The h Bar

Cows

00:56

Guys . . . People are doing epic things . . . youtube.com/watch?v=plcKVSld6ak&t=9s

user1732

01:14

yeah, the chinese did the first monkey clone also

danielunderwood

02:08

Is there a term for a set of graphs?

user2236

02:20

a number line

Secret

When the sky turns black gray and white
It's a sign that They arrive
Towering titans of plight
And the Last Great Stronghold set alight
-----Triangulum Collective

Secret

03:20

-2

Q: Is there any scientific multiverse theory that contains impossible worlds? (even if it is highly hypothetical)

I found an article written by physicist George Ellis that confused me a little. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.498.4569&rep=rep1&type=pdf At some part, he says: 3.2 Non-uniqueness: Possibilities There is non-uniqueness at both steps. Stating “all that is possible, ha...

Well, technically you can do "logic" with irrationality. It's just that whole language is emotions and intuitions, locked in some kind of chain fashion

> The concept of multiverses is not well defined until the space of possible universes has been fully characterized

First, we need to stop thinking in terms of abstract space and start embracing spacelessness, because frankly there isn't always a "container" that contains everything indefinitely

> • Weak variation: e.g. only the values of the constants of physics are allowed to vary? This is an interesting exercise but is certainly not an implementation of the idea ‘all that can happen, happens’. It is an extremely constrained set of variations.

Changing the constants can have profound impacts. But perhaps not breaking enough

> • Moderate variation: different symmetry groups, or numbers of dimensions, etc. We might for example consider the possibility landscapes of string theory as realistic indications of what may rule multiverses. But that is very far indeed from ‘all that is possible’, for that should certainly include spacetimes not ruled by string theory.

That changes the underlying symmetries, which is one level up from physical constants

> • Strong variation: different numbers and kinds of forces, universes without quantum theory or in which relativity is untrue (e.g. there is an aether), some in which string theory is a good theory for quantum gravity and others where it is not, some with quite different bases for the laws of physics (e.g. no variational principles).

That changes the postulates, and hence the laws. Things start to get very wild here but still you are dealing with spacetime

> • Extreme variation: universes where physics is not well described by mathematics; with different logic; universes ruled by local deities; allowing magic as in the Harry Potter series of books; with no laws of physics at all? Without even mathematics or logic? Which is claimed to be the properties of the multiverse, and why? We can express our dilemma here through the paradoxical question: Are the laws of logic necessary in all possible universes?

The minimal definition of logic is a set of inference rules. We all knew that irrational behaviour does not subscribe to these rules. As for the magic angle, an extreme version is explored recently in factory floor:

in The Factory Floor, yesterday, by Hosch250

Exactly. I think you just reinvented the concept of a timeless, spaceless god.

But these 4 levels are not extreme enough

> Level 5: Universes which cannot be described, comprehended, reasoned, intuited or otherwise. The concept of nowhere is one such example

And thus we have the following hierarchy:

Constants < Symmetry < Postulates < Logic < Unknown

Want inconsistent universes? Break logic. Want something even weirder in the seething chaos? Meet Cthulhu

Semiclassical

04:36

@Secret reminds me of an old line (originating from a 15th century German philosopher): God is an infinite circle whose center is everywhere and whose circumference is nowhere.

(I guess Azathoth would sorta be the inversion of that)

Secret

Agreed, and one of the artists I spoke to on the subject of spacelessness is that revelations and prayers are some of the best analogy on spacelessness: God can talk to you, even though He is technically nowhere

So in a way, He can chat locally with people, but in a way, the notion of where makes no sense to Him, even if the answer to "where" is everywhere or nowhere

Thus one of the characteristic of spacelessness is kinda like this: Stuff happens, it does not need to travel through anything, has no physical or tangible form, cannot be pinpoint, cannot be measured and because of all of that, it bypasses any barrier that is being erected

In short Spacelessness: It will get there no matter what

Nowhere, meanwhile is an even stranger concept, and I experience emotions much more powerful than dissociation after being in a gallery that talked about nowhere a few weeks ago

3

Q: Is there any neuroscience research on the emotion of feeling nothing?

