Travel into the Wonders of Space and Time...
How could it be that we cannot accelerate something to go faster than light? Surely we could kick a ball again and again and again until it travels faster right? No. The reason is quite interesting: As something is moving with respect to another object we say that the moving thing has a certain amount of energy by virtue of its motion. Energy is the ability to do some work, and, indeed, a moving thing can be lassoed and made to pull a car, (of course in so doing it looses energy and slows down).
Now when we have the above object moving it will have a certain amount of energy and, Einstein argued, the only way we can insure that it cannot be accelerated indefinitely, is if there is a universal equivalence between mass and energy: the more energy an object has the heavier it will be so when we speed it up a little bit is becomes also a bit heavier and therefore it also becomes a bit harder to speed it up further. In fact the closer we are to the speed of light, the larger the force is needed to accelerate the object, and an infinite force is needed to speed up a material object to the speed of light: it never happens!
But there is more to the equivalence of mass and energy, for it also implies that an object of mass m has energy, just by virtue of its existence; the specific relationship is
This formula plays a basic role in nuclear reactions (and in atom bombs, for that matter): in these processes an atomic nucleus of initial mass M is transformed (either because the environment is tailored to insure this or because is is unstable and disintegrates spontaneously) into another object of smaller mass m. The difference in mass is released as energy in the amount ( M - m ) c2.
To give an idea of how powerful this is, suppose we initially have a sheet of paper weighing 6gr, and that at the end we have something weighing half this amount. The energy released is then so big as to turn on a light bulb of 100W for about 86,000 years, or run a hair-drier for about 4000 years.
