Since light cannot pass through a black hole does that mean light has mass? Also why does light form a singularity in a black hole? Is that like a fixed point on a map or something?

Don_Dickle@lemmy.world · edit-2 7 days ago

Since light cannot pass through a black hole does that mean light has mass? Also why does light form a singularity in a black hole? Is that like a fixed point on a map or something?

pomegranatefern@sh.itjust.works · 6 days ago

Light in a vacuum does not have rest mass, because there is no frame of reference where you can measure light at rest, because light famously always moves at the speed of light in any reference frame. You could define mass as including the kinetic energy, and physicists did at one point define mass that way, but it led to less intuition and more complicated math and definitions, so they dropped it to only really consider rest mass. (Good video on it here: https://www.youtube.com/watch?v=wiBsfvW5AWY)
What exactly do you mean by the velocity of a black hole? Do you mean the velocity it’s moving through space with respect to an observer? Is this about how the universe can expand at a speed that’s calculated to be above the speed of light?
Once it’s in a black hole, it’s not coming out.

This is a long playlist but I recommend watching the videos that jump out at you: FloatHeadPhysics is really good at helping explain relativity and quantum mechanics without complicated math and building intuition. https://www.youtube.com/playlist?list=PLawLaqps30oAcpVd4r-wj8hGodzpPRYTT