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The "deeper theory" is that the universe is causal. In a causal universe there must be a maximum speed for communication; experiment teaches us that this is the speed of light. It is possible to fra …

If you use some process to create energy, E, then you must have consumed an amount of mass, M, such that $$E=Mc^2$$. This reduces your starting mass by the amount M. If this were not so, then you wo …

The first such work was the Hafele–Keating experiment, 1971. The results are summarized here. Hafele and Keating aboard a commercial airliner, with two of the atomic clocks and a stewardess. Th …

This is a clever experiment, but nature already does something similar for all transparent materials. Transparent materials (glass, air) transmit images; if the image is distorted or indistinct, we k …

The observer standing by the tracks would observe that the baseball is travelling faster than the train, but less than the speed of light. There is an equation for the addition of velocities: see See …

They all agree on the spacetime interval.

From the Minkowski metric plus the first assumption of Special Relativity, the rest may be derived. That is, if it is assumed that physical laws are the same in all inertial reference frames, which …

Usually the energetic process results in a very localized and extremely high energy density; e.g., a group of electrons are ejected from a target by means of a very short, intense laser pulse; some of …

The internal energy of a system must be considered as part of the total energy of that system. This would include all of the parts that are being measured to obtain the total rest mass. In that case …

Kinetic energy in Special Relativity is $KE=(\gamma -1)mc^2$, where $\gamma $ is the Lorentz factor. This is derived from the relativistic equation for total energy, $E^2 = (pc)^2 + ((mc)^2)^2$; the …

The value of c was derived by Maxwell, using his equations, ~1862. It required experimental values for two of the physical constants, ele tric permittiviy and magnetic permeability. You can also cal …

Consider reflection from a piece of glass; the glass is made up of amorphous silica, an atom of silicon and two atoms of oxygen. Light can be modeled as an electromagnetic wave, with the frequency of …

The rate emission of photons is a measure of total power: 100 photons per second vs 1,000,000,000 photons per second. The individual photon emitters are, for example, electrons being driven back and f …

The spacetime interval is a relativistic invariant, and is proportional to the travelers proper time. So in a since you are traveling one second per second, per your own wrist-watch. Every other mea …

The answer would seem to be "no", because you make a medium less dense by removing material from it. Once you get to a vacuum, you are only left with how good is the vacuum? An experiment for an und …