E=MC². What does formula E=MC² really mean?

The important part of my post was “which can be observed”.
In pretty much all of the “speed of light” statements Einstein was talking about what could be seen using light as an input for observation. His espoused philosophy, the philosophy of science then as well as now (mostly), was that truth in science must be limited to what can be observed. Even if you observe an object at a place and later at another place such that it could have gotten to the second place only by moving faster than the speed of light, under the philosophy of science you cannot say that you have observed it moving faster than light speed or that it did move faster than light speed; you must entertain another explanation.

We are getting close to recording lightspeed.

To answer the OP question.

E=MC² is an equation that describes the interrelational values of Mass, Motion, and Energy.

The Essential Relationship between Mass and Energy

In Newtonian mechanics, the mass, time, length and energy are independent respectively; but in special relativity, these four quantities all have something to do with speed and mass and energy that can convert into each other, which makes the physics academia in a great mess.

Therefore, people should do everything from the angle of philosophy, discuss the original relationship between mass and energy and clean the false influence of the special relativity.
https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.518.7097&rep=rep1&type=pdf

Not a particularly interesting paper. Einstein’s expressions describe what objects in motion “look like”. Newton describes what things “are”. Big difference.

As for the speed of light being constant, what is more likely, that light is propagated without any energy consumption or degradation or that the propagation takes some energy to accomplish and we witness that as red shift.

As for the universe being 3-D, it is not. The material Universe, our universe of Fermions, has one dimension and that dimension is volume. In the material Universe everything that exists occupies a specific volume and no other thing that exists can occupy that volume. We commonly use three “dimensions” to describe the volume of our material Universe but any number of similar “dimensions” may be used to describe it as well. The geometry is easier to envision when a regular geometric construct (polyhedron) tessellates the volume.

As for energy, energy is not a “thing”. Energy does not exist. It is a description of the capacity of things to displace other things.

As for time, time is not a thing. Time does not exist. Time does not influence any thing. Time is a description, from memory, of the relative states of things.

I think it worth noting that displacement of a thing by another thing is the only mechanism (force) we know of for achieving motion of things.

I always thought that "redshift " was a result of the “Doppler effect” as the lengthening of wave lengths, due to the expansion of the universe.

The farther a galaxy is, the faster it expands away from us and the more its light appears… [+] redshifted. A galaxy moving with the expanding Universe will be even a greater number of light years away, today, than the number of years (multiplied by the speed of light) that it took the light emitted from it to reach us. But we can only understand redshifts and blueshifts if we attribute them to a combination of motion (special relativistic) and the expanding fabric of space (general relativistic) contributions both.

What Causes Light To Redshift?

What does formula E=MC² really mean?

I’m told it’s what makes this possible.

WIRED

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