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Comment by acconrad | Hacker News Reader

For some reason I feel this is only going to reduce the significance of anti-matter. I remember first hearing about it as some ominous "substance" that only exists in the emptiest depths of the universe. If it happens all of the time on earth, I'm sure we'll be able to conclude that anti-matter is as common here as it is elsewhere in the universe, and won't exhibit any super-interesting properties that we once thought it did.

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>I remember first hearing about it as some ominous "substance" that only exists in the emptiest depths of the universe.

It doesn't exist in appreciable amounts anywhere, that anyone knows of. Maybe you're confusing it with dark matter, which has only observed in distant galaxies (because it's only detectable -- to date -- by its gravitational effects).

Antimatter exists on earth. You're generating antimatter right now. One isotope of natural potassium (K-40) emits an antielectron in one in every 10^5 decays [1]. A typical meatbag has enough K-40 for 4,400 decays per second [2] (i.e., 4.4 kBq), so you're spontaneously emitting, on average, about 3 antielectrons per minute from this path.

[1] http://www.nndc.bnl.gov/chart/decaysearchdirect.jsp?nuc=40K&...

[2] http://www.physics.isu.edu/radinf/natural.htm

Sorry but that last sentence of yours doesn't make sense to me. From the discovery that it is created frequently on Earth, it does not follow that it won't exhibit any interesting properties nor that it is common in the universe (except by a generous definition of "common"). Anyhow, the main mystery remains: the Universe should be 50% matter and 50% antimatter, so where has all the antimatter gone?

> the Universe should be 50% matter and 50% antimatter

Out of curiosity, where does this come from?

The big-bang did not create particles or atoms, merely energy. In the very initial stages of the big-bang all of the mass of the entire Universe was locked up in bosons (photons, W & Z bosons, etc.), with virtual quarks and other exotic particles existing only ephemerally. At this stage the Universe is essentially an enormously hot photon gas. As the Universe cooled lower energy particles (such as electrons and protons) became more stable, and more and more energy started to become locked up in them. Interactions involving high energy photons can create particle / anti-particle pairs, in theory these should be exactly balanced. However, in practice it appears as though there is much more matter than anti-matter in the Universe. Likely this is due to some slight imbalance in particle/anti-particle pair creation, but we do not sufficiently understand this (though there have been a few hints).

I think that's a good question. It is natural to require that the total charge in the universe was zero at the start of its life (same goes for all quantum numbers). Otherwise, there was something before there was anything! Seriously, either this matter-antimatter asymmetry was an initial condition (in which case we can't hope to understand it) or it appeared at some point during the course of things.

The problem of finding the exact mechanism that gave us the matter-filled universe we observe today, with all the antimatter gone is an open question. There are a bunch of hypotheses, and experiments coming son to a large hadron collider near you will help physicists gather pieces of the puzzle.

Thanks (both you and InclinedPlane), I guess that makes sense.

I thought there were some theories that early-universe physics were very different from what they are now, though I'm not sure how that would help.

What super-interesting properties are you thinking of? Antimatter has been pretty pedestrian for a while now.

Hm. I'm not sure I'd go so far as to say it's pedestrian. Well understood by theoretical physicists, perhaps. Inherently, though, it's still pretty damn interesting.

Interesting scientifically, sure, just like electrons and protons and Newtonian physics and all sorts of other things. But there's not much mystery to it. I agree with uvdiv, acconrad was almost certainly thinking dark matter/energy.

Or he's been misled by, like, every work of science fiction ever. They almost all portray it as the sort of mysterious, otherworldly stuff he's describing. I've known a lot of people who were kind of disappointed to learn that antiparticles are uncommon, but not that uncommon.

Still holding out hope from star trek I imagine.

Anti-matter has been created in the laboratory routinely for decades. And it has existed in nature forever. Cosmic rays routinely create showers of particles and anti-particles in the upper atmosphere. Radioactive decay generates positrons continuously throughout nature (in Earth's rocks and soil, in the oceans, in bananas, inside your own body). Every second of every day you are bathing in an ocean of anti-neutrinos, mostly from the Sun.

But that hardly changes the remarkable nature of anti-matter. A single grain of sand of anti-matter would be a sufficient energy source to power a Toyota Prius for an entire century. A chunk of anti-matter the size of an aspirin tablet could be used to create a bomb as powerful as a nuclear weapon or power 100 homes for a year.

And conversely, it would take us the amount of energy sufficient to power a toyota prius for an entire century to create a grain of anti-sand, and we'd have to dump enough power to run 100 homes for a year to create a piece the size of an aspirin tablet.

Antimatter isn't free.

It does make an awesome battery, does it not?

Antimatter isn't free, and current production efficiencies are actually astronomically low (one trillionth efficient or something like that). My point was that matter/anti-matter reactions are nevertheless remarkable and amazing even though anti-matter reactions are common in nature.

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