3 ms·

Sure, but the amount of kinetic energy (in sensible frames of reference) isn't really significant compared to the amount of energy locked up as mass energy of s

Sure, but the amount of kinetic energy (in sensible frames of reference) isn't really significant compared to the amount of energy locked up as mass energy of stuff. To close approximation the kinetic energy of something is 1/2 * mv^2 and the mass energy is m c^2 so to have a meaningful contribution to the total energy thespeed has to be close to the speed of light. We generally don't observe big things (stars, black holes, galaxies) moving anywhere near to that fast and their energy is basically entirely due to their mass rather than their speed.

ganzuul 5y ago
Wouldn't that stuff have taken leave right at the beginning?
- eigenket 5y ago
  Things can't really "leave", well they can, but the best guess we have is that there is no particularly special place in the universe, everywhere is roughly the same. So if even if all the really speedy stuff from here "left" we'd see the speedy stuff arriving from other places.
  - ganzuul 5y ago
    I thought 'no special place' was meant to say physics was the same everywhere; not the environment. If you have a sparse gas with a random distribution of velocities and you let it sit for a while, you will find that the outliers on the upper end have have moved further away from cluster center. They have boiled off.
    - 8note 5y ago
      On average though, you'll find similar outliers in whatever direction you look.
    - eigenket 5y ago
      The point is that as far as we can tell there isn't a "center" of the universe.
      - ganzuul 5y ago
        Because it is an open set?
      - scotty79 5y ago
        Try simulating this: Start with bunch of objects at coordinates 0,0,0. Give them random velocities from 0 to c. Then just let them move according to Newtons laws of motion, ignore gravity. Now focus on single random object and narrow down your field of view so you won't see the edge. Look at other objects. They will seem to be moving away directly from the point you focused on with velocities proportional to distance from it. I made such simulation and calculated that the relative velocities of other points face directly away from the point I'm observing. And they really do. There's definitely a center of this system, yet from the point of view of any object far enough from the edge to not be able to see it, it seems like there's no center and other objects just move away from us, and from each other with speed proportional to the distance.
        317070 5y ago
        But in that model you would not see a uniform distribution of objects within your field of view. It's observably anisotropic, while we observe the universe to be isotropic.
        scotty79 5y ago
        In that model if you can't see the edge because you are far enough from it the distribution you observe is exactly isotropic regardless of which object you choose as your point of view. Same way that you can't figure out where the center is, you can't figure any special direction or plane. Try sumulating this model yourself. Everything looks exactly as if you were in the center of Big Bang, even when you are not.
- scotty79 5y ago
  Not really if the initial speeds were random from 0 to c. Some stuff would leave but some would stay relatively close. And you wouldn't be able to tell what's your speed when you look at how other stuff moves. Everythin would look like moving away from you with speed proportional to the distance.
scotty79 5y ago
Really? Distatnt galaxies move away from each other at insane speeds. That seems like a plenty of kinetic energy to me... What if kinetic energy is the only thing responsible for galaxies moving away from each other? Or at least the bulk of it? Maybe the part that we interpret as a period of super fast inflation right after the big bang? Maybe this rapid inflation is just a way of interpreting matter having huge amount of kinetic energy relative to each other right from the beginning?
- eigenket 5y ago
  That would mean that we are (as in our galaxy is) in a very, very special position because we see all distant galaxies moving away from each other with velocities proportional their distance from us. This is exactly what we would expect if the universe is expanding isotropically but under the "galaxies actually moving away from each other" hypothesis this is only possible if Earth is exactly at the center of a sort of "explosion of galaxies". A second issue with this theory is that we see objects with redshifts that would mean that if their apparent motion is actually real motion then they would be moving away from us faster than the speed of light. As far as we know this is completely impossible for actual motion but is exactly what we would expect from expansion.
  - scotty79 5y ago
    Not really special. Try simulating this: Start with bunch of objects at coordinates 0,0,0. Give them random velocities from 0 to c. Then just let them move according to Newtons law. Now focus on single random object and narrow down your field of view so you won't see the edge. Look at other objects. They will seem to be moving away directly from the point you focused on with velocities proportional to distance from it. I made such simulation and made calculations to ensure that the velocities of other points face directly away from the point I'm observing. And they really do. Even in completely flat Newtonian universe there could have been a sort of Big Bang with epicenter and it could be as simple as "give matter random speeds" and we living on a one speck of matter would have no way to figure out that there is a center or where is it. When I asked about this on physics stack exchane I got a shurg that, yeah cosomology is basically that but with Einstein not Newton. All that talk about spacetime inflating is just a result of matter 'dragging' the spacetime along as it moves. The faster than light galaxies far away are not a problem because the speed of their movement that we measure is sum of their kinetic movement (which could be almost at light speed) and expansion of the space time between us and them as the spacetime is 'dragged' by them with GR. But you can equally well interpret the math and data as galaxies roughly at rest and all the speed coming from spacetime expansion and for I have no idea what reasons people actually prefer to do that.

