andrew s

It's not going to be down that long is it? Regards Andrew

You could try observing or writing your next paper? Regards Andrew

I grant you dominion over the whole observable Universe. Now deliver. 👹 Regards Andrew

@robin_astro I found the link to the re-analysis of Romer's velocity measurement. Unfortunately, it's a book but I managed to read some of it on line. It seems you can have a isotropic speed of light that make sense but they predict the same outcomes as the normal Einstein synchronisation protocols. It did not address your proposal. Giving it more thought, let's assume you measured a shift. The issue is then how to interpret it. It could be due, to an anisotropic change in c or in distance. For example we assume the Hubble red shift is due to expansion rather than changes in c or t. As far as I can tell it is a convention to adopt Einstein's synchronisation protocol and indeed this is now fixed in our system of units where the value of c is fixed. Regards Andrew 1 in 10^4 is good but not conclusive in the esoteric realm of the measurement of fundamental constants 😀 No Nobel prize just yet but it's nice to have an upper bound.😏

I think you would need to specify exactly how you would make the measurement for me to comment on if it's doable or not. The devil is in how you do the measurement. The "one way" speed derived from the timing of the Jovian moon eclipses (used as a clock) can give different results depending on how you analyse it. I'll look out the reference. In your proposal the lamp acts as a clock so it may be analogous. As I have said before there is no evidence for any anisotropy, if there were Maxwell's equations would need to change and you would still need the two speed to be c. Yes, the wavelength, frequency and velocity are geometry no argument there but that is exactly what GR and SR are geometry. Also your wave is governed by Maxwell's equations so to my mind they are on a similar footing. Regards Andrew

I think there would be issues of getting the required accuracy but I need to think about if its possible in principle or not. It's not unlike using Maxwell's equations and its constants being measured in different directions. Regards Andrew PS On reflection (pun intended) you would need to known the there was no relative motion between the lamp and the receiver to the required accuracy. I can't see how you could do this without using a light interferometer which brings you back to a two way light beam.

We new the speed of light very accurately but now it is a defined value and time is defined in terms of it rather than c = d/t

Can you provide a diagram showing the difference as I am struggling to work out what you mean? Any circular aperture viewed off axis will look elliptical so that's why I am confused. Thanks Andrew

Unfortunately, you can't measure the one way speed of light within SR as you need to synchronise clocks using something like the Einstein synchronisation protocol. It is in this sense you would need a new theory that legitimise a one way measurement. Yes I agree in the limit it would need to reduce to SR. Regards Andrew

If it does it will need to provide a new theory of relativity as well so that it can be measured. Given its track record on providing testable predictions I wouldn't hold my breath. ☠ Regards Andrew

At a glance that looks right but if you are not on the equator it will drop off as you approach a pole. There is some good stuff here http://www.threehillsobservatory.co.uk on Robin's site. Regards Andrew

There are also live feeds https://www.nasa.gov/connect/chat/allsky.html as an example. Regards Andrew Just noticed the post above sorry for the repeat.

Very impressive with some fine detail in the full resolution version. What telescope or lens did you use? Regards Andrew

Yes that is how I understand it. Regards Andrew

Don't be put off @jif001 it's not a real astro image without diffraction spikes. They add a touch of class that purist refractor boys and girls just fail to appreciate . 👹 Regards Andrew

Photon energy is not a constant but frame dependent as in blue and red shift s seen in stellar spectra. It's difficult to say what the impact would be if c were anisotropic as our best theories are based on it being isotropic. The fact SR, GR and QED do so well experimentally rather supports the view that c is isotropic. Regards Andrew

No, only the average average speed was the same. The light goes back and forth in both legs of the interferometer. Regards Andrew

I think it would be ok as long as the round trip average were c. However, there is no evidence for any anisotropy that I am aware of. Regards Andrew

Within special relativity it is impossible to measure the one way of light. The reason is that you need to synchronise the clocks at the two ends and depending on the protocol you use you can either get whatever answer you like or you have to assume the one way speed of light is the average of the two way speed. There is a long discussion here One way speed of light. Obviously, as @saac points out Maxwell's equations provide an indirect method of measuring c. Regards Andrew

If you are new to Astronomical spectroscopy try look at this site http://www.astrosurf.com/buil/index.html Regards Andrew

It's because uniform motion is relative to another body where as proper acceleration is not. You can measure acceleration locally but not velocity as it requires another object. If there were radiation with uniform motion it would violate the principles of relativity and in particular the fact that all inertial frames are equivalent. Regards Andrew

good summary George, thanks Andrew

Impressive I like that a lot. Regards Andrew

+1 Regards Andrew

I don't know what you mean 2020's perhaps? Regards Andrew