The Shalimar Treaty

[AngleWyrm]

Sometimes truth is stranger than fiction.

The Shalimar Treaty is a strange treaty about the light-speed barrier, and it's implications on causality. On the surface it is a fictitious peace treaty between Klingon and Federation forces, that backfires. Secondarily, it is between the camps of Einsteinian Special Relativity, and the observers of superluminal events.
http://www.sciencenews.org/articles/20000610/fob7.asp

Mostly, it is about cause and effect, and has as it's theme something from the future-fiction Star Trek drawn into the present-reality to describe a causality paradox.
http://www.ma.utexas.edu/users/clong/newlumin1.html
http://scienceworld.wolfram.com/physics/CausalityProblem.html

However the arguments used to describe the paradox seem to apply equally well to the sound barrier. Let's say our FTL ship starts at position #1, and broadcasts "A". It travels towards the observer to position #2, where it broadcasts "B", and continues to position #3 where it broadcasts "C". To the observer, the ship arrives first, then it sees "C" then "B" then "A". Apparently backwards in time, and one might even say that it could prophesize the occurance of "A", given that it saw "C" and then "B".

http://home.comcast.net/~anglewyrm/ftl.jpg

But if we switch the scenario to sound waves, say the craft is using morse code, and traveling at mach 1.1, then what is the difference?
What do you think of this?

[Thermodyne]

Arrggg…………………It’s just Startrek science. The event happens when ever; it is only the observation of said event that would be influenced. Also, Einstein’s limit on the maximum speed that mater can obtain, is based on the theory that mass increases with speed. This foundation of his work has yet to be demonstrated. So everything built upon it is still theory.

Now to add a question of my own. What is the terminal speed of gravity?

[douglas]

Thermodyne said:
Also, Einstein’s limit on the maximum speed that mater can obtain, is based on the theory that mass increases with speed. This foundation of his work has yet to be demonstrated. So everything built upon it is still theory.


On the contrary, particle accelerators have pushed various subatomic particles to very near the speed of light with a resulting increase in mass sufficient to require designing new kinds of particle accelerators (at least of the circular variety) to take the mass increase into account before being able to achieve even higher speeds. The amount of the mass increase corresponded quite well with the predictions of relativity. For a little bit of reference material, go here (http://www.factmonster.com/ce6/sci/A0860257.html).

[Slick]

This is what happens when you propose a situation that follows established physics for one part (the propagation of the signals) and makes up jibberish for another part (FTL travel). You can prove anything.

I am not totally discounting that we may one day figure out how to travel faster than light. However, if we do, it will mean that we have to change our ideas about basic physics. If this ever happens, this discussion would have to be done using the new physics, not a bastardization of the current physics. As of right now, we just can't travel FTL. There are some interesting experiments that are going on at the sub-atomic level that may lead to new understandings; but these experiments have so far only yielded results which confirm or are consistent with our current accepted understanding of physics. And our current physics predicts that nothing can travel faster than the speed of light; indeed nothing with mass can even achieve the speed of light.

To some people this is the motivation to discover something new to expand our understanding of how the universe works. I certainly applaud these efforts and hope for their success.

Until we figure it out, or even figure out a theory that can be tested and agrees with observations, FTL travel is currently not possible under our current established theories.

Yes, there are ideas about wormholes, extra-dimensional effects, strings, superstrings and a myriad of other theories that would make FTL travel, time travel and other SciFi concepts possible. Until these theories are reconciled with observations and put into a theory that makes predictions that can be tested, they are just fun things to think about and put into science fiction stories.

That's just my opinion, of course.

[Slick]

Thermodyne said:
Now to add a question of my own. What is the terminal speed of gravity?



"Gravitons" or gravity waves, depending on what property you focus on (similar concept between photons vs light waves) are theorized to travel at the speed of light.

[AngleWyrm]

Our physics predicted nothing could travel faster than the speed of sound. One argument against it was that if you were the target of a supersonic bullet, you would hear the bullet hit, then you would hear the bullet travelling downrange, then you would hear the bang of the bullet leaving the gun; you would witness events going backwards in time, which seemed to present a temporal paradox. This is exactly what happens. The target witnesses the arrival of the bullet, and can even have the time to radio back to the gunner and announce that the firing is still in the target's future (measurable and recordable as such with a tape recorder). But of course the firing is in the gunner's past, so it is meaningless to ask the gunner not to fire.