ganzuul 5y ago

Wouldn't that stuff have taken leave right at the beginning?

eigenket 5y ago
Things can't really "leave", well they can, but the best guess we have is that there is no particularly special place in the universe, everywhere is roughly the same. So if even if all the really speedy stuff from here "left" we'd see the speedy stuff arriving from other places.
- ganzuul 5y ago
  I thought 'no special place' was meant to say physics was the same everywhere; not the environment. If you have a sparse gas with a random distribution of velocities and you let it sit for a while, you will find that the outliers on the upper end have have moved further away from cluster center. They have boiled off.
  - 8note 5y ago
    On average though, you'll find similar outliers in whatever direction you look.
  - eigenket 5y ago
    The point is that as far as we can tell there isn't a "center" of the universe.
    - ganzuul 5y ago
      Because it is an open set?
    - scotty79 5y ago
      Try simulating this: Start with bunch of objects at coordinates 0,0,0. Give them random velocities from 0 to c. Then just let them move according to Newtons laws of motion, ignore gravity. Now focus on single random object and narrow down your field of view so you won't see the edge. Look at other objects. They will seem to be moving away directly from the point you focused on with velocities proportional to distance from it. I made such simulation and calculated that the relative velocities of other points face directly away from the point I'm observing. And they really do. There's definitely a center of this system, yet from the point of view of any object far enough from the edge to not be able to see it, it seems like there's no center and other objects just move away from us, and from each other with speed proportional to the distance.
      - 317070 5y ago
        But in that model you would not see a uniform distribution of objects within your field of view. It's observably anisotropic, while we observe the universe to be isotropic.
        scotty79 5y ago
        In that model if you can't see the edge because you are far enough from it the distribution you observe is exactly isotropic regardless of which object you choose as your point of view. Same way that you can't figure out where the center is, you can't figure any special direction or plane. Try sumulating this model yourself. Everything looks exactly as if you were in the center of Big Bang, even when you are not.
scotty79 5y ago
Not really if the initial speeds were random from 0 to c. Some stuff would leave but some would stay relatively close. And you wouldn't be able to tell what's your speed when you look at how other stuff moves. Everythin would look like moving away from you with speed proportional to the distance.

scotty79 5y ago

Really? Distatnt galaxies move away from each other at insane speeds. That seems like a plenty of kinetic energy to me... What if kinetic energy is the only thing responsible for galaxies moving away from each other? Or at least the bulk of it? Maybe the part that we interpret as a period of super fast inflation right after the big bang? Maybe this rapid inflation is just a way of interpreting matter having huge amount of kinetic energy relative to each other right from the beginning?

eigenket 5y ago
That would mean that we are (as in our galaxy is) in a very, very special position because we see all distant galaxies moving away from each other with velocities proportional their distance from us. This is exactly what we would expect if the universe is expanding isotropically but under the "galaxies actually moving away from each other" hypothesis this is only possible if Earth is exactly at the center of a sort of "explosion of galaxies". A second issue with this theory is that we see objects with redshifts that would mean that if their apparent motion is actually real motion then they would be moving away from us faster than the speed of light. As far as we know this is completely impossible for actual motion but is exactly what we would expect from expansion.
- scotty79 5y ago
  Not really special. Try simulating this: Start with bunch of objects at coordinates 0,0,0. Give them random velocities from 0 to c. Then just let them move according to Newtons law. Now focus on single random object and narrow down your field of view so you won't see the edge. Look at other objects. They will seem to be moving away directly from the point you focused on with velocities proportional to distance from it. I made such simulation and made calculations to ensure that the velocities of other points face directly away from the point I'm observing. And they really do. Even in completely flat Newtonian universe there could have been a sort of Big Bang with epicenter and it could be as simple as "give matter random speeds" and we living on a one speck of matter would have no way to figure out that there is a center or where is it. When I asked about this on physics stack exchane I got a shurg that, yeah cosomology is basically that but with Einstein not Newton. All that talk about spacetime inflating is just a result of matter 'dragging' the spacetime along as it moves. The faster than light galaxies far away are not a problem because the speed of their movement that we measure is sum of their kinetic movement (which could be almost at light speed) and expansion of the space time between us and them as the spacetime is 'dragged' by them with GR. But you can equally well interpret the math and data as galaxies roughly at rest and all the speed coming from spacetime expansion and for I have no idea what reasons people actually prefer to do that.