AKA play Skyrim for the next two hours and pray they don't ask questions about the stuff I didn't cram for.
@Qmechanic 1) Can you please give a hint on how to derive the identity mentioned in this? 2) Do you know of an accessible review of (super-)string field theory newer than arXiv:hep-th/0102085? Lubos recommended that in a fews years old post and mentioned it didn't cover some newer stuff. I found the string field theory presentation in BBS to be completely unsatisfactory, yet intriguing.
@0celo7 the top priority, as a matter of unspoken fact, is to 'educate' the young into producing the wealth required to keep the retired boomers living in relative luxury.
@KyleKanos I won't add it because I won't be starting any new projects in the next year (maybe even two) that don't have "string theory" or "large scale structure of space-time" in the titles.
@NeuroFuzzy Actually, I'll check it out later, applets are a pain. I could see the pattern emerging if two point sources came out of the slit. Is this perhaps a better animation
@Howcan Heheh they are but it's a really fantastic applet! Uh chrome hates them, but internet explorer doesn't mind them.
That is indeed a much better animation that shows interference!
chrome removed all its support for something involving applets I think. It's a bit sad that so many cool java applets are just too big of a pain to use now.
Well then you really can go through all the math for this :)
@Howcan Maybe you can find someone to walk you through it, but really all you need is integration by parts and the rest follows! (I would but I have a crapton of homework to do)
I have a crapton of work too, I really should not have procrastinated. And yeah I'll go through it with a friend or something. Do you maybe have a source for it?
I would just google for it, but here's how I'd solve the problem: This equation completely describes everything in all the animations you've posted: en.wikipedia.org/wiki/Wave_equation#Introduction you can remove time dependence (so as to just look at intensity!) by going to the Helmholtz equation en.wikipedia.org/wiki/Helmholtz_equation, and then you can do a Fourier transform with respect to the Y axis.
You're left with an equation of the form $\frac{\partial^2 \Phi}{\partial x^2}=A*\Phi$, which has sine/cosine as its solution
(Right? I hope you agree that $d^2\Phi/dx^2=A\Phi$ is a pretty simple equation to solve)
someone has to have worked this out in a nice PDF where they also introduce the Fourier transform
The Fourier transform isn't magic. You just have a function $f(y)$ and you multiply by $e^{-i \omega y}$ and integrate from $-\infty$ to $\infty$. $f(y)\mapsto g(\omega)=$\int_{-\infty}^{\infty} f(y)e^{-i \omega y} dy$
so it's just another integral (used in a clever way)
@0celo7 There have been a number of high profile scandals in recent years. Mostly in biosciences, but once a bureaucracy gets moving its not likely to be discriminating.
In the US you've had to declare conflicts on interest in the grant application paperwork for some time.
This question has nothing to do with dark matter.
This question is discussing a theory which states the notion of dark matter is incorrect and the Milky Way is moving through and displacing the 'dark mass'.
Some physicists are starting to realize the notions of dark matter and the dark matter p...
Is anyone else concerned that this "paradox" doesn't seem to have a clear resolution?
It think the answer should be similar to "shutting the pole in the garage" in the pole-barn paradox - something about our reasoning in the frame of the nail must be off.
The answer by Haz seems to be the correct one.
user54412
3:11 PM
@ACuriousMind My only concerns are (1) that there are wrong answers and (2) that the tradition of teaching relativity via paradoxes is still going strong.
user54412
Seriously, it's not like it's considered acceptable to teach biology in terms of riddles, or topology in terms of brainteasers, or mechanical engineering in terms of limericks. Why are we still teaching relativity in a maximally confusing way?
This has bothered me too, and I think the answer is because Einstein set it up with all these weird gedankenexperiments, and everyone is emulating Einstein although our modern understanding of SR and GR probably surpasses everything Einstein knew.
user54412
Was it from this site that I was pointed to the paper Einstein tried to publish proving gravitational waves can't exist?
@ACuriousMind The answer by Haz is correct and is the same as the resolution as for the barn and pole paradox, just hidden behind the veil of our day to day assumptions about what it means for an object to be solid.
@ChrisWhite It's historical isn't it? I mean, that is the way the powerhouse minds of the early twentieth century posed question about the meaning of relativity to each other.
And it is a problem because we ask the same questions of people without the maturity of physical-thought to accept the consequences.
