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I recently calculated the PSD of the vibration data in a car at constant speed. I would like to know what this means and what if I calculate PSD of the vibration data in a car for the total journey with varying speeds? What do both PSDs signify?
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Einstein initially added the Cosmological Constant because (if I get this right) it seemed to him that the universe should be static. I agree that back then this would have been an obvious assumption. I'm curious now, before Hubble, where there any opinions/debates about whether the universe would be expanding or contr... |
I saw an interview with Ed Witten, where he said one way to confirm string-theory is to observe a giant string floating in space, left over from the Big-Bang.
How does one observe such a string, does it have thickness?
Is this string any different then the strings that (hypothetically) make up elementary particles?
Wha... |
In a interaction-round-a-face model of $n^2$ particles in a lattice, a weight $W(a,b,c,d)$ is assigned to each face in the lattice based on the spins $a,b,c,d$ (listed say from the bottom-left corner in counter-clockwise fashion) of the particles at the corners of the face. Based on this, a partition function is forme... |
What are some physics applications of the golden ratio?
$$\varphi~=~ \frac{1+\sqrt{5}}{2}~\approx~ 1.6180339887\ldots$$
Does it ever function specifically as a constant in any formulas or theorems?
EDIT: Original title said Golden Radio... facepalm. I originally asked this question at math.stackexchange but the answe... |
Given recent events in Japan, this got me wondering. Is it possible to determine radiation levels reliably not having Geiger counters near the possible radiation contaminated zone? According to wikipedia the Chernobyl disaster was first (other than Soviet Union naturally) detected by Swedish via radioactive particles f... |
So far, the quarks and leptons appear to be fundamental particles. But they're complicated enough that there's always been some speculation that they might be composite.
What experimental evidence would be needed to show that a lepton is composite?
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My question might sound convoluted but my mind is twisting right now so my apologies in advanced.
Why is it that when I have one proton and one electron it is Hydrogen a clear flammable gas, and when I have say, twelve, it is carbon the driving force of life as we know it and then we end up with 239 and we have uraniu... |
Which type two s-wave superconductor has the smallest London penetration depth? What is l_lamda ?
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I understand that information cannot be transmitted at a velocity greater than speed of light. I think of this in terms of the radio broadcast: the station sends out carrier frequencies $\omega_c$ but the actual content is carried in the modulated wave, the sidebands $\omega_c\pm\omega_m$. The modulation envelop has it... |
Hey all, are there any theories out there on the origins (or infinite existence of) the universe beside the big bang that actually adhere to current scientific knowledge and fact?
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If lead can absorb or block radiation, would it be possible to pump molten lead into a reactor core which is melting, so that it would eventually cool and contain the radiation?
Is there something that can be dumped into the core that will both stop the reaction (extremely rapidly) AND will not combine with radioactive... |
The graph of nuclear binding energy is relatively smooth going from H to U, except for He4 (alpha particle). Why is He4's binding energy so anomalously high compared to its neighboring isotopes?
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Sometimes old faulty CRT monitors generate nasty high-frequency squeal sound. What element might be responsible for generating such sound? I have heard that it might be dry electrolytic capacitor; is it? What is the physics of generating this sound (how it is generated)?
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Consider a lift, which is at rest in an homogeneous gravity field. There is a thin layer(with thickness $h$) of water on the floor of the lift. At some moment a single cable, supporting the lift, breaks and the lift begins free falling(forever). It is easy to describe qualitatively what happens with water, i think: the... |
What does it mean to say that mass "approaches infinity"?
I have read that mass of a body increases with the speed and when the body reaches the speed of light, the mass becomes infinity.
What exactly does it mean to say that the mass "approaches infinity" or "becomes infinity"? I am not able to get a picture of "infi... |
As I understand, the hydrogen is produced by water thermolysis, which need quite high temperature. This temperature is close to previously observed corium temperatures. So:
Is the eutectic temperature of the corium of those type of reactors known and publicly accessible?
Isn't the hydrogen presence a proof of meltdown... |
Given an uncharged continuum the EM field produces no force on it. Yet in a discrete system we know that atoms are not uncharged locally and momentum can be exchanged due to the electric field(Which Maxwell's equations are suppose to govern).
viz., The transfer of momentum between atoms is due to the electric field(alt... |
The explosions at the Fukushima nuclear reactors were caused by a build of hydrogen. I was wondering where this hydrogen came from.
