The h Bar

skullpatrol

9:00 AM

:-D

Anonymous

@NovaliumCompany Eh, I'd advise learning Linear Algebra, first then

Novalium Company

Where can I learn Quantum Mechanics for free, on a pretty solid level?

Yep, I'll be developing my math as well.

I don't think Khan Academy can teach me Quantum Mechanics on a good level?

Anonymous

If you want to learn properly, read Shankar and watch Balakrishnan's lectures. I must warn that it's a math-heavy subject and you're not going to gain much if you don't learn it rigorously. Secondly, it is going to take you quite some time (~6 months - ~1 year)

John Rennie

@NovaliumCompany I would avoid the history of QM. Most theories become better understood as time goes by so modern textbooks benefit from 100 years of figuring out exactly how QM works.

Also, there are two different ways to learn QM.

Anonymous

Also I'd avoid books like Griffiths, Dirac, etc. Shankar is the only legit introductory book, which does not go loose on the rigor.

John Rennie

9:04 AM

The traditoonal way used in books like Griffiths is to start with the Shrodinger equation and look at it's solutions and their properties. This is the way I learned QM and the advantage of this approach is that it's easy to get started - the maths needed isn't that awful, just badic calculus.

But ...

The heavy duty QM heads will say, quite correctly, that this doesn't really help you understand QM in depth

Novalium Company

I first want to understand it on a basic level, after that, in depth :D

John Rennie

The approach Blue is alluding to, using linear algebra, will give you a really good understanding of the theory but it's maths heavy and difficult to get started.

Dawood ibn Kareem

@NovaliumCompany I don't think it works that way

John Rennie

You pays your money and takes your choice I guess.

Novalium Company

So finally, I should start first with: youtube.com/… and develop my maths?

Anonymous

9:06 AM

I mean since you're just 15 you could start with the basic physicsy version of QM which is taught to 1st year undergrads. But I never liked that approach. Even after that basic course lot of things remained unclear to me until I actually got hold of the math. For that type of course I think MIT OCW's QM I and QM II will be useful.

John Rennie

I think you'll find the Shankar book heavy going unless your maths is a lot more advanced than most 15 year olds.

Dawood ibn Kareem

It's extremely hard to get a picture of what's going on. All the entities you meet learning QM look like nothing you've ever seen before. But you can learn the mathematics and solve the problems.

ACuriousMind

Learn classical mechanics first. I'm still firmly convinced that a thorough understanding of classical Hamiltonian mechanics is immensely helpful to get a grasp on QM, and in particular understand where it is and it is not different from classical mechanics

Anonymous

@ACuriousMind Yes, that too! I agree. But I'm not sure if that will bore away a 15 year old from the subject. Learning CM properly is hard, really hard, and time-consuming too

ACuriousMind

I'm not sure I'm advocating a 15 year old to try learn QM at all - I'm much more a fan of learning other things - classical mechanics, linear algebra, etc. - first and then coming back after a while, able to truly appreciate QM.

Anonymous

9:11 AM

@ACuriousMind I totally agree with that

Novalium Company

I see a big potential in QM for the future. I would like to develop different technologies based on the principles, that's why I am aiming to learn it.

And the earlier I start, the better.

ACuriousMind

I think QM without the actual mathy and crunchy formalism is much more likely to cause misunderstanding than enlightment ;P

9

Novalium Company

I would like to first start with the actual concepts in QM, without really getting in depth with the math. Is that possible?

ACuriousMind

@NovaliumCompany Well, I applaud a desire to learn! But In this case, my opinion is the place to "start" is really classical physics and linear algebra.

Dawood ibn Kareem

@NovaliumCompany I answered that question with my last comment.

ACuriousMind

9:14 AM

@NovaliumCompany That's what I'm trying to get at - in my opinion, very few of the concepts of QM make much sense if you don't know how they actually work in the formalism.

Novalium Company

So math is needed to understand QM?