@ACuriousMind Hah, we've had this discussion so many times
@0celo7 About 75% of people, as far as I can tell
Btw, do "your countries" also have some day during which they have a few minutes of silence to commemorate World War II (or I? Maybe in France?)? Today's the day in the Netherlands, but I'm curious whether this is a widespread thing or not
@yuggib I really want to post "please leave this site, and do not bother returning"
@ACuriousMind This is probably quite late, but I haven't read all of the Lie algebra lecture notes, and I've since moved on to two textbooks recommended by Danu.
@Danu The second Sunday before the first Sunday of advent is Volkstrauertag here, which commemorates all victims of wars, and in particular the dead of WWII, and it is a "silent day", where some "non-silent" activities are actually forbidden by law.
@yilduz It varies from federal state to federal state and what specific day it is, but on Volkstrauertag, in all states, most public events that include loud music or cheering of some sort (think sports events, dances, etc.) are forbidden.
@yilduz Yeah ... but it annoys some of the people who live near those things and contributes to reduced property values near sites that host those events which may be a piece in the urban decay jigsaw.
I guess it would depend on how a person/community views mourning and respect, especially for military.
Baseball is viewed as an American thing, so to play baseball on Memorial Day makes sense because you're honoring those who died serving our country by doing something very American.
It can also be viewed in a sense that, "don't mourn my death, but celebrate my life". Some people prefer that.
I can understand that people look at such things in different ways, but to have actual laws about it is what is weird to me.
I mean no disrespect or anything. I just found it interesting, and it kind of caught me by surprise.
@yilduz Well, it's not explicitly commemorating the soldiers (since we did want to set it apart from the old Nazi "day of heroes"), it's commemorating all those killed by war. It's not meant to honour anyone, really.
I guess just being American makes me look at it from a very different way. Obviously we would see the war itself from a different view as well.
But the idea of a law as you've described being proposed here, I imagine would be met by fierce opposition. People here would look at that and say "The government has no place telling me how to mourn, celebrate, show respect, or otherwise."
@yilduz The law is met with opposition and petitions for abolition on days like Good Friday, but no one is seriously proposing abolishing it on commemoration day, I think, since just saying "freedom of speech/expression/whatever" doesn't cut it here on things with historical baggage such as that day.
Even the people wanting to dance on Good Friday do not play music loudly and dance to it, they meet in front of churches dancing to music from headphones to protest while not actually breaking the law :D
@JamalS The political power of the churches in Germany is still surprisingly large for a nominally secular state. E.g. the largest policital party is explicitly Christian, and they will never agree to removing the dance ban.
@ACuriousMind Part of the problem there is that the side that is winning the culture war right now (label them H) is using a bunch of old law (public accomodation rulings) to force people from the group currently losing (label them S) to behave the in a particle set of ways that H considers to be right and moral. Now, just 40--50 years ago, H was protesting the way S was using those laws to try to force certain behaviors on H, but apparently its OK now because H is certain that they are right.
A more libertarian take would allow people to be a**holes if they want and hope that the market and time would sort it out. Alas, that doesn't work in a sick enough culture so we got used to bringing in the big governmental club in the 50's--80's.
@dmckee I'm not quite sure what you mean. I don't see that some inversion of power between any groups has taken place. The people who see their traditional influence on society waning simply cling to every bit of it they can keep, and tradition and bureaucracy are slow to change, but their influence is waning.
@Danu Say we have some other convention, e.g. a convention used in GR. Would you say it's the "general relativity convention" or the "general relativistic convention"? I think either is acceptable.
@0celo7 I actually debate this with myself all the time. I also wonder what happened to the hyphen in "general-relativistic" when used as an adjective before a noun.
@0celo7 Well, in some equations it makes them neater, but in others it makes them messier; in the end it's just a factor of 2, and a transition can't be made now since the vast majority of texts use $\pi$.
user54412
8:53 PM
@0celo7 Moot. Use a unit system that gets rid of all the areas of spheres everywhere :P
@0celo7 Obviously, things like $8\pi$ don't actually simplify by using $\tau$. Counting only explicit $2\pi$'s will NOT yield a lot, clearly. Try any book on GR or QFT ($4\pi$ is much more common, I think)
@JamalS Do you know how to prove Eq. (4.24) in BBS / Eq. (4.1.22) in GSW? Furthermore, is the commutator in (4.23) in BBS implicitly evaluated on the SUSY vacuum (so the second term in the commutator vanishes)?
@0celo7 Yeah but...I don't even know whether I should be surprised by that result or not. Precisely because I love Noether, I'm not surprised when stuff that's conserved in some way turns out to be a Noether charge ;)
