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I am wondering: If I have a regular octahedron as my starting point, oriented along the x-y-z axis, and now Jahn-Teller suggest I elongate or compress along the $z$-axis, what happens along the other axis? I expect that these move in the opposite direction, but by how much? Say my displacement in $z$-direction is $\del... |
Extending my previous question Angular moment and EM wave, does it make sense to talk about the angular momentum of electromagnetic waves in an anisotropic medium? It is not obvious that the angular momentum is conserved in this case. However, if the anisotropy is introduced by the external magnetic field (eg, magnetiz... |
Just wondering about the definitions and usage of these three terms.
To my understanding so far, "covariant" and "form-invariant" are used when referring to physical laws, and these words are synonyms?
"Invariant" on the other hand refers to physical quantities?
Would you ever use "invariant" when talking about a law? ... |
There is a known thought experiment, connected to quantum immortality: a duel between physicist and a philosopher.
Each turn physicist and philosopher fire at each other with a pistol. The quantum immortality predicts that each of the participants will find themselves alive and the opponent dead after a number of shot... |
I have a problem with energy conservation in case of interfering waves.
Imagine two harmonic waves with amplitudes $A$. They both carry energy that is proportional to $A^2$, so the total energy is proportional to $2A^2$. When they interfere, the amplitude raises to $2A$, so energy is now proportional to $4A^2$ and bigg... |
For the last few years, My friend worked on figuring out the "theory of everything". She is afraid of sharing her theory with well known physicists, because she doesn't want other people to take credit for her idea. So, my here's what I'm wondering:
1) What is the best way for her to validate her theory with experience... |
Question 7584 illustrated a procedure to forecast the decay rates of isotopes with known long average lifetimes. Lifetimes of the many U isotopes vary from micoseconds to gigayears. F has only one stable isotope while Sn has 10. Can Standard Model principles be used to predict the stability of isotopes and the average ... |
With this being a potentially subjective question I know I'm threading on thin ice, but this is an actual "physics" problem I face from time to time:
The situation is this: I hear about some phenomenon. For the sake of definiteness, let's say it is the Jahn-Teller-Theorem. I'd then like to find a good source that has a... |
SWITL - what could this be? Ultra thin paper with some adhesive that binds to fat? (or as I originally thought, a hoax)?
A robotic hand to scoop gel-like substances...
http://japantechniche.com/2009/06/09/the-world-first-robotic-hand-scoop-switl/
Truly weird video - looks like some kind of super gluey paper
http://fur... |
I'm interested in the size of atoms (extent of the outermost electron cloud), in particular its cross-sectional area and how it scales by increasing Z. (I trust that this won't be affected much by the number of neutrons?)
I recognize that for a given atom/ion one can simply look up the data, but I'm interested in a mo... |
usually on physical theories one would have Lagrangians or Hamiltonians with multiple fields; say, a vector $A_{\mu}$ and a scalar $\phi$ and one would postulate ad hoc a coupling between the fields which will be used to derive some physical states and then, retroactively support the coupling from a match with the phys... |
The curve for a chain hanging between two poles in a uniform gravitational field is known as the catenary.
Is there known an expression for the curve of a hanging chain on a planet of mass $M$ which has a gravitational field of $M/r^2$ ?
Let the rope have length $L$, uniform mass-density $\rho$ and negligible thickness... |
How can we calculate the change in distance over time between (say) two galaxies that they are at rest in respect to each other?
In other words, how do we modify the "classical" equation:
$$ \ddot{\mathbf{r}} = -G\frac{\mu}{|r|^2}\hat{\mathbf{r}} $$
to take into account expansion, $G$ changes over time, etc?
|
I am interested in theoretical and practical considerations.
|
Is it something unexpected?Why universality in cold atomic gases is important?What researches are looking for?Can this be useful for topological quantum computers?
Can we expect a whole myriad of these states?
http://arxiv.org/abs/1012.2698
thanks
|
I am going to learn some math about functionALs (like functional derivative, functional integration, functional Fourier transform) and calculus of variation. Just looking forward to any good introductory text for this topic. Any idea will be appreciated.
|
At first I thought it's because of Coriolis, but then someone told me that at the bathtub scale that's not the predominant force in this phenomenon.