This question Fukushima - Isn't the hydrogen presence a proof of meltdown? suggests that the hydrogen is caused by thermolysis of water.
But surely this can't be the case? If it were, wo... |
To focus this question let us consider first classical mechanics (which is time-symmetric). Given a final condition (and sufficient information) one can calculate the system conditions of an earlier time (retrodiction).
Given Quantum Mechanics (which is time-symmetric) and a final condition what is the status of retrod... |
I live at roughly $(52.4^\circ,-2.1^\circ)$. On sunny evenings I've often looked at the Moon and the Sun and noticed that the light part of the Moon does not appear to line up with the Sun. For example, at about 17:00 GMT on 13 Mar 2011, I noticed the half Moon was facing toward a point roughly $10^\circ-20^\circ$ abov... |
What I am interested to see are specific examples/reasons why gravity should be quantized. Something more than "well, everything else is, so why not gravity too". For example, isn't it possible that a quantum field theory on curved space-time would be the way treat QFT and gravity in questions where the effects of neit... |
This is related to this earlier question I had asked.
I am using the so called ``Majorana" representation of gamma matrices in $2+1$ dimensions in which everything is real. After doing the dimensional reduction of the $\cal{N}=1$ supersymmetry transformations of the components of the vector superfield in $3+1$ dimensi... |
There are many papers about the running of coupling strength as a function of momentum/energy scale,
but are there any experimental papers about coupling strength as function of distance?
Also, are there any good books about this topic?
oops ,really sorry i forgot to specify "experimental"paper
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A modern flywheel rotor is suspended in a vacuum by magnetic bearings. This means that nothing touches the rotor as it spins. When time comes that we need to recover that stored kinetic energy, how do we recover it?
I imagine a clutch making contact with the rotor, but wouldn't that give quite a jolt, slowing down the ... |
Will a machine or a technique ever be possible that allows artificial gravity in interplanetary space?
And I ask out of pure curiosity. I know there is the "Vomit Comet" that allows for a non-gravity 'simulation' (for lack of a better word) on Earth, and I was thinking about if there would be a way to reverse that and ... |
If I understand correctly, when an earthquake occurs, energy will be transferred to the water, resulting in water waves. As the waves reach seashore, because the sea depth is getting shallower and wavelength is getting shorter, the height of the wave gets push up, resulting in tsunami. In other words in deep sea, water... |
I've come upon Dr. J. Marvin Herndon's theory that the earth's magnetic field is generated by a hot nuclear reactor operating in the center of the earth. This is backed by various papers, some of them peer reviewed:
http://www.nuclearplanet.com/Herndon%27s%20Nuclear%20Georeactor.html
His theory purports to explain vari... |
I know that there's no evidence at this point for "white holes" however would it even be mathematically possible for a black hole to be connected to a white hole (total opposite so everything would be expelled, after some really extreme physical conditions)? Maybe with a wormhole connecting them? If this was even possi... |
Are there any examples of common substances whose decay is not exponential?
We're used to thinking about radioactivity in terms of half-lives. This is a concept that makes sense only for a decay that is exponential. However, there are plenty of physics articles on the subject of non exponential decay. It seems to be th... |
For an accelerated charge to radiate, must an electromagnetic field be the source of the force?
Would it radiate if accelerated by a gravitational field?
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Why is the amplitude of the Power spectral density higher for shorter period of time as compared to a longer period of time when calculated for any vibration data?
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Super string theory establishes that at each point of our 4 dimensional spacetime, there is attached a 6-dimensional Calabi-Yau (CY) manifold which encodes the geometry of the additional compactified spatial dimensions needed to formulate the theory. It is postulated that the size of these compactified dimensions is of... |
Some threads here touching speed of gravity made me think about that. This lead to some questions.
The speed of gravity was not measured until today (at least there are no undebated papers to that effect).
It seems common knowledge/belief among physicists that the speed of gravity is the same as the speed of light.
... |
Imagine three light beams are "sent" to a lens simultaneously, they start at the same position but move towards the lens at different angles. The first light beam passes the lens at its edge, the second light beam passes exactly through its mid whilst the last light beam passes somewhere in between. Behind the lens, th... |
I'm curious to learn how people discovered that electric and magnetic fields could be nicely put into one simple tensor.
