« first day (2999 days earlier)   

12:49 AM
Hey guys. I got an exercise in front of me and I am kind of confused. This is the exercise: https://i.imgur.com/k0JYHi9.png, https://i.imgur.com/R7PMbF9.png

1) With $\beta' = 0$ this reduces to $L''= 0$. Integrating this twice and applying the other two conditions I get $L = c_1 \cdot u + c_2 - 1$. Fairly easy so far.

2) Doesn't $\beta = 0$ for all $u$ imply that $\beta' = 0$? Wouldn't this also reduce the differential equation to $L'' = 0$? Integrating this twice and applying the other conditions gives me. $L = (c_1 + 1) \cdot u + c_2 - 1$.
 
 
5 hours later…
5:53 AM
@Blue What exactly do you think that comment's supposed to mean though? I can't make anything of it... presumably subscript--> superscript, but what's the whole thing with 'different heights'?
 
6:06 AM
@Mo_ What's wrong with the Land of the Free™?
 
 
1 hour later…
7:09 AM
Starting to wonder whether h bar will become a car exhibit lol
 
7:37 AM
$\require{package}$ works ?
$\require{mhchem}\ce{H2O}$
If its messing up with other stuff
Enclosing $\require{package}$ uses the package for only there once not for the entire page
$\ce{H2O}$
ok i was wrong
apologies
 
 
2 hours later…
10:08 AM
@Chair Apparently, it looks something like this with the physics package.
Compare it with $$\frac{\mathrm{d}^nf}{\mathrm{d}x^n}.$$
 
 
1 hour later…
11:18 AM
$\require{mhchem}$ seems to work, but $\require{physics}$ doesn't. Not sure why.
Both of them are third-party extensions.
 
11:43 AM
@GodotMisogi You can use the Sandbox room for testing purposes.

Sandbox

Where you can play with chat features (except flagging) and ch...
 
@Blue Thanks!
Weird, \dv is in the macros:
<tr>
<td><span class="math">\( \dv{ x } \)</span></td>
<td><code>\dv{ }</code></td>
</tr>
 
12:00 PM
Did two light rays reach the detector at exact same time (michel morley experiment), what would be the result if there was an ether
 
12:15 PM
@Blue Hm? There is no subscript $n$ in that expression.
 
@Loong Indeed, I believe they meant superscript.
There are some spacing issues, when using the physics package. But I don't think it's related to the vertical heights of the $n$-superscripts.
2 hours ago, by Blue
user image
 
Yes, that looks like a bit more than just bad kerning.
But I don't think that this issue is covered by the international standars for typesetting in natural sciences and technology. I would have to check my typography books instead.
At least the d is correctly set upright. :-)
So many posts do such big things wrong so that I don't think that small spacing issues are a matter of priority.
 
12:54 PM
0
A: Sandbox for Proposed Questions

preguntonNon-Euclidean geometry where objects appear bigger the farther they are (draft) science-based reality-check alien-geometry Summary In our ordinary flat geometry, the apparent size of objects grows proportionally to the inverse of their distance from us. However, in curved space this relatio...

Probably that will be a spacetime of negative curvature
or something...
 
anybody , i want to ping or tag the past (talk about )comment , what i need do . in phone
 
find the arrow next to the message, and click reply
 
1:14 PM
Essentially a duplicate of Why are muons considered to be “elementary particles” in the Standard Model? with "muon" replaced by "Higgs" (which was also a HNQ). Are we going to do a HNQ for every particle of the Standard Model now? — ACuriousMind ♦ 7 secs ago
grrrr
I really don't like closing a HNQ unilaterally but in this case I'm sorely tempted to.
 
2:06 PM
@ACuriousMind If you're still around... Loong was convinced it was a duplicate, and flagged it accordingly. I've also cast a VtC. I'm quite sure it would be appropriate to mod-hammer that one.
I think the fact that the duplicate post mentions electrons and muons is what really convinces me that both questions are talking about the same general point regarding how we can supposedly use particle collides to 'break apart' fundamental particles.
 
if a cat travels towards you at half the speed of light, do you observe its length being shorter or longer?
 