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If I have an ocean with constant temp 10 degrees celcius and I throw in an 8 gram iron ball that's 50 degrees celcius, I'd like to find how to calculate the amount of energy that flows into the water before equilibrium.
How would I go about doing this?
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There are many stories about radioactivity and the relative danger of it in the news lately, but very little actual information. The radioactivity levels around Fukushima Daiichi are high, but seem negligible in just somewhat removed locations.
The real danger seems to stem from ingesting radioactive particles. Just ho... |
on the wikipedia article about the equivalence principle there is a mention about testing the EP against parity-violating masses;
"The equivalence principle is untested
against opposite geometric parity
(chirality in all directions) mass
distributions. A parity Eötvös
experiment contrasting solid single
crys... |
If you take apart a syringe you are left with one piece that is a tube with a tiny hole in one end and the open end of a tube at the other. If you then submerge this underwater and cover the small hole, then lift out of the water, the water remains in the tube/syringe until you release your finger from the small hole. ... |
Suppose you have two thermodynamical systems $X_1$ and $X_2$ (for example water and air) with different temperatures ($T_1 > T_2$). Now put them into thermal contact. Is there a formula which describes, how $T_1$ and $T_2$ changes with time?
|
What does it mean to "weakly gauge" a global symmetry in a gauge theory? I have seen this term used in a number of papers, but have not seen it defined.
|
In discussion of LHC searches for SUSY particles, physicists seem to assume they will decay quickly to the lightest SUSY particle which then remains stable (at least within the time it takes to leave the detector). As an example: http://physics.aps.org/articles/v4/27
The stability of the lightest SUSY particle is desi... |
In 2006 the IAU deemed that Pluto was no longer a planet because it fails to "clear" the neighborhood around its Kuiper Belt orbit. Presumably, this is because Pluto (1.305E22 kg) has insufficient mass to do the job. How massive must a body in Pluto's orbit (semi-major axis 39.5 AU) be to "clear" its orbit? Would Mars ... |
I am speaking about GR with classical fields and energy. One question, spread over three increasingly strict situations:
Is there an energy density limit in GR? (literally, can the energy density have an arbitrarily large value at some point in space at some point in time)
Is there an energy density limit beyond which ... |
This is not a question pertaining to interpretations, after the last one I realized I should not open Pandora's Box ;)
For theories to be consistent, they must reduced to known laws in the classical domains. The classical domain can be summed up as:
$$\hbar=0 ; c=\infty$$
Which is OK. I need to know, however, is that... |
Here's a question inspired by Edward's answer to this question.
It's my understanding that the average energy density of a black hole in its rest frame is $\rho_\text{BH}(A)$, a function of surface area. I calculated $3c^2/2GA$ for a Schwarzschild black hole, but that's presumably not applicable here since I'm talking... |
To maintain the surface tension which formed our original bubble (in order to keep the bubble from breaking), we may change the temperature/pressure of air on both sides of the bubble varyingly, with different rates.
Is such a configuration possible? Examples of any such system?
|
Whenever I read about the curvature of spacetime as an explanation for gravity, I see pictures of a sheet (spacetime) with various masses indenting the sheet to form "gravity wells." Objects which are gravitationally attracted are said to roll down the curved sheet of spacetime into the gravity well. This is troubling ... |
I don't know how to ask this more clearly than in the title.
|
So, there is a sound at $S$, whose intensity $I$ obeys the inverse square law ($I \sim \frac{1}{x^2}$). At point $P$, at a distance $r$ from $S$, the air molecules oscillate with an amplitude of $8μm$. Point $Q$ is at a distance of $2r$ from $S$. What is the amplitude of the air molecules at $Q$? What is the relationsh... |
I'm currently reading a nice introductory book (german, could be translated as "Physics with a pencil"). The author works a lot with differential calculus and antiderivatives (integrals will be used later). I'm stuck at a kind of mathematical question inmidst the easier physics:
So he takes the equation of force:
$m \d... |
I.e. online discussion with your friends. A forum is probably too overkill in this case.
