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

That is called the rest energy of matter.

Energy and matter are the same thing. If you put enough energy into one spot, it becomes matter (and an equal amount of antimatter). 1kg of mass is the same as 90000 Terajoules of energy.

In particle accelerators, when we smash particles together at high speeds, they crash into each other with so much energy that more matter and antimatter are created.

The only way to convert 100% of matter into energy is to annihilate it with an equal mass of antimatter.

During a nuclear reaction, some mass is also turned into energy. Fusing deuterium into helium, you lose a little bit of mass, but gain an equal amount of energy. When you split U-235, some mass gets turned into energy. Iron has the biggest mass discrepancy, meaning if you add or take away a proton from an iron atom, it requires you turn energy into mass.

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