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?
In: 0
It makes most sense if you think of it in terms of atomic bombs.
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Uranium-235 atom undergoes fission after a neutron hits it just right.
If you add up the masses of the U-235 atom and the neutron before they collide you get:
> 235.0439 Da + 1.008 Da = 236.0519 Da
If you add up the masses of the Kr-92, Ba-141, and three neutrons that result after the collision you get:
>91.9262 + 140.9144 + 3(1.008) = 235.8646 Da.
But that doesn’t add up! There is 0.1873 Da worth of mass missing!
Isn’t “Conservation of Mass” supposed to be a thing? And “Conservation of Energy” too for that matter?!
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Well, if you carefully measured the energy of all the light and heat that was generated, while measuring the speed of the Krypton and Barium atoms and those three neutrons, you can use those numbers to calculate the total energy produced by the fission reaction.
If you do multiple kinds of experiments like this in a big old particle accelerator, you eventually find that there is a relationship between the amount of energy you get from a specific fission reaction and the before-and-after mass change.
If you plot it out, you get a linear relationship where ΔE changes linearly with Δm, so ΔE/Δm equals a constant… and what is that constant equal to after all the units are worked out? c^2 .
ΔE=Δmc^2 essentially says that energy you get out of the fission comes from the mass lost during fission.
So E=mc^2 is essentially saying that you do still have conservation of energy… if you remember to account for all of the before-and-after mass energies in your accounting.
This mass-has-energy concept is what made it somewhat profound; combine that with the fact that it is so easy to remember and you get a “famous equation”.
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