First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[SteelCurtain]

That makes sense.

I read somewhere that the leading theory for why there is no antimatter (probably dumbed way down) was that at the moment of the Big Bang, there was slightly more matter than antimatter, and the two annihilated each other, leaving only the excess matter left over.

[Excited Penguin]

Why is it a mystery that there's none of something that doesn't exist?

[chimp3]

Alex K : Any reason to fire up the LHC again? What is planned for the device?

[Excited Penguin]

Just in case no one understood my question, what's all the mystery about anti-matter about?

[Alex K]

Alex K : Any reason to fire up the LHC again? What is planned for the device?

The LHC will be running continuously for many years to come. The data being presented this week are just the first official snapshot of this year's measurements. The more data you collect, the better statistics you get, the smaller error bars you get, the smaller are the effects you can see in the data. It's like taking a longer and longer exposure photo of the sky - the noise cancels and you can see fainter and fainter objects.

[Alex K]

From the photons and matter in the universe, one can estimate that initially, matter and antimatter were there in almost exactly equal proportions, with a tiny difference like in the 10th digit, giving an advantage to what we call matter. This tiny surplus is what we are made of today, while all the rest annihilated to photons, which subsequently were redshifted.

People are thinking about particle physics mechanisms how one could produce the observed tiny surplus of matter from an equilibrium after the Big Bang, and already 50 years ago, a russian guy named Sakharov, who was also involved in the soviet nuke but later became a kind of pacifist, he identified what conditions have to be met in order for such a surplus to arise - the fundamental laws of physics must have a slight asymmetry between matter and antimatter (such that they aren't exact mirror images of each other), there must be a violation of so-called baryon number (because otherwise, for each proton that is created, you'd have an antiproton), and the universe must be out of thermal equilibrium because in thermal equilibrium, any differences get erased. Those are the Sakharov conditions. The question is now, what is the exact particle physics mechanism in nature which accomplishes this. There are several proposals on the table, and it would be nice if one could study this mechanism at colliders to determine which one of them is maybe correct, or none. It is however not clear whether that is possible. Some of these proposals rely on new particles that would be observable at the LHC at some point.

That makes sense.

I read somewhere that the leading theory for why there is no antimatter (probably dumbed way down) was that at the moment of the Big Bang, there was slightly more matter than antimatter, and the two annihilated each other, leaving only the excess matter left over.

Why is it a mystery that there's none of something that doesn't exist?

[bennyboy]

If particles erupting out of space are in a natural state of equilibrium, wouldn't an imbalance necessarily mean that particles or energy are being injected into the Universe from outside it? If so, would this make us a "matter" Universe on the whole, and is it possible that there is an "animatter-dominant" partner Universe in another dimension? If so, wouldn't that mean that you don't have to search for any special mechanism, or that there might be none to be found?

[Alex K]

If particles erupting out of space are in a natural state of equilibrium, wouldn't an imbalance necessarily mean that particles or energy are being injected into the Universe from outside it? If so, would this make us a "matter" Universe on the whole, and is it possible that there is an "animatter-dominant" partner Universe in another dimension? If so, wouldn't that mean that you don't have to search for any special mechanism, or that there might be none to be found?

I'm not sure how you come from a matter-antimattee imbalance to energy being injected. Antimatter has positive energy like normal matter (despite the name), they don't cancel each other out.
It is surely imaginable that there is some kind of mirror universe with the opposite contents, but that's pretty far out. It can't inhabit the same space as we do, we'd have noticed that through gravity.

[LastPoet]

My understanding of this is very limited.

Alex, do we know if anti matter forms atoms? Like an anti helium atom? If so, what would happen in am encounter between a heavier element and a lighter anti element? Or vice versa for that matter.

[Alex K]

My understanding of this is very limited.

Alex, do we know if anti matter forms atoms? Like an anti helium atom? If so, what would happen in am encounter between a heavier element and a lighter anti element? Or vice versa for that matter.

Yes, they are regularly produced (although only antihydrogen) e.g. at the CERN Antiproton Decelerator (AD), and analysed by experiments like ALPHA. I once had the opportunity to visit AD and ALPHA, impressive setup, not as big as the LHC stuff of course, but still impressive.

Producing heavier antiatoms deliberately is more difficult because you still have to make the antiprotons fuse after you produce them. Antihelium has however been observed as an accidental product of collisions afaik.
We know the laws of physics governing antimatter very precisely, and they are almost exactly (but not exactly) the same as those of matter. Antiatoms must have basically indistinguishable structure and spectra, and the same periodic table.

If an atom and and anti-atom of any type meet, the electrons and positrons in them will pair-annihilate into gamma rays, and the protons and neutrons will pair-annilhilate with the antineutrons and antiprotons into gamma rays, neutrinos etc.