Yet so far nothing can beat direct communication.
Important feature: the ability to archive discussions. We don't want to retell our story to people who just missed the "conference" (let the newcomers dig through the archives by th... |
Firstly, I understand that we have no observational evidence for 'wormholes'. They are theorised solutions to general relativity equations.
That said, if macroscopic wormholes do exist---how do they work? I've been thinking about this for the past couple of days, and I have some questions.
What does the mouth of a wor... |
In the book "Kinetic theory in the expanding Universe" (J. Bernstein, 1988, Camb. Univ. Press), it was stated that
"for nonstationary Robertson-Walker
matrixes [sic] there is no spacelike
Killing vector."
(page 6, footnote.)
But we know this is not true, since one can see that the generators of spatial translati... |
Given: Law of Conservation of Angular Momentum.
Reverse spinning with dense atmosphere (92 times > Earth & CO2 dominant sulphur based).
Surface same degree of aging all over.
Hypothetical large impact is not a sufficient answer.
Assuming any object large enough to alter a planets rotation or even orbit would likely d... |
This paper was published in a peer review journal, and claims the answer is yes.
http://arxiv.org/abs/physics/0607090
The derivation in the paper seems more like dimensional analysis hand-waving in the beginning. But then uses some specific results from differential geometry to uniquely get to Einstein's field equatio... |
Time travel -- often featured in movies, books, or facetiously in conversation. There are also theories treating time as simply another dimension, which to the layperson might imply forward and backward movement is possible at will.
But what do we know scientifically with respect to the possibility or impossibility of ... |
I'm working with a megapixel sensor with a 1/2" format. I would like to know which parameters have to be taken into account in order to design a lens that can be fit with 1/2" format.
The light source wavelenght is 850 nm produced by high power leds.
The working distance is about 15 meters.
Thanks,
Raphael
|
What is the minimum thickness of an aggregate concrete membrane to prevent radioactive particles from escaping a broken reactor?
I am interested in calculating the amount of concrete required to entomb a reactor.
|
With the notion of causality, firmly fixed by GR, we derived the concept of a singular point from where space-time begun. Causality alone gives us the possibility to talk about a known past (i.e. every effect has a cause) and by this we can trace back in time every event. To reach the moment of the Big Bang we only hav... |
According to some source or other (I forget which now) it is theoretically impossible for bumblebees to fly by virtue of their size/bulk/aerodynamic properties. Is this old adage apocraphyal or true? And if its true, how come they do fly?
|
We’re told that ‘all forces are gauge forces’. The process seems to start with the Lagrangian corresponding to a particle-type, then the application of a local gauge symmetry leading to the emergence of the force bosons via the associated symmetry group.
But where did exactly four forces come from? Could new, perhaps s... |
Say that I have 2 qubits - 2 spin half fermions.
my initial condition is $|00\rangle$ in the spin-wave function and some anti-symmetrical spacial wave function.
I'm wondering about what happens when applying a NOT gate. The Fermions total wave function still has to be inverted when swapping the particles. so does it me... |
Suppose you have semigroup instead of typical group construction in Noether theorem. Is this interesting? In fact there is no time-reversal symmetry in the nature, right? At least not in the same meaning as with other symmetries (rotation, translation etc). So why we construct energy as invariant of such kind of group ... |
Does salt water conduct mostly by the ions travelling through the solution, or by electrons collectively flowing or hopping through the solution like in metals?
|
I have seen in popular media, claims that Hawking does not believe the Higgs boson exists due to microscopic black holes and even made a bet against it. This is based on something published in journal Physical Review D.
I don't have access to journal Physical Review D, and I can't find a clear detailed explanation wha... |
I am trying to reconcile data that I have found in one publication (Allen 1969) with data that I found in another publication (George 2003) that synthesized this data. The
data is root respiration rate, it was originally measured at $27\ ^\circ C$.
