Mowgli

Spoken like a true believer And sounds like Einstein himself, "If the facts don't fit the theory, change the facts."

Sorry. In fact, it was t(1+d), which is multiplicative. t just happened to be 1 ns. Hmm... I have to think about this. As you surely see, I'm basically doing the twin paradox here, trying to eliminate the need to accelerate or decelerate one of the twins. Yes, I was saying "after correcting for light travel time effects", not ignoring them. Along that line, can I ask you something else? If the observer is a point mass, and the spaceship is in a stationary orbit around the observer, then can I say that the spaceship is an intertial frame and apply SR?

Because the observer is sending out his pings at the rate of one every nanosecond, he expects to get the replies every nanosecond (after correcting for the light travel time effects).

Assume a stationary observer, sending a series of "pings" at the interval of one nanosecond toward a spaceship. The spaceship also has an identical pinging device, sending one ping a nanosecond. Furthermore, the spaceship has a transponder; every time it gets a ping from the observer, it sends back a reply. (Think of the ping as a laser flash and the reply as a reflection.) The observer receives two serieses 1. the spaceship pings, and 2. the replies. The observed interval between the spaceship pings is 1+d nanoseconds (d being the time dilation factor), and the interval between the replies is one nanosecond. As far as the spaceship is concerned, the observer is moving. So the pings it receives from the observer comes in at a rate of one per 1+d nanoseconds, and the spaceship is sending replies at the same rate. The spaceship is sending out its own pings one every nanosecond. Assume that one reply and one ping are sent out at an instant t = 0. They will be observed together in oberver's time, let's say at the instant t_o = 0. The next ping is sent out at t = 1 nanosecond (observed at t_o = 1+d ns), and the next reply is sent out at t=1+d nanosenconds (observed at t_o = 1ns). In other words, the spaceship ping sent out at t = 1 nanosecond is observed later than the reply sent at t = 1+d nanoseconds. Why is the ping sent at an earlier time received later by the observer? Where do they cross paths? (In order to minimize the light travel time effect, let's assume that the spaceship is flying over the observer's head, and at the instant t=0.5ns, it is at its point of closest approach to the observer.) --- http://www.TheUnrealUniverse.com

Okay, getting back to the original question about hypothetical faster than light travel and time travel -- I think mr d is right. If you did go faster than light toward a star (or if the star flew toward you faster than light), you would see a time reversal; the star would be getting younger. My answer is based on what is given at http://www.TheUnrealUniverse.com. - Mowgli

This argument can be turned around - if all the articles published by a particular journal have to comply with established theories, then that journal won't be able to contribute to any breaktrhoughs. PRD, for instance, will reject a phenomenolgy that violates the Lorentz invariance, even though the proposed idea may explain some unexplained experimental observations. This rejection stems from the belief that the Lorentz invariance was derived from physical assumptions by Einstein in SR. If Einstein actually made a silly mistake in his derivation, then there is no physical basis for Lorentz invariance, nor for rejecting an article simply because it violates the L. invariance. So it's important to check the algebra in SR. Do you think the algebraic error reported at the relativitychallenge site is real? Mowgli

Well' date=' not if the derivation in SR contained an algebraic error. An error would mean that the Lorentz transformation [i']cannot [/i] be derived from the postulates of SR. The transformation itself may be correct, but does not follow from the postulates. Unless, of course, the error is inconsequential, in that correcting it does not derail the derivation. Mowgli

In fact, there is peer-reviewed journal that encourages "dissident" physics. It is "GALILEAN ELECTRODYNAMICS" (http://www.galileanelectrodynamics.com/). Mowgli

I'm intrigued... Did you mean "observed reality" as opposed to the absolute, physical reality? Mowgli

SR is typically presented starting from the Lorentz transformation. ie, you writex' = L x and describe what the matrix L looks like. At least, this is the way it was taught to me. There was no derivation. The body of evidence is another matter. An algebraic error in the orginal derivation may mean that the reason for the observed phenomena is something other than the assumptions proposed in the original derivation. Mowgli

I guess the implication is that SR is "inaccurate." Its predictions may be right for reasons other than the arguments on which its derivation is based, because the derivation is flawed.

