What does e = mc^2 actually mean?


What does e = mc^2 actually mean?

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Energy and mass are the same thing. It’s like recognizing that light and radio are the same thing.

Einstein determined that matter can be converted to energy, which is what happens in a nuclear reaction. The products weigh a bit less than the reagents, and the missing mass is converted into energy according to that equation.

The E is for energy, m is for mass, and c is for the speed of light

I find it funny that robot chicken did a sketch on e=mc2. It’s very basic.

The equation is pointing to that the total energy any matter has. is directly related to its mass.

The C in the equation is speed of light in a vacuum. It’s so strange that the raw speed of light. is fundamental in so much of physics.

The robot chicken video.


The ELI5 is that for special relativity to work, things going faster have to be harder to accelerate. It’s a consequence of the two postulates of special relativity, physics are the same for everyone, and everyone in the same inertial reference frame (accelerating at the same rate) sees light moving at speed c.

As a result things moving faster must gain inertia and therefore mass. Therefore the mass/inertia -in general- should be the result of energy. Kinetic energy is one form of it. Nuclear binding energy is another. In fact 99 percent of mass a proton or neutron is a result of the binding energy of the quarks that make it up.

Individual particles like quarks and electrons do still have a rest mass, but even that is still considered equivalent to energy as when something like a particle and antiparticle collide all the stuff that must be conserved (called quantum numbers) add up to zero, the particles cancel each other out, and you are left with energy. Alternatively when you have a crapton of energy in one spot that energy can spontaneously form particles via pair production.

Basically this is what particle accelerators do. Speed up some particle so it has a crapton of energy, smash it into something, and watch all the stuff that gets spontaneously formed.

The full explaination involves math that’s a good deal beyond basic calculus :F

When an object is at rest (compared to the observer), then that object has energy equal to its mass times the square of the speed of light.

You can indeed release some of this energy, depends on what kind of object it is and what process you use, and afterward the mass of the object will be reduced.

Note that in the old days physicists used to interpret this equation as saying mass and energy is the same, but we no longer do that now, not in that simplistic manner. That interpretations have problems when the object is moving. So now mass is only directly correspond to energy when the object is at rest (compared to the observer). Unfortunately, the old interpretation still stick around in lower level textbook.