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Nov
24
comment Is there a principal difference in acceleration from an impulse and the free fall of a body in the orbit around a gravitational mass?
HolgerFiedler: +1 for having asked a question admitting an answer that's expressed in terms of spacetime intervals (or suitable generalizations) and which therefore points in turn to the more fundamental and pressing problem of how exactly spacetime intervals (or suitable generalizations) ought to be determined strictly from "determination of space-time coincidences {such as} encounters between two or more {...} material points" in the first place.
Nov
12
answered Is there a principal difference in acceleration from an impulse and the free fall of a body in the orbit around a gravitational mass?
Nov
12
comment Is presuming that any linear uniform motion is transformed into another one sufficient to assume that Lorentz transformation must be linear?
failtrolol: "[...] uniform motion must be a uniform motion in any reference frame." -- Perhaps "any reference frame" is here meant to be understood as "any inertial reference frame". (Otherwise, "uniform motion in a non-inertial frame" seems a paradoxial notion. Though it can be said in any case that "mutual rest of participants being described" is a intrinsic, proper notion.) If so, yes: the (pairwise) motions of members of distinct inertial systems is mutually uniform, and moreover with mutually equal speed. But all that's independent of coordinate assignments, or transformations.
Nov
12
comment Is it appropriate to attribute an entangled state description to only one trial?
Timaeus: "The word measurement is just a (rather silly) name for certain kinds of interactions." -- No (that'd be silly), but moreover: to record and to evaluate relevant interactions (or their absence); noting "with whom" and "in which sequence (or in coincidence)", and applying subsequent measurement/evaluation operators. "[Is it possible to quantify ...] No." -- Well, there seem to be some attempts after all, such as this (though admittedly I haven't figured out yet how this particular approach might be applied to my specific question).
Nov
12
comment Is it appropriate to attribute an entangled state description to only one trial?
Timaeus: "Edited. [...] common to have decay products be in an entangled state." -- Sure. Does this impede distinguishing the state attributed to the products of just one decay from the state atttributed to products of an ensemble of decays? "there is simply no empirical evidence that [...]" -- Claims of "evidence" (or lack thereof) can only be convincing if it's already agreed what constitutes (and how to gather) "evidence".
Oct
29
comment Is it appropriate to attribute an entangled state description to only one trial?
Timaeus: Thanks for your detailed and notably rapid answer; +1. "The way you tell it" ... "It": the (suitably numerous) ensemble ... "was in the [entangled] state [...] by considering lots of potential different types of measurements." -- Right (not least, to determine ratios between coefficients). Thus: just one trial is not enough for this characterization. "Being entangled is about the state prior to measurement." -- That's unacceptable. Even "preparing" an ensemble is about first measuring, and then discarding trials (as "invalid") which didn't match the prep. prescription.
Oct
29
awarded  Custodian
Oct
29
reviewed Looks OK Angular momentum of rotating black holes
Oct
29
comment What is the dilation relation of the distance to a moving point (in special relativity)?
aayyachi: "frame $F_a$ is being translated with a speed $v$ according to another frame F_b$" -- These frames are thus two inertial systems; where (mutually) the members of one determine the speed of each member of the other as the same value $v$. "point $A$ is attached to $F_a$. $B$ is attached to $F_b$" -- Alright. (Instead of "is attached to" I'd say "was and remained a member of"). "$D_a$ is the distance $AB$ [...]" -- No: distance values are attributed to pairs of members of the same IS. The relation between $A$ and $B$ is characterized not by some distance, but by speed $v$.
Oct
29
asked Is it appropriate to attribute an entangled state description to only one trial?
Oct
29
reviewed Approve Molecular Dynamics simulation question
Oct
29
comment Quantum entanglement and Compton Effect
Timaeus: "Entangled just means not factorizable. [...] you have a definite correlation [...] there are lots of entanglements and degrees of entanglement [...] we do need the energies to be different to be entangled." -- These are fair, crisp descriptions; +1. I'd like your answer even more if you could address how this relates to calling only one pair "entangled" (cmp. OP: "Suppose we generate 2 entangled photons [...]"). p.s. If you decide to edit your answer there are also some typos to correct.
Oct
29
comment Quantum entanglement and Compton Effect
Timaeus: "One way to entangle photons is to have a state like $$\frac{1}{\sqrt 2}\left|\nu_{i,1}+\right\rangle_1\otimes\left|\nu_{i,1}+\right\rangle_2+\frac{1}‌​{\sqrt 2}\left|\nu_{i,2}+\right\rangle_1\otimes\left|\nu_{i,2}+\right\rangle_2$$ [...]" -- Not to argue about style and taste, but your expression is even wrong by confusing indices which are distinct. Better write: $$\frac{1}{\sqrt 2}\left|\nu_{i,\text{low}} +\right\rangle_A\otimes\left|\nu_{i,\text{low}} +\right\rangle_B+\frac{1}{\sqrt 2}\left|\nu_{i,\text{high}} +\right\rangle_A\otimes\left|\nu_{i,\text{high}}+\right\rangle_B$$.
Oct
28
comment Difference between Distance and Space
@Hep: "So what you're saying is that we can measure their separation [...]" -- If A and B found (separately) constant and (mutually) equal ping durations of 2.000.000 years each then they're attributed a value of their mutual separation: 1.000.000 light years. "but [we can] not [measure] their distance from one another" -- If A and B found their ping durations as described, and are accordingly being attributed a mutual separation of 1.000.000 light years, but if the region containing them was not flat (due to whatever), then we don't call this result a "distance" value.
Oct
28
reviewed Approve What is the mechanism of heat exchange of a bouncing ball?
Oct
28
answered Difference between Distance and Space
Oct
27
comment Delayed Choice Quantum Eraser: Am I missing something here?
Related: "Kim delayed choice experiment" (PSE/q/214040).
Oct
27
reviewed No Action Needed Physical background to the ODE $y'(x) + \frac{1}{x} = y(x)$
Oct
27
comment Kim delayed choice experiment
@John Fistere: "Thanks." -- Sure. "Is there a reason [Kim et al.'s] setup is such that you can record coincidences only exclusively with one of D1-D4?" -- The main idea is to analyze one laser photon "at a time". Asking for coincidences between D1 and/or D2, D3, D4 necessarily involves several photons. (I'm sure this could be set up and analyzed, too; but I'm not sure that's in any way considered "interesting".) "You also say that D0 records "long enough"." -- A large count ($n \ge 150$) of "D1+D2+D3+D4" being recorded with D0 "at any one spot $x$"; with recorded coincidences $\le n$.
Oct
27
answered beta minus decay: expression for maximum electron energy