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"I would never die for my beliefs because I might be wrong."

-- Bertrand Russell


Nov
23
comment Rope tension question
Yeah, I think Mark is right. That, or I'm always explaining it incorrectly to students. Please, don't say I screwed up so bad. :p
Nov
22
comment Linearity of quantum mechanics and nonlinearity of macroscopic physics
You start with a huge mistake. Newton's equation of motion is in general non-linear. Only for special cases such as the harmonic oscillator is the equation linear. Take for instance Newton's equation for the Kepler problem (two gravitating masses) and see if you can combine two solutions linearly to obtain a new one. It is however correct that linear equations will never lead to chaos, but that doesn't mean that linear equations can't be difficult. As you correctly point out, quantum systems have exponentially more variables as compared to their classical counterparts.
Nov
20
answered Modified Maxwell's equations
Nov
20
answered What is the difference between “kinematics” and “dynamics”?
Nov
20
comment Escape velocity from long ladder
There's a guy who often shows up in my university town who uses the escape velocity argument to demonstrate that the moon landings and all space travel are a big government conspiracy. That's not the only flaw in his argument(s). Funny dude, but totally off his rocker.
Nov
19
comment Is it guaranteed that wavefunction is well behaved everywhere?
For sure Marek, but I don't see why the Schrödinger equation is not considered a mathematical idealization then? After all, it's only a non-relativistic approximation. And if we're gonna start like this, everything that has ever been conceived of in physics is an idealization. Your decision to consider one more physically relevant than the other is arbitrary if you don't specify the bounds within which the approximation is valid or not. So, without doubt, the Schrödinger equation can do more than models for Anderson localization which are not unphysical, only less broadly applicable.
Nov
19
comment Is it guaranteed that wavefunction is well behaved everywhere?
Take the Bloch electrons in Noldorin's post. Some of the models describing the wave functions of these electrons satisfy neither 1 nor 4. As a result, the wave functions can be fractal.
Nov
18
comment Is it guaranteed that wavefunction is well behaved everywhere?
@Robert: seems to me the bound state of the Dirac potential doesn't fulfill condition 4. Keenan is still correct. Anyway, wether we agree to include 0 or not, I don't think condition 4 is necessary.
Nov
18
comment How can I stand on the ground? EM or/and Pauli?
Well, it's not enough to look at atoms really, so in that sense, I agree my answer is incomplete yet. There's more going on in materials than the atoms, there's binding between atoms, in molecules or in crystals, etc... I think I should expand a bit on my post. The most important work concerning stability of matter has been done by Eliott Lieb and coworkers. I'll see if I can find some comprehensive summary.
Nov
18
revised How can I stand on the ground? EM or/and Pauli?
added 34 characters in body; added 32 characters in body
Nov
18
comment How can I stand on the ground? EM or/and Pauli?
OK, what I wanted to say is that if electrons were bosons instead of fermions, then atoms would still have a minimal radius, courtesy of the Heisenberg uncertainty principle. Your remark about degenerate electron gases in metals is well-received though. I'll adjust my comment accordingly.
Nov
18
answered How can I stand on the ground? EM or/and Pauli?
Nov
18
comment How does classical GR concept of space-time emerge from string theory?
The string theories I know of are formulated against a static space-time background. So your idea of many strings forming space-time is not quite correct, although if I remember how GR's equations arise in string theory, there's something to it. But the way you present your ideas now makes me think more of loop quantum gravity than string theory. I learnt the basics of string theory from a primer many years ago, I think it was from Polchinski. I'd advise to avoid anything Polchinski. :p
Nov
18
comment Common false beliefs in Physics
Well, the devil is always in the details.
Nov
18
comment Is it guaranteed that wavefunction is well behaved everywhere?
Which proves Keenan's point.
Nov
18
comment Is it guaranteed that wavefunction is well behaved everywhere?
Momentum is represented by the derivative operator, up to a factor.
Nov
18
comment Distinguishing mechanical systems from general dynamical systems
There are also many "cartoon" models used in mathematical physics which are not realistic but feature the most important characteristics of realistic systems, depending on what we want to study of course. I think of baker maps, cat maps, kicked tops, etc...
Nov
18
comment Is it guaranteed that wavefunction is well behaved everywhere?
It violates the condition in 0 of course.
Nov
18
comment conversion of information to energy
True, New Scientist is even worse. But just read the report for this article on Nature's website, and you'll see that even they are screwing up... so there...
Nov
18
answered conversion of information to energy