The h Bar

Sir Cumference

02:43

0

Suppose I were moving at 0.9$c$ relative to the ground, and I wanted to run half way across the Earth. The time of certain objects, like the Sun, would progress faster relative to me, right? Before I reach the far side of the planet, would the Sun's time have progressed so much that it would beco...

Anyone know the answer?

ACuriousMind

@SirCumference zeldredge's comment contains the answer: Your idea that the time of the sun goes faster from your perspective is simply wrong. Time dilation is symmetrical: If two things move relative to each other, both see the time of the other go by slower.

If you think this is confusing, you're not alone - search this site for endless variations on the twin paradox, for instance.

Sir Cumference

Ah, I get it now

Secret

03:08

@vzn But I thought chaotic systems are still predictable at least at the time interval very early in the evolution of the system?

because the uncertainty in the prediction only diverges exponentially

DanielSank

@SirCumference Awwwwww, I made really cool plots to illustrate this!

And then the post was deleted. Booooo!

Secret

I think I am looking for a type of dynamics so extreme that no matter how large or small the window one pick (temporal or spatial), no matter which stage of the evolution of the system and which point you pick, you cannot predict the evolution of the system based on all the information at that point and its history?

is this actually a non deterministic system the one I am seeking?

DanielSank

@Secret Sure sounds like it.

@SirCumference I'm sad that your post was deleted. Here are my plots:

Awwww, is there a way to paste images into chat?

ACuriousMind

@DanielSank Click "upload"

Secret

try upload them one by one

I always did that

DanielSank

03:13

Yay!

Ok check it out: The green lines are the left and right edges of Earth.

The black line is your world line as you move across the Earth.

The Black dot is when you cross the right edge of Earth, and the Green dot is when you cross the left edge.

TanMath

What is this discussion about? Time dilation?

Secret

yup

DanielSank

The red dot is when the sun explodes and the red line is the "shockwave of death" from the sun's explosion.

@SirCumference Are you following?

Note that you cross the shockwave of death when you're 1/2 of the way across the Earth.

Now here's the same thing from your point of view:

TanMath

Exactly what about time dilation?

DanielSank

Here the sun explodes way earlier.

TanMath

03:16

I see world lines! First time seeing them used as an application apart from in my GR textbook that I am reading

DanielSank

However, look at this zoom-in on the interesting part:

TanMath

@DanielSank whose perspective?

DanielSank

It's the frame of the moving person, i.e. the black line.

TanMath

Who is accelerating? What are the inertial frame?

DanielSank

That's why the black line is now vertical, i.e. stationary.

@TanMath The first frame is co-moving with the sun and Earth (assuming sun and Earth are not moving relative to each other).

The second frame is co-moving with the person whose world line is black.

@SirCumference The death ray still hits you when you're 1/2 of the way across the Earth. This has to be true because events which occur at the same time and same position are always the same time and position regardless of frame.

TanMath

03:18

@DanielSank how is that possible? The sun is not moving and the Earth is!

DanielSank

@TanMath Dude, it's an approxmiation.

TanMath

Fine...

I cannot follow this discussion...

DanielSank

@TanMath Also, to say that the sun is not moving and the Earth is moving is not true. Which one is moving depends on your frame. Motion is relative in relativity.

Anyway, @SirCumference, I hope this clears things up for you. If you study the diagrams you'll understand everything.

TanMath

@DanielSank true...I cannot imagine a frame where they are both moving at the same speed

DanielSank

@TanMath Well, there's definitely a frame where they're moving at the same speed but in opposite directions.

TanMath

03:21

Really?

DanielSank

@TanMath Well, yeah. At least, in a 1D world...

Secret

" This has to be true because events which occur at the same time and same position are always the same time and position regardless of frame.
"

Now that's kinda new (unless my memory fails me again), I thought only the squared interval between two events is invariant for all frames and not the events themselves

ACuriousMind

@TanMath Of course - the frame of something orbiting the sun (in the sun's rest frame) at exactly half the radius of the earth orbit with such a velocity that sun-thing-earth is always a straight line In the thing's rest frame, sun and earth are orbiting it at the same speed.