Dawood ibn Kareem

Yes

skullpatrol

have you taken calculus?

Novalium Company

My math is for a 15 yr/o level.

Pieter

@NovaliumCompany Complex numbers, calculus.

Novalium Company

9:15 AM

I'm from Bulgaria and I am not familier with the concept names in English.

Slereah

Also a lot of QM issues are related to classical mechanics concepts

Which it is best to learn as well

Pieter

Differential equations

ACuriousMind

@NovaliumCompany given the range of 15 y/os I've seen in this chat room over the years, that doesn't really nail it down ;)

skullpatrol

do you like math?

Anonymous

@NovaliumCompany Keep in mind that learning things at an easy level and developing misconceptions, and then having to re-learn is more time consuming than learning a thing properly, from the beginning. It's very good that you're interested in QM, though. If you really really want to get started I'd say start with 1) Reading basic linear algebra and complex numbers 2) Get Shankar's book 3) Watch Balakrishnan's lectures 4) Read a basic book like "QM for Dummies" on the side, for when you lose enthusiasm

Dawood ibn Kareem

9:17 AM

I'd do calculus and complex numbers before linear algebra, quite frankly. But all three are important. And so, of course, are classical physics and special relativity.

Novalium Company

Ok then. I will start improving my math and I'll start reading QM for Dummies. Is that a good start?

Dawood ibn Kareem

I'd forget the "QM for dummies".

Anonymous

@NovaliumCompany Yup. Sounds good. Math is very important.

Anonymous

@DawoodibnKareem It's okay I think. It was my first QM book. Taught me all the notations and stuff

ACuriousMind

@DawoodibnKareem I'm always for linear algebra because I like algebra, but yes, the order is flexible ;)

Anonymous

9:18 AM

But it surely shouldn't be your "main read"

Novalium Company

Ok guys. Thanks for the support. I'll be going off now. See you later :)

skullpatrol

have fun!

:-)

Novalium Company

Also guys, last question. Is there any good Quamtum Mechanics books I can get from Amazon's Kindle Unlimited? (That way I'll not wait and pay for delivery and so on...)

Slereah

You know what QM you can do without too much math tho?

Finite dimensional QM

All the quantum computing stuff

ACuriousMind

@Slereah You still need complex numbers, linear algebra and all that

Anonymous

9:23 AM

@NovaliumCompany You'll get pdf versions of most books you need from Library Genesis, for free

Novalium Company

Oh ok. Thanks :)

ACuriousMind

@Blue You may want to point out questionable legality of that, though :P

skullpatrol

@NovaliumCompany amazon.ca/Quantum-Mechanics-Theoretical-Leonard-Susskind/dp/…

Slereah

@ACuriousMind true

Anonymous

@ACuriousMind Shhh :P

ACuriousMind

9:25 AM

I didn't mean the mathematically rigorous part of infinite-dimensional Hilbert spaces when I said actual formalism - just the regular physics treatment is mathy enough from the viewpoint of someone who doesn't yet know much math

Anonymous

@Slereah I actually think learning Quantum Computing before Quantum Mechanics is not a bad idea

Anonymous

Things are just easier in finite dimensions and beginners can pick it up easily

Novalium Company

Oh, should I read a Quantum Computing book first then? I tought you first need to know QM to understand QC?

skullpatrol

@NovaliumCompany I think Susskind would be be good for you

7 mins ago, by skullpatrol

@NovaliumCompany https://www.amazon.ca/Quantum-Mechanics-Theoretical-Leonard-Susskind/dp/04650629‌03

Anonymous

@NovaliumCompany I meant that QC books or lectures generally start with a brief introduction of finite dimensional QM which you can easily pick up. Whether that'll suit you or not, I don't know. Vazirani's lectures are up there on YouTube, you can check them out. However, you'd still need to learn QM properly, so the approach I told you before, is the proper one.

skullpatrol

9:32 AM

@NovaliumCompany check him out on youtube

Shankar's book is good

Novalium Company

Ok, I'll start with QM for dummies as for a beginning.

skullpatrol

@NovaliumCompany ask your physics teacher

Novalium Company

...

