# Search results

1. ### LQG Introduction Material

LQG is a subject that is built off of general relativity and quantum field theory, so you should understand that a good introduction would still assume 2 years of graduate coursework... Regardless, I found the following to be a pretty good intro: http://arxiv.org/abs/1102.3660 I also read...
2. ### Schools Does distribution of grades matter when applying to grad school?

Not that I have any kind of experience you ask for, but I tend to hear that admissions like to see positive trends in your grades (though of course, they prefer a 4.0). It's (probably) better to have your A's in your difficult senior level courses than in your easy freshman ones, if you can only...
3. ### Simple Big O analysis question

Well, I know of at least one computer science textbook that agrees with me, and it's where I learned this definition. The book is http://sist.sysu.edu.cn/~isslxm/DSA/textbook/Skiena.-.TheAlgorithmDesignManual.pdf [Broken], and on it's 36th page Skiena writes: "The Big Oh notation provides for...
4. ### Simple Big O analysis question

Inaccurate, but not incorrect, at least according to: http://en.wikipedia.org/wiki/Big_O_notation#Formal_definition (If you use n^2 as f(x) and n^3 as g(x), the formal definition is easily satisfied) This is just semantics, but my guess is that the prof was trying to illustrate this point.
5. ### Simple Big O analysis question

If I recall correctly, big O notation refers to an upper bound. So strictly speaking, an algorithm that is O(n^2) is also O(n^3), because the latter will be larger than the former. However, it is best to hold a fair amount of precision in your upper bound: simply stating that an algorithm is...

7. ### Commutation of derivatives.

Oh I see. My first thought is that this would be a lot of work for something we basically already have: a representation of non commuting operators. But my second thought is that this might be a way to create some non standard physical situations, where for example energy and momentum would not...
8. ### Commutation of derivatives.

From one perspective, all currently known fundamental physics is based on theories where derivatives do not commute. A simple example: in electromagnetism, we can define D_\mu = \partial_\mu - ieA_\mu , which acts just like (because it is) a derivative operator. From which we compute...

your if statement is always true, when you typed "if (speed == "f" || "F")", you are asking if speed == "f" is true, or the statement "F" is true. "F" is true, so the first line is run. the line should read: if (speed == "f" || speed == "F"){ ... }
10. ### Permutations with BFS

Breadth first should do it too, but at far as I know the algorithm is usually depth first. I think it has to do with memory optimization. You only need one path in memory at one time in the depth first approach, which can be helpful if the graph is "wide". I could be mistaken, but breadth first...
11. ### Permutations with BFS

It's not entirely clear how you attempted to solve it before because you didn't post any sample code, but the type of algorithm used to generate all permutations is called backtracking. (http://en.wikipedia.org/wiki/Backtracking) Maybe you already knew that. The basic idea is you have a...
12. ### How many higgs particles are there in the universe

When we combine quantum mechanics and special relativity, we end up with quantum field theory. Essentially what we learn is that the field and the particle are part of the same thing. Whenever we detect a particle, what we are really detecting is that the field has been excited in that local...
13. ### What courses can I expect after calculus?

There should be some sort of course catalog, or an adviser you can consult. You should check those places. I mean, what textbooks would you order anyways? Wouldn't you want to buy the book that is used in your course? You don't just buy random books do you?
14. ### How to become a genius ?

Different individuals have different levels of intelligence, depending on a variety of factors. But typically the most important factor for success is not intelligence, but work ethic. There are plenty of examples of people who are clearly very smart, but who just can't bother working hard...
15. ### A gentle Introduction on CFT

Presumably someone with more knowledge of the subject will come by, but for a quick intro to CFT almost any string theory textbook has a chapter on it (if I recall correctly, most of the interest in studying CFTs comes from their connection to string theory). It's probably not worth purchasing a...
16. ### Difference in 3rd/4th Year Undergrad Physics

That depends on the school. My university scheduled the 2nd and 3rd year physics courses so you could "double up" on them, and complete the first three years of the major in two. I chose this option, so my first two years covered the standard undergraduate courses, and my last two years were...
17. ### C linked list with an array inside

Think about it at the hardware level: If you need to keep track of say, 9 different arrays, how many arrays would you need to allocate in memory? Each block of memory can only hold one value at a time, so in order for your computer to "remember" what the content of each array is, it needs to...
18. ### Torn Between Money and Passion 12th Grade Year

I was assuming the physics major had taken the time to enroll in fluid dynamics courses. But you are right, both are caricatures of who they were supposed to stand for. The point was just that physics and engineering have different goals, and those differing goals reflect on the skills of the...
19. ### Torn Between Money and Passion 12th Grade Year

A physics degree offers a lot of things. You'll get very good at applied mathematics (depending on the school, you'll be even better than the math majors). You'll become a great problem solver, and most importantly you'll learn how the universe works (to the best of the fields knowledge)...
20. ### Torn Between Money and Passion 12th Grade Year

If you're thinking of Aerospace, you should learn some engineering in college. I don't know if you need an engineering degree or not, but a physics degree doesn't prepare you especially well for engineering work. Modern design techniques are the result of decades of innovation; they aren't...
21. ### Dirac Delta Function

The vector just means that it is a function of x, y, and z. Beyond that, I would say that you should try a bit harder to learn about the delta function without just asking us to explain it. It is typically introduced in either a Quantum mechanics course or an Electromagnetism course...
22. ### Question on Partial Derivative.

Sounds like you have the right idea. The derivative is linear, which means you can calculate it term by term. Just relax and think about it: You are taking a derivative with respect to y. The first term does not depend on y. Therefore the first term will contribute nothing to your final answer...
23. ### Question on Partial Derivative.

I don't think the question is warning you about a "wrong" way to do it. Rather, it seems to be warning against a harder way to do it. The order doesn't matter for getting the right answer, but it does make getting the answer easier. Consider the first term. If you first take the derivative with...
24. ### Quantum uncertainty after passing through a slit

Yeah that's the idea. Basically, what I'm thinking is: what's the furthest in one direction it could be? what's the furthest in the other direction? Presumably the particle is somewhere in between these two points. Also I figured out why the v_z matters: if there was no v_z, then the particle...
25. ### Quantum uncertainty after passing through a slit

Ok, that's right. (I think you should check that it's really supposed to be an initial v_z and not an initial v_y) If you have a range of potential initial y positions, and a range of potential y velocities, how would you compute the range of potential y positions in the future?
26. ### Quantum uncertainty after passing through a slit

I'm not sure I understand this problem entirely but... To start, ignore the z axis. What does the uncertainty in y position tell you about the uncertainty in y momentum?
27. ### Quantum: why can't you square every operator?

For clarity: Griffiths suggests that you do this whenever you compute a commutator. You can extend that rule of thumb to any operator computation: always use a test function for operator equations.
28. ### Quantum: why can't you square every operator?

The last term you forgot that the product rule will be invoked. (d/dx) x is not just 1 because d/dx will also act on the state.
29. ### What background one needs to have to study QFT?

The more prepared you are the better, but I think it would be possible to learn QFT on your background. Keep in mind that QFT builds off of a lot of other fields of physics, so a strong knowledge of electricity and magnetism (if you've never heard of a gauge transformation, your lacking here)...
30. ### Transmission & Distribution Department or Power Generation Department

I'm not an EE person, so I don't know enough about the two different departments to tell you which might be better. However, YOU hopefully do know enough to do so. And since each person is different, you should explain what you like/dislike about Transmission & Distribution, and the same for...