The h Bar

danielunderwood

12:10 AM

Meanwhile it's already dark here on the east coast

Avantgarde

12:44 AM

Turn on the light

Akash. B

4:44 AM

@JohnRennie is there a difference in time of the cloak in space?

John Rennie

@Akash.B the clock in space runs fastest, the clock on Mars runs slightly slower and the clock on Earth runs slower still.

Akash. B

5:43 AM

@JohnRennie how gravitational force influence the speed of flow of time?

John Rennie

@Akash.B do you know what gravitational potential energy is?

Akash. B

@JohnRennie No

John Rennie

Hmm, then this is going to be tricky to explain

Akash. B

Do you mean gravitational force?

John Rennie

I think for now you're just going to have to accept that gravity makes time move more slowly.

Akash. B

5:50 AM

But how ???

@JohnRennie

Avnish Kabaj

6:35 AM

@Akash.B finish your highschool physics first

You won't be able to understand the answers to the questions you ask

John Rennie

7:06 AM

@Akash.B General relativity tells us what happens and how to calculate, but it doesn't tell us why it happens. That is, if you ask what is actually happening when time is dilated there is no answer to that.

And as Avnish says, explaining how we calculate the time dilation really needs a more detailed grasp of maths than you currently have.

Anonymous

7:27 AM

-2

Q: Can you find any hole or bug in the attached theory?

I found the perfect theory of everything, it explains everything mechanically without contradicting QM or relativity including why the speed of light is constant(26:09) see: https://www.youtube.com/watch?reload=9&v=omOlPH_4G5U it takes a while to watch it, but it explains everything and makes s...

Anonymous

Spheroid Theory of Everything

►

Anonymous

Damn, I appreciate the effort put in XD

Secret

9:23 AM

Even if this is consistent and fits experimental data, it seemed to be a lot more complicated than the mainstream method

Encourage this guy to just work out the maths in detail, then try get it published in a peer reviewed journal, before we will comment

Emilio Pisanty

10:05 AM

dammit, Rod

I don't want to climb that ladder

heck, I didn't even want to go above @dmckee

Anonymous

10:19 AM

Bounties are calling ;)

John Rennie

You'll just have to stop posting awesome answers :-)

4

Psychologists at the University of Bath have discovered that hungover people have poorer attention, memory and psychomotor skills such as co-ordination and speed compared to when sober

Really? Who would have thought it? If they'd asked me I could have told them that for free.

Anonymous

The experiments conducted must have been fun, I imagine. :D Government grants for free alcohol!

Emilio Pisanty

10:43 AM

@JohnRennie thanks =)

though I wouldn't necessarily call a +2 score a massive hit rep-wise

Also, the scammy Schrödinger-cat salesman doesn't get nearly enough attention in the pop-sci press

ACuriousMind

11:03 AM

On-topic or off-topic?

2

Anonymous

Looks pretty bad

Anonymous

This appears to be less a question about physics and more about the English language: "as small as a fraction of an X" means effectively the same as "smaller than an X". — ACuriousMind ♦ 2 mins ago

Anonymous

I agree ^

Anonymous

It belongs to ELL SE

user1732

he wants a translation from words into symbols

How will write it mathematically? 10^-20 angstrom? — Saksham Sharma 4 mins ago

@ACuriousMind on

Anonymous

11:12 AM

Is fraction of anything be represented as divided by what equals to in numerator of the fraction? In this case fraction of an angstrom 10^-20/10^-20? — Saksham Sharma 32 secs ago

Anonymous

Can't parse the sentence...

user1732

the OP has forgotten the definition of a fraction

ACuriousMind

I think the comments make it even more clear that the OP has a language problem rather than a problem with anything specially related to physics.

