Reddit Reddit reviews Introduction to Quantum Mechanics (2nd Edition)

We found 68 Reddit comments about Introduction to Quantum Mechanics (2nd Edition). Here are the top ones, ranked by their Reddit score.

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Introduction to Quantum Mechanics (2nd Edition)
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68 Reddit comments about Introduction to Quantum Mechanics (2nd Edition):

u/VoodooSteve · 44 pointsr/Physics

My undergraduate courses in quantum mechanics used Introduction to Quantum Mechanics by Griffiths and is a really good introduction with enough details.

u/TheNicestMonkey · 31 pointsr/Bitcoin

>Can you describe quantum mechanics

Intro to Quantum Mechanics


This is effectively what you have done...

u/[deleted] · 15 pointsr/Physics

Griffiths for Quantum Mechanics and E&M

Taylor's Classical Mechanics

Kittel & Kroemer for Statistical Thermodynamics

These are the only ones I can attest to personally, they're for undergraduate level understanding. Kittel&Kroemer can seem dense and difficult to understand at first, but once you work through problems and spend time on each chapter, it will become apparent how efficient the book is.

u/rcochrane · 12 pointsr/math

When I've got a clear aim in view for where I want to get to with a self-study project, I tend to work backwards.

Now, I don't know quantum mechanics, but here's how I might approach it if I decided I was going to learn (which, BTW, I'd love to get to one day):

First choose the book you'd like to read. For the sake of argument, say you've picked Griffiths, Introduction to Quantum Mechanics.

Now have a look at the preface / introduction and see if the author says what they assume of their readers. This often happens in university-level maths books. Griffiths says this:

> The reader must be familiar with the rudiments of linear algebra (as summarized in the Appendix), complex numbers, and calculus up to partial derivatives; some acquaintance with Fourier analysis and the Dirac delta function would help. Elementary classical mechanics is essential, of course, and a little electrodynamics would be useful in places.

So now you have a list of things you need to know. Assuming you don't know any of them, the next step would be to find out what are the standard "first course" textbooks on these subjects: examples might be Poole's Linear Algebra: A Modern Introduction and Stewart's Calculus: Early Transcendentals (though Griffiths tells us we don't need all of it, just "up to partial derivatives"). There are lots of books on classical mechanics; for self-study I would pick a modern textbook with lots of examples, pictures and exercises with solutions.

We also need something on "complex numbers", but Griffiths is a bit vague on what's required; if I didn't know what a complex number is than I'd be inclined to look at some basic material on them in the web rather than diving into a 500-page complex analysis book right away.

There's a lot to work on here, but it fits together into a "programme" that you can probably carry through in about 6 months with a bit of determination, maybe even less. Then take a run at Griffiths and see how tough it is; probably you'll get into difficulties and have to go away and read something else, but probably by this stage you'll be able to figure out what to read for yourself (or come back here and ask!).

With some projects you may have to do "another level" of background reading (e.g., you might need to read a precalculus book if the opening chapters of Stewart were incomprehensible). That's OK, just organise everything in dependency order and you should be fine.

I'll repeat my caveat: I don't know QM, and don't know whether Griffiths is a good book to use. This is just intended as an example of one way of working.

[EDIT: A trap for the unwary: authors don't always mention everything you need to know to read their book. For example, on p.2 Griffiths talks about the Schrodinger wave equation as a probability distribution. If you'd literally never seen continuous probability before, that's where you'd run aground even though he doesn't mention that in the preface.

But like I say, once you've taken care of the definite prerequisites you take a run at it, fall somewhere, pick yourself up and go away to fill in whatever caused a problem. Also, having more than one book on the subject is often valuable, because one author's explanation might be completely baffling to you whereas another puts it a different way that "clicks".]

u/BugeyeContinuum · 10 pointsr/askscience

Griffiths > Eisberg > Sakurai > Zee > Peskin

Peres and Ballentine offer a more quantum information oriented approach, read em after Griffiths.

Shankar before Sakurai, after Griffiths.



In that order. Your best bet though, is to find the appropriate section in the nearest university library, spend a day or two looking at books and choose whatever looks most interesting/accessible. Be warned, it seems that everyone and their cat has a book published on quantum mechanics with funky diagrams on the cover these days. A lot of them are legitimate, but make little to no effort to ensure your understanding or pose creative problems.

u/quantum_guy · 10 pointsr/IWantToLearn

Why hello there... How much math do you know?

It would be best if you understood basic differential and integral calculus, and can then learn the basics of linear algebra. From there, you could pick up a book such as Griffith's Introduction to Quantum Mechanics and start learning at the undergraduate level.

u/Weed_O_Whirler · 9 pointsr/Physics

First, the study of QM is really going to hinge on you grasping the fundamentals of linear algebra. Knowing calculus and differential equations would be very helpful, but without linear algebra, nothing will make sense. Particularly, you need to understand eigenvectors and eigenvalues as the Schrodinger Equation is an equation of that type. Here is a link to the MIT OpenCourseWare Linear Algebra Class complete with video lectures, etc. Completion of this class shouldn't require much more than a 16 year old's math understanding.

From there, if you are actually serious about pursuing this, get this book by David Griffiths, which is an into to QM that doesn't require too much calculus and it really good at explaining the concepts. With that book in hand, and actually trying to work through some of the problems, find another MIT OpenCourseWare class on the topic.

Secondly, please, please, please don't whine about downvotes. Every submission that gets popular at all gets some downvotes. Why? Who knows why, but it really isn't worth complaining about, and you will find there is a large portion of people who will downvote you simply because you complain about it.

u/armour_de · 8 pointsr/askscience

These rules arise from the solutions of the Schroedinger equation for a central potential.

The nucleus of the atom provides an attractive potential in which electrons can be bound. As the mass of even a single proton is roughly 1800 times that of an electron the nuclei can be treated as stationary charged points that the electrons orbit around. The resulting coulomb potential is a central potential, that is it only depends on the distance from the nucleus, not the direction from the nucleus.

See http://en.wikipedia.org/wiki/Hydrogen-like_atom for some of the derivation, but if you don't know differential equations and quantum mechanics at least at an introductory level it will not make much sense. Griffiths does a good introductory quantum text if you are interested in reading more. Link on amazon.com.

As it is a bound system in quantum mechanics only certain values of energy and momentum can be taken. The allowed energy levels are denoted by the quantum number n. The energy of a level is given is proportional to -1/n^2 in the simple hydrogenic atom model where the energy is negative that gives a bound state, and energies above zero are unbound, so as the energy increase the electrons in the higher n orbitals require less energy to become unbound.

