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I have read that the fine structure constant may well not be a constant. Now, if this were to be true, what would be the effect of a higher or lower value? (and why?)
The Wikipedia article on deep inelastic scattering suggests that the experiment shows baryons have three point of deflections (corresponding to three quarks) and mesons have two points of deflection. How are the electrons fired in this experiment being detected, and how exactly do the two or three points of deflection ...
Imagine an electromagnetic wave (a monochromatic one for example). The electric field amplitude and its variations travel in the propagation direction. So, if there really exists a propagation direction, what happens in other directions? I mean, is there an oscillation in those other directions? Does something (electr...
This question appeared quite a time ago and was inspired, of course, by all the fuss around "LHC will destroy the Earth". Consider a small black hole, that is somehow got inside the Earth. Under "small" I mean small enough to not to destroy Earth instantaneously, but large enough to not to evaporate due to the Hawking...
It's been a couple years since I've taken a physics class, and I have been wondering about this basically since I bought my car: I drive a 2010 Honda Fit, which has a street weight of approximately 2489 pounds (1129 kg). One feature of the Fit is that the back seats can sit upright like a normal car, or they can compl...
I am sending a couple of questions which seem a bit more specific than others on this site, partially to probe if there is a point in doing so. Not sure what is the range of expertise here, and no way to find out without trying, so here goes: I am wondering what is known about QCD, or other field theories, in the regim...
I am sending a couple of questions which seem a bit more specific than others on this site, partially to probe if there is a point in doing so. Not sure what is the range of expertise here, and no way to find out without trying. This one is also not terribly focused, but nonetheless here goes: I am wondering if there a...
What happens if you perform a double slit experiment near an event horizon, if one of the slits is outside, one is inside the event horizon?
I'm trying to reproduce a result from a paper (T. Thatcher, Boundary Conditions for Grad's 13 moment equations, equation (32), page 6), however, I haven't been able to do so. Hopefully someone can provide some help. The general problem concerns the Couette flow: A flow passes through two infinite parallel plates at dis...
How would I figure out the Cartesian graph that describes a bar clamped flat for a length on one end with downward force being applied to the other? I have an idea that the bar will try to average out the stress over the free length. Does it in fact evenly distribute stress over the whole free length? If so, can I us...
I've been looking with interest at a recent biology paper claiming that DNA molecules give off electromagnetic signals which can cause the same types of molecules to be reconstructed at a remote location. The Slashdot crowd seems to think the idea is pretty ridiculous, and I'm inclined to agree, but I still think it's ...
Electromagnetic waves can be shielded by a perfect conductor. What about gravitational fields or waves?
Say there was some situation where you have a lot of subatomic particles interacting with each other and decided to draw (say, by joining Feynmann diagrams) those interactions- so that you got some sort of (?directed) graph... what kind of network would you obtain? Would it be scale-free? Would it be a complex network ...
Imagine a bar spinning like a helicopter propeller, At $\omega$ rad/s because the extremes of the bar goes at speed $$V = \omega * r$$ then we can reach near $c$ (speed of light) applying some finite amount of energy just doing $$\omega = V / r$$ The bar should be long, low density, strong to minimize the amount of e...
Recently I started to play with some massive Gaussian models on a lattice. Motivation being that I work on massless models and want to understand the massive case because it seems easier to handle (e.g. cluster expansion makes sense thanks to contours carrying mass). Consider a Hamiltonian $$ H(x_{\Lambda}) = \sum_{<i,...
Visualizations of hydrogen's wavefunctions / electron orbitals are abound. I could not however locate a visualization of the wavefunction of a proton. The reason I was looking for one is to see whether the three quarks that make it up "occupy" disjoint regions of space (i.e. the maximum probability locations are separa...
