104,525 reputation
7143294
bio website motls.blogspot.com
location Czech Republic
age 40
visits member for 3 years, 9 months
seen 9 hours ago

Hi, I am a string theorist and a publicist.


Apr
9
revised How is formula for converting pressure from mmHg to Pa derived?
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Apr
9
revised How is formula for converting pressure from mmHg to Pa derived?
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Apr
9
answered How is formula for converting pressure from mmHg to Pa derived?
Apr
9
comment projectile power with air resistance
I think that your equations are not correct. Shouldn't $V_x,V_y$ be derivatives of $X,Y$? They surely aren't in your case. They're related by transformations that resemble the deletion of random characters. ;-) Moreover, $\theta$ seems to be dimensionless from some equations and frequency from other formulae.
Apr
9
comment Perturbation of a Schwarzschild Black Hole
Moreover, the main reason why my and our analytic calculation became more famous than it deserved was that it proved the appearance of $ln(3)$ in the frequencies, in agreement with a heuristic guess based on numerical calculations, and this constant has been used to defend "discrete models of black holes", including loop quantum gravity, before it became very clear that the result doesn't generalize to other black holes and the "discrete interpretation" is misguided for many other reasons, too. See also motls.blogspot.com/2005/03/…
Apr
9
comment Perturbation of a Schwarzschild Black Hole
Thanks a lot, @Daniel, but it is very undeserved. I and we with Andy just calculated highly damped quasinormal modes (with high $Im(\omega)$ of the frequency) of the Schwarzschild in 3+1 and then any dimension and the Reissner-Nordstrom one, with some incomplete results on others. The long-time behavior is dominated by the low-lying quasinormal modes (those that are not highly damped) with the lowest Im(omega), those that are hard to calculate. In the Schwarzschild time, $\delta g_{\mu\nu}$ then goes like $\exp(-Im(\omega)_{\rm min} t)$.
Apr
9
comment Perturbation of a Schwarzschild Black Hole
Thanks, @Deepak, your generosity is appreciated but your compliment is undeserved. ;-) I didn't discover the concept of quasinormal modes or the fact that the ringing modes describing the exponential approach to the static black hole solution at later times. I (and, later, we with Andy Neitzke) just analytically calculated the quasinormal frequencies (of the highly damped modes) for some common black holes. However, the long-term behavior of the deviation from the sphericity etc. is governed by the low-lying quasinormal modes with a small Im(omega) - I haven't found anything new on them.
Apr
9
revised Radioactive nuclear fuel?
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Apr
9
comment Is there a good Modern English translation of Newton's “Philosophiæ Naturalis Principia Mathematica” available for free viewing or download?
Dear @user2843, if you want to download the books from Google Books, just download the Google Books Downloader, softpedia.com/progDownload/… ... Almost all these things are doable.
Apr
9
comment Do open strings with both ends attached to the same D-brane really exist?
To see that your conclusion is wrong, just take e.g. type I string theory on a circle, with Wilson lines. There are open string modes that change the values of the $SO(32)$ Wilson lines. Still, if you add condensates of these strings, you don't change anything about the unbroken supersymmetry, so these open string modes clearly preserve the same supercharges as the original type I background. It is not true that the SUSY preserved by the two endpoints has to be incompatible. The intersection is often nonzero, especially for unoriented theories like type I where the reason is obvious.
Apr
9
comment Do open strings with both ends attached to the same D-brane really exist?
Your "derivation" of the non-BPSness is "strange". The BPSness of a configuration may only be judged if one looks at the whole object "simultaneously". But if you still wanted to separate the open string to pieces, the bulk of the open string is just a "string" and a fundamental string locally preserves 1/2 of the supercharges. The end points may also preserve 1/2 of SUSY, and in fact, the same one.
Apr
9
comment Do open strings with both ends attached to the same D-brane really exist?
Dear @Shankar, the D-branes and $p$-branes are physically the same objects, not "two complementary objects". However, D-branes and $p$-branes are two descriptions of them. So maybe, to make your last hint relevant, you could say that D-branes are like a wave function in the position representation and $p$-branes in the momentum representation. They still describe the same wave function, but in two different ways.
Apr
9
comment Has somebody ever tried to measure the gravity oscillations of nearby rotating masses?
@lurscher, in that case, it would be just a question about the detection of normal gravitational waves - like LIGO and the (freshly defunded in the U.S.) LISA? If that's so, why are there the comments about the "nearby" rotating masses? If the distance is much shorter than the wavelength of the gravitational wave expected in GR, and in all the "lab situations" it surely is, then it is a question about some Newtonian waves, and my answer applies.
Apr
9
revised Einstein's box - unclear about Bohr's retort
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Apr
9
answered Does the HUP alone ensure the randomness in QT?
Apr
9
comment Can the Big Rip really rip apart an atomic nucleus?
I think you would have to ask the Big Rip proponents because no one else believes that those scenarios are compatible with the physics we know. I have asked similar questions to the Big Rip champions and the answers never made any sense, either. So I can only say that I totally share your sentiments.
Apr
9
revised Einstein's box - unclear about Bohr's retort
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Apr
9
answered Einstein's box - unclear about Bohr's retort
Apr
9
comment Matrix solution of an equivalent resistance circuit problem
I think it's misleading to use the word "matrix" for this table of numbers because there is no natural linear structure on this space, as far as I can see. So the formulae to invert the conductances to resistances won't be a natural linear algebra formula - it won't be a "function" of the matrix, in particular, it won't be the inverse matrix, I guess. The most striking deviation from the "matrix logic" is that the entries $C_{ii}$ are either zero or infinite.
Apr
8
reviewed Approve suggested edit on Collision time of Brownian particles