## Search found 100 matches

- Tue Sep 23, 2014 9:55 am UTC
- Forum: Science
- Topic: what to study to be a string theorist?
- Replies:
**9** - Views:
**3650**

### Re: what to study to be a strig theorist?

But for a graduate degree you would (at least in the US) be solely in a physics dept rather than a math dept. And you would want a PhD, a master's in theoretical physics is silly. Thanks for responding, what kind of master would you recomend me? or go direct to the phd? :) Outside the US you might ...

- Wed Dec 11, 2013 6:51 pm UTC
- Forum: Mathematics
- Topic: condition for Det of order 2n =0
- Replies:
**5** - Views:
**2084**

### Re: condition for Det of order 2n =0

Alright. I gave the answer to your question implicitly, but since you didn't pick up on my post, t assume you might not know what linear dependence is. So here we go. A bunch of vectors, let's call them A, B, C, D are linearly dependent if there are numbers - which we will call s, t, u, v such that ...

- Wed Dec 11, 2013 4:02 pm UTC
- Forum: Mathematics
- Topic: condition for Det of order 2n =0
- Replies:
**5** - Views:
**2084**

### Re: condition for Det of order 2n =0

Recall that determinants are zero if and only if the row- or column-vectors are linearly dependent.

EDIT: Fixed a typo - I wrote "linearly independent"...

EDIT: Fixed a typo - I wrote "linearly independent"...

- Mon Dec 09, 2013 1:54 am UTC
- Forum: Mathematics
- Topic: Question about differential equations!
- Replies:
**5** - Views:
**2327**

### Re: Question about differential equations!

evinda wrote:Is it right so far??And how can I continue?

It's what I got. However, something must be wrong, or you need to do something pretty damn fancy. I asked mathematica to compute the limit and didn't get anything sensible.

- Wed Dec 04, 2013 11:42 pm UTC
- Forum: Mathematics
- Topic: Line bundles over complex projective space
- Replies:
**2** - Views:
**2342**

- Tue Nov 12, 2013 1:12 am UTC
- Forum: Science
- Topic: Matter/Antimatter Symmetry--a tricksy proposal
- Replies:
**38** - Views:
**8373**

### Re: Matter/Antimatter Symmetry--a tricksy proposal

Dude. Just no.

What you're doing is like saying: "If the British call left right and right left, all the Europeans drive on the same side of the road!"

Changing the name for a thing doesn't change the thing.

What you're doing is like saying: "If the British call left right and right left, all the Europeans drive on the same side of the road!"

Changing the name for a thing doesn't change the thing.

- Tue Nov 12, 2013 1:01 am UTC
- Forum: Mathematics
- Topic: Dogma in Math
- Replies:
**98** - Views:
**15042**

### Re: Dogma in Math

Uh. It doesn't really matter, but since people seem to be lining up at the end of this thread to tell frog how apparently inappropriate his way of questioning was: I don't agree with what people are writing here. His initial posts contains the obvious clumsy, ill-conceived, and ill-advised attempt a...

- Mon Nov 11, 2013 10:15 am UTC
- Forum: Mathematics
- Topic: Capability to do mathematics.
- Replies:
**7** - Views:
**2083**

### Re: Capability to do mathematics.

So, Any tips or reassurances? What kind of abstract/mathematical mind is really expected from someone who is going to dabble in the areas of Physics (and it's sub parts like astrophysics, quantum physics, etc)? Without sounding condescending: Not that much. You might have heard that research in mod...

- Sun Nov 10, 2013 12:24 am UTC
- Forum: Mathematics
- Topic: Idea for using pi approximations to get close to 1
- Replies:
**24** - Views:
**6729**

### Re: Idea for using pi approximations to get close to 1

What if instead you take the actual value of pi divided by the pi approximation (or vice versa) to get a value that is close to 1. I'm not quite sure what you're trying to do here. However, it might be worthwhile to point out that you cannot play with the value of pi. (We had a student who thought ...

- Fri Nov 08, 2013 11:10 am UTC
- Forum: Mathematics
- Topic: Dogma in Math
- Replies:
**98** - Views:
**15042**

### Re: Dogma in Math

Dude... I'm on Lesson 3 of Intro to CS. No need to go all drill sergeant on me yet. The exercises right now are to focus on some new, small tidbit and encourage thinking about how problems can be broken out and described. Best practices will have to wait until I've actually learned a few practices....