DanielSank

@Secret Yeah, so if the squared interval is zero in one frame it's zero in all frames :-)

Secret

no I mean, i am not sure if a single event themselves are invariant to all observers, because that seemed to be what you are implying?

DanielSank

03:32

Hey @ACuriousMind, I made a broke-ass program to plot space time diagrams.

@Secret Of course not, and I don't think I said that.

Here's a clearer way to say it: "Two events A and B, if they are coincident in one frame, are coincident in all frames."

Secret

"The death ray still hits you when you're 1/2 of the way across the Earth. This has to be true because **events which occur at the same time and same position are always the same time** and position regardless of frame.
"

ok this one "Two events A and B, if they are coincident in one frame, are coincident in all frames."
" makes a lot more sense

Secret

(unrelated) Sometimes I am glad that we live in a minkowski spacetime and not an alien spacetime based on p adic numbers en.wikipedia.org/wiki/P-adic_number else I don't think we will have nice aids such as spacetime diagrams to guide us and we will have to deal with the whole business fully algebraically

DanielSank

04:19

If any of you guys close those cryogenics questions for being "off topic" I will likely go insane.

TanMath

04:31

@DanielSank can I have this program, or is it closed source?

Martin - マーチン

05:03

Would the following be on regarded a good fit for your site? Do you maybe have already a question adressing that phenomenon? chemistry.stackexchange.com/questions/43338/the-color-black

user54412

05:36

@Martin-マーチン Cross posted: physics.stackexchange.com/questions/227794/black-and-reflection

user54412

Whatever we do, we're not going to migrate to chemistry, so feel free to close that one.

Mikhail

@Martin-マーチン I just made a shitty reply. I hope your happy.

Martin - マーチン

@Mikhail ;)

@ChrisWhite I am going to do exactly that.

Thanks for helping me out.

0celo7

06:52

Dammit Ubisoft, Assassin's Creed: Indian Simulator is not fun

been running around for 3 hours and still haven't gotten Assassin gameplay

Sidarth

11:06

Hi everyone!

I just earned the chat privilege!

Anyone active here?

Sidarth

12:09

hmmm

David Z

12:47

@Sidarth depends on time of day

4

Q: How do proteins perform their function

Let's, for example, take a ribosome. It is an enzyme that is in turn just a molecule that must follow the laws of physics. Correct me if I'm wrong, but it can be looked upon as a molecular machine made up of several pieces. What exactly makes those pieces work together? Why does the ribosome bi...

quantum-mechanics biophysics molecules interactions

It's been proposed that this sort of thing should be on topic for us. Thoughts? For people who think it's off topic, how far off? In other words, how much would need to be changed (regardless of whether it would actually be a valid edit) to make this on topic?

ACuriousMind

13:09

@DanielSank That would be a useful thing to have - do you have it on github or something? I bet @JohnRennie and other frequent relativity answerers could use that.

Bass

@DavidZ IMHO this is more a chemistry or biophysics question than one about biology. These proteins are known as molecular motors, the most widely known class are myosins which are responsible for muscle contraction. AFAIK their mechanic force comes mostly from covalent bonds, so the chemistry SE seems like a good place for this question.

David Z

Well, the question is not really where is the best place for it, but whether it's on topic here

or rather, whether it should be on topic here

ACuriousMind

@DavidZ Voted to reopen. The physical explanation of biological mechanisms is the physics part of biophysics, and hence on-topic here.

Bass

@DavidZ At least with the edit it's not off-topic: What forces would move it along this strand? Is it electromagnetism?

Sidarth

@DavidZ ok

wassup?

can I ask a doubt on COMSOL Multiphysics FEA software?

David Z

13:24

Sure, anything goes here in the chat (subject to some basic rules about civility and such)

Sidarth

Cool.....how can I give an Induced current equation in 3D analysis ?

ie.e, I want to write the "velocity, lorentz term " en for 3d analysis

knzhou

@DavidZ IMO it's on topic, even though it is more biology than physics, because there are aspects of the question only a physics approach can answer. In any case, it's a much more interesting question than the 10th entanglement / twin paradox question of the day.