Supposed I have an position vector $$\vec{r}=\begin{pmatrix} 10.0 & -30.0 & 25.0\end{pmatrix}$$ expressed in $\mathrm{millimeters}$. What is the correct notation to display $\vec{r}$ $\begin{pmatrix} 10.0 \\ -30.0 \\ 25.0\end{pmatrix}\text{ [mm]}$ $\begin{pmatrix} 10.0\text{ [mm]} \\ -30.0\text{ [mm]} \\ 25.0\text{ [m...
Consider the following experiment: a double-slit set-up for firing electrons one at a time. Let's now add a second electron (orange), which is fired parallel to the first one, but in the opposite direction, and so as to pass closer to one slit than the other, and, importantly, above the plane in which interference occu...
I've been toying with the idea of making a 3D scanner that uses an IR distance sensor to find position vectors of an object in space and then translates that into a 3D computer model. One of the greatest challenges in this case is optical phenomena. If the surface has holes, or dimples that reflect the IR beam or cause...
If you said someone had a velocity of $-12\,{\rm mph}$ and they were traveling north? Wouldn't it mean that they were traveling $12\,{\rm mph}$ south? This is a quote from here: if something [object-x] moving to the right was taken to have positive momentum, then one should consider something [object-y] moving to the ...
How can an electron distinguish between another electron and a positron? They use photons as exchange particles and photons are neutral, so how does it know to repel or attract?
I need the general expression for the lagrangian density of a linear elastic solid. I haven't been able to find this anywhere. Thanks.
When my wife uses her laptop, if I touch her skin, I can feel a buzz. She doesn't feel the buzz, but she can hear it if I touch her ear. So I'm guessing it's a faulty laptop, and she's conducting an electrical current. But why would she not feel anything, and what would it be that she would be hearing when I touch her...
There are 2 balls in a vacuum, next to each other but not touch. They are on the edge of a surface they will both leave the table at exactly the same time. One gets pushed harder than the other. The earth is completely flat. Apparently both balls will hit the floor at exactly the same time and even further be at the sa...
If we observe light that originates X light years away, but it passes between black holes X/2 light years away, will it be normal or red shifted or blue shifted? What if the black holes were X/4 or 3X/4 light years away? I have always wondered if the apparent red shift of distant galaxies must be due to relative vel...
In popular science books and articles, I keep running into the claim that the total energy of the Universe is zero, "because the positive energy of matter is cancelled out by the negative energy of the gravitational field". But I can't find anything concrete to substantiate this claim. As a first check, I did a calcula...
Why is the number of molecules in a standard volume of gas at a standard temperature and pressure a constant, regardless of the molecule's composition or weight? Let's say I have a closed box full of a heavy gas, one meter on a side. It has a certain number of molecules inside. I want to be able to add a lighter gas ...
I need to get a nice picture about how electron moves around nucleus? I find concept of probability and orbitals quite difficult to understand?
EDIT: Further clarification in the context of answers/comments received to 20 Jan has been appended EDIT: 21 Jan - Response to the Lubos Expansion appended [in progress, not yet complete] EDIT: 23 Jan - Visser's calculations appended EDIT: 26 Jan - Peter Shor's thought experiments rebutted Summary to Date (26 Jan) The ...
i know that the claim is that nucleosynthesis models say that the observed abundance of deuterium is too high for dark matter to be baryonic, but couldn't deuterium be a waste product of civilizations? you say that postulating civilizations is not the simplest explanation, but isn't it far more complex to postulate th...
This number is thrown around a lot so I'd like to understand its origin. I know that it counts compactifications of string theories on (not only) Calabi-Yau manifolds and probably also some other ingredients. 1. What precisely are those ingredients that differ among the stringy vacua? But as far as I know no one know...
Consider an electromagnetic wave of frequency $\nu$ interacting with a stationary charge placed at point $x$. My question concerns the consistency of two equally valid quantum-mechanical descriptions of the electromagnetic wave. First I will describe the classical picture, then the two quantum mechanical descriptions, ...