They're looking for a "mathematical" explanation of an idiom of common speech, which simply doesn't exist

Anonymous

I tried to explain a bit in the comments, but yeah. The language barrier seems high

user1732

nice try :-)

Anonymous

11:19 AM

Phew, now you can clean up the comments, lol

Avnish Kabaj

@Blue Thanks Blue. — Saksham Sharma 1 min ago

He gottit

user1732

victory^

:-D

Emilio Pisanty

@ACuriousMind stop answering in comments and answer in answers instead =P

You too @Blue

Anonymous

There are some arguments against encouraging off-topic questions :P So I wasn't sure whether to write an actual answer

ACuriousMind

@EmilioPisanty Well, I'm not going to answer in an answer a question that I think is off-topic. My comment is intended more as my explanation to why I think it's off-topic. That it simultaneously answers the question is unfortunate :P

@Blue If "encouragement" is your argument, then it makes no difference whether you give the answer in an answer or in a comment, at least from the viewpoint of the asker.

Emilio Pisanty

11:27 AM

@ACuriousMind I've just popped that into Argument Rater out of curiosity, and it gave it a straight 4 out of 10

user1732

lol

ACuriousMind

@EmilioPisanty What's Argument Rater?

Emilio Pisanty

@ACuriousMind it's a sister website to Sarcasm Detector =)

user1732

the one that rates arguments :P

ACuriousMind

@EmilioPisanty Ah. Those modern neural networks can do amazing things, can't they?

2

Emilio Pisanty

11:29 AM

though this was more of a well-intentioned joke than sarcasm

user1732

mine too

Anonymous

@ACuriousMind But from the viewpoint of the website if you had closed it as off-topic it would have been deleted by the Roomba later on (unless the OP improved it). Anyhow, another reason is that I'm avoiding writing answers much these days, unless the question is really interesting

ACuriousMind

@Blue Why? We need good answers even to uninteresting questions! (I also feel that many questions commonly perceived as "interesting" are actually just "ill-defined" :P)

Anonymous

Okay, well, I like ill-defined questions at times :P They give you more scope to beat around the bush and write essay type answers, lol

Anonymous

For instance this is an ill-defined question:

Anonymous

11:36 AM

11

Q: What is the use of Categorical quantum mechanics?

I recently noticed that Oxford's computer science department has started offering a grad course on Categorical quantum mechanics. Apparently they say that it is relevant for the study of quantum foundations and quantum information, and that it uses paradigms from category theory. Questions: Ho...

quantum-information categorical-quantum-mechanics quantum-foundations

Anonymous

The answer was quite enlightening

Anonymous

About the answering uninteresting questions bit: yeah it's true that they too need good answers, but I'm a bit short of time these days to write "good" answers for them

Anonymous

I'll resume answering sometime later I guess :)

user54826

12:12 PM

if someone happens to know how are maxwell equations satisfied when there is inelastic scattering, feel free to answer my question at physics.stackexchange.com/questions/424571/…

coz as I understand it, I see no way for the interfacial conditions to be satisfied at all times. because that scattering means omega differs in the incident and reflected waves, which seems to go against the interfacial conditions on the fields

Avnish Kabaj

Top that

:P

Adding a wow at the end makes it a 92

Adding a wow! Just amazing makes it a 95

Adding a wow! Just absolutely amazing makes it a 96

user54826

12:38 PM

you hacker reverse engineer an algorithm

user1732

12:57 PM

@AvnishKabaj they have a -100 reading?

Abcd

@AvnishKabaj I don't understand how "oh wow thanks" is sarcasm in anyway

user1732

negative sarcasm would be sincerity

Avnish Kabaj

1:18 PM

@user1732 indeed

Anonymous

@AvnishKabaj What's your highest till now?

Avnish Kabaj

@Abcd

@Blue 96

Anonymous

I got 97 :P

Anonymous

Modified yours to Oh oh, gee! Wow! Absolutely stunning! I didn't know that thanks a lot for enlightening me.

Anurag Baundwal

Okay people, a few questions? [This one here] and [that one

Oops ... misclick

0

Q: How do I find the energy stored in a capacitor that has unequal charges

So, while discussing problems with friends, I came across a capacitors problem which looked something like this: So, my questions are: Can this be called a capacitor even though it same polarity of charge on the plates? Charge – After closing the switch, will there be equal chares on both p...

homework-and-exercises electrostatics electric-fields capacitance

-1

Q: Earthing the plates (one or both) of a parallel plate capacitor — How can one make use of the fact that the potential of the plate is zero?