The best argument against gravity having speed that I've read was by Sir Aurthur Eddington: "If the Sun attracts Jupiter towards its present position S, and Jupiter attracts the Sun towards its present position J, the two forces are in the same line and balance. But if the Sun attracts Jupiter toward its previous position S', and Jupiter attracts the Sun towards its previous position J', when the force of attraction started out to cross the gulf, then the two forces give a couple. This couple will tend to increase the angular momentum of the system, and, acting cumulatively, will soon cause an appreciable change of period, disagreeing with observations if the speed is at all comparable with that of light."
http://home.comcast.net/~anglewyrm/orbits.gif

[Slick]

Galileo proved that light moved faster than sound and he probably was't the first to prove it. No modern phyisics predicted that the sound barrier was impossible to break. The term "sound barrier" was coined in the World War II era when countries were trying to make airplanes go faster than sound. They knew it was possible, but were encountering extreme difficulties as they approached the speed of sound. Aerodynamic forces on the airplanes was so great that it caused many failures, crashes and deaths. Hence the term "barrier".

Regarding the question on "terminal speed of gravity". I find it interesting that you quote from the first article that appears in a google search for "speed of gravity" even though it does not represent the vast majority of scientific acceptance; which is that gravity is transmitted at the speed of light. Their pic is nice too. Instantaneous transmission of gravity is correct under Newtonian physics, but not under relativistic physics. If gravity was transmitted instantaneously, I could vibrate a mass to send signals everywhere in the universe instantaneously using gravity as a carrier. This would violate the theory of relativity. The theory of relativity may one day be proven wrong, or I should say incomplete; because its predictions have been observed and verfied many times over and so far it has been shown to be consistent for all observable tests performed. Indeed, NASA has used and does use relativistic physics in its calculations. Even as "slow" (relative to the speed of light) as our Mars missions have travelled, their trajectories were calculated using relativistic physics. If they relied on Newtonian physics, they would be off course. Until the theory of relativity is shown to be wrong, incomplete or it is replaced by a superior theory that more closely agrees with observation and is tested to verify its correctness, I'll consider Einstein to be correct.

[AngleWyrm]

Thanks for clarifying the sound-barrier. That makes much more sense.

I read that article on "speed of gravity" several years ago; that it is now on top of the google search is interesting to me. However discussing credibility of the author avoids the subject material. They called Galileo a worker of black magic when he showed that a grape and a grapefruit fall at the same speed.

Is it true that the calculation of planetary locations must take the force of gravity to be instantaneous?

[Slick]

I don't think so.

Here's the "argument": 'If the sun were to suddenly disappear, it would be unrealistic for the earth to continue to orbit nothing for another 8 minutes.'

I see some problems with this line of thinking:

- First, these same people wouldn't have a problem thinking that the earth would still see the sun for another 8 minutes as the light continued to travel to the earth. But somehow gravity seems different to them. It's probably because we have indisputable proof of the speed of light and the layman can witness its effects. Gravity has yet to be actually measured, which is why I said above that it was theorized to travel at the speed of light (based on principles). Scientists find measuring the speed of gravity acurately very difficult, but they are trying; and the prevailing theory is that it travels at the speed of light under the limits of the theory of relativity. So for some people, no-can-see, no-can-believe. And that's fine with me.

Second, under our current understanding of physics, the sun just can't disappear. So, it's one of those garbage-in-garbage-out arguments. We know of no way to instantaneously remove mass, so of course there is no theory about what happens next.

Last, orbits of planets around the sun are actually ellipses. Also, the sun is actually pulled and moved slightly by each planet. The sun's "orbit" is less than its diameter so it kinda just wobbles a little in response to each planet, but we can measure it. Since our source information (light) travels at the speed of light, we can't see instantaneous effects, if they existed. In a practical sense, the speeds of planets, the sun, the solar system, the galaxy, the local supercluster, etc., are small compared to the speed of light so it limits our accuracy of measurment.

