How can blackholes warp time? What is time?



Im kinda piggybacking from an older post, where the OP asked what exactly time is. How can the blackholes warp time, if time (as i know) only a measurement on how old everything is?

In: Physics


*Age* is a measurement of how old something is.

Time is a measurement of the rate of change.
An object’s “time” is also described relative to another thing’s “time”.

Time and space are (as far as we know) bound together and inseparable. If an object is massive enough to distort space it will also distort time.

A black hole is a really massive object compared to the earth, so space (and this time) become stretched, and elongated. Time around it moves slower *relative* to the time on earth.


Here is an interesting and possibly helpful perspective:

Stationary objects are moving through time but not through space. When you get accelerated by a gravitational field, this means you start moving through space in addition to time.

Because of the way maths in general relativity works, your ‘velocity’ through the 4-dimensional spacetime must always be constant (and equal to the speed of light, *c*). So when you start moving through *space*, this means you slow down in *time* – otherwise your total velocity would be too high.

Incidentally, it’s not just black holes that warp time, *anything* that exerts *any* amount of force warps time, because it’s the act of *moving through space* which is what slows down time. You are warping time every time you walk to the supermarket. The gravitational field is just a good way to accomplish that, since especially black holes can accelerate things extremely well.

Time is an observable phenomenon. Things change. From one state to another. We observe things changing over time, and can measure time by looking at things that change in predictable patters. The sun rises every day, and Caesium-133 wobbles a little faster.

That said, the rate of these predictable events isn’t always the same. We’ve found that at high speed and near mass, the rate of time slows down.

Black holes warp space and time in the same way that ALL mass warps space and time. Warping space is literally gravity. Things fall in. Warping time is another side of that. Like how magnetism and electricity are two sides of the same thing, space and time are likewise related. Near mass, things experience less time.

And none of that answers how it does it.

There have been theories about it being a sort of light gas, working like an electrical field, or with mass emitting gravitons, but those kinda fall short. Recently we saw two black holes merge, which told us some stuff which supports the idea that it’s like radiation. But instead of wave-legths measured in distance, the gravity radiation’s wave-lengths are measured in time. I honestly still don’t quite get it.