10-03-2020, 11:58 PM
(10-03-2020, 08:42 PM)Bear Wrote: Specifically, about gravity waves. In the same way you can take a static force like magnetism and make it oscillate, creating electromagnetic energy, black hole mergers take a static force like gravity and make it oscillate creating gravity-wave energy.
A static force doesn't have energy, and therefore the force itself doesn't have mass. Gravity waves are different, because gravity waves do have energy. And since Einstein worked out E=mc2, we know that means they also have mass.
And so the mass of the universe includes the energy expressed as gravity waves, in exactly the same way it includes the energy expressed as light waves.
Erm. I don't think it's accurate to say gravity waves have mass in and of themselves any more than it's accurate to say that light has mass. Matter and energy are interchangeable and can be neither truly created or destroyed, just converted. Stars shining convert matter into energy, they don't create energy out of nowhere. Similarly, black hole mergers or other events that generate large amounts of gravity waves are converting the mass of the black holes or some other form of mass-energy into gravity waves, not creating them out of nothing.
As far as the contribution of gravity waves (and light) to the total mass of the universe -
While 9 solar masses of gravity wave energy is impressive by the standards of our current civ, it's really utterly insignificant when compared to the hundreds of billions to a trillion solar masses of a galaxy like the MW or Andromeda. Similarly, while the amount of EM radiation produced by a star (of a galaxy) is huge by the standards of our RL civ, the real question is what it works out to as a percentage of the total mass of all the stars (and possibly nebula and to a tiny degree the planets orbiting the stars - although the last is so insignificant as to likely be something we can ignore at least for a first approximation).
As far as taking even a first shot at figuring out how much mass-energy is tied up in radiation zipping back and forth across the universe since the Big Bang - it should be possible to produce at least a rough initial number and then compare that against the estimated mass of dark matter/energy believed to exist in the universe based on current observations. Let's see...
Per Wikipedia, the estimated annual energy output of the Sun = 1.2e34J
Multiply that by the age of the sun - ~ 5 billion years
Multiply that by the estimated mass of the MW galaxy in solar masses. Assume that each solar mass is a star like the sun (obviously it's not, but this is a rough first approximation).
Multiply by how much older the universe is than the Sun - Maybe x3? or x2.5?
Multiply by the estimated number of galaxies in the universe
Possibly multiply by some value for a fudge factor to allow for additional galaxies we haven't found yet and/or things like gravity waves. Maybe just up the number from everything before by 1-2 orders of magnitude to be 'conservative'.
Take the resulting value and run it backward through E=mc2 to get how much mass that adds up to.
If the result is only a tiny fraction of the estimate mass or mass-energy of the universe, then it seems unlikely that radiant energy - in whatever form - is contributing in any significant way to the missing mass in the universe.
Interestingly enough this Wikipedia page - LINK -also lists the total mass-energy of the MW and the Virgo Supercluster including dark matter and dark energy. Not sure if that might impact anything but it might provide a basis of comparison somewhere along the way.
Just some thoughts,
Todd