1,200 reputation
721
bio website dotancohen.com
location
age 36
visits member for 3 years
seen 8 mins ago

May
13
revised Is the environment around an asteroid harsher than in interplanetary space?
edited tags
May
13
asked Is the environment around an asteroid harsher than in interplanetary space?
Mar
24
accepted Why is Jupiter so sharply defined?
Mar
21
comment Why is Jupiter so sharply defined?
Thanks. Looking through the paper I see lots of formulae with r^2 but nothing that would suggest a sharp cutoff, such as (r-n)^2 or the like. Where is there mention of a sharp cut off for the pressure and density at some specific r? Thanks for the reference, it does seem to address quite what I am asking about.
Mar
20
comment Lowest gravity on Earth's surface?
The colour coding of GRACE is fine. The lack of an X to mark the lowest point is my question.
Mar
20
comment Lowest gravity on Earth's surface?
Thank you. I did see that, but as you mention it does not pertain to the entire Earth's surface but rather only to the relatively small portions of the Earth's surface which constitute large human population centers.
Mar
20
comment Why is Jupiter so sharply defined?
I agree that the image that I posted was edited. For one thing, the phases of Jupiter and Io are different though their centers lie in about the same camera direction.
Mar
20
asked Lowest gravity on Earth's surface?
Mar
20
asked Why is Jupiter so sharply defined?
Mar
17
accepted How do we know the masses of single stars?
Mar
17
comment How do we know the masses of single stars?
Thank you jdmcbr!
Mar
17
asked How do we know the masses of single stars?
Mar
10
accepted Repulsive gravity
Mar
3
comment Second law of Thermodynamics: Why is it only “almost” always true that entropy is non-decreasing?
Thanks, Arnold. I had not considered the possibility of a metastable system, and if that is in fact the reason for the word "almost" then I think that it should be clarified or even omitted.
Mar
2
comment At what fraction of the speed of light have people traveled?
@VineetMenon: I suppose that would be the velocity of the Milky Way with respect to the CBM, which is about 600 km/s I think.
Mar
2
comment Repulsive gravity
Thank you. I understand the term antiparticle to mean a particle with opposite electric charge from a "normal" particle. I don't think that this implies that the particle is also of opposite "gravitational charge". In fact aren't particles and antiparticles supposed to annihilate one another upon contact? Doesn't contact imply some attractive force between them? Or is that attractive force the different charges, which would overcome the supposed "repulsive gravity effect" just as the repulsion of like-electric charges overcome the attraction of gravity?
Mar
2
comment Repulsive gravity
Thank you. I'm not sure that the universe is so smooth on large scales. The CBM has a dipole anisotropy, and even the existence of the Great Attractor indicates large-scale unevenness. As for inflation, my silly idea actually could help explain it: when the two particles were still mixed up in the early universe, the universe expanded rapidly due to the repulsion. Only after the two particle "charges" were able to conglomerate and separate from one another did the blobs of conglomerate stop expanding rapidly. Our whole observable universe is just the blob that we wound up in.
Mar
2
asked Repulsive gravity
Mar
2
comment How does such strange microscopic behavior at the atomic level (quantum mechanics) lead to the macroscopic behavior at our level?
Can you clarify the first word of your post? "Mcroscopic" is missing a rather critical vowel!
Mar
2
comment Relativity in Real Life
@dmckee: Although I agree that the question is not about physics, it is about a subject that is often confused with physics. At least, I had a similar question asked of me once, with the asker also thinking that it is a physics question. On that basis I suggest an answer of "This question is not physics even though it appears so to the layman" and close it at that. Other similar questions that will surely pop up can then be duped to this one.