Q stringlengths 18 13.7k | A stringlengths 1 16.1k | meta dict |
|---|---|---|
Do high/low pass lenses exist? For an experiment I will hopefully be soon conducting at Johns Hopkins I need two different lenses.
The first needs to allow all wavelengths above 500 nm to pass (thus a high pass filter) and cut off everything else.
The second needs to allow all wavelengths below 370 nm to pass (thus a l... | What you're looking for isn't a lens so much as a filter. There are filters for whatever purpose you might want out there in the world, and they are relatively inexpensive. Doing a google search on Optics Filters, I came across a couple of sites that might help you.
*
*Edmond's Optics
*Optical Filters USA
| {
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Would you be weightless at the center of the Earth? If you could travel to the center of the Earth (or any planet), would you be weightless there?
| The simplest way to think about it is that there is mass all around you in the center of the Earth so you get an equal gravitational "pull" from all directions. The pulls cancel out so you get no acceleration.
If one assumes constant density for the Earth (which isn't strictly speaking true but it is close enough for t... | {
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Is there a limit to loudness? Is there any reason to believe that any measure of loudness (e.g. sound pressure) might have an upper boundary, similar to upper limit (c) of the speed of mass?
| Let's talk about the sound waves in the air first. Physically they are longitudinal waves of pressure. The bunch of air in one place will get compressed (in comparison with equilibrium state) and after that will expand, compressing the adjacent air and so on the wave propagates. These (single frequency) waves are essen... | {
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The final death of a black hole What are the different death scenarios for a black hole? I know they can evaporate through Hawking radiation - but is there any other way? What if you just kept shoveling more and more mass and energy into the black hole?
| If you shovel lots of mass and energy into a black hole, you will most likely get a bigger black hole. It will not get indigestion, and it will not explode due to being full. You may get accretion and jets if your shoveling is suitably generic.
Any list of possible "final death" scenarios will depend on your threshol... | {
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Why GPS is at LEO? 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.
| This question always interested me.
I found this recently -
"Another issue we wrestled with is which satellite orbits to use. We did not want to be in geostationary or geosynchronous orbits. The reason was these alternatives would force us to deploy ground stations on the other side of the globe, whereas, by putting th... | {
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Accuracy of the Boltzmann equation 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 obt... | @Robert Smith
Well you're asking a question about the accuracy of an equation. The equation is created under certain assumptions about small objects sometimes called "particles" or "atoms". So if the equation accurately describes the system in question, then the behavior of the sytem should be described by solutions ... | {
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Derivation of Maxwell's equations from field tensor lagrangian 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 ... | Well, you are almost there. Use the fact that
$$ {\partial (\partial_{\mu} A_{\nu}) \over \partial(\partial_{\rho} A_{\sigma})} = \delta_{\mu}^{\rho} \delta_{\nu}^{\sigma}$$
which is valid because $\partial_{\mu} A_{\nu}$ are $d^2$ independent components.
| {
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movement of photons 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... | Dear Peter, the pictures are drawn to indicate that the photons are there. They are there even if you don't see them. There are many things that we can't see - or we can't see directly or at a given moment - but they still exist. And of course, you don't see the photons (with a wrong direction) by normal methods - you ... | {
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When one thinks of a field of operators in QFT, is it reasonable to think of a matrix being associated with each point in space time? Is it correct to visualize operators existing as matrices parameterized by spacetime coordinates in the context of QFT?
| Given that a quantum field is a field of operators and given that you can think of operators as (possibly infinite) matrices acting on a Hilbert (or, better, Fock) space, your assumption is correct. However, I wouldn't call it "visualizing" as I find operators more tangible than Matrices.
| {
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Why is quantum entanglement considered to be an active link between particles? 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 affect... | I think that the best picture to understand this correlation is given by many-worlds interpretation:
A singlet decomposes in a coupled pair of particles superposition $|+⟩_A|-⟩_B + |-⟩_A|+⟩_B$, so observer A sees a simple superposition of $|+⟩ + |-⟩$ (which is a partial trace of the global density matrix) and so does ... | {
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Vortex in liquid collects particles in center At xmas, I had a cup of tea with some debris at the bottom from the leaves. With less than an inch of tea left, I'd shake the cup to get a little vortex going, then stop shaking and watch it spin. At first, the particles were dispersed fairly evenly throughout the liquid,... | My simple non-mathematical theory to explain this counter-intuitive behaviour is based on hydrostatic pressure.