Approach
I am trying to convert a rate of oxygen consumed as volume p... |
Please note, I am only interested in classical mechanics discussion on this. Please do not involve quantum mechanics.
Inspired by this question: Is Angular Momentum truly fundamental?
My question is:
Can there be a concept of angular momentum separate from "orbital" angular momentum in classical mechanics? For exampl... |
Why does the air we blow/exhale out from our mouths change from hot to cold depending on the size of the opening we make with our mouth?
It's not just a subtle difference, but significant in my opinion. I'm inclined to discredit the notion that it's just a matter of speed because I can blow fast with an open mouth and ... |
Since strings are extended objects, is all angular momentum in string theory essentially "orbital" angular momentum? Or is there still a kind of intrinsic angular momentum assigned to a string?
Either way, is there anything that prevents the "intrinsic spin" of a particle represented by a string from being arbitrari... |
What are the major recent findings and their corresponding contributions to an overall picture?
How well explained are the various regions of the dome, is there any thing that is pretty well understood?
What is left and how are people trying to figure it out?
|
While the microscopic mechanism leading to type II superconductivity is still debated, do scientists at least have a handle on the phenomonology?
Specifically, are the experimental properties of type II superconductivity understood well enough that it is possible in principle for the properties of a newly discovered ma... |
Consider a pendulum, consisting of a string of length $l$ tied to a ball of negligible mass and radius $r$. The bob is filled with water, which has density $d$, and the pendulum is given a small push and left to oscillate. There is no friction or damping.
This is an analysis I've heard during a high school class. Quali... |
When I look at pictures taken by a modern spacecraft (like that one showing the surface of Titan:
and taken by Cassini) I kinda understand how they might be produced. There might be some kind of CCD sensor installed and the data is later transmitted to Earth.
But then I think about it I start to wonder how cameras w... |
What makes zinc so desperate to give up its electrons? Silver has one extra electron, and zinc has two, but why is zinc more reactive?
|
My wife's kindergarten class asked, "What would happen to a tree planted on the moon?" Aside from the obvious that it would die from lack of water/air, what physical effects would happen to a tree exposed to the vacuum of Space?
|
Because of the apparent discrepancy of how some CFT and GR books define conformal transformation unlike in string theory area, I wanted to get rid of all the confusion from McGreevy's lecture notes:
http://ocw.mit.edu/courses/physics/8-821-string-theory-fall-2008/lecture-notes/lecture10.pdf
I have understood and happ... |
I'm working through Polchinski's book on string theory, and I ran into something that I don't think I understand. I'm hoping that someone who knows this stuff can help me out.
Before calculating the Dp-brane tension in Chapter 8, Polchinski says that we could have obtained the same result by calculating the amplitude f... |
I tried this sight before to find filtering options and got fantastic results, so let's try again!
I am setting up an experiment that requires light of two different frequencies (445nm and 350nm). The light ultimately needs to be focused on a small area. I can think of two good ways to make this happen:
Get a broad ... |
Ok, from astronomical observations we can tell that the observable matter is separating - so rewind the clock about 13.7 billion years and it was all at a single point.
However, how do we distinguish between the following two options:
Universe is expanding
Matter distribution is increasing into infinite void
Clar... |
In regards to the right hand rule, given Earth's electric and magnetic field, in which "direction" would a particle go?
|
Are there any massless (zero invariant mass) particles carrying electric charge?
If not, why not? Do we expect to see any or are they a theoretical impossibility?
|
How does an antenna behave when it is cooled so that its black-body radiation is emitting energy at its resonant frequency?
Edit: To clarify, its not how they're related in general, but how might thermal radiation and resonance interact with each other when their spectra are aligned well?
Edit: Also, I'm sure that the ... |
I was reading Landau and Lifschitz's "Classical Field Theory" and came across a comment that the action for electromagnetism must be a scalar, not a pseudoscalar (footnote in section 27). So I was wondering, is it possible/interesting to construct a classical field theory with a pseudoscalar action? If not, why not?
