
ALPHA observes light spectrum of antimatter for first time - dnetesn
http://phys.org/news/2016-12-alpha-spectrum-antimatter.html
======
hughes
> Antihydrogen is made by mixing plasmas of about 90,000 antiprotons from the
> Antiproton Decelerator with positrons, resulting in the production of about
> 25,000 antihydrogen atoms per attempt. Antihydrogen atoms can be trapped if
> they are moving slowly enough when they are created. Using a new technique
> in which the collaboration stacks anti-atoms resulting from two successive
> mixing cycles, it is possible to trap on average 14 anti-atoms per trial

The amount of work that goes in to producing 14 anti-hydrogen atoms is
astonishing. It's simultaneously the height of human technical accomplishment
yet vanishingly small quantities of the most primitive element possible.

~~~
jerf
If you enjoyed that, you may also enjoy the discussions of how people
synthesize super heavy elements, such as in this video:
[https://www.youtube.com/watch?v=z3oY-
XHwss8](https://www.youtube.com/watch?v=z3oY-XHwss8)

Superheavy elements even beat antihydrogen on this scale; one of the ones
recently named was confirmed to have been synthesized based on only three
atoms!

~~~
jhayward
Yes, it's amazing work. Also, don't be fooled that because it is so difficult
to produce today that it can't be scaled immensely. Plutonium production was
scaled from nanogram levels to ton levels in less than a decade.

~~~
hughes
Well... 14 anti-hydrogen atoms is a lot less than a nanogram. It's about
1/100th of a trillionth of a nanogram.

If we scale up production in the next decade at the same pace you're
describing, we _might_ get to nanogram levels.

~~~
jhayward
> we _might_ get to nanogram levels

Right! Now we're talking about some antimatter!

Kidding of course. But there is no reason to believe ab initio that it could
not be scaled to whatever quantity is useful given enough incentive for that
use.

~~~
AnimalMuppet
A nanogram of antimatter is 90 kilojoules waiting to be released if it touches
any regular matter. Not the biggest bomb in the world, but something to be
treated with at least mild respect.

------
bmh100
In case anyone is wondering about what antimatter actually is, antimatter is
basically like normal matter, but the electrical charges are reverse. Take
hydrogen for example. It is a massive, positive particle (the proton), orbited
by a light, negative particle (the electron). Anti-hydrogen is a massive,
negative particle (the antiproton) orbited by a light, positive particle (the
positron) [1].

Why do matter and antimatter annihilate each other? Matter and antimatter are
very similar, except for opposite electrical charges. Opposite charges
attract. If antihydrogen meets normal matter, the positrons quickly find and
combine with the electrons, and the antiprotons do the same with protons.
These combinations all release radiation. Therefore, one of the main challenge
with studying antimatter is making sure that it doesn't touch normal matter,
which is basically everything in the lab.

Why don't electrons and protons normally combine, being oppositely charged?
Electron sit in stable orbitals, volumes of space with associated energies.
These orbitals are like valleys. While an electron nearing the nucleus will
fall into an orbital, it would take extra energy to get the electron out of
the orbital and into the nucleus [2].

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

[2]: [http://physics.stackexchange.com/questions/30939/what-
keeps-...](http://physics.stackexchange.com/questions/30939/what-keeps-
electrons-in-an-atom-from-flying-away-or-falling-into-the-nucleus#30943)

~~~
euyyn
"Falling into the nucleus", as stated in that Stack Exchange question, is a
classical (as in "wrong" :) ) way to look at it.

The 1s orbital of the electron is spherically symmetric, with non-zero
probability of the electron being right in the center of the atom (so within
the nucleus), and decreasing probability of it being farther away. So e.g. a
good approximation of the He atom is of two neutrons, two protons, and two
electrons, all in exactly the same position (with the electrons having "more
spread").

At the end of the day, there are interactions that are seen in Nature and
interactions that aren't. We codify the patterns as conservation of lepton
number, baryon number, etc. If the numbers of what you have add up to zero,
they can annihilate.

These conservation laws also accommodate other weird things, like beta decay,
in which a neutron decays ("splitting") into a proton, an electron, and an
anti-neutrino. It's not that the neutron is "composed" of those three things.
But its total energy is higher than the sum of the energy at rest of those
three particles: Whenever that's the case and the conservation laws allow it,
we see it happen naturally.

~~~
neikos
As someone who hasn't studied this (yet) does that mean that the reason
protons and electrons don't annihilate is because their Baryon Number wouldn't
sum up to zero? (With Protons having 1 and Electrons 0 if I understood
correctly)

~~~
euyyn
That's what we currently observe, yes. The particles of matter in the Standard
Model are quarks (that join to form protons and neutrons among other things)
and leptons (electrons, muons, taus, and neutrinos). The number of {quarks -
antiquarks}, as well as that of {leptons - antileptons}, is conserved.

If you start with a proton and an electron, you have 3 quarks and 1 lepton, so
whatever the interaction you have to end up with 3 quarks and 1 lepton (plus
any number of quark-antiquark and lepton-antilepton pairs). E.g. for beta
decay:

neutron (3 quarks) -> proton (3 quarks) + electron (lepton) + antineutrino
(antilepton)

------
_rpd
> Today's ALPHA result is the first observation of a spectral line in an
> antihydrogen atom, allowing the light spectrum of matter and antimatter to
> be compared for the first time. Within experimental limits, the result shows
> no difference compared to the equivalent spectral line in hydrogen. This is
> consistent with the Standard Model of particle physics

~~~
colechristensen
>consistent with the Standard Model

Is generally one of the most disappointing phrases one can read in science
news. Hooray for progress and all, but everybody is hoping for exactly the
opposite result.

