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ALPHA observes light spectrum of antimatter for first time

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Re: ALPHA observes light spectrum of antimatter for first time

#31

Post by eanzenberg »

HarryHirsch wrote: post #22
plandis wrote: post #17

Earlier quoted context omitted.

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

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.

Now we know something is up with dark energy and early inflation of the universe, essentially fudge-factors to make certain things appear nice.

Re: ALPHA observes light spectrum of antimatter for first time

#32

Post by nitrogen »

duncanmeech wrote: post #28

Stop posting physics articles on hacker news. Just because everyone here has watched too much Star Trek and Star Wars doesn't mean we actually understand a single solitary shred of this stuff...although it sounds cool.

You may want to reread the HN guidelines. And although I am not a physicist, some HN readers are.

Re: ALPHA observes light spectrum of antimatter for first time

#33

Post by spott »

jessriedel wrote: post #14
cshimmin wrote: post #8

Earlier quoted context omitted.

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…

> combination of parity and antimatter conjugation is a symmetry of the universe It's only an approximate symmetry. Look up CP symmetry violations.

CP symmetry violation is the reason that the universe appears to be made more of matter than antimatter. Though if I'm not mistaken, the scale of the violations that we have seen, and the violations that must exist in order for the observable universe to be mostly matter aren't in agreement. We don't see enough CP violating processes to explain this asymmetry in the universe.

One of the big open problems in Physics.

Re: ALPHA observes light spectrum of antimatter for first time

#34

Post by tjohns »

lutorm wrote: post #18
josho wrote: post #16

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

Not a theory at all. You get antimatter out of many common radioactive materials: https://en.wikipedia.org/wiki/Positron_emission It's the building atoms out of it that's tricky, but antimatter is nothing new.

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

Re: ALPHA observes light spectrum of antimatter for first time

#35

Post by TacoRabbit »

josho wrote: post #16

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

Not only is it not just a theory, it's actually used in Medicine!

For example, PET Scans use positrons: https://en.wikipedia.org/wiki/Positron_emission_tomography

Re: ALPHA observes light spectrum of antimatter for first time

#36

Post by recycleme »

josho wrote: post #16

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

> I still thought antimatter was a theory.

Your use of the word "theory" here seems to be a misnomer akin to the common statement "But X is just a theory."

Re: ALPHA observes light spectrum of antimatter for first time

#37

Post by dguest »

duncanmeech wrote: post #28

Stop posting physics articles on hacker news. Just because everyone here has watched too much Star Trek and Star Wars doesn't mean we actually understand a single solitary shred of this stuff...although it sounds cool.

I work at CERN. Before I worked there I worked on trapping "normal" atoms (as opposed to antimatter ones). So some of us do understand this stuff.

Re: ALPHA observes light spectrum of antimatter for first time

#38

Post by corndoge »

duncanmeech wrote: post #28

Stop posting physics articles on hacker news. Just because everyone here has watched too much Star Trek and Star Wars doesn't mean we actually understand a single solitary shred of this stuff...although it sounds cool.

Reading is how you learn.

Re: ALPHA observes light spectrum of antimatter for first time

#39

Post by lutorm »

mikeash wrote: post #20
lutorm wrote: post #19

Earlier quoted context omitted.

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... ;-)

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

:)

Re: ALPHA observes light spectrum of antimatter for first time

#40

Post by 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

[2]: http://physics.stackexchange.com/questions/30939/what-keeps-...

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