# Speed of light constant

#### optrix

I've been looking at the Michaelson-Morley experiment for determining the speed of light using an interferometer, and managed to find a boxplot diagram on wiki, showing the results of a number of attemps. Now I'd like to see a setup and results from a similar experiment that takes the light from sources at different speeds, thus confirming that the speed of light is constsnt no matter what the speed of the source.

I suppose it is only a very slight modification to the Michaelson-Morley experiment, having sources at different speeds, and the results must be similar if the speed of light is indeed constsnt, but does this experiment go by a different name or is there any webpages that focus on this specifically?

Thanks

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#### russ_watters

Mentor
I think you may be missing the point: by orienting the device at different directions wrt the earth's rotation and/or doing it at different times throughout the year, you can do the experiment many times, at many different speeds relative to the supposed fixed aether

It seems you want to make the light source move wrt the rest of the experimental apparatus. That wasn't the purpose of the experiment, but there are many practical devices that require such a setup, including the GPS system.

#### optrix

Ah ok I see your point thanks.

#### Naty1

If you are interested in the magnitudes of change in GPS due to orbital velocities on one hand and the lower gravitational potential at satellite altitudes, you should be able to find data online. There are 'significant' corrections that must be made to maintain GPS accuracy to the roughly one meter range.

#### optrix

Thanks, but I'm only interested in (the experimental verification of) why the speed of light is constant. I thought the experiment arose from contradictions with newtonian mechanics, i.e. for a light source moving 300m/s, the measured speed of light will be the same as for a stationary source, and so I thought that the speed of the source was varied w.r.t to measuring equipment. I'm not sure I fully understand the implications of the aether with this experiment actually.

#### russ_watters

Mentor
Think of the aether like the air around you. If you are stationary and make a noise, the sound travels as a wave on the air, at about 750 mph. If you drive in a car at 50 mph, the speed of sound relative to the car is 700 mph forward and 800 mph backwards.

It seems like you are thinking of addition of velocity as if light were a particle. Ie, if you throw a baseball backwards at 50 mph from a car moving 50 mph, it drops straight down wrt a person standing on the ground. If you throw it forward, it moves at 100mph wrt a person on the ground. That isn't how light was believed to behave - light was believed to be a wave on a medium for the purpose of the MMX.

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