If I see a (presumably very angry) cat coming at me at half the speed of light, I'm not going to try to guess it's length, I'm gonna run!
3
 
@kartikc.p meta.stackexchange.com/q/273727 Anything helpful there?
 
(but of course you "see" it contracted, i.e. shorter, with the caveat that "see"ing there really means "measuring its length by some reliable means". What you really see is a Terrell rotated version of the cat.)
 
2:28 PM
Hmmm, my second monitor has decided to display a blue rectangle outline in the middle of the screen
I have no idea what caused this, and no idea how to revert it
 
2:43 PM
@ACuriousMind But if its trajectory is always collinear with your line of sight, you wouldn't observe any contraction?
 
@GodotMisogi Unless the cat is fattest at the head, you could see the posterior parts being closer regardless, no?
If the cat is fattest at the head, you should shoot it at a veterinarian, not a physicist
 
Hm, I'll think of Garfield as an example. Although I can't imagine him performing such feats of exercise
 
Duh, it's a cylindrical or spherical cat.
 
Garfield is an appropriate approximation for a spherical cat, I think
 
@GodotMisogi Does sound like something that would happen to him on a Monday, though
 
2:45 PM
Is the cat dead or alive?
 
Doesn't matter. If it's approaching at c/2, you will die regardless. :P
 
@Blue You are already dead
 
@GodotMisogi Oh, then let it come. I'll get company in death.
 
You need to raise your meme level, @Godot.
 
2:51 PM
I...don't know how to respond to that. I don't think anyone here is ready for what's in my Work folder
Might as well test the waters:
 
Oh, Meme-Theoretic Theoretical Physics Memes on Facebook has a nice set
 
I was about to say that
I kept my facebook account practically only for that page
 
2:58 PM
@ACuriousMind but my (probably incorrect) spacetime diagram suggests that it should be longer...
 
Wow, coincidentally:
 
@LeakyNun Post an image?
 
@LeakyNun spacetime diagrams cannot be trusted for comparing lengths due to the minus sign in the metric iirc
 
user image
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The pi formula:
The Basel problem is a problem in mathematical analysis with relevance to number theory, first posed by Pietro Mengoli in 1650 and solved by Leonhard Euler in 1734 and read on 5 December 1735 in The Saint Petersburg Academy of Sciences. Since the problem had withstood the attacks of the leading mathematicians of the day, Euler's solution brought him immediate fame when he was twenty-eight. Euler generalised the problem considerably, and his ideas were taken up years later by Bernhard Riemann in his seminal 1859 paper "On the Number of Primes Less Than a Given Magnitude", in which he defined his...
 
3:04 PM
The future of The h Bar is becoming increasingly clear now. :P
 
Who doesn't love these math/physics/engineer ones :p
 
Drifting slightly off this lovable meme trend, I never really investigated how this infinite product is evaluated:
$$ \lim_{N\to \infty} \prod_{n = 1}^{N-1} \left(1 - \left(\frac{x}{n\pi}\right)^2\right) = \frac{\sin x}{x} $$
 
is there a limit or is the product truly independent of $N$?
 
Damn, too late to edit. $\lim_{N \to \infty}$
I asked some number theorist about it casually once, and he said it was a result of Hadamard factorisation or something
B-Big Brother is editing my messages?
 
mod abuse @Blue
 
3:09 PM
@GodotMisogi I'm watching you. ;)
 
War is peace. Freedom is slavery. Ignorance is strength.
2
 
I tried taking the log and exchanging the sums and it made it diverge, my analysis professor told me this would happen some day
I didn't believe him
 