When people entering anechoic chambers, logically there is a sensation of silence because relatively speaking, the sound levels are much lower compared to some normal baseline Likewise, when there is emotional numbness there isn't a feeling of emotions nor there is an awareness that there isn't ...

cognitive-neuroscience emotion sensation

user1732

Wow! deep question...

Secret

The best way to describe that emotion is: Imagine you felt your consciousness is on the verge of being switched off, and the reason you are aware of that is the same reason why cold is the absence of heat: The sensations, feelings and even thoughts are at such a low intensity that the absence of it informs its presence

It is a lot more dissociating than being in an anechoic chamber, a very strange emotion

Feeling empty is nothing compared to this emotion as there isn't a sense of dread , doom or worry

and it is also not being idle either because being idle you still aware of the surroundings

and reading some buddhist stuff, it kinda reminds me of the descriptions on Nirvana

and if that is true, then I probably have been to Nirvana twice in my sleep, lol

user1732

04:54

they say sleep is when the brain grows the most

Secret

If you like, this highly dissociating emotion is the feeling of as if your emotion is being forcibly robbed, but not quite yet. I think that is the closest to what thinking about absolutely nothing is like

It really does put the concept of death in perspective: What if when you die, you don't aware you have died...?

Captain Bohemian

05:53

as long as I am hungry, I can't read and think well.

2

unfortunately hunger haunts me too often for me to hunt for food to keep hunger-free most of times.

user157860

07:06

@JohnRennie, Hi John, do you have a min to comment/discuss my question: physics.stackexchange.com/questions/421668/…

John Rennie

@user157860 the frequency shift is due to gravitational time dilation.

user157860

@JohnRennie, yes, I have a problem with the formula, where is my formula wrong?

John Rennie

@user157860 I don't understand where you got your equation from. The Hyperphysics equation gives the gravitational time dilation at a distance $r$. The time dilation means the oscillating atom is slower than it would be far from the black hole by the factor of $\sqrt{1 - r_s/r}$

You give the equation without the square root. Where did the square root go?

@user157860 ah, I see what you're asking

user157860

@JohnRennie, if GM/rc^2 is the value of the ratio between the decrease of frequency and the original photon, then the frequency of the photon at infinity f_infinity is given by the original frequency f minus the ratio times the frequency f: f-f * ratio = f(1-GM/rc^2)

John Rennie

It's because the paper has used a binomial expansion to approximate the square root.

$$(1 - x)^{1/2} \approx 1 - x/2$$

user157860

07:18

@JohnRennie, is it not an official formula?

the final result does not change

John Rennie

@user157860 I see Rob Jeffries has posted an answer saying basically the same as I've said above.

user157860

@JohnRennie, also, in the same article they say that the observed value is 76% of the predicted value, but not for strong lines? is that so or is some technical problem?

John Rennie

@user157860 I don't have access to the article so I can only see the first page.

That looks more like a scatter plot than a graph :-)

user157860

The ratio (lambda_observed/lambda predicted) was found to be 0.76 + 0.24 (PE) for all the lines. Strong lines, numbering 74 in all,
gave for the same **ration** 0.97 • 0.16 (PE). These strong lines were chosen on the basis
of having a reduced equivalent width greater than or equal to 100 m.~. In addition,
some attempt was made to eliminate obviously blended lines from a visual inspection
of the Kitt Peak Photoelectric Atlas.
Figure 1, taken in part from Pierce and Breckinridge (1972) shows clearly how the

John Rennie

So what are you asking?

user157860

07:30

@JohnRennie, is the disagreement due only a technical glitch

John Rennie

@user157860 I don't know. Maybe it's discussed in the rest of the paper that I can't see.

user157860

is ration a typo?

that's the end of the article

John Rennie

@user157860 Yes, I think so. The word should be ratio.

