lightspeed comm

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Guarionex</i>
<br />...aimed orthogonally...<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Orthogonal from one frame is not orthogonal from any other frame. Hence conclusions based on the assumption of orthogonality will usually fail to represent SR correctly.

Stick with LR and avoid all these paradoxes. -|Tom|-

Tom,

I expected a yes or no answer and an expanation in simple terms if possible. If you are not interested maybe someone else can expain the result. I want to know how either theory explains it.

guarionex

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Guarionex</i>
<br />I expected a yes or no answer and an expanation in simple terms if possible.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">"No". If the two ships are side-by-side as judged by the "rest" frame, each ship will see the other lagging behind because it takes light a finite time to travel the distance between them. According to SR, both views claiming to be the leading ship are equally valid.

As for specifics, the term "orthogonal" is undefined in your example. Will you aim your narrow beam at the light now arriving from a retarded spacecraft position, or at your inference of where the real spacecraft ought to be now, or at where the spacecraft will be by the time your beam can get to it?

Certainly, there is no mandatory reason for you to lose communication unless you point your narrow beam in the wrong direction.

In LR, you could just use gravitational forces for signaling. Because gravity travel billions of times faster than light, communication is nearly instantaneous and can't be lost because of spacecraft speed, and all frames agree about the relative positions of the spacecraft. -|Tom|-

Thanks for your answer.
First, the rest frame for both ships is the same. Think of it. This is all theoretical. Just imaging that we could not compare the acceleration of one spaceship respect to the others. No measurement on Earth would have any validity as we know it! Second, orthogonality is based on Euclidean geometry since it doesn't necessarily apply in SR. Two ships can accelerate at the same rate and keep parallel to each other, regardless whether they are noticed (by themselves or otherwise). Else is like asking the question does a tree make noise if we are not in the woods to hear it? Granted, under SR theory one may seem retarded respect to the other, but it should be the same with the other spaceship. This will imply parallelism. Of course, these spaceships, if they were running an experiment to verify communication, they would have to work out a few details that I spared for brevecity. It boils down that what I was asking: Does light carry the momentum of the source? It seems to me than in SR sometimes, light carries this momentum, other times it does not, to the convenience of the deliverer.

Second, the speed of gravity hasn't been proven, only the effect, which is not the same. Under GR, gravity does not exists (curved space!) and it is the best model so far. So, measuring the speed of gravity, something that doesn't exist... well is meaningless. It occurred to me as I wrote: maybe we could modulate the curvature of space and communicate that way!

Third, I came to this site looking for answers. If you can't dazzle and baffle me, I will look somewhere else.


guarionex

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Guarionex</i>
<br />Granted, under SR theory one may seem retarded respect to the other, but it should be the same with the other spaceship.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">This entire picture of yours presumes a universal instant of "now", which in fact does not exist in SR. So it is literally meaningless in SR to claim that the two spaceships can remain orthogonal to each other with respect to their directions of acceleration because they do not exist in the same time. The time at each point in one ship's every-changing frame will be different than time in the other ship's frame. Your comparisons are not being made across space at a common time, but across space and time.

I recommend my article "What GPS tells us about thet twins' paradox" at metaresearch.org/cosmology/gravity/gps-twins.asp
It might help you acquire a deeper understanding of SR, if you want that.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Does light carry the momentum of the source?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Light's momentum is contained within its frequency, not its speed. It is true under all circumstances in both theories, LR and SR, that lightspeed is independent of the speed of its source. The deSitter double star experiment proved that in 1913. (Independence from source speed is also a universal property of waves.)

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">the speed of gravity hasn't been proven<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Your information is out of date. My two articles citing the six experiments relevant to the speed of gravity are:
“The speed of gravity – What the experiments say”, T. Van Flandern, Phys.Lett.A 250, 1-11 (1998); also available at metaresearch.org/cosmology/gravity/gravity.asp
AND
“Experimental Repeal of the Speed Limit for Gravitational, Electrodynamic, and Quantum Field Interactions”, T. Van Flandern and J.P. Vigier, Found.Phys. 32(#7), 1031-1068 (2002); preprint under the title "The speed of gravity -- Repeal of the speed limit" available at metaresearch.org/cosmology/gravity/speed_limit.asp

The bottom line is that the propagation speed of gravitational force can be no less than 20 billion c. And no experiment disagrees with that conclusion. However, be sure you are not confusing gravitational force or changes therein with gravitational waves. This last, assuming they even exist, must propagate at speed c, but are too weak to affect anything in the solar system at a level that can be detected by even our most sensitive detectors (e.g., LIGO).

This also means that LR is correct and SR is falsified, because in SR, nothing can propagate at FTL speeds in forward time. Yet gravitational force does. This point is made in the last reference cited above.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Under GR, gravity does not exists (curved space!) and it is the best model so far.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">These are myths. First, no one knowledgable claims "curved space". That is a misunderstanding of the meaning of "curved spacetime" that I suspect is allowed to flourish to avoid embarrassing questions from students. See our web site article "Does space curve?" at metaresearch.org/cosmology/gravity/spacetime.asp
Note that Misner, Thorne & Wheeler's "Gravitation" says essentially the same thing on pp. 32-33. It is wrong to think of spacetime as space plus time (it is more like proper time), and it is wrong to think of space as curved at all.

Second, the geometric interpretation of GR (curved spacetime) is just one of the two classical physical interpretations of GR, the other being the field interpretation. Although the field interpretation was preferred by such notables as Einstein, Dirac, and Feynman, it is seldom taught anymore because of fascination with the geometric interpretation. That is most unfortunate because the geometric interpretation has now been falsified both theoretically and experimentally. See the Foundations of Physics paper cited above.

Third, the best and the most complete model of gravitation that currently exists is contained in the book <i>Pushing Gravity: New Perspectives on Le Sage's Theory of Gravitation</i>, M. Edwards, ed., Apeiron Press, Montreal, 93-122 (2002). See especially my chapter on pp. 93-122 and the immediately following chapter by V. Slabinski.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">measuring the speed of gravity, something that doesn't exist... well is meaningless.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">That would leave us with no explanation why light and gravity from the Sun do not arrive from parallel directions, or why the maximum gravitational force of the Sun on the Moon is delayed typically about 40 seconds after the middle of a total solar eclipse, or why computer experiments (which must use a force of gravity to compute orbits) show that only near-instantaneous gravity works correctly, but light-speed gravity causes orbits to spiral outward rather quickly, or ... lots of other things.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">I came to this site looking for answers. If you can't dazzle and baffle me, I will look somewhere else.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Some answers, we have. For entertainment, you will need to look elsewhere. But if you seek a deeper understanding of nature, this is the place to be. However, you can't acquire that knowledge without putting in the time to read, check citations, study the experiments, learn what works and what doesn't and why or why not, then ask questions of multiple sources until you are satisfied which answers make sense and which require a little magic to stay viable. If you are making your judgments based on the weight of authority, then this is not the place for you. Check out the Meta Research home page to see why: metaresearch.org -|Tom|-

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The bottom line is that the propagation speed of gravitational force can be no less than 20 billion c. And no experiment disagrees with that conclusion.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Im able to imagine that if it wasent for one Q:
Some time back I read in a science magazine that the speed of gravity had been measured to about 1c. gravity having about the same speed as light and so enforcing Einstains theory.
Is this result not valid or is there something else that interfears ?