
Physicists Just Generated a Particle That Acts as Its Own Antiparticle - happy-go-lucky
https://www.sciencealert.com/physicists-made-a-particle-that-behaves-just-like-its-own-antiparticle
======
mmastrac
Ugh, science writing:

> Physicists Just Generated a Particle That Acts as Its Own Antiparticle

[...]

> Physicists now have the next best thing – a particle-like system that
> behaves just like the kind of matter Majorana predicted

~~~
gus_massa
If you talk with someone that works in solid state physics, they act as if
these kind of particles were real as elementary particles. The most usual are
holes [1] and phonons [2]. So it's standard notation in that area, but it may
be confusing for the general public.

At least they didn't call it an "angel" particle, like in the previous
submissions.

[1]
[https://en.wikipedia.org/wiki/Electron_hole](https://en.wikipedia.org/wiki/Electron_hole)

[2]
[https://en.wikipedia.org/wiki/Phonon](https://en.wikipedia.org/wiki/Phonon)

~~~
jessriedel
The distinction between fundamental particles and composite particles is more
a statement about the extent of human knowledge rather than anything physical
about those particles. That is, saying "this is a fundamental particle" tells
you that we haven't discovered any constituent parts to it, not that there
aren't any. Protons used to be fundamental particles until we discovered they
were made of quarks, and quarks may yet turn out to be composite particles
built from preons.

So yes, if you were attracted to this article because you thought they found a
new fundamental particle, then it was clickbait. But the real point is that
it's a Majorana fermion (with well-defined momentum eigenstates, a scattering
matrix, etc.).

It's possible in the future that we discover neutrinos are Majorana fermions

[https://en.wikipedia.org/wiki/Double_beta_decay#Neutrinoless...](https://en.wikipedia.org/wiki/Double_beta_decay#Neutrinoless_double_beta_decay)

at which time they will be "fundamental Majorana fermions"... and _then_
discover after that the neutrinos are just composite particles.

[https://arxiv.org/abs/1510.07988](https://arxiv.org/abs/1510.07988)

(There are some subtleties here. Some quasi-particles don't have all the
properties we normally associate with fundamental particles. And there are
weak theoretical arguments that some fundamental particles can't be composite
unless their constituents have properties that are subjectively inelegant.)

~~~
gus_massa
The gyromagnetic ration of a truly elementary particle is g=2. With the
current theories, a electron has a cloud of virtual particles, but no internal
structure. With this assumptions the theoretical value is approximately
g=2+2.alfa/2pi+...~=2+1/(137*pi). The experimental value of the g of the
electron agree with the theoretical value up to 14 digits, so it's a very good
hint that the electron is really an elementary particle.

Obviously there can be future theory were the electron has internal structure,
but it will be a breakthrough, not a small fix.

The theoretical and experimental value of g for a muon almost agree, but only
10 digits. So there is a small chance of something interesting there. But IIRC
most people think that it may be a new particle in the cloud of virtual
particles, not an internal structure of muons.

Protons and neutrons have internal structure, a lot of internal structure, so
the value of g is a difficult to calculate number that is not 2. In
particular, g=+5.6 and g=-3.8.

~~~
jessriedel
This is just a way of saying that we have probed the electron for internal
structure to a significantly more precise level than the level necessary to
reveal the known internal structure of nucleons. But it's just an upper bound.
For all we know, the next accelerator (if there is one) could reveal composite
structure just below the bound.

------
CurtMonash
Well up above the tropostrata

There is a region stark and stellar

Where, on a streak of anti-matter

Lived Dr. Edward Anti-Teller.

Remote from Fusion’s origin,

He lived unguessed and unawares

With all his antikith and kin,

And kept macassars on his chairs.

One morning, idling by the sea,

He spied a tin of monstrous girth

That bore three letters: A. E. C.

Out stepped a visitor from Earth.

Then, shouting gladly o’er the sands,

Met two who in their alien ways

Were like as lentils. Their right hands

Clasped, and the rest was gamma rays.

by Prof. Harold P. Furth (1930-2002)

------
ColinWright
Most of the discussion is here in this submission, but there are also two
comments here:
[https://news.ycombinator.com/item?id=14817322](https://news.ycombinator.com/item?id=14817322)

And there's another comment here:
[https://news.ycombinator.com/item?id=14818725](https://news.ycombinator.com/item?id=14818725)

There are also other submissions:

[https://news.ycombinator.com/item?id=14817206](https://news.ycombinator.com/item?id=14817206)

[https://news.ycombinator.com/item?id=14833208](https://news.ycombinator.com/item?id=14833208)

[https://news.ycombinator.com/item?id=14840123](https://news.ycombinator.com/item?id=14840123)

------
c517402
I have personally been producing particles that are there own anti-particles
since childhood. And, I continue to do so as I write this comment. Photons!

------
CurtMonash
I guess it would be tough to keep these around in any substantial quantity.

~~~
thaumasiotes
It's not usually a problem to have a large number of photons?

~~~
adrusi
Which are different because the result of a particle/antiparticle collision is
the emission of photons so the quantity of photons is not changed by
collisions.

------
rbanffy
> for every type of fundamental particle in the Universe there is the
> equivalent of an evil twin complete with an opposing charge

Do they have goatees?

------
exabrial
So did I but I can't find it.....

