2,986 reputation
817
bio website about.me/danieldf
location Providence, RI
age 38
visits member for 3 years, 9 months
seen Feb 22 '13 at 21:12

Nov
13
comment Are the physical laws scale-dependent?
@Sklivvz: it's not true that wavefunction collapse is related to scale; see quantum decoherence. For more on this, see my answer below.
Nov
13
comment Are the physical laws scale-dependent?
@mbq: show me a single "Newtonian dynamics" effect that predicts the phenomena of Radiation decay, e.g., X-Ray radiation. Yet, its effects are very "macroscopic": you can get your X-Ray slide with you and show it to your doctor. Radiation decay is a purely quantum effect.
Nov
13
comment Are the physical laws scale-dependent?
Sklivvz: the statement of "scale independence" in Physics is usually associated to Conformal symmetry, ie, whether or not the theory in have in hand has conformal symmetry. In this sense, GR is scale dependent, for not all solutions of Einstein's Field Equations are conformally symmetric.
Nov
13
comment What is an “Idea” in terms of time space and matter?
@LarsH: That's why i made a point, above, about "Representation Theory". Physics consists of the modeling of physical reality through a certain 'representation' of the phenomena at hand. In this sense, your criticism would not hold.
Nov
13
comment What is an “Idea” in terms of time space and matter?
@Gerard: i don't think you understood the question: it's not asking how ideas play along in Physics, but rather what they are "made" of.
Nov
12
comment What is an “Idea” in terms of time space and matter?
@DavidZ: I tend to agree with you, with only one exception: "Representation Theory". All objects in Physics have a certain representation that ultimately grants us calculational power. If this discussion here will be about different ways to represent information, i think it should be allowed. Otherwise...
Nov
12
comment Is energy really conserved?
@coneslayer: that's a good example. The principle behind the calculation that Sean performs is what i mentioned above, "global hyperbolicity". In some general grounds, you can think of it this way: if changing reference frames can change your matter content, why would the number of particles remain constant?
Nov
11
comment Is it possible/correct to describe electromagnetism using curved space(-time)?
Just to add a reference to Eric's answer: Maxwell's Eqs in Curved Spacetimes.
Nov
11
comment Why does kinetic energy increase quadratically, not linearly, with speed?
Here's a link to the derivation of the kinetic energy, as already hinted by Gerard, Robert Smith and David Zaslavsky above.
Nov
11
comment Why does kinetic energy increase quadratically, not linearly, with speed?
The physical reason is, in some twisted way, Nöther's Theorem: the Energy is the conserved quantity with respect to time translations. And this can be calculated and shown to be the formula we all know and love.
Nov
11
comment Why does kinetic energy increase quadratically, not linearly, with speed?
What's the physical reason that $F = m a$? Using this and a bit of differential calculus, it's possible to prove that the Energy is conserved (with respect to time derivatives) — and the formula for the Energy is this one you already know.
Nov
10
comment Number theory in Physics
Thanks Mark — it really helps (i thought my reputation score would be "transfered" from some of the other StackExchange sites i've already used, but...). ;-) Anyway, as for pt_BR, try Google Translate: not perfect but, gives you a flavor. 8-)