The h Bar

David Z

04:04

@ACuriousMind Honestly I bet someone has tried that :-p I could imagine either creating a compiler that turns (a subset of) Python code into standalone machine code, or making a low-level Python interpreter that can run underneath an operating system. Of course it would be horribly inefficient.

Feeds

04:21

John Rennie has removed an event from this room's schedule.

2

Guru Vishnu

@Feeds Good bye "Physics Chat Session".

JMac

My meta answer worked. You fell for it. "There is currently no schedule for this room" May anarchy reign!

David Z

04:52

lol

Secret

05:06

I wonder if COVID-19 will bring new physics because most of the phenomenologists are now stuck at home analysing data

home.cern/news/news/cern/covid-19-cern-coming-weeks

Secret

06:38

rt.com/op-ed/484041-west-suicide-covid19-response

Of all things I knew about Motl, I never guessed he is conservative

ACuriousMind

@DavidZ Well, yes, "you can't" is probably a bit too strong given that people have written things like an assembly transpiler that transpiles any x86 machine code into code using only the MOV instruction :P

David Z

07:05

Yeah, that sounds about right

Avyansh Katiyar

08:20

@coronapatrol Thanks for the link

@ACuriousMind This gave me much more clarity

thank you

Loong

08:36

Oh, the Johns Hopkins map tool now also offers a logarithmic scale.

Is it nice to have it or sad that we need it?

Anyway, it’s nice to see the exponential growth or any deviation from exponential growth.

Slereah

09:09

morning

Student404Mus

10:50

@ACuriousMind Can we say that the position eigenvalues are physical quantities which should be invariant regardless the frame of reference?

0

Q: Symmetry transformations: a doubt about the relations that we assume true

When we deal with symmetry transformations in quantum mechanics we assume true that, If before the symmetry transformation we have this $ \hat A | \phi_n \rangle = a_n|\phi_n \rangle,$ and after the symmetry transformation we have this $ \hat A' | \phi_n' \rangle = a_n'|\phi_n' \rangle,$ the...

ACuriousMind

@Student404Mus An eigenvalue is just a number (regardless of whether it's position or something else). Any transformations in QM act on states and operators, not on numbers, so I don't know what (in)variant is supposed to mean here

Student404Mus

indeed. scalars themselves are invariant

under transformations

ACuriousMind

It's not even that it's a "scalar", it's just not even part of the space the transformations act on

Student404Mus

In general speaking

rather to say "numbers", we know scalars are invariant under transformations

@ACuriousMind The answer above yours states, if we assume $x$ is the origin, Does eigenvalue makes sense to be an origin?

ACuriousMind

Sorry, I do not understand your question.

Student404Mus

10:59

That question, someone answered it differently

and says, "suppose $x$ is the origin,..."

ACuriousMind

Yes, I have read MannyC's answer

I do not understand what you're trying to ask me about it, though

Student404Mus

Does $x$ really could represent an origin

rigorously

$x$ still represent an eigenvalue, why it is an "origin"?

ACuriousMind

1. "Does...could" is not grammatical English, you don't use 'do' with other auxiliary verbs like 'can'. 2. I do not understand what you mean by "$x$ representing an origin".

Manny is just saying that the position eigenstate with eigenvalue $x=0$ is the origin.

And that in each frame, you will associate the origin of that frame with the eigenstate of the position operator in that frame with the eigenvalue $x=0$.

Student404Mus

No he didn't. He said, "suppose $x$ is the origin,"

is different from says, the position eigenstate with eigenvalue x=0 is the origin.

since, according to the question, $x$ represents an eigenvalue

ACuriousMind

I was paraphrasing what (I think) he's trying to say.

Student404Mus

11:06

that's where we mismatched each other

ACuriousMind

@Student404Mus He's making an example, by picking the (undetermined) value $x$ from the question to be $x=0$.

I don't understand what the problem is with that.

Student404Mus

Yes, that what he tried to describe

I think the problem was the definition of frame

that's it.

2. Your exclamatory about "representing" an eigenvalue in an origin's frame

does't this make any sense?

I think all what we do when trying to understand a theorized thing is to represent it?!

@ACuriousMind "The equation $\hat{x}\lvert x_n\rangle$ becomes" Doesn't seem to be an equation?

