The h Bar

Anonymous

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. $L = (c_1 + 1) \cdot u + c_2 - 1$.

user351417

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'?

GodotMisogi

6:06 AM

@Mo_ What's wrong with the Land of the Free™?

Secret

7:09 AM

Starting to wonder whether h bar will become a car exhibit lol

Avnish Kabaj

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

Anonymous

10:08 AM

Anonymous

@Chair Apparently, it looks something like this with the physics package.

Anonymous

Compare it with $$\frac{\mathrm{d}^nf}{\mathrm{d}x^n}.$$

Anonymous

11:18 AM

$\require{mhchem}$ seems to work, but $\require{physics}$ doesn't. Not sure why.

Anonymous

Both of them are third-party extensions.

Anonymous

11:43 AM

@GodotMisogi You can use the Sandbox room for testing purposes.

Anonymous

Sandbox

Where you can play with chat features (except flagging) and ch...

3

137

GodotMisogi

@Blue Thanks!

Weird, \dv is in the macros:
<tr>
<td><span class="math">$ \dv{ x } $</span></td>
<td><code>\dv{ }</code></td>
</tr>

kartik c.p

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

Loong

12:15 PM

@Blue Hm? There is no subscript $n$ in that expression.

Anonymous

@Loong Indeed, I believe they meant superscript.

Anonymous

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.

Anonymous

2 hours ago, by Blue

Loong

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.

Secret

12:54 PM

0

A: Sandbox for Proposed Questions

Non-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...

kartik c.p

anybody , i want to ping or tag the past (talk about )comment , what i need do . in phone

Secret

find the arrow next to the message, and click reply

ACuriousMind

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.

user351417

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.

user351417

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.

Leaky Nun

if a cat travels towards you at half the speed of light, do you observe its length being shorter or longer?

ACuriousMind

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

user351417

@kartikc.p meta.stackexchange.com/q/273727 Anything helpful there?

ACuriousMind

(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.)

ACuriousMind

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

GodotMisogi

2:43 PM

@ACuriousMind But if its trajectory is always collinear with your line of sight, you wouldn't observe any contraction?

ACuriousMind

@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

GodotMisogi

Hm, I'll think of Garfield as an example. Although I can't imagine him performing such feats of exercise

Anonymous

Duh, it's a cylindrical or spherical cat.

GodotMisogi

Garfield is an appropriate approximation for a spherical cat, I think

ACuriousMind

@GodotMisogi Does sound like something that would happen to him on a Monday, though

user351417

2:45 PM

Is the cat dead or alive?

Anonymous

Doesn't matter. If it's approaching at c/2, you will die regardless. :P

GodotMisogi

@Blue You are already dead

Anonymous

@GodotMisogi Oh, then let it come. I'll get company in death.

GodotMisogi

Anonymous

You need to raise your meme level, @Godot.

GodotMisogi

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:

One Point English Lesson

►

bolbteppa

GodotMisogi

Oh, Meme-Theoretic Theoretical Physics Memes on Facebook has a nice set

user2723984

I was about to say that

I kept my facebook account practically only for that page

GodotMisogi

bolbteppa

Leaky Nun

2:58 PM

@ACuriousMind but my (probably incorrect) spacetime diagram suggests that it should be longer...

GodotMisogi

Wow, coincidentally:

bolbteppa

GodotMisogi

@LeakyNun Post an image?

user2723984

@LeakyNun spacetime diagrams cannot be trusted for comparing lengths due to the minus sign in the metric iirc

bolbteppa

The pi formula:

Basel problem

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...

Anonymous

3:04 PM

The future of The h Bar is becoming increasingly clear now. :P

bolbteppa

Who doesn't love these math/physics/engineer ones :p

GodotMisogi

Drifting slightly off this lovable meme trend, I never really investigated how this infinite product is evaluated:
$$ \lim_{N\to \infty} \prod_{n = 1}^{N-1} \left(1 - \left(\frac{x}{n\pi}\right)^2\right) = \frac{\sin x}{x} $$

user2723984

is there a limit or is the product truly independent of $N$?

GodotMisogi

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?

