# Is there red shift evidence for light?

1. Feb 4, 2014

I'm aware of the doppler effect for sound waves. But light waves are different, e.g., light travels through a vacuum but sound does not. Has there been any laboratory confirmation for red shift for LIGHT. I could find only ONE paper by Bélopolsky, A. in 1901 using rotating mirrors. But there were no photos; only numerical data. Thank you.

2. Feb 4, 2014

3. Feb 4, 2014

### phyzguy

Have you ever seen a police "speed gun"? It works by comparing the frequency of the outgoing electromagnetic waves with the ones reflected back from the moving car. The difference in frequency caused by the Doppler shift tells you how fast the car is going. Does this satisfy you, or does it have to be visible light? If so, try reading about laser Doppler velocimetry. It works the same way but uses laser light to measure the velocity of fluids. Another example is that GPS receivers use the Doppler shift to calculate your velocity. There are many, many more examples.

4. Feb 4, 2014

Speed guns and laser doppler velocimetry refer to doppler shift caused by the REFLECTION of light. GPS is by trilateration of radio signals. Red shift of stars is taught as caused by movement of light from its primary source i.e. not shifted by reflection.
Is there empiric laboratory evidence that light can be red shifted by the movement of its primary source?

5. Feb 4, 2014

### Staff: Mentor

Yes. See the following link for an explanation of the experiment. (About 1/3 of the way down the page)

http://spiff.rit.edu/classes/phys314/lectures/doppler/doppler.html

6. Feb 5, 2014

### phyzguy

It's true that the first two are a reflected signal, although I'm not sure why it matters. But for GPS, the radiation is emitted by the GPS satellite, and your receiver looks at the frequency it receives and compares it to a reference to determine your velocity. Also, try looking up the Doppler shift in reference to the Sputnik satellite. Observers were able to calculate the satellite's speed by the shift in frequency of the detected radiation. Also, here is a nice study of using satellite Doppler shift to measure a satellite's orbit. Since in all of these cases, the satellite is emitting the radiation, they should meet your criteria.

What is your point? Are you trying to argue that the Doppler shift, which is clearly in the category of well established science, might not occur? If so, I urge you to re-read the rules of this site, since you are close to violating them.

7. Feb 11, 2014

### Algr

In addition to those experiments, there is really no other explanation for what we see when we look at far away stars. How else could we get familiar patterns of spikes on a spectrogram, but at the wrong frequencies?

8. Feb 11, 2014

In the Book Big Bang by Simon Singh, he mentions that cooler stars are more red. How is this different from a red shift? i.e., if all spectra are red shifted, how can we tell whether it's due to the star receding or from being cooler?

9. Feb 11, 2014

### Algr

When we say that a star is "red shifted", we are not talking about the color it appears to the naked eye, but to the location of the spikes I was just talking about. The sun looks redder at sunset, but if you did a spectrograph at sunset the spikes would be in exactly the same places. Nothing else but motion can move the spikes.

10. Feb 11, 2014

### Staff: Mentor

If you look at the spectra of two stars, one blue and hot, the other red and cool, the emission and absorption lines for each element are in the exact same spots in each spectrum. Redshift causes these lines to move.

11. Feb 11, 2014

### Chronos

You can have some minor variance due to gravitational redshift, but, is not much a factor for most stars.