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bio website motls.blogspot.com
location Czech Republic
age 41
visits member for 3 years, 11 months
seen 13 hours ago

Hi, I am a string theorist and a publicist.


Dec
22
comment How can we take pictures of something billion of light years away?
Dear Joshua, maybe Tolga wants to take a picture of someone this far, but she wants him to smile, so she first says "cheese", waits when the subject starts to smile, and press the trigger. Incidentally, the end of the visible Universe is currenly about 40+ billion light years from us, not 14, because those regions continued to expand between the moment when light was emitted and now.
Dec
21
awarded  Nice Answer
Dec
20
comment Is it acceptable to base a physical theory on a philosophical idea?
You can get the idea for a theory from any source, previous theories, philosophy, religion, drugs (this was a frequent source in recent decades), or something else. But to be successful, you must formulate the resulting hypothesis/theory in a quantitative language that makes some predictions about the phenomena in Nature and these predictions can't be true tautologically - there has to be something non-obvious about them. And these predictions have to agree with the empirical data. When they don't, the theory is killed. When they do, it is strengthened.
Dec
19
comment Does lunar module need the same amount of fuel for landing and take off?
Landing and taking off are opposite to each other so the signs of the energy change are opposite, right? Maybe you are asking about the amount of fuel but that's something different than energy. Fuel has to be spent - the sign is always decreasing - but the energy may change in both ways, to mention a difference between the two. The switching between the orbit and the surface are opposite processes, so the energies are opposite but the amount of fuel may be the same. To get to a low orbit is 1/2 of the energy needed to escape the gravitational field completely.
Dec
18
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.
Dec
17
awarded  Necromancer
Dec
16
awarded  Enlightened
Dec
16
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 warming
I 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
awarded  Enlightened
Dec
12
awarded  Nice Answer
Dec
12
awarded  Nice Answer
Dec
12
comment Intensity in rainfall and global warming
I 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 warming
Someone 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 warming
And 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 warming
This 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 warming
The 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.