[Petrochemicals (OP)]

If light cannot exeed 'C' in a vacuum, and has a constant velocity that is independant and absolute, it must be possible to create a speed gun to measure an Absolute velocity ?

If you had a sphere with a vaccuum  within, and at the centre a light source. At the periferies of the sphere detecting the light are sensors. The sensors read back to a display

You fire the gun

Would these sensors detect at which direction, and at which velocity you where going. Last time I got as far as relativity ie this being different time for different observers. You fire the gun (in your hand) and  the readout says you are stationary ? Or would it work ? The mickelson morley says it would have no effect, but the rebka -pound disagrees.

Someone who observed you fire the gun as you passed by, reads the display ? What then. The clock is in the gun or do we observe a paradox ?

[Kryptid]

Admittedly, I'm not sure I completely understand the set-up. Does the gun make a laser-like beam of light that lands on only one point of the sphere, or does it emit light in all directions? If the light goes in all directions, then the sensors could tell from the relative values of redshift and blueshift at different points along the sphere's internal surface what direction and speed the gun was moving in.

If It was only hitting one particular spot on the wall, you could at least tell the direction that the gun was fired. Redshift measurement would only work in that case if you knew the frequency of the light that the gun was designed to emit, and that would only work if the gun wasn't moving perpendicular to the sensor that received the light and if you knew the angle that the gun was fired from. Of course, if it was moving perpendicular to the sensor, then other sensors could pick it up and tell by the relative timing of received signals how fast the gun was moving. The speed of light doesn't have to change for you to do any of these things.

All of this relative to the sphere itself, that is. Other observers in different reference frames will get different values for the gun's speed.

[Colin2B]

The mickelson morley says it would have no effect, but the rebka -pound disagrees.

I’m also having problems understanding the set up. And why pound Rebka should disagree with MM.
Could you explain please?

[Petrochemicals (OP)]

Yep a lightsource in a sphere emmitting light in all directions, with sensors all the way around the sphere.

The PR experiment would say that the red shift/blueshift should be be measurable and your absolute velocity and absolute vector would be apparent.

The MM experiment though found no lag in the aether, that wasnt there. But by firing light beams in two seperate directions 90 DEG to each other this would have replicated the process of light at different directions and aether or not, should have found some discrepancy in the light at the reciever. One light beam has a long parralell and short perpendicular to the reciever, the other has the opposite. The experiment has been repeted manytimes with different orientations, but no differences in speed have been detected otherwise they would have been said to be evidence of the aether.

Something has to happen as if two light beams pass and you are riding on one of them, the other is not going 2C.

[alancalverd]

Problem is that there is no such thing as absolute velocity.

Velocity is the rate of change of a distance vector. There being no absolute origin, any velocity is relative to some arbitrary origin.

[Kryptid]

The PR experiment would say that the red shift/blueshift should be be measurable and your absolute velocity and absolute vector would be apparent.

In that particular reference frame. In other reference frames, the redshift would be measured as having a different value.

Something has to happen as if two light beams pass and you are riding on one of them, the other is not going 2C.

Length contraction and time dilation.

[jeffreyH]

The speed of light is the fastest velocity possible and yet cannot be reached by massive objects. This makes it the perfect yardstick. At a particular instant a photon is at position x. At a later time t it is at x + dx. This will not vary in a vacuum in the absence of other forces such as gravity. So that spacetime intervals can map to the path of photons if considering special relativity. All other velocities are relative and influenced by time dilation depending upon the frame of the observer. This makes it extremely difficult to make any determination of the one way speed of light. It will always be observer dependent.

[Petrochemicals (OP)]

Problem is that there is no such thing as absolute velocity.

Velocity is the rate of change of a distance vector. There being no absolute origin, any velocity is relative to some arbitrary origin.

You are travelling at 0.5c and you turn on your headlights, the light travels at 0.5c ? Light is not dependant on origin is it ?

The speed of light is the fastest velocity possible and yet cannot be reached by massive objects. This makes it the perfect yardstick. At a particular instant a photon is at position x. At a later time t it is at x + dx. This will not vary in a vacuum in the absence of other forces such as gravity.

Thats the idea, only influenced by your velocity, and the gravitational field, which i hadnt taken into account !

The PR experiment would say that the red shift/blueshift should be be measurable and your absolute velocity and absolute vector would be apparent.