John Rennie

13:43

@ACuriousMind @DanielSank I'd certainly be interested to see the app ...

0celo7

15:06

ヽ༼ຈل͜ຈ༽ノ

huh

apparently you can have that as a YouTube username

0537

15:34

lol

Qmechanic

16:29

@DavidZ : This question (v3) is (besides being off-topic) too broad. It currently contains around 10 sub-questions.

user54412

@DavidZ I can appreciate the call to not exclude biophysics, but at the same time the question is rather meandering and unfocused, so I hesitate to say it's focused on (bio)physics.

user54412

What really confuses me is why some people insist only physicists are equipped to handle these sorts of questions.

user54412

If I were asking how to calculate the probability of DNA linkages breaking due to thermal collisions with solvent molecules, given that I know the structure of DNA and don't know stat mech, then sure, I might go to a physicist.

user54412

But asking how enzymes/DNA/organelles work in general is exactly what biologists do.

0celo7

17:01

@ChrisWhite Pretty sure biology is just carbon electron shell physics

DanielSank

17:18

@JohnRennie I'll put it on github later today if I remember. It's pretty simple. You give worldlines in one frame and then it plots them in other frames.

0537

17:32

@0celo7 I think that's organic chemistry.

ACuriousMind

@0537 And biology is just applied chemistry.

dmckee

Dear person annoying me,

Please, please, please! Just stop %&^!@~# guessing and throwing mud against the wall in the hope of a pity vote or two. This site is for grownups or those who can do a good job of imitating one.

Sincerely, me.

ACuriousMind

I'd take a bright child willing to learn over some of the grownups every day, though :P

dmckee

@ACuriousMind Fair enough. I would too.

0celo7

17:49

where is the puppet person

is he gone

John Rennie

@0celo7 puppet person?

0celo7

@JohnRennie the one who accused us of being puppets

and DS being the master

John Rennie

@0celo7 ah. I assume he/she/it eventually grew up.

ACuriousMind

That they grew bored is more likely, though...

John Rennie

As it happens they stopped the silly posts immediately after I told them to seriously consider growing up :-)

@dmckee naming no names, but does their username rhyme with Kylo Ren?

@DavidZ If the question was along the lines of what determines the force between two molecules then it would be on topic here.

As it is, you need to know a lot of biology first to understand what the (bio)molecules are doing before you can start trying to explain their behaviour using physical principles.

ACuriousMind

18:13

Mentioning Kylo Ren, is the spoiler ban

Dec 16 '15 at 5:47, by DanielSank

Please do not spoil Star Wars in this chat over the next couple weeks.

still in effect?

dmckee

18:23

@ACuriousMind It's been about three weeks since the opening, no? I'm supposing that we can allow vague statements like "It doesn't suck and someone dies." (my first pass non-spoiler review).

0celo7

18:38

Someone does die

Name rhymes with Anderson Cooper

David Z

18:52

@JohnRennie Generally speaking, I think there are many good questions that will require some background information about a specific topic, and I don't think that itself should make them off topic.

Could be just a difference of opinion

Emilio Pisanty

19:07

@ACuriousMind Not sure, but given loweringthebar.net/2015/12/… you might want to take it easy in case anyone takes it hard.

(Obviously not implying Daniel would do any of that, in case it needs saying.)

Mike Miller

@ACuriousMind: Gimme two weeks.

bolbteppa

"The lumped circuit approximation enables one to get around the problem of finding the actual fields in the vicinity of a circuit. The key idea is to regard the circuit as made of elements-resistors, capacitors, inductors, sources of emf" Any idea what the (vague jist of the) logic is to get from the EM Lagrangian to this statement?

In other words, understanding Kircchoff and other stuff from basic EM books using microscopic EM coming from a Lagrangian

Emilio Pisanty

@MikeMiller ↑

dmckee

19:23

@EmilioPisanty Of course not. He'd send one of his alter-egos to do it. If you haven't done a mission since Christmas is might be you.

Emilio Pisanty

@dmckee Will probs give it a pass, I think. Not too keen on getting arrested for doing dumb stuff online.

Physics Meta

20:00

0

Q: What are the bondaries of "biophysics" on Physics SE?