I've been searching and have not been able to find a formula for calculating the impedance of differential lines on inner layers where the dielectric above and below it is not symmetrical. I've seen plenty of examples of symmetrical stackups, but that would not help in my case. Does anyone know what the formula would ...
Why GPS/GLONASS/Galileo satellites are on low earth orbit? Why geostationary orbit is so bad? Sattelites might be placed there 'statically' and more precise... The only problem I can see is navigation close to poles, but they have this problem anyway.
Is it true that the whole galaxy is actually revolving, and powered by a black hole? Has it been proven, and if it is true, how can our solar systems actually keep up the momentum to withstand the pull?
A Newtonian homogeneous density sphere has gravitational binding energy in Joules $U = -(3/5)(GM^2)/r$, G=Newton's constant, M=gravitational mass, r=radius, mks. The fraction of binding energy to gravitational mass equivalent, $U/Mc^2$, is then (-885.975 meters)(Ms/r), Ms = solar masses of body, c=lightspeed. This giv...
this is my mental picture for how they travel without a medium, how (like water waves) some can't stay still, why they have wave and particle properties, energy/mass equivalence, conservation, etc. it might capture uncertainty too -- i've heard that all waves have an uncertainty relation (say in their power spectrum),...
I am working on a complex configuration of magnets and every time I make an experiment something unforseen happens. Now I believe I could speed up the development by sitting down and calculating the configuration in all scenarios. My question is however: Is there any software that can help me to calculate the forces be...
What is the exact shape of the universe? I know of the balloon analogy, and the bread with raisins in it. These clarify some points, like how the universe can have no centre, and how it can expand equally everywhere in all directions. But they also raise some questions, like if you are on the surface of a balloon and ...
Some time ago I was talking to a professor in college about some of the fundamental aspects and origin of General Relativity. I was surprised to learn, in fact, that a pretty good approximation to GR can be achieved simply by using Special Relativity and applying a series of (infinitesimal?) Lorentz boosts to simulate ...
So if you have a light bulb in a room, and you had a tool to measure the amount of light that's in the room, then let's assume the amount of light only caused by the bulb is "1" If you place a mirror next to the bulb, does the amount of light in the room in crease to "2"? Can you keep going so that the light in the roo...
I am currently reading journal articles about semiconductor physics in solar cells. What is injection level? I'll try to start off with what I understand. Photons hitting the silicon cause its electrons to jump to a higher energy state. Some of these electrons jump high enough that they cross from the valence band into...
Possible Duplicate: Why isn't dark matter just matter ? The evidence usually presented in support of dark matter is larger-than-expected masses in galaxy clusters: the mass required for the gravitational lensing is far larger than the mass detected in the galaxies themselves. So why, then, is the assumption that thi...
I have had this question for some time now. Hopefully someone can answer it. I know that the Boltzmann equation is widely regarded as a cornerstone of statistical mechanics and many applications have been explored with a linearized version. I also know that it's extremely hard to obtain exact solutions, which has star...
We all experience things spinning, whether it's water down a drain, the earth on its axis, planets round the sun, or stars in a galaxy - even electrons round an atom. But why is spin so common in the universe? I think there are some physical laws governing this, but perhaps my question is deeper than stating and expla...
Since the total mass-energy for the neutrino presumably does not change when a neutrino changes lepton flavor, though the mass is different, what compensates for the gain or loss of mass? Does the propagation speed of the neutrino change?
What are zero modes in quantum field theory, and what are they used for? Or, where can I read about them? I was never able to find a good introduction on the subject. I am particularly interested in zero modes that appear in the context of Yang-Mills, QCD and QCD-like theories, at zero or finite temperature. My doubt c...
For example: the role it might play in a theory of quantum gravity (ie causing space-time curvature)? I realize that inertial mass can result from binding energy alone. Has the equivalence principle been tested on elementary particles (like the electron) whose mass would be entirely due to the Higgs coupling? It seems ...