In that particular reference frame. In other reference frames, the redshift would be measured as having a different value.

Something has to happen as if two light beams pass and you are riding on one of them, the other is not going 2C.

Length contraction and time dilation.

But the point is that within the sphere with all going at equal velocity the red shift blue shift from the emitter should be apparrent. I got to time dilation last time. The observer is the readout, so if you who are travelling with the sphere and your best frien d who is observing your progress read the readout, you both observe the same reading.

Would forward momentum dilate time, so as to balance out the fore and aft readings ?

[Kryptid]

But the point is that within the sphere with all going at equal velocity the red shift blue shift from the emitter should be apparrent. I got to time dilation last time. The observer is the readout, so if you who are travelling with the sphere and your best frien d who is observing your progress read the readout, you both observe the same reading.

If your friend was moving by the sphere and could somehow see the readout on the sphere's sensors, they would indeed see the same numbers as a person who is on the sphere. If they performed their own measurements of the redshift of the light inside the sphere, in their own reference frame, they would get different numbers. There's nothing strange about it. The same thing would happen if you passed by a police car that was using a radar gun to measure the speed of another car, You'd see the same numbers on the cop's radar as the cop would. If you had your own radar gun, however, you'd get a different number because the redshift values would be different for you.

[Petrochemicals (OP)]

Ok so you both observe the reading, no paradoxes or anything. The readings in the sphere measure identical fore and aft ? As the sphere and you are in there own timeframe ? So if you turn your headlights on at 0.5c you see light  as normal at 1c but your friend sees light al 0.5c  as your friend  is not at the same  velocity and therefore time dilation.

That must mean the ad you are in your own clock and time dilation and light infront of  you and behind you appears the same, you would have to have two time dilations for the light to appear constant in both directions, in reference to the observer on the ground, who is observing the constant C .

[Bored chemist]

Petrochemicals,
I'm just trying to check that I understand the setup correctly.
You have a flash bulb in the middle of a sphere.The surface of the sphere has detectors on the inside.
If it's not moving, the flash from the bulb reaches the detectors at the same time.

The ideas is that, if the system is moving, the light will have further to travel to the "back" of the sphere than to the "front".

Is that what you mean?

[Petrochemicals (OP)]

Petrochemicals,
I'm just trying to check that I understand the setup correctly.
You have a flash bulb in the middle of a sphere.The surface of the sphere has detectors on the inside.
If it's not moving, the flash from the bulb reaches the detectors at the same time.

The ideas is that, if the system is moving, the light will have further to travel to the "back" of the sphere than to the "front".

Is that what you mean?

Yep thats what i mean. Seemed so simple when i wrote it down.

[Colin2B]

Yep a lightsource in a sphere emmitting light in all directions, with sensors all the way around the sphere.

The PR experiment would say that the red shift/blueshift should be be measurable and your absolute velocity and absolute vector would be apparent.

Ok, assuming you + light gun and sphere are moving together.
PR detects a red/blueshift if there is either a difference in gravitational potential or, by equivalence, an acceleration. If your sphere is accelerating you would feel a force as well as detecting a PR shift. If the sphere is constant velocity you won’t detect anything.
At constant velocity you will only detect a shift if the sphere wall is moving relative to you/gun.
PR does not disagree with MM, they are measuring different things.

Ok so you both observe the reading, no paradoxes or anything. The readings in the sphere measure identical fore and aft ? As the sphere and you are in there own timeframe ? So if you turn your headlights on at 0.5c you see light  as normal at 1c but your friend sees light al 0.5c  as your friend  is not at the same  velocity and therefore time dilation.

No, your friend measures the light as 1c, not 0.5c. Maxwell’s equations.

[Petrochemicals (OP)]

Ok, assuming you + light gun and sphere are moving together.
PR detects a red/blueshift if there is either a difference in gravitational potential or, by equivalence, an acceleration. If your sphere is accelerating you would feel a force as well as detecting a PR shift. If the sphere is constant velocity you won’t detect anything.
At constant velocity you will only detect a shift if the sphere wall is moving relative to you/gun.
PR does not disagree with MM, they are measuring different things.

ok i think i got it, the pr experiment is due to the acceleration of gravity and thus increacing  velocity creating a doppler effect as you decend toward the earth surface, mot because of a doppler effect due to increaced speed in the light used, so at the constant velocity there is no red shift. So if a galaxy is departing from us at a constant velocity, no red shift is experienced

No, your friend measures the light as 1c, not 0.5c. Maxwell’s equations.