(N... |
Science and science fiction alikeScience fiction describes black holes as these amazingly different entities in space that don't behave according to the same laws of physics that the rest of the universe is bound to. I've heard them described as wormholes to other universes, singularities, or tears in space-time.
Howev... |
According to an answer in this thread on Skeptics:
If you take one of the little 12V
garage door opener batteries and short
out (directly connect) the two
terminals with a piece of wire or
something else. You'll get a light
current flow through the wire or
metal. It may get a little warm. This
battery is... |
I understand that in nature wind would never get high enough, but I am just curious as to whether physics would allow this to occur or not.
|
The many-worlds interpretation of quantum physics is built around a configuration space, where the position of a particle is three components of the position of that universe.
What happens with particle-antiparticle creation or annihilation? It can't just change the number of dimensions, can it?
|
The question assumes the standard formalism with projector-valued measures rather than POVMs. Suppose a measurement has two possible outcomes, and the corresponding probabilities are greater than 0 and less than 1. Neither outcome is therefore certain. Then why is it certain that either outcome is obtained (as it seems... |
A condensate of open strings with both ends attached to the same D-brane can be equivalent to a displacement of the D-brane with no open string condensate.
A solution to the D-brane Born-Infeld action gives rise to a semi-infinite string extension which is entirely equivalent to an open string with one end attached to ... |
My physics teacher explained the difference between voltage and current using sandwiches. Each person gets a bag full of sandwiches when they pass through the battery. Current = the number of people passing through a particular point per unit time. Voltage = the (change in) number of sandwiches per person. In a para... |
What do you guys think of alternative career paths in physics away from academia free from the usual academic shackles?
Examples: Garrett Lisi who spends his time surfing and skiing while not working on E8.
Or Daniel Bedingham who is able to support himself part-time as an investment banker when not working on quantum ... |
Please can anyone explain the concepts of electromagnetic induced transparency? I am having problem with the technicality of the explanation on wikipedia. Please I am an engineer with a physics background though and would love if this can be explained with little to no jargons . I am working on optical buffers and stud... |
I have no prior experience of using matlab. My teacher want me to solve this question. I have been trying for a couple of hours now with no luck, please help!
The mass of 100 g hanging in a spring with spring constant 40 N / m. The mass is set into vibration by the spring is stretched 14 mm. Neglecting any energy loss.... |
This is a follow up question from: Massless charged particles
Since by definition such a particle would interact with photons- resulting in some change in momentum- would the particle emit Bremsstrahlung during this interaction? If it does, it seems that there is a problem as the particle cannot decelerate, yet the Bre... |
During solar system formation, many bodies achieved hydrostatic equilibrium, a spherical shape where their self gravitational force was balanced by internal pressure. Many also achieved differentiation, where a body is seperated into layers of different density (core, mantle and crust). Differentiation was mainly the r... |
From Michael on Skeptics Stackexchange:
How about a wire that's grounded?
Safe to touch, right? WRONG.
________________ 30 amps -> ________________
| |
+ |
220V Load
- ... |
Searching for this on google proved to be quite tedious, but I reckon that someone working with crystals a lot might know this off the top of his head:
Is there a good source that lists the Madelung constants for a variety of geometries? I'd be particularly interested in that for a NaCl-type 110 surface.
|
This is a follow-up question to "In QM, why do the probabilities ... add up to 1?".
No actual measurement is perfect. While theorists may ignore this, experimenters know well enough that in many runs of a given experiment no outcome is obtained. (The efficiency of many real-world detectors is rather low.) This means th... |
Currently the charge-to-mass ratio of the electron is known to 10 orders of magnitude.
However, i'm curious if:
Are there any experiments trying to bound the anisotropy of this ratio for different directions of space? Over what time does the data needs to be averaged to get to our current ten-figure precision? Less th... |
If I search online for how radio telescopes work, the found articles talk about how RF is on the spectrum, etc, how the parabolic collector is the aperture which contributes to the sensitivity and reflects the signals into the detector at the focal point. Then they skip to the signal processing circuitry the leads to ... |
Does the rotational speed of a planet consistently become faster and faster given that there are no conflicting events?
|
Suppose we have an atom with several energy levels (e.g. an hydrogen), and it is hit by photons.
