Greg Egan on Nostr: nprofile1q…ufa4k Yeah, the whole mix of gravitational and Doppler ...
nprofile1qy2hwumn8ghj7un9d3shjtnddaehgu3wwp6kyqpqknzsux7p6lzwzdedp3m8c3c92z0swzc0xyy5glvse58txj5e9ztqaufa4k (nprofile…fa4k)
Yeah, the whole mix of gravitational and Doppler redshifts/blueshifts is hard to anticipate by intuition alone.
For example, if you free-fall radially into a black hole from infinity, then light that is also from infinity reaches you with its frequency multiplied by:
1 / (1+√[2M/r])
when the light is from directly behind you, i.e. a redshift, ranging across the sky to::
1 / (1–√[2M/r])
i.e.a blueshift, when the light is coming directly towards you [actually the black hole is either blocking or diverting light coming in from infinity in precisely that direction, but you know what I mean.]
Yeah, the whole mix of gravitational and Doppler redshifts/blueshifts is hard to anticipate by intuition alone.
For example, if you free-fall radially into a black hole from infinity, then light that is also from infinity reaches you with its frequency multiplied by:
1 / (1+√[2M/r])
when the light is from directly behind you, i.e. a redshift, ranging across the sky to::
1 / (1–√[2M/r])
i.e.a blueshift, when the light is coming directly towards you [actually the black hole is either blocking or diverting light coming in from infinity in precisely that direction, but you know what I mean.]