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...what would be the immediate consequences?

Or putting it better, if (from big-bang or whathever), the universe were always made of what we call Anti-matter what would it be?

The scientists of this universe would call 'Matter' 'Anti-Matter'.

Will the universe looks like exactly the same? By "looks", I mean the laws of Physics, the constitution of the universe with its superclusters of galaxies containing clusters containing galaxies and so on...

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up vote 3 down vote accepted

It would look very similar, but tiny differences are suspected, see e.g. this LHC experiment.

Here a list of more antimatter experiments at CERN.

See also CP violation on Wikipedia hinting towards tiny differences between matter and antimatter.

Immediate consequence: The CP violation parameter of the CKM matrix in this Wikipedia article would be different, because of different quark generation probabilities.

If you also reverse time, you'll get to the CPT theorem (Charge, Parity, Time). Matter and antimatter are thought to be symmetric in this sense.

Or to state it with simpler words: Antimatter behaves like matter travelling backward in time.

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