Eduardo Guerras Valera

1,722 reputation

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I am an astrophysicist. What I do is mainly computational and observational, focused on extragalactic astronomy and gravitational lensing. Additionally, I like to improve my modest background in theoretical physics.

	1,722 reputation	bio	website		visits	member for	7 months
214 badges		location	Spain		seen	7 hours ago

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May 15	comment	Gauge covariant derivative in different books Why the h*** don't they stick to the original convention in the very first paper for everything? It is really so painful, or do they have some need to appear as original? The Susskind lectures have now the + sign, and the David Tong notes have God knows what convention in the Faraday tensor. Everytime I try to cross some details between books and specially the first time I use a new document or internet page, I have to spend the hell of a time figuring out which is the arbitrary convention of that author. The first ten times it was even funny, now it is a pain in the neck. Damn them all!
May 11	comment	How does my hand amplify an FM radio signal? I cannot resist adding a couple of additional amazing links: another Lydia Kavina performance, and a curious amateur thereminist playing The Beatles in front of M51
May 11	awarded	Convention
May 10	comment	Modelling the movement and jumps of a chalk while drawing a dashed line on a blackboard See a truly expert in action, here (Walter Lewin)
May 10	revised	How does my hand amplify an FM radio signal? added 1 characters in body
May 10	revised	How does my hand amplify an FM radio signal? added 133 characters in body
May 10	revised	How does my hand amplify an FM radio signal? added 133 characters in body
May 10	revised	How does my hand amplify an FM radio signal? added 133 characters in body
May 10	revised	How does my hand amplify an FM radio signal? added 133 characters in body
May 10	answered	How does my hand amplify an FM radio signal?
May 9	comment	How much of the universe is observable at visible wavelengths? Interesting, related link: the SpaceWarps project
Apr 30	comment	Keep my salad cold in the microwave And, no, don't try cooking an egg. It really explodes with some violence. I destroyed a brand new oven when I was a teenager. The egg was inside a glass which broke into pieces.
Apr 30	comment	Keep my salad cold in the microwave In the name of scientific laziness and curiosity, just wrap the salad in aluminium foil .AND. don't allow anybody to stay in the kitchen while the oven is working (that includes you of course). What you won't be able to avoid is some lettuce heating due to the hot vapors from the steak. Don't make the oven work that way very long, since there is some risk that you ruin it, by reflecting microwaves in directions where materials are not designed to receive them so directly.
Apr 30	comment	English translation of Helmholtz' paper: “On the Physical Significance of the Principle of Least Action” I am used to Einstein's original papers, and that "Princips" with C is hurting my eyes... Germans have had some (from my point of view) horrible spelling reforms. I believe at least two in the last decades, but I am not sure.
Apr 28	comment	Why we see upright images? Because we haven't drunk enough.
Apr 25	comment	Cancel out Earth's Magnetic field @DavidH, statements based on experimental facts are quite doubtful here, specially if the faraday cage is far from perfect, because magnetic compasses are very sensitive, unless you are talking about a real experience in some well built laboratory cage aimed at that purpose. Frankly, I have not paid any further attention to this question, but the decisive fact here would be either a good theoretical explanation, or at least a reference to a paper. I guess some simple explanation involving a closed fictitious surface and Ampère's law or something similar is required. Nothing too complicated.
Apr 25	comment	Cancel out Earth's Magnetic field I am not so sure. At least an iron cage will deviate and concentrate the magnetic lines through the walls, thus leaving the room inside the cage devoid of lines. Look for example here (I guess the issue with other, non-ferromagnetic material is different, but this with iron is close to the picture I have in mind)
Apr 24	comment	Cancel out Earth's Magnetic field Mmm, I'll think about it. Thanks!
Apr 24	comment	Earth's Magnetic Field, Human Brain and Sleep You have to note the position of the window in your experiences, to be sure that the correlation you are detecting is not due to that variable. The position of the window does matter, because it affects how the air moves inside the room. See my comment below the main question.
Apr 24	comment	Earth's Magnetic Field, Human Brain and Sleep The popular belief against sleeping with your head towards north has to do with the position of the window, that usually is on the south wall. The air near the window cools down and so there is slow but significant convection inside the room. By sleeping with your head just in the opposite direction to the window, you are more likely to get a cold because the air you breathe is being renewed relentlessly during the night, than by sleeping with your body normal to the convective stream.