Comment by modeless
1 day ago
This piece argues that antimatter could be feasible for space propulsion and we could start developing it now: https://news.ycombinator.com/item?id=46073414
1 day ago
This piece argues that antimatter could be feasible for space propulsion and we could start developing it now: https://news.ycombinator.com/item?id=46073414
For those who are time-rich and knowledge-poor:
https://youtube.com/watch?v=i6jMnz6nlkw
(Angela is genuinely a great science communicator and that video is time well spent if you are interested in this topic.)
You can skip the first 42 minutes that are about how bad is an article titled "how antimatter space craft will work". This part is absolutely boring as hell !
But also relevant to the topic…
Angela is great, albeit her rants can get quite windy.
If you can electromagnetically trap enough antimatter to use it as fuel you could as well trap a miniature charged black hole that can be fed regular matter to produce power, which skips the whole inefficient part of making antimatter.
Miniature black holes would just evaporate. Antimatter wouldn't.
That's the point, evaporation turns matter into energy. You can tune power by chosing mass of the black hole and then feed it regular matter at a steady rate.
Minor nit-pick but Hawking Radiation hasn't been observed and remains a theoretical prediction.
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Not before efficiently converting a large amount of mass into usable energy.
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Depends. Do we know how to obtain a miniature black hole?
There have been several proposals. This paper proposes a feasable mechanism[1]:
-"a SBH could be artificially created by firing a huge number of gamma rays from a spherically converging laser. The idea is to pack so much energy into such a small space that a BH will form."
1. https://arxiv.org/abs/0908.1803
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We know how to make antimatter and have actually done it. We have no realistic way to obtain a black hole of any size.
If you can create enough AM to last a space voyage you certainly know how to build big enough particle accelerators.
They made a movie about this. It didn’t end so well for the crew.
I admit to invoking the phrase “Where we’re going, we won’t need eyes to see” at least once a year when something feels like it’s going horribly wrong.
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The romulan empire does this.
> a miniature charged black hole that can be fed regular matter to produce power,
What form of power and through what principle?
Hawking radiation, I think. Yes, this is at best speculatively feasible.
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Before we get too excited, this current "breakthrough" is making less than 1 antihydrogen atom per second. This corresponds to a delivered annihilation power of less than 1 nanowatt.
Neutrons were first definitively observed in 1932.
First nuclear reactor was 1942, and bomb was 1945.
Once the science is established, we have smart engineers to make a short work out of it.
Fusion energy is really the only counterexample in history, which makes me think we are still missing some crucial physics about how it works, for example in stars. Specifically the particle physics view of how it's reliably triggered with minimal energy.
The antiproton decelerator at CERN has been operational for 25 years, and they have plenty of smart engineers there. Unlike in the 1940s, the underlying physics has been well understood for many decades. I would argue that nuclear fission is the counter example that happens to be surprisingly easy to do.
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> Fusion energy is really the only counterexample in history, which makes me think we are still missing some crucial physics about how it works
This is magical thinking. We know how fusion works in great detail. And “reliably triggered with minimal energy” is essentially not a thing, unless by minimal energy you mean something like 10 million times the energy of an air particle at room temperature, for every particle in a reactor.
What we’re trying to do is recreate the conditions at the core of a star - which is powered by gravity due to hundreds of thousands of Earth masses. And since we don’t have the benefit of gravity anything like that, we actually have to make our plasmas significantly hotter than the core of a star. And then contain that somehow, in a way that can be maintained over time despite how neutron radiation will compromise any material used to house it.
The reality is, we still don’t know if usable fusion power is even possible - there’s no guarantee that it is - let alone how to achieve it. The state of the art is orders of magnitude away from even being able to break even and achieve the same power out as was put into the whole system.
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There was also a great episode on antimatter engines recently by PBS Space Time.
https://www.youtube.com/watch?v=eA4X9P98ess
What's the key point regarding how we would get a bajillion times more anti-matter than we can now generate, and without expending all the energy we now expend on getting it?
His point seems to be that we haven't yet seriously tried optimizing for energy efficiency of producing antimatter. It's a call to action. If we actually tried it's plausible that we could get to a level that, while still fantastically inefficient in an absolute sense, would still be worthwhile for spaceflight propulsion, where energy density is vitally important. As far as I know, antimatter is the most energy dense fuel possible in known physics by many orders of magnitude.
Also he proposes a few ways that antimatter could be practically used for propulsion, including as a catalyst for fission which seems interesting.