robphy's latest activity

Is this the paper you seek? From the WIkipedia article.... Bel, L. (1958), "Définition d'une densité d'énergie et d'un état de radiation...

Here's a 2025 interview with Abhay Ashtekar (Penn State), split into parts. (I was especially interested in his stories with Robert...

So are we! :welcome:

MENTOR NOTE: This thread has been split into two parts. This part discusses the Static Equilibrium and is now closed, while the...

And so, a model (motivated by physically observed phenomena) and a set of tools to analyze the model lead to testable predictions, which...

The Michelson-Morley apparatus is essentially a [typical] transverse light-clock (whose light-signal is perpendicular to the direction...

You can't - that would contradict the second postulate.

In special relativity, there is no such reference frame (that is equivalent to that of a typical ["timelike"] observer) where light is...

My thoughts are just the opposite. I think it's the very first thing that ought to be introduced. Of course only qualitatively at first...

I had the same thoughts. Without other cubes of different metals, e.g., Mo, Fe, Cu, Al, there a limited uses for a single cube. One...

Is it just Tungsten, or are there other metals available (in the same size)? These could be useful for measurements of mass and volume...

In my experience this definitely takes a great deal of time and effort. Reading something like Spacetime Physics by Taylor and Wheeler...

You can also derive ##d \gamma = \gamma^3 (\vec \beta \cdot d \vec \beta)## fairly easily and use that to do a change of variables...

Good afternoon, This is not Paul, but rather his son Robert. I am very sad to write here that my dad passed away on Saturday...