1
vote
1answer
1k views

Hollow Wheels Down a Hill

Lets say I have a hoop of mass $M$ and radius $R$. It is rolling down a hill without slipping, so I don't need to worry about friction doing work on it. Lets say the angular speed is $\omega = ...
1
vote
1answer
124 views

Would a projectile keep going forever in empty space?

Would a projectile fired in space and assuming there were no stars or planets in the way, would the projectile continue on to infinity, since the x-component of the projectile's velocity never changes ...
3
votes
2answers
268 views

2012: Is there some astronomical event happening?

The news media has publicized that 2012 is the end of the Mayan calendar, and that all the planets will be aligned. Is there any truth to this?
0
votes
1answer
337 views

Accelerometer Orientation Conversion

Got two accelerometers that are measuring accelerations oriented at +/- 45 deg from horizontal. I am looking to determine the conversion of the accelerometer measured data to accelerations in the ...
2
votes
1answer
287 views

Can particle physics be represented as an algebra?

Possibly the most useful thing anyone could tell me about particle physics: Naively, one could try and make an algebra by enumerating all the types of particles and defining equivalence relationships ...
2
votes
1answer
373 views

How broad is the term “String Theory”?

How broad is the term "String theory"? Typical brief descriptions of string theory focus on the fact that it describes fundamental particles as being string-like rather than point-like, or, more ...
20
votes
3answers
261 views

Twistors in Curved Spacetime

I am looking for good and recent references to constructing twistor space for curved spacetime. This could be a general spacetime, or specific ones (say maximally symmetric spaces different from ...
7
votes
1answer
959 views

How to turn water opaque by pouring the smallest quantity of matter into it? [closed]

Consider a glass of water and a glass of coffee. Their contents differ by no more than a few grams of particles coming from the roasted and ground coffee, yet the former lets almost all visible light ...
8
votes
3answers
259 views

Which are the simplest known contextual inequalities?

It is well-known that quantum mechanics does not admit a noncontextual ontological model, and there are countless different proofs of it. I'm interested in the simplest proofs that can be cast as an ...
5
votes
8answers
7k views

Definition of “direction”

Is there an actual definition of "direction" (that is, spatial direction) in physics, or is it just one of those terms that's left undefined? In physics textbooks it's always just taken for granted ...
3
votes
2answers
2k views

Classical car collision

I have a very confusing discussion with a friend of mine. 2 cars ($car_a$ and $car_b$) of the same mass $m$ are on a collision course. Both cars travel at $50_\frac{km}{h}$ towards each other. They ...
5
votes
2answers
147 views

Is there any way to anticipate exceptional Aurora Borealis viewing conditions?

I've always wanted to see the Aurora Borealis, but never had the opportunity, since it is so rarely visible in my area (Pennsylvania). However, last week was apparently a rare opportunity of ...
2
votes
1answer
231 views

functional determinant and WKB approximation

let be a Hamiltonian in one dimension, i would like to evaluate the functional determinant $ det(E-H) $ in onde dimension i believe that $ det(E-H)= Cexp(iN(E)) $ here $ N(E)$ is the number of ...
6
votes
6answers
3k views

Is there any anti-gravity material?

I want to know if there is any anti-gravity material. I am thinking of making flying vehicles which are made up of anti-gravity material so that they will not experience any gravity on them and can ...
1
vote
2answers
241 views

Impulse situation

I am wondering if a physical system subjected to an impulse $=A\delta(x-a)$ makes any sense. I reckon that a force could take that form -- thought of as a finite impulse applied over an infinitesimal ...
7
votes
1answer
82 views

What's the most accepted theory for Blue Stragglers These Days?

I'm working on a post against a recent creationism article about blue stragglers. From when I was in undergrad, the general explanation was that they were likely second generation stars within ...
1
vote
1answer
496 views

Poisson's Equation

First up, I needed to compute the potential at some external point due to charge stuffed inside the region between two concentric cylinders, the volume charge density being given. Two methods came to ...
3
votes
1answer
478 views

How far can you get (in quantum mechanics) with just commutation relations?

