Mass-Energy Equivalence

The famous equation by Einstein is not so easy to explain. Basically, it says that mass and energy are equivalent.
For example, when the nucleus of Uranium-235 decays(breaks down) into two daughter nuclei, the sum of masses of the daughter nuclei is less than that of the original U-235 nucleus. Instead, we get energy which is equal to the “missing” mass times speed of light squared.

For more technical explanation, see this:

For more equations in Physics, see Famous Equations in Physics

Planck’s Hypothesis: Quantization of Energy

When trying to explain the cavity radiation(or blackbody radiation), Planck hypothesized that the radiation is absorbed or emitted only in discrete quantities, unlike classically accepted model of continuous waves of light. Einstein extended this idea to all electromagnetic radiation and suggested that all electromagnetic radiation, from X-rays to visible light to microwaves to radio waves, all kinds of “light” exhibits the discrete (or quantum) nature. There is a lot to this story which is very interesting and shows how limited our assumptions are, regarding the basic laws of nature.

For a quirky explanation, see this:

For more equations, see Famous equations in Physics

Hubble’s Law

Everything in the universe appears to be moving away from each other on the cosmic scale. The larger the separation between two objects, faster is their receding velocity (measured by redshift).

For more details, go see http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html

For more equations, see Famous Equations in Physics