acceleration?  But gravity sez I'm always "accelerating" -- that's what "holds" me to the surface of the Earth; what "holds" my planet in its orbit; what holds my solar system to its galaxy, and so on.  So my personal time and length must be dilating in a gazillion different ways at once?

Killydd on December 07, 2011, 09:15:28 am
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Because these are non-inertial reference frames, you can't say that from the point of view of the traveler the Earth accelerates three times.

OK, that's interesting.  Still, what am I to make of a trip that goes out in a wide circle, so that there is only the (relative) acceleration at the start and (relative) deceleration at the end?

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special relativity implies length contraction as well as time dilation.

Does length contract to zero at speed c?  I'd understood (perhaps incorrectly) that mass increases with speed and becomes infinite at c, thus one reason why lightspeed is impossible for matter to attain; if length contracts to 0, that would be another barrier.  It would also mean that for the photon, the distant quasar and the human telescope (and everything in between) are in the "same" place.  ?

What happens to me if I take my little starcruiser out and identify a position at {x,y,z} and arrange to stay there "motionless" with respect to, say, the solar system, watching it zip away on its orbit around the Milky Way at 220 km/s?  I guess I'm asking, how close to motionless is it possible to get?

I do understand that there are heh heh challenges to establishing the abovementioned {x,y,z}, thus to establishing anything like absolute rest.  And that means that I am travelling at A% of c with respect to one entity, B% relative to another, and so on; I am travelling at as many different relative speeds as there are stellar entities.  Perhaps special relativity applies only to change in speed, aka acceleration?  But gravity sez I'm always "accelerating" -- that's what "holds" me to the surface of the Earth; what "holds" my planet in its orbit; what holds my solar system to its galaxy, and so on.  So my personal time and length must be dilating in a gazillion different ways at once?

Well, it might not be obvious, but going in a big wide circle really means you just have a low, constant accelleration throughout, just like how you feel when you take your car around a corner.  It's possible to do math in this reference frame, just ugly as you add in the acceleration as hidden.

Photons(and gravitons) are funny:  they don't have a concept of the passage of time, or of distance, since both are always zero.  Everywhere is the same place, and the same time. 

What do you mean by "motionless watching it zip away"?  That doesn't make sense to me.  How can you talk about it being motionless and moving at the same time?

mellyrn on December 07, 2011, 11:54:34 am
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Well, it might not be obvious, but going in a big wide circle really means you just have a low, constant accelleration throughout, just like how you feel when you take your car around a corner.

Yes; and -- from my perspective making that curve -- isn't the Earth I'm leaving also "making" the same low constant acceleration?

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What do you mean by "motionless watching it zip away"?  That doesn't make sense to me.  How can you talk about it being motionless and moving at the same time?

 :o Oh, yeah, I totally misphrased that, didn't I?  I should have said, "motionless relative to my magic {x,y,z} point" -- which was the whole point of designating the point in the first place . . . d'oh!

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Photons(and gravitons) are funny:  they don't have a concept of the passage of time, or of distance, since both are always zero.  Everywhere is the same place, and the same time.

And doesn't it make you wonder what can meaningfully be said about the nature of the universe and existence when the best sense we can yet make of existence says there are entities for which neither space nor time exist?  What are we humans -- figments of a photon's imagination?  :D

sam on December 07, 2011, 07:00:30 pm
Yes; and -- from my perspective making that curve -- isn't the Earth I'm leaving also "making" the same low constant acceleration?

No. 

If your accelleration was actually constant, in the same direction all the time, then you could apply general relativity, and assert that the earth was freely falling in a vast gravitational field, while you were standing still, but if we introduce general relativity when you have not altogether understood special relativity, that will confuse you even more.

trench on December 07, 2011, 08:59:13 pm
Yes; and -- from my perspective making that curve -- isn't the Earth I'm leaving also "making" the same low constant acceleration?

No, since you're in a non-inertial reference frame. Take the previous example of driving a car around a curve. While making that turn, you'll feel the g-forces of the acceleration, while the corner will not. In that case, if it looks to you like the corner is accelerating, it's only because you're not looking hard enough, which is a case we tend to ignore.

As a point of interest, both standing on the surface of the Earth and orbiting it are  non-inertial reference frames.

:o Oh, yeah, I totally misphrased that, didn't I?  I should have said, "motionless relative to my magic {x,y,z} point" -- which was the whole point of designating the point in the first place . . . d'oh!

The question then becomes "what is that point motionless with respect to?" x, y, and z are presumably spacial measurements from something... but from what? It sounds like what you really mean is what would happen if you could make yourself motionless with respect to the center of the galaxy, in which case it would be exactly as you describe.

As for how close it's possible to get to being truly motionless, it isn't. That is to say, there's no such thing as "truly motionless", because the whole point of special relativity is that you always have to ask "relative to what?" As long as anything in the universe is moving at all, than everything else is moving with respect to it. It also turns out that because of a whole lot of other things it's more or less impossible for everything in the universe to stop moving all at once... at least until the very end, but my guess is that physics will be working quite differently at that point anyway, so it hardly matters.

It's tempting to suggest that since the universe is probably finite and probably symmetrical, at least from far away (very much emphasis on probably in both cases), that there is a theoretically identifiable center of the universe, relative to which you could theoretically make yourself motionless. But there's a few too many probably-s in there and so it's far from certain. Also even if there were such a center to the universe and even if you could find it, I imagine dark energy would make it impossible to be motionless relative to it anyway.

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Photons(and gravitons) are funny:  they don't have a concept of the passage of time, or of distance, since both are always zero.  Everywhere is the same place, and the same time.

And doesn't it make you wonder what can meaningfully be said about the nature of the universe and existence when the best sense we can yet make of existence says there are entities for which neither space nor time exist?  What are we humans -- figments of a photon's imagination?  :D

It's not really that for them time and space don't exist, it's that they don't perceive them. A particle moving at the speed of light would, I suppose, have an infinitely large Lorentz factor, meaning (among some other things) that for it time would dilate infinitely and length would contract infinitely (so actually "space" would always be zero while "time" would be infinite). This means for that particle any "event" in time would always be infinitely far away, so it would appear to it as if time had stopped. Similarly though, any... er, "event" in space would be no distance from it at all, so it would appear as if the entire universe is a single massive singularity.

So it wouldn't really look like there is no time and no space, it would just look like there's only one point of space and that time has stopped moving.

Does that help?

 

anything