For a given n there are certain values of angular momentum that can occur, and these are designated l and range from 0 to n. For a given l there are then the m_l magnetic quantum numbers ranging from +l to -l in integer steps. In the simple atom models the m_l do not effect the energy level.

Higher angular momentum of the electron implies a higher energy So 2s (n=1,l=0, m_l=0) has lower energy than 2p (n=2, l=1, m_l= 1,0,-1)

Each letter corresponds to an l value and arose from the way the lines looked in spectrographs and the meaning of the letter abbreviation is pretty much ignored these days with the current understanding of the the underlying quantum numbers.

s-> l=0 (sharp lines)

p->l=1 (principle lines)

d->l=2 (diffuse lines)

f->l=3 (fundamental lines)

http://www.tutorvista.com/content/chemistry/chemistry-iii/atomic-structure/electronic-configuration.php

Shows some of the simpler rules for determining the order of filling of the orbitals based on the energy level of the combined n and l values.

Two show how oxygen needs an octet to be stable we can do:

Oxygen has 8 protons and will be neutral with 8 electrons.

2 go into the 1s orbital, and it it is designated 1s^2, the superscript giving the number of electrons present in the n=1 l=0 m_l=0 and m_s =+1/2,-1/2. m_s is the magnetic quantum number for the electrons own internal angular momentum which has s=1/2 so can take m_s=+1/2 or m_s=-1/2.

The next higher energy orbital (look at the squiggly line diagram giving the filling order for electrons into orbitals, this is essentially filling in order of lowest energy orbitals first) is the 2s and it can have two electrons like the 1s, so we write 2s^2 for the full orbital.

There are now 4 more electrons to take care of, and they can go into the 2p orbital and that can hold up to 6 electrons, but we only fill in 4 for 2p^4 .

We can fully write the electron configuration as 1s^2 2s^2 2p^4 . If the oxygen borrows two more electrons (say one each from two hydrogens) they can move into the remaining 2p orbitals that are not full.

In the n=2 orbitals that then gives a total of 8 electrons.

Going into the higher orbitals requires more energy than the lower orbitals so it would not be a stable ground state. To put it differently if two hydrogen atoms are going bond to an oxygen it needs to go into a lower energy state than the separate atoms. If a bound state does occur with the lower energy atoms this is then an excited state that will decay into the grounds state by emission of a photon (light).

u/Bleulightning · 8 pointsr/Physics

I have personally enjoyed Griffiths Introduction to Quantum Mechanics. It requires a reasonably basis in undergraduate level physics, but is definitely not a text for doctorate students.

u/Araraguy · 8 pointsr/askphilosophy

The domain of physics is very narrow and the modern state of the field is highly specialized, so keep that in mind. If you have classical mechanics, multivariable calc, and preferably linear algebra (if not, MIT has tons of lectures online), you can start with quantum mechanics or statistical/thermal physics:

Griffith's Quantum Mechanics

Schroeder's Thermal Physics

Electromagnetism

I can't remember which physical chemistry text we used, but if you're concerned with atoms and molecules, you'll need that too. If you're concerned with nature at smaller scales, you'll need particle physics (and lots more math). Until you have a solid foundation in classical, thermal, and quantum, it's not a good idea to move on. You can't, for example, do much with quantum field theory if you don't have quantum mechanics. Both Shankar's and Susskind's lectures (and corresponding texts) go very quickly through classical and quantum, but skip much of the necessary examples that one requires when learning how to do physics. Just looking through these books will give you a general idea of what physics does concern itself with. If you want to skim through something more advanced (and not understand much of it) you could pick up Zee's QFT. This is also a good guide.



u/Nexusty · 8 pointsr/PhysicsStudents

A great introductory read would be "Introduction to Quantum Mechanics by David Griffiths"

Great Author and great textbook. Pretty much most intro QM courses use this text.

Amazon Link

u/omgzpplz · 8 pointsr/Physics

David J. Griffiths: E+M book, QM book.

Chances are you recognize him now?

u/ianmgull · 7 pointsr/quantum

This is the standard textbook that undergraduates first encounter. It assumes you already have a pretty firm grasp of calculus and linear algebra however.

https://www.amazon.com/Introduction-Quantum-Mechanics-David-Griffiths/dp/0131118927

I know it's not a site, but if you want to REALLY learn QM, this is how to start.

u/BlackBrane · 7 pointsr/quantum

This sub can be pretty good, but you're sure to find much more activity over on /r/physics. We usually like to direct questions to /r/AskPhysics but it's definitely not as well trafficked.

The main introductory textbook for physics undergrads is Griffiths, and for good reason. It's widely agreed to be the best book to begin a proper undertaking of QM if you have the key prerequisites down. You definitely need to be comfortable with linear algebra (the most important) as well as multivariable calculus and basic concepts of partial differential equations.

Im sure you can find some good free resources as well. One promising free book I've found is A Course in Quantum Computing (pdf). It actually teaches you the basics of linear algebra and complex numbers that you need, so if you feel weak on those this might be a good choice. I haven't really used it myself but it certainly looks like a good resource.

Finally, another well-regarded resource are Susskind's lectures at his website The Theoretical Minimum. He also has a book by the same name. They tend to be rather laid back and very gentle, while introducing you to the basic substance of the field. If you wanted, I'm sure you could find some more proper university-style lectures on Youtube as well.

u/themeaningofhaste · 5 pointsr/AskAcademia

Griffiths is the go-to for advanced undergraduate level texts, so you might consider his Introduction to Quantum Mechanics and Introduction to Particle Physics. I used Townsend's A Modern Approach to Quantum Mechanics to teach myself and I thought that was a pretty good book.

I'm not sure if you mean special or general relativity. For special, /u/Ragall's suggestion of Taylor is good but is aimed an more of an intermediate undergraduate; still worth checking out I think. I've heard Taylor (different Taylor) and Wheeler's Spacetime Physics is good but I don't know much more about it. For general relativity, I think Hartle's Gravity: An Introduction to Einstein's General Relativity and Carroll's Spacetime and Geometry: An Introduction to General Relativity are what you want to look for. Hartle is slightly lower level but both are close. Carroll is probably better if you want one book and want a bit more of the math.

Online resources are improving, and you might find luck in opencourseware type websites. I'm not too knowledgeable in these, and I think books, while expensive, are a great investment if you are planning to spend a long time in the field.

One note: teaching yourself is great, but a grad program will be concerned if it doesn't show up on a transcript. This being said, the big four in US institutions are Classical Mechanics, E&M, Thermodynamics/Stat Mech, and QM. You should have all four but you can sometimes get away with three. Expectations of other courses vary by school, which is why programs don't always expect things like GR, fluid mechanics, etc.