@user157860 no, that's just the first two pages of the paper.

user157860

Thanks for editing my question, is that formula in GR or is it derived? 2) if instead of a photon we shoot an electron, is the formula still valid?

(I see, there is a paywall!)

John Rennie

Yes, the formula comes from GR. The spacetime geometry around a spherically symmetric object is given by the Schwarzschild metric, and we can use this to calculate the gravitational time dilation. The result is the equation you got from Hyperphysics.

user157860

07:37

@JohnRennie, what about an electron?

John Rennie

@user157860 what properties of the electron are you thinking about?

user157860

@JohnRennie, imagine we shoot an electron from outside a neutron star or other, with same KE energy of a photon's. does the same formula apply to them both?

John Rennie

An electron is a massive particle, so it speeds up as it falls towards a massive object just like if you drop something on Earth it speeds up as it falls downwards.

Light is different because it always travels at the speed of light.

user157860

@JohnRennie, I meant the opposite, we shoot a photon and an electron off a neutron star/other with Ke equal to the photon's frequency. Will the decrease at infinity or anywhere else be the same? can we apply the above formula to the electron or a massive body?

John Rennie

No

Calculating the velocity of the electron is more complicated. I have done it in an answer on the main site.

Here:

14

Q: Will an object always fall at an infinite speed in a black hole?

Most of you if not everybody will agree that the stronger the gravitational pull, the faster an object will fall. For example, on a planet with 50 times the gravity of Earth, any object will hit the ground on that planet much quicker than it would on Earth. So taking all of these into the equatio...

general-relativity gravity black-holes speed-of-light faster-than-light

user157860

08:07

@JohnRennie, I see is the reverse of the issue we discussed lat time. Thanks

John Rennie

@user157860 ah, was it you discussing how objects fall in a Schwarzschild metric? As I recall you decided you didn't believe me :-)

user157860

08:20

@JohnRennie, oh no, I did and also developped my personal simplified version of the formula: $$V_B=\sqrt{1 - \frac{cos_A^2\times(1-r_s/B)}{1-r_s/A}} $$

what I really couldn't/can't believe is that no matter what is the mass of a black hole a massive body always reaches the same speed = c. That is simply impossible

John Rennie

GR is full of stuff that's hard to believe. However experiments show GR is correct.

user157860

@JohnRennie, can anyone make experiments on a black hole? consider a black hole of the mass of the sun (3 Km wide), how can it give enough energy to reach c? Einstein himself states that reaching c is impossible

John Rennie

@user157860 See here

@ACuriousMind morning :-) Off work with the ankle?

ACuriousMind

@JohnRennie Morning! Yeah, I'm on sick leave today and probably working from home the rest of the week.

John Rennie

I don't know whether to congratulate you or commiserate with you. On the one hand you have the day off, but on the other hand I used to love going into work so a day off wasn't actually that great.

I get the impression you enjoy your job as much as I did mine.

user157860

08:32

@JohnRennie, how does that refer to the fact that a black hole with the mass of the sun can givesame or less acceleration than one with 10^6 solar masses?

ACuriousMind

@JohnRennie It sucks having the day off and nowhere to go. Which is why I'm only on sick leave for today and not longer - the doctors said as long as my job doesn't involve actually using the foot I can work just fine

John Rennie

@user157860 The event horizon is much closer to the singularity for a solar mass black hole than for a supermassive black hole, so the falling object gets much closer to the singularity before it reaches the horizon. The two effects cancel out. On the one hand the solar mass black hole has a lower acceleration for any given distance $r$, but on the other hand you get much closer to it and the acceleration increases (approximately) as 1/r^2.

@ACuriousMind if your're bored I have a question about QFT that is probably too ill thought out to make sense ...

ACuriousMind

@JohnRennie Shoot. I'm indeed beginning to be bored and the day has just begun :/

John Rennie

Suppose I collide two electrons and I want to calculate the probability for some interaction.