I don't think I am avoiding the subject material. The credibility of the author is certainly important. For every theory out there, there's somebody who is convinced it is wrong and has a counter-theory. Yes, occasionally these people who we consider to be nut-cases sometimes, rarely, are the true geniuses who are actually correct. This doesn't mean that I should believe every counter- or conspiracy- therorist. The process is well established for objectively presenting a new theory, testing it, and adopting it if valid. People with these outlandish theories all claim the same thing: I can't prove it because the scientific community won't grant me any $$$ to use their XXX (equipment, satellite, telescope, collider, reactor, fill in the blank). Most of these guys are just that, nut-cases who are hell bent on trying to get their inane experiments (and their wallets) funded. The scientific community is portrayed by these people as extremely closed-minded, status-quo, establishmental, and rigid. My impression is that this is as far from the truth as possible. The reason why these nut-cases are ignored is because their theories are fundamentally flawed. The last thing the "real" scientists would want is to be on the wrong side of the fence if/when a new correct understanding of the universe is proven. Good theories are tested every single day. Experiments are being done as we "speak" to learn the fundamentals of our universe. That is what the XXX (equipment, satellite, telescope, collider, reactor, fill in the blank) *is* being used for.

[AngleWyrm]

Hypothesis: The effect known as gravity is instantaneous. Null hypothesis: The effect of gravity displays a finite transit delay (presumably comperable to speed of light).

Experiment: If light and gravity both arrive from the sun, then earth's trajectory through space should be a tangent to the center of the observed position of the sun, eight minutes west of current position. On the other hand, if gravity does not travel, then earth's trajectory should be a tangent to the sun's current position, eight minutes east of observed.

Is there a method of measuring earth's current trajectory by ameteur equipment? Could it be plotted via planetary positions or the like?

[Slick]

Not as of yet, no accurate method for determining gravity really exists. That method sounds to me like it would work, however its effect is very very small. The determination of gravity would obviously have to be a vector; strength and direction and be made extremely accurately such that the error in measurement is small compared to the value.


Since gravity has no maximum range, the earth is also being pulled by everything else in the universe (closer than the age of the universe x the speed of light). Since the force of gravity drops by the inverse square law, effects from mass outside our solar system will probably be too small to detect for a very long time, if ever.

There are other effects too that would affect the results:

Curvature of space - currently postulated, but measurement inaccuracy is far too large compared to numbers that we would need. At least our local section of space is "flat" i.e. not curved to the best of our measurements.

Dark matter - matter that does not give off light. Rocks, dust, gas, etc. Some scientists have postulated exotic forms of mass (wimps - weakly interacting, massive particles), but these too haven't been observed. But dark matter does exert gravitational forces. Based on rotational dynamics in the galaxy, there has to be a huge amount of dark matter; far more than the luminous matter that we can see. Not sure how much is in our solar system; or if it has a significant effect.

"Dark energy" - I really don't want to go there. Possible, but unobserved, and rather controversial. If it exists, though, it could/would affect gravity.

Expansion of space - the exact rate is debated, but it has upper and lower bounds based on observations. I'd have to see the numbers, but my guess is that this is too small to have an effect on our local orbit around the sun.

And of course the catch all - how can we know if there is something else that is currently totally unknown by us???

[Parasite]

Please don't forget about the speed of the sun around the galaxy and the galaxy through the universe. These would have to also all have to be taken into account. Check out the Michelson Morley experiment and what it failed to prove for more insight. There are also conservation of momentum issues with Jupiter speeding up around the sun. I suspect that there is a problem about the sun pulling Jupiter, then Jupiter pulling the sun, when the force is constant.

The state of gravity detector technology is such that they are not yet acurate enough to find the currently predicted size of gravity waves from things like galaxies colliding and black holes forming.

In regards to sound, the sonic boom rumbles on long after the plane has passed. This is the sound that started far away just now arriving (and echos and things). I suspect that a very good stereo microphone could do a back plot of a plane's position and path just from the sound it made when it passed and the boom afterward.

[narf poit chez BOOM]

Do they have proof that gravity moves at the speed of light? The only arguements I've heard is that 'Nothing moves faster than the speed of light, so gravity can't move faster'.

