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Comment by sp332 | Hacker News Reader

This would also work for radio waves, right? We would be able to listen in on radio broadcasts from a distant planet.

Yes, it's possible but the refractive index decreases with increase in wavelength to the point that this would not be feasible.

Radio wavelengths are ~9 orders of magnitude larger than optical, meaning the detector would need to be placed roughly 30 light years from earth. A bit out of our reach.

(assuming I did my back of the envelope math right)

Uh, never realized that gravitational lensing was stronger for higher frequencies ... is that a fact? Any reference?

[EDIT]: the formula on page 4 of the book below does not seem to have a frequency parameter ...

Also, they seem to consider that objects worth looking at are at infinity, which is why there is a well-defined focal distance from the sun.

What seems to involve frequency is that the gain of the lens varies (same book, page 9).

http://erewhon.superkuh.com/library/Space/Spacecraft/Deep%20...

Oops my bad, thought this was a comment under another thread discussing terrestrial lensing which uses Earth's atmosphere, not gravitational lensing. Disregard!

But we're using a lens that bends spacetime. I'm not sure index of refraction is relevant. On the recent image from JWST, I don't see any refraction artifacts on the lensed images of galaxies. https://www.nasa.gov/image-feature/goddard/2022/nasa-s-webb-...

Oops my bad, thought this was a comment under another thread discussing terrestrial lensing which uses Earth's atmosphere, not gravitational lensing. Disregard!

I wonder whether any stars 30 light years away have interesting objects behind them.

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