Instant IQ test: If you think the speed of light is a constant, you fail. Though this is what is taught in every university, it's provably false.
It should be self-evident, for example, that the speed of light slows when entering water, or a prism, or any any refractive solid. I'm not going to bother explaining this if you don't already know it.
So then people say no, the speed of light in SPACE is a constant!
That's not true either. We already know that light follows the curvature of spacetime, which is impacted by the "gravity" projection of mass.
That alone tells you that light's speed, relative to us, depends on the fabric of spacetime. If you stretch spacetime, light appears to move faster. If you condense it, light appears to move more slowly. If you bend spacetime, light follows the bend because from the point of view of the light, it's still traveling in a straight line... but REALITY is now curved.
And at the event horizon of a black hole, right at the edge, the "speed" of light, of course, reaches zero.
Obviously.
So no, the speed of light is not a constant. That's maybe 7th grade physics. Most people still believe it, though. Which just tells you that people don't think much beyond whatever they were told in the name of "science."
REAL scientists are people who are curious about the universe. Those are precisely the people who are called "anti-science" by the authoritarian science establishment which insists you question nothing and swallow everything.
Like a black hole swallowing light.