In my previous article related to relativity I explained the basic meaning of relativity and the difference between general and special relativity. If you haven’t read it then my suggestion is to read it first and then come here.

Until Einstein, mass and energy were seen as completely separate things. His work proved that the principles of the conservation of mass and energy are part of a bigger, more unified conservation of mass-energy. Matter, therefore, can be turned into energy and vice versa due to the fundamental connection between them. That is, frankly, amazing.


This formula states that the equivalent energy (E) can be calculated as the mass (m) multiplied by the speed of light (c = ~3×108 m/s) squared. Similarly, anything having energy exhibits a corresponding mass m given by its energy E divided by the speed of light squared c2. Because the speed of light is a very large number in everyday units, the formula implies that even an everyday object at rest with a modest amount of mass has a very large amount of energy intrinsically.

In relativity, removing energy is removing mass, and for an observer in the centre of mass frame, the formula m = E/c2 indicates how much mass is lost when energy is removed. In a nuclear reaction, the mass of the atoms that come out is less than the mass of the atoms that go in, and the difference in mass shows up as heat and light with the same relativistic mass as the difference (and also the same invariant mass in the centre of mass frame of the system). In this case, the E in the formula is the energy released and removed, and the mass m is how much the mass decreases. In the same way, if m increases then E also increases.

You may be now thinking that: What if the mass of any particle is 0 like photon???

If you are thinking like this, then I can assure you that you are thinking like a physicist…..

Coming to the answer: See, the particles like photon has no rest mass. They has relativistic mass.

Okay don’t panic….see my post regarding the difference between rest and relativistic mass.

For now, just accept that there is two types of mass: rest mass and relativistic. So, their relativistic mass is simply their relativistic energy, divided by c2, or mrel = E/c2.The energy for photons is E = hf, where h is Planck's constant and f is the photon frequency. This frequency and thus the relativistic energy are frame-dependent.

Was Einstein the only person who figured out the relation between energy and mass???

The simple is no. But, if I speak technically then; yes. 

In 1873, Nikolay Umov pointed out a relation between mass and energy for ether in the form of Е = kmc2, where 0.5 ≤ k ≤ 1. The writings of Samuel Tolver Preston, and a 1903 paper by Olinto De Pretto, presented a mass–energy relation. 

Nikolay Umov
Nikolay Umov
Bartocci (1999) observed that there were only three degrees of separation linking De Pretto to Einstein, concluding that Einstein was probably aware of De Pretto's workAlso, Gustave Le Bon in 1905 speculated that atoms could release large amounts of latent energy. Among all these scientists Einstein figured out the correct formula and that's why he is credited with its discovery.

In my upcoming articles, I am going to simplify the difference between rest and relativistic mass so, don’t forget to subscribe to our website and follow me on social media for updates…..

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Thanks for reading.....

See you next time!!!

                                                                    -Ratnadeep Das Choudhury
                                                      Founder and Writer of The Dynamic Frequency