@ACuriousMind Suppose I have a linear map $f:\mathbb{R}^2\to\mathbb{R}^2$. I want to determine if $\operatorname{im}f$ is a point, a line, or the plane. I know I can just do three test points and if I get the plane, I'm golden. But what if I just happen get three colinear points? What's the elegant way of doing this?
Apologies that I have made too many typos when I ask this question yesterday... It should all be fixed now @David Z @ChrisWhite @ACuriousMind Consider a double slit experiment set up where at the double slit there is a detector 1 and 2 at each slit, and ahead instead of a phosphor screen there is an array of detectors (that play the same role as the phosphor screen). The hamiltonian of the setup is described by: $$\hat{H}_{doubleslitsetup}=T_{e-}(\dot{\mathbf{r}})+V_{routing tube}(\mathbf{r})$$
@ACuriousMind I strongly disagree with the sentiment of that message.
2
The point of sites like this is to be user driven. I think that means that we accept new users. In fact, I think we expect and need a flux of new users.
The notion that the status quo shall not change is not helpful.
Implying that new users should not offer opinions on how the status quo should shange is also not useful.
Obviously, new users should take some time to learn about the community and offer criticism thoughtfully, politely, and through appropriate channels.
Anyway, at what point did my criticisms of the site turn from "barging" in to useful feedback? I don't know. I think nobody knows, so we shouldn't pretend it's so simple defined.
Meanwhile however there's a space propulsion related thought (that might sound star treky) inspired from a dream I have last night
Google for "Spacetime turbulence" cannot find anything sensible in the context of GR, thus I suspect I have a wrong intuition on how spacetime works under warp drive conditions
see the maths above Daniel sank's post, it concerns modifying the double slit experiment and wonder what happen if a wavefucntion collapsed electron get send to the slits to be deffracted again, will it still be able to give an inteference pattern?
so you mean if I initially have an electron (whose state is a superpositon of position states) fired at the slits with the slit detectors on, then the state will be collapsed and I get no interference pattern.
And this will hold true even if afterwards the measured electron get routed by the electric fields in the tube back to the firing tube again to fire at the same slits (not another series of slits) but with the slit detectors now off?
No I mean something like this (more like an augmented version of the detector slits double slit experiment)
and what I am wondering is that whether that electron being routed back to fire at the slits for a second time (but this time all slit detectors are off) will be able to give an interference pattern
Because (If I have not made a conceptual mistake with the Hamiltonian when I do the maths above) then since in the first run the electron's state is being collapsed by the measurement of the slit detector, it should not be able to be diffracted again even if we route it back to be fired at the slits for the second time (since wavefunction collapse is known to be irreversible, thus after the mea…
--- If I extend this reasoning further, then in the environment there are many possible scenarios which a similar thing can happen, so in the end we might expect all particles should have been measured already and thus no longer able to display quantum effects (because their wavefunctions will eventually be collapsed, and collapse is irreversible). But we know form our experiments that the quantum effects are still there, so this suggest I have a wrong reasoning but I am not sure what went wrong
@DanielSank The point was that, in this case, a single user is ranting against the entire (active) chat community---this is a similar situation as that recent meta question, where you reacted similarly to a comment of mine:
I don't think your messages take into account the context of the things you react to well enough. In particular, you're preaching to the choir! I don't think ACM (or me) fail to realize how valuable change can be, as exemplified by the way you yourself have made some changes to this site.
We're just taking a stand against "angry shouting", as opposed to constructive proposals for change.
TL;DR: I don't think the sentiment you're against is actually the sentiment expressed in that message.
Although, taken out of context, I can see how you'd think that it is.
@Secret Make sure you become a moderator: We get to edit all messages at any time ;)
Anyways @DanielSank you probably already knew all of this.
@Shing What do you mean by survive? I need about ~800 euros per month to live. You can definitely go lower than that, probably to around 600 at least, if you manage to get a place with low rent etc.
@Danu Where do you get the money? Do you take a loan, or work part-time or during the summers? Or is education typically funded by parents or scholarships?