I'll start with QM for dummies.

Anonymous

@skullpatrol Leave it. Don't confuse the poor kid any further. :P

Master Yushi

Who likes kinematics and circular motion?

skullpatrol

9:41 AM

@Blue yes sir :P

Anonymous

@MasterYushi Engineers

ACuriousMind

As a resident of a planet currently in (sorf-of) circular motion, I'm kinda a fan

Master Yushi

You'd like to solve this ring and disc problem then

Slereah

@ACuriousMind sorry to disappoint but it's elliptic

Orbit isn't even closed thanks to GR!

ACuriousMind

@Slereah Maybe we're not talking about the same planet. ::ominous music plays::

Slereah

9:43 AM

Oh no

skullpatrol

::shots fired::

Slereah

@ACuriousMind is sitting very still at his desk because he knows circular orbits are unstable under perturbation

Master Yushi

I'm stuck on this problem

skullpatrol

Problem Solving Strategies

General chat for high school physics. For MathJax see [here](m...

here^ please

for JEE

Anonymous

Strange that we don't yet have any "Mechanical Engineering SE"

Anonymous

9:53 AM

The "Engineering SE" is sort of a mixed bag and still in beta

Anonymous

EE SE is doing quite well on the other hand

skullpatrol

Electrical engineering has always been the dominate department in that faculty.

Anonymous

@skullpatrol Which faculty?

skullpatrol

The faculty of engineering.

Anonymous

I am not so confident about that

Anonymous

9:59 AM

Maybe

Anonymous

Mechanical + Aerospace + Structural guys would make up a large bunch too

skullpatrol

6 mins ago, by Blue

EE SE is doing quite well on the other hand

Anonymous

At my uni I think they have nearly 3 times more students in Mechanical compared to Electrical or Electronics. So maybe that's why I'm biased

Anonymous

What the bigger picture is, I don't know

skullpatrol

which has the highest math requirements?

to get in

Anonymous

10:06 AM

@skullpatrol Among the engineering departments?

skullpatrol

yup

Anonymous

The admission is based on the combined test scores of three subject: Math(100 marks) + Physics(50) + Chemistry (50). The highest ranking department (in terms of marks required to get in) is CS closely followed by Electronics and Electrical. Then you have Mechanical, Civil, Production, Biotechnology etc.

Anonymous

So the answer to your question would be CS I guess.

skullpatrol

yeah, CS has recently become popular

Anonymous

Actually CS was a sub-part of our department, few years back. Very recently it got separated. Still in our building though.

skullpatrol

10:12 AM

they got popular mostly due to the internet

Anonymous

And the huge number of software jobs immediately after you graduate ;)

skullpatrol

;)

Anonymous

However, nowadays many go for higher studies as well

Anonymous

Which is a good sign

skullpatrol

still, half your ranking is based on math

Anonymous

10:20 AM

True.

skullpatrol

cya, pal

Good luck on your exams.

Anonymous

See you. Thanks

Slereah

What does the standard FRW model look like in Dilaton-Graviton theory, anyway

Master Yushi

10:45 AM

Art woman arrives

Secret

lol

Balarka Sen

@ACuriousMind I only do hyperbolic orbits

Very stable

CooperCape

ohai

Balarka Sen

your tearing me apart lisha

CooperCape

::hasn't watched the room::

Balarka Sen

10:49 AM

i know all the inside jokes

so i dont need to :3

CooperCape

guess it saves some time

I barely know that it's from what it's from

Balarka Sen

Good soundtrack for life : youtube.com/watch?v=R8SO93JlxRQ

CooperCape

"James Lynch played bass on the one that sounds like an elf orgy." Uh huh...

Balarka Sen

:P

Dawood ibn Kareem

Oh dear. The IDF shot and killed a journalist in Gaza. Wearing the standard blue jacket with "PRESS" in giant letters. Is nobody safe?