- Thu Nov 07, 2013 11:33 pm UTC
- Forum: Mathematics
- Topic: Dogma in Math
- Replies:
**98** - Views:
**15042**

### Re: Dogma in Math

@tooyoo: I actually looked at that n!/(k! (n-k)!) business, and it works just as well if 0! = ( ). Nope. Doesn't. As you wrote somewhere else, you'd rather define 0! to be the empty set which you denote "()". However, multiplication with and division by a set - least of all the empty one ...

- Thu Nov 07, 2013 7:27 pm UTC
- Forum: Mathematics
- Topic: Dogma in Math
- Replies:
**98** - Views:
**15042**

### Re: Dogma in Math

Nice. Personally I'd rather stick with exactly zero bricks, for which there are exactly 0! results to insert them (hint: not at all = 1). On a more serious note: Look up the wikipedia article on binomial coefficients, look at the interpretation in terms of combinatorics. You'll find something along ...

- Tue Nov 05, 2013 8:49 am UTC
- Forum: Mathematics
- Topic: Is this ambiguous? Is it fallacious?
- Replies:
**92** - Views:
**19390**

### Re: Is this ambiguous? Is it fallacious?

Interesting. I hadn't known that Verlinde's paper had made impact in condensed matter circles. I haven't heard much about the whole story in a while, yet last time I discussed this with somebody I got the idea that wikipedia is right (regarding the controversy).

- Mon Nov 04, 2013 9:47 pm UTC
- Forum: Mathematics
- Topic: Is this ambiguous? Is it fallacious?
- Replies:
**92** - Views:
**19390**

### Re: Is this ambiguous? Is it fallacious?

As physics has progressed we have recognised that the macroscopic view of matter doesn't hold at microscopic scales. But the same realisation hasn't been applied to space (vector space) at small scales. The Euclidean Geometry that originally arose from Macroscopic observations at the Earth's surfac...

- Mon Nov 04, 2013 6:13 pm UTC
- Forum: Mathematics
- Topic: Is this ambiguous? Is it fallacious?
- Replies:
**92** - Views:
**19390**

### Re: Is this ambiguous? Is it fallacious?

What is "real space"? This is probably the first time in my life that I regret not having read the first volume of Weinberg ("The quantum theory of fields"), but I was always under the impressions (a) that the cluster decomposition principle was a crucial ingredient in quantum f...

- Sun Nov 03, 2013 10:49 pm UTC
- Forum: Mathematics
- Topic: Line bundles over complex projective space
- Replies:
**2** - Views:
**2342**

### Line bundles over complex projective space

Hi. I've been studying a bit of complex geometry lately - mainly reading parts of Huybrechts and the first volume of Voisin - and I have a hand full of questions that I'd like to clarify. I think they're not specific enough for stackexchange, so maybe someone can comment on them here. Thanks in adva...

- Sun Oct 27, 2013 10:03 pm UTC
- Forum: Science
- Topic: Energy-time uncertainty relation
- Replies:
**1** - Views:
**1805**

### Re: Energy-time uncertainty relation

I think there's a bunch of people on this forum who can answer this much better than I can. Since none of them is answering your question though, I can maybe give a first approximation to an answer... The energy-time uncertainty relation isn't a normal kind of uncertainty principle in non-relativist...

- Sat Oct 26, 2013 7:31 pm UTC
- Forum: Science
- Topic: Why do we perceive a 4-dimensional universe as 3?
- Replies:
**98** - Views:
**16055**

### Re: Why do we perceive a 4-dimensional universe as 3?

Tchebu wrote:People don't really solve Einstein's equations... they look up the solutions in a big blue book

Nice.

Of course some solutions haven't made it into that book yet, so that some people make a decent living out of finding them.

- Sat Oct 26, 2013 5:34 pm UTC
- Forum: Science
- Topic: Why do we perceive a 4-dimensional universe as 3?
- Replies:
**98** - Views:
**16055**

### Re: Why do we perceive a 4-dimensional universe as 3?

And quantum mechanics (nevermind qft) is significantly more complicated than relativity, even general relativity. GR is still classical. The curved space mathematics can be a bit intricate but it's still very much a classical smooth geometry where things proceed nicely, just along some curvy geodes...

- Sat Oct 26, 2013 10:41 am UTC
- Forum: Science
- Topic: Why do we perceive a 4-dimensional universe as 3?
- Replies:
**98** - Views:
**16055**

### Re: Why do we perceive a 4-dimensional universe as 3?

I'm not trying to "reason from intuition to QM", as you say you can't really do that. I'm looking for easily teachable approaches to QM (at least, at the high-school or freshman physics level) that won't need to be un-learned by those inspired to go further. There is far too much "th...

