OT: System Clock Loses Hour

[douglas]

se5a said:what narf is saying, is if you use said torch, and mesure the amount of time it takes for light to get from the torch to an known distance, you should be able to work out how fast, and in what direction the torch is moving, and therefore be able to say what "still" is.

What I'm saying is that this exercise will just tell you that whatever you had already decided was "still" for purposes of calculation was, in fact, correct. Simply stating that something is moving at speed X inherently requires a definition of what is at rest. The point of relativity is that this definition can be absolutely anything and the speed of light will be the same regardless.

For example:
Suppose you are on Earth trying to carry out that torch experiment. You carefully measure the distance between the torch and a mirror, you light the torch, and you time how long it takes for the reflected light to get back to you. You will calculate from this data that you (actually your measuring device) are at rest.

Next, you move to Mars and repeat the whole experiment. You will again calculate that your measuring device is at rest even though it is clearly moving at a different velocity than it was on Earth. Consideration of this simple fact is how the entirety of the Theory of Relativity was derived.

[se5a]

that contradicts what fyron said.
I think...

[narf poit chez BOOM]

I think it may have something to do with the time slowdown.

[AngleWyrm]

douglas said:
For example:
Suppose you are on Earth trying to carry out that torch experiment. You carefully measure the distance between the torch and a mirror, you light the torch, and you time how long it takes for the reflected light to get back to you. You will calculate from this data that you (actually your measuring device) are at rest.

There was no mirror in the original torch example. Whether or not it has travelled the same distance/taken the same time in both directions is what is at question.

In this illustration, a red bulb sends a signal to a red mirror. Time goes by, and the bulb/mirror experiment moves to position green. The pulse strikes the green mirror and heads back. More time goes by, and the bulb & mirror move to position blue. The light pulse returns to the bulb at position blue.

If it takes a different amount of time on each leg, then we can say that the experiment moved (as illustrated), and the speed of light was the same throughout. And as Narf said, it implies that the speed of light is relative to something other than the bulb&mirror. If it comes back in the same amount of time that it took to go out, then something is amiss.

Shouldn't the stars change color sleightly as the earth approaches them, and then as the earth pulls away? If earth's motion about the sun is about 29km/sec, or roughly [edit]0.001%[/edit] speed of light, then there should be a +/-1% red/blue shift in colorbands throughout the year.

[douglas]

AngleWyrm said:If it comes back in the same amount of time that it took to go out, then something is amiss.

According to any device that is moving at the same velocity as the experiment, that is exactly what would happen. Scientists tried to do something like that to determine the speed of the Earth as long ago as 1881 with the most famous "failed" experiment ever. No matter what speed you are moving at, your perceptions of time and distance will conspire to give the same result.

AngleWyrm said:Shouldn't the stars change color sleightly as the earth approaches them, and then as the earth pulls away? If earth's motion about the sun is about 29km/sec, or roughly 1% speed of light, then there should be a +/-1% red/blue shift in colorbands throughout the year.

Yes. The speed of the light involved remains the same, however, no matter how much the light wave's frequency may change.

[AngleWyrm]

The Michelson-Morley experiment was trying to detect wind from the earth passing through aether--the fluid that conducts light waves. It failed to notice any, and is considered proof that there is no aether.

your perceptions of time and distance will conspire to give the same result.
I recently read a philosopher's quote, that I'll paraphrase: A theory which claims to be unmeasurable is probably best left unspoken as well.

Walter Ritz proposed Emitter Theory that suggested light speed was added to local motion, but that was not observed in binary stars as they orbited each other. The example given is that light from the approaching orbit would appear to be C+orbital speed, and therefore the light would overtake previous light, and our observation would be...strange. (maybe reversed)

[douglas]

AngleWyrm said:
your perceptions of time and distance will conspire to give the same result.
I recently read a philosopher's quote, that I'll paraphrase: A theory which claims to be unmeasurable is probably best left unspoken as well.

Except it's not unmeasurable. There are all sorts of experimentally measurable implications of the constancy of the speed of light independent of reference frame, and many of them have been tested and found to be correct. For example, take two atomic clocks and synchronize them. Then put one of them on a supersonic jet, have it fly around at high speed for a while, and put them back next to each other. One of the implications of the speed of light being constant regardless of reference frame is that the two clocks will now be out of sync - they will disagree about how much time has passed since they were synchronized. The exact amount of the difference can be calculated using equations derived strictly from conceptual analysis of what would have to be true for the observed fact about the speed of light to be true. This experiment has actually been conducted, and the result was well within experimental error of the calculated value.

[AngleWyrm]

(Tricia Helfer, Battlestar Galactica)

[capnq]

narf poit chez BOOM said:
Why not just measure the speed of the earth relative to the speed of light?

Because that results in the inconveniently small number (0.001% of c) that AngleWyrm mentioned further upthread.

[narf poit chez BOOM]

...I'm totally lost. Too many explanations.