Please take a look at this question : In the figure, plate $A$ has $100 \times 10^{-6}$ C charge, while plate $B$ has $60 \times 10^{-6}$ C charge. Find the values of $q_{1}, q_{2}, q_{3}, q_{4}$ when Both switches are open (no doubts here) Only switch $S_{1}$ is closed Swit...

homework-and-exercises electrostatics potential

These are the two questions. I think they're reasonably well written, and I've even places bounties ... but no good answers so far.

Would you guys take a look?

Thanks.

Anonymous

1:35 PM

@AvnishKabaj 98 now!

Anonymous

I'm getting addicted to this, lol

Anonymous

99, yay!

Anonymous

Gotta reach 100

Anonymous

Done, reached 100 :D @AvnishKabaj

Anonymous

I am trying to get in negative

Anonymous

1:42 PM

Anonymous

Oh, I didn't know that you are an expert on me and my life! Continue, please!  Wow! Absolutely stunning! I didn't know that thanks a lot for enlightening me.  You must be the smartest man alive on Planet Earth!

Anonymous

Lol, I combined all the sarcastic sentences into one

Anonymous

Now we can begin the reverse engineering

Anonymous

Is this an open source project btw?

Anonymous

@IceInkberry Gotta get -100 to beat me ;)

Anonymous

1:44 PM

(Oops, nah. Even then we'd be equals at best :P)

Anonymous

Getting a negative is difficult!

Anonymous

Ooh, got the key.

Anonymous

Insults help you get a negative score

Anonymous

Type in the worst explicit insults you know

Abcd

1:50 PM

@IceInkberry how to upload images from mobile

Anonymous

@Abcd Open desktop site and then upload.

Anonymous

On Chrome, it's in right top options.

Anonymous

Got -99 ._.

Abcd

@IceInkberry but this is not authentic

Anonymous

1:56 PM

@Abcd Yeah, but it's fun :p

Anonymous

It doesn't get my high level sarcasm.

Anonymous

github.com/topics/sarcasm-detection

Anonymous

It's on GitHub apparently

Anonymous

@IceInkberry Eh, that's showing only -26 for me

Abcd

-100 not possible @IceInkberry

Anurag Baundwal

2:01 PM

Pffff

Anonymous

@Blue There's much more before that ;)

Anonymous

Ah

Anonymous

Not suitable to post the statement.

Anonymous

It would be nice to have the datasets they used for training

Abcd

-100 Impossible

Stuck on -99

Ice did you get-100

Anonymous

2:03 PM

Yeah, same.

Abcd

@IceInkberry you typed only that much?

I typed a para then got -99

Anonymous

2 mins ago, by Ice Inkberry

@Blue There's much more before that ;)

Abcd

Anonymous

Be too good, or too bad.

Abcd

Ya

Anurag Baundwal

2:09 PM

Oh, come on. You guys have way better things to do rather than waste away with this stupid algorithm.

Anonymous

@AnuragBaundwal Right. Need to get back to ionic equilibrium.

Akash. B

hi

vzn

2:26 PM

Have scientists found evidence of another UNIVERSE? 'Ghost black hole' from ancient universe that died before the Big Bang has been discovered, physicists claim dailymail.co.uk/sciencetech/article-6095669/…

Akash. B

@vzn Really?

Secret

daily f88888888888888888 mail, the media that only knew to bullshit
*checks another source*

vzn

> The eccentric view has come from Oxford University mathematical physicist Roger Penrose, State University of New York Maritime College mathematician Daniel An and University of Warsaw theoretical physicist Krzysztof Meissner. arxiv.org/abs/1808.01740

@Secret did you find another source? see it there 1st? DailyMail gets a lot of flak but maybe try judging the tabloid not merely by its cover sometimes... chat.stackexchange.com/transcript/71?m=46316175#46316175

Secret

kipac.stanford.edu/events/are-we-seeing-hawking-points-cmb-sky

and then of course, there's the arxiv

hmm...

vzn

@Secret nice, recent Penrose talk on subj, but doesnt incl the recorded lecture, and the summary leaves a lot out too.