Captain Bohemian

11:04 AM

there is never a terror attack here.

Anonymous

@DawoodibnKareem Journalism in such areas is a dangerous job...:/

Anonymous

@CaptainBohemian You never know when...

Balarka Sen

Usually the consensus is that journalists will not be put under threat, I thought.

Oh, the Israeli forces shot him.

Wow.

This sucks

Dawood ibn Kareem

From the OTHER SIDE of the border fence.

Anonymous

@BalarkaSen That's a joke. In a two-side the other side doesn't care you are.

Anonymous

11:08 AM

Even doctors and nurses are shot down, often

Dawood ibn Kareem

Could you imagine if Trump ordered the USA National Guard to fire live rounds into Mexico?

This is the same thing!

Anonymous

It's also a bullshit notion that humans are fundamentally peaceful and good. They're not.

Anonymous

@DawoodibnKareem True.

Dawood ibn Kareem

@Blue Yes, but they're not defending themselves. They're committing murders, one after the other.

Anonymous

@DawoodibnKareem Yes, of course not

Anonymous

11:13 AM

It's more of muscle flexing at this point, on their side.

Tanuj

Best of luck to everyone giving JEE MAIN tomorrow , and thanks for all your wishes SE family :)

Dawood ibn Kareem

14/15 of the UN Security Council want to launch an investigation into recent events in Gaza. USA keep vetoing it.

Balarka Sen

I expect sometime soon we'll have a situation similar with Israeli government vs Hamas in Gaza with innocent Palestinian civilians dying in the middle of the fight

In the India-Pakistan borders or something

Dawood ibn Kareem

Yeah, we get that every few years; it seems to come in cycles. Remember July 2014?

Balarka Sen

Yeah...

@DawoodibnKareem Also, ugh.

Anonymous

11:20 AM

@DawoodibnKareem I've always suspected some US involvement in all Middle East cases. But I wouldn't elaborate on it.

Balarka Sen

USA needs to pull their noses back from the middle east

Dawood ibn Kareem

I remember Trump on the campaign trail promising to treat Palestine and Israel equally. One meeting with Bibi later, he had completely changed his tune.

Anonymous

@BalarkaSen Well, the "money"!

Dawood ibn Kareem

I also remember Trump saying that USA were right to invade Iraq in 2003, but wrong to leave without taking the oil.

Balarka Sen

@Blue Well, even modulo oil industry, the political campaign of the current USA government is counter-terrorist to the point of war-mongering and anti-Islamic.

Dawood ibn Kareem

11:23 AM

Not really anti-Islamic. The current administration cosies up to the leaders of Egypt, Saudi Arabia and UAE. The anti-Islamic bit was just to win votes from rednecks.

Anonymous

Whether they're actually anti-Islamic or not is a matter of debate. In my personal opinion, religion has actually nothing to do with all this. It's plain and simple wealth and economy. Causing religion-based wars causes more weapon sales and production, keep that in mind.

Balarka Sen

@DawoodibnKareem Fair. It just irks me how many of the times the Trump-supporting right bring out the issue of Islamic totalitarianism in their narratives to justify their meddling with the middle east.

It's a colonial manifesto

"I'm going to invade in the affairs of your country because you can't handle your shit"

Whilst the true motif is exploitation.

Anonymous

@BalarkaSen That.

Dawood ibn Kareem

Yup. But heaven forbid that Russia should meddle in the affairs of USA.

Balarka Sen

Lol

Dawood ibn Kareem

11:28 AM

Damn, I promised John Rennie I wouldn't bring politics into this room again.

skullpatrol

tsk tsk :P

Dawood ibn Kareem

in Problem Solving Strategies, 8 mins ago, by John Rennie

But I'm afraid I can't look at this in any detail right now as I'm busy with something else. Sorry.

