# Luboš Motl

Czech Republic

motls.blogspot.com

Age: 41

Hi, I am a string theorist and a publicist.

 18h comment How do I calculate the perturbations to the metric determinant?Hi, one may do the calculations in both ways - but your way would have to be fixed by adding the factor of 1/2 on the right hand side. My way assumes that $g_{\mu\nu}$ is a general tensor, not necessarily symmetric, and only treats the symmetricity as a "random feature of the initial conditions". Your way would effectively differ from mine by defining $g$ as the symmetric part of "my" $g$ but one must be careful about such things. My way is surely the standard way how the derivatives are calculated. 1d awarded Necromancer 2d awarded Enlightened 2d awarded Nice Answer Dec 15 comment What is a path integral?I've already answered how you use path integrals. Dec 15 comment What is a path integral?No, it is a function - a mathematically similar object - but it is meant to be a classical field, and a classical field is something else than a quantum wave function. The value of a classical field - in the whole spacetime - describes a history of a physical system (the field). The integral is a "sum over histories". Except that it is not a sum of a small/finite number of terms. It is an integral, a path integral which is even more "integral-like" sum than the ordinary integral. Dec 14 comment What is a path integral?Dear @TAbraham, it is a functional which needs to be explained more operationally to be useful in the calculation of the path integral, and in my explanation (or lattice regularization of the path integral), $S[\phi(y)]$ is a function $S$ of finitely many variables called $\phi(0),\phi(0.01)$, and $\phi(y)$ for $y$ in the finite set that approximates the real interval. Dec 13 comment Intensity in rainfall and global warmingI have only talked about the sorry state of that field because you have opened this sociological debate, it was not my initiative. You have not presented a glimpse of a problem with my physics arguments - de facto proofs - that all these effects are negligibly small and that's what matters here. ... I agree that something isn't textbook material just because someone wrote it in a book and he calls it a textbook. But these basics of atmospheric physics in Lindzen's book are textbook material. Dec 12 comment Intensity in rainfall and global warmingI am totally sticking to the content. It is you who is, instead of discussing the physics involved in this question, trying to bully others by references to some friends of yours who don't have any valid arguments and evidence, just like you don't have, and their non-existent authority and non-existent credibility. This may be how some political or religious organizations decide about answers to scientific questions but it's not how it works in science. In science, questions are being answered by evidence, rational arguments, and calculations, not by intimidation. Dec 11 comment Intensity in rainfall and global warmingSomeone may be "established" but what's more important is whether the papers or claims are right or wrong and what you write is wrong – whether or not you may find a few hundreds other wrong people and call it "consensus". In this discussion, we were not talking about the greenhouse effect per se. You are completely distorting what happened. We were discussing about a particular extra hypothetical consequence of a warming - regardless of the reasons of the warming - and I explained why this effect is tiny enough to be unobservable. The physics is robust and you dislike it for corrupt reasons. Dec 10 comment Intensity in rainfall and global warmingAnd it is certainly not true that there are "thousands" of good scientists doing this global warming stuff - the same kind of twisting of usually elementary physics facts and laws done in order to defend the indefensible and promote risks that can't exist according to the laws of Nature - the same type of rhetorical exercises that you have just shown us. The number of good scientists who are in your discipline today could be counted by fingers on two hands. Dec 10 comment Intensity in rainfall and global warmingThis is a server about physics and this problem is a physics question. It may be answered - in this case approximately - by the usual methods of physics and the answer is what I wrote. What some uncontrolled mindless computer models say or do not say is completely irrelevant. Precipitation doesn't appear in any tails. Precipitation is started when a function of the humidity, pressure, and temperature reaches a critical value that is going almost exactly through the center of the parameter space. So no strong dependence on tiny shifts of parameters is possible here. Dec 9 comment Intensity in rainfall and global warmingThe entropy obviously increases with the temperature but there is nothing wrong about the entropy or absolute temperature higher by a fraction of a percent, and it does not detectably increase the intensity of hurricanes, torrential rains, or anything else. The 2nd law implies that the energy lost in the thermal chaos won't spontaneously be extracted and become useful macroscopic motion such as the wind. All thermal engines etc. require temperature differences, not just high temperatures. If you don't understand this comment, you should immediately return your PhD. Dec 9 awarded Caucus Dec 9 comment Intensity in rainfall and global warmingEven if this dependence exists, the surface-to-tropopause temperature difference would change by that 1 °C or 2 °C per century at most – which means from 100 °C to 101 or 102 °C, so by one or two percent. The rainfall intensity or whatever is at most a small-exponent power law, so it would change by a percent or two, too. It is absolutely ludicrous to suggest that this change could be measured in the real world – or that it is even dangerous. Dec 8 answered What gives the higgs boson mass? Dec 6 comment Intensity in rainfall and global warmingI mentioned a critical thing here - textbook material of atmospheric physics, namely a commonly used graduate textbook covering all these basic physical processes and written by a famous MIT professor. You attacked it, without a glimpse of rational evidence, and even criticized that I used the word "textbook stuff" for textbook stuff, and you suggested something that every good high school student knows to be impossible - namely the suggestion that the thermal motion of atoms is converted to hurricanes. Energy lost in heat can't be turned into useful motion - 2nd law of thermodynamics! Dec 6 comment Intensity in rainfall and global warmingNo, the gradients don't increase - the vertical gradients are given by the lapse rate. What increases is the height of the tropopause - the thickness of the troposphere. This increase due to "global warming" - CO2 or otherwise - is nearly negligible and the hurricane activity is proportional to a power of the height with a moderate exponent, so any impact of these vertical changes on the hurricane activity is guaranteed to be unobservable. It is you, not me, who is attacking atmospheric physics, starting from its most standard graduate textbooks (and from the 2nd law of thermodynamics). Dec 5 comment Intensity in rainfall and global warmingMy statement that it is a "textbook material" means that every competent atmospheric physicist must learn this stuff before he or she may start to do actual serious research. The fact that a bunch of incompetent, corrupt, and ideologically driven pseudoscientists wants to make a fact about physics controversial doesn't change anything about that. What you write is complete nonsense from a physics viewpoint. All motion in the atmosphere and anywhere is always governed by gradients. A higher or lower but constant temperature clearly can't induce any macroscopic circulation. Dec 4 comment How can the Gallilean transformations form a group?The whole transformation identified by these 10 numbers - how much you shift the velocity, how much you rotate around which axis, and how much you move in space and time - is an element of the group. The composition of the transformations is the group operation. You just transform the spacetime twice and you get another transformation that may be identified as one of those I have already described, and parameterized by those 10 numbers. There is also the identity element - transformation that keeps $t,x,y,z$ fixed - and inverse transformations.