# PeterDonis's Recent Activity

1. ### PeterDonis replied to the thread B Conservation of energy in GR.

SR formulas are not valid here. We're using curvilinear coordinates in curved spacetime.

Oct 20, 2018 at 8:06 PM
2. ### PeterDonis liked stevendaryl's post in the thread I The definition of velocity in the de Broglie relation.

Yes, you're right, that the velocity $v = \frac{p}{m}$ in quantum mechanics is the group velocity, rather than the phase velocity. Are...

Oct 20, 2018 at 2:35 PM
3. ### PeterDonis replied to the thread B Conservation of energy in GR.

No, this is not true everywhere along the geodesic. It is only true that the point at the top of the trajectory, where the ball is...

Oct 20, 2018 at 2:32 PM
4. ### PeterDonis replied to the thread B Conservation of energy in GR.

History, mostly. Many physicists thought of this constant of the motion as "the energy an observer at infinity would observe the object...

Oct 19, 2018 at 11:17 PM
5. ### PeterDonis replied to the thread B Moving Charge in a Magnetic field Problem.

Then this thread is closed. If you find a reference, you can PM it to any of the Mentors who has posted in the thread.

Oct 19, 2018 at 10:08 PM
6. ### PeterDonis replied to the thread B Conservation of energy in GR.

Remember that the formula for energy at infinity (per unit mass) is $\xi^a u_a = g_{ab} \xi^a u^b$, where $\xi^a$ is the timelike...

Oct 19, 2018 at 10:03 PM
7. ### PeterDonis replied to the thread B Conservation of energy in GR.

I already answered that in post #15: the energy at infinity is a constant of geodesic motion in GR, for spacetimes in which it is...

Oct 19, 2018 at 8:16 PM
8. ### PeterDonis replied to the thread I How can there be fluctuations in the inflaton field value?.

Yes, this I agree with.

Oct 19, 2018 at 6:40 PM
9. ### PeterDonis replied to the thread I How can there be fluctuations in the inflaton field value?.

Isn't this too strong as you state it? The expectation values of all observables are constant in time; but I don't think you are...

Oct 19, 2018 at 4:45 PM
10. ### PeterDonis replied to the thread Query processing in DBMS.

What book?

Oct 19, 2018 at 3:36 PM
11. ### PeterDonis replied to the thread B Special Relativity - Self Contradiction?.

This one looks like a better one to me. Regarding your original question, you are confusing different quantities that play different...

Oct 19, 2018 at 10:34 AM
12. ### PeterDonis replied to the thread I Is the ground state energy of a quantum field actually zero?.

Ah, ok, as I thought, you are using the term "vector representation" differently from the way I'm used to seeing it used. Your usage is...

Oct 19, 2018 at 10:18 AM
13. ### PeterDonis replied to the thread I Is the ground state energy of a quantum field actually zero?.

Probably this is just an issue of terminology. By "vector representation of SU(2)", do you mean the fundamental representation? As...

Oct 19, 2018 at 10:10 AM
14. ### PeterDonis replied to the thread B Special Relativity - Self Contradiction?.

Please provide a link. We need to know precisely which English translation (the actual "original thesis" was written in German) you are...

Oct 19, 2018 at 10:04 AM