I have the vague idea that at infinity the electron states are basically free particle states. So we start with two free particles.

Then we calculate what happens as the particles approach and the reaction products head off to infinity as free particles again.

Does that make sense so far?

ACuriousMind

@JohnRennie Mhhh, we don't really "calculate what happens". You have to specify the final state of free particles after the collision you're interested in, and then we can compute the probability of that outcome.

John Rennie

08:42

OK, that's fine, that wasn't the crux of my question.

ACuriousMind

Carry on, then

John Rennie

What I'm interested in is what the calculation looks like in general terms - if that's possible to say, maybe it isn't.

Is this where the Feynmann diagrams come in i.e. you're using them to calculate the probability?

ACuriousMind

@JohnRennie Yes. We usually calculate the probability via perturbation theory, and each diagram is a specific term in the perturbation series

John Rennie

Thanks. So if we took for example an electron and positron pair annihilating to two photons we'd start with the incoming particles given some initial momentum and end with two gamma photons.

Then to calculate the probability would require evaluating the integrals represented by the Feynmann diagrams?

(the Feynmann diagrams with ep on one side and 2 gamma on the other)

ACuriousMind

@JohnRennie Yes, exactly

John Rennie

08:55

Aha, thanks. OK the vague idea I had about what the calculation does wasn't too far off :-)

ACuriousMind

If fermions are involved there's also some annoying bookkeeping about the relative sign between the terms related to the number of crossings of fermion lines

John Rennie

One day I will dive into that copy of QFT for the gifted amateur that I bought five years ago!

Are the particles at infinity treated as Fock states?

ACuriousMind

@JohnRennie Yes, they're free Fock states

John Rennie

So if one were brave enough to put a physical interpretation on this we would be calculating the probability that energy in Fock states of the ep field ends up as Fock states of the photon field.

The calculation is then describing how the two fields couple to each other.

ACuriousMind

Yup

John Rennie

09:05

Cool thanks. That's it for today's questions :-)

Anonymous

09:21

@JohnRennie Is it a good book? I see many people reading it in the library

John Rennie

@Blue it has very good reviews. I'm not sure it's ideal if you're actually trying to learn QFT. For someone like myself who is mostly interested in understand what QFT does in general terms it's probably pretty good.

I can't comment further since I've never read it :-)

From the skim through that I've done it isn't pop science. There is plenty of scary maths in it.

Anonymous

I see. It seems pretty expensive :P I'll download a pdf first :D

Anonymous

The reviews do look good!

Kenshin

sup ppls

is there a prize for proving the twin prime conjecture

Slereah

ten dollars

Kenshin

09:35

c'mon it should be a million dollar puzzle

i just solved it

danielunderwood

11:14

@Blue I haven't gotten terribly far, but it seems easier to get into than Zee or Peskin/Schroeder

I don't think it goes into as much detail though

user1732

11:41

@ACuriousMind how long do you have to keep the cast on your ankle?

ACuriousMind

@user1732 It's not a real cast, but it's gonna take about 6 weeks all the same

user1732

@ACuriousMind what makes it different than a normal cast?

ACuriousMind

It's a "shoe" that I can take off e.g. to shower.

user1732

niiice :-)

especially during the summer heat

ACuriousMind

Well, it still has to stay on when it's not absolutely necessary to take off, but yes, much better than being stuck with a cast for 6 weeks

user1732

11:50

you should be up and running for Octoberfest?

ACuriousMind

Not that I ever would want to go there, but yes :P

user1732

you shouldn't do any running anyway for many months

ACuriousMind

I haven't been running for many months, either :P

user1732

did they give you any pain medication?

Advil is pretty good

ACuriousMind

12:38

@user1732 I declined painkillers, it's not that bad

user1732

12:55

using crutches is a pain in the #ss

no way to use a mobile device

while walking

ACuriousMind

@user1732 lol, that's your problem with it? How about not being able to carry a plate or cup?

user1732

right right

danielunderwood

Attach a cupholder to the crutches!

