Theory of Relativity

Page 3 - Seeking answers about space? Join the Space community: the premier source of space exploration, innovation, and astronomy news, chronicling (and celebrating) humanity's ongoing expansion across the final frontier.
Status
Not open for further replies.
S

Saiph

Guest
I can understand your concern about the atmosphere, and that is why most accurate measurments of C are done in vacuum chambers. So that particular issue has been taken care of.

Now that I've gotten more sleep, an experiment very similar to the one you proposed has been done with jupiter's moons. By plotting their apparent positions vs their known orbits we can determine if there is a light travel time discrepancy over the distance covered by their path. I.e. from when they are furthest from us, and nearest to us. Because of lights finite speed you will notice the moon seem to lag behind where it should be when it's on the far side of jupiter, compared to when it's on the near side. Because the satellites aren't actually slowing and speeding up rhythmically in their orbit.

By noting a lag in their apparent position when they are far from us, you can use that to calculate a speed at which the signal propagates...which is found to be C.

That's a vacuum nearly all the way here, and any discrepancy in the speed of light introduced by short path through our atmosphere is nothing compared to the 45 minute travel time between here and Jupiter, or the 6 light second diameter of say, ganymede's orbit.

And since you're comparing two outside phenomena for a difference in them, any bias introduced by your instruments (and the atmosphere) are removed from consideration as it's present in both the far and near measurements, and you're doing a difference comparison. Elaboration: Consider a scale that's off by 10lbs. You weight a dog 50lbs, and a cat, 30lbs, and find they are 20lbs apart in weight. Does that change with a scale that is completely accurate, or say 15lbs off? This is another common technique to eliminate instrument bias in experiments.



On particle half lives you say:
And that same effect would be measured if acceleration and/or high velocity effects the all atoms equally and slows down their interactions proportionally to the degree of acceleration and/or velocity.
I might give you the acceleration point, except that if all atoms react identically (slowed identically) it's the same as if time is slowed, as you can't tell the difference. Time, afterall, is the interval between change.

But I won't give you the point with 'high velocity'. Somehow those particles are determining their speed in a uniform frame of reference. How do they know they're moving at all? What do they consider themselves moving relative to? Just us on the ground? The sun? the moon? Distant galaxies? Even in newtonian mechanics velocity is completely relative and entirely dependent upon the frame of reference.

And how come the observed lifespan will be different for two observers, watching the same particle, but traveling at different speeds? Somebody moving with the particle, but at a different speed, will disagree with the ground based observer on how long it lived (and also how far it traveled).
 
M

mental_avenger

Guest
derekmcd":38vlvpsp said:
I've always appreciated your debating style, so I'm a bit surprised by this non-answer to a rather direct question. All you have done is offer what the speed is in one frame of reference.
That is, after all, the point of contention here as I see it. It isn’t possible for light to actually be traveling at exactly c in reference to both of two separate objects that are moving relative to each other along the same axis as the light is traveling. Therefore, any discrepancy in the observed speed of light must be due to an illusion created by the occupants of different frames of reference. While it is easy to explain this illusion using one observer on a train, and a second observer on the platform that the train is passing, that illusion should not hold for events taking place radially from the observers. Example: A man on a train bouncing a ball may see it traveling up and down 3 feet with each bounce, while a man on the platform may see the ball bouncing up and down 4 feet at an angle as the train passes. However, a man standing on the tracks directly behind the train will see the ball bounce up and down three feet, regardless of how fast the train is moving. So, frame of reference is not so easily applied the same to all situations.

derekmcd":38vlvpsp said:
Just so we are clear, in the context of Special Relativity, the speed of light doesn't concern itself with whatever medium you might conjure up that it is propagating through. It also doesn't concern itself with the various scattering theories.
However, light itself does concern itself with the medium it is traveling through, else lenses and interfaces between different mediums would not have an effect on the passage of light. While theory may dictate a set of conditions, the practicality of physically measuring the speed of light must take these things into consideration. If the BEC scientists are correct, then light is absorbed and re-emitted, as opposed to merely passing through. And that is a very important point.

derekmcd":38vlvpsp said:
I framed my question in a basic way... a basic answer will do.
As explained, clarification of the nature of the frames of reference is required.

derekmcd":38vlvpsp said:
Replace the second car and 100 mph with a photon and C respectively, do you get similar results? Does the reference frame of the first car see the photon as travelling at 10 mph less than C?
You should get similar results. In this case, since the direction of travel is radial to the observer in the same direction, it should be 10mph less than c.

derekmcd":38vlvpsp said:
Again, a simple question. A simple answer will do. A direct answer here would answer my question in the previous post and would assist me in try to understand you point of view concerning time dilation.
If there really were a simple answer, this discussion and others like it would either be much shorter or totally non-existent.
 
M

mental_avenger

Guest
Saiph":2ixzmwuz said:
I can understand your concern about the atmosphere, and that is why most accurate measurments of C are done in vacuum chambers. So that particular issue has been taken care of.
I wonder about that. Since light travels so fast, it would seem helpful to have it travel a long distance, which is not possible in small vacuum chambers.

