115,951 reputation
7178345
bio website motls.blogspot.com
location Czech Republic
age 41
visits member for 4 years, 7 months
seen 7 hours ago

Hi, I am a string theorist and a publicist.


Aug
14
answered Why is the $dx$ right next to the integral sign in QFT literature?
Aug
13
answered Why is stimulated emission necessary for detailed balance?
Aug
12
comment Dimensionless Constants in Physics
This is very interesting.I am sure that I would reject the paper if I were the referee.
Aug
12
comment Why didn't the Big Bang create heavy elements?
Dear Peter, yes, at temperatures much higher than 10 MeV (over $k$) or so, the high edge of the characteristic energy/temperatures of nuclear physics, it's so hot that complicated nuclei split into simpler ones, like hydrogen and helium, quickly. There was a lot of photons per baryon - lots of bullets that bombard nuclei to split all complicated nuclei to pieces. If the Universe gets through this hotter-than-nuclear stage, nothing is remembered about the initial isotopic composition.
Aug
11
comment Why is the speed of light limited to (only) 299.792.458 m/s?
The numerical value of the speed depends on the units, which were clearly social constructs based on random properties of objects in the world, namely the circumference of the Earth (meter: the circ. is 40,000,000 meters) and the time it takes for the Earth to spin (solar day, and second which is 86,400 times smaller). Now, one meter is defined so that the speed of light is 299,792,458 m/s automatically and exactly.
Aug
11
comment Why is the speed of light limited to (only) 299.792.458 m/s?
The "thing" that is causing light to have the speed it has, and that is causing millions of similar facts, is called the "laws of Nature" or "laws of physics" (in combination with the definitions of units such as one meter and one second) and the discipline working to understand what the laws actually are and say is called "physics". The relevant physical laws are e.g. Maxwell's equations for the propagation of light (electromagnetic waves). Another severe problem with the question is that it contains no question mark.
Aug
11
awarded  Nice Answer
Aug
10
answered Why didn't the Big Bang create heavy elements?
Aug
10
comment Will drinking ice cold water and eating cold food cause weight loss (over a period of time)?
Well, if you're a gym teacher, you're surely trained to say things like "drinking 54 liters a day can't replace physical exercises". But is this moralistic statement really true at the scientific level? Do you have evidence? From the viewpoint of energy budget, such replacements are surely possible. I actually think that dealing with cold - like swimming in cold water - is something that many fat people who dislike sport dislike just like other sports.
Aug
10
comment Will drinking ice cold water and eating cold food cause weight loss (over a period of time)?
@AcidJazz, well, there are no available simple recipes for weight loss. It is still plausible that simple algorithms do exist and in principle, this could be one. Whether it works or not, I am pretty sure that someone could earn lots of money by selling the "cold diet plan" books etc. Jimself: I don't understand what's wrong with "physical estimates". This is a physics server and even if it were not, biology ultimately depends on the same laws of physics, too. The pure heat needed to warm some water is given by physics. There may be some "overhead" in biological systems, too.
Aug
10
comment Will drinking ice cold water and eating cold food cause weight loss (over a period of time)?
Right, Zach. The total energy one needs to heat the body and all the water/ice heavily depends on the external temperature. @Jimself: no doubt about that, I have never claimed otherwise – that humans don't walk. I have just calculated the term related to the heating of the water. But for you to label this heat term as "normally unused fraction" is a tendentious description. All energy is the same and there's no genuine evidence that the required heat to warm the water will be taken from the "unused fraction" of food energy. It may very well force one to eat more and keep the fraction constant.
Aug
10
answered Will drinking ice cold water and eating cold food cause weight loss (over a period of time)?
Aug
9
comment Order parameter in Landau's theory for second order phase transition
Hi, the terms he means are $C\Psi^2$ and $D\Psi^4$. $\Psi^4\ll \Psi^2$ for $\Psi\to 0$, so this quartic term goes to zero more quickly than $\Psi^2$. The term $C\Psi^2$ goes to zero more quickly than $\Psi^2$ as well because the limit near criticality has $C\to 0$ as well, as I mentioned above, so there is an extra suppression by the small factor $C\to 0$ on top of $\Psi^2\to 0$.
Aug
9
comment Momentum of particle in a box
Sorry, Alejandro, the momentum operator on an infinite line is always $-i\hbar \nabla$ regardless of the value of the potential $V(x)$ and there are never ever any additional "boundary conditions". That's why the spectrum of $p$ is always continuous if no values of $x$ are identified with each other. You may be confusing the momentum $p$ with the energy $E$. The latter is quantized in the box but $E\neq p^2/2m$. Instead, $E=p^2/2m + V$ where $V$ is infinite outside the box so there's no contradiction between continuity of $p$ and discreteness of $E$.
Aug
9
answered Can we charge any two bodies (insulators) by rubbing?
Aug
9
comment Question about lens maker's formula
Good, Kelvin. Is there still a problem? The role of the two indexes may look reversed because the first interface is air-to-glass and the second one is glass-to-air, so you have to first flip the whole picture from the left to the right, to get the mirror image, and then derive all the rules of refraction. There may be hypothetically mistakes in partial explanations but when you do the whole calculation, which you're encouraged, you will surely get the same results for the whole lens as the result widely quoted.
Aug
9
answered Order parameter in Landau's theory for second order phase transition
Aug
8
comment Question about lens maker's formula
Generally, a lens is composed of two boundaries between different environments. So the direction of a light ray is changing twice. You calculate how it changes on the first boundary - that's some insight that says that one creates some image of the original object and the redirected photons seem to come from the image. And these redirected photons change their direction once again, on the other boundary, when they leave the lens again. So you apply the same transformation once again. One must be a bit careful to distinguish the object and image, and signs, and it gives what it gives.
Aug
8
comment Question about lens maker's formula
The Google Books don't seem to be freely available.
Aug
8
revised Definition of probablity current in dirac space not including spatial dimension?
added 145 characters in body