Show HN: Throw Alice and Bob into Sagittarius A*
github.comBlack Hole Lab is an open source physics simulation of a rotating black hole and two observers, Alice and Bob. You can launch Alice and Bob on paths around or into the black hole and watch events play out. The simulation lets you see a slice of the physics with one or two dimensions of space plus one of time.
As a fun extra, Alice and Bob each have a beacon that can transmit a radio wave in all directions. The simulation calculates and shows the wavefront of these signals, accounting for the warping of space and time by the black hole. The simulation also records whenever Alice and Bob receive each other's transmission.
The simulation takes pains to respect Einstein's equations of general relativity. To the precision of the numerical integration, the effects shown in Black Hole Lab are really what the math of general relativity says will happen. Black Hole Lab specifically uses the Kerr metric, which is an exact solution to Einstein's equations of general relativity for a rotating mass. That said, physicists agree that general relativity cannot be the final word on black hole physics. Nobody can say what would really happen to Alice and Bob.
My original goal for black hole lab was to try to understand the strange time compression effects at the inner horizon, which physicists call infinite blueshift. IMHO, Black Hole Lab succeeds in showing this effect in an understandable way. I added a specific discussion of infinite blueshift in the readme.
Is it possible to compare the rotating version with a non rotating one? There was a recent article about that.
Not possible. Black Hole Lab is strictly the rotating hole case, which is probably every real black hole in our universe. What did you have in mind to compare?
Can't you just put J=0 and get a non spinning one?
I'm wondering about "The Milky Way's fastest star could expose our black hole's spin" https://www.scientificamerican.com/article/the-milky-ways-fa... (Tiny discussion https://news.ycombinator.com/item?id=49377498 and a few more)
Is it posible to simulate that scenario in your program? Is it possible to compare side by side a scenario with the rotating black hole and a magical copy that is not rotating?
If the rotation of the black hole is not perpendicular to the direction of the object, is the orbit not in a plane like in Newton Mechanics?
Yes, you can set spin to zero and still get an accurate simulation since the Kerr solution reduces to the non-rotating Schwarzschild solution when spin = 0. This reduction animates in real time as you move the spin slider control, making it easy to compare the spinning and non-spinning environments.
The program simulates one black hole at a time, but you could run two simulations simultaneously.
At least one physics physics problem is that the simulation assumes Alice and Bob lie on the perfectly equatorial plane vs. a real star with an inclined orbit.
Interesting idea though.