Light Speed question

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I have stacked with the following question : Let assume that the light speed was 5 Km/h and we attempting to measure it. What would be the result of that measurement?

George

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5km/hr of course.

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Your question seems to be a tautology.

If the speed of light is 5 (in some units), then you measure it to be 5 (in some units).

I do not understand what you are asking.

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I want to know if something is absolute (like the speed of light) then is measurable too.

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Is there some reason you think it might not be?

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In other word if everything are running in 4th dimensional time space with the same speed how can find a methodology to measure it? For example a increase in SOL will cause a clock to tick faster and all reactions will be faster including the observator 4th dimensional speed.Let imagine that we have 2 mirrors in distance 30 *10^8 meters then an observator measure the time that takes a ray of light to go from one mirror to another; it finds that it take one second. Now if the SOL decrease and the he want to repeat the measurement what would be the result? That i m asking.

George

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Absolute means it is invariant (does not change) under the action of some symmetry group.

For light speed we are thinking of the Lorentz group.

I think your question should be more the other way around. If something is measurable/observable then is it invariant?

Well, it is clear that you can measure things that are not invariant under what ever group you are thinking of.

For example, time and distance are not Lorentz invariants. This means they cannot have any deep meaning. However the space-time interval which "mixes" space and time is invariant and this does have a real meaning.

Another example is the electric and magnetic fields. Only combined into the electromagnetic field do they have "deep meaning".

The modern perspective is that observables with "deep meaning" are invariant.

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If everything happens faster to the same degree, then nothing has actually changed, has it? What would "faster" mean?

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Then somehow that's interesting the SOL could increase or decrease without any consequences

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Then somehow that's interesting the SOL could increase or decrease without any consequences

I don't know what would happen if the speed of light could somehow increase or decrease. If the speed of everything is dependent on the speed of light to the same degree (which is not necessarily true), then I'm saying it can't be any faster or slower. If nothing has changed, then nothing has changed.

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As the SR says (and is proved with many experiments) that is the speed of everything in this world is same and it has the same value with the SOL. So far that we know...

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Let put this a little bit different: Now we have a SOL as we know it and then a cosmic acceleration is happening; the world would be the same before and after that acceleration? in this case something has changed an acceleration happened (even is theoretical and forbidden by the SR).

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Ps: with cosmic acceleration i mean SOL acceleration sorry any misleading s

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I think that my questions are boring.... (and my English bad)

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• 2 weeks later...

Or even worse if everything in the world changes their 4D speed at the same rate then an observer could "feel" this change but would still measure the same value for SOL.....

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regarding all relativity problems we find that experimenters are talking of clocks synchronised when they have a relative speed between them. if we synchronise two clocks at rest and one pf them starts to move, attains a velocity near about that of light then will light have a constant speed with respect to those two clocks?

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regarding all relativity problems we find that experimenters are talking of clocks synchronised when they have a relative speed between them. if we synchronise two clocks at rest and one pf them starts to move, attains a velocity near about that of light then will light have a constant speed with respect to those two clocks?

Yes, it will be constant with respect to either of them. But the clocks will not be in sync anymore.

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Yes, it will be constant with respect to either of them. But the clocks will not be in sync anymore.

I've asked this on another thread but can you list the experiments carried out to verify this?

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Yes, all measurements of speed of light (in a vacuum) give a speed c, regardless of how fast the measuring equipment is moving. And atomic clocks get out of synch when one of them is riding in an airplane.

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thanks Mr. Skeptic... can you tell me about any particular experiments using moving sensors.

I'm aware of the atomic clocks speeding up the further you get from earth but specifically i'd like to see results on experiments where lasers are directed at sensors moving towards the light source and sensors moving away from the light source...

it must be something that's done with satellites on a daily basis?

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Well I suppose the delays in the radio messages of the Luna astronauts whilst on the moon could count? In the recordings of them you can hear their own messages bounced back and coming through their own headsets from that you can work out a distance and compare to how far the craft travelled...

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Was the craft travelling fast enough to cause significant time effects?

I would say the experiment would need to be carefully planned out so all the variables are accounted for...

Maybe it can't be done?

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GPS would give errors if c wasn't constant, or if other parts of relativity were incorrect.

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I've asked this on another thread but can you list the experiments carried out to verify this?

As above, GPS is a great example. The first satellite didn't have the timing correction made prior to launch so that this could be measured. The difference was as predicted; after confirming this they adjusted the oscillator frequency to the value required by relativity.

There's also the Vessot rocket experiment, where a hydrogen maser was launched and the effects of general relativity were measured.

And there's the continual experience of timing labs in doing this. You have to account for the Sagnac effect and both the kinematic and gravitational potential terms of relativity when you move clocks.

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Yes I was aware of GPS but is that not to synchronise clocks and has more to do with inertia than light speed (if you ignore the intrinsic links)?

My hypothesis predicts that light speed will be measured as c where a sensor is moving towards a light source because the sensors time will have sped up in proportion to the addition of speeds keeping light speed at c.

I want to see the results of experiments where the sensor is moving away from the light...

I'll take a look at the Vessot rocket experiment, cheers.

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just looking at vessot and again it is just meauring clock tick rates.

this is different to measuring 'c' from a moving observers perspective.

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Yes I was aware of GPS but is that not to synchronise clocks and has more to do with inertia than light speed (if you ignore the intrinsic links)?

My hypothesis predicts that light speed will be measured as c where a sensor is moving towards a light source because the sensors time will have sped up in proportion to the addition of speeds keeping light speed at c.

I want to see the results of experiments where the sensor is moving away from the light...

I'll take a look at the Vessot rocket experiment, cheers.

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just looking at vessot and again it is just meauring clock tick rates.

this is different to measuring 'c' from a moving observers perspective.

Clocks changing rates is a consequence of the constancy of the speed of light and the effects of gravity in general relativity. Showing that the rates change as predicted is evidence for the constancy of c.

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not really, it shows that time is related to the speed of one object relative to another... yes the constancy of light comes into the equation... but it doesn't verify that c is constant to all observers.

so what you're saying is there have been no practical experiments done with moving observers and light sources?

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not really, it shows that time is related to the speed of one object relative to another... yes the constancy of light comes into the equation... but it doesn't verify that c is constant to all observers.

Actually, it does. All of relativity and the predictions thereof are a consequence of C being constant to all observers. If this interests you, you should begin by looking into what special relativity is all about.

so what you're saying is there have been no practical experiments done with moving observers and light sources?

To the contrary, the constancy can be observed simply by calculating its speed between planets at different times of year (and thus at different relative velocities).

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I don't think it can because you'd have to have someone on the planet or star with a (somehow) synchronised stop watch sending out a signal...

I understand that relativity states that c is constant to all observers, but this has generally been used to show how clocks are altered by movement and the intensity of a gravitational field.

I want to see results of an experiment of light being shone on a moving target... can it be done?

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