alternate ways to measure light.

[Didymus]

Giving this another honest shot. It's said that long ago, we proved that a source of light traveling either toward or away from measuring equipment will still emit light that will be measured at C.

 

The only ways I would know to measure the speed of light would involve bouncing that light off of an array of mirrors.

 

My question is: Does anyone know of a an experiment to measure the speed of light from a source moving relative to the measuring equipment that used a method that did not involve reflecting that light through a mirror array?

 

Can anyone describe how it would be measured without a mirror array?

[Sensei]

Source- laser.

Target- photoresistor, photodiode, phototransistor or solar panel.

Connect target to amplifier and record result in oscilloscope preferably connected to computer through USB.

It would be good that computer will be controlling laser. Length of cables must be known.

Between signal starting laser and moment in which photo element will detect beam of photons there will be delay.

If you will place f.e. water container between laser and photo element delay should be longer.

 

Instead of air you can have fiber wire. It would make easier long distance measurement.

 

ps. What a coincidence. I just returned from the electronic shop with new photoresistor..

 

[Didymus]

Correct me if I've misread, but that sounds like that only measures the delay based on light transferring through different mediums rather than relative speed.

 

I.e. measuring timing over a fixed distance rather than actually measuring the relative speed of the incoming photons. No?

 

I'm particularly interested in the tests verifying that the speed of light is the same even with a moving source. Once the light bounces off the first mirror in the array, that mirror is the new source of light and the speed of light is still only being measured relative to a stationary source (each mirror it bounces off of).

[John Cuthber]

But the signal is carried back down the cable by an em field, so the effect is the same as just reflecting the light.

It's still a "round trip" time, but you have relabelled the return part of the trip as "delay".

 

An optical fibre works by bouncing light signal round inside it so it effectively has many mirrors.

[Didymus]

Can you reference when this technique was used in an experiment testingthe speed of light where the source and receiver or moving relative to each other?

 

Preferably testing both a moving source and stationary receiver vs. A moving receiver and stationary source.

[Fred Champion]

Giving this another honest shot. It's said that long ago, we proved that a source of light traveling either toward or away from measuring equipment will still emit light that will be measured at C.

 

The only ways I would know to measure the speed of light would involve bouncing that light off of an array of mirrors.

 

My question is: Does anyone know of a an experiment to measure the speed of light from a source moving relative to the measuring equipment that used a method that did not involve reflecting that light through a mirror array?

 

Can anyone describe how it would be measured without a mirror array?

I suggest you consider how light is produced at the source. If we could reduce a source of light to a singe atom that atom will produce a discrete "pulse" of light at each excitation/de-excitation cycle. That pulse will be produced at a particular location and will radiate out from that location. This is true for that pulse and every subsequent pulse emitted. If the source is moving each pulse will be emitted from a different location. The changing location of the emissions is what produces the Doppler effect, not any distortion in the emission.

 

So, you should not expect to see the speed of light vary with the motion of the source. If the pulses are emitted at regular intervals (a specific frequency) the motion of the source will not change that frequency. An observer may see the frequency of the pulses change as the motion of the source changes, but the speed of the light from each pulse reaching the observer will not change. We may liken this to someone flying over a lake dropping rocks into the water. Each wave produced will progress through the water at the same speed, but from a different location. The rate at which the waves reach an observer will be a function of the location of the observer relative to the flyer's path, the speed of the flyer and the rate at which the rocks are dropped.

 

You may also note that as far as we know all objects are in some sort of motion, so it will not be possible to establish an experiment with a source and an observer which are not in motion.

[Enthalpy]

[...] If the pulses are emitted at regular intervals (a specific frequency) the motion of the source will not change that frequency. [...]

 

Yes it does, experimentally. Both the frequency of the light and the interval between the pulses.

[Fred Champion]

 

Yes it does, experimentally. Both the frequency of the light and the interval between the pulses.

Well, perhaps I miss something. I believe we were considering the interval between the pulses to be the frequency.

 

A remote observer may see the frequency change, depending on the relative motion between the observer and the source, but this is not due to any change in the frequency of the emissions at the source. In the case where there is no increase or decrease in the distance between the observer and the source there will be no apparent change in frequency except when both the source and the observer are accelerating.

[studiot]

 

Well, perhaps I miss something. I believe we were considering the interval between the pulses to be the frequency.

 

You do indeed miss something.

 

Frequency is not a term applicable to pulses.

Pulses are much more complicated than simple waves, consequently pulse theory has many more terms to describe the various elements of a pulse train.

Furthermore the interval between pulses is just exactly that.

The interval between pulses.