The heuristic argument is that the zero's of $\sin(x)$ are $0, \pm \pi, \pm 2 \pi, \dots , \pm n \pi, \dots$ so we might expect the fundamental theorem of algebra to generalize from finite to infinite polynomials, thus $\sin(x) \approx x (x - \pi)(x + \pi)(x - 2 \pi)(x + 2 \pi) \dots \approx C x(1 - (\frac{x}{\pi})^2)(1 - (\frac{x}{2\pi})^2) \dots $ (for some constant $C$), this kind of thinking leads to the Weierstrass factorization theorem which can be extended into Hadamard's version
2
 
@LeakyNun see:
15
A: "Reality" of length contraction in SR

John RennieLorentz contraction is easy to understand once you realise that it is not a contraction at all. Instead it is a rotation and the length of the object, or more precisely its proper length, doesn't change at all. To see this take the usual example of a rod of length $2a$ aligned along the $x$ axis...

 
3:24 PM
user image
2
 
@bolbteppa This is gold, lol.
 
We've all wondered it :p
 
@bolbteppa I fell off my chair laughing at this
 
plz anybody
 
@kartikc.p what's up?
 
3:28 PM
@kartikc.p I'm not sure I understand your question
The Michelson-Morley experiment observes no interference pattern, and hence concludes that no ether exists
 
@kartikc.p To reply to a specific message in the mobile app, tap on it lightly and menu bar pops up at the top. Click on the reply arrow. To ping a specific user start writing @<username>.
 
I'm not sure if the contrapositive holds (Ether exists ⇒ interference pattern observed)
@kartikc.p For starters, I think the ether itself would not be a well-defined physical substance, other than its hypothesised physical effects pertaining to its nature as a medium of propagation for light.
 
3:56 PM
Particle physicists want money for bigger collider. Well ... duh! When did you last hear (experimental) physicists not wanting to do a cool new experiment?
2
 
> up to €21 for the big vision
sounds cheap
 
@JohnRennie Are you free for 1 minute easy concept- doubt?
 
@Abcd yes?
 
1
Q: Shape of magnets in moving coil galvanometer

Ritwik DasWhy are the magnets placed across the moving coil shaped in a semi-circular way?

@JohnRennie why is magnet curved in moving coil galv.?
 
@Abcd I don't know to be honest but I'd guess it's to try and keep the field lines at the same angle to the coil as the coil rotates. That way the response will be as linear as possible i.e. angle of rotation proportional to current in the coil.
 
4:07 PM
@JohnRennie do you have 5 more minutes? (for continuation of this because i found something)
 
@JohnRennie There is this wsj.com/articles/… interesting rebuttal from a few years ago to this kind of proposal. Unfortunately it's behind a paywall and I can't find an easy workaround but in short order the author (who certainly has expressed radical views in the past) basically argues that the $$ would be better spent on other science projects.
 
@Abcd yes I have 5 minutes ...
 
@JohnRennie ah...there we go... Here's the cut-and-paste:

David J. Gross and Edward Witten misapprehend the future of physics. It doesn't lie in particle physics, where the "great discovery" of recent years was the confirmation of a 50-year-old prediction of the Higgs particle ("China's Great Scientific Leap Forward ," op-ed, Sept. 25).

Particle physics is a mature, nay, dying, branch of science, stymied by the technological and economic difficulty of advancing beyond present particle accelerators. The authors tacitly admit this when they say, "starting in the 2030s, the goal is. . . ." S
 
@JohnRennie (3:57) youtube.com/watch?v=JedCxr3Wg2w He says that it is for keeping $\mu $ always perpendicular to $B$... But I really cant understand what' happening. Top view is very unclear. Just dont get anything.
 
@ZeroTheHero "Particle physics is a mature, nay, dying, branch of science" - and the proof that this is anything more than Prof. Katz's opinion is ... ?
 
4:15 PM
@JohnRennie I did say the author had expressed radical opinions...
 