- Sat Oct 26, 2013 10:19 am UTC
- Forum: Science
- Topic: Miscellaneous Science Questions
- Replies:
**2962** - Views:
**730926**

### Re: Relativity

keenin wrote:My question is can the person in the spacecraft make the opposite happen? So instead of time slowing down for the person in the spacecraft time speeds up for the guy in the spacecraft.

Nope.

- Tue Oct 22, 2013 1:33 am UTC
- Forum: Science
- Topic: Why do we perceive a 4-dimensional universe as 3?
- Replies:
**98** - Views:
**16055**

### Re: Why do we perceive a 4-dimensional universe as 3?

I'm trying to get away from things that make little intuitive sense. a "field that describes the probability that there's an electron at any given place" seems rather circular and non-informative an an answer to "what is an electron?" Sure, it works , no arguments there. But it'...

- Tue Oct 15, 2013 9:37 am UTC
- Forum: Science
- Topic: "Center of mass" of humanity
- Replies:
**8** - Views:
**3694**

### Re: "Center of mass" of humanity

Well, I think it's pretty safe to say that nobody has calculated this yet. And that there's no name for it. At least that's what I'd guess since I cannot really think of a good reason why this would be interesting. So yeah, I guess you'll have to calculate it yourself. Which should be sort of straig...

- Mon Oct 14, 2013 11:52 pm UTC
- Forum: Science
- Topic: Why do we perceive a 4-dimensional universe as 3?
- Replies:
**98** - Views:
**16055**

### Re: Why do we perceive a 4-dimensional universe as 3?

Why do I have to perceive the universe moment-by-moment, instead of perceiving my entire timeline at once, like Dr. Manhattan? Actually, neither is correct. Strictly speaking you're not perceiving the universe moment by moment, nor in its entirety. Think about it. Let's say you're sitting in a room...

- Wed Oct 09, 2013 10:58 pm UTC
- Forum: Science
- Topic: Gravitational time dilation at the center of a planet...
- Replies:
**37** - Views:
**8163**

### Re: Gravitational time dilation at the center of a planet...

i guess it's clearer if you think about it in terms of potential difference.

- Fri Sep 13, 2013 1:37 pm UTC
- Forum: Language/Linguistics
- Topic: disc over = discover
- Replies:
**3** - Views:
**2550**

### Re: disc over = discover

I thought the etymology was "disco - ver". The moment you can see a club from the other end of the street and can estimate how long the queue is. A discovery made anew any time you head out.

- Tue Aug 27, 2013 2:15 pm UTC
- Forum: Science
- Topic: Singularities and gravity
- Replies:
**39** - Views:
**11483**

### Re: Singularities and gravity

Always wondered...both a neutron star and a singularity are collapsed stars. Why does one form a black hole and the other just a neutron star out there spinning, like the Crab? Mass of the object? Yes. There might be something deeper here if you do proper astrophysics, but from the point of view of...

- Fri Aug 23, 2013 9:05 am UTC
- Forum: Science
- Topic: Dark Matter and Novel Forces
- Replies:
**4** - Views:
**2099**

### Re: Dark Matter and Novel Forces

In principle: What Andy said. He's a god, after all. And, if nothing, has anybody written anything about the possibility? Since you're asking for people who've written about this, I also pulled up some random lecture notes on supersymmetry that include sections on mediation of SUSY breaking from a h...

- Wed Aug 21, 2013 9:27 am UTC
- Forum: Science
- Topic: There is only one* model consistent with CPT Symmetry
- Replies:
**129** - Views:
**39639**

### Re: There is only one* model consistent with CPT Symmetry

As such, you can't [...] dismiss my assertion that there is only one system consistent with XYZ Symmetry. So what. You use some sort of Schur's Lemma type of argument to state that all representations of some algebra are equivalent. But they're equivalent as representations. That's it. That doesn't...

- Tue Aug 13, 2013 6:24 pm UTC
- Forum: Science
- Topic: There is only one* model consistent with CPT Symmetry
- Replies:
**129** - Views:
**39639**

### Re: There is only one* model consistent with CPT Symmetry

Is there a place where we get to rank how good a crackpot thread is? Or is it just determined by the number of replies? Jup. There's John Baez's crackpot index . Alternatively you could come up with your own index based on Warren Siegel's comments . I think 't Hooft might have also something on his...

