## Stream: maths

### Topic: black hole

#### Kenny Lau (Apr 11 2019 at 02:05):

can we prove that the picture we saw yesterday is that of a black hole?

#### Kevin Buzzard (Apr 11 2019 at 03:18):

I'm not even sure we can prove that anyone saw anything

#### Kenny Lau (Apr 11 2019 at 07:21):

maybe we can prove that 1/u+1/v=1/f

#### Keeley Hoek (Apr 11 2019 at 07:47):

(I could just google this, but) is gravitational lensing even the same as the optical kind?

no

#### Mario Carneiro (Apr 11 2019 at 08:07):

optical lensing happens because the speed of light is slower in a medium, and gravitational lensing happens because space isn't flat

#### Scott Morrison (Apr 11 2019 at 08:22):

Media aren’t “optically flat”?

#### Mario Carneiro (Apr 11 2019 at 08:44):

I see the resemblance, but I would still argue that they are really different. As another analogy, with gravitational lensing the light goes straight the whole time, and comes out going a different direction somehow. In the material case you can locally "see" the distortion at a medium boundary or change in refraction index

#### Mario Carneiro (Apr 11 2019 at 08:46):

Of course I don't need to explain to a room of mathematicians the weird things that "straight lines" can do on curved manifolds, even when there is no curvature (e.g. flat torus)

Last updated: May 10 2021 at 08:14 UTC