Recent content by James_Harford

"Something deeper than math that cannot be encoded." What would that be? That notion is imaginable, and easily communicated. But no example can be found. It cannot be communicated, not even as a thought between the hemispheres of one's own brain, because communication requires an encoding...

The article is dated November 2011. So, I would think any question about its importance would be settled by now.

A 100 watt light bulb radiates 100 Joules per second in a wide range of frequencies, only some of which are in the visible part of the spectrum. So in 1 second 100 Joules of photons are emitted in many colors. E=hv gives the energy of just *one* photon, and v=E/h its color. Since, there is...

Does the following thought experiment illustrate your concern? First, perform this experiment in a remote region of space far from detectable gravitational fields. Second, *temporarily* forget about special and general relativity. This is a *relatively* simple Newtonian experiment. Consider...

Another thought... If the point event outside of the EM is not in its equatorial plane, the radial path will not cross the center of the rotating EM -- but will it cross the axis at some point within the EM? If so, then an interesting special case is an infinitely thin disk, in which case...

Ok, thanks PeterDonis.

The rear of the train is further forward (closer to the front) than it otherwise would be. Doesn't properly account for the Lorentz Contraction, but interesting.

Ach! Instead of space-like geodesic, I mean geodesic within the sheet of 3-space of constant time, and instead of point, point-event.

Ah, I should add that this radial direction is ascertained from the relative accelerations of a small sphere of test particles.

Points taken. If I understand correctly, the conditions you gave (with caveats) could be stated as follows: Given an EM that rotates uniformly, is axisymmetric, has a well-defined equatorial plane of symmetry perpendicular to its axis of rotation, there exists for every inertial frame at...

Thank you PeterDonis for these very interesting comments -- caveats included. It is interesting that the "convergent-pointing-to-center" effect occurs in so many cases, and in particular under what to me seem the somewhat generous conditions described in your second-to-last-paragraph. I...

Thank you for these observations about the use and misuse of the notion of tidal gravity. First of all, yes, I am asking about phenomena whose measurements are specific to particular idealized reference frames. And yes, the test masses were meant to be extended objects I should have used...

Correction: the word "my understanding" in the 3rd paragraph is not correct.as I do not know this to be a fact.

Thank your helpful observations. I attempted to reformulate the question in a way that avoids the many pitfalls of the first version that you pointed out, including removing all references to CM. Here is attempt #2 -- I hope it is not too verbose or unclear -- and thanks again for your...

Consider a solid globe of mass M and of of uniform density. My understanding is that its external gravitational field, in the absence of any other forces, will apply an instantaneous acceleration to any small test mass directly towards the center of the globe. Is that still true in the...