@vzn Who said what? If you can't find it on the internet, I probably made it up myself, but don't want to claim that it's from me, jus in case it isn't. :-)
@JohnRennie I believe VLQ flags can only be cast on posts less than a week old.
@JohnRennie this was cleared with the mods in advance - we don't really have any comments to make.
@DanielSank here's the clear explanation: for two weeks, starting tomorrow, the mods will not decline any VLQ flags. That means people are free to flag things which ordinarily wouldn't be considered VLQ, and they will sit in the low-quality review queue for as long as it takes for the community to deal with them.
@JohnDuffield you're very welcome and if you decide to have a look at inkscape, I have always had the impression that there is quite a large community online with a lot of tutorials and the like being available
but again, there might be better suited programs I don't know
I second that; Inkscape is good for general figures. For specific types of drawings, there may be more specialized software (e.g. JaxoDraw for Feynman diagrams) but Inkscape will in theory do anything.
Personally I use TikZ for most of my figures; I like the results better. But the learning curve is higher than Inkscape.
Task
Show off your best scientific illustration !
The main purpose of this question is to share beautiful scientific pictures, preferably with an educational aspect.
Content
Your post must contain a nice picture and the associated code. One can post several pictures, but it must be done in...
@JohnRennie : we won't make the world a better place by parroting bad science either. For example this answer has over a hundred upvotes, and it's wrong. We will make the world a better place by encouraging people to do their own research and think for themself.
@JohnRennie : there is no consensus. But there are some high-rep users who want more power. And as we all know, power corrupts.
@Sanya This doesn't represent any official policy, it's just the way things have worked out. Having said that, I'm delighted that an educational resource like the PSE is available. I just wish it had existed in the 1970s when I was an enthusiastic young physics nerd!
@JohnRennie it's just refreshing to see someone describe the status quo instead of upholding the flag of "PSE is for research level questions only (which are less than 5% of our questions, but still!)". Apart, I can understand your sentiment, I'd have been happy myself to have discovered this website at the beginning of my studies too :)
I know about the meta question. All these sources are copying from the same exchange we had in chat, where we agreed on the 12th, but at the time I thought the 12th was the date of our regular chat session.
@JohnRennie probably my tone was a bit off and I shouldn't have written that - but I just get tired of seeing questions where I feel that the OP can't even take the time to write down a decent question
this is a sign that I'm taking things too seriously and should stay calmer ...
Suppose I have an equation $A+Bx=y(C-Dx)$, where $A,B,C,D$ are nonzero constants . If I assume $C-Dx=0$, then I get $x=\frac{C}{D}$ but at the same time I get $x=-\frac{A}{B}$. Does it means that $\frac{C}{D}=-\frac{A}{B}$ or because this equation is a deg 2 polynomial in 2 variables, the two x I calculated are actually two different solutions of x?
I fail to see how x = \frac{C}{D} solves in that case ... anyway, shouldn't we first worry about y=0 and $y \neq 0$? Then we can proceed from there, no?
[For the theoretical guys to be coming in the h bar later of the day/night] http://physics.stackexchange.com/questions/273032/what-exactly-is-a-photon
This question reminds of one thing: How do we know experimentally a photon has no substructure in that it is not simply an overally neutral object made of massless positive and negative charges such that it has some nth order multipole moment where $n > 2$
it perpetuates the popscience myth that photons are forever popping into existence like magic, spontaneously, like worms from mud.
Sadly this myth is there in the photon Wikipedia article too. It isn't true. Hydrogen atoms don't twinkle, and magnets don't shine. Because as anna said virtual particles only exist in the mathematics of the model. So, who can tell me what a real photon is? Or refer me to some kind of authoritative informative definition that is accepted and trusted by particle physicists? I say all this because I think it's of param…
As an edit suggestion, If I were you, I will try to remove any terms that is perceived as subjective or emotional by others , such as "myth".
When i aks questions, I often strip of any terms that might sound neutral to me, but probably sound emotionally or subjectively driven by others in order to get others to focus on the issue without the distractions by emotions
@Secret : we know the photon is not made of massless positive and negative charges because radio-wave photons can be 1000m long. And because of electron-positron annihilation to two (or three) gamma photons.
@Secret : noted. I've edited the question accordingly.
:Secret : annihilation means you start with two charged particles and you get two photons. When you perform gamma-gamma pair production it's the reverse process. And mass and charge always come as a package. There are no stable massive particles that have no charge. Even a neutron has charge. Its magnetic moment is the evidence that it has charge like a hydrogen atom has charge. It just doesn't have any net charge.
A differential complex is a series of the form $C^\bullet:\cdots\to C_{p-1}\stackrel{\mathrm d}{\to}C_p\stackrel{\mathrm d}{\to}C_{p+1}\to\cdots$ such that $\mathrm d^2=0$.
Once I've reached the event horizon, then will time outside of the black hole have speed up so much, the black hole has already evaporated due to hawking radiation?
Again, that needs a better GR expert than me to answer. All the usual treatments use Schwarzschild black holes, which don't experience Hawking radiation and are unchanging in time.
@SirCumference That sounds right. I suppose one could get the same conclusion with a Kerr black hole; the important part is that it's static in time. (Which means no Hawking radiation.)