So I might be safe for now! :-)

skullpatrol

I'm sure he'll clean up the transcript ;)

Anonymous

SE doesn't really have any specific rules against talking politics, as long as you're respectful of other's viewpoints.

Balarka Sen

Let's talk shit so that the conversation hides itself from the piercing Eye of John

skullpatrol

11:30 AM

shit

Dawood ibn Kareem

@Blue I try to be careful. But I realise that this room may well contain Trump supporters, and/or Zionists.

Neither of whose viewpoints I'm capable of being respectful towards.

skullpatrol

shoot

Anonymous

This is some interesting data: tradingeconomics.com/united-states/weapons-sales

Dawood ibn Kareem

Certainly a big jump from 2016 to 2017. I wonder what change within USA could possibly have caused that?

It would be interesting to see how much of those totals consists of sales to Saudi Arabia and Israel.

Anonymous

I think some of the export-import data is public

Dawood ibn Kareem

11:41 AM

Yeah, I could probably find the required numbers without too much effort.

Truth be told, I don't know what $12billion buys in terms of weapons.

Anonymous

Well, that's the amount that you've got publicly revealed. There might be a lot of black market sales going on, too. You don't know. Anyhow, even 12 billion is a LOT. India's total military budget is around ~60$ billion I think.

Anonymous

A single nuclear weapon costs around $1 million.

Dawood ibn Kareem

But presumably that $60b is not just weapons. That's building and maintaining army bases; paying personnel; feeding the troops etc.

Anonymous

@DawoodibnKareem Yes, that too.

Anonymous

So, $12 billion is quite a lot, in terms of just weapons

Dawood ibn Kareem

11:48 AM

@Blue John Rennie could probably afford one of his own.

Anonymous

He used to work (or maybe even now) for some nuclear energy company. He can make one of his own, in his backyard, if he gets access to the "resources". ;)

ACuriousMind

@DawoodibnKareem He's probably doing the IT for them, anyway :P

Balarka Sen

This is a hot meme

@JohnRennie has an unauthorized nuclear weapon in his backyward that he simultaneously bought for a million bucks and also made himself somehow

Star if you want this legend to be told through the history

Speaking of, we have never actually seen John's backyard. He has posted a few pictures of the front lawn of his home before, but NEVER his backyard.

Anonymous

Lol.

Secret

we need a pentathonk

John Rennie

11:55 AM

@BalarkaSen didn't I post a picture of myback lawn when it snowed?

Balarka Sen

Hm, I thought that was the front lawn

So was the snow deep enough to hide the nuke?

Balarka Sen

Good theory ^

John Rennie

Sadly the stuff I do for the nuclear guys is just related to corrosion in reactor cooling systems. It's physical chemistry rather than physics.

Secret

11:58 AM

how big does a nuke have to be? :P

John Rennie

Though it's probably good that the reactor cooling systems don't corrode and blow up.

Secret

I wonder if we can afford pinhead nukes now :P

Master Yushi

@JohnRennie I posted a shot at the solution in the problem solving room, can you take a look?

Dawood ibn Kareem

@JohnRennie So if you waste too much of your time in Stack Exchange chat rooms, nuclear reactors all over the world will start blowing up?

Secret

Davy Crockett (nuclear device)

The M-28 or M-29 Davy Crockett Weapon System was the tactical nuclear recoilless gun (smoothbore) for firing the M-388 nuclear projectile that was deployed by the United States during the Cold War. It was one of the smallest nuclear weapon systems ever built, with a yield between 10 and 20 tons TNT equivalent (40–80 Gigajoules). It is named after American folk hero, soldier, and congressman Davy Crockett. == Development == The Davy Crockett recoilless spigot gun was developed in the late 1950s for use against Soviet and North Korean armor and troops in case war broke out in Europe or the Korean...

mick

12:11 PM

0

Q: Spirals in newtonian celestial mechanics?