There's something known as a "resonating valence bond" (RVB) state, which plays a role in at least some attempts to understand physics of high-$T_c$ superconductors. This, roughly, involves a state that's in a superposition (hence the "resonating" part of the name, if I understand correctly) of different ways to pair e...
I got a question concerning the scattering of phonons and electrons. I read an introductory explanation to this process that is somehow not very satisfactory. It goes like this: Let $\psi_{k}$ and $\psi_{k'}$ be Bloch-waves within a solid. We denote the probability of transmission between these two states by $P_{k,k...
If the Earth left the solar system for some reason. Assuming its moving at the same velocity it's currently exhibiting. How long would it take for the atmosphere to freeze. Would we get methane clouds like Titan. Would there be an atmosphere or would it all be frozen on the ground?
It is experimentally known that the equation of motion for a charge $e$ moving in a static electric field $\mathbf{E}$ is given by: $$\frac{\mathrm{d}}{\mathrm{d}t} (\gamma m\mathbf{v}) = e\mathbf{E}$$ Is it possible to show this using just Newton's laws of motion for the proper frame of $e$, symmetry arguments, the Lo...
A positron is odd under charge conjugation and parity reversal but nevertheless even with respect to time reversal. Is a theoretical positron which would be odd under all three symmetries (C, P, T) physical?
Possible Duplicate: Why space expansion affects matter? Imagine two tiny spacecrafts that are moving with the Hubble flow and so are moving away from each other. Let's assume that they've been that way since the very early universe, never firing their engines, just drifting along their Hubble flow geodesics in a hom...
I thought light like singularity is where the geodesics end on a lightlike hypersurface and can't be extended anymore. I guess its different than light cone singularity. Lot's of places have mention of it, but I wanted to know its definition for sure.
Sometimes in quantum cosmology, when we are thinking about 'wave functions of the universe' we have in mind some sort of formal path integral, where we include not just the variations in the dynamical fields (metric and so forth), but also possibly some sort of prescription for summing over all possible topologies. At...
I couldn't think of a better title because I'm not sure what's going on with this phenomenon--someone who has an answer, please edit to fit this better. I noticed that when I cook rice, at some point after most of the water has evaporated and the rice is settled at the bottom of the pot, there is a "lattice" of regular...
May be not neutrinos, but antineutrinos? Or both types? In the last case, why they didn't annihilate and what is the ratio of relic neutrinos to relic antineutrinos? Is that ratio somehow related to the barion asymmetry? For reference: Relic neutrinos or cosmic neutrino background Like the cosmic microwave backgroun...
I've started reading Peskin and Schroeder on my own time, and I'm a bit confused about how to obtain Maxwell's equations from the (source-free) lagrangian density $L = -\frac{1}{4}F_{\mu\nu}F^{\mu\nu}$ (where $F^{\mu\nu} = \partial^\mu A^\nu - \partial^\nu A^\mu$ is the field tensor). Substituting in for the definition...
I understand that people explain (in layman's terms at least) that the presence of mass "warps" space-time geometry, and this causes gravity. I have also of course heard the analogy of a blanket or trampoline bending under an object, which causes other objects to come together, but I always thought this was a hopelessl...
The simplistic undergrad explanation aside, I've never really understood what energy really is. I've been told that it's something when converted from one kind of something to another kind, or does some "work", as defined by us, but what is that something? Moreover, if the total amount of energy in the universe is fini...
Is the fact that weak eigenstates are not mass eigenstates completely arbitrary? Or is there a deeper reason for the existence of the PMNS and CKM matrices?
I have this relative simple-looking question that I haven't been able to solve for hours now, it's one of those questions that just drive you nuts if you don't know how to do it. This is the scenario: I have a spring that is on a flat surface, the springs details are like this: spring constant = 100N/m height = 0.1m ma...