It's clear that the tensor provides many beautiful simplifications to the original theory, by applying the abstract theory of tensors to this particular problem. For example, the strange formulas for... |
As a general rule of thumb, massive particles (both composite and fundamental) tend to decay rapidly through the weak force, while less massive particles tend to be more stable. Hence, taus are shorter lived than muons, top quarks are shorter lived than charm quarks, and all mesons and baryons except protons and neutr... |
So I know that when you collide particles with high enough kinetic energy, (kinetic energy = at least the rest mass of the particles you are making), you get particles.
How come potential energy cannot make particles? Say you have an electron held at a potential such that the amount of potential energy it has equals a... |
So I have learned in class that light can get red-shifted as it travels through space. As I understand it, space itself expands and stretches out the wavelength of the light. This results in the light having a lower frequency which equates to lowering its energy.
My question is, where does the energy of the light go? E... |
I'm trying to understand what would really happen when large quantities (e.g., 10g) of anti-matter collide with matter. The normal response is that they'd annihilate each other and generate an expanding sphere of gamma ray photons.
However, thinking about it in more detail, what I see is that the anti-electrons annihi... |
I can't seem to find any info on connected rigid bodies by a joint. Can someone explain the basics to me? I'm trying to do a little research to find out how feasible it would be to implement 3d ragdoll physics for my first person shooter game.
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A recent experimental paper measures a difference between the top quark and anti-top quark masses:
Fermilab-Pub-11-062-E, CDF Collaboration, Measurement of the mass difference between $t$ and $\bar{t}$ quarks
We present a direct measurement of the
mass difference between $t$ and
$\bar{t}$ quarks using $t\bar{t}$
... |
Between 1947 and 1962 the US conducted 105 tests of nuclear weapons in the "Pacific Proving Grounds". I'm wondering how much radiation exposure resulted on the west coast of the US. These were part of the 1056 nuclear bombs that the US has ignited over the years (most underground, but two notably in Japanese cities).
S... |
Suppose we perform a double-slit experiment with a detector placed at a position of minimum intensity (maximum destructive interference), off-center where the path lengths differ by half a wavelength. The light source is alternately turned on and off (or blocked and unblocked near the source) and the intensity over ti... |
I am taking an intro level quantum mechanics class. Our textbook gives a problem like this:
The deuteron is a nucleus of "heavy hydrogen" consisting of one proton and one neutron. As a simple model for this nucleus, consider a single particle of mass $m$ moving in a fixed spherically -symmetric potential $V(r)$, defin... |
Special relativity was well established by the time the schrodinger equation came out. Using the correspondence of classical energy with frequency and momentum with wave number, this is the equation that comes out, and looks sensible because this is of the form of a wave equation, like the one for sound etc, except wit... |
Sorry, I know y'all are probably getting a lot of questions re: Fukushima, but I had a very specific one and no-one has been able to answer it.
I am specialised in medical radiation, and have been explaining the risks to workers in this accident, but I need to know what are the rough proportions of alpha, beta (+/-) an... |
How did Nima Arkani-Hamed come up with the following nonzero space-like commutation relation in string theory?
$$\left\langle \left| \left[ \hat{\mathcal{O}}(\vec{x}), \hat{\mathcal{O}}(\vec{y}) \right] \right|^2 \right\rangle \sim \exp \left( -\frac{k\left| \vec{x} - \vec{y} \right|^{D-2}}{8\pi G} \right)$$
His explan... |
In free space, the linear momentum density of an EM wave is given by the Poynting vector $\vec S$ over the speed of light squared, $\vec g=\frac{\vec S}{c^2}$.
In a medium, $S$ is generally not directed along the wave vector $\vec k$. If $v_g$ is the group velocity and $W$ is the density of EM wave energy, then $S = v... |
Cost per Power Capacity
For a number of energy technologies I'd like to know what the minimum costs are to install a given power capacity. Are there any such comparisons available?
Research Spendings
Technologies often own much to publicly funded research efforts so I'm also interested in estimations regarding develop... |
I am not sure that this notation is specific to supersymmetry theories but I ran into this while studying that.
