Assuming that you have some sort of education in physics to a respectable level, you will know about fundamental particles. You will most probably know that all fundamental particles have anti-particles also.
One of the more known examples is the electron anti-particle; the positron.
Fundamental particles exist in 2 families (as of we know, although a third [and more] families are being theorised), Leptons and Hadrons.
The particles I want to concentrate on most, are the electrons, the protons, and the neutrons, which naturally occur and make up you and I, and their alternative opposites, positrons, anti-protons, and anti-neutrons.
Anti-particles have been observed and factually exist, yet do not naturally occur. And when an anti-particle meets it's opposite, they will both annihilate into waves or further elementary particles depending on the speed of collision, and the type of particles involved, (Hadron, or lepton).
Today I had an interesting thought; can I manufacture, somehow, an anti-atom?
It's simple to visualise, Anti-neutrons and Anti-Protons making up the nucleus, held together by the strong force they are subject to, and positrons whizzing about the outside.
Why has this never happened before at some far away area of the universe?
The mass and stability of the atom should be exactly the same, it should behave exactly like any other atom would when introduced to another anti-atom.
This anti-atom, whatever it may be, should experience covalent, ionic, and metallic bonding in exactly the same nature as a normal atom should.
This anti-atom should experience intermolecular forces such as Anti-Hydrogen Bonding, Anti Van de Waals.
The maths add up, so why don't the statistics?
Well, me being abruptly curious of my own observation, decided to further theorise on my thoughts.
I know that an entity made of anti-particles, and an entity made up of normal particles, should annihilate in the same way that a singular particle would annihilate with it's corresponding anti-particle, and with that in mind, I began to visualise the very very start of the big bang - The very moment the first atom was made.
I began to think that the only factor that effects the existence of anti-particles today, is the fact that the first particle to exist separately from it's anti-correspondent, was a particle which naturally occurs today. The very thing that stopped Anti-particles from occurring naturally was the existence of a higher concentration of naturally occurring particles.
Therefore, the first atom created, was an atom made out of protons with positive charge, neutrons with no charge, and electrons with negative charge.
It was the imperfections of the big bang, which has allowed life to exist as it does.
Had it happened another way, we could be made out of anti-particles and anti-atoms.
When we drink water, we would be drinking anti-water. When we eat food, we would be eating anti-food, entirely the opposite yet similar in every way.
I mused on this theory for a while, before I got struck by a disturbing thought.
Do other universes exist, in which things happened differently, and by chance, what we know as anti-particles are the norm there?
Presuming the strengths of the four forces of nature are exactly the same in this anti-universe (further presuming there are only four forces), this universe could be very much like our's in every way, yet entirely opposite.
Now we know opposites annihilate, and I have heard theories of parralel universal membranes colliding, and using this as an example, the energy produced from two small entities annihilating, something as small as a 2 pence coin and an anti-2 pence coin, harbors the force of a nuclear bomb.
So how will the entire universe react when annihilating with the entire constituents of an "Anti-Universe"?
Big Bang II perhaps?
Just an interesting thought.