HACKER Q&A
📣 denton-scratch

What is E=mc^2 saying?


The way it's presented in popsci (and very often by pros) is that c is a very big number - bigger than any other possible speed - so c^2 must be REALLY big. Therefore a small amount of mass is equivalent to a really lot of energy.

So here's the question: is this bullshit?

The value c is a constant; so c^2 is a constant. That means the equation can be rewritten as "E=mK", and since there are no units, that's the same as "energy is proportional to mass".

Is that wrong? Or is the standard formulation a standard piece of science PR bullshit, whose only purpose was to make people go "Wow!" Did Einstein do science PR?

  👤 db48x Accepted Answer ✓
Yes, cĀ² is a constant and energy is proportional to that constant.

Actually, Einsteinā€™s formula was EĀ² = |š©|Ā²cĀ² + (mcĀ²)Ā². š© is the momentum vector, and we need to square the magnitude of that vector to find the energy due to momentum. Since momentum is often zero, that term can be neglected leaving you with E = mcĀ². When considering light, however, it is mass that is zero, leaving you with just the energy due to momentum. None of it is ā€œPR bullshitā€.

👤 timonoko
My father, born in 1912, explained Einstein thus:

"The kinetic energy of a moving object is 1/2mv^2. So when the object has accelerated to light speed, you have wasted half of its mass. And when you brake down from light speed you have to waste the other half. So may be you can travel faster than light, but cannot Ever Arrive Anywhere."

At age 12 I thought this was quite brilliant, because he was not educated in this and he thought 12 Volt battery was as dangerous 220 Volt plug.

👤 UmYeahNo
Other much smarter HN'ers might respond, but the formula is called the mass-energy equivalence formula, so - yes, energy is proportional to mass, and yes, mass has an absolutely gargantuan amount of energy locked up in it.
👤 al2o3cr 

    So here's the question: is this bullshit?
Here's the answer: no
👤 ohiovr
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