For example iron. A metal spoon heats up much quicker than a wooden/plastic one. Why?
If a planet of radius $R_1$ has a constant sub-surface temperature $T_0$ at $R_0<R_1$, what is the long-term equilibrium surface temperature $T_1$? Say we assume constant thermal diffusivity of the planet material, surface emissivity $1.0$, no atmosphere, and no incoming radiation. I figure the temperature profile is...
The claim is often made that the discovery of the Higgs boson will give us information about the origin of mass. However, the bare masses of the up and down quarks are only around 5 MeV, quite a bit smaller than their "constituent" or "dynamical" mass of around 300 MeV. (Remember that a neutron, for example, is one up ...
Just assume that I understand that a field in quantum field theory is an operator-valued distribution. For simplicity, forget about the distribution and think about a function $\varphi:M \rightarrow L(H)$ that assigns an operator to each point of spacetime. Can someone explain to me what (mathematically speaking) physi...
If two black holes collide and then evaporate, do they leave behind two naked sigularities ore? If there are two, can we know how they interact?
How to calculate number of exchanged virtual photons per unit of time between two electromagnetically interacting objects?
I've recently started studying the $k\cdot p$ method for describing electronic bandstructures near the centre of the Brillouin zone and I've been finding it hard to find any pedagogical references on the subject. In every paper I read there's simply a statement of the Hamiltonian and it is followed by the definition of...
What is a good place to learn the details of symmetry breaking? What I am looking for is a more serious exposition than the wiki-article, which explains the details, especially the mathematical part, but at the same time less detail than the typical quantum field theory book. Preferably I would like to see a clean made...
In modern cosmology, it is commonly stated to the public that as we look deeper and deeper into space, we are seeing further into the past. CMB is the relic of the big bang after photon decoupling following recombination. However, if we pushed further back in our conceptualization, eventually we get to the period of ...
Suppose we have two galaxies that are sufficiently far apart so that the distance between them increases due to Hubble's expansion. If I were to connect these two galaxies with a rope, would there be tension in the rope? Would the tension increase with time? Is the origin of the tension some sort of drag between the ...
In a typical photon experiment the photon is depicted as moving across the page, say from right to left. Suppose we were actually able to witness such an experiment, from the side (to position of reader to a page). If the photon is actually moving from left to right can I, standing at 90 degrees to the motion, see the...
What are the quantum mechanisms behind the emission and absorption of thermal radiation at and below room temperature? If the relevant quantum state transitions are molecular (stretching, flexing and spin changes) how come the thermal spectrum is continuous? What about substances (such as noble gases) which don't form ...
Alright, so we have all seen the movies where someone gets blasted out of the airlock on their starship, or their suit decompresses while on a space walk. The poor schmoe usually either decompresses so violently that blood is oozing out of every orifice in their body, or they freeze instantly. From this I have two ques...
Updated: In order to fold anything in half, it must be $\pi$ times longer than its thickness, and that depending on how something is folded, the amount its length decreases with each fold differs. – Britney Gallivan, the person who determined that the maximum number of times a paper or other finite thickness materials...
On the Answers.com page on Planck length, I see two almost-same formulas for the Planck length that differ only by the use of h and hbar. However, the constants are the same, and my calculator gives the correct answer for hbar instead of h, so the first use of h was probably intended to mean hbar. Why doesn't the Oxfor...
If U238 ions were circulating in a particle accelerator would their neutron absorption cross section spectra change?
The theory of Divergent Series was developed by Hardy and other mathematicians in the first half of the past century, giving rigorous methods of summation to get unique and consistent results from divergent series. Or so. In physics, it is said that the pertubative expansion for the calculation of QFT scattering amplit...
Decoherence times can be estimated and are inverse functions of mass. Since there are no upper bounds on mass, can decoherence time be shorter than Planck time?
