Greg Egan

https://mathstodon.xyz/@gregeganSF

I am a science fiction writer and computer programmer.
Latest novel: MORPHOTROPHIC.
Latest collection: SLEEP AND THE SOUL.
Web site: gregegan.net

Web site: https://www.gregegan.net
Location: Perth, Western Australia

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Last Notes

2024-11-22 08:22:17 UTC

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When you’re a little way outside a black hole (with no accretion disk), what you see when you face it is (as you say) not the absence of light emerging from the hole itself, but rather light emitted by the infalling matter that formed the hole in the distant past.
But this light will be *enormously* red-shifted, with the frequency and luminosity so low that for all practical purposes it will be utterly black.
Equally, inside the hole (free falling), unless something luminous fell in just ahead of you, you will see a big black circle.
An app with visuals here:
https://www.gregegan.net/PLANCK/Tour/TourApplet.html
The calculations behind it:
https://www.gregegan.net/PLANCK/Tour/TourNotes.html

2024-11-21 19:23:57 UTC

- reply

And the coolest tidal fact of all (which Rob once prompted me to realise) is that the near-perfect angular size match in solar eclipses means that essentially all the difference in lunar vs solar tidal strength (in the approximation that the separation distances are much larger than the radii of the bodies) is due to the ratio of densities between the sun and the moon.