@ iLED009..... Einstein equation help us understand that there is a relationship between energy and mass. I didn't mean a precise mathematical number for matter when I said we can calculate matter.
Yes, H20 can take shape of liquid water, solid and gaseous state. But, in all these three states, it is the same ingredients! Only arrangements differ in these three states as a result of different circumstances; in your words, pressure, temperature etc. Vapor can be changed into solid water and solid water can be changed into liquid water. I am interested in the essence of substance not how they appear. Whether it be vapor, or solid water or liquid water, I am interested in the real ingredients of these substance. At this point scientist know that atoms are the smallest unit of matter. When I know all matter is nothing but atom, then I am interested in atoms rather than varieties of things that are made out of atoms because until I don't understand about atoms, I will not understand matter!

Just because something appears solid through your sense perception doesn't mean it is solid. When you rotate a fire, it appears as a circle! Which one is correct? Is there really a circle or is it just a fire? A rope can appear as snake at night but when you truly investigate getting closer to that rope, you will realize that there was no snake at any time, whatsoever. It was just your mind that thought there was a snake! Whose problem is this? Rope's or your own mind?

If matter is real then you would never be able to destroy any matter at any time. That which is real and truly exist no matter what will have to be indestructible. The law of conservation of energy states that energy can neither be created nor destroyed. So, you can ask yourself whether matter is superior or energy?