The question Presumably biophysics question run a wide range from those that are primarily biology questions with a little physics input to those that are primarily physics questions applied to a situation that appears in a biological processes or system And presumably some fraction of them are...

discussion scope tags

Danu

@EmilioPisanty What is it with you and Kyle Kanos?

dmckee

@bolbteppa Are you able to follow the development of the lumped circuit approximation given in most sophomore level texts? I suspect the way to go it to pass from the Lagrangian to the sophomore style rules for fields and charges (forces and energies) and then add in an argument about circuits in normal conductors.

Or are you looking for even more microscopic detail than that?

Danu

@DavidZ This is definitely physics (IMO). I in fact know physicists working on similar matters at AMOLF

I definitely think it appears to be too broad (as Qmechanic also noted)

Emilio Pisanty

@Danu We've had disagreements in the past.

Danu

20:18

@EmilioPisanty Just about on/off-topicness of questions?

I mean... Kyle got really mad at me at some point too but we got over it.

(also about on/off-topicness of questions, funnily)

In any case, I guess disengaging is always the best.

It's hard to get Kyle to give an inch ;)

But I feel like both of you are good guys deep down, so you should be able to get over the bickering

0celo7

@ACuriousMind Did you play Assassins's Creed 3 or did you stop at Revelations?

ACuriousMind

@0celo7 The latter

Mike Miller

not a bad choice

Emilio Pisanty

20:46

@Danu There have been more personal frictions but there's no use in recounting them. I agree that some discussions tend to get slightly unprofessional despite my best efforts, but on the same vein it would be unprofessional to discuss them further here (particularly on a chat venue that he can't access easily, cf. his profile).

Danu

@EmilioPisanty Agreed.

alarge

@DavidZ The question is badly formed and they are too many, but this should definitely be on topic at physics SE; How kinesin motors move in itself is a large field and a lot of research into it is being published primarily in physics journals.

0celo7

@ACuriousMind It's not nearly as good as the previous ones.

Danu

In general, currently I think it is better to err on the lenient side of things when it comes to biophysics.

dmckee

@Danu That's my bias, too, but I am almost totally unschooled in the field and don't have a strong sense of where that leaves us. Nor, it seems, does the community have a consensus or even an agreement to disagree.

Danu

20:58

The basic point that we're struggling with right now is the following: Is a physics-type question that requires a lot of biology background on-topic?

I'd say yes, definitely since this exactly what we say for all other subjects.

Of course, we sadly happen to have only (very) few ($\epsilon>0$?) people who have the relevant background.

But that's something we ought to change (also per the meta post)

alarge

@dmckee This is like physical chemistry/chemical physics: it's sometimes difficult to classify what is what. Are phase transitions physics or chemistry? How about thermodynamics? How about a model about two chemical components reacting and diffusing in space that uses the theory and equations of thermodynamics/phase transitions? What if we swap the chemical components with lipids or some other biologically relevant molecules?

Bass

When a scalar field is expressed in creation/annihilation operators like $\phi(x)=\int \mathrm{d}^3\mathbf{k}\{a(\mathbf{k})e^{-ikx}+a^\dagger(\mathbf{k})e^{ikx}\}$, am I right that in the exponent $k_0=\omega_k$ is defined as a function $\omega(\mathbf{k})=\sqrt{\mathbf{k}^2+m^2}$?

ACuriousMind

@Bass Yes

Danu

Yup

On-shellerino

Bass

cool, thanks!

Danu

21:03

@ACuriousMind Can I interpret your lack of response as "I'm not doing anything interesting physics-wise, currently"? :P

ACuriousMind

@Danu Uh...yes. Although that might change shortly.

Danu

:\

Are you also experiencing a lack of motivation to do most types of physics lately?

ACuriousMind

@Danu No, not really. I'm rather getting eager to do a bit more than I did lately.

Danu

Okay.

