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A video showing Albert Einstein explaining his most famous equation (perhaps the most famous equation) in physics has been widely shared on Twitter.
The video shows Einstein talking through E=MC2, the equation describing mass-energy equivalence.
"It followed from the special theory of relativity that mass and energy are both but different manifestations of the same thing – a somewhat unfamiliar conception for the average mind," Einstein says in the video.
"Furthermore, the equation E is equal to m c-squared, in which energy is put equal to mass, multiplied by the square of the velocity of light, showed that very small amounts of mass may be converted into a very large amount of energy and vice versa. The mass and energy were in fact equivalent, according to the formula mentioned above. This was demonstrated by Cockcroft and Walton in 1932, experimentally."
The experiment by John Cockcroft and Ernest Walton he referred to saw the two bombard a lithium and beryllium targets with a beam of protons. The team was attempting to disintegrate atom nuclei, which they did, splitting lithium into two helium nuclei. However, as an added bonus, when they came to measure the total kinetic energy of the new helium nuclei they noticed that it was greater than the original hydrogen and lithium nuclei, and also that there was a corresponding loss of mass, confirming E=MC2.
After repeating their experiment with a range of other atomic nuclei, they were awarded a Nobel Prize for Physics in 1951.
