PAllen's latest activity

No, that's not the issue I realized. You have a piece of ##E^2## embedded in ##S^3##, all embedded in ##E^4##. I was thinking that a...

What I was thinking of here was based on the 3-sphere embedded in ##E^4## being able to contain a surface that is metrically ##E^2##...

I am saying this is not necessarily true. True is that you can find a hypersurface containing it such it is a geodesic of the...

I am not sure that is always true. Consider, by analogy, a 3-sphere embedded in Euclidean 4 space. It can contain a geodesic of the...

Yes.

Actually, if you take any small part of the geodesic, and a small neighborhood around that part, then that geodesic segment is minimal -...

True, but that is just a recipe for constructing a pure Riemannian manifold, that happens to a submanifold. So it is actually covered in...

No, not longest distance - you can deviate from a non minimal great circle path and make it longer - by any amount with squiggles. In...

Let’s keep in mind that the shadow would have to be 300 meters for a one microsecond delay between front and back. I don’t think the...

Consider the scenario for a slow moving object (close to a screen, far away flash bulb). What do you see? How is the fast moving object...

If you make the distant light source a flash bulb (at rest in screen frame), the fixes simultaneity. Then, you will definitely see a...

A number of teachers have been interested in collecting the black and white films that were part of the PSSC program in the 1960s. Many...

Possibly useful: www.reddit.com/r/Physics/comments/162yl28/all_the_classic_pssc_physics_films_i_have_found/ and the last URL in that...

Happy holidays folks. So I spent some time over the Thanksgiving holidays and developed a program that renders electric field lines of...

Regarding post #21, the formula given for area minimizing ##\theta## simplifies to ##\tan\theta=c/d##. The minimum area just becomes...