@SirCumference Not necessarily, not if the hole is very large
I don't understand what it is saying, for example I want to grab this template en.wikipedia.org/wiki/Template:NumBlk for use in my wiki, but I cannot find any code of sorts
@DanielSank okay, well then... I think you're right, it's probably better to do it the 12th, as advertised. It won't be during a chat session, so the planning is entirely up to you and @vzn.
Then we will have our chat session on Tuesday the 9th as usual. I'll make sure somebody drops a note about the changed AMA scheduling during the chat session.
@SirCumference sorry about that, I had to go earlier. Basically, tidal force is related to how much gravity changes over a fixed distance. For a black hole, that's roughly proportional the size of the object divided by the radius of the black hole. For a large black hole, the tidal force is small.
But from my perspective, I would see the Universe moving at $0.999c$ relative to me. So it should see me age quickly, right? The question is: which one of us ages quickly?
@DanielSank "Planning" basically involves pushing off anything I'd considered putting on the agenda during that chat session. (Or anything anyone else had suggested for the agenda.) For an AMA outside the chat session schedule, I don't think much planning is needed.
I guess it would be useful to have someone lined up to introduce you, unless you want to introduce yourself.
There's still a whole lot of stuff missing in the NumBlk. I am not sure exactly how many templates NumBlk needs and what those are doing http://secretuniverse.wikia.com/wiki/Template:NumBlk
I would say we should make sure to have at least one moderator or room owner around, preferably more, just in case things get out of hand. (Not that they ever have, really) But I'll be here at the time.
@SirCumference There's a page I am still writing. I need the NumBlk template to display equation numbers. Otherwise may need a rather code ugly workaround
Can someone help me out with my 'rotating charged ring radiation' question? I simply dont seem to be able to smoothen things out using the poynting vector.
So, you're comparing a situation where you're moving at high speed relative to the ground, with one where you're standing still relative to the ground?
No, you can't even compare your age to the rest of the universe because you're not moving at the same velocity. You're in a different reference frame from the universe.
@DavidZ Oye...here's a new idea. I'm standing on a flat plane, and I travel at 0.99c relative to the ground. My clone is standing still relative to the ground. He counts for one second. I then instantly go back to 0mph relative to the ground. By that time, which of us will be older?
@SirCumference The same way(s) you know in Newtonian mechanics. Test if an object subject to net zero real forces accelerates or not. Or by determining if the frame is in constant velocity motion relative some other frame already known to be inertial.
The title question is rather ilustrative. I suppose the real question would be:
Is heat cumulative?
Put it back into an example:
If I have a lit candle right beneath an iron bar, assuming the candle will lit indefinitely, and that the heat-losing rate is below the heat-getting rate. Will the ...
@DanielSank @#%& sigh bummed out over the date mixup. but dont think a new date is a big deal as long as we give ~1wk lead time to everyone & maybe state sorry date change. it seems to me like more ppl show up for the routine/ regular chat session & that better attendance in that slot is more likely. its not exacty a convenient time for me. think wknds might be better for multiple ppl who have jobs but then worry about building up attendance in a new slot. DS will go with whatever you choose
@WilliamOliver I already know most of the subjects (but could use some repetition), but I have a copy, so feel free to ping me if you want to discuss anything.
@PhysicsGuy Cool, also let me know if you know of anyone else who might be interested. Keep in mind I am a beginner. I've been reading it on my own, but I know it would be better if I had some other people to work with. I know the Newtonian formulation of classical mechanics, but never learned much more.
@Sanya I'm looking for people who are looking to go through the whole thing and do problem sets. One reason is certainly to be able to discuss, but another is motivation to do the problem sets and to get through the whole thing.
@PhysicsGuy Well, I am looking to go through their books, starting with mechanics. Not really focusing on anything specific
Teaching myself cause I can't really afford college right now.
@0celo7 I don't know what d'Alembert's principle is yet exactly, but as far as I understand it, the theories are equivalent from a mathematical perspective. Its a just a different way of thinking about it. Using newton's laws some things are much harder to derive apparently, but everything can be derived eventually.
@PhysicsGuy Hamiltonian vector fields of conserved quantities are symmetries and infinitesimal symmetries are Hamiltonian vector fields of conserved quantities if the first de Rham group vanishes?
@yuggib Let $F:\Omega\times [0,\tau]\to\Bbb R$ be smooth, where $\Omega\subset\Bbb R^n$ is open. Suppose $\partial_t F\le\Delta F+C\tau^{-2}$ on $(0,\tau]$, where $C>0$ is a constant. Why does the maximum principle imply $\sup_\Omega F(\cdot, t)\le C\tau^{-2}t$?
Oh, also $F(x,0)=0$ for all $x$.
Hmm, maybe I have to define $\tilde G=F-C\tau^{-2}t$, then plug that into the PDE, run maximum principle on that?
@privetDruzia I think the confusion you may be having is that potential energy can change forms (Its not always mgh). I am pretty sure its more that the potential energy is defined using that equation, its not derived to be that way (or force is defined using that equation depending on how you look at it).
Task
Show off your best scientific illustration !
The main purpose of this question is to share beautiful scientific pictures, preferably with an educational aspect.
Content
Your post must contain a nice picture and the associated code. One can post several pictures, but it must be done in...
The title question is rather ilustrative. I suppose the real question would be:
Is heat cumulative?
Put it back into an example:
If I have a lit candle right beneath an iron bar, assuming the candle will lit indefinitely, and that the heat-losing rate is below the heat-getting rate. Will the ...