Clearly it is possible to derive a set of commutation relations from some Hamiltonian, and certainly they give useful and interesting invariants when investigating the behavior of quantum systems. ...
5
votes
6answers
1k views

Why don't experimental physics groups have statisticians in it?

Perhaps someone can clear up a bit a cognitive dissonance I am experiencing. Pollsters are under constant scrutiny of statisticians for even the most mundane of survey topics. With so much riding on ...
4
votes
1answer
628 views

What is / are the primary criticism(s) against Einstein-Cartan-Evans field theory?

What is / are the primary criticism(s) against Einstein-Cartan-Evans (ECE) field theory? On Wikipedia the references provided were: arXiv:physics/0607186, MR2372785 (2008j:83049b), MR2218579 ...
13
votes
2answers
533 views

Renormalization in string theory

I'm taking a course in string theory and have encountered renormalization for the first time (and I suspect it isn't the last). Specifically, while quantizing the bosonic and spinning strings, an ...
3
votes
1answer
676 views

Neon lamp: minimal breakdown voltage

I am looking at this formula from wiki for breakdown voltage in gas discharge lamps, and I see its linear by length (d) (oops, I see it's divided by $ln$) $$\frac{Bpd}{\mathrm{ln}\ Apd-\mathrm{ln}\ ...
4
votes
1answer
135 views

What theories allow for “Tractor Beams”?

NASA recently announced $100k grant to study the possibility of using laser tractor beams. What tractor beam concepts have been published but not been dis-proven?
2
votes
2answers
4k views

Voltage and Current in transformers

In transformers, the ratio of the voltages equals the ratio of the turns - so double the output coil's turns and the output voltage doubles. Then, in order to conserve energy, current halves. This ...
2
votes
1answer
117 views

Creating/Downloading a large Galaxy Dataset

I was wondering where I can get a more or less complete set of a galaxy to test an n-body simulation (preferably two colliding galaxies with approx 300k to 1M elements). Is it possible to extract ...
4
votes
1answer
377 views

Avogadro's number

Could I get an explanation of Avogadro's number and how it relates to determining the mass of a substance? My chemistry textbook only serves to confuse me and the Wikipedia article is aimed towards a ...
4
votes
1answer
237 views

1D Wave mechanics (string)

Suppose I have a wave traveling to the right described by $e^{iw(t-{x\over c})}$. (It obeys the 1D wave equation). AND at $x=0$, there is a mass $M$ fixed to the string such that we have $M{d^2y\over ...
12
votes
2answers
338 views

Holographic Renormalization in non-AdS/non-CFT

In AdS/CFT, the story of renormalization has an elegant gravity dual. Regularizing the theory is done by putting a cutoff near the conformal boundary of AdS space, and renormalization is done by ...
25
votes
1answer
969 views

State of Matrix Product States

What is a good summary of the results about the correspondence between matrix product states (MPS) or projected entangled pair states (PEPS) and the ground states of local Hamiltonians? Specifically, ...
2
votes
3answers
302 views

mirror house gedanken experiment

Imagine a mirror house i.e. completely made of mirror with no traces of whatsoever light absorbent. Now, you introduce a light beam into that room and observe somehow through a hole. Would the room ...
1
vote
2answers
519 views

What is a good introductory text to astronomy [closed]

What is a good and easy to read introductory text for an adult with limited basic scientific knowledge to astronomy for someone without a telescope and lives in a big city and why do you think that ...
3
votes
2answers
808 views

The Energy-Momentum Tensor and the Ward Identity

I have a question regarding a homework problem for my quantum field theory assignment. For the purposes of the question, we can just assume the Lagrangian is that of a real scalar field: ...
4
votes
1answer
522 views

Compound lenses and virtual images

Ok so I have this problem where I have a system of two lenses. All I know is that the distance between the object and the first lens is 30cm, the distance between the object and the final image is ...
1
vote
1answer
246 views

why evaluate at lambda = 0

I am trying to understand Herbert Goldstein's introduction to 4-vectors. He describes a 1-D curve in spacetime $ P_(\lambda) $ then he says a 4 vector is defined as the tangent vector to this curve ...
13
votes
2answers
189 views

Decoherence and measurement in NMR

It seems that the Bloch equations, or a suitable generalization thereof, are enough to phenomenologically model the measurement process in NMR. Has anyone attempted a fully quantum mechanical model ...
4
votes
1answer
417 views

Numeric method to calculate the charge distribution on a conducting surface?