I hope that helps!

u/oh_jonas · 5 pointsr/math

I strongly agree with these choices. Additionally, Introduction to Quantum Mechanics by Griffiths.

u/swimmer91 · 5 pointsr/AdviceAnimals

Yeah quantum sucks. If you're not already using it, Griffiths's Introduction to Quantum Mechanics is pretty good:
http://www.amazon.com/Introduction-Quantum-Mechanics-2nd-Edition/dp/0131118927

And this guy has posted solutions with thorough explanations to most (maybe all?) of the practice problems:
http://physicspages.com/index-physics-quantum-mechanics/griffiths-introduction-to-quantum-mechanics-problems/

u/lejaylejay · 5 pointsr/quantum

What's your background? I'd probably start with math (sorry). Calculus and linear algebra.

Then Griffiths is probably to go-to intro text book. Though I never really got it until I read Sakurai. I'm not sure where to go for calculus and linear algebra self-study. Perhaps others can suggest.


http://www.amazon.com/Introduction-Quantum-Mechanics-2nd-Edition/dp/0131118927


http://www.amazon.com/Modern-Quantum-Mechanics-2nd-Edition/dp/0805382917

u/InfanticideAquifer · 5 pointsr/Physics

If you understand multivariable calculus, you're pretty close to being able to handle an introductory quantum mechanics textbook. If you know what a differential equation is, then Griffiths Intro to QM isn't really out of reach. If you want to really understand QM, you'll need to do this eventually...

u/iamiamwhoami · 5 pointsr/AskPhysics

Maybe try applied math programs. Some of them seem to have astrophysics faculty https://www.princeton.edu/gradschool/about/catalog/fields/applied_mathematics/. You'll probably have an easier time getting in with your background and can take the math GREs. In a physics BS you would at least have the knowledge of these books:

http://www.amazon.com/Classical-Mechanics-John-R-Taylor/dp/189138922X,

http://www.amazon.com/Introduction-Electrodynamics-4th-David-Griffiths/dp/0321856562/ref=sr_1_1?s=books&ie=UTF8&qid=1396384599&sr=1-1&keywords=griffiths,

http://www.amazon.com/Introduction-Quantum-Mechanics-David-Griffiths/dp/0131118927/ref=sr_1_2?s=books&ie=UTF8&qid=1396384599&sr=1-2&keywords=griffiths,

http://www.amazon.com/Introduction-Thermal-Physics-Daniel-Schroeder/dp/0201380277/ref=sr_1_1?s=books&ie=UTF8&qid=1396384625&sr=1-1&keywords=schroeder+statistical+physics.

The more you know from those books, the better. Although an applied math program, probably wouldn't expect you to have read all of them. Also try x-posting to /r/askacademia. I'm sure someone there could be more helpful.

u/thepastry · 4 pointsr/Physics

I just want to point out one thing that everyone seems to be glossing over: when people say that you'll need to review classical mechanics, they aren't talking only about Newtonian Mechanics. The standard treatment of Quantum Mechanics draws heavily from an alternative formulation of classical mechanics known as Hamiltonian Mechanics that I'm willing to bet you didn't cover in your physics education. This field is a bit of a beast in its own right (one of those that can pretty much get as complicated/mathematically taxing as you let it) and it certainly isn't necessary to become an expert in order to understand quantum mechanics. I'm at a bit of a loss to recommend a good textbook for an introduction to this subject, though. I used Taylor in my first course on the subject, but I don't really like that book. Goldstein is a wonderful book and widely considered to be the bible of classical mechanics, but can be a bit of a struggle.

Also, your math education may stand you in better stead than you think. Quantum mechanics done (IMHO) right is a very algebraic beast with all the nasty integrals saved for the end. You're certainly better off than someone with a background only in calculus. If you know calculus in 3 dimensions along with linear algebra, I'd say find a place to get a feel for Hamiltonian mechanics and dive right in to Griffiths or Shankar. (I've never read Shankar, so I can't speak to its quality directly, but I've heard only good things. Griffiths is quite understandable, though, and not at all terse.) If you find that you want a bit more detail on some of the topics in math that are glossed over in those treatments (like properties of Hilbert Space) I'd recommend asking r/math for a recommendation for a functional analysis textbook. (Warning:functional analysis is a bit of a mindfuck. I'd recommend taking these results on faith unless you're really curious.) You might also look into Eisberg and Resnick if you want a more historical/experimentally motivated treatment.

All in all, I think its doable. It is my firm belief that anyone can understand quantum mechanics (at least to the extent that anyone understands quantum mechanics) provided they put in the effort. It will be a fair amount of effort though. Above all, DO THE PROBLEMS! You can't actually learn physics without applying it. Also, you should be warned that no matter how deep you delve into the subject, there's always farther to go. That's the wonderful thing about physics: you can never know it all. There just comes a point where the questions you ask are current research questions.

Good Luck!

u/SegaTape · 4 pointsr/AskScienceDiscussion

David Griffiths' textbooks on E&M and quantum mechanics were easily the best textbooks I had as an undergrad. Clear, concise, refreshingly informal, and even a dash of humor.

u/CurvatureTensor · 3 pointsr/Physics

Math, math and more math. If you don't feel comfortable with differential equations, or if you're like I was after freshman year you don't know what a differential equation really is, then that's where you should start. Quantum Mechanics basically starts with an awesome differential equation and then goes from there.

Learning the math of this level of Physics on your own would be challenging to say the least, but if you want to dive in I'd suggest Mathematical Methods in the Physical Sciences by Boas. Pairing that with Introduction to Quantum Mechanics by Griffiths might be fun.

Nuclear theory goes into statistical mechanics, classical mechanics is multivariable calc/linear algebra, quantum field theory combines those two with differential equations and sprinkles in a bunch of "whoa that's weird" just to keep you on your toes. But it's really important that you know the math (or more likely you fake your way through the math enough to gain some insight to the Physics).

u/NoSmallCaterpillar · 3 pointsr/Physics

Because Griffiths is infamous amongst those in the know, but not really to a wider audience, I'll leave this here:

https://www.amazon.com/Introduction-Quantum-Mechanics-David-Griffiths/dp/0131118927

He also has an excellent book on Electromagnetism that is a staple in the undergraduate curriculum.

u/BeautyAndGlamour · 3 pointsr/Documentaries

Griffiths is excellent.

u/destiny_functional · 3 pointsr/AskScienceDiscussion

No, but here is a devastating critique of it

http://physics.ucsc.edu/~michael/qefoundations.pdf

See the abstract

>Abstract The central claim that understanding quantum mechanics requires a conscious observer, which is made by B. Rosenblum and F. Kuttner in their book “Quantum Enigma: Physics encounters consciousness”, is shown to be based on various
misunderstandings and distortions of the foundations of quantum mechanics.

and for a quicker read jump to chapter 2 to see what's wrong with it.