ACuriousMind

@danielunderwood I can't tell whether that is a very good or very bad idea, but I like it!

danielunderwood

I suppose it would depend on how good you are at keeping the crutches upright. No idea for plates, so I guess you have to eat smoothies hah

user1732

13:03

cdn.instructables.com/FXX/Z2MT/IM0VNG1F/…

\o @dmckee

Physics Meta

0

Q: Misuse of [measurement-problem] tag

It seems to me that the measurement-problem tag is misused almost as much as the mathematical-physics tag. Would it make sense to (1) put a more clear warning on the tag description and maybe (2) introduce a new tag for questions involving quantum mechanical measurements, e.g. [quantum-measureme...

discussion tags

vzn

14:58

found this on youtube related videos after hitting cows link... wonder where this is described? its an entropy analysis of bell entanglement states that leads to intriguing new insights... The Quantum Conspiracy: What Popularizers of QM Don't Want You to Know Ron Garret

The Quantum Conspiracy: What Popularizers of QM Don't Want You to Know

►

Emilio Pisanty

15:16

@JohnRennie I rather don't think that this is a duplicate, but thanks for the extra rep =)

also, it's weird seeing your name on a dupe close that's not a dupehammer, particularly in tags that do have gold-badgers, but I guess even the runaway winners of this site's gamification have their limits =P

@vzn it's intriguing only if you don't know QM very well

previously discussed on this site at

7

Q: Does the following experiment disprove the Copenhagen interpretation?

I have a question concerning the scientific experiment proposed in the following video, (25:00-29:00) titled the "EPR Thought Experiment", which bears resemblance to the quantum eraser experiment. The Quantum Conspiracy: What Popularizers of QM Don't Want You to Know. Ron Garret, Google Tech...

quantum-mechanics quantum-interpretations bells-inequality epr-experiment

Note in particular that the talk's presenter shows up and attempts to walk back most of the claims made in the talk

> the EPRG paradox is intended to be a straw man

in a way that's definitely not made explicit in the talk

... and also in a way that shows up the talk's title for what it is: pure hype.

John Rennie

15:33

@EmilioPisanty I am hung over today so my patience with OPs who can't be bothered to research their question before posting is severely limited :-)

4

Yellow

Hello. I am currently a high school student preparing for the iPhO. I am really interested in physics and mathematics. I know single variable calculus, classical mechanics and electromagnetism but in an undergraduate level. What kind of a syllabus should I follow for learning advanced mathematics and physics from the ground up?

user2236

How old are you?

Yellow

16

does it matter tho?

vzn

@EmilioPisanty thx for the ref/ answer (+1) but it doesnt seem to explain his entropy calculations in the video in the venn-like diagrams at the end. am aware of basic Bell theory.

Yellow

Anyways anykind of help is appreciated :)

user2236

15:38

A little bit :-)

Yellow

Do you have any advice?

user2236

Have you looked on the main site for reference requests?

Yellow

no actually

user2236

please try

Yellow

Can you link me to the exact posts you are referring to?

user2236

15:40

Follow your interests :-)

ACuriousMind

@user2236 You're not being particularly helpful, especially since a question of this type would be off-topic on the main site.

Anonymous

@Yellow Did you see the past papers: ipho.org/problems-and-solutions_5.html?

Anonymous

If you know the material in the syllabus better start solving problems for practice

Anonymous

Also check your regional and national level papers

ACuriousMind

@Yellow You see, I don't think there is such a thing as a single syllabus one could recommend for learning "from the ground up", nor even agreement on what "from the ground up" really means. For instance, some people like to learn everything superficially and then do a deep dive, others can't move on from a topic before having explored it in depth.

