The law of conservation of mass, or principle of mass conservation, states that for any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. Hence, the quantity of mass is “conserved” over time. The law implies that mass can neither be created nor destroyed, although it may be rearranged in space, or the entities associated with it may be changed in form, as for example when light or physical work is transformed into particles that contribute the same mass to the system as the light or work had contributed. The law implies (requires) that during any chemical reaction, nuclear reaction, or radioactive decay in an isolated system, the total mass of the reactants or starting materials must be equal to the mass of the products.
teenage girls are reminded constantly by adults (and everyone else) that we’re immature and too young to understand anything but the minute we make a mistake those same adults tell us we’re “old enough to know better” and refuse to help us
"I’ll tell you one thing about the universe, though. The universe is a pretty big place. It’s bigger than anything anyone has ever dreamed of before. So if it’s just us… seems like an awful waste of space. Right?" — Contact, Carl Sagan