Secret

2:38 PM

ok, I have briefly read the paper, the stuff looks consistent, thus there could be hint of a CCC model, but for now, I will be skeptical and wait until more results arrive. It will be more interesting that if those are hawking points, then the first question to ask is that what can they told us what the previous universe is like

Avnish Kabaj

@Blue aw man

vzn

@Secret they used something like a monte carlo simulationn, found some anomalies that arent or cant be explained by other theories. an earlier paper (maybe without the data, more just the conjecture/ model) met with skepticism/ maybe counterarguments etc. science in progress. honestly it sounds outlandish & hard to follow to me too. are they claiming entire universes exist inside massive black holes, or the previous universe turned into a single supermassive black hole turned big bang, or ...?

Secret

physicsforums.com/threads/…

there's also a physicsforum discussion here

Anonymous

-5

A: Hamiltonian for systems with sub-lattice geometry

A Hamiltonian system is a dynamical system governed by Hamilton's equations. In physics, this dynamical system describes the evolution of a physical system such as a planetary system or an electron in an electromagnetic field. These systems can be studied in both Hamiltonian mechanics and dynamic...

Secret

probably a bot

Anonymous

2:53 PM

-1

A: About the Level of Non-Abelian Chern Simon theory

Planar physics – physics in two spatial dimensions – presents many interesting surprises, both experimentally and theoretically. The behaviour of electrons and photons [or more generally: fermions and gauge fields] differs in interesting ways from the standard behaviour we are used to in classica...

Anonymous

Another

Anonymous

@Secret Maybe...

Anonymous

Or maybe they're just trying to spread their app

Secret

Even if so, I don't treat these as human beings

because they are inefficient

danielunderwood

Looks like a solid effort on an app for a bad advertising method

Anonymous

3:01 PM

@Secret I, on the other hand, thought inefficient is a perfect definition for human beings. ;)

Secret

It's already demoralising enough to talk to people outside one's inner sphere, and coding programs, I don't need to talk to anyone who basically is a piece of code doing prescribed and boring things

Anonymous

@danielunderwood Indeed. Would be a good example of "How not to advertise your app" :P

Secret

perhaps when capitalism dies, then nobody will be so preoccupied with the notion of money and thus stop doing such stupid inefficient things

but then, socialism might starve us to death if it retraces its path in history

Anonymous

But then there's the notion of fame

Secret

conclusion: Humanity is doomed

Abcd

3:09 PM

@IceInkberry revising?

Anonymous

3:20 PM

That bot is on Chemistry SE as well.

Anonymous

@Abcd Yes, we have class 11 topics in our tests.

danielunderwood

4:18 PM

So this may be ridiculous, but is the frequency of neutrino interactions due to time dilation?

dmckee

5:08 PM

@danielunderwood No. It's due to being mediated only by the weak interaction.

With the right experimental set up (I'm looking at you G^0 and Qweak) it is possible to explicitly extract the weak interaction rate of electrons with matter, too. And it is similarly small.

But at reasonable energies electrons do most of the their interacting by way of the electromagnetic interaction which neutrinos don't have.

danielunderwood

Ahh does time dilation affect interactions at all? I was thinking of muons making it to the Earth's surface, but I didn't really know how that affects the interaction between two particles

dmckee

Keep in mind that time dilation ins't changing anything about anything. It is nothing more or less than a disagreement on the 'obvious' way to measure the time difference between two events.

All observer must agree on physics, but they can (and do) get very different values for quantities appearing in their calculation.

And that is not special to Einstein's theories: it appears throughout classical mechanics as well.

Consider a simple, 1D elastic collision between identical masses.

The amount of energy in the system depends on your frame. There is more in the lab frame (where one mass starts at rest) than in the center of mass frame (the masses move toward each other symmetrically).

But both observers will conclude that the energy after the event is the same as it was before the event.