Yellow

15:44

So how should I rephrase my question for a better mutual understanding? @ACuriousMind

John Rennie

@Yellow if you're training for the iPhO the no. one best strategy is to train on questions from past Olympiads.

Yellow

@Blue 1 I solved some of the last papers. 2 I checked the syllabus and I am solving problems. 3 I solved the regional national level papers.

Avnish Kabaj

Jaan Kalda's study guides are pretty good

Anonymous

@Yellow Okay, so you do seem to be on the right track. So what are you asking about?

Yellow

@JohnRennie I said I was preparing for iPhO to indicate my current level of knowledge of physics.

user2236

15:47

What are you interested in?

John Rennie

@Yellow So what is your aim? To get your knowledge up to iPhO level?

Yellow

Ok I will clarify everything for everyone, once and for all.

user2236

::drum roll::

:-)

Anonymous

Take your time. Communicating precisely is as important as gaining knowledge.

Yellow

Agreed.

user2236

15:50

::very long drum roll::

heather

sometimes i want my computer to be able to talk so i can yell at it...or rather, i'd like the programs on my computer to be able to talk, specifically the verilog ISE i have...

Avnish Kabaj

🥁

user2236

^

Avnish Kabaj

@Blue

Jee level is wayyyy below ipho right?

I'll be giving the indian physics Olympiad

Yellow

My plan for the future partially consists of double majoring in physics and mathematics and as a graduate student working on mathematical physics (Quantum Field Theory, Gravitation) and computational neuroscience. What I want is to better spend my time in highschool so I can get a headstart in my future studies as an undergraduate student in the fields mentioned above.

Thus I would really appreciate it if you guys could give an even vague pathway in approaching these fields, since probably some of you are working on these subjects.

Avnish Kabaj

15:55

I just feel so disappointed with myself when I see such motivated kids

Yellow

@Blue @JohnRennie @user2236 Hope this one is clear enough :D

Anonymous

@AvnishKabaj It's certainly not much more difficult compared to JEE but rather "different". IPhO problems tend to be longer and more subjective. So maybe you'd need to spend an hour on those trying different approaches, whereas for JEE problems you get just ~5 mins for each problem. But then you have a lesser number of problems to solve in the IPhO!

Yellow

@Blue And iPhO is much more fun!

Avnish Kabaj

@Blue hmmmmm

Anonymous

@AvnishKabaj I never appeared for NSEP though. So probably I'm not the best person to advise regarding this.

Avnish Kabaj

15:57

I'm supposed to be good with those 1 hour problems

Anonymous

I just solved some papers but due to school work never got enough time to actually prepare for the Olympiads

Avnish Kabaj

Exactly

Sometimes I feel like reading up some cool physics stuff

Anonymous

But some of my friends who had been preparing since 9th grade did appear for those exams

Avnish Kabaj

But I never get the time

Anonymous

Don't beat yourself up about it :P

Avnish Kabaj

15:59

@Blue since 9th grade

O.o

switches stream to humanities

enumaris

o.O

heather

i like physics and math, but i've looked at some olympiad problems and...man, i don't know how people do it.

Anonymous

@AvnishKabaj There are JEE prep courses starting from 5th grade these days XD

Anonymous

7 years prep plan

heather

@Blue that is horrifying.

Anonymous

16:00

Don't know how much it helps though, lol

enumaris

like any other test, the problems mostly test your ability to do those particular test problems mmmhm

like the SAT tests mostly for how much you've studied the SAT

etc...

Anonymous

@enumaris That is true

Avnish Kabaj

@enumaris SAT's a joke

No offense but man

Whut

enumaris

why would that offend me lol

I don't work at the testing company :P

heather

@AvnishKabaj don't ever look at Iowa's standardized tests then...

those are just...hmph.

Avnish Kabaj

16:03

@heather will not thanks for the heads up

Anonymous

SAT tests are just low pass filters. They aren't the main criteria for admission anyway. So it's fine. :P

Avnish Kabaj

Yaa

True that

Yellow

@Blue Please tag me when you write your answer for the question regarding learning mathematics and physics.