- Wed Jul 31, 2013 9:22 am UTC
- Forum: Science
- Topic: Fundamental Forces Question
- Replies:
**8** - Views:
**5771**

### Re: Fundamental Forces Question

Awesome, thanks Schrollini! So Maxwell didn't unify them, special relativity did! There's a pretty good Stanford set of lectures I just found that'll help, thanks! Well. Not quite. Take a look at how the electromagnetic wave equations are derived. While both wave equations seem to include only the ...

- Fri Feb 22, 2013 5:28 am UTC
- Forum: Science
- Topic: Styer's "The Strange World of Quantum Mechanics"
- Replies:
**4** - Views:
**1302**

### Re: Styer's "The Strange World of Quantum Mechanics"

Ah. I don't know of anything for quantum mechanics that filled this gap (i.e. non-student/specialist books with some mathematics). Penrose tried this for high energy theory in "The Road to Reality", but in my opinion it's a more challenging read than Feynman's lectures. As a starter, you m...

- Wed Feb 20, 2013 2:29 am UTC
- Forum: Science
- Topic: Styer's "The Strange World of Quantum Mechanics"
- Replies:
**4** - Views:
**1302**

### Re: Styer's "The Strange World of Quantum Mechanics"

unfortunately i haven't read the book. so feel free to ignore anything i'm writing. still here? well. the point i'd like to make is that it's virtually impossible to actually understand some physics without using a little maths. since styer seems to be doing exactly that, i'd recommend that you read...

- Fri Feb 08, 2013 7:12 am UTC
- Forum: Science
- Topic: Four-body Celestial Mechanics Problem
- Replies:
**24** - Views:
**4110**

### Re: Four-body Celestial Mechanics Problem

I thought about this for 5 minutes. Honestly, I don't think it's possible to have a setup that guarantees "always light". Sure you can assume some symmetry, as krogoth did, but that will usually not be stable. Moreover, even if you find stable orbits (you should be able to do so by "c...

- Tue Jan 08, 2013 4:33 am UTC
- Forum: Science
- Topic: Popular unified relativity/quantum theories?
- Replies:
**3** - Views:
**2020**

### Re: Popular unified relativity/quantum theories?

In addition:

While citation metrics are not the most important thing in the world, I did quickly take a look at citations for the papers that the phys.org article is based on. And the only one who cited them is the guy who wrote them, which is usually a bad sign.

See here, for example.

While citation metrics are not the most important thing in the world, I did quickly take a look at citations for the papers that the phys.org article is based on. And the only one who cited them is the guy who wrote them, which is usually a bad sign.

See here, for example.

- Mon Jan 07, 2013 7:07 am UTC
- Forum: Science
- Topic: Popular unified relativity/quantum theories?
- Replies:
**3** - Views:
**2020**

### Re: Popular unified relativity/quantum theories?

The Grand Unified Theory, mythical yet quite real Holy Grail of physics. The biggest well identified break is, so far as I know, that between Quantum Mechanics (Standard Theory or what have you) and General Relativity. Just to get the terminology right: What you're asking about is usually referred ...

- Mon Dec 17, 2012 7:42 am UTC
- Forum: Science
- Topic: What is a wave?
- Replies:
**13** - Views:
**2314**

### Re: What is a wave?

Have you really never heard of the media? :) Amazingly I have. Some time last week, I think. Apparently I read your post too quickly though. Apologies. Having said that, your own post ends up considering the vacuum as a medium, which is really not a good terminology. In your abstract definition it ...

- Mon Dec 17, 2012 6:00 am UTC
- Forum: Science
- Topic: What is a wave?
- Replies:
**13** - Views:
**2314**

### Re: What is a wave?

The whole worrying about the medium complicates things. Let's start with something simple: When you think of a wave, it's perfectly fine if you think of macroscopic mechanic phenomena such as - Oscillations travelling along a spring - Waves in water Note that in both cases there is a medium, but it'...

- Wed Dec 12, 2012 7:45 am UTC
- Forum: Science
- Topic: Magnets: how do they work?
- Replies:
**9** - Views:
**3961**

### Re: Magnets: how do they work?

As far as I know, it's impossible to get a decent understanding of magnetism without some quantum mechanics. Which is why all explanations given in high school or undergraduate courses tend to be flawed. To be fully honest, I never bothered studying the glorious details, but magnetism is actually a ...

- Wed Dec 12, 2012 4:20 am UTC
- Forum: Science
- Topic: What is a wave?
- Replies:
**13** - Views:
**2314**

### Re: What is a wave?

If the above is true, how can there be waves without a medium? Your initial description/definition of what a wave is is flawed. I.e. there is no need for a medium. I think the problem might be that you're trying to think about these things in a mechanical way - e.g. particles pushing and pulling ag...