Antimatter : The missing puzzle of the Universe?

Is Antimatter a real thing in the Universe?

If so,

Where did all the antimatter go after the Big Bang?

Seriously, where did all the antimatter go after the Big Bang? This is the one question that created confusion among physicists of all kinds - particle physics, astrophysics and cosmology - all together at once. 

The whole idea regarding the existence of an antiparticle partner for every ordinary particle was officially bought up on the table when the first anti-electron - known as positron - was discovered in 1932. Since then, scientists theorized that if an electron has its antiparticle, then ordinary matter that is composed of electrons and other sub-atomic particles should also, in practice, have their corresponding antimatter pair. Be it a chair, or an apple, or an entire solar system, it should have its antimatter pair. 

But what exactly is antimatter? 

Simply, it's just the opposite of any ordinary matter. Opposite, in the sense that in terms of its charge and quantum properties, but with the same mass. For example, the antiparticle of an ordinary proton (which has a positive charge), is called an antiproton, which is just a proton with a negative charge. An electron has a negative charge, but its antiparticle, positron, has a positive charge. Similarly, the antiparticle pair of a hydrogen atom would be an antihydrogen atom, with opposite charges and properties. 

Now the weirdest part about its properties is that since matter and antimatter are opposites of each other, they cancel each other out by annihilating each other. Just like +2 and -2 adds up to zero, particle-antiparticle pairs annihilate to zero when they come in contact, thereby conserving the net energy of the system. It can be thought of as a simple analogy where a particle needs to borrow energy from the system of a magnitude of +2, but since this disrupt the constant net energy of the system, there will be an antiparticle with a  -2  magnitude of energy, so that when these particles come together and annihilate each other, the total energy of the system is back to zero. 

Annihilation of particle-antiparticle pairs

These particle-antiparticle pairs are also known as virtual particles in quantum field theory, whose random appearances and disappearances cause quantum fluctuations even in a vacuum, a phenomenon called the Casimir Effect.  (click Casimir Effect for more detailed info)

There's also another theory that antiparticles might possess negative energy density, which can cause gravitational repulsion instead of attraction, but it just remains a hypothetical idea and hasn't been proven yet.

Based on the sole idea that there is corresponding antimatter for every matter, scientists speculated whether all of the observable matter in the universe had its equivalent antimatter, existing in our universe itself. It's like the observable universe and the energy associated with it was dug out of the empty space, and to make the energy back to constant, there is an equivalent amount of antimatter existing, just like the empty pit from which the pile of energy was dug out. If this is the case, then the universe at its beginning would've had equal amounts of matter and antimatter, and even in the present situation, there must be the same amount of antimatter as that of ordinary matter in the universe as a whole!

But we know that's not the reality. We don't see antimatter stars or antimatter galaxy clusters, let alone a simple antihydrogen atom. We can say that all the antimatter produced since the Big Bang would've annihilated with the ordinary matter by now. But even then, why is there an extra amount of matter left out, if the total amount of matter and antimatter were supposed to be equal? 

Well, we don't know the reason for it yet. It could be the reason that maybe antimatter is just spread out over spacetime in tiny concentrations so that when we consider it as a whole, it'll make up for the observable universe. Or maybe antimatter exists and interacts in strange ways that we still don't know yet.

 Whatever it is, one thing is for sure - antimatter exists. And there's evidential support that it does. But we still have to go a long way to actually figure out its real nature and properties.