[AngleWyrm]

As near as I can tell, the main argument against information travelling faster than the speed of light is that of causality. Most folks accept that effect cannot precede cause (in absolute time). Note how this is different from the assertion that time is relative. I tend to think that witnessing an effect before a cause does not necessarily violate causality. Like being struck by a bullet before hearing the gun go off. How is it different if we switch the media from sound to light?

Tom van Flandern has argued that the speed of gravity is much faster than light (like at least 200billion times c) in physics letters A 250 (http://www.ldolphin.org/vanFlandern/gravityspeed.html). Steven Carlip argued against him in Aberration and the Speed of Gravity (http://arxiv.org/abs/gr-qc/9909087). Carlip accepts as a given that gravitic effects appear to arrive at earth from the sun much faster than the speed of light, even instantaneously. His argument against this effect is purely mathematical, and he suggests that some velocity-dependant factor in the formula almost cancels out the effects of propagation delay. He states other interpretation models are of course possible, but would cost the unity of the current mathematical model.

As for me, I've got my very own theory. It goes like this:
AngleWyrm's Gravitic Aether Pressure Theory.
Gravity is not an attractive force, it is a pressure experienced by all matter as it rushes "upward" through the aether. Aether is a sort of rain pressure/resistance that is the "downward" push that is imagined in the rubber-mat imagery, that causes things to roll downhill.

Hey, it seems to work for me http://forum.shrapnelgames.com/images/smilies/happy.gif

[Spoo]

AngleWyrm_2 said:I tend to think that witnessing an effect before a cause does not necessarily violate causality. Like being struck by a bullet before hearing the gun go off. How is it different if we switch the media from sound to light?



You CANNOT observe an effect before the cause, regardless of reference frame. You can be struck by a bullet before hearing it because the sound doesn't make the bullet hit you.

[AngleWyrm]

Spoo said:
You CANNOT observe an effect before the cause, regardless of reference frame. You can be struck by a bullet before hearing it because the sound doesn't make the bullet hit you.


Seeing the bullet exploding from the gun does not make the bullet hit you. Nor does observing the gunner shout "I will kill you now" and hearing the explosion that propelled the bullet. Observation of an event by an observer is something separate from the event itself.

I have clearly demonstrated a real and recordable instance of observing an effect before observing a 'cause'.

[Spoo]

AngleWyrm_2 said:

Spoo said:
You CANNOT observe an effect before the cause, regardless of reference frame. You can be struck by a bullet before hearing it because the sound doesn't make the bullet hit you.


Seeing the bullet exploding from the gun does not make the bullet hit you. Nor does observing the gunner shout "I will kill you now" and hearing the explosion that propelled the bullet. Observation of an event by an observer is something separate from the event itself.

I have clearly demonstrated a real and recordable instance of observing an effect before observing a 'cause'.



Seeing the bullet leave the gun must happen first from anybody's point of veiw. Note that in this case there is a profound difference in using sound and using light to tell when the gun was fired. The speed of sound changes relative to the observer's motion. The speed of light, however, is always the same (by "speed of light" I mean the speed that photons travel at). This is why it's possible to hear the gun being fired after it hits you.

Let's say that the event of the bullet leaving the gun is the cause, and the bullet striking you is the effect. Suppose that I'm standing next to the gun. Clearly, I see and hear the gun go off before the bullet hits you.

Now let's say that I start running towards you at the speed of sound just before the gun is fired. I still see the gun go off before the bullet hits you, although I never hear the gun fire.

Finally, let's say I run towards you arbitrarily close to the speed of light. I still see the gun go off first. There is nothing that I can do, as an observer, to witness you being hit by the bullet before the gun goes off.

Regarding:

Observation of an event by an observer is something separate from the event itself.



Yes they are seperate. The actual event and it's observation are another example of cause and effect. You can't observe an event before it happens!

[Phoenix-D]

The speed of light is NOT always the same. You can very easily slow light down, you just can't kick it up past C.

"Finally, let's say I run towards you arbitrarily close to the speed of light. I still see the gun go off first. There is nothing that I can do, as an observer, to witness you being hit by the bullet before the gun goes off."

Say you have a gun that teleports the bullet to the target on firing. The target doesn't see anything, the bullet hits, and then a while later they see the flash, and hear the report.