Actually, we don't know that there won't be an electromagnetic boom. If there is one, we may very possibly mistake it for something else. Let me explain it this way: imagine human-beings were all blind and we heard a sonic boom. Would we think of it as something moving faster than sound or an explosion of some sort? We would have to think of it as a strange explosion because that is what we hear. In an exact analogy, because we don't have a stronger sense to "see" what is going on in our sense of sight, we may mistake a "luminal" boom for something else -- a gamma ray burst, for instance. Mowgli

You can have a Doppler effect even when the speed of the waves involved is not changed. Janus gave you an example: you are standing at a railway station, a train passes by, whistling. The tone of the whistle is changed by the Doppler effect. You can calculate the speed of the train from the Doppler shift. Mowgli

I found this web site http://www.relativitychallenge.com, which claims that there is an algebraic error in the 1905 paper. Has this been discussed in this forum? I could not find it using a forum search. Here is a direct link to what the author points out as a mistake: http://www.relativitychallenge.com/math1905Mistake.htm. Looking at it, it seems that the transformation of a coordinate (x,y,z,t) to its boosted values is valid only if t=x/c. Which, of course, is not generally true. The author does not seem to be physicist and is interested only in the mathematical correctness of the derivation, not the physical interpretation nor the experimental validation. He makes a pretty good case, IMHO. Any comments? Mowgli

Yes, I guess I misunderstood your statement as "there is nothing more to be had than SR." In time, SR and GR as theories will be superseded by other, more general notions of space, time and reality.

Well, that is because we are not bats We don't sense our world using sound. If we echolocated our way around, we would have found that the speed of sound was a fundamental constant in our physics.

An object moving away from an observer can never appear to be moving away from an observer faster than the speed of light. This is because the speed of light is independent of the state of motion of the object emitting the light, and it takes some finite time for the light to reach the observer. Even if the object was actually flying away faster than light, it would appear to be slower than light. And, as the apparent speed approaches that of light, then the real speed tends to infinity, which of course, takes an infinite amount of energy to reach. If we attibute this effect to the basic property of space and time, then you get the coordinate transformation of SR. BTW, this attribution is valid, because space itself is a cognitive model created by our brain based on the light inputs our eyes receive. It is always possible to redefine the properties of space and time in order to account for the distortions in our perception due to motion. Well, nothing will happen to you at light speed. To an observer (with respect to whom you are traveling faster than light), you would appear contracted and aging slower etc. And you would appear to be still traveling slower than the speed of light (if you are moving away from him, that is.) See http://www.TheUnrealUniverse.com Mowgli

Time and space are both creations of our brain. They do not exist outside our mind and experience. I know this sounds a little crazy, but compare space to sound. What is sound? Sound is an experience created by the brain based on the electrical impulses from our ears that roughly map the air pressure waves reaching them. The air pressure waves are created by vibrating bodies. While we can find some mathematical correlates to the properties of sound (eg, low frequency == boomy), the experience of sound itself is incommunicable. Sound is not a property of the falling tree or breaking glass, it is just a congitive mapping of the air pressure waves. In an exact parallel, space is a mapping of our visual inputs created by light. Now, don't you see why light enjoys such a lofty, fundamental status in our space? Its speed is a fundamental constant just because our reality is a reality created by light. But this sanctity accorded to light holds only in our space and time, our perceived reality. Special relativity (the coordinate transformation part, ie) can be thought of a description of the distortions in space and time due to the finite speed of light. See http://arxiv.org/abs/physics/0507177 - regards, - Mowgli

Space is a cognitive model created by the brain out of our visual inputs. It is not a part of the "real" reality out there. "Space and time are modes by which we think, not conditions in which we live," as Einstein put it. I guess Kant also said the same thing. So, no, space and time did not exist before the big bang. And the big bang did not exist till we created it fifty or so years ago. Getting back to BobbyJoeCool's statement about 3D and 4D, the real reason why space has three dimensions is that we have two eyes. If we had only one eye, then space would have only two dimensions. And if we had three eyes, space would have a larger number of dimensions; I haven't figured out how many yet - cheers, - Mowgli

Hmmm.... this seems to imply that the light emitted by the particle going left will never reach the particle going right, in my frame of reference. This implies that the light from the first particle will always reach the other particle, in the frame of reference of the first particle. Now, reality cannot change (at least, I don't think it can ) just because we change frames of reference. Genuine paradox or pure ignorance on my part?

Space and time are modes by which we think, not conditions in which we live. It is not easy to think of time in moving coordinate systems, because motion mixes space and time. The best model we have so far to handle it is SR, which does not apply to FTL travel. So don't ask questions about the nature of time for FTL travel and expect sensible answers SR has been around for about 100 years, may be we will have a better model soon...