Can Dark Matter be the energy source of the future - a rough estimate

[Alex K]

@tor asked me the question via pn, and I couldn't help but make a back of the envelope calculation. Now I don't know where to dump it, so I thought I'd post it here.

Dark Matter is a substance hypothesized to permeate the entire universe. There is strong indirect evidence from astrophysical observations and the cosmic microwave background that it exists, and we know that it makes up roughly 20-25% of the energy density of the universe, and is therefore at least five times more plentiful than ordinary matter.

The most probable explanation for it is that it exists as a new, as yet unknown, type of elementary particle akin to neutrinos, but heavier.

The dark matter particles would then obviously interact very weakly with ordinary matter, just like neutrinos, and they stream through us permanently without us noticing.

The question is: if we ever discovered a way to stop and collect them and let them annihilate to energy, how much energy can be gained from them?

The calculation goes like this: we need the energy of the dark matter per volume, e,
and the speed with which it flows by us, v. The energy per area per second, so the Wattage which can be collected per square meter is then simply P = e*v.

v can be estimated by the speed with which the earth rotates around the galaxy, 300000 meters/second to be on the conservative side (not all Dark matter will have maximum speed). e is also controversial because it is prone to local fluctuations in density, but estimates are 0.3 GeV/ cm^3, which corresponds to 300000 GeV / meter^3.

This gives us 9*10^10 GeV per square meter per second, or converting GeV to Joules, that's

P_dark matter = 14.4 Watts / square meter.

contrast this with full-on sunshine

P_solar = 1300 Watts / square meter.

So while it is not negligible, it seems that dark matter as an energy source, even if it becomes technologically feasible, will always lose against solar power.

[Angrboda]

Since dark matter might only interact with the weakest of the four forces, gravity, that would likely mean converting it into useful energy would be less efficient than converting other forms of matter which interact more strongly with the other three forces.

[Alex K]

Since dark matter might only interact with the weakest of the four forces, gravity, that would likely mean converting it into useful energy would be less efficient than converting other forms of matter which interact more strongly with the other three forces.

Yes,this weakness of interaction is a (I'd say the) major hindrance and a big if . But there is a good chance that one can convert the mass of the DM to pure energy with 100% efficiency. That's not possible with ordinary matter.