This is undoubtedly the most popular physics equation ever. Its like even fuckin’ junkies out there know about it, but few actually understand it. My understanding goes as follows (the bold part is the answer to your question, the remaining part is for better understanding) :
E represents energy
M represents mass
c represents the speed of light
We know that,
Energy can neither be created nor be destroyed it can only be converted from one form to another. This is still true, but Einstein added that mass can also be converted into energy. And if you convert a mass M into energy, the energy obtained is equal to that mass M multiplied by the square of the speed of light. This energy is usually pretty huge even for little masses, do the math, you are multiplying mass with , this makes the resultant value i.e. the energy, really BIG. You can have a better understanding of it if you know how this equation is applied. Here are a few interesting instances:
- It can be used to proof that nothing can travel at the speed of light as follows: When a body moves it gains energy and due to the previously mentioned equivalence of mass and energy, after a point the extra gained energy is converted to mass as per , so when it reaches the speed of light, its mass must have reached a very high value so it can no more be accelerated and it slows down thus failing to reach the speed of light.
- It accounts for the stability of nucleus and as to why protons inside the nucleus despite being likely charged stick together and don’t fall apart: After a radioactive decay if we see the initial and final values of the decaying isotope and the resulting nuclei, we find an unexpected difference, according to the law of conservation of energy the initial masses should be equal to the final masses thus it was concluded that the difference in the masses is because the “missing” mass was converted to energy. Thus energy was released and this is what stabilizes the whole process, makes it feasible and hence the nucleus is stable.
I know that was some real nerd-lish but, well, who are we taling about here? Einstein, right? The terra-nerd.
There are a real bunch of such uses out there just fiddle around the links in the below Google search and slowly your understanding will grow. You really can’t understand it at once.
If you are asking for a mathematical proof, I wrote one here:
P.S: I typed all this myself, i didn’t copy-paste it. So, vote me up :D