>2 Critique of Selected Quotations from QE

Stay away from it. It isn't going teach you anything, and will probably give you so many misconceptions that it's going to make it difficult to actually learn quantum theory at a later time. If you want to learn quantum theory, read a textbook ( probably the easiest English book on it https://www.amazon.com/Introduction-Quantum-Mechanics-David-Griffiths/dp/0131118927 you can find pdfs on google).

General rule: if a book on quantum theory mentions the word consciousness prominently (say in the title), then that's a red flag and be careful.

u/BitRex · 3 pointsr/askscience

Here's the second edition.

u/ELS · 3 pointsr/Physics

I think the most widely-used textbook for a junior level introductory quantum mechanics class (at least in US universities) is this book by David Griffiths.

u/erdaron · 3 pointsr/AskScienceDiscussion

Introduction to Quantum Mechanics by Griffiths is indeed an excellent textbook, and a standard in many undergrad courses. I would also recommend brushing up on vector calculus and linear algebra before diving into QM.

Honestly, Wikipedia articles often do a good job of explaining the fundamentals in a clear, accessible way. And its scientific accuracy is quite good.

There are also free courses online, such as through Coursera and MIT's OpenCourseWare.

u/woodne · 3 pointsr/Physics

I used Griffiths for my upper level Electro & Magnetostatics class.

http://www.amazon.com/Introduction-Electrodynamics-3rd-David-Griffiths/dp/013805326X/ref=sr_1_1?ie=UTF8&qid=1314035153&sr=8-1

Also I know the university I'm at uses the Griffiths book for Quantum Mechanics, however I have not taken the class.

http://www.amazon.com/Introduction-Quantum-Mechanics-David-Griffiths/dp/0131118927/ref=sr_1_2?ie=UTF8&qid=1314035153&sr=8-2

Disclaimer: I am a math major.

u/The_MPC · 2 pointsr/Physics

That's perfect then, don't let me stop you :). When you're ready for the real stuff, the standard books on quantum mechanics are (in roughly increasing order of sophistication)

  • Griffiths (the standard first course, and maybe the best one)
  • Cohen-Tannoudji (another good one, similar to Griffiths and a bit more thorough)
  • Shankar (sometimes used as a first course, sometimes used as graduate text; unless you are really good at linear algebra, you'd get more out of starting with the first two books instead of Shankar)

    By the time you get to Shankar, you'll also need some classical mechanics. The best text, especially for self-learning, is [Taylor's Classical Mechanics.] (http://www.amazon.com/Classical-Mechanics-John-R-Taylor/dp/189138922X/ref=sr_1_1?s=books&ie=UTF8&qid=1372650839&sr=1-1&keywords=classical+mechanics)


    Those books will technically have all the math you need to solve the end-of-chapter problems, but a proper source will make your life easier and your understanding better. It's enough to use any one of

  • Paul's Free Online Notes (the stuff after calculus, but without some of the specialized ways physicists use the material)
  • Boas (the standard, focuses on problem-solving recipes)
  • Nearing (very similar to Boas, but free and online!)
  • Little Hassani (Boas done right, with all the recipes plus real explanations of the math behind them; after my math methods class taught from Boas, I immediately sold Boas and bought this with no regrets)

    When you have a good handle on that, and you really want to learn the language used by researchers like Dr. Greene, check out

  • Sakurai (the standard graduate QM book; any of the other three QM texts will prepare you for this one, and this one will prepare you for your PhD qualifying exams)
  • Big Hassani(this isn't just the tools used in theoretical physics, it's the content of mathematical physics. This is one of two math-for-physics books that I keep at my desk when I do my research, and the other is Little Hassani)
  • Peskin and Schroeder (the standard book on quantum field theory, the relativistic quantum theory of particles and fields; either Sakurai or Shankar will prepare you for this)

    Aside from the above, the most relevant free online sources at this level are

  • Khan Academy
  • Leonard Susskind's Modern Physics lectures
  • MIT's Open CourseWare
u/somnolent49 · 2 pointsr/AskWomen

Food:

  • I make large batches of food which I can freeze and reheat.
  • I eat less meat, and when I do cook meat I eat it with rice or pasta to lower the overall cost.
  • I buy large boxes of snack bars at costco, and toss a handful in my bag. When I get tempted to buy food while I'm out and about, I eat a snack bar instead and wait until I get home to eat.
  • I eat smaller portions, and force myself to wait 10-15 minutes before going back for a second portion, to make sure I'm actually still hungry.

    School:

  • I buy international edition textbooks when available. For instance, the regular edition of one of my textbooks cost $136, while the international edition only cost $16.50. The only difference between the two is that my edition has a few extra book problems the regular edition does not.
  • I go to office hours for professors and TA's when possible. I'm paying thousands of dollars just to sit in a giant lecture hall for three hours a week, yet I can easily get another hour or two of one-on-one teaching from people who are brilliant in their field for free.
u/cowboysauce · 2 pointsr/askscience

Do you want a formal understanding? If so, then there's a problem. The 4 fundamental interactions are not completely understood. The electromagnetic is very well understood and is covered by quantum electrodynamics. The weak interaction is also understood quite well and has been unified with the EM interaction into the electroweak interaction.

The strong interaction and gravity are not as well understood. There is no widely accepted theory of quantum gravity (gravity is currently described by general relativity). The strong force is described using quantum chromodynamics (QCD), however QCD is vey complicated (due to the fact that gluons carry color charge and interact with each other).

If you fine with that, then I have to ask, are you comfortable with classical physics? If not then start there. If you are, then you can continue on with quantum physics, this book is a very good quantum mechanics book.

If you want a lay person understanding, then I suggest you do some searches here on askscience, because there is a wealth of information regarding particle physics here.

One more thing, very few people call it "quantum physics", it almost always goes by the name "quantum mechanics".

u/wafflesforlife · 2 pointsr/chemistry

In addition to the McQuarrie book mentioned (my text for pchem), I would take a look at Griffiths book for QM. The two books are complementary to each other and I think reading them both gave me a big leg up!

u/HQuez · 2 pointsr/AskPhysics

For math you're going to need to know calculus, differential equations (partial and ordinary), and linear algebra.

For calculus, you're going to start with learning about differentiating and limits and whatnot. Then you're going to learn about integrating and series. Series is going to seem a little useless at first, but make sure you don't just skim it, because it becomes very important for physics. Once you learn integration, and integration techniques, you're going to want to go learn multi-variable calculus and vector calculus. Personally, this was the hardest thing for me to learn and I still have problems with it.

