107,007 reputation
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bio website motls.blogspot.com
location Czech Republic
age 41
visits member for 3 years, 11 months
seen 19 mins ago

Hi, I am a string theorist and a publicist.


Jan
16
answered How much energy does lowering an object into a black hole generate?
Jan
16
comment Does electron go through a forbidden state when annihilate with positron?
No, an electron doesn't go through any forbidden state, surely not along a specific path of the kind you drew in the momentum space. The annihilation event is instantaneous, the momentum and energy are always perfectly conserved, and all external particles are always exactly on-shell.
Jan
15
comment How is this classical “paradox” resolved in electromagnetism?
Dear @Ron, it's always the electric force $q\vec E$ that is doing work. If $\vec E=0$ in a given frame, then there's no work being done. What's your problem?
Jan
15
comment Should you run when under rain?
If you want to minimize the volume of water you absorb per unit time, you should better stay still (more precisely be at rest with respect to the horizontal components of the raindrops' velocity). However, people usually run because they have a place to hide. The faster they run, the earlier they can hide. If you multiply the water per unit time by the actual time you need to hide somewhere, be sure that it's a rational idea for people to run! ;-) For speeds much greater than the (total) speed of rain, it doesn't matter much whether you speed up even more.
Jan
15
comment Do we need a quantum theory of gravity in order to describe photons blueshifted past planck energy?
I gave you +1, Ron, despite your misspelling of Karl Schwarzschild's name.
Jan
15
answered Modular invariance for higher genus
Jan
14
comment Why is there a flux of radiation in the Hawking effect but not in the Unruh effect? (and other questions)
Dear @Tom, as Peter sketched, objects without event horizons can't emit the Hawking radiation because that would violate the energy conservation law. The horizon is a "one-sided membrane", as you correctly wrote, but the Earth's surface isn't asymmetric in this way. Things can go up and down. The region beneath the horizon is hidden so the mass it stored may change, thus rendering the energy conservation law irrelevant. But the Earth would have to get the energy somewhere. The situations aren't the same: black holes are different from stars and planets.
Jan
14
comment If humans were able to catch all sun energy reaching the earth for their use, will the climate change?
Dear @EnergyNumbers, be sure that my statement about the impossibility to isolate the terms is right. This is reflected in all the climatological literature (including the IPCC report) as well. For example, the error margin of the climate sensitivity is as high as the climate sensitivity itself (2.0-4.5 deg C in the IPCC; 0.7-1.3 deg C in better literature). Climatology doesn't know whether the CO2 is responsible for a tiny minority of the 20th century warming or most of it or even more than what we have seen, with some compensations. Everyone who tells you something else is lying to you.
Jan
14
comment If humans were able to catch all sun energy reaching the earth for their use, will the climate change?
Dear @Nathaniel, nope, your "energy consumption" numbers are not right. Most energy we use is consumed by electric motors which move material from one place to another. Some of them - like streetcars and elevators - get back and forth. But some of them don't, like electricity helping to build skyscrapers or get coal out of the Earth. Concerning the first point, the OP clearly stated that the humans are able to catch all the incoming solar energy, so they would not allow some clouds to interfere with this goal. You are solving a different problem.
Jan
14
comment What was missing in Dirac's argument to come up with the modern interpretation of the positron?
Dear @Whelp, none of these two people has gone through (even rudimentary) education in formal quantum field theory that is needed to answer these questions. Penrose is a mathematician (and guy in classical general relativity), Tully is an experimenter. I've taught these things at Harvard and I was explaining you that all high-frequency oscillations that could be called Zitterbewegung are unphysical. BTW $e_R$ and $e_L$ are indeed coupled by the mass term proportional to $m$ but that just gives the particles mass; only the (unobservable) overall phase oscillates, there's no observable oscil.
Jan
14
answered How is this classical “paradox” resolved in electromagnetism?
Jan
14
answered Do Maxwell’s Equations contain the Ideal Gas Law?
Jan
14
answered Earth-Centered Inertial (ECI) reference frame as approximate inertial frame of reference
Jan
13
awarded  Yearling
Jan
13
comment what co-operates with a Super Symmetry Transform
OK, I didn't understand what sensible could possibly be hiding in the original question, so I gave it -1, but your answer doesn't seem to be even containing the keywords of the questions, like "cooperation with mirror symmetry", so although it would be fine in other contexts, I don't think it's answering the question here...
Jan
12
revised If humans were able to catch all sun energy reaching the earth for their use, will the climate change?
added 671 characters in body
Jan
12
revised Can heat be extracted and concentrated?
added 74 characters in body
Jan
12
revised Can heat be extracted and concentrated?
added 103 characters in body
Jan
12
answered Can heat be extracted and concentrated?
Jan
12
answered Can a black hole be explained by newtonian gravity?