If I have an arbitrary (closed?) conducting surface and a nearby charge density, is there a simple numeric way of computing the induced charge distribution on the surface?
2
votes
1answer
66 views

On the topic of action and reaction

So, let's say we have a spacecraft in deep space. It activates its rocket engines, to keep it simple. The engine reaction channels exhaust through the aft nozzle, right? How does that chemical ...
8
votes
1answer
120 views

Finding two dimensional critical point

I'm reading an article about bi layered membranes which state that for the free energy function $f(\theta) = \theta \ln \theta + (1-\theta)\ln(1-\theta) + \chi \theta (1-\theta)$ Where $\phi_i$ is ...
1
vote
2answers
2k views

Is it true that our solar system belongs to another galaxy which collides with the milky way galaxy?

I have just read an article about it here(http://www.greatdreams.com/2012.htm)(Scroll to bottom). I'm just a website developer, and I really want to know if this is really true. I'm curious. I'm ...
6
votes
1answer
1k views

The gravitational potential of ellipsoid

In the literature (Kirchhoff G. - Mechanic (1897), Lecture 18 or Lamb, H. - Hydrodynamics (1879)) one can find the following analytical closed form expression for the gravitational potential of ...
3
votes
2answers
513 views

What is the mathematical formulation for buckling?

Argument: Buckling is an engineering concept that can only be applied to thin columns with compressive loading. (Is it possible to) Prove the above sentence right or wrong with mathematical ...
1
vote
0answers
37 views

Conveyor scales modeling [duplicate]

Possible Duplicate: Conveyor scales modeling Assume we have a conveyor scales. Which consists of scales, and motor with conveyor belt placed above, so that the boxes can be measured ...
1
vote
2answers
2k views

Measuring the Electromotive Force and Internal Resistance of a Battery?

Here is a problem that emerged some time ago: We needed to measure the emf(electromotive force) and internal resistance of a car battery. The only instruments were voltmeter and ammeter. ...
3
votes
0answers
660 views

What formulae for calculating fluid pressure change involves these parameters? [closed]

Okay... this is a bit desperate... I am reverse engineering an excel program that is used for calculating outputs for a pressure vessel used for industrial process fluid heating. There is a part in ...
6
votes
4answers
542 views

Interpretation of Wigner function in optics

I work in the field of synchrotron radiation sources where radiation (often x-rays) is produced from an electron beam going through magnetic fields. The quality of the resulting x-ray beam is ...
9
votes
2answers
2k views

What is the minimum wavelength of electromagnetic radiation?

As a first approximation, I don't see how a wavelength of less than 2 Planck distances could exist. The question is: Are there any other limits that would come into play before that? For example: ...
13
votes
4answers
52k views

Does the rotation of the earth dramatically affect airplane flight time?

Say I'm flying from Sydney, to Los Angeles (S2LA), back to Sydney (LA2S). During S2LA, travelling with the rotation of the earth, would the flight time be longer than LA2S on account of Los Angeles ...
1
vote
0answers
159 views

Conveyor scales modeling

Assume we have a conveyor scales. Which consists of scales, and motor with conveyor belt placed above, so that the boxes can be measured (weight) while moving above. What I want is to create the model ...
5
votes
4answers
6k views

Torque vs Moment

I was wondering, why in Newtonian physics torque is called "torque" while in static mechanics they call it "moment"? I prefer by far the term "torque", for not only it sounds strong, but also ...
3
votes
2answers
848 views

Why did Schrodinger never budge on the meaning of $|\Psi|^2$

Schrodinger believed that the phisical interpretation of the wavefunction $\Psi$ was the vibration amplitude and $ |\Psi|^2 $ was the electric charge density. While no-one disagrees with his ...

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