Re: Will Dark Energy ever replace Dark Matter? Is that even possible?

Hi Shawn!

That's a great question. You're correct in thinking that, as the Universe expands, new dark energy appears. However, in our current model, the dark energy isn't replacing anything. All of the original ordinary matter is still there, and all of the original dark matter is still there. The dark energy, however, will continue "appearing" as long as the volume of the Universe gets bigger---the energy seems to be associated with empty space itself. The expansion of the Universe makes new empty space, and this space (for unknown reasons) seems to have gravitational energy in it by default.

Anyway, if you've got two fixed energy sources, and one expanding source, the first two sources will make a lesser and lesser proportion of the total budget. But this is different than "replacement", isn't it?

By the way, there's not necessarily a distinction between dark matter and visible matter in this scheme. A black hole, for example, doesn't care whether it formed by sucking in dark matter or visible matter. Also, if our theories are right, dark matter can be turned into visible matter (and vice- versa) by high-energy collisions. (For example, the Large Hadron Collider---a proton-proton supercollider---may manufacture a handful of new dark-matter particles; some telescopes can look for dark-matter particles colliding and turning into photons and neutrinos.) So, perhaps we should just say that the "ordinary mass" budget is fixed, and the dark energy is growing. The ordinary mass is a nearly fixed (but not exactly fixed) mixture of dark and visible matter.

There's another place where we have to be careful: I always want to say that the "ordinary mass density is fixed". But it isn't---the density is decreasing all the time, since the Universe is expanding and things are spreading out. It's also hard to say the "total ordinary mass in the Universe is fixed"---but here you have to be careful about where you draw the boundaries of the Universe. Things do get a bit complicated! But it sounds like you're off to a good start in thinking about it. Good luck!

Cheers,

-Ben