# Luboš Motl

less info
reputation
7121246
bio website motls.blogspot.com location Czech Republic age 40 member for 3 years, 3 months seen 18 hours ago profile views 34,576

Hi, I am a string theorist and a publicist.

# 6,372 Actions

 May18 revised Why can't I see far when I look in a mirror? added 234 characters in body May18 answered Why can't I see far when I look in a mirror? May18 comment Quantum Mechanics The physical interpretation of the theory is that it is a gadget calculating and using probability functions. So I guess it means that the answer to the question "What is the physical interpretation of theory rather than using probability functions" is "Nothing". May17 revised Are all superalgebra's clifford algebra's added 471 characters in body; added 136 characters in body May17 answered Are all superalgebra's clifford algebra's May17 comment Incommensurability between different observers describing the same universe? Dear @Jerry, the term "horizon" above always refers to the event horizon which is a null hypersurface. That's the relevant type of horizon that is helpful to answer questions such as "can Alice inform Bob", your horizon isn't, and the answer is No. May17 comment Equations for bent paper Correction from "by the way": By the way, I have mentioned the exponentially increasing and decreasing solutions in my answer as well and I don't know how to make them realize in practice. The pressure between the end points of the paper should probably have the opposite sign in this case, because of the opposite sign of $\lambda$, and I don't think it's possible. So I think that only the trigonometric plus quadratic solutions are relevant. May17 comment Equations for bent paper Dear @Martin, $a$ in your equation has to be negative, so that its square root is imaginary, so that you have the complex exponential, and it has to be combined to the trigonometric functions - by having $c_1=c_2^*$ - for the result to be real. By the way, the positive $a$ solutions - which are exponential (and which I have surely mentioned in my answer as well) - may be shown to be unstable. They require the opposite sign of $\lambda$ which is translated to the shape's being a local maximum, rather than minimum, of the energy. May17 revised Equations for bent paper added 158 characters in body; added 376 characters in body May17 revised Equations for bent paper added 351 characters in body; added 414 characters in body May17 comment Equations for bent paper +1 for your good intuition/memory. ;-) May16 comment Equations for bent paper Dear @Vintage, I agree that if one is allowed to sharply bend the paper at $x=0$ and $x=L$, then the paper in between will make an arc of a circle, or - in my approximation - $y=ax^2+bx+c$. This is a sort of trivial solution. I think that the OP meant 1) that the paper is never sharply bent and it continues as flat plane on both end points. May16 comment How is a magnetic field translated into physical force? @qftme, haha, you're having fun that someone could be tortured by an unanswerable question, right? Feynman was asked the same question, why magnets work, and after some confused babbling - and successful efforts to regulate his anger about the stupidity of the author of the question - he said the right thing, that it's the wrong question because the magnetic forces are fundamental while what the asker can imagine and knows is not fundamental: youtube.com/watch?v=wMFPe-DwULM May16 comment Incommensurability between different observers describing the same universe? Tx for your refinement, Jerry. Still, one can't get out of the black hole. May16 comment Equations for bent paper Dear @yayu, the $(y')^2$ term vanishes if the paper is straight. If it is curved at a given point $x$, the term is nonzero. It's quadratic because you may really imagine that there are springs on both sides of the paper, trying to keep is straight, and the $(y')^2$ term generalizes the $kx^2/2$ potential energy of a spring. May16 revised Equations for bent paper added 227 characters in body May16 comment Equations for bent paper Dear ysap, excellent to hear about it. But is it really intuition, or just plain good old memory that remembers someone else's intuition or, more likely, calculation? ;-) May16 answered Equations for bent paper May16 revised Incommensurability between different observers describing the same universe? added 968 characters in body May16 comment Incommensurability between different observers describing the same universe? Is there some reason why you create a new account for every new question (or, one could say, a new copy of your question)?