Saiph":2ixzmwuz said:
On particle half lives you say:
And that same effect would be measured if acceleration and/or high velocity effects the all atoms equally and slows down their interactions proportionally to the degree of acceleration and/or velocity.
I might give you the acceleration point, except that if all atoms react identically (slowed identically) it's the same as if time is slowed, as you can't tell the difference. Time, afterall, is the interval between change.
That is another point of debate. IMO the reactions can slow down while the actual passage of time remains the same. It would be difficult if not impossible to figure out a way to measure which is which. However, the distinction is important and IMO there is a very real difference. In fact, it is that possible difference which may well prove or disprove time dilation. IOW, the wayward twin didn’t age more slowly due to time dilation, but rather merely due to molecular interactions slowing down.

Saiph":2ixzmwuz said:
And how come the observed lifespan will be different for two observers, watching the same particle, but traveling at different speeds? Somebody moving with the particle, but at a different speed, will disagree with the ground based observer on how long it lived (and also how far it traveled).
Again, depending upon the physical arrangement of the frames of reference, that may be merely part of the illusion, and in any case difficult to definitively test.
 
S

Saiph

Guest
I'm curious as to your interpretation of the experiment using Jupiter's moons.

as for terrestrial vacuum tests, they often involve interferometry.

There is of course particle accelerators and the LIGO facility which are quite large and deal with these phenomena on a daily basis.
 
M

mental_avenger

Guest
Saiph":1j2mi45v said:
I'm curious as to your interpretation of the experiment using Jupiter's moons.

as for terrestrial vacuum tests, they often involve interferometry.

There is of course particle accelerators and the LIGO facility which are quite large and deal with these phenomena on a daily basis.
That particular example appears to be relatively straightforward, but it only addresses the speed of light over the distance from the Earth to the Jupiter moon relative to the Earth. I don’t see how it addresses the possible difference in the speed of light relative to its source.

As for other experiments, if so many people firmly believe the constancy of the speed of light, and feel they have proven it, why would they still be testing it?
 
S

Saiph

Guest
but the moon of jupiter (pick one) and earth can have a wide variety of relative motion, the moon would thus have a range of velocities over which it is a 'source'. Some examples, you have the earth moving towards, away, or parrallel to jupiter's path, then you have the moon doing the same...
Earth's orbit alone can give you a speed range 60 km/s, it's rotation alone gives a 1km/s range. Throw in Jupiter's full range (~26km/s) and you can get some pretty hefty velocities do do your comparisons over.

If you consistently get the same speed over that entire range, I'm pretty sure it's case closed MA.

The reasons for retesting are simple:

A) Practice for new students and grad students. There are many classic experiments that use fundamental appraoches used in such labs.

B) New techniques. Sometimes people come up with interesting new ways of measuring it.

C) Often related to B: Secondary results. Often people are looking for one thing, and find the speed of light as part of their observations. If it's a novel enough way of finding it, it makes it's way into the literature (i.e. 'B').

D) Error checking: If your instrument doesn't give C when it should you'd have a problem, so it's a highly checked value when setting up instrumentation.

E) Increased precision: The speed of light is widely considered a very well understood value, and known to a very high precision. Enough so that it is used in the formulation of many our standards of measurement (length of meter, time).
 
M

mental_avenger

Guest
Saiph":2cf46a6s said:
but the moon of jupiter (pick one) and earth can have a wide variety of relative motion, the moon would thus have a range of velocities over which it is a 'source'. Some examples, you have the earth moving towards, away, or parrallel to jupiter's path, then you have the moon doing the same...
Earth's orbit alone can give you a speed range 60 km/s, it's rotation alone gives a 1km/s range. Throw in Jupiter's full range (~26km/s) and you can get some pretty hefty velocities do do your comparisons over.

If you consistently get the same speed over that entire range, I'm pretty sure it's case closed MA.
Good point, and for now I’ll concede that one, but I will think about this some more.

What I still have a problem with is the basis upon which the theory of light constancy is based. That is; That Maxwell’s equations must be satisfied in all inertial frames, that the laws of physics must be the same in all inertial frames of reference. While I would agree with that, it appears that it is demanded that the speed of light alone must be the same, not only in all inertial frames of reference, but between different frames of reference at the same time. I also have a problem with the fact that all the proofs essentially are based upon what an outside observer can observe, rather than what might actually be happening. This is not a small distinction. I have already shown that the physical arrangement of different frames of reference can have a dramatic effect upon what is observed between them.
 
D

derekmcd

Guest
mental_avenger":22nemh3n said:
derekmcd":22nemh3n said:
Replace the second car and 100 mph with a photon and C respectively, do you get similar results? Does the reference frame of the first car see the photon as travelling at 10 mph less than C?
You should get similar results. In this case, since the direction of travel is radial to the observer in the same direction, it should be 10mph less than c.
This is in line with Ritz' Emission Theory and has been shown to be problematic. Here's a paper that should be included on the wiki page... I'm quite surprised it is not as it is one of the best observation that light is constant and independent of source velocity which is the basis of emission theory.

http://www.uam.es/personal_pdi/ciencias ... r-1977.pdf

It just seems counter-intuitive to me that one light beam could pass another. Observations of binary stars and pulsars tells us that this does, in fact, not happen.
 
