Yesterday, my good friend (and SWAB reader) Brian wrote a great comment about the practical reasons to explore space, where he talked about the overall economic impact that Space Exploration has had on the economy, as well as the impact it has had on our knowledge and understanding of the Earth, its environment, and how to manage/mitigate the threats to it. And that’s wonderful for exploring our Solar System and others.
But what do I do in the meantime? After all, this isn’t what I study or explore. So I asked this:
The practical arguments as to why exploration of space is worthwhile certainly hold a lot of water! But by that argument, the stuff that I do — looking for dark matter, trying to figure out dark energy, galaxy formation, the fate and birth and evolution of the Universe, etc. — is completely worthless. I agree that understanding the Universe helps us to understand our place/role in the Universe, but is there then a practical argument for understanding the stuff that is unrelated to us?
And so I thought about it: long-term, is there anything practical about studying dark matter? Well, the most abundant and efficient source of energy in the Universe is nuclear fusion, such as what goes on in our Sun: 4 Hydrogen nuclei fuse into one Helium nucleus, emitting about 25 MeV of energy per Helium nucleus. That’s about 0.7% efficient: for every kilogram of hydrogen that you fuse, 0.7% of that mass becomes pure energy. Is there anything more efficient than that? Sure: if you collide a hydrogen nucleus (a.k.a. a proton) with its anti-matter counterpart (an antiproton), that is 100% efficient!
Well, this happens to all particles and antiparticles: you run them into one another, and what you get out is 100% pure energy. There’s very little anti-matter in the Universe, and most of it would be very very detrimental to a spaceship, as it would annihilate with whatever it came into contact with first!
But dark matter, which we know doesn’t interact much with (and certainly doesn’t annihilate) normal matter, is very special. Because all realistic models of dark matter that we have consist of a very special property: Dark Matter is its own antiparticle! The Universe is also full of dark matter. So, if we could figure out how to collect and collide dark matter particles, we would have a 100% efficient source of energy that would virtually be unlimited. Because finding dark matter is 5 times easier than finding normal matter in the Universe.
Is this a long way off? You bet. But is this, long-term, the most efficient source of energy imaginable? Well, let’s see, at 100% efficient? You bet. And that’s the most practical thing I can think of about dark matter. All it’ll take, I’m sure, are some good sci-fi writers to put this in the public’s imagination!