They just disagree on how much there is.

Semiclassical

5:25 PM

Energy is conserved, but not invariant.

Secret

Actually, I wonder if W and Z bosons are too short ranged thus they travel so little distance for any time dilation effect to be apparent, thus a weak decay seen at rest in lab frame may be more or less as frequent as a weak decay seen in the moving frame

meanwhile, as shown in both the dirac and klein gordon equation, relativistic motion seemed to have no effect on the shape of the resulting wavefunction

danielunderwood

hmmm I guess I should sit down and work some examples

But say when you have time-dependent physics like an exponential decay rate. The decay rate would need to be adjusted between frames. Does that mean there's some Lorentz invariant rule that we could actually use?

dmckee

5:48 PM

@danielunderwood Physics in invariant, which means that you have to be able to calculate it in terms of invariant quantities. Radioactive decay doesn't depend on "time" (which is observer dependent) it depends on "proper time" (which is invariant).

I have a very big problem with most popular treatments of relativity and those in secondary school books because they try to emphasize the weird instead of hammering away at what you can actually count on.

The result is that they convince you that things are complicated, mysterious, and difficult when they are generally quite simple if you adopt the proper frame of mind.

Learning to adopt that frame is the way to make propgress in relativity.

danielunderwood

Ahh right using proper time would make more sense

Secret

hmm... so that will mean a muon travelling at 0.2c and a muon travelling at 0.8c will decay at the same rate as seen from the lab frame?

danielunderwood

And yeah all my courses that handled relativity looked at the paradoxes and didn't really look at working out any typical physics problems

dmckee

@Secret The lab observer has no trouble computing the proper time associated with decays, and if they do that then yes. Of course that will be a different rate computed based on the wall clock, but the wall clock is measuring the wrong this for either of those particles.

danielunderwood

Is there a book that's essentially like a typical mechanics book, but handles things from a relativistic view?

user1732

5:53 PM

French's Special Relativity is a classic.

Secret

I will originally though that since we can talk about number of counts per minute, radioactive decay will depend on coordinate time like any other time dependent quantity, but it isn't, I might need to revise about relativistic mechanics to work out why

dmckee

I don't know of one. I used Tackeuchi's An Illustrated Guide to Relativity to introduce the a geometric basis and then added my own notes to hammer away at the use of invariants.

user1732

it builds on his Newtonian Mechanics textbook

Secret

what my guess is that the decay rate is tied to the tunneling rate of a process, thus it is utimately determined by the width of the energy barrier, which is independent of time

(assuming all particle decays can be approximate to first order like the alpha particle decay model)

user1732

as dmckee said, few high school textbooks emphasize invariants

danielunderwood

6:01 PM

Awesome both of them have fairly cheap versions on amazon

user1732

in the spirit of "invariance" I would stick with just one book to start :-)

17 mins ago, by dmckee

Learning to adopt that frame is the way to make propgress in relativity.

*progress :P

19 mins ago, by dmckee

The result is that they convince you that things are complicated, mysterious, and difficult when they are generally quite simple if you adopt the proper frame of mind.

danielunderwood

I'd probably make a lot more progress if I stuck to one book

I marked L&L's field theory book a few weeks ago and it starts with relativity and mechanics, so I guess I'll start with that

user1732

6:22 PM

the sooner you dive-in the sooner you'll learn to swim :-)

Anonymous

@danielunderwood But a single book doesn't normally contain all the best possible approaches specially suited for you :P The eternal dilemma!

Anonymous

For me, it's been around 5 years since I read a single book cover-to-cover

user1732

have you been self-learning for the last 5 years?

Anonymous

@user1732 Not really. In high school we never had any specific books. We'd just follow class notes and refer to other reference books as and when required

Anonymous

Same in uni

bolbteppa

6:33 PM

@danielunderwood Landau ftw

danielunderwood

6:44 PM

@Blue yeah I realized that in QM when I just didn't get something in Griffiths for whatever reason. I feel like it sometimes doesn't make me learn the whole thing in its entirety if I jump between books

Though I went for Cohen Tannoudji over Griffiths, which seems a funny choice in retrospect

What does an outlined star mean?