ACuriousMind

mod abuse @Blue

Anonymous

3:09 PM

@GodotMisogi I'm watching you. ;)

GodotMisogi

War is peace. Freedom is slavery. Ignorance is strength.

user2723984

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

bolbteppa

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

John Rennie

@LeakyNun see:

15

A: "Reality" of length contraction in SR

Lorentz 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...

bolbteppa

3:24 PM

2

Anonymous

@bolbteppa This is gold, lol.

bolbteppa

We've all wondered it :p

GodotMisogi

@bolbteppa I fell off my chair laughing at this

kartik c.p

plz anybody

John Rennie

@kartikc.p what's up?

GodotMisogi

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

Anonymous

@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>.

GodotMisogi

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.

John Rennie

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?

Loong

> up to €21 for the big vision

sounds cheap

Abcd

@JohnRennie Are you free for 1 minute easy concept- doubt?

John Rennie

@Abcd yes?

Abcd

1

Q: Shape of magnets in moving coil galvanometer

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

magnetic-fields

@JohnRennie why is magnet curved in moving coil galv.?

John Rennie

@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.

Abcd

4:07 PM

@JohnRennie do you have 5 more minutes? (for continuation of this because i found something)

ZeroTheHero

@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.

John Rennie

@Abcd yes I have 5 minutes ...

ZeroTheHero

@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…

Abcd

@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.

John Rennie

@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 ... ?

ZeroTheHero

4:15 PM

@JohnRennie I did say the author had expressed radical opinions...

John Rennie

@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.

Abcd

@JohnRennie ??

Leaky Nun

John Rennie

@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.

Leaky Nun

@JohnRennie my worldline is the line x=0

the two parallel lines are the worldlines of the head and tail of the cat

John Rennie

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.

ZeroTheHero

... 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".

Abcd

@JohnRennie I feel that $\mu$ is parallel to $B$

Leaky Nun

@JohnRennie the horizontal distance between the two points is longer than the length of the cat

John Rennie

@Abcd no, quite the contrary.

Abcd

@JohnRennie what does dotted rect show?

John Rennie

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.

Abcd

@JohnRennie 1 sec

@JohnRennie See his diagram at 2:00 : youtube.com/watch?v=JedCxr3Wg2w

bolbteppa

"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."

Abcd

From that I feel that $\mu$ is parallel to $B$

bolbteppa

This is simply unbelievable, literally anti-science

John Rennie

That? If so, this diagram shows the coil face on i.e. the dipole is coming out of the page towards us.

Abcd

4:27 PM

@JohnRennie Got it. Thanks. I was assuming something else.

John Rennie

Cool :-)

@bolbteppa she's got into a anti-big science mindset at the moment.

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.

Physics Meta

0

Q: How can a question be marked as a duplicate if it's been asked **earlier** than a similar question?

This 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?

discussion questions duplicates

ZeroTheHero

@bolbteppa yes this is a milder version of Katz' argument.

John Rennie

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.

Anonymous

4:45 PM

@JohnRennie It's a pity that my head can't go through the screen. ;)

John Rennie

@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.

Anonymous

Lolol :P

Sid

The Virat Kohli curse is real. :(

Anonymous

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

Anonymous

Getting a response from Davide Cervone himself. Only possible on SE. :P

Mo_

5:15 PM

@Blue Not available on libgen :/

Anonymous

@Mo_ It's on Scribd. Get the 30 days free trial. ;)

Emilio Pisanty

5:43 PM

Relevant HEP community discussion about the The Reference Frame blog.

For completeness, there's also a response in TRF (with some remarkable mis-readings of what was actually said).

ZeroTheHero

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.

Emilio Pisanty

@ZeroTheHero which post?

ZeroTheHero

backreaction.blogspot.com/2019/01/… orginally posted by @JohnRennie

You know how much the two bloggers love one another...

Loong

> 100 TeV (or 100k GeV)

ugh

Emilio Pisanty

6:17 PM

@ZeroTheHero is there a Motl connection there that I missed?

@ZeroTheHero I mean, apart from that, in the general sense

ZeroTheHero

6:28 PM

@EmilioPisanty well... I thought Motl had commented on the "Backreaction" post originally posted by JR, and that the link you posted was somehow related to this, but obviously I was completely wrong. Motl has historically been vitriolic towards Hossenfelder.

(and others)

Emilio Pisanty

@ZeroTheHero Indeed, and there's a hearty dosis of vitriol in the TRF response to Harlow.