I know that in order to have the atom change energy levels, the photon must have an energy level precisely equal to the energy difference of the two levels.
What happens if the photon has more energy than the ionization en... |
One of the weirdest things about quantum mechanics (QM) is the exponential growth of the dimensions of Hilbert space with increasing number of particles.
This was already discussed by Born and Schrodinger but here's a recent reference:
http://arxiv.org/PS_cache/arxiv/pdf/0711/0711.4770v2.pdf
and another one:
http://www... |
If one starts with a flat piece of paper, removes a wedge, and tapes the paper together, you get a cone. The angle of the removed wedge is called the "angular deficit".
Now if this is done in 3 spatial dimensions, removing a 'wedge' along an entire line, there is similarly an angular deficit around the line defect. Us... |
For example it is stated that if supersymmetry breaking is soft then stability of gauge hierarchy can be still maintained.
|
This is a serious question from someone engaged in evaporating large quantities of water to turn sap into syrup at this time of year.
Probably some background will help. When sap boils vigorously it creates quite a bit of foam, which will overflow the evaporator (incidentally filling the building with a pleasing maple ... |
I'm trying to explain to someone learning elementary physics (16 year old) that linear momentum and energy are conserved independently in a 2-body collision. I'm not a professional physicist and haven't tried to explain this stuff for years, and I can't think of any convincing elementary argument to show that this is t... |
Given a stream of random binary numbers(*)
Is there any way to differentiate if they came from a Truly Random or from a formula/algorithm ? how?
if there is no way to decide this, then, I can't find any basis, to keep denying that behind the "truly random" of quantum mechanics can be a hidden algorithm.
I know I am tal... |
I recently bought some buckyballs, considered to be the world's best selling desk toy. Essentially, they are little, spherical magnets that can form interesting shapes when a bunch of them are used together.
After playing around with these buckyballs for a while, I wondered: "Can these guys ever lose their magnetism?" ... |
I wonder how one can show that general relativity is ghost-free? By ghost I mean the negative norm state that breaks the unitarity. I think it is a well-known "fact" but I just couldn't find any derivation or proof in any reference. Thanks!
|
According to Rindler the geodetic effect can be considered as consisting of Thomas precession combined with the effect of moving through curved space.
Wolfgang Rindler (2006) Relativity: special, general, and cosmological (2nd Ed.) p234
However according to Misner, Thorne, and Wheeler, Gravitation, p. 1118, Thomas prec... |
I apologize for this simple question, but I lost a factor of 2 and can't find it anymore, so now I'm looking on the internet, perhaps one of you has some information about its whereabouts. :-)
Consider the electromagnetic field tensor $F_{\mu\nu}$ which corresponds to a differential form $F =\frac12 F_{\mu\nu} dx^\mu \... |
Suppose Stanford Research Systems starts selling a two-level atom factory. Your grad student pushes a button, and bang, he gets a two-level atom. Half the time the atom is produced in the ground state, and half the time the atom is produced in the excited state, but other than that you get the exact same atom every tim... |
1.
Why is the wave function complex? I've collected some layman explanations but they are incomplete and unsatisfactory. However in the book by Merzbacher in the initial few pages he provides an explanation that I need some help with: that the de Broglie wavelength and the wavelength of an elastic wave do not show simi... |
If you rubbed a balloon with a towel, where would the electrons go: the balloon or the towel? Why?
I'm guessing the electrons would go to the object with a larger mass, but it's just a guess. :)
|
Can someone point to a good review article covering contemporary developments in big bang nucleosynthesis, beyond what's covered in Kolb and Turner's The Early Universe? Thanks.
|
Prof Brian Cox mentioned on Wonders of the Universe when discussing chemical elements that Carbon 12 consists of 6 protons and 6 neutrons, he also mentioned that Helium consists of 2 protons and 2 neutrons. He then went on to say that by combining certain elements we can create others - can anyone explain what he means... |
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