Novalium Company

7:06 PM

youtube.com/watch?v=MkJommMrIJc At 5:52 I don't understand what exactly is going on. I mean, I know that we have to multiply by the velocity in the x direction, but how multiplying the total velocity by cosine gives us the x velocity?

danielunderwood

So you have your velocity vector, which essentially forms the hypotenuse of a right triangle where the legs are the x and y components. If you measure your angle as the angle between the vector and the x axis, the x component of the vector picks up a cosine

Basically just use your vector to draw a triangle and work out some trig

Novalium Company

Yeah, I get it but something is not very clear. The cosine of the angle is basically the x/hyp. How does that give us the x velocity?

Oh wait.

I mean, why dividing the x velocity by the total velocity (hyp) would give us the x velocity... hmmm

Ahh... something so simple and I can't get my head round to it..

danielunderwood

So if you have $\cos \theta = \frac{x}{h}$ where $h$ is the hypotenuse, then you just multiply to get $x = h \cos \theta$

Keep doing physics long enough and you'll start to see triangles in your sleep!

Novalium Company

Yep, exactly what I just thought of :D

user1732

haven't you covered trig in algebra yet?

Novalium Company

7:16 PM

I have, just my mind blocked for a second.

Sometimes my mind seeks too much reason and logic, which I suppose is not bad.

danielunderwood

Good ol mind blocks!

Novalium Company

20 days until school :((((

user1732

:(

danielunderwood

hmmm writing out that cosine expression actually helped me get around one of my own mind blocks I think

Novalium Company

Hmm, why do photons lose energy when they travel away from the sun (e.g to Earth or some other nearby planet)? There is nothing for them to collide into, no air...?

Nvm, I should have just googled it, doing it now, sorry for distracting.

danielunderwood

7:28 PM

Any of you guys happen to know the history behind metric conventions? It seems more intuitive to me to use a $+i, +, +, +$ rather than $-,+,+,+$ or $+,-,-,-$. I don't know that I've ever seen a complex metric in a math sense though

Novalium Company

Hmm, I just read that photons lose energy due to the expansion of the universe (although I don't know how the expansion of the universe would effect the photon's wavelength) but does this lose of energy really effect it that much. I mean, the planets close to the sun are hotter and I suppose brighter and the ones far from the sun the coldest. I suppose they are cold becuase the photons have lost the energy due to the expasion but is this expansion really effecting the photons that much?

danielunderwood

I guess I may just be happier to see hyperbolic trig functions than square roots

The expansion probably doesn't affect anything as close as our solar system. The plants father away are colder because they have fewer photons hitting them

Novalium Company

Why? The photons don't bump into anything?

danielunderwood

When you look at the number of photons, they're more or less distributed evenly among a spherical surface. As you go out, the surface gets larger so you have fewer photons per unit area

Say you have a balloon and mark dots on it. Then you blow it up. Same number of dots, but they're farther apart

Novalium Company

Ohh, yes, exactly! I forgot for a second that they spread in the form of a sphere.

I imagined a single ray of photons and that's why.. :D

danielunderwood

7:35 PM

And I've been told that's how we get inverse squared laws, though I'm not sure how valid that is

Novalium Company

Is that to me?

oh yeah

I googled.

danielunderwood

It was kind of a side comment. Either for you or for someone to point out that I was wrong

Novalium Company

When we shoot a light laser, what causes the light to slightly spread out? Is it the photons bumping into air molecules?

danielunderwood

Well you can't make anything perfect and that would include the direction of the emitted photons. I don't know if there's anything else happening though

Novalium Company

Maybe there is a slight diffraction as the beam goes off from the laser.

user54826

8:12 PM

what does it mean to watch a tag?

i watch 1 tag, i dont see any difference with not watching it

danielunderwood

@NovaliumCompany this may be some interest to you en.wikipedia.org/wiki/Collimated_light

Avantgarde

11:51 PM

Helloooo

Transcript for