While you're learning calculus you can do some lower level physics. I personally liked Halliday, Resnik, and Walker, but I've also heard Giancoli is good. These will give you the basic, idealized world physics understandings, and not too much calculus is involved. You will go through mechanics, electromagnetism, thermodynamics, and "modern physics". You're going to go through these subjects again, but don't skip this part of the process, as you will need the grounding for later.

So, now you have the first two years of a physics degree done, it's time for the big boy stuff (that is the thing that separates the physicists from the engineers). You could get a differential equations and linear algebra books, and I highly suggest you do, but you could skip that and learn it from a physics reference book. Boaz will teach you the linear and the diffe q's you will need to know, along with almost every other post-calculus class math concept you will need for physics. I've also heard that Arfken, Weber, and Harris is a good reference book, but I have personally never used it, and I dont' know if it teaches linear and diffe q's. These are pretty much must-haves though, as they go through things like fourier series and calculus of variations (and a lot of other techniques), which are extremely important to know for what is about to come to you in the next paragraph.

Now that you have a solid mathematical basis, you can get deeper into what you learned in Halliday, Resnik, and Walker, or Giancoli, or whatever you used to get you basis down. You're going to do mechanics, E&M, Thermodynamis/Statistical Analysis, and quantum mechanics again! (yippee). These books will go way deeper into theses subjects, and need a lot more rigorous math. They take that you already know the lower-division stuff for granted, so they don't really teach those all that much. They're tough, very tough. Obvioulsy there are other texts you can go to, but these are the one I am most familiar with.

A few notes. These are just the core classes, anybody going through a physics program will also do labs, research, programming, astro, chemistry, biology, engineering, advanced math, and/or a variety of different things to supplement their degree. There a very few physicists that I know who took the exact same route/class.

These books all have practice problems. Do them. You don't learn physics by reading, you learn by doing. You don't have to do every problem, but you should do a fair amount. This means the theory questions and the math heavy questions. Your theory means nothing without the math to back it up.

Lastly, physics is very demanding. In my experience, most physics students have to pretty much dedicate almost all their time to the craft. This is with instructors, ta's, and tutors helping us along the way. When I say all their time, I mean up until at least midnight (often later) studying/doing work. I commend you on wanting to self-teach yourself, but if you want to learn physics, get into a classroom at your local junior college and start there (I think you'll need a half year of calculus though before you can start doing physics). Some of the concepts are hard (very hard) to understand properly, and the internet stops being very useful very quickly. Having an expert to guide you helps a lot.

Good luck on your journey!

u/Cpt_Burrito · 2 pointsr/astrophysics

We're not even sure the constants are constant. It's entirely possible they do change in some complicated relationship on levels too large, too small, too fast or too slow for us to notice 'easily'. I know that dodges your question, but it's one hell of a question and answering it directly would be a marked step forward in our understanding of the universe.

Like chip said, the math is just a 'best fit' solution to the events we observe. If you've got the free time you could crack open this book and try moving things around and see what your new maths describe.

I hadn't even passed algebra when I graduated high school though so if you're in the same boat I was in then this book (specifically the later chapters) might give you a better perspective.

u/icecoldmind · 2 pointsr/Physics

In case you're new here. We ( well not me really ) physicists really hate the example of Shrödinger's cat. It's a poor example that only raises questions in the wrong direction. It goes right into the weird type of philosophy that we, as scientists, try to avoid at all costs. If you want to know more about quantum mechanics, which is supposed to be the subject of the so-called Shrödinger's Cat, there are plenty of pop-sci books and YouTube channels. If you want to know the real physics, as in the math, you can try Griffiths ( You need calculus and some algebra ).

u/Dank_Hamiltonian · 2 pointsr/AskPhysics

First and foremost, you're going to need to get very comfortable with special relativity and quantum mechanics. QFT is heavily rooted in both subjects since it's essentially a way of reconciling the two, so you're going to need to get familiar with the formalism. For quantum mechanics, I recommend starting off with Griffiths if you haven't taken a class on the subject at an undergraduate level. It's pretty much the gold standard in undergraduate physics curricula. But that alone is not enough to fulfill the necessary background in quantum. After that you'll want to go through a graduate text such as Sakurai. You need to get very familiar with the Dirac formalism since it plays a large role in formulating quantum fields.

Special relativity isn't usually offered as a course on its own in most universities (as far as I know). Typically, it's part of a course on classical dynamics or electrodynamics. You could look for the relevant chapters in textbooks on those two subjects (such as Griffiths electrodynamics) or just go with the introduction that pretty much every QFT textbook has at the beginning. The main thing here is that you'll have to get used to working with tensors since they show up in Lagrangian densities, which are principal objects of study in QFT. This is also where classical field theory comes in, as classical fields are also described by Lagrangians.

Those are the main areas of physics that you need to know coming into the subject. As others have mentioned, you'll want to understand Hamiltonian and Lagrangian mechanics as well as classical E&M since a lot of the formalism involved in QFT stems from those subjects. Most people are introduced to quantum through the Hamiltonian formalism, and while you can do calculations in quantum without understanding where the formalism comes from in classical mechanics, you might be confused as to why the calculations work the way they do. You can also do calculations with a Lagrangian in QFT without really understanding what actually is, but again, if you truly want to understand the material it won't get you quite far enough. It is a graduate subject, after all. So you'll probably struggle to understand the material without having a solid undergraduate background in physics, but it's not impossible. It's also the kind of subject that requires multiple attempts to understand it. I took one semester of it as an undergraduate and there were a lot of gaps in my knowledge at the time, so I found it quite difficult. Then I took another class on it again after going through first year graduate courses in classical mechanics, quantum, and electrodynamics, and I had a better feel for the subject.

u/MahatmaGandalf · 2 pointsr/AskPhysics

You sound like a great audience for the series I recommend to everyone in your position: Lenny Susskind's Theoretical Minimum. He's got free lectures and accompanying books which are designed with the sole purpose of getting you from zero to sixty as fast as possible. I'm sure others will have valuable suggestions, but that's mine.

The series is designed for people who took some math classes in college, and maybe an intro physics class, but never had the chance to go further. However, it does assume that you are comfortable with calculus, and more doesn't hurt. What's your math background like?

As to the LHC and other bleeding-edge physics: unfortunately, this stuff takes a lot of investment to really get at, if you want to be at the level where you can do the actual derivations—well beyond where an undergrad quantum course would land you. If you're okay with a more heuristic picture, you could read popular-science books on particle physics and combine that with a more quantitative experience from other sources.