I see people talking of component fields of a chiral superfield as $\phi$ and $\bar{\psi}$ in the adjoint representation of some gauge group. (One sometimes also seems to use the notation of $\bar{\psi}_+$ t... |
Assume that alpha & beta particles and gamma photons each reach skin at the same energy. It's known that they penetrate most deeply in order by gamma, beta and alpha. How would they compare in terms of total biological impact? In other words, which would be most harmful?
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1) Why is a hot air balloon stiff?
2) Is the pressure inside the balloon higher than the pressure outside (atmospheric pressure)?
3) If the pressure inside is higher than the outside, how is it explained by ideal gas law?
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As pointed out before, it orginated inside the reactor vessel but exploded outside: how did it get there? Did it pass the shell by diffusion or was it released by the engineers?
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How do we calculate the effective mass of an electron in an Aluminium lattice? Is there any simple analytical way to work it out?
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I was reading the Feynman lectures in physics and after thinking about it for a while it seems particularly unreasonable to talk about hidden variables. Let us say that the electron has some internal variables as yet unknown which determine its trajectory given a set of initial conditions just like in classical mechani... |
This might be stupid, but is gravity a form of energy? And, if so, couldn't we use it for power?
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According to the reports, the shutdown procedures at all the Fukushima reactors were successful, and all the control rods were fully inserted.
So - if there was a meltdown, would the control rods also melt and blend into the resulting material (corium)? If so, would that have the effect of "diluting" the corium in radi... |
Is there any good reference for conceptual problems for students which learn nuclear physics first time? I am not searching problems that involve difficult calculations. Quite the converse, they should be computational rather simple but conceptually difficult.
|
How to find velocity and displacement equations from a given force equation? For instance, it was given the following 1-D equation:
$$F = b_1(v_1-v) - b_2 v$$
$v_1$, $b_1$ and $b_2$ are constants.
I know that $F = ma = m\frac{\mathrm{d}v}{\mathrm{d}t}$, but I can't find how to integrate $F$. Is there any technique that... |
Do sound waves in a gas consist of phonons?
What about a glass? Or other non-crystalline materials such as quasicrystals?
How does the lack of translational symmetry affect the quantization of the displacement field?
All the answers so far have treated this question at a much more elementary level than I was expecting.... |
In all the discussions about how the heavy elements in the universe are forged in the guts of stars and especially during a star's death, I usually hear that once the star begins fusing lighter atoms to produce iron (Fe) that's the end of the star's life and the whole system collapses onto itself; and based on how mass... |
The professor asked us to do this one:
"..Determine all potentials $V(r,\theta, \phi)$ for which it is possible for find solutions of the time independent Schrodinger equation which are also eigenfunctions of the operator $L_{z}$."
I try to solve this problem by assuming separation of variables, and I get $$\Phi(r,\the... |
Can anyone point me to a reference (preferably either something online or something a small liberal arts school would be likely to have in its library) that goes through a derivation of the minimum uncertainty wavefunction in more detail than in the Griffiths?
Edit I've moved the second part of my original question to ... |
The reply to a question about nucleosynthesis, that heavier than iron elements are produced in supernovae explosions, raised for me the following question which I could not answer by googling. Partially because the search for planets and stars brings out astrology answers!
Explosions are dispersive, nevertheless we fin... |
Possible Duplicate:
Are tidal power plants slowing down Earth's rotation?
Since we have various energy acquiring facilities that harvest energy from earth rotation. (e.g. wind, tidal power planet)
Will our earth rotation be slower down? Is there any form of force to accelerate earth rotation speed?
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I don't really know anything about physics even though I pretended studying it for years.
How is this explained?: http://andrewsullivan.theatlantic.com/the_daily_dish/2011/01/if-you-think-youre-cold-.html
What is there to be said about it?
My apologies if you find the question too vague or silly.
|
A BWR reactor core may contain up to 146 tons of uranium. Why does it not form a critical mass when molten? Are there any estimates of the critical mass of the resulting zirconium alloy, steel, concrete and uranium oxide mixture?
|
My aim is to draw a plot of $GaAs_{1-x}Sb_{x}$/InP (GaAsSb on InP substrate) band offset as a function of As/Sb composition.