ZeroTheHero

(sample can be found here: fias.uni-frankfurt.de/~hossi/Bored/bolubos_short)

not my highlights... and I dunno who is the author of the file...

anyways... It was just truly a coincidence that you happened to link to Harlow shortly after JR linked to a blogpost by Hossenfelder, and I mistakenly thought the posts were correlated.

Emilio Pisanty

@ZeroTheHero fair enough.

@ZeroTheHero yes, all of that is well-known. I'd rather we didn't link to more of it.

vzn

7:05 PM

@EmilioPisanty lol Lumo not so much brought down by incorrect physics but runs afoul of PC/ me2/ misogyny. not a bad writeup/ summary, but who is Daniel Harlow? who is he speaking for? how is his self-important announcement/ self-appointed representation different than any other random post in cyberspace? another day, just another flamewar in cyberspace... now, on other hand, if a professional organization or news media wrote up this debate/ controversy, thatd be different...! :o o_O

Anonymous

@vzn FWIW he's a professor at MIT's physics department.

vzn

@Blue ok. but views expressed do not reflect those of ones employed organization...™ ps walter lewin was also an MIT physics prof... :o o_O

Emilio Pisanty

7:41 PM

> Lumo not so much brought down by incorrect physics but runs afoul of PC/ me2/ misogyny

I don't think you understood that post.

And it's kind of concerning that you're phrasing that reading in the same vitriolic language that Motl uses to slander the people he disagrees with.

Anonymous

8:07 PM

@rob Thanks for the migration. Feel free to send over programming, cryptography or algorithm based QC questions in the future too. I've noticed that they very rarely get answered on Physics. I was wondering whether my comment there was appropriate though. Wouldn't want to appear as a spammer. :)

Emilio Pisanty

8:27 PM

@vzn language matters.

"PC/ me2/ misogyny" is (part of) the kind of language that's at issue here.

You're using the same language that Motl uses, which puts you in the same problematic area.

I don't know what model you have in mind about what my opinions are, but if you think that your initial comment here is agreeing with my views, then that model is badly inaccurate.

I appreciate that maybe some comment of mine might be an incomplete or inaccurate representation of my views - which comment above are you agreeing with?

Novalium Company

In quantum mechanics, the precise location of an electron is unknown and is said to be 'random' at random times, but what if God was staying on the other side, 'pushing the buttons' where the electrons will be, therefore forming reality. Are we God?

If we think about it, someone must have created God, and the creator of God must have a creator as well........ what is this illusion, help meee :D

Everything must have a creator, and even the creator of the creator must have a creator and so on... so when does it end, what's going on...

Emilio Pisanty

@NovaliumCompany in a word,

no

Novalium Company

no what?

What if the world was actually governed by randomness? It seems the most logical.

It seems the only way. Or at least the only way our little neural networks called minds can think of.

It's like something is missing...

Welp, looks like I'm desperate for a 5 hour long philosophical discussion, but don't worry, I won't waste your time.

I'll go watch Shrek and live in the deception that I'm alive.

rob

8:46 PM

@Blue The asker requested migration in a flag --- though probably in response to your comment.

Sir Cumference

Sigh wtf

Anonymous

@rob Oh, I see.

Novalium Company

What will happen if you add more 'brain' into a brain. Will that person become more smarter, emotional...?

I was wondering of ways to enchance the brain (us, because we are brains)

What if we add some sort of a substance, like silicon in boobs, and will it somehow adapt, the brain should rewire the new substance to the existing one.

2

As far as I know, the brain is just neural connections, so why just not add more connections?

I asked those question in stack overflow neuroscience, so don't bother anymore.
You wouldn't have bothered anyway. I'm not sure if someone is even reading my messages... :D

ZeroTheHero

10:33 PM

@bolbteppa This is relevant: jakobschwichtenberg.com/decentralization-science

vzn

11:46 PM

Higgs on the Moon/ Adam Falkowski / inference review

> IT MAY THEN COME as a surprise to learn that particle physics is currently experiencing the most serious crisis in its storied history. The feeling in the field is at best one of confusion and at worst depression. How could this be? A complete theory perfectly describing experimental data is surely cause for celebration! Not so.

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