~~~
PavleMiha
Maybe we're running out of surprising things.

~~~
plandis
Lord Kelvin said something similar in 1900 about there being nothing left to
discover. Within 30 years quantum mechanics would be discovered/created.

~~~
HarryHirsch
At that time everyone knew there was something up with blackbody radiation,
classical physics gave no guide why the equipartition theorem should not apply
any more at short wavelengths.

~~~
openasocket
And now we know something's up with gravity, because we can't seem to
reconcile it with quantum mechanics.

~~~
HarryHirsch
I know, and the Lord Kelvin quote is too suspicious to be credible, a man like
him would never have said such a thing.

If we can trust Wikipedia he never did:
[https://en.wikiquote.org/wiki/William_Thomson#Misattributed](https://en.wikiquote.org/wiki/William_Thomson#Misattributed)

~~~
IgorPartola
Didn't Isaac Newton die thinking that he solved all of physics though?

~~~
0xfaded
Newton was the first to experiment with light reflectance of glass of various
thicknesses. He found the relationship but had no idea how a light corpuscule
could know the thickness of the glass when it decided to reflect or not.
Newton published his corpuscular theory of light but I certainly don't think
he would have claimed to know what was going on.

------
ianai
I remember Feynman said to check the spin of the photons emitted from alien
species. If they're 90 degrees out of phase with ours then they're made of
antimatter and we shouldn't shake hands. (At least I think it was spin, been a
while since I read QED)

~~~
cshimmin
Actually his story was about trying to explain the difference between left and
right in terms of nuclear spin experiments. You also explain that humans greet
by shaking their right hands. If you meet the alien and he extends his left
hand to shake, he must be made of antimatter (since the combination of parity
and antimatter conjugation is a symmetry of the universe).

edit: jess is correct, and that's the whole point of the story actually. if CP
was invariant you wouldn't be able to tell they were antimatter by describing
the nuclear physics decay experiment. instead the antimatter version of the
parity experiment gives the opposite result. I shouldn't try to physics so
early in the morning :)

~~~
jcoffland
Assuming a two handed alien of course.

~~~
hossbeast
Many handed

~~~
Semiapies
But only bilaterally symmetrical. Radially symmetric aliens with hands give no
indication!

(Well, aside from whether or not they blow up whatever local matter surface
they're standing on.)

~~~
grkvlt
That's neither necessary or sufficient! Notice that they could be bilaterally
symmetric and two arms/hands positioned vertically on their front (anterior?)
so no left/right hand distinction (but top/bottom instead) or; they could be
asymmetric but have two hands/arms on one side, and one on the other, still
giving them a left/right side choice.

------
glandium
So, if antimatter has the same light spectrum as matter, what makes us
theorize that there is currently more matter than antimatter in the universe?

~~~
btouellette
If you're asking how do we know there is more matter than antimatter in the
universe the answer is that it is consistent with the
observations/calculations surrounding Big Bang nucleosynthesis and CMB
anisotropies. If you're asking what do we theorize is the reason there is more
matter than antimatter in the universe there isn't a satisfactory answer yet.
It's one of the biggest open problems in physics.

------
nonbel
Dumb question: Is it easier to create antimatter if you already have some? I
mean using it as a nucleation point, or perhaps energy source.

~~~
jessriedel
Nope. It's a sensible question, but it doesn't help.

~~~
lutorm
It would be easier if you could build your entire experimental apparatus out
of antimatter, but if you could do that you're probably beyond making
experiments with single atoms of it... ;-)

~~~
mikeash
I would not want to be in charge of filing the Environmental Impact Statement
for such a facility.

~~~
semi-extrinsic
Yeah, you should see the paperwork they make us fill out for something as
simple as a few hundred lbs of mercury.

------
josho
Simply amazing. I still thought antimatter was a theory. Can anyone recommend
a book on this topic for the layman?

~~~
lutorm
Not a theory at all. You get antimatter out of many common radioactive
materials:
[https://en.wikipedia.org/wiki/Positron_emission](https://en.wikipedia.org/wiki/Positron_emission)

It's the building atoms out of it that's tricky, but antimatter is nothing
new.

~~~
tjohns
Not only that, but a PET scan (a common medical imaging technique,
tangentially similar to an MRI or CT scan) relies on antimatter. The name
stands for _Positron_ Emission Tomography, in fact.

The general idea: You get injected with a tracer containing a β+ emitter. This
produces positrons (antimatter) through radioactive decay. When the antimatter
collides with regular matter inside your body, it annihilates, producing a
pair of gamma rays moving in opposite directions. Those gamma rays can be
detected and used to triangulate where the annihilation occured, generating a
3D image of where the tracer has accumulated in your body.

Typically, the tracer will be something that looks like glucose to the body,
so it's accumulated in areas of high metabolic activity. This allows us to see
what parts of your body are active. (For example, seeing which neurons in your
brain are firing.)

More reading:
[https://en.wikipedia.org/wiki/Positron_emission_tomography](https://en.wikipedia.org/wiki/Positron_emission_tomography)