@alarge It's a mix. I think a lot of people are supported, at least in part, by parents. However, I also know people who are on very generous scholarships, and also a few who work part-time.
However, the program I'm in is rather demanding so I don't think many earn about, say, 500 euros per month.
@Danu thanks for answering, I mean not starve to death :P is it easy for master students to get a (theoretical) research assistance position for around 700 euros ?
user54412
2:59 PM
@Danu The thing about Hubble expansion, where recession velocity is proportional to distance, is that it's Galilean invariant: If $v = Hr$, then $v - v_0 = Hr - Hr_0 = H (r-r_0)$ for all $v$ and any new reference point $0$.
But I saw that warning banner that to be more careful when asking questions and (as acuriousmind knows more about the details) I have 3 consecutive downvoted questions
After the banner is up, I have another question that got downvoted hence SE system determine it as poorly received)
I don't know how many more chance I have before the system question banned me due to too many "poorly received" question
and to make things more hairy, two of the downvoted questions were deleted by the system, thus no chance to fix them
@Secret Well I mean, looking at your last q, if you keep the question short and precise (ie don't just rant about something confusing) and show your ideas/work succinctly things would work a lot better.
Yeah, @Secret, in order to have well-received questions it's crucial that they're not walls of confused text. I know how hard that is for you, but it matters...
@Danu Yes, I understand the context, and I understand that my reaction ignored that context. This was intentional. The message itself expressed a sentiment with which I disagree.
Other messages carrying a similar sentiment show up elsewhere on the site.
Thought I should provide some counterpoint.
Holy crap, @JamalS! I haven't see you around in a while.
@Danu That whole message could be reworded to say "if you think there's a problem with behaviors here, take some time to understand why they are that way, and then voice concerns/criticism via a well reasoned meta post with some links to examples."
That's what we really want. It draws a line against unhelpful ranting, expresses the importance of understanding how current practices got to where they are, and gives the user a good means to express their problem.
Whenever we see an outrageous quote by a politician that turns out to mean something different when viewed from context we tend to call out the journalist
@Secret Now, concerning you question above, the collapsed state is an eigenstate of the detection, not necessarily of free-propagation and more or less certainly not of the "bend the path around so it can go through again" mechanism.
Allow me to clarify: Everybody calls me Danu in all settings except official ones; my passport has Daniël on it (that's the Dutch spelling, and yes the pronunciation is different from the English one).
I should clarify something @Danu. Any user calling the chat room a "disgrace" is obviously way out of line. Name calling is unhelpful and makes people not want to listen to concerns.
@DanielSank I'm still unsure how to pronounce Danu when I'm introducing myself to Americans; Do I go full-US or do I try to preserve the original sound?
@DanielSank Anyways, I think that even the "other people's" was justified within the given context; It had been made more than clear that there was no intent on the part of the other user to constructively participate in chat (on this particular day).
@Danu I see. My context for that message included a post on the meta which also said something like "don't come to an established community and expect to change it". This troubled me, because if y'all had said that to me at the beginning I probably would have left. The fact that people we're willing to discuss things made me happy to duke it out.
@Danu I'm not saying ACM "should" be aware of all written posts on this site when crafting statements.
I mean only to say that an over-generalized statement, one whose literal meaning extends far beyond the situation at hand, is usually not a great idea.
It's unclear what you mean by "not a great idea" here. So far, the only justification for your reaction that you've given is that a hypothetical innocent bystander could misconstrue the message. Correct?
@DanielSank I know that you were aware of the context---however, now you have not provided any argument as to why this message by ACM was potentially "not a great idea"
One reader (you?) may read the message and its context and think "Ok, this is obviously just a reaction to JD's behavior and nothing deep is meant here. ACM only means to correct JD in some way and the statement has no meaning outside the immediate context".
Another reader (me) may read the message and its context and thing "Ok, this is meant as a response to JD's behavior. Fine. Also, ACM seems to think that users shouldn't expect to change anything on an established site. I disagree."
@Danu It's hard to say. "You" is used as a word for "generic person" in English.
Also, why would I expect ACM to think only JD should have this expectation?
