-"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."
Otherwise you just have a bomb.
Reactors are much much simpler to pull off, which is why US had the first reactor whole 2.5 years before a nuclear bomb.
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.
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.
What form of power and through what principle?
Now as to whether you could use all that power....
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.)
Also he proposes a few ways that antimatter could be practically used for propulsion, including as a catalyst for fission which seems interesting.
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.
Also, 25 years to the breakthrough discussed in the article seems like a reasonably good pace.
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.
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.
[1] https://en.wikipedia.org/wiki/CNO_cycle
[2] https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain
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.
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.
is it though? I mean literally everything has to start there and the only way get to heavier elements is via stars and many-many iterations.
it's not like heavier things popped into existence.... or did they...
The alt text is on point.
Earth's biosphere is profoundly 'lucky' on several very disparate time-scales. And then there's the size of the moon...
So we can identify in meteorites or on the surface of other bodies not affected by weather, like the Moon or asteroids, small mineral grains that are true stardust, i.e. interstellar grains that have remained unchanged since long before the formation of the Earth and of the Solar System.
We can identify such grains by their abnormal isotopic composition, in comparison with the matter of the Solar System. While many such interstellar grains should be just silicates, those are hard to extract from the rocks formed here, which are similar chemically.
Because of that, the interstellar grains that are best known are those which come from stellar systems that chemically are unlike the Solar System. In most stellar systems, there is more oxygen than carbon and those stellar systems are like ours, with planets having iron cores covered by mantles and crusts made of silicates, covered then by a layer of ice.
In the other kind of stellar systems, there is more carbon than oxygen and there the planets would be formed from minerals that are very rare on Earth, i.e. mainly from silicon carbide and various metallic carbides and also with great amounts of graphite and diamonds.
So most of the interstellar grains (i.e. true stardust) that have been identified and studied are grains of silicon carbide, graphite, diamond or titanium carbide, which are easy to extract from the silicates formed in the Solar System.
And elements down to the mass of iron can also be formed. But iron is at the bottom of the well.
The Universe that we can see has started from a mixture of equal amounts of free neutrons and protons (at a temperature of a few tens of MeV, matter has the simplest possible structure, consisting of free neutrons, free protons, free electrons, free positrons, photons and various kinds of neutrinos; upon cooling, nuclei form, then positrons annihilate, then atoms form), which have formed in the beginning hydrogen, helium and some lithium. Then, through fusion, the next elements until iron have been generated.
Iron is not the last element generated, a few elements after it have also been generated by fusion, because while they have lower binding energies than iron, their binding energies are still greater than of the lighter elements that can fuse into them.
However after the peak of the iron, the abundance of the following elements generated by fusion drops very quickly, e.g. down to germanium that is about 8 thousand times less abundant than iron.
The elements heavier than germanium are produced only in negligible amounts by fusion. They are produced mostly by neutron capture and sometimes by proton capture, and such events happen mostly during supernova explosions or neutron star collisions, because only then high concentrations of neutrons with high energies are present.
Neutron capture produces elements with Z until 100, i.e. until fermium (after that, spontaneous fission happens too fast, before beta-decay can raise the Z and enough extra neutrons can be captured to form a nucleus with long enough half-life). However the half-life of the heaviest elements decreases very quickly with Z, so the elements heavier than plutonium usually decay before reaching a stellar system from the explosion that has generated them. At its formation, it is likely that Earth also contained plutonium (244Pu has a half-life of over 80 million years, enough to survive an interstellar journey), but it has completely decayed until now, leaving uranium as the heaviest primordial element on Earth.
Why shouldn't we observe clouds of anti matter and matter annihilating millions or billions of light years away? Why does the annihilation have to have happened so early on that we can't see any evidence anywhere?
I think there does need to be an explanation and it can't be an anthropic principle cop out.
People who entertain the idea of an initial state with equal amounts of matter and antimatter do this because thus the properties of the matter that are conserved, except the energy, would sum to zero in the initial state.
However, such people forget that not only the particle-antiparticle pairs that can be generated or annihilated through electromagnetic interactions have this property that the conserved quantities except the energy sum to zero.
The particle-antiparticle symmetry is important only for the electromagnetic interactions, while other interactions have more complex symmetries.
All the so-called weak interactions are equivalent with the generation or annihilation of groups of 4 particles, for which all the conserved properties except energy sum to zero. Such a group of 4 particles typically consists of a quark, an antiquark, a charged lepton or anti-lepton and a neutrino or antineutrino.
For instance the beta decay of a neutron into a proton is equivalent with the generation of 4 particles, an u quark, an anti-d quark, an electron and an antineutrino. The electron and the antineutrino fly away, while the anti-d quark annihilates a d quark, so the net effect for the nucleus is a change of a d quark into an u quark, which transforms a neutron into a proton.
The generation and annihilation of groups of 4 particles in the weak interactions are mediated by the W bosons, but this is a detail of the mechanism of the interactions, which is necessary for computations of numeric values, but not for the explanation of the global effect of the weak interactions, for which the transient existence of the W intermediate bosons can be ignored.
So besides the symmetry between a particle and an anti-particle, we have a symmetry that binds certain groups of 4 quarks and leptons.
There is a third symmetry, which binds groups of 8 particles. For instance, there are 3 kinds of u quarks, 3 kinds of d quarks, electrons and neutrinos, a total of 8 particles that belong to the so-called first generation of matter particles (i.e. the lightest such particles).
All the conserved quantities except energy sum to zero for this group of 8 particles. The neutrino is necessary in this group so that the spin will also sum to zero, not only the electric charge and the hadronic charge.
These 8 kinds of particles are exactly those that are supposed to compose in equal quantities the matter of the Universe at the Big Bang.
So all the conserved quantities except energy sum to zero for the Universe at the Big Bang, when it is composed entirely of ordinary matter, without any antimatter.
Therefore there is no need for antimatter in the initial state.
There is no known reason for this symmetry between the 8 particles of a generation of quarks and leptons, except that this allows for the initial state at the Big Bang to have a zero sum for the conserved properties.
It can be speculated that this symmetry might be associated with a supplementary hyper-weak interaction, in the same way as the symmetry between certain groups of 4 quarks and leptons is associated with the weak interaction. Such an interaction would allow the generation and annihilation of ordinary matter, without antimatter, but with an extraordinarily low probability.
We detached this comment from https://news.ycombinator.com/item?id=46075749 and marked it off topic.
chasil•2mo ago
https://news.ycombinator.com/item?id=45979220
https://news.ycombinator.com/item?id=46011889
gus_massa•2mo ago
> It increases the rate of production of neutral antihydrogen from antiprotons and positrons by a factor of 8. It doesn't increase the efficiency of production of antiprotons, which is the extremely inefficient, energy intensive part.