@Abcd Suppose your meter uses a helical spring, then this is going to be roughly Hookian i.e. the torque exerted by the spring is roughly proportional to the deflection angel.
 
@JohnRennie ??
 
@Abcd The needle of the meter is connected to a spring that keeps it at the zero point. When you pass a current through the coil that produces a torque p x B where p is the dipole moment and p is proportional to the current.
 
@JohnRennie my worldline is the line x=0
the two parallel lines are the worldlines of the head and tail of the cat
 
4:18 PM
@Abcd the torque on the dipole deflects the needle until the torque is equal and opposite to the torque produced by the spring.
 
... and while the author is certainly provocative in the way the opinion is expressed many will hold milder versions of it. It's the old argument against "big science".
 
@JohnRennie I feel that $\mu$ is parallel to $B$
 
@JohnRennie the horizontal distance between the two points is longer than the length of the cat
 
@Abcd no, quite the contrary.
 
@JohnRennie what does dotted rect show?
 
4:21 PM
@Abcd I think that just shows the plane of the coil.
We are looking at the coil sideways i.e. we see it edge on.
 
@JohnRennie 1 sec
@JohnRennie See his diagram at 2:00 : youtube.com/watch?v=JedCxr3Wg2w
 
"Therefore, investment-wise, it would make more sense to put particle physics on a pause and reconsider it in, say, 20 years to see whether the situation has changed, either because new technologies have become available or because more concrete predictions for new physics have been made."
 
From that I feel that $\mu$ is parallel to $B$
 
This is simply unbelievable, literally anti-science
 
That? If so, this diagram shows the coil face on i.e. the dipole is coming out of the page towards us.
 
4:27 PM
@JohnRennie Got it. Thanks. I was assuming something else.
 
Cool :-)
@bolbteppa she's got into a anti-big science mindset at the moment.
2
I'm not saying she's wrong, I'm just pointing that of course CERN are going to propose building an even bigger collider. That's what they do. Whether they get the money is up to the funding bodies.
 
0
Q: How can a question be marked as a duplicate if it's been asked **earlier** than a similar question?

descheleschilderThis question has been asked 6 years and 10 months ago. How can it be a duplicate of this question, which has been asked 4 years and 4 months ago? Shouldn't the second be marked as a duplicate?

 
@bolbteppa yes this is a milder version of Katz' argument.
 
The only way to find out if a bigger collider really won't discover anything new is to build it. Even if it doesn't directly discover new particles it will be able to do precision measurements on the Higgs that could show new physics.
Speaking of experimental physics, here is my latest attempt to create a lunch so big that it spontaneously collapses into a black hole:
Sausage rolls with melted cheese over them.
 
4:45 PM
@JohnRennie It's a pity that my head can't go through the screen. ;)
 
@Blue too late anyway. It has spontaneously collapsed into ... erm ... my gut. Not exactly a black hole though it's probably pretty dark in there.
 
Lolol :P
 
Sid
The Virat Kohli curse is real. :(
 
For security reasons, \require{} only loads extensions that are in the core MathJax distribution. The mhchem extension is there because I did a version of it some time ago, but the physics extension is a third-party extension. So it can't be loaded in that way unless the site sets it up specifically to allow that, which is not the case here. — Davide Cervone 47 mins ago
Getting a response from Davide Cervone himself. Only possible on SE. :P
 
Mo_
5:15 PM
@Blue Not available on libgen :/
 
@Mo_ It's on Scribd. Get the 30 days free trial. ;)
 
5:43 PM
For completeness, there's also a response in TRF (with some remarkable mis-readings of what was actually said).
 
5:56 PM
@EmilioPisanty is this in the context of the "Backreaction" blogpost?
which it can't be given the time stamp...
oh never mind.
 
@ZeroTheHero which post?
 
backreaction.blogspot.com/2019/01/… orginally posted by @JohnRennie
You know how much the two bloggers love one another...
 
> 100 TeV (or 100k GeV)
ugh
 

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