I know the laws of Kepler , the 3 laws of Newton and that conic sections are the trajectories of noncolliding two point masses. But I wonder about point mass A eventually colliding with point mass B. In particular When B is taken as stationary without initial velocity and A having a non-zero ve...

Help :)

Dawood ibn Kareem

You've answered your own question in the first sentence.

Logarithmic spirals are not conic sections.

mick

But What about spirals are not Conic sections either ???

Dawood ibn Kareem

OK, no kind of spiral is a conic section. So you're not going to get a spiral solution to the two-body problem. Ever.

mick

But Why is that ?? Im confused. I think spirals can happen ..

Dawood ibn Kareem

Nope. Only conic sections.

If one object is approaching another rapidly, you either get a direct hit, or it zooms past on a conic trajectory.

If it's going quickly enough, you'll get a hyperbola, which means it doesn't get captured, but carries on forever.

If it's not going quickly enough, it'll get captured into an elliptical orbit.

mick

12:20 PM

How does that work mathematically ?

Dawood ibn Kareem

And there's a boundary case where it's a parabola.

I'm sure you can find the mathematics online somewhere.

mick

I did not Find a good one

Dawood ibn Kareem

math.ksu.edu/~dbski/writings/twobody.pdf

astrowww.phys.uvic.ca/~tatum/celmechs/celm9.pdf

Anonymous

@mick The main reason you don't get spirals is because the potential function is inversely proportional to $r$. If you had a potential function inversely proportional to $r^{2}$ (say), you could get spiral trajectories.

Physics Meta

1:54 PM

0

Q: Reserving the use of the 'non-mainstream' close reason

In my opinion, the purpose of the 'non-mainstream' close reason is for non-mainstream theories. It's for people who have invented their own theory of everything, put it on Vixra, self-published a book about it, and want to have us look at it. This is a legitimate reason to close, as we get a coup...

discussion close-reasons non-mainstream-physics

0

Q: Somebody scraped our answers and sold them as a book

I don't know if this has come up in discussion, but somebody scraped various tags on Phys.SE and copy-pasted the results together into several books, including one on QFT, one on GR, and one on optics. The books in print cost about \$6 while the ones out of print can cost up to \$1000. The prices...

discussion

user42819

2:09 PM

Can anyone please help me with this question? I have been trying for days but I dont find a solution.

2

Q: Forces on a rolling cone on a plane surface

I came up with a question in while studying pure rolling in mechanics. Consider a hollow cone on a flat surface with its curved side lying on the floor. On applying an impulse on the cone at the curved side, close to the centre of mass of the cone, it is observed that the cone undergoes pure roll...

forces classical-mechanics rotational-dynamics

Tuki

2:24 PM

Hello. Atomic mass only includes mass of atom's nucleus ? not nucleus + electrons ?

meaning only mass of all protons + neutrons ?

Master Yushi

~the mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom~

~For atoms, the protons and neutrons of the nucleus account for almost all of the mass, and the atomic mass measured in u has nearly the same value as the mass number.~

Balarka Sen

@Tuki Yes. You want a characteristic measure of the atom: including electrons would be a bad idea because the number of electrons change all the time when you ionize the atom. So indeed, the atomic mass is the mass of the nucleus. But there's a catch: "true" mass of the nucleus is not blatantly equal to mass of protons + mass of neutrons.

Tuki

So if i have lets say ion (has lost one electron -> positive charge +e). Then i have electric field which accelerates this ion with voltage U. It's velocity will be $v=\sqrt{\frac{2eU}{m_{\text{ion}}}}$.

Balarka Sen

There's an error which comes from the binding energy in the nucleus.

It's called the mass defect.

Tuki

if we are on "low" velocities that relativity isn't necessary

So how much difference it makes if i don't take into account that it has lost one electron because of the ionization ?

So it's probably wise to just not try to count the electron mass ?

Use just the atomic mass units -> convert to kilograms and i am good with this ?

Master Yushi

2:46 PM

yeah electrons are pretty much "massless"

it won't make a lot of difference