This does notviolate cause and effect! The bullet was still fired before it hit..its exactly the same as seeing the hit then hearing it.

[Spoo]

Phoenix-D said:
The speed of light is NOT always the same. You can very easily slow light down, you just can't kick it up past C.



That's why I specified that I was refering to the speed that photons travel at. Light appears to move slowly through certain materials, but the individual photons still move at ~3x10^8m/s. In these cases what's happening is that photons are constantly being absorbed and reemitted, which makes the light appear to be moving slowly.


"Finally, let's say I run towards you arbitrarily close to the speed of light. I still see the gun go off first. There is nothing that I can do, as an observer, to witness you being hit by the bullet before the gun goes off."

Say you have a gun that teleports the bullet to the target on firing. The target doesn't see anything, the bullet hits, and then a while later they see the flash, and hear the report.

This does notviolate cause and effect! The bullet was still fired before it hit..its exactly the same as seeing the hit then hearing it.



Teleportation is science fiction. http://forum.shrapnelgames.com/images/smilies/rolleyes.gif

[AngleWyrm]

Spoo said:
Seeing the bullet leave the gun must happen first from anybody's point of veiw. Note that in this case there is a profound difference in using sound and using light to tell when the gun was fired. The speed of sound changes relative to the observer's motion. The speed of light, however, is always the same (by "speed of light" I mean the speed that photons travel at). This is why it's possible to hear the gun being fired after it hits you.


The Doppler effect (http://electron9.phys.utk.edu/phys135d/modules/m10/doppler.htm) applies to both sound (pitch changes) and light (red shift). It does not change the speed, only the frequency. The speed of sound changes with the rigidness of the medium through which it travels, and the speed of light changes (http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html) with the refraction index of the medium through which it travels.

Now let's say that I start running towards you at the speed of sound just before the gun is fired. I still see the gun go off before the bullet hits you, although I never hear the gun fire.

Finally, let's say I run towards you arbitrarily close to the speed of light. I still see the gun go off first. There is nothing that I can do, as an observer, to witness you being hit by the bullet before the gun goes off.


These two examples are not orthinagonal. In the sound example, the traveller is accepted as travelling at the speed of sound, but in the light example the traveller is accepted as travelling less than the speed of light. It could be just as valid to switch the roles, and say running towards the target at light speed means you never see the gun go off, but running at some speed arbitrarily close to the speed of sound you still hear the gun go off.

[Slick]

That thump you just heard was Einstein rolling over in his grave.

[Spoo]

AngleWyrm_2 said:
The Doppler effect (http://electron9.phys.utk.edu/phys135d/modules/m10/doppler.htm) applies to both sound (pitch changes) and light (red shift). It does not change the speed, only the frequency. The speed of sound changes with the rigidness of the medium through which it travels, and the speed of light changes (http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html) with the refraction index of the medium through which it travels.



I'm not talking about Doppler shift (which is different than red shift, by the way). Sound travels at roughly 340m/s at sea level. If I'm moving at 100m/s away from the sound source, as far as I'm concerned the sound is moving at 240m/s. This is not the case with light, however. Light (or information, if you prefer) travels at 3x10^8m/s. If I'm moving away from the light source at 1x10^8m/s, then as far as I'm concerned, the light is still moving at 3x10^8m/s.


These two examples are not orthinagonal. In the sound example, the traveller is accepted as travelling at the speed of sound, but in the light example the traveller is accepted as travelling less than the speed of light. It could be just as valid to switch the roles, and say running towards the target at light speed means you never see the gun go off, but running at some speed arbitrarily close to the speed of sound you still hear the gun go off.



Again the difference is that's possible to travel faster than sound, while it is impossible to travel faster than light (information).

EDIT: Let me add that it would take infinite energy to accelerate a massive object (like a spaceship/person/electron) to light speed (3x10^8m/s).

[AngleWyrm]

These guys seem to think red shift and Doppler shift describe the same phenomenon:
http://www.answers.com/topic/redshift
http://zebu.uoregon.edu/~soper/Light/doppler.html
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/redshf.html

If light is being emitted from a source at 3x10^8m/s and I travel away from that source at 1x10^8m/s, then the light will approach me at 3x10^8m/s - 1x10^8m/s = 2x10^8m/s.