But if you are thinking of doing this over a very long period of time, I would suggest that you could pretty easily attain an advanced-undergraduate understanding of particle physics through self-study—enough to do some calculations, though the actual how and why may not be apparent. If you're willing to put in a little cash and more than a little time for this project, here's what I suggest:

  • Pick up a book on introductory physics (with calculus). It doesn't really matter which. Make sure you're good with the basic concepts—force, momentum, energy, work, etc.

  • Learn special relativity. It does not take too long, and is not math-intensive, but it can be very confusing. There are lots of ways to do it—lots of online sources too. My favorite book for introductory SR is this one.

  • Use a book or online resources to become familiar with the basics (just the basics) of differential equations and linear algebra. It sounds more scary than it is.

  • Get a copy of Griffiths' books on quantum mechanics and particle physics. These are undergrad-level textbooks, but pretty accessible! Read the quantum book first—and do at least a few exercises—and then you should be able to get a whole lot out of reading the particle physics book.

    Note that this is sort of the fastest way to get into particle physics. If you want to take this route, you should still be prepared to spread it out over a couple years—and it will leave a whole smattering of gaps in your knowledge. But hey, if you enjoy it, you could legitimately come to understand a lot about the universe through self-study!
u/Ninja_of_Physics · 2 pointsr/math

I'm assuming this is an undergrad QM class so what you have will be more than enough. If you're in the states odds are the book they will be using is Giffiths Amazon link, PDF of the first edition. If you can Taylor expand and find eigenstates you'll be fine.

First semester undergrad quantum is mostly focused on learning how to solve the Schrodinger equation for a variety of Potentials. Expect it to be like first semester calculus, you gloss over the deeper mathematical rigor, and focus on being able to take limits and derivatives. First semester quantum is the same, learn how to solve the Schrodinger equation, and learn what physical meaning you can get from it.

u/Devook · 2 pointsr/battlestations

>I love reading quantum mechanics.

cringe
Reading the pop-sci layman's guide to physics is not the same as "reading quantum mechanics." You wanna "read quantum mechanics" you're going to have to start with two years of calculus, a year of linear algebra, a year of statistics, a year of number theory, and this book.

u/ngroot · 2 pointsr/AskReddit

> Can you, or anyone else, link to some information that accurately defines quantum mechanics?

There's always the relevant Wikipedia article; Griffiths' book on introductory QM is also very clear.

If you want a brief, fairly non-technical summary, though, it's what I said before: in QM, the state of an object is contained in a wavefunction. That function evolves over time (following the Schrödinger equation). For a given wavefunction, you can find the probability of measuring a classical property (e.g,. position, momentum, energy) as having a particular value or falling within a range of values by applying an appropriate operator.

The uncertainty principle follows from this. A wave function which will result in most measurements of position being in a tight clump (i.e., an object with a well-defined position) will result in measurements of momentum that will vary widely, and vice-versa.

The usual analogy (which is actually very close to the mathematics in QM) that I've encountered is a rope under tension. If you give it a sharp jerk and induce a single peak that travels down the wave, the question "where is the wave" makes sense, but "what's its frequency" does not. The converse is true if you induce a standing wave: you can talk easily about the frequency, but the wave is everywhere along the rope.

> What I always end up with is this idea of perception=reality. That since we cannot measure where the electron is, it simply isn't. I don't buy this for a second.

Close, but let's be more precise: it's not that the electron doesn't exist, it's that classic properties that we think of as fundamental (position, momentum, etc.) aren't. In QM, a particle always has a wavefunction; that wavefunction determines the distribution of values you'll get if you try to measure a classical property. This means that generally you can't say that a particle "has" a particular position/momentum/whatever; you can only talk about the probabilities of finding it with such-and-such a position or momentum.

If you don't like the fact that this implies that classical properties are fundamentally random, you're in good company; that's what prompted Einstein's "God does not play dice" quip. Unfortunately, Bell's theorem and subsequent tests and confirmations of it essentially eliminate the possibility of local "hidden variables" which contain the "real" position/momentum/whatever of a particle. This leaves us stuck between accepting a stochastic universe and non-local interactions (which thanks to relativity, introduce causal paradoxes.)

u/GroundhogExpert · 2 pointsr/cringepics

http://www.amazon.com/Introduction-Quantum-Mechanics-2nd-Edition/dp/0131118927

Just flipping through the first pages should make it obvious how much previous knowledge is required just to begin understanding quantum mechanics.

Maybe this one is better: http://www.amazon.com/Quantum-Physics-Dummies-Steve-Holzner/dp/1118460820/ref=sr_1_1?s=books&ie=UTF8&qid=1408628463&sr=1-1&keywords=quantum+mechanics+for+dummies

I just went through the first chapter in the dummies book, it's not much better.

u/susySquark · 2 pointsr/IWantToLearn

This is THE book for that

Multivar calculus understanding more or less necessary, and familiarity with classical mechanics is pretty handy for tackling QM. Linear algebra is absolutely critical to understand everything well, mathematically speaking.

I personally liked Griffiths' book. The concepts are explained well and the examples are cleanly worked out. It's a decently accessible book and an easy read, which is always a plus.

u/drakeonaplane · 2 pointsr/AdviceAnimals

Griffiths Quantum Mechanics book features a live cat on front and a dead cat on back.

u/kentaro86 · 2 pointsr/UCSantaBarbara

I don't have any old problem sets off hand, but I could point you towards all the topics you should know and be familiar with. It's basically the first 3 chapters of Griffiths -- by the end of the quarter you should know everything from these chapters extremely well.
As for an explicit list of things to do, I would recommend (in this order, more or less)

  • get familiar with using probability distributions, complex numbers (i.e. integrating probability densities to find probabilities, means, standard deviations, complex conjugates, norm squared, normalization, etc.)

  • try to grasp the idea of operators (e.g. position, momentum), observables/hermitian operators, commutation relations, and what is means when two observables commute or not (thing about eigenstates, sequential measurements, uncertainty principle,...)

  • derive solution to infinite square well (0 < x < a ; -a < x < a)

  • derive solution to harmonic oscillator (focus on algebraic derivation, raising and lowering operators are extremely
    important later on)

  • calculate expectation values of x, x^2 for the oscillator using ladder operators (this is to highlight orthogonality of eigenstates)

  • derive free particle, examine scattering (E > 0) and bound (E < 0) states

  • derive delta well, finite square well and calculate transmission/reflection coefficients (and bound states for delta well)

  • read up on and use Dirac notation until it is second nature. redo first bullet point with this notation (this could be useful to do first so that you can practice it)

  • understand the level of abstraction for a ket and what it means to "multiply" by a bra and express an equation in the basis (as described by the bra)

  • revisit the idea of operators in a specific basis

  • derive generalized uncertainty principle, revisit non-commuting operators

    Hopefully, that gets you started off, but for 110A it may be worth the time to learn Einstein summation notation -- it'll come in handy.