S

Saiph

Guest
That Maxwell’s equations must be satisfied in all inertial frames, that the laws of physics must be the same in all inertial frames of reference. While I would agree with that, it appears that it is demanded that the speed of light alone must be the same, not only in all inertial frames of reference, but between different frames of reference at the same time.
Except it isn't the speed of light alone. It's all laws, all frames, at all times. The problem is when you derive velocities for various objects you always get a +C term, a constant tacked onto the equation (by virtue of integrations) that designates that the velocity is a certain equation, plus an arbitrary constant. That constant is deemed to be the relative velocity of that frame of reference (i.e. the velocity of the observer).

So when you do force calculations to find an acceleration, then integrate the resulting equation over time to produce a velocity, you're left with an arbitrarily scalable answer.

EXCEPT!!! That when you try to derive the speed of light from maxwell's equations, there is NO such constant appended in math. Once that was published people were wondering relative to WHAT?! It had to be constant relative to something. Experiments showed it wasn't relative to the source, and there was no aether either...so that's what set the stage for Einsteins intuitive leap, relative to --everything--



Reading that wiki on emmission theory seems to fit the bill well. I especially like the point that if C is relative to the source, we'd see some pretty scrambled binary star systems as the light overtakes eachother in various ways at various times...
 
M

mental_avenger

Guest
derekmcd":1ztd7oil said:
This is in line with Ritz' Emission Theory and has been shown to be problematic. Here's a paper that should be included on the wiki page... I'm quite surprised it is not as it is one of the best observation that light is constant and independent of source velocity which is the basis of emission theory.
Thank you. That is very interesting. I am not a physicist, and had not really heard of that theory before. What I have been posting is my own interpretation based apparently on Newtonian science and my own solid working knowledge of how physics works in the real world.

derekmcd":1ztd7oil said:
It just seems counter-intuitive to me that one light beam could pass another. Observations of binary stars and pulsars tells us that this does, in fact, not happen.
I would think that most people would find it counter-intuitive that one light beam could not pass another. Special Relativity itself is the counter-intuitive concept. If you think of one photon zipping through space at 300,000 kps after being emitted at 300,000 kps from a source, and another photon zipping through space at 300,000 kps after being emitted at 300,000 kps from a source that is moving at 10kps relative to the first source, it would seem that the second photon would pass the first one.
 
M

mental_avenger

Guest
Saiph":3tseis79 said:
Except it isn't the speed of light alone. It's all laws, all frames, at all times.
I phrased that poorly. It seems that the speed of light is the only law that is expected to remain constant when viewed from different frames of reference at the same time. All other laws work within their own frame of reference.
 
S

Saiph

Guest
It seems that the speed of light is the only law that is expected to remain constant when viewed from different frames of reference at the same time. All other laws work within their own frame of reference.
Not so. All mathematical descriptions of an object must be able to translate between different frames of references. If I see an object accelerate, the description of it, and the resulting velocity must be expressible in a stationary, and a mobile frame of reference.

The catch is, as I explained in my last post, that the speed of light is the only derived velocity that is constant. period. It's derivation does not leave you with any scalable terms, it leaves you with with two universal constants...that's it. So I suppose it is unique in that it's required to be constant in all frames, but it is NOT the only law expected to translate over the frames of reference. It's treated just like the others.

I'll outline an example of what I mean with the actual math involved, maybe that'll help.

A space ship of 100 kg (yeah, tiny ship!) is undergoing a force that varies in time according to 100t^2. Describe the ships velocity:

Well, f=mA, so 10t^2=mA; A=100t^2/m = t^2.

A = dV/dt, so we integrate A over a time interval to find V. This produces: 1/3*t^3 +c = V.

The 1/3*T^3 is the straightforward result of the integration, the +C is thrown in because integration is about finding the area under a curve. By integrating, you can get all the bit under the curve, except you don't know where the curve starts on a graph, you don't know the initial conditions.

In the stationary case, we set C = 0. And we have no problem. However if we are moving relative to the ship, we substitue instead our relative velocity, which we could consider as the ships initial velocity before the engines fired. But in both cases the velocity is expressed as 1/3*t^3+C..it's uniform in all frames of reference.

Now, lets take a super diminutive scientist and put him on our tiny ship, and have him derive the speed of light from maxwell's equations, and he gets: 1/sqrt(u*e) where u & e are universal constants.

There are no scalable quantities from integrations, no variables, nothing, just two universal constants.

Now we do it here, where the space ship is already moving and we get...the same thing.

This is completely counter-intuitive when based on Newtonian mechanics, and were I think you keep getting tripped up.
 
Status
Not open for further replies.

ASK THE COMMUNITY