[Spoo]

AngleWyrm_2 said:
These guys seem to think red shift and Doppler shift describe the same phenomenon:
http://www.answers.com/topic/redshift
http://zebu.uoregon.edu/~soper/Light/doppler.html
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/redshf.html




Using "red shift" and "Doppler effect" interchangably is a common mistake. While it is true that a Doppler effect is measurable for stars in our galaxy and for nearby galaxies (the shift can be "red" or "blue"), in most cases, when an astronomer refers to "red shift" they mean the stretching of photons by the expansion of the universe. To quote your first source,
"...all distant galaxies show a red shift proportional to their distance from the earth as a result of the general expansion of the universe (see Hubble's law)..."
In other words, the Doppler effect is an example of red shift, but not all red shifts are caused by the Doppler effect.

But this is getting off topic.



If light is being emitted from a source at 3x10^8m/s and I travel away from that source at 1x10^8m/s, then the light will approach me at 3x10^8m/s - 1x10^8m/s = 2x10^8m/s.



Wrong. "The speed of light is the same for all observers, no matter what their relative speeds." (http://www2.slac.stanford.edu/vvc/theory/relativity.html)

[AngleWyrm]

If light is being emitted from a source at 3x10^8m/s and I travel away from that source at 1x10^8m/s, then do you believe that it will still approach me at 3x10^8m/s? What about the guy I pass along the way; does it approach him at 3x10^8m/s also?

It seems to me that the light will reach the guy I pass before it reaches me.

[Phoenix-D]

Spoo said:

Phoenix-D said:
The speed of light is NOT always the same. You can very easily slow light down, you just can't kick it up past C.



That's why I specified that I was refering to the speed that photons travel at. Light appears to move slowly through certain materials, but the individual photons still move at ~3x10^8m/s. In these cases what's happening is that photons are constantly being absorbed and reemitted, which makes the light appear to be moving slowly.



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.



Teleportation is science fiction. http://forum.shrapnelgames.com/images/smilies/rolleyes.gif



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.


Wrong. "The speed of light is the same for all observers, no matter what their relative speeds."




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.

[douglas]

AngleWyrm_2 said:
If light is being emitted from a source at 3x10^8m/s and I travel away from that source at 1x10^8m/s, then do you believe that it will still approach me at 3x10^8m/s? What about the guy I pass along the way; does it approach him at 3x10^8m/s also?

It seems to me that the light will reach the guy I pass before it reaches me.


The stationary observer will indeed measure that the light's velocity relative to you is only 2x10^8m/s. For you, however, time will pass more slowly. When you measure the speed of light, you might come up with the same distance covered as the stationary guy measured, but your figure for the time will be lower. As a result, your measurement of light speed relative to yourself will come out exactly the same as the stationary observer's measurement of light speed relative to himself. Actually, your measurement of the distance will be somewhat off as well, but the net effect is that no matter what your speed, any attempt to measure the speed of light in a vacuum relative to yourself will always give the same result.

[AngleWyrm]

So I'm zooming away from an pulsar, and pass a stationary witness, who observes me travelling at 1/3c and the light from the pulsar flying along at c, closing the gap between itself an myself at a rate of 2/3c (twice my speed).

On the one hand, the pulses would reach me with longer gaps between (from the stationary witness point of view), because I am racing away from them (doppler effect). Does this time compression thing say the amount of time between pulses would be the same to me as it was when I was stationary, because time has slowed down for me?

This seems to say that I cannot perceive a change in pulsar timing, no matter what my speed.

[douglas]

I don't know the exact equations for it, but you actually would observe a difference in the pulsar's frequency depending on your speed. Because you are moving away from it, each pulse would have a greater distance to travel to reach you, and so the observed period would increase by the time required for the light to cover the extra distance since the last pulse reached you. This increase in period is exactly linear with respect to your speed relative to the pulsar. The time dilation due to high speed movement is not linear, so it will generally not exactly cancel the doppler effect. There might be one particular speed where you would observe the same pulsar frequency as the stationary observer, but in most circumstances it would be different.