Nice :)

bolbteppa

21:27

@dmckee more microscopic detail, basically just a first principles discussion of those sophomore book chapters worthy of fitting into Landau amazon.com/Electrodynamics-Continuous-Media-Second-Edition/dp/… something I can't really find browsing that difficult book, if such a thing exists?

dmckee

That's not going to be a common thing, and I don't know of one myself. I mean, why bother? As long as you can get from QED ro the classical field expressions and from the field expressions to Kirchoff's laws (with enough input about materials) you're good, right?

Danu

First principles are such a turn-off.

ACuriousMind

@DavidZ @dmckee @Qmechanic: There is an inconsistency on how to deal with non-mainstream answers. The faq says: "For answers, use a custom moderator flag mentioning that it is non mainstream." while this later answer by DavidZ says: "I can't speak for the other mods, but if I see flags like that, I usually decline them."

3

Is the faq encouraging flagging that will almost certainly be declined?

Danu

I also think this is a problem.

In general, the non-mainstream thing is hard to deal with.

dmckee

21:44

@ACuriousMind I take a pretty liberal view of "could be reasonable under this interpretation and that limitation" when deciding if I will or won't deploy moderator superpowers delete a non-mainstream answer.

If there is some interpretation under which it might represent an actual answer I tend to leave it. On the other hand, I'm pretty liberal with the downvotes, too.

Danu

Look, I think it's pretty clear that you guys will pretty much never delete non-mainstream answers so long as they're genuine attempts.

ACuriousMind

@dmckee I was less asking about what you actually do with those answers than whether or not you want flags indicating them. (Because the faq says to flag it, but then the general rule is that just being wrong shouldn't be flagged, so...?)

dmckee

The question of accept or decline is harder and I don't have a good policy.

I think that we want moderators to see the more egregious posts, but we don't want people flagging as a means of punishing other users, which leaves me in a quandary.

Emilio Pisanty

The problem is mostly that we still don't have a big- and active-enough population of users with answer deletion privileges, and it's very hard to get them all to see and act on the bad cases.

The VLQ queue does have the mechanisms to act on this, via the Recommend Deletion button that's accessible to a much broader and more active population.

The problem is getting deletion-worthy answers on that queue in the first place, which is normally via flags, but that can't happen if the standard advice is "don't flag for quality issues, even including nonmainstreamness".

With said standard advice reinforced by disputed / declined flags which are sometimes hard (or at least laborious) to trace.

The ideal is to get the bad answers removed via community moderation, right?

But I'm unsure that we've got effective enough mechanisms for that as yet.

Danu

@EmilioPisanty Sorry but AFAIK the VLQ-queue is not intended for factually wrong, crackpot-type answers. Just for "not an answer"-type things.

@EmilioPisanty Oh, right.

Emilio Pisanty

21:56

@Danu I'm not sure, and I don't think that a strict adherence to The SE Model is necessarily what's going to work out best for the community and for the site here.

Non-mainstream answers are bad for the site. (claim 1)

We do get a steady stream of such answers that are so bad that they do need to be removed. (claim 2)

2

It is better if they are removed via community moderation rather than moderator intervention. (claim 3)

Therefore we require an effective mechanism that will enable community moderation to remove such answers. (claim 4)

ACuriousMind

@EmilioPisanty I think if we think that users with direct delete votes should delete crap answers because they are wrong (which you seem to imply), then we should also send them into the VLQ queue.

Danu

@ACuriousMind I also think so.

@EmilioPisanty That's an interesting POV.

I would also like to act more harshly against crackpottery.

ACuriousMind

@EmilioPisanty That's the one claim here to be debated, probably. Is there harm in them sitting there downvoted?

Emilio Pisanty

@Danu I mean something a bit more specific. The SE team has provided tools, and we should use them in the way that's best for the site, not in whichever narrow way they were originally conceived.

Danu

@ACuriousMind I think that, sometimes, there is.

(<10% of cases)

Emilio Pisanty

22:01

@ACuriousMind Maybe not. But then they need to be heavily downvoted, at least until they gray-out zone. And they won't necessarily get that much attention, particularly with answers to old questions.

Thus there's still a need for the ability to put those questions on a review queue that has the power to downvote them.

ACuriousMind

@Danu Soo...this would mean putting things in the VLQ queue which will in the majority of cases not be deleted? Because a policy any muddier than "flag non-mainstream answers" or "don't flag non-mainstream answers" will just lead to confusion.