The first part is easy if I'm doing this correctly: I found VBO (valence band offset) parameters for GaAs and GaSb, then the bowing parameter for $GaAs_{1-x}Sb_{x}$ VBO and finally the bowing par... |
I'm interested in the extent to which quantum physical effects are seen at a macroscopic level. I might get some of the physics wrong, but I think I'll get it close enough that I can ask the question:
Let's sat that we create a bonfire and let it burn until it burns out. As the smoke rises from the fire, turbulence t... |
By what mechanism do quantum effects become observable in normal life at the macroscopic level? For instance, when two molecules "collide" is the momentum a probabilistic event wherein the end state is not unique? Another example, during a chemical reaction, it is a probabilistic event at the quantum level whether or... |
The Dirac operator at 2 dimension can be written as
$$
D=\sum_{k=1,2}\sigma^{k}D_{k}=\left( \begin{array}{cc}
0 & \partial_{x}-i\partial_{y}-i(A_x-iA_y)\\
\partial_{x}+i\partial_{y}-i(A_x+iA_y) & 0
\end{array} \right) ,
$$
where $A_i$ is a gauge field.
If we add some other terms to the operator above, such as $\... |
Well, reading about "Raman Effect" I saw that when the electron absorb some energy, with frequency $ \omega_{abs} $, that is different from $ \omega_{n} - \omega_{n-1} \neq \omega_{abs1} $, it go to an "virtual energy level" that is unstable, but nevertheless we could measure its lifetime. And more, the electron could ... |
I was not able to find an answer for this question...
Some radioactive elements have half-life measured in thousands of years and some others even in millions, but over 4.5 billion years all the radioactive material that was part of the initial material that formed the planet earth should have decayed by now?
However, ... |
According to Hubble's law, light and other kinds of electromagnetic radiation emitted from distant objects are redshifted. The more distant the source, the more intense is the redshift. Now, the expansion of the universe is expected to explain the redshift and its nearly linear dependence on distance between source and... |
There is no tunneling in the case of infinite potential barrier, but there is when we have a finite well. In the classical analog, in the first case we have a particle bouncing between to infinitely rigid impenetrable walls and there is no tunneling, same as the quantum case. But if we have a finite barrier, means we h... |
Based on the 1D case mentioned in Griffiths, I decided to try looking at the features of 3D Gaussian wavefunctions, i.e. (position basis) wavefunctions of the form $\psi(\mathbf{r}) = Ae^{-\mathbf{r}^\dagger\mathsf\Sigma\mathbf{r}/4}$, where A is a normalization constant, r is position, Σ is a positive-definite symmetr... |
We're finding forces (and whether they're in tension or compression) using the Method of Joints and Method of Sections. I don't understand why sometimes it's necessary to find the support reactions, but sometimes it's not. Please help. Thank you!
|
Starting with a pot of cold tap water, I want to cook a hard-boiled egg using the minimum amount of energy. Is it more energy efficient to bring a pot to boil first and then put the egg in it, or to put the egg in the pot of cold water first and let it heat up with the water?
|
Let me put things into perspective by comparing with other applications of string theory. Nowadays review papers written by cosmologists about inflation models often discuss string theory scenarios such as brane inflation, among other non-stringy models. Also you often hear about heavy-ion theorists and experimentalist... |
Schwarzschild singularities are described by the Kantowski-Sachs metric with a contracting S2. Of course, T-duality doesn't apply to S2. But what about a Kasner-type singularity with two contracting spatial dimensions compactified over a torus T2, and an expanding spatial dimension? The T-dual of the torus gives rise t... |
I was reading Wikipedia which stated
....Voyager 1's current relative velocity is 17.062 km/s, or 61,452 kilometres per hour (38,185 mph).....
It travels away from sun. So sun's gravity must slow it down. What propels Voyager to that speed?
|
Who hasn't heard about the double-slit experiment? It figures in any book of quantum physics. But there is something no one can explain to me: I understand why the light cannot be described only as a wave, but I do not understand why it cannot be explained only in terms of a particle, having some trajectory, following ... |
I understand from basic conservation of energy and momentum considerations, it is clear in classical electrodynamics that the fields should be able to have energy and momentum. This leads to the usual Poynting vector and energy density relations for electromagnetic fields.