[AngleWyrm]

If I use the doppler effect of pulsar timings to measure my speed, then these two statements seem to indirectly conflict:

"As a result [of lower time figure], your measurement of light speed relative to yourself will come out exactly the same as the stationary observer's measurement of light speed relative to himself."

"The time dilation due to high speed movement is not linear, so it will generally not exactly cancel the doppler effect."

It would help if we had the formula used for this.
EDIT: Found a derivation of time dilation (http://www.drphysics.com/syllabus/time/time.html) which is easy to read.

[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:

Spoo said:

Phoenix-D said:
The speed of light is NOT always the same. You can very easily slow light down, you just can't kick it up past C.



That's why I specified that I was refering to the speed that photons travel at. Light appears to move slowly through certain materials, but the individual photons still move at ~3x10^8m/s. In these cases what's happening is that photons are constantly being absorbed and reemitted, which makes the light appear to be moving slowly.



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:

Spoo said:
Teleportation is science fiction. http://forum.shrapnelgames.com/images/smilies/rolleyes.gif



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:

Spoo said:
Wrong. "The speed of light is the same for all observers, no matter what their relative speeds."




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. http://forum.shrapnelgames.com/images/smilies/happy.gif

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:

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).




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. http://forum.shrapnelgames.com/images/smilies/wink.gif

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.

[Spoo]

AngleWyrm_2 said:
Here is a paper on Experimental Evidence of Near-field Superluminally Propagating Electromagnetic Fields
http://xxx.lanl.gov/ftp/physics/papers/0009/0009023.pdf




An interesting read, however the conclusions that the author draws are incorrect. Basically, the observed phenomenon is a superposition of waves that each travel at the speed of light. Within a quarter wavelength, the superposition itself appears to move at superluminal speed, however, no information travels superluminally. This paper explains it better than I can: http://www.grc.nasa.gov/WWW/bpp/pdf/Mojahedi-JPC.pdf
The main point being that special relativity remains valid.



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.




...Nowhere in this article does it say that relativity is wrong. The fact that relativity survives testing by this type of experiment only bolsters its correctness. Now, that's not to say that there won't be any corrections (or even replacements) to the theory sometime in the future. Believe me, if a physicist could disprove relativity, they'd be set for life. Nonetheless, if you believe the majority of scientists, relativity is essentially correct.




It's pretty funny watching the media squirm, redefining words and making exceptions and calling doesn't count.



Yes, the media often does this when reporting about science. This is bound to happen when simplifications are made to make the story easy to read. Take the second source you posted for example. Reading this, you might get the impression that scientists are "calling doesn't count" with regards to phase velocity being able to travel faster than the speed of light. The thing is, this was known all along. The article you posted even gives an example:

Nevertheless, velocities greater than c can be observed. Suppose a lighthouse illuminates a distant shore. The rotating lamp moves quite slowly, but the spot on the opposite shore travels at a far greater velocity. If the shore were far enough away, the spot could even move faster than light. However, this moving spot is not a single "thing". Each point along the coastline receives its own spot of light from the lighthouse, and any information travels from the lighthouse at c, rather than along the path of the moving spot. Such phenomena are described as the "motion of effects", and are not forbidden by relativity.

[Slick]

I thought this might be appropriately referenced here.

http://www.cnn.com/2005/TECH/science/04/14/mit.prank.reut/index.html

http://forum.shrapnelgames.com/images/smilies/wink.gif

[narf poit chez BOOM]

The author of the Mageworld books (Does it say something about me that I can remember the series name but not the author name?) did something similair once. A certain publisher that had been labelled a 'vanity press' put out a statement saying that they rejected 80-90% of submitted material.

This author wrote a very general book script (Sometimes just a few sentences), got a bunch of other authers interested and had them all write out each chapter, seperatly and simultaneously. The result was submitted, accepted and *Published*. You could even buy it on Amazon, at the time I heard of this.

I've posted this elsewhere here if you want the full story. Probably in 'Jokes and Riddles', but I'm not sure.

* Edit: The book was submitted under the name of 'Travis Tea' and the 'book' was 'Atlanta Nights'. And here's the Amazon link to buy it:
http://www.amazon.com/exec/obidos/ASIN/1411622987/qid=1113529867/sr=2-1/ref=pd_bbs_b_2_1/102-9095302-6134538