undefined | Better HN

0 pointsben_w2y ago0 comments

That you'd be able to see it with the naked eye?

α = 4GM/((c^2)b), where b is the impact parameter[0].

Apparently human visual acuity is 0.3 milli-radians, so if b = 1 meter, that's approximately "the moon" (in at most a 1 meter radius volume)…

…assuming I didn't mix up my units in this formula I never used before, though it feels about right given the Schwarzschild radius of the Earth is ~ centimetres.

[0] never heard of this before just now; I think it's the shortest distance between the central point and the path the light would have taken if it hadn't been deflected?

0 comments

adtac2y ago

The Schwarzschild radius [0], which defines the radius at which the escape velocity equals the speed of light, is given by 2GM/c^2. I don't know what the impact parameter is either, but given these two expressions, it sounds like b is dimensionless.

I don't know how fast the radius of curvature drops off as a function of the Schwarzschild radius, but I'd imagine it's at least R^-1. So assuming a spherical cow^H^H^H oven with gravitational lensing dying out at ~100x the event horizon, we need a Schwarzschild radius the size of a tennis ball in order to still see the curvature a few metres out. The oven needs to weigh ~4x the Earth's mass for that.

[0] https://en.wikipedia.org/wiki/Schwarzschild_radius

treeman792y ago

There is also Superman’s key. Made of neutronium.

https://dcmovies.fandom.com/wiki/Fortress_Key_(All-Star_Supe...

Last I tried to calculate (poorly), if you were to touch it. You liquify and be sucked into it just before contact.

ben_wOP2y ago

(Superhero physics is vague and unrealistic at the best of times).

Assuming "dwarf star material" means "neutronium" (which is unstable at any level less than a neutron star) and the "half million tons" mass quote for the key…

That's about the energy content of all the world's fossil fuel reserves being released in a 10 minute half-life.

j / k navigate · click thread line to collapse