Physicists drive antihydrogen breakthrough at CERN

An interesting fact is that while almost all of the Solar System has started as gas, which has then condensed here into solid bodies that have then aggregated into planets, a small part of the original matter of the Solar System has consisted of solid dust particles that have come as such from the stellar explosions that have propelled them.

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.

The elements heavier than iron are not formed by fusion because of the asymmetry in the initial conditions.

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.

There’s a recent paper on the formation of such a “kugelblitz”; it’s argued to be unfeasible.

https://arxiv.org/abs/2405.02389

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.

How could we harness this energy and make it usable?

But you want that to happen in space and to control the output of energy.

Otherwise you just have a bomb.

In the same way that atomic weapons and radioisotope generators both convert mass into energy. It's just a matter of slightly different timescales.

It's pretty widely accepted though. He himself hated the idea so you can expect he did the calculations thoroughly.

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.

Probably more like a water wheel - matter spinning around the hole can be accelerated.

But it was one hell of a ride! ;-)

This is a silly claim. Creating black holes is many orders of magnitude more difficult than creating antimatter.

CERN is trying to do fundamental physics, not trying to weaponize antimatter. If/when it comes to that, the pace will pick up.

Also, 25 years to the breakthrough discussed in the article seems like a reasonably good pace.

> 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.