$\hat{x}\lvert x_n\rangle = x \lvert x_n\rangle $

Student404Mus

11:47

@ACuriousMind Shouldn't this question be duplicate?
https://physics.stackexchange.com/questions/540141/lorentz-invariance-of-action-or-lagrangian/540147#540147
to this https://physics.stackexchange.com/questions/47556/lorentz-invariance-of-the-integration-measure/47559

ACuriousMind

@Student404Mus If you think a question is a duplicate, please just flag it as a duplicate.

2

Student404Mus

Alright

this won't affect the user's reputation

?

ACuriousMind

no, it won't, up- and downvotes are the only thing that affects reputation.

Student404Mus

Thanks.

ACuriousMind

well, these and spam flags

Johan Liebert

14:16

227

Q: "Which answer in this list is the correct answer to this question?"

I received this question from my mathematics professor as a leisure-time logic quiz, and although I thought I answered it right, he denied. Can someone explain the reasoning behind the correct solution? Which answer in this list is the correct answer to this question? All of the below...

logic soft-question

Charlie

14:34

am i crazy or does this not make sense?

this is from my GR notes, specifically the special relativity section

ah wait nevermind

i zoomed in a lot and the first one is actually a tilde, the second is a bar

not the nicest notation to use

PM 2Ring

14

Q: The Follow Questions and Answers feature is now live across the Network

We are happy to announce that the previously announced follow question and answer feature is now live across the Network, including Stack Overflow, all Stack Exchange sites, and all Meta sites. (International Stack Overflow sites will have it turned on in a day or two once we have translations al...

discussion announcements follow-post

Yay! I have great hopes for this Follow feature. It'll make it a lot easier to respond to edits on downvoted & close-voted posts.

Charlie

15:23

If I, in theory, watched a particle travel between A and B and wanted to parameterise it's trajectory with its proper time, I would need a clock that ticks in my frame at $\gamma$ ticks per second, right?

assuming it's just travelling in a straight line along an axis

Aaron Stevens

0

Q: Vertical circular motion experiment - feasible?

Okay at school (closed, unfortunately), we have completed a practical the involves determining the force experienced by a rubber stopper in a horizontal plane. And just before the school closes (corona), my teacher asked the class to modify this experiment in order to address our own related hypo...

homework-and-exercises newtonian-mechanics experimental-physics home-experiment centripetal-force

How has this not been closed yet?

Oh I completely missed that the same user posted almost all of the answers

PM 2Ring

15:38

@AaronStevens Yeah. But now they understand that we don't do that on SE.

Sorry, shall not do that again! Essentially spamming. — Kishan Bhatt 13 mins ago

@AaronStevens I suppose it should be closed as homework. OTOH, I think this part is ok because it's a conceptual question: "Is the slotted mass responsible for the centripetal force in vertical circular motion?"

Aaron Stevens

16:02

@PM2Ring But then you have "Also is this a good experiment to do (constant tension vs varying tension)? What variables should I change instead?"

And "How can I calculate the initial velocity of the mass? Given the small mass (25 g), the mass of the slotted mass (150 g), radius (1 m) and period (0.7) available."

PM 2Ring

16:30

@AaronStevens Oh, I agree that that stuff makes it close-worthy, especially the stuff asking for a specific calculation, but the existing answers avoided doing that calculation.

Aaron Stevens

16:54

@PM2Ring Yeah, I am just talking about the question :)

PM 2Ring

I did cast a close vote on it, and left a comment. I'd happily vote to reopen if the question were cleaned up, but I think that's pretty unlikely, at this stage.

SM Sheikh

17:15

Hey homework questions are not accepted where can I ask them?

knzhou

@AaronStevens There's nothing wrong with this question! I mean, it suppose contains Newtonian mechanics, and I guess a lot of people here dislike that, but that's not a reason to close.

John Rennie

@AaronStevens BOOM! :-)

Aaron Stevens

@JohnRennie I need to be faster on the draw :P

@knzhou I don't think I have ever advocated for a question to be closed because it contains Newtonian mechanics, nor have I ever seen anyone do that

JMac

@SMSheikh You might be able to get some help in the problem solving strategies chat chat.stackexchange.com/rooms/54160/problem-solving-strategies

@AaronStevens I'd have like no rep here if that was the case lol

Aaron Stevens

@JMac Haha right. I answer many Newtonian Mechanics questions. It is the only tag I have gold in right now

@knzhou "How can I calculate the initial velocity of the mass? Given the small mass (25 g), the mass of the slotted mass (150 g), radius (1 m) and period (0.7) available." is basically an off-topic homework question. "Also is this a good experiment to do (constant tension vs varying tension)? What variables should I change instead?" Is an opinion-based question.