    Good luck!

    Edit: formatting
u/i_am_cat · 2 pointsr/LearnJapanese

4000 yen on amazon.jp or $50 on amazon.com is not even close to insanely expensive. Many physics books and similar subjects are closer to the $100-200 range. The cheap ones are $50.

u/WillWeisser · 1 pointr/books

Personally, I think you would get great suggestions on /r/physics. But since you're here...

Since you seem like you're just dipping your toes in the water, you might want to start off with something basic like Hawking (A Brief History of Time, The Universe in a Nutshell).

I highly recommend Feynman's QED, it's short but there's really no other book like it. Anything else by Feynman is great too. I found this on Amazon and though I haven't read it, I can tell you that he was the greatest at explaining complex topics to a mass audience.

You'll probably want to read about relativity too, although my knowledge of books here is limited. Someone else can chime in, maybe. When I was a kid I read Einstein for Beginners and loved it, but that's a comic book so it might not be everyone's cup of tea.

If you really want to understand quantum mechanics and don't mind a little calculus (OK, a lot), try the textbook Introduction to Quantum Mechanics by Griffiths. Don't settle for hokey popular misconceptions of how QM works, this is the real thing and it will blow your mind.

Finally, the most recent popular physics book I read and really enjoyed was The Trouble with Physics by Smolin. It's ostensibly a book about how string theory is likely incorrect, but it also contains really great segments about the current state of particle physics and the standard model.

u/nebos11 · 1 pointr/AskReddit

You might laugh me out of the building so to speak, but I'd add David J. Griffiths' introductory college-level book to that list. (http://www.amazon.com/Introduction-Quantum-Mechanics-David-Griffiths/dp/0131118927/ref=sr_1_1?s=books&ie=UTF8&qid=1348157753&sr=1-1&keywords=david+j+griffiths+quantum+mechanics). It's not going to blow anyone's mind with crazy philosophical mumbo jumbo, but I think it's the right place to start if you're unfamiliar the basics, i.e. Heisenberg uncertainty, Hilbert space, Schrodinger's Eq, and so on. Understanding the formalism and the fundamentals of QM is vital if you want to get into more esoteric stuff.

u/dolphinrisky · 1 pointr/trees

I meant his quantum book. There are a lot of varying opinions on Griffiths, but personally I enjoy his more informal writing style. It's nice when studying quantum because the physics can get a bit abstract and intangible, and Griffiths does a good job of giving you plain-English explanations of what is happening.

u/guenoc · 1 pointr/Physics

Sweet. I think the best curriculum to approach this with, assuming you're in this for the long haul, would be to start with building a good understanding of calculus, cover basic classical mechanics, then cover electricity and magnetism, and finally quantum mechanics. I'm going to leave math and mechanics mostly for someone else, because no textbooks come to mind at the moment. I'll leave you with three books though:

For Math, unless someone else comes up with something better, the bible is Stewart's Calculus

The other two are by the same author:

Griffith's Introduction to Electrodynamics

Griffith's Introduction to Quantum Mechanics

I think these are entirely reasonable to read cover to cover, work through problems in, and come out with somewhere near an undergraduate level understanding. Be careful not to rush things. One of the biggest barriers I've run into trying to learn physics independently is to try and approach subjects I don't have the background for yet: it can be a massive waste of time. If you really want to learn physics in its true mathematical form, read the books chapter by chapter, make sure you understand things before moving on, and do problems from the books. I'd recommend buying a copy of the solutions manuals for these books as well. It can also be helpful to look up the website for various courses from any university and reference their problem sets/solutions.

Good luck!

u/tikael · 1 pointr/Physics

The two intro texts you'll see all the time for quantum are Shankar and Griffiths. I would recommend Shankar of those two since Griffiths skips a bunch of critical mathematical definitions. However, even Shankar may be a bit above your current math level. I don't know what 6th form or A-level means but quantum can get into ugly math and weird notation very quickly.

u/firekow · 1 pointr/Physics

If you have taken a solid introductory physics course, this standard text steps through a good number of classic problems in an understandable fashion.

EDIT: Calculus, vectors, linear algebra (clarifies a whole lot of the concepts), ODEs and PDEs.

u/badmathafacka · 1 pointr/explainlikeimfive

If you want to talk about Quantum Mechanics, maybe you should be reading this book instead.

u/Alekanekelo · 1 pointr/quantum

Op is referring to this book. But yeah I laughed quite a bit too.

u/Platypuskeeper · 1 pointr/askscience

> Cultural beliefs do actually influence ways of thought, scientific method included

The scientific method is not a "way of thought". It's a method. You're not providing any evidence to support that claim. The fact that different cultures have different patterns of thought is well-established, the idea that this makes science culturally relative is not. Are you saying logic is culturally dependent as well?

> Westerners tend to rely more on formal logic and insist on correctness of one belief over another when investigating conflicting opinions or theories, while easterners consider all the interacting environmental relationships,

A vague and unsubstantiated orientalist over-generalization if I ever heard one.

> One can even argue the Scientific Method is actually an invention of the western tradition

The automobile is a western invention too, and yet the Japanese understand them just the same way as we do.

>TL;DR: read something like The Geography of Thought for intriguing trends in how your Asian lab partner interprets data differently from you.

I've never run across a case where he did. Read a good book on philosophy of science to understand why natural science strives to eliminate bias, including cultural bias. It's not contingent on it but the exact opposite.

>Difference being Goswami was a quantum physics professor

There's no such thing as a 'quantum physics professor' or really a 'quantum physicist'. All physicists study quantum mechanics and nearly all use it, to different extents. Goswami's actual expertise is apparently nuclear physics, which does not imply any greater understanding of the foundations of quantum mechanics than that of most physicists.

> who wrote respected college textbooks

As far as I can tell, he's written one textbook on introductory quantum mechanics. I've never heard of him or his textbook before, and I see little reason to believe it's 'well-respected' or popular, as it only has 5 amazon reviews, as compared to 70 for Griffiths, an actual well-regarded textbook. Sakurai's "Modern QM" and Shankar's "Principles of QM" are popular and well-respected as well. Griffith's is also known for the consistent-histories interpretation of quantum mechanics, while the latter two are 'Easterners', yet don't subscribe to any of this kind of nonsense.

> My background is not in quantum physics, but sooner or later you guys will have to (you should?) reconcile your understanding of reality with how different cultural traditions interpret reality.

