Why are fundamental particles the same?

[Rev. Green]

When a high-energy photon forms an electron/positron pair the electrons always have the same mass, charge, etc. Why?
If you sent dough to several locations to be made into loaves, the loaves would all be different sizes unless some uniform measuring tin was supplied. What is the equivalent to the uniform measuring tin which confines electrons (or any other fundamental particle) to always have exactly the same properties wherever in the universe they are created?

[factor-fiction]

Hi Reverend- I'm not sure I understand your point. Loaves will usually be of different sizes because the number of fundmental particles will vary from loaf to loaf. One fundamental particle, however, will always be the same size, won't it?

[ChuckFickens]

I think the equivalent to the measuring tin would be the laws of physics.

[vascop]

Yes, it's all down to quantum mechanics and Dirac - explains it all perfectly.

[CanisMajor]

in the unlikely event that an electron/positron pair is created they would instantly annihilate as one is the anti particle of the other. Anyway assuming you mean Electron/proton, the analogy is flawed, the fundamental particles are used to build everything else so sending some "dough" to make some "bread" is equivalent to sending some fundamental particles to make an Aeroplane or perhaps a tank. They are fundamental because they are the constituent parts of everything. Just as dough is the constituent part of many forms of baked product.

[Old_Geezer]

One should beware assuming the while universe is identical. Who says the constants we observe is the same beyond the edge we can see ? Maybe the constants are all different there.

Right, "fundamental" is the important word I think. Your hypothetical loaves aren't, but are made of other "stuff" and you can vary the quantity, or even the recipe and still have something you can call a loaf. But by definition the particles you refer to are all the same because they consist of the same things (or else they'd be a different particle).

Sure one can smash one set of particles to create others; so clearly the building blocks can be used to make different particles. But then they are different particles by definition. You can't willy nilly add a quark or two to make a fat electron, for example. Even if it were possible (and it seems it isn't) you'd no longer have an electron but something else.

[beso]

CanisMajor // in the unlikely event that an electron/positron pair is created they would instantly annihilate as one is the anti particle of the other. //

It happens all the time and they are do not annihilate because they move apart.

http://en.wikipedia.org/wiki/Pair_production