During discussion on another question, the question of singularties in modern physical theories arose. The big-bang is an obvious singularity in modern conceptions of the cosmos. Is it a goal of modern theories to find a way to remove the big bang singularity from theory, and how is that accomplished in theories being...
I'm having a hard time to find a good (and modern) classification scheme for phase transitions and related universality classes. Can someone recommend a paper/book/site? Detailed mathematical aspects are very much welcome.
Is it correct to visualize operators existing as matrices parameterized by spacetime coordinates in the context of QFT?
I am having this silly confusion! Suppose I have a system (a Hamiltonian or an action say) and also suppose I have a perturbation parameter present (say only one in sight) in there, using which I can find out some kind of perturbative solution of that problem. Suppose now we also found out a non perturbative solution t...
(Note: I will let the question stand as is, it has generated a good answer, but the question is too "wishy washy" and needs to be tighter.) We know that the uncertainty principle tells us that the product of the standard deviation of energy and the standard deviation in time must always be greater than h-bar. Since the...
Possible Duplicate: Rotate a long bar in space and reach c Sorry this is very naive, but it's bugging me. If you had a straight solid stick attached on one end and rotating around that attachment at a certain rpm, there would be a length at which the end of the stick would theoretically reach, with that rpm, the spe...
Is it possible to make an insulator have two poles like a magnet? If yes, how to make it?
For a spherical mirror, an object at the mirror's center has an image that is also at the center. Its magnification is $-1$. For a video showing this, see here. If you stand slightly behind the center of a large spherical mirror and hold out your right hand, as if to shake, you will see a reflection of yourself, upsi...
When water freezes in a pipe it can crack the pipe open. I assume this takes quite a lot of energy as when I try to crack a pipe it can be hard work! I think water freezing is a result of energy (heat) being lost from the water and out of the pipe into the freezing environment around it. So what energy is cracking the ...
As I have understood it, the Standard Model includes particles that carry the different forces, e.g. the electromagnetic (EM) force, the gravitational (G) force. When talking about EM fields such as visible light or microwaves, the associated particle is said to be the photon. But what about a static EM field without a...
Can someone explain to me what the KKLT paper says, and what has and hasn't it achieved regarding the ability to construct solutions with a small positive or negative cosmological constant in string theory?
In which color human eye is most sensitive?
In late 2003, Edward Witten released a paper that revived the interest in Roger Penrose's twistors among particle physicists. The scattering amplitudes of gluons in $N=4$ gauge theory in four dimensions were expressed in a simple way using the twistor variables. Witten also proposed a particular model, the topological ...
What "breakthrough" from a theoretical point of view is needed for solar energy to become feasible energy alternative?
Through unit analysis, one can identify the following relationship linking energy, action and power: $$\mathrm{energy\ ^2 = action \times power}.$$ Alternatively, we rewrite this expression as: $$\mathrm{power = \frac{energy^2}{action}};$$ or $$\mathrm{action = \frac{energy^2}{power}}.$$ In light of this tight relation...
So I'm pretty sure I'm approaching this problem in the wrong way and I need some guidance (my first hint is that I think I'm thinking about a quantum mechanical problem too classically) Suppose there is an isolated molecule in the gas phase with an average cross-sectional area to be exposed to radiation of $A$. (For m...
From everything I've read about quantum mechanics and quantum entanglement phenomena, it's not obvious to me why quantum entanglement is considered to be an active link. That is, it's stated every time that measurement of one particle affects the other. In my head, there is a less magic explanation: the entangling meas...
When an atenna transmits radiowaves isn't it true that the electromagnetic pulse is radiated away from the accelerating electron as a spherical wave in all directions simultaneously, and if so how can the associated photon be "everywhere" on this rapidly expanding sphere?
While this concept is widely used in physics, it is really puzzling (at least for beginners) that you just have to multiply two functions (or the function by itself) at different values of the parameter and then average over the domain of the function keeping the difference between those parameters: $$C(x)=\langle f(x'...

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