Anonymous

Just checks whether you have sufficient knowledge of English to survive in the USA

enumaris

hmm...this cookie...isn't great...

Abcd

16:05

Is anyone able to see the image I have uploaded^?

Yellow

Yes

heather

@Abcd i am...there's imgur issues for a lot of people

lemme see if i can find the meta post

27

Q: Failed to upload an image, "An error occurred at imgur"

Currently I'm unable to upload an image to everywhere on site: e.g. posts or chat. Is this problem with imgur?

support bug imgur uploader

contrary to the answer, it's not fixed. it's just that for some people it's fine, others it's not.

Anonymous

@Yellow I'm a bit confused about your aim...you say you want to study GR, QFT and computational neuroscience later on....so why bother about IPhO (unless of course you love solving those type of problems)? Start reading GR and QM yourself, get the sufficient math background, and if possible get involved in some research work in computational neuroscience (hot field these days!). There probably are lots of professors who will be willing to help you if you show some interest.

Anonymous

And if possible get a math, physics, CS or engineering degree if you interested in those fields. Of course the last 2 won't be very helpful for GR and QFT...

Abcd

@heather Hmm...its not even working fine on mobile.

heather

16:10

@Yellow well in my completely inexperienced opinion - maybe look at multivariable calc/vector calc (for the latter, try Div, Grad, and Curl), linear algebra (see 3blue1brown's videos, and Strang), then QM with Shankar (Griffiths is cheaper/easier to find I've found, but Shankar is better I've heard). you could look at Feynman's summary of QFT (QFT: the strange theory of light and matter) before diving into that. For GR, Zee is a good text that you could for sure handle.

In particular with GR, 0celo7 on the main site has a fabulous list of books for learning GR after you've finished Zee.

4

if you want to major in math, then i could give you book advice there too...naive set theory with halmos is very smooth reading, and wildly useful, topology is generally studied with munkres but i really like some YouTube videos for intuition, i can find the channel real quick...

advanced QM is generally sakurai, but there we're getting far beyond my experience level.

enumaris

Is Zee a good intro GR text?

I've not read it

Usually I recommend Schutz or Hartle for intro GR

Anonymous

@Yellow Also I feel the "headstart" thing is sort of a myth, unless you mange to learn a lot by yourself.

heather

ah, Ben1994 for topology videos (also has a bunch of medical videos, but his math videos are excellent).

@enumaris 0celo recommended it to me once, and i finally got ahold of a copy. i don't understand all of it, but i'm far below Yellow's level, it sounds like, and i very much like the writing style and the fact i understand any of it at all speaks to its competence.

enumaris

hmmm

well just don't use Wald or MTW as an intro text and you'll prolly be good lol

Carroll is borderline too

heather

@enumaris lol, MTW as an intro text

enumaris

16:16

(One could recommend Hawking's Monograph as an intro text...but then one would be evil so...)

heather

anyway. i read more book recommendation posts than the actual books, so take everything that comes out of my mouth with grains of salt =P

Yellow

@Blue I believe I learn a lot by reading bymyself and iPhO is just for fun. Right now I am reading some linear algebra. After that I plan on finishing the multivariable calculus lectures on MIT ocw.

enumaris

generally one learns multivariate calc before linear alg

but I suppose there isn't a concrete reason why that must be the case

heather

sometimes it can be very useful to sort of look at a topic and revisit over time, more and more deeply each time.

@Yellow if you are learning linear algebra, watch 3blue1brown's videos...they are outstanding.