This is why I think it should be closed

Not because it involves Newtonian mechanics

Additionally, due to the many questions, it is not a well-focused question

Do they want a calculation? Do they want feed back on their experimental design and ideas? Do they want to understand more about centripetal forces and circular motion?

JMac

17:27

I'm surprised there aren't votes for needs more focus. That's what I'm VTCing for.

Aaron Stevens

Like @PM2Ring said, the final part is fine. The other ones are not, and the fact that all exist in the same post makes it a not focused question

@knzhou I do recognize that I tend to be stricter with closing questions, and I think you tend to be more lenient, so I would love to hear why you think the question is fine as it is. I like to learn about what other people think to help inform myself in how to think of other questions in the future

Oh well :(

Johan Liebert

17:53

42

Q: My question was closed on Phys.SE. Can you recommend me another internet site where my question might be on-topic?

My question was closed1 on Phys.SE. Can you recommend me another internet site where my question might be on-topic? Here we keep a list of other internet sites that might help students2 of physics. One site per answer. To keep the list at a reasonable size, please only include sites which fulfil...

discussion faq closed-questions homework-and-exercises

When can I expect to see the implementation of the suggestions made here(👇)?

11

Q: Let's make the best of the new Ask page design for this site

As you may or may not have noticed, the new ask page is now live on the network. Go and have a look! Some of the new features are only visible to new users, but it still looks noticeably different even from old accounts. Now, the new design of the Ask page allows for a fair amount of per-site cu...

discussion featured ask-page

knzhou

18:26

@AaronStevens Well, disagreement is perfectly fine. We're high rep users, we make the rules here! So in some sense, every individual high rep user's close/reopen votes are correct, by definition.

But personally I liked the question because it's open ended enough to not just be a boring calculation, yet not open ended enough to be unanswerable. Also, I like the OP as a person given what they wrote, they sound curious and open-minded.

In fact, I would prefer to have one more of these nice Newtonian mechanics questions than, e.g. yet another question about checking a tedious calculation in a QFT homework problem.

But the votes have spoken, and that's fine!

Aaron Stevens

@knzhou Right, those are positives. If the question can be edited to be more focused and not opinion based or requesting a specific calculation without prior effort, then I think it could be a fine question about how the hanging mass relates to the centripetal force applied to the spinning mass.

Slereah

Today was a good day on PSE

Because I got to mention the November tensor

Didn't expect to

Aaron Stevens

The emphasis would also need to be changed. The title and bold question at the end make the main point about if the experiment should be done in the way they want to, or if it should be done in a different way

@Charlie Random tip: There is no need to edit really poor questions that have already been closed, e.g. this one. It bumps the question into the reopen queue and to the top of the home page. This isn't horrible, but I just don't think it is necessary.

The new "follow" option is interesting

Charlie

19:02

Ah my bad I forgot it bumps the question

PM 2Ring

@Charlie In addition to what @Aaron just said, it's generally a bad idea for someone other than the OP to edit a freshly closed question. If the question is fixable by the OP they should be given that opportunity.

The very first edit of a closed question sends it to the reopen review queue, but any subsequent edits do not (although they do bump it to the home page). So if that first edit doesn't fix the question the odds are it won't ever get reopened, even if the OP later turns it into a perfect question.

2

Charlie

I did not realise that either, will avoid it in future thanks

PM 2Ring

Yeah, it's one of those "features" of the system that aren't widely publicized...

However, there are some significant changes currently being worked on to the whole closing process. See meta.stackoverflow.com/q/394871/4014959 for details. As you can see by the downvotes, comments & answers there, the SO community aren't completely happy with some of the proposed changes.

In particular, the ability for an OP to automatically reopen their closed question merely by making a substantial edit to it...

PM 2Ring

19:41

The OP reposted physics.stackexchange.com/q/540205 to astronomy.stackexchange.com/q/35627/16685 as was (kind of) recommended in comments. Should it be close-voted (or flagged)? It already has 1 answer on Physics.SE but that answer's pretty useless, so hopefully it won't get upvoted (which would stop the OP from deleting the question).

Student404Mus

20:00

When a phase factor is introduced for identical physical states?

Aaron Stevens

21:50

@PM2Ring I think a flag would be fine

David Z

22:38

Yeah, when in doubt, cast a flag. TBH I really don't know what is a good way to handle those cases. As much as SE discourages exact crossposting, I don't think it should really be our responsibility ("our" meaning the Physics SE community) to handle what people do on other sites.

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