You haven't shown any depth of knowledge about 'cultural traditions'. You've made gross generalizations and outright false statements about these things. Calling Western philosophy 'materialist' while 'eastern' is supposedly uniformly 'idealist' (both terms are from Western philosophy) is flat-out wrong.

> Furthermore, the jump is discontinuous in that the electron is never in any orbit not defined by one of the probability clouds.

That's saying that mixed states and quantum superpositions do not exist. It's wrong, and introductory level understanding of formal quantum mechanics is enough to know it.

>Can you please point me to a more accurate description?

Show that the eigenfunctions of the electronic Hamiltonian are no longer eigenfunctions under the action of a perturbing external electromagnetic field.

> What is the interesting part of the delayed-choice experiment then if it's not that what we observe depends on how we measure it?

Did you make any effort at all to find out on your own, such as reading the wikipedia article? I don't see why I should spend time explaining it otherwise. The fact that "what we observe depends on how we measure it" is already evident in the double-slit experiment.

> the most interesting scientific discoveries come when interpretations of science and philosophy butt up against each other.

No, they don't. The most interesting scientific discoveries come when a well-established theory is proven wrong. Metaphysics has nothing to do with science. The Bell test is not philosophy, it's science. It's an empirical test of an empirically-testable thing.

> it appears that a non-local signal (that is, a deliberate faster-than-light transmission) is impossible

It's not the Bell test that says that, it's special relativity.

> Help me understand reality as you interpret it.

Now why the heck would I spend any time on doing that? There's a huge number of good, factual popular-scientific books on quantum mechanics and modern physics. There are plenty of good textbooks. There are good books on science and philosophy of science as well. But instead you waste your time on reading Goswami's nonsense, which would clearly be out of the mainstream to anyone who'd bothered to do a modicum of web searching beforehand. Then you defend it all, basically by stating that you know better than an actual scientist how science works.

You haven't shown that you've made even the slightest bit of a good-faith effort to understand either science, the scientific method and mindset, or established quantum physics. To me it appears that you came here seeking confirmation of what you'd already decided you wanted to believe.

Stephen Hawking, Brian Greene, Carl Sagan, Richard Feynman, Neil Tyson, Stephen Weinberg and Murray Gell-Mann, among others, have all written good popular-scientific books on modern physics. Just about all of them say something about quantum mechanics and the more popular interpretations of it. And for a more in-depth study of the philosophy of science surrounding quantum mechanics, read e.g. Omnes' "Quantum philosophy".

u/wacky · 1 pointr/science

> I'm not sure which QM textbooks hardcore physicists use.

NOT that one.

If you're doing quantum physics, you're probably not interested that much in how molecules work. At some point you'll learn a little bit, so you know in what direction that goes, but quantum physicists leave chemistry to the chemists.

As for textbooks, I had Griffiths first (Griffiths is amazing, his E/M book too), then Sakurai, and then Nielsen and Chuang in the 5 courses I've taken so far. And we didn't get through each of those textbooks in full; just covered chapters here and there, like science classes always do.

u/blueboybob · 1 pointr/HomeworkHelp

halliday and resnick for general physics

1 - goldstein

2 - griffith

3 -

4 - griffith or jackson

u/LennartGimm · 1 pointr/explainabookplotbadly

While you’re working on the rules, you might want to think about what types of books are permitted. Are scientific books like the Griffiths allowed? I could just give a very simplified description of QM and have people guess. Are historical books like Rubikon allowed? Opening the sub to simplified tellings of historical events.

I think this really depends on what type of content you and the users want to see. I personally would like the sub to remain focused on fiction and novels, but maybe on Sundays every type of book can be allowed in order to vent the chaos and have a little fun.

Also: You might want to ban certain books from this sub, if they are overdone. I could imagine Harry Potter, LotR and the bible to be posted often.

u/Coffee__Addict · 1 pointr/Physics

https://www.amazon.com/Introduction-Quantum-Mechanics-David-Griffiths/dp/0131118927

For the QM

And

https://www.amazon.ca/Mathematical-Methods-Physical-Sciences-Mary/dp/0471198269

For the math.

Edit: I'm rereading both of these over the summer as a refresher. They make a great combo.

u/jai-a-jai · 1 pointr/todayilearned

Negative motion literally just means multiplying each velocity component by -1, i.e. reversing the direction of the velocity vector.

You're probably referring to negative energy. Negative energy is possible, and is allowed by relativistic quantum mechanics (where E^2 = m^2 c^4 + p^2 c^2 , which is Einstein's famous equation). Particles with negative energy are moving backwards in time, and have reversed properties to their forward-moving counterparts. These particles are antimatter. Sounds wild. It is.

Regarding absolute zero: The magnitude of temperature is just a way to describe how much randomness there is in the energy of a system. A higher magnitude of temperature means that more and more particles want to seep out of the absolute zero state. What is the absolute zero state? That depends on the sign of the temperature, which is the whole point of the OP's article. It's not as simple as "being zero". It matters how you approach zero. There are two ways to approach zero: from the left, and from the right. For example [-1,-.5,-.25,-.125,...] approaches zero, but from the left (negative values). Whereas [1,.5,.25,.125,...] approaches zero from the right (positive values). The sign of the temperature is a simple way of saying whether you take the limit to 0 from the left or from the right.

If the temperature is negative, approaching absolute zero will squeeze the particles into the highest energy state. If the temperature is positive, approaching absolute zero will freeze the particles into the lowest energy state.

The important thing to understand is that the lowest energy state (ground state) does not mean no energy, it means the lowest energy. Let's talk a bit about quantum mechanics. Position, momentum, energy, etc. are observable properties. You can measure them. In quantum mechanics, measuring a particle either may change the state that the particle is in, or it may not. Particles which are in states which are unchanged by measuring position are called "position eigenstates". Particles which are in states which are unchanged by measuring energy are called "energy eigenstates", and so on.

In quantum mechanics, it is impossible to find a state which isn't changed by measuring position that is also not changed by measuring momentum. If you think about it a little bit, this has a very important implication: position and momentum cannot be defined simultaneously. It's straight up fucking impossible. The more you know about where a particle is, the less you know about how much momentum it has, and vice versa. In other words, confining a particle to an arbitrarily small region will mean that the particle can have an arbitrarily large momentum.

So now you see why "no molecular motion" is absolutely nonsensical. It leads to a contradiction, if we think in quantum mechanics. If you assume a particle has no motion, then it must have a fixed position. But in the limit of having a fixed position, it must now have an arbitrarily large momentum, which contradicts our assumption of the particle having no motion. There is no notion of having no motion.

If you are interested in this wild fucking shit, read up on linear algebra and get this legendary book on quantum mechanics by David Griffiths.

u/Banach-Tarski · 0 pointsr/Drugs