Avnish Kabaj

Isn't linear algebra

enumaris

16:20

just worship the Eigen-gods and your linear alg will be fine

Avnish Kabaj

X + Y = 3

Yellow

@enumaris You are sort of right since algebraic definition of planes rely on dot products and the algebraic definition of cross products are based on determinants.

enumaris

uhhhh, no not really

@AvnishKabaj linear algebra is actually the study of matrices basically

Anonymous

@Yellow Fair enough. My point about "headstart" is that lot of kids (including the past me) feel that they have learned a subject just by watching some lectures online and reading some textbooks. The main way in which formal courses differ from these "informal courses" is that they include a lot of active exercises and discussions. So unless you're somehow supplementing that by yourself, you're not really learning much.

enumaris

more than "algebra concerned with linear functions"

Avnish Kabaj

16:21

The name is deceptive

Yellow

@Blue I totally understand you. When I am reading on material I usuall discuss what I've studied with myself and solve an extensive amount problem sets.

enumaris

It's deceptive to beginners yeah, but an "algebra" is much more involved than the "algebra" you learn in high school

so I guess it's internally consistent

@Yellow I think cross product and determinants is more of a two similarly structured operations happen to have cross functional uses rather than one is based off the other.

Yellow

There is an equivelance of algebraic and geometric definitions.

I did not say cross-products are based on determinants. I said that the algebraic definition of cross-products are based on determinants.

enumaris

well a cross product is not a real determinant...it's just you can calculate it by constructing a "determinant-like" set of operations.

Yellow

I know

heather

16:25

i've found as well the best way to learn a subject is to learn it "out of necessity" - for a project or something.

Yellow

From adopting one definition, either geometric or algebraic(determinant definition), you can construct the other.

heather

ex: this summer i learned a lot about numerical integration because i was using it for a project. i can now wax on about higher order newton-cotes methods.

which, it's debatable how good of a thing that is, but ;)

Abcd

0

Q: Unable to see any image

I have tried all browsers and even the mobile app but I am unable to see any picture that's there, in questions/ answers/ chat. As evidence, here are two pictures^ . I have uploaded them but am unable to see them, it reads "enter image description here". Please fix this.

feature-request support chat

Anonymous

@Abcd Did you try to log out and log in again?

Anonymous

Maybe it's a problem on your end

Abcd

16:30

I have tried alllll of that.

Two -three times

Avnish Kabaj

in The Periodic Table, Aug 5 at 12:47, by Avnish Kabaj

Have you tried turning your computer on and off?

Abcd

Done that

Anonymous

@Abcd Better add your device and browser specifications in the MSE question

Abcd

1

Q: Acetaldehyde with few drops of concentrated sulphuric acid

Acetaldehyde on treatment with a few drops of concentrated $\ce{H2SO4}$ gives? Attempt: First, I formed an enol intermediate in acidic medium $\ce{CH2=CHOH}$. Then, I performed electrophilic addition of another acetaldehyde molecule on this enol intermediate to get $\ce{CH3CH(OH)CH2CHO}$....

organic-chemistry reaction-mechanism

@Blue Please see @Zhe's comment

The comment also has a upvote.

Means I am not the only one stuck with this.

Anonymous

Possible. Maybe the imgur server is down

Anonymous

16:35

Or having some issues

Anonymous

Can you access this: imgur.com

Anonymous

And upload images there?

Anonymous

1

A: Failed to upload an image, "An error occurred at imgur"

It's working now. Android Firefox. North America. If it's not working for you please comment on the question, including your OS and browser.

Abcd

ya see

imgur.com/a/3oy29SS

Anonymous

OK, then the best course of action would be to mention your current location and device configurations on the question. SE will probably contact imgur

Abcd

16:38

Will India work as location

Anonymous

Should be sufficient for a start

Abcd

That answerer has mentioned north america

heather

@Blue it still doesn't work for a lot of people.

@Abcd isn't the only one having this problem.

Captain Bohemian

17:14

I find reading continuously for too long on the computer screen makes me feel moped.

enumaris

17:29

then don't do it

ez pz lemon squeezy

Captain Bohemian

but I find most useful or interesting information is on web.

enumaris

lots of bs on the web too lol

enumaris

17:47

weezltcotl

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