However, I do not know how to interpret situat... |
Edward Nelson's book "Quantum Fluctuations" (Princeton UP, 1985) gives an alternative way to introduce trajectories, quite different to the trajectories of de Broglie-Bohm type approaches. I've read the book in the past and university libraries generally have copies, but I've been unable to find a good open web referen... |
Recently there have been some interesting questions on standard QM and especially on uncertainty principle and I enjoyed reviewing these basic concepts. And I came to realize I have an interesting question of my own. I guess the answer should be known but I wasn't able to resolve the problem myself so I hope it's not e... |
Does GR provide a limit to the maximum electric field?
I've gotten conflicting information regarding this, and am quite confused. I will try to quote exactly when possible so as not to confuse things more with my paraphrasing.
The author of the Motion Mountain physics textbook claims in his book there is a limit, and... |
If I calculate the energy contained in the electric field for an electric dipole p in an electric field E, I get (ignoring the terms independent of orientation):
$U = - \vec{p} \cdot \vec{E}$
which is as expected. However, if I do the same for a magnetic dipole m in a magnetic field B, I get (again ignoring the terms ... |
If there is a non-zero expectation value for the Higgs boson even in "vacuum", since the Higgs boson has a mass unlike photons, then I would expect it to have a rest frame.
So why doesn't a non-zero expectation value for the Higgs boson not only break electroweak symmetry, but also break Lorentz symmetry?
|
Facts agreed on by most Physicists -
GR: One can't apply Noether's theorem to argue there is a conserved energy.
QFT: One can apply Noether's theorem to argue there is a conserved energy.
String Theory: A mathematically consistent quantum theory of gravity.
Conclusion -
If one can apply Noether's theorem in String Theo... |
This should be a very easy question. If you look at the bottom of "Identical Particles" in Wikipedia, you see Table 1, which gives you the two particle statistics for bosons, fermions and distinguishable particles. The problem is to extend this table for three, four and five particles, or give an equivalent formula. ... |
In the last year there has been fuzz regarding metamaterials studied for the purpose of cloaking, and it seem to me they are somewhat glorified 2D waveguides, but in any case it seems a reasonable application of this to funnel radiation captured over a wide area of incidence into smaller area, and i thought that this c... |
My current understanding of gravitational lensing follows
When a star or other massive body passes between us and another star, the phenomenon
generally labeled 'gravitational lensing' occurs. The term 'gravitational lensing' refers to the bending of light rays due to the gravitational influence of the massive body. ... |
If I had a light "diode" - an object that only allowed light (at least for a range of frequencies) to travel through it in one direction, would this necessarily allow violations of the 2nd Law of Thermodynamics? Or would it be possible to restrict other properties of the device such that it could be okay.
Why I think ... |
I want to heat one side of an aluminum plate enough to hold the other side of that plate $100K$ above ambient. I'm willing to assume that the heated side of the plate is "well" insulated (along with the edges, if it's significant). The plate is $500cm^2$ and is open to air in a normal room.
I think the formula is sim... |
Earth's N and S magnetic poles "wander independently of each other and are not at exactly opposite positions on the globe" [from WIKI's "Earth's magnetic field"]. Can these independent motions be consistent with the supposed "dynamo effect" from electric currents of a liquid outer core? Can Earth's spheroidal shape be ... |
Bell's inequality theorem, along with experimental evidence, shows that we cannot have both realism and locality. While I don't fully understand it, Leggett's inequality takes this a step further and shows that we can't even have non-local realism theories. Apparently there are some hidden variable theories that get ... |
The title question would be too long if I tried to specify it clearly. So let me be more clear. Consider the class of theories having the following properties:
The lagrangian density is only dependent of scalars created from the curvature tensors (for example $R, R^{ab}R_{ab}, R^{abcd}R_{abcd}, C^{abcd}C_{abcd}, (R)... |
I still don't really understand what contextuality means in reference to quantum mechanics. If someone could give a clear definition that would be great. It sounds like it means you can't always relate the state of a system to its wavefunction or something? That confuses me since it seems to violate quantum mechanic... |
If water is introduced in a container maintained at 20 °C in vacuum conditions, a gaseous phase will appear and the pressure will stabilize at the vapour pressure for the given temperature inside the container. So far so good.
Now imagine the experiment is repeated but instead of vacuum conditions, the water is presuri... |
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