Danu

@ACuriousMind No, I'm advocating only putting the ones that I do think need to be deleted in it (ain't that obvi? ;) )

Emilio Pisanty

@Danu I think there is, but I do not have data on it. It's definitely a very small fraction of the total answers we get, but they cause a sizable amount of damage. Again without any data off the cuff.

@ACuriousMind The thing is that the LQP queue does not allow you to downvote, for reasons I've never understood.

Danu

@ACuriousMind I'd naively agree with your second sentence. But well, I never really thought about letting go of the standard SE protocol as Emilio suggests.

@EmilioPisanty Yeah, it sucks.

Maybe we should make a Meta Stack Exchange post about that

unless there already is...

ACuriousMind

@EmilioPisanty Agreed (there is a meta.SE post about this, but it's never made much sense to me, either)

Danu

22:05

29

Q: Add downvote option to Low Quality Review Queue list of potential actions

VLQ flagged posts are now being shown in the Low Quality review, which allows: Looks Good Edit Delete Skip but no option to vote on the post. My suggestion is to add downvoting as options: Downvote Downvote/Delete (this would replace current Delete) There have been times I want to downvot...

discussion feature-request down-votes low-quality-posts

ACuriousMind

26

A: Why is voting removed from new review system?

Voting is one of the main components of SE communities. While surfing or reviewing posts I am eager to vote on them. Answering is also one of the main components. Flagging's gotten pretty big too. But neither of these are available in the current review queues. Note that you can't close or...

Emilio Pisanty

@Danu That sort of explains why I never understood it. It was never explained.

tongue-in-cheek implied.

Danu

No, I do not, @apaul - and I'm not sure how either of those discussions justify such a thing. Is there a particular reason that legitimate but mediocre answers should be deleted instead of downvoted? Is there a particular reason that answers some users found helpful should be deleted based on a flag? Are you forgetting that VLQ flags deemed helpful come with an automatic downvote? — Shog9 ♦ Jun 3 '14 at 19:57

That's pretty much an answer.

Emilio Pisanty

Makes no sense to me.

Danu

Also zero sense to me.

Emilio Pisanty

22:10

The LQP is there so experienced users can see potentially-bad posts and take appropriate action.

Sometimes that is deletion, but often it's not.

Danu

Perhaps the low quality queue is completely different on other sites?!

Emilio Pisanty

If the post is bad but not bad enough that it warrants deletion (most of the time) then the appropriate community action is downvoting.

@Danu Probably. I do think that our non-mainstream problem is relatively unique among the network.

Danu

Yeah... physics

Emilio Pisanty

@Danu "relatively" unique.

I suspect TCS probably has a similar problem.

Danu

TCS?

Emilio Pisanty

22:12

As probably does Biology with anti-Darwin people

@Danu Theoretical Computer Science

ACuriousMind

@Danu Theoretical Computer Science

Danu

@EmilioPisanty I'm not so sure about that!

This problem is probably dealt with quite easily by them because it's so unique and easy to detect.

Emilio Pisanty

@Danu Maybe not, in which case lucky them.

Danu

I think physics is unique in its way of attracting crackpots

Emilio Pisanty

@Danu Math and TCS hold their own too.

Danu

22:14

with math, probably, but there it's arguably easier to separate the good from the bad?

Yeah, hmm...

Interesting topic of discussion.

Emilio Pisanty

Ever read of the guy whose job it was to sort through submitted proofs of Fermat's Last Theorem?

It's in Simon Singh's book, at the very least

Danu

Yeah... Math :P

Emilio Pisanty

47

Q: Handling unsolicited proofs of famous mathematical problems

I have been receiving mails from (most probably amateurs), who claims to have proved famous mathematical problems, like the ABC Conjecture or Goldbach Conjecture. But invariably, they all contained mistakes. I decided not to waste my time on such unsolicited documents. But recently something inte...

etiquette peer-review

Danu

22:31

Good night, all!

0celo7

23:20

@Danu My Dirac belt photon question was deleted after being closed as non-mainstream :(

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