# Where does the kinetic energy come from if galaxys are moving apart due to the expansion of the universe?

We know the universe is expanding because of the red shift of far away galaxies, the further away the galaxies are the faster they recede. We also know that the energy in the universe (mass and other forms) will slows the expansion. If there is enough energy we will end up with the big crunch and if not enough, the slow death. (Please correct me if there is a fundamental error in the above)

So it seems to me that if there was less mass energy (or at least less than currently) in the universe then the the size (volume) of the universe would have been greater than it is due to the (Mass) energy it currently has ( ie a larger volume, 13 billion years after the big bang.)

Now if space ("the vacuum") has energy, (ie so and so joules per cubic meter,) then a larger volume would have a larger energy content. (assuming the same energy density of course.)

Assuming that energy can't be created or destroyed so that the total energy of the universe is constant ( maybe a dodgy assumption ...but anyway..) Then the total vacuum energy of the universe is less due to the matter and stuff in the universe than the vacuum energy would be if there was less matter and stuff in the universe. (assuming the energy density of the vacuum is the same in the two scenarios.).

But all the galaxies are receding from each other, so they are all ncreasing their kinetic energy (ie moving faster).

So on the one hand we have more kinetic energy (moving galaxies) and on the otherhand less vacuum energy (smaller volume due to the effects of mass/gravity)

So my question is, could mass somehow be converting the vacuum energy into the kinetic energy?

ie Kind of sucking space into mass which would cause effects similar to gravity , and of course, the moving space would give rise to different geometries of the space much like the different geometry of water flowing down a plughole vs when the plug is in place and as such "bends space" to give gravity ala general relativity.

• Read Dark energy here at en.wikipedia.org/wiki/Dark_energy Oct 7, 2015 at 16:15
• Oct 7, 2015 at 16:29
• So Dark enregy is causes the expansion, but we have no idea what it is which is why it is dark, so that doesn't really explain anything, and if energy isn't conserved in an expanding universe, then where does the "new" energy come from.... Perhaps you can quote the experiment that "proves new energy is being created all the time int he expanding universe"?
– andy
Oct 8, 2015 at 12:04
• And "dark energy" creates or destroys energy in the universe so energy is not conserved? Are you trying to tell me this is a scientific proven fact.. Is it not just a proposition, because nobody understands what we are seeing.
– andy
Oct 8, 2015 at 12:16
• Conservation of energy is a local phenomenon in general relativity. It cannot be applied to a collection of different inertial frames. Dec 24, 2016 at 20:23

Apparent velocity of distant galaxy is not real velocity, and its acceleration doesn't mean its real momentum has raised (no perceived pseudo-force in its referential, for instance): it is the space in between that have elongated. So it does not make sense to consider this as kinetics energy (or as the temperature of a "universe gas"). Indeed at a distance (= "event horizon") you would find that this energy is infinite. Or... considering the time compression, you could consider that its apparent clock is frozen, and consider various related energy measurements as null (e.g. through wavelength of radiations). And for greater distances, things no longer even make sense.

To wrap up, apparent velocity (or acceleration) of objects are not real properties of objects, and as such are not bounded by objects physical limits and equations (they can go faster that light as a shadow can, and you wouldn't consider the kinetic energy of a shadow as well ;-) ).

• so you are saying that the far galaxies are not moving away from us with a real veocity? Just an "apparent" velocity? Therefore as kinetic energy has only to do with "real" velocity" there has been no gain in kinetic energy of galaxy moving away from us? So they are not really moving away from us?
– andy
Oct 12, 2015 at 13:46
• And The observed dipole indicates that the Solar System is moving at 368+/-2 km/sec relative to the observable Universe in the direction galactic longitude l=263.85o and latitude b=48.25o with an uncertainty slightly smaller than 0.1o. And so you are saying that far away galaxies dipole anistropy hasn't changed despite the fact that they are receding away from us? Can you quote an experiment that proves this?
– andy
Oct 12, 2015 at 13:48
• For those far away galaxy we are moving away ultra-fast, and for some we are even at relativistic appearent speed (and for some, we disappeared behind the event horizon since we ran further than c). BTW, for them we are apparently accelerating. Still, we could measure absolutely no (pseudo)force corresponding to this acceleration, contrary to what happen in you car when you accelerate or turn. So, the whole point is that "distance is growing and accelerating (which is the most important)" is a property of space in between, not a property of objects. Oct 12, 2015 at 14:58
• And that is exactly my point. "distance is growing and accelerating" If there was less mass in the universe ( and hence less gravity) then "distance would grow and accelerate faster" SO somehow the mass ( and hence gravity or the otherway around) slows the "distance growing and accelerating" HOw does it do this? My conclusion is then that mass must somehow absorbs space. ie it is a local (quantum?) phenomenon If mass then absorbed space, then would any mass then not distort space around the mass? ie end up with GR from such a (quantum ?) phenomenon?
– andy
Oct 12, 2015 at 15:25
• I just thought using the kinetic energy and the volume difference, you could then calculate things, it doesnt have to be the whole universe, you could take 2 given volumes ( spheres say) of space, one with mass in it and one without, and from the center of both calculate the change in velocities of the masses at a later time (relative to the center of the sphere) and the difference in volumes at the later time.
– andy
Oct 12, 2015 at 15:36