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 !
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.
It's a pretty fundamental prediction though, and it's been derived in many different ways, all of which give the same prediction.
It's closely related to the Unruh effect, which is a direct consequence of pure QFT. The Unruh effect describes how an accelerated observer sees a different vacuum from an inertial observer - they see radiation that the inertial observer doesn't.
Hawking radiation is essentially this same effect, except that "acceleration" is replaced by "gravity" (Einstein's equivalence principle.) There's a bit more to it, but that's the basic intuition.
For Hawking radiation to be wrong would require some fundamental changes to GR, QFT, or both.
A lot of great science progress followed after some "fundamental prediction" turned out to be wrong :). Wouldnt it be awesome to learn that blackholes, in fact, do not evaporate at all? That would be exciting
> A lot of great science progress followed after some "fundamental prediction" turned out to be wrong
For example? What I mean by “fundamental” is that we have very strong reasons to believe in the correctness of a prediction, because e.g. it follows mathematically from more than one model (in this case), and doesn’t involve dependence on uncertain physics.
> Wouldnt it be awesome to learn that blackholes, in fact, do not evaporate at all? That would be exciting
These kinds of attitudes don’t seem to me to involve an interest in science. You don’t appear to actually have much understanding or knowledge of what we’re discussing. You’re just looking for a fix.
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.
It's much easier to make a fission reactor than a fission bomb, and much easier to make a fusion bomb than a fusion reaction. They are not even that similar.
It's way easier to make a fission bomb than a fission reactor. I reactor has to stay in the very narrow window where it's critical but not prompt critical. Even pure fission bombs can be marvels of engineering but the simplest gun-type bomb is easier to build than the simplest nuclear reactor.
Without a precisely timed neutron initiator you'll get a fizzle. Either way, gun-type bombs require highly enriched uranium. A simple reactor can be literally just brickwork of natural uranium and graphite.
Reactors are much much simpler to pull off, which is why US had the first reactor whole 2.5 years before a nuclear bomb.
Something that explodes with the force of 100 tons of TNT is still a bomb, even if it isn't a bomb as impressive as the one you were hoping for. And getting the reactor you're thinking of to the point that it worked without exploding took a lot more effort than you're suggesting.
You can even dissolve the uranium in the water and use the same substance for both fuel and propellant and so capable of reaching far higher temperatures than those that would cause any engine to melt.
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."
The biggest problem is that if you're creating it with lasers, you're only going to get the energy out that you put in. You really want to be able to feed it matter, which would effectively make it an anything-to-gamma-radiation converter, which means you have to feed it quite a lot of matter, against the radiation pressure of all that energy coming out. The paper mentioned assumes a worst case of not being able to feed the black hole at all, but doesn't (in my skim) address the fact that this means you have to put in all the energy you'll be using for the lifetime of the black hole at the creation of it, which seems significantly more outrageously infeasible than the bare necessity of creating a black hole at all.
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.
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.
All experiments at the AD are strongly limited by the low rates. If there was a straightforward way to improve this by many orders of magnitude, they would have done it a long time ago.
> 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.
> at the core of a star - which is powered by gravity
That is what I meant, I doubt we really understand what 'powered by gravity' means. You could win a Nobel prize or two by discovering all the details involved here. You would also win a Nobel prize by definitively proving that nothing special happens, you just have high temperatures and high pressures.
The way we are trying to study fusion is like rubbing larger and larger rocks to produce more fire.
The processes involved in solar fusion have been well understood since the 1930s [1,2]. Hans Bethe won a Nobel Prize for this in 1967. The problem is that one cannot produce stellar densities and pressures in any kind of apparatus.
We have an extremely good understanding of how gravity operates, both inside and outside of stars. There are no Nobel prizes waiting for things you describe, because that’s all well-established and settled science.
Quantum physics tells us exactly why high temperatures and pressures are needed, and predicts numerically what values are needed. We have a great deal of confidence in its correctness, especially because classical physics predicted values that were far too high - it’s only with quantum tunneling that we get values that match observations.
> The way we are trying to study fusion is like rubbing larger and larger rocks to produce more fire.
This is an incorrect opinion borne of ignorance of the very well-understood physics involved.
I'm amused at your confidence in stating that we have a good understanding of what's literally the most prominent open problem in physics, gravity at small/particle scales.
We do have an extremely good understanding of how gravity causes stellar fusion. We don't need quantum gravity to model that. The gravitationally-induced pressure due to the star’s total mass provide the conditions needed for fusion.
If you're thinking along the lines that if we knew how gravity worked at the quantum scale, we might find some sort of way to achieve fusion under much less extreme conditions, we probably can't entirely rule that out, but there's been many decades of work in that area, so it's seeming pretty unlikely. Also, that has nothing to do with what's happening inside a star.
We know about the need to overcome the electrostatic Coulomb barrier, we know what energies are required to overcome it and have models that predict those energies very accurately, we know how quantum tunneling allows this barrier to be penetrated, etc.
We can even do things like muon-catalyzed fusion, where we substitute muons for electrons in hydrogen atoms, which lowers the Coulomb barrier.
As such, the claims in the comment I originally replied to were just completely wrong.
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.
