# Deflection of light around a massive body

## Main Question or Discussion Point

I thought this would be an easy lookup. However, after farming several sources, I couldn't find a discussion on it..

Anyway, my question is is this, does a shorter wavelength/higher energy photon bend more around a massive body than a lower energy photon? For instance, if we had two photons, one high energy and one low energy, from a distant source moving around the sun at the exact same distance from it's center and we were measuring their deflection during an eclipse, would there be a difference in the amount of deflection between the two (that is, if the difference were measurable)?

My guess would be that the higher energy photon would be deflected more but I haven't been able to find a reference to it.

Also, a related question would be the "gravitational redshift" of said photons in the example above. That is, would each of these photons experience such a blueshift (in this example) as they were being deflected around the sun, and would the amount of that blueshift be similarly affected by their energy?

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ChrisVer
Gold Member
Looking at the deflection angle, and also at its derivation, I don't see where the momentum/energy of the photon goes into the game. It exists but it's replaced [with the angular momentum] by the impact parameter, that has a different physical meaning. So I guess no light will be deflected more or less, they will accept the same deflection if they are coming near the massive lens with the same parameters.

For your related question, check here

DrGreg
Gold Member
Photons follow null geodesics. Once you've specified the starting event and the starting direction in 4D spacetime, you have uniquely specified the geodesic. The starting direction in 4D spacetime is uniquely determined by the starting direction in 3D space, because the time component then depends only on the speed, which is the same for all photons.

So all photons passing through the same event with the same spatial direction follow the same path regardless of frequency.

Ok, got it. Thanks for the clear responses.

jtbell
Mentor
I seem to remember reading that the (lack of) dispersion of electromagnetic radiation with different frequencies has been tested by studying the deflection of radio signals from distant sources in the Sun's gravitational field.