The rotating liquid develops a vortex shaped surface that makes the centre of rotation the shallowest and the periphery the deepest region. The hydrostatic pressure at the periphery is therefore higher than a... | {
"language": "en",
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Is there a maximum possible acceleration? I'm thinking equivalence principle, possibilities of unbounded space-time curvature, quantum gravity.
| For QED there is a critical acceleration, which is the acceleration felt by an electron subject to the Schwinger field (http://en.wikipedia.org/wiki/Schwinger_limit).
This is at the critical acceleration
$$
a_S = \frac{m_ec^3}{\hbar} = 2.33 \cdot 10^{29} \frac{m}{s^2}
$$
Beyond this field, nonlinear effects if the QE... | {
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What would happen if you put your hand in front of the 7 TeV beam at LHC? Some speculation here:
http://www.youtube.com/watch?v=_NMqPT6oKJ8
Is there a possibility it would pass 'undetected' through your hand, or is it certain death?
Can you conclude it to be vital, or only loose your hand?
Would it simply make a small ... | Back in the 1970s there were some researchers who put seeds in a beam path to see what would happen. The plants which grew from the seeds were deformed. One would have to look this up to get the details.
If you put your hand in the LHC beam one question is what would hurt the most; the damage due to high energy par... | {
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Free electrons and energy states Ok, background - studying for the physics part of my radiology exams, and came across a question that went something like this
An electron fired through a tungsten target loses energy by:
a) Bremsstrauhlung
b) collisions with bound target electrons
c) giving off characteristic radiation... | The (c) option is badly worded, in my opinion. The characteristic radiation is emitted by the atom and this indirectly contributes to the original electron (say, A) losing energy.
This is how it happens, roughly: An electron A fired into the target can ionize one of the atoms which ejects an electron B. In doing so, t... | {
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Why does a ballerina speed up when she pulls in her arms? My friend thinks it's because she has less air resistance but I'm not sure.
| Joe's answer is of course right and I gave it +1. However, let me say some slightly complementary things.
Whenever the laws of physics don't depend on the orientation in space, a number known as the angular momentum is conserved. For a rotating body - including the body of a lady - the angular momentum $J$ may be writt... | {
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Two slit experiment: Where does the energy go? In Physics class we were doing the two slit experiment with a helium-neon red laser. We used this to work out the wavelength of the laser light to a high degree of accuracy. On the piece of paper the light shined on there were patterns of interference, both constructive an... | It goes where the photons go. Best explanation I've seen is in Feynman "QED: the strange theory of light and matter". One does not have to unlearn anything. It is even more interesting after reading his more technical works.
| {
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Why are snowflakes symmetrical? The title says it all. Why are snowflakes symmetrical in shape and not a mush of ice?
Is it a property of water freezing or what? Does anyone care to explain it to me? I'm intrigued by this and couldn't find an explanation.
| Not all snowflakes are symmetrical. One can disrupt the symmetry quite easily by introducing impurities or some mechanical artifact. In nature, snowflakes have plenty of time to form and it is more natural for them to form symmetric shapes because of the molecular structure of water.
That is, when there is more time fo... | {
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Stopping Distance (frictionless) Assuming I have a body travelling in space at a rate of $1000~\text{m/s}$. Let's also assume my maximum deceleration speed is $10~\text{m/s}^2$. How can I calculate the minimum stopping distance of the body?
All the formulas I can find seem to require either time or distance, but not on... | If the speed is $1000 m/s$ and the deceleration is $10 m/s^2$, