Black hole darkness a result of gravity or temporal distortion?

Question

Please correct me if I am wrong as I may have made some incorrect assumptions.

Okay so we know that at some stage of "nearness to a black hole", light is no longer reflected back at us from the black hole itself. Some scientists have proposed the speed of light and it's relationship to relativity is natures way of adjusting the rate at which time passes seemingly to disallow "weirdness that could result" .. for example the fast moving object would become more massive.

We also know that the mass of the black hole causes a nearby observer to behave as if he/she were moving at incredible speeds and subsequently slows time for the observer "relatively speaking of course".

I realize that from the perspective of the observer light is traveling to and away from him/her at it's normal rate even though effectively the observer is traveling very fast. Imagine however what would happen to the frequency of the light. The red/blue shift would undoubtedly be obscene.

Since we here on earth are "relatively speaking" experiencing time passing at our normal "earth rate". I can't help but imagine that immense gravity near a black hole is distorting time and its darkness is a result of either extreme red/blue shift or the light is somehow phased or altered by the temporal distortion. Yes gravity is the origin of the darkness but is the direct cause or an indirect relationship where the rate of time passing is the culprit?

Answer 1

As an object falls towards a black hole, light emitted by the object will become red-shifted by the gravity. As photons rise out of the gravity well of the black hole they lose energy, they can't slow down but their wavelength is stretched. The object will go dark as it approaches the event horizon due to gravitational redshifting.

Photons starting from the event horizon would be redshifted to zero energy, and no photons can travel from inside the event horizon.

We also will observe gravitational time dilation, the last second before the object reaches the event horizon will be stretched out indefinitely. The two effects are all part of the same relativistic theory of gravity. You can't unpick the two effects.

Answer 2

The fact is, the gravity and the distortion of the rate of time are the same thing. A free-falling object follows a spacetime geodesic into the future, which just means a path that is as straight as possible subject to the curvature of spacetime. But "as straight as possible" translates to "the path in spacetime where the traveler experiences the most time passing over all possible paths". That's analogous to the way a geodesic on the Earth is the path with the shortest distance. (The geometry of spacetime is not just the natural 4D generalization of 3D geometry, but instead it's more of an analogue with special rules based on the way physics actually works.)

It turns out that the curve with the most "proper time" (time experienced by the traveler) is one that curves towards wherever time passes more slowly, and time passes more slowly near a massive object. That means that, as you move into the future, your path through spacetime curves towards the massive object. In other words, you move faster and faster towards the massive object. You fall.

And of course it makes sense that a slowing down of time will reduce the frequency of a clock or a beam of light.

And, what's more, the slowing down of time is a part of the curvature. Any time you have the scale of measurement changing as you move from place to place, if it does so in a way that causes geodesics to change, then we call that curvature. And curvature is arguably the fundamental phenomenon. And so I would say that it really is the slowing down of time (along with the deformation of space) that is the basic cause of light not being able to escape.

Answer 3

Gravity is in fact a side-effect or result of spacetime distortion.

Consider this simple diagram:

The blue grid representing timespace, and the orange sphere being a high-mass object.

Moving through space means going from one tile to another, so when light passes into the distorted dip in spacetime it not only has to simply pass from square to square, but do so whilst those squares are being pulled in towards the massive object. For a planet or average star, this distortion is negligible as far as light is concerned, but the dip a Black Hole would make would be many, many times deeper than the above diagram - space would be flowing in to the hole as fast, or faster than light can travel along said space to pass through it.

Like trying to climb up a downwards escalator that always moves faster than you can climb it.

But spacetime flows, it should eventually be dragged out, like pulling a table cloth out from under a load of dishes, but the mass of a black hole is so great, timespace essentially becomes pinned, like jamming your fork into the tablecloth as your friend tries to pull it away; time comes to a standstill at the epicentre of the hole.

It's important to note that at no point does light slow down travelling through the vacuum of space here, it's just space is moving in the opposing direction preventing the light from escaping in any meaningful amount beyond the expected level of Hawking Radiation.