The Shalimar Treaty

[douglas]

You can use the doppler effect on the pulsar's frequency to measure your speed relative to the pulsar, and then only if you know the pulsar's actual frequency. This has absolutely no effect on the measurement of your speed relative to light.

[AngleWyrm]

I point my space ship at some pulsar, and count the rate, then I turn and point my space ship way from the pulsar and count the rate. The arrival of pulses at a stationary frame of reference is half way between the two rates.

[douglas]

Sorry, but just changing the direction you're ship is pointing won't change the measurements at all. You'd have to change your velocity for that, and you'd have to already know your velocity relative to the pulsar in order to tell when you had exactly reversed it, which renders the whole exercise pointless.

There's also another slight problem here. You know all these "stationary" observers we've been talking about? Technically whether something is stationary or not depends entirely on your frame of reference. There is no "absolute" or "superior" reference frame which defines what it means to be "stationary". The term "stationary" only really has meaning when you specify something like "stationary relative to the pulsar," which just means it's velocity is exactly the same as the pulsar's.

[AngleWyrm]

The term "stationary" refers to an object that does not move relative to some reference point. It has no meaning outside that context. Saying stationary with respect to blah blah is redundant.

The space ship, as you have surmized, is in fact moving relative to the pulsar. This is of course how come there is a difference in measurement between ingress and egress.

This conversation has lapsed into nit picking.

[Spoo]

Phoenix-D said:

True, but somewhat irrelevent..Take the extreme example: a system set up so sound travels unimpreded, but light must go through a large barrier than slows it down to below the speed of sound.

You'll now hear the blast, THEN see the shot. And this still doesn't violate cause and effect.

I think we're arguing different things. My point is that you can't violate cause and effect (and it seems you agree). Yes, you could contrive some situation where the light from the bullet was slowed to the point that you hear it before you see it (so in this case, I agree with you). You could also just close your eyes while the bullet was firing, then you'd never see it. That's the problem with using the term "speed of light". So just to be clear, when I say "speed of light", I mean the speed of light in a vacuum (which is the speed that information travels at).

Phoenix-D said:

Thank you for missing the point. And 700 years ago a weapon that could fire projectiles at greater than the speed of sound was the same thing.

The point is it doesn't matter what the observer sees first because that doesn't change the order of events.

A gun that shoots teleporting bullets would violate causality, since the bulletes would effectively be travelling faster than the speed of light. The victim would be shot, then later see the gun firing (we'll say that there is vacuum between the two people). The order of the two events would be changed in this frame. Causality requires that all observers observe cause and effect in the correct order.

Phoenix-D said:

Which leads to some incredibly -weird- physics.

Two people are accelerating away from me, one at twice the speed of the other. I fire a laser at both. Both, if they could measure it, would see that the light is approaching at C..despite the fact that light's speed is 'constant' and one is moving faster than the other.

Yep. That "incredibly -weird- physics" is called special relativity.

[Parasite]

Anglewyrm, I loved you link to the time dilation page. What a blast from my past. It was fun to go over the formulas again.

The Lorentz contraction is now believed to really be a rotation, but the formula is a bit more complex I believe.

Thanks all for an interesting read!

[AngleWyrm]

Here is a paper on Experimental Evidence of Near-field Superluminally Propagating Electromagnetic Fields
http://xxx.lanl.gov/ftp/physics/papers/0009/0009023.pdf

And here is an article on a light pulse that was seen leaving a gas-filled chamber before it even entered
http://physicsweb.org/articles/world/13/09/3.

It's pretty funny watching the media squirm, redefining words and making exceptions and calling doesn't count. Like the universe as we know it will topple. So? We've had Black Holes, Superstring foam (or whatever they call that), spatial distortions of curved space, intangible aether, ftl tachyons, Heisenberg uncertainty principle, frame dragging, increasing entropy, and many other phantoms. The universe as we know it is in a constant state of redefinition. Life will go on, new professors will be hired.

[Phoenix-D]

Trimming quotes..

Spoo said:

I think we're arguing different things. My point is that you can't violate cause and effect (and it seems you agree). Yes, you could contrive some situation where the light from the bullet was slowed to the point that you hear it before you see it (so in this case, I agree with you). You could also just close your eyes while the bullet was firing, then you'd never see it. That's the problem with using the term "speed of light". So just to be clear, when I say "speed of light", I mean the speed of light in a vacuum (which is the speed that information travels at).

We're arguing different things.

A gun that shoots teleporting bullets would violate causality, since the bulletes would effectively be travelling faster than the speed of light. The victim would be shot, then later see the gun firing (we'll say that there is vacuum between the two people). The order of the two events would be changed in this frame. Causality requires that all observers observe cause and effect in the correct order.

You're confusing information with cause still. Both the bullet leaving the barrel and the sound are -effects-, not causes. Simiarlly, getting hit my the bullet is a effect. So is SEEING the bullet.

We've already established it doesn't matter what order you see the effects in. That was the point of the light-slowing barrier comment. In that scenerio, exactly the same thing happens- the observer sees the impact, THEN sees the shot. So, why does a FTC bullet violate causulity in a way this other example does not?

[AngleWyrm]

Which begs the question: What exactly is a cause?

Could we say that the explosion of the propellent is the cause of the bullet's motion? Or is that just an effect of a chemical reaction? Is the chemical reaction in the gun powder the cause of the bullet's motion towards the target? What about the barrel and the gunner?

[Phoenix-D]

What the cause is depends on what the effect is.

The trigger being pulled is a cause that causes the hammer fall.

The hammer is a cause that sets of the powder.

The exploding powder is a cause that propels the bullet.

The impacting bullet is a cause for whatever effect is has on the target.