“A stitch in time saves energy “. In 1905, it was not just Albert Einstein, who found mass and energy are interchangeable through the equation E=MC^2. Let us begin this interchangeability with a story. Before 1820, many scientists and chemists believed that energy exists in different forms and all of them were unique or different. But, Humphry Davy and Michael Faraday disproved this belief by their experiments. They found that energy in any form gets transformed into another energy and they are interconnected.
Humphry Davy and Michael Faraday
Humphry Davy and Michael Faraday experiment about mass-energy equivalence proved that when one kilogram of gold metal is heated to 10°C from its normal temperature lead to an increase in mass. Here, heat energy is converted to mass. When the metal is cooled, the metal loses the mass that it gained. So from this, it was proved that mass and energy were the same. Though, people did not realize this and started arguing how mass and energy could be the same during conversion.
Speed of Light
To answer “why the mass of any object is multiplied by the speed of light to determine how much energy it has inside?” , whenever you convert part of an object or any other piece of matter to pure energy, the resulting energy is by definition moving at the speed of light. We are aware that the speed of light is 186,282 miles per second or 299,792 kilometers per second, and nothing can travel faster than light. This gave rise to the theory of special relativity by Einstein over a period of time.
According to special relativity, distance and time are linked to objects that are moving at a consistent speed in a straight line. The equation E=MC^2 is based on special relativity, which explains energy and mass are interchangeable and just that they are different form of the same thing. If the whole mass of an object is converted into energy it proves how much energy would have been in that object. This could be imagined as how powerful an atomic explosion would be after its mass is converted into an explosion. The same equation also demonstrates how mass increases with speed, which as a result puts a speed limit on how fast things can move.
Coming back to special relativity, time moves relative to the observer, meaning that time travels more slowly when someone is moving than when someone is standing still. Einstein theory can be imagined to a moving car at a point in the straight line equally between two trees. If a thunder-light hit both trees at the same time, due to the motion of the car, the person inside the car would see the thunder-light hit one tree before the other tree. But the person outside would see simultaneous strikes.
Einstein decided that concurrence is relative, that being said the events that are simultaneous for one observer may not be the same for another. This led Einstein to the conclusion that time flows differently according to the state of motion, and to the conclusion that distance is also relative.