eli5, E = mc squared

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Tried watching a few videos and reading articles, dumbed down even for me, still can’t get my head around it.

Let’s assume it is a 1 kg lead weight in the vacuum of space floating at 1mph.

if its floating through space then apart from kinetic energy which sent it there, and the gravitational energy which made it, what energy is there in that object which makes it applicable to the equation. “A small amount of mass is equal to a large amount of energy” but how?

Also, why is it the speed of light squared? Surely it’d just be the speed of light. If squared that’d be a massive speed so why is it used here?

Finally how come it’s so important? Why is it still important today? Don’t want to sound reductionist but this really makes no sense to me to why it’s so famous.

There are plenty of explanations, none of which make this equation make sense. So assume I am actually 5 years old and somehow figured out how to make a reddit post, how would you explain it?

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14 Answers

Anonymous 0 Comments

The lead weight is made up of atoms of lead. The atoms have a nucleus of protons and neutrons held together by the strong nuclear force. That is a large amount of energy holding each nucleus together.

If you were to break all those nuclei up converting your solid lead mass to just free roaming protons and neutrons (annihilating the matter completely) all that stored energy would be released and it would be huge. In fact it would be exactly equal to the square of the speed of light times the mass.

I’m not sure exactly why it’s exactly the square of the speed of light or how the speed of light comes into play here but that’s the beauty of the equation to me. Somehow these fundamental constants tie together at the most basic levels of reality.

Mass is just energy clumped together! Imagine how much energy is contained in the sun and even in the atoms on earth

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