Parth G | When E=mc2 FAILS (because it is incomplete) | Mass-Energy Equivalence in 60 Seconds #shorts @ParthGChannel | Uploaded 3 years ago | Updated 1 hour ago
In this #shorts I answered a question about the mass-energy equivalence relation, Einstein's famous equation E=mc2.

The question was that if a photon has no mass, then this equation tells us that it must also have no energy. But a photon is often called a "packet of energy" - so where's the fallacy?

Well as it turns out, the relation E = mc^2 only applies for an object at rest, that has some mass (i.e. m is not equal to zero).

The full equation actually accounts for the (rest) mass of our object being considered, as well as its momentum.

And it turns out that photons do have momentum, despite not having mass. This means that the energy of the photon is not in fact zero!

The full equation (as accurately as I can write it here) looks like this:
E^2 = (mc^2)^2 + (pc)^2, where E is the energy of the object being considered, m is its rest mass, p is its momentum, and c is the speed of light.

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