Ok to the rear your friend measure the light at 1c and forward he measures the light at 1c, the constant C. Your friend as he sees you move does not/would  not see a doppler efect in the light due to the emmitter being in motion, he sees the light 1c relative to the emmitter.

You however also see the light fore and aft at 1c completley independant of your friend, due to time dilation due to your clock. Does that mean you do not need relativity as you both see the light ?

[Colin2B]

Ok to the rear your friend measure the light at 1c and forward he measures the light at 1c, the constant C. Your friend as he sees you move does not/would  not see a doppler efect in the light due to the emmitter being in motion, he sees the light 1c relative to the emmitter.

Your friend sees a doppler effect if he is moving towards/away the gun because he is crossing the wave crests more/less frequently than if the gun were stationary relative.

You however also see the light fore and aft at 1c completley independant of your friend, due to time dilation due to your clock. Does that mean you do not need relativity as you both see the light ?

Its somewhat the other way round. Light is constant because Maxwell’s equations are the result of 4 very important physical laws covering electricity and magnetism and we have experiments that show that these laws are independent of the inertial frame. Time dilation and length contraction are a result of this - independence of the laws and the constant speed of light - rather than the cause. So we need relativity to explain why our measurements appear to be, at first sight, unbelievable.
Hope that helps.

[puppypower]

The speed of light is the same in all references. To get an absolute speed, we need to measure with respect to the speed of light since this is a standard for all references. We make the speed of light become the zero reference. Relative reference only applies to two or more inertial references. Relative reference has no meaning at the speed of light.

Here is an analogy. Say we have a mountain coming out of the sea. Sea level is the same place for everyone no matter where you stand on the mountain. As we move up the mountain, the potential with sea level increases and will define an absolute hierarchy.

Relative to two people standing at different places on the mountain (ignore sea level), you can get the same potential difference for a large number of scenarios. It becomes relative. If one person is at the bottom and one person is half way up, this has the same potential as one person half way and one at the top. If we have the half way person and the top person both step down, one step, this is still the same potential. You cannot get an absolute reference on the mountain. You need to have one person always at sea level or C-level, zero potential separate from the mountain.

We live on the earth in an inertial reference. We still use the very ancient earth centric thinking since this is how the natural brain will process data; visual. Instead you need to think in terms of standing at C-level with the mind's eye,  Then we can find the center of the universe with respect to C and absolute zero velocity.

When there was only the primordial atom, we only had one inertial reference and the speed of light reference. There was no such thing, yet, as relative reference, until the BB. The primordial atom set the maximum potential with C. It was the top of the mountain that was sticking out of the C-level reference. The BB lowered this potential. The universe is heading down the mountain.

[Petrochemicals (OP)]

Your friend sees a doppler effect if he is moving towards/away the gun because he is crossing the wave crests more/less frequently than if the gun were stationary relative.

So not acceleration ? The pr experiment was used to measure doppler effect in  light under the influence of gravity wasnt it ? The light frequencies extended due  to increaced speed  because of gravity ?

[Petrochemicals (OP)]

The speed of light is the same in all references. To get an absolute speed, we need to measure with respect to the speed of light since this is a standard for all references. We make the speed of light become the zero reference. Relative reference only applies to two or more inertial references. Relative reference has no meaning at the speed of light.

Thats pretty much  what I thought. And you do seem to agree.

By the way this mountain analogy, youve not been reading about Numenor in the silmarillion ?

[Colin2B]

So not acceleration ?

yes, my reply was for contstant speed scenario, but also for acceleration, however, the shift would vary as speed increased.

To get an absolute speed, we need to measure with respect to the speed of light since this is a standard for all references. We make the speed of light become the zero reference.

As this is new theories, please explain how you find your absolute speed by measuring wrt light?
[/quote]

[guest4091]

In the 2D analogy, a moving circle is length contracted so that observer A in the center receives simultaneous reflections from a signal emitted from the center.
In the 3D equivalent, the sphere becomes an ellipsoid with the same results.
The moving inertial frame behaves like a rest frame.
The clock in the radar gun will be affected by time dilation. The device will sense an earlier time and calculate a shorter distance, just as a human would, resulting in the same relative speed for the target.