# Recent Content by PeterDonis

1. Post

### I Energy-momentum formula and deBroglie wavelength

Post by: PeterDonis, Jan 20, 2018 at 12:44 PM in forum: Special and General Relativity
2. Post

### I Exceeding the speed of light (stars seem to exceed c in our Earth's rotating reference frame)

This is how I understand Kretschmann's argument, yes. Basically it says that you can give any theory a tensor formulation, so saying "a valid...
Post by: PeterDonis, Jan 20, 2018 at 12:34 PM in forum: Special and General Relativity
3. Post

### I Why is position-space favored in QM?

This is true for continuous observables, but not for discrete ones like spin.
Post by: PeterDonis, Jan 20, 2018 at 12:55 AM in forum: Quantum Physics
4. Post

### I Star Gravitational Binding Energy Questions

You're welcome!
Post by: PeterDonis, Jan 20, 2018 at 12:54 AM in forum: Astronomy and Astrophysics
5. Post

### I Topology of the Universe and infinities

You might not mean to, but the language you are using seems self-contradictory: It's flat, but it's not flat? You're contradicting yourself....
Post by: PeterDonis, Jan 20, 2018 at 12:52 AM in forum: Cosmology
6. Post

### I Star Gravitational Binding Energy Questions

The variation in the Earth's density is much less than the variation in the Sun's density. The Earth's density varies over less than an order of...
Post by: PeterDonis, Jan 20, 2018 at 12:07 AM in forum: Astronomy and Astrophysics
7. Post

### MIT Exercises

We don't give links to homework solutions. MIT's open courseware site is easy to search. Thread closed.
Post by: PeterDonis, Jan 19, 2018 at 6:06 PM in forum: Classical Physics
8. Post

### I Energy-momentum formula and deBroglie wavelength

He postulated that the formula $\lambda = h / p$ can be applied to particles other than photons. He did not postulate that the formula ##E =...
Post by: PeterDonis, Jan 19, 2018 at 5:06 PM in forum: Special and General Relativity
9. Post

### I Topology of the Universe and infinities

No. It would be curved, but the curvature would not be measurable by us.
Post by: PeterDonis, Jan 19, 2018 at 5:03 PM in forum: Cosmology
10. Post

### A theoretical flotation device using a vacuum (for a novel)

Moderator's note: moved to the Sci-Fi/Fantasy forum.
Post by: PeterDonis, Jan 19, 2018 at 4:38 PM in forum: Science Fiction and Fantasy
11. Post

### I Topology of the Universe and infinities

If the universe is spatially infinite, it can't have a geometry that can only be spatially finite. However, it is possible for the universe to be...
Post by: PeterDonis, Jan 19, 2018 at 4:36 PM in forum: Cosmology
12. Post

### I How much time dilation is there within a contracting remnant

And where does that equation come from? Your "reference point" for "zero time dilation", yes. I'm not disputing that. But the point whose time...
Post by: PeterDonis, Jan 19, 2018 at 2:20 PM in forum: Special and General Relativity