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Comment by maxander | Hacker News Reader

The thing that pop-science stories about GUT always seem to fail to explain is- what does it mean for a symmetry to break at a certain point in time? In the present day physical symmetries (isotopy of space, say, or conservation laws) are just static laws of nature; what was going on in the first microseconds that could mess with the laws of physics itself?

...I'm sure my question contains within it at least several misconceptions, but let that just be an illustration of how confused this kind of article leaves laypeople.

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The symmetry breaking should be thought of as a phase transition that occurs as the temperature of the universe changes, like liquid freezing and becoming ice. The universe was initially very hot, but rapidly cooled down as it expanded and went through phase transitions when it passed the "freezing temperature", i.e the temperature at which the laws of physics prefer to spontaneously break the symmetry.

I've always been curious about that as well. Suppose you took a small region of the universe and reheated it to be unification temperature today, presumably you would restore the symmetry, but presumably when you let it cool down, the symmetry would not randomly break in a different way, but deterministically in the same way; isn't that a way the analogy does not hold?

To get random breaking in a different way, presumably no amount of mere heating of matter would suffice; you would have to somehow restore the high-energy false vacuum of the Big Bang itself? I don't suppose there's any way to do that in today's universe, even in principle?

You are confused because phase transition is not a good description of symmetry breaking (sorry cohomologo).

You have to understand that there already is a difference between the two things (forces, particles, whatever). It's just in certain temperatures or forces, or size ranges (whatever) that broken symmetry is not visible and the two appear to be identical.

So the search is on to understand why these two things should act so identically in certain ways, and yet not identically in other ways, i.e. what breaks their symmetry.

Finding out what breaks their symmetry tells you a LOT about the particle, it tells you what is identical, and what is different.

For example an up and down quark are identical in all ways - except mass and charge. So in certain experiments they appear identical, in others those things show up - their symmetry is broken.

But noticing that they are identical in certain situations tells you a lot about quarks, and noticing where they differ tells you even more.

> Suppose you took a small region of the universe and reheated it to be unification temperature today...I don't suppose there's any way to do that...?

You're describing a particle accelerator. When we talk about the LHC accessing "higher energies" than the Tevatron [1] we are saying it is "baking" small parts of the universe to higher and higher temperatures.

[1] http://blogs.discovermagazine.com/cosmicvariance/2009/11/30/...

Yep. But even if we could build a particle accelerator capable of reaching GUT energy level, it wouldn't spawn new universes, would it?

Symmetry breaking just means when I look at an object at a certain range (energy range, size, whatever), it looks identical to another object. But then when I widen my view suddenly it diverges from that other object and act different.

So there is a search for why.

For example an up and down quark look virtually identical, because they are quite similar. But at a certain point something differs in an experiment, and you realize it's because their masses are not identical, and in a certain situation the symmetry is broken and you can see the different masses.

You're implying that there is some way to write such an article that simply explains particle physics to the layman with out causing any confusion.

Since we don't have physics 'figured out', it's confusing even to the experts in places. It's just confusing to the non-experts in about every place.

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