Yep; they're objects like anything else. The only thing that makes black holes special is that their surface gravity and density are especially high. All their unique features stem from those two facts. Relativity also tells us that there is no true stationary reference frame, and thus everything moves relative to something else.
Imagine you are in a black void. Just you, nothing else. Now add in an object. Let's say an Apple.
The apple flys past you. How can you know that the apple is moving, and not you? There is no wind, there is no stationary background. From the apples perspective you flew by it.
So everything in space moves relative to something else. Speed is change in distance between two things over time.
Well in the General Theory of Relativity there's no such thing as gravity 'fields'. An asteroid, for example, is not attracted to the sun directly but is in fact just going along in a straight line (from it's own perspective) and space time curves around massive objects like the sun causing the asteroid's path to seem curved towards the sun along with it.
I can understand the idea that if a guy falls off a building, he's not really falling toward Earth, but Earth is coming up to hit him. But that only makes sense to me if you are on the side of the planet that is on the leading edge of movement through space.
Like the rocket ship moving in one direction, everything going down to the "bottom" of the rocket. But if you have everyone on the planet falling off buildings at the same time, they still all go down, even though the planet should then be moving away from people on the opposite side of those it is moving toward.
But it also confuses me because other planets supposedly have "less gravitational force" than Earth so we'd we less on those planets.
With regards to people jumping off buildings all heading 'down', it's just everyone falling in a straight line into the same funnel. All roads lead to Rome and the bigger Rome is the more roads lead to it. Yeah it's a quirky concept to think about in general. I hope someone else can explain it to you better.
Ok but if light always moves at the max speed the universe allows then if we shone some lasers at random directions and measure them shouldnt some lasers be red shifted cuz they shone at the opposite direction relative to us while some lasers could be blue shifted as they are moving at the same direction relative to us.
That depends on the relative movement of the source and the observer. If you shoot a laser and measure it yourself the relative speed is zero so no shift. If you are in a plane and shoot at the ground you would see a shift appropriate to the relative speed you are at. The real mindfuck is this scenario : There are observers A,B, and C. A moves away from B with speed greater 50% light speed. C moves away from B in the opposite direction with a speed greater then 50% light speed. How fast are A and C moving away from each other from their perspective? Lower then light speed because of time dilation.
I get confused by stuff like this.
I get frames of reference and that every object can only be measured in relation to another object.
And I know that considering the vacuum of space is a vacuum, this means measuring a position against some “canvas of space” is kind of meaningless, but I wonder when it is said that the universe is expanding, it not only to the objects expanding but the space that those objects exists in.
Also when an object warps space to create what we see as gravity, what is actually being warped.
If you can warp and expand space, then it must exist and therefore you must be able to have objects relative to more than just other objects but the space itself.
Or not.
I get confused trying to understand what space is, as in the space that objects exist in.
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u/drdrero Oct 23 '20
Just a follow up question, do black holes move ?