Luboš Motl

Czech Republic

motls.blogspot.com

Age: 41

Hi, I am a string theorist and a publicist.

2h
comment Do apparent event horizons have Hawking radiation?
Yes, it's directional. The "apparent source" at infinity has no preferred direction but we're observing it from a direction. Yes, it's from behind. Because of the equivalence principle, one may see that the direction is the same in the black hole case or Unruh case. The direction where the "source" sits is the side on which the stomach presses the interior of your belly. That's true for a black hole above which you try to keep your distance, so it must be true for any acceleration. The source is a distant point from which you accelerate away.
13h
comment Suntan: UV absorption vs daytime
Good for reminding me about this question, Rick, I missed anderstood's comment before - even though I was interested about this question every summer including this one. ;-) The drop in the morning and afternoon seems almost linear - I sort of expected it to be more brutal, exponential, like exp(-t) in the evening, because of the exponentially decreasing transmission through the absorbing layer, but it apparently ain't so.
18h
awarded Nice Question
1d
comment How does work function transform in Einstein's special theory of relativity?
Plain and old special relativity holds anywhere and everywhere and always (at least if GR is not needed - if the gravity is weak or otherwise easily incorporated). The laws have the simple form in all reference frames. Just the laws describing the properties of materials, including ionization, are simpler in the rest frame of the material. But in each frame, you may simply say that the law is "whatever you get by Lorentz-transforming the laws in the rest frame into our frame".
1d
comment Difference between "Leiden school" and "mainstream" Indo-Europeanists?
Dear @PavelJetušek - understood. So maybe the division of the IEists is based on some historical difference in the opinions that has faded away, and now the polarization is just because two groups of people don't like each other? ;-)
2d
revised Why speaker beeps when a cellphone is kept near it?
added 177 characters in body
2d
revised Why speaker beeps when a cellphone is kept near it?
added 476 characters in body
2d
answered Why speaker beeps when a cellphone is kept near it?
Aug
25
comment How does work function transform in Einstein's special theory of relativity?
In the movie frame, the metal is moving, and the minimum energy of the photon to knock off an electron is then obviously different, so that the condition is equivalent in all frames. The minimum energy to knock off an electron is normally specified in the metal's rest frame.
Aug
24
comment Was Germany's post 1939 expansionism necessitated by essentials needs?
@Arjang - When A occupies B and dismantles the army of B, many things may happen. Which of them do you think to be "the" outcome? In Fall 1938, the Munich Treaty castrated Czechoslovakia. The country of (Second) Czecho-Slovakia had the task of moving to the core of the (indefensible) reduced country and selling weapons that seemed excessive now. In March 1939 when Bohemia and Moravia were occupied and became protectorate, the Czecho-Slovak army was peacefully disbanded (ended at the end of 1939), honor of the ex-soldiers was respected, and they were given civilian jobs. Sad but smooth.
Aug
24
comment Was Germany's post 1939 expansionism necessitated by essentials needs?
@Arjang, the trip of the Moon didn't have to happen. It was in no way guaranteed even though the technology became available. Political considerations were actually essential for it to happen. America was humiliated by the Soviet leadership in space research, so it worked hard and became the #1 country when it sent the people to the Moon etc. The trip to the Moon has been a dream of many generations. The dreams were helpful; and a few other conditions had to be obeyed, too.
Aug
24
awarded Enlightened
Aug
24
answered Why do electrical storms cause metal objects to vibrate?
Aug
24
answered Does deceleration (or negative acceleration) feel like acceleration?
Aug
23
awarded Guru
Aug
23
answered Do physicists have idea about medium that would be required to perceive other dimensions?
Aug
23
revised Matter to energy conversion
added 360 characters in body
Aug
23
answered Matter to energy conversion
Aug
23
comment Was Germany's post 1939 expansionism necessitated by essentials needs?
@Arjang - the question was about the causes or justifications of the expansion itself, not about its consequences and applications (what the expansion allowed), so your comments are just not relevant for this question. Buzz Aldrin just used the trip to the Moon to pocket $30 or so for travel expenses which doesn't mean that the trip of the Moon was necessitated by Aldrin's need for extra $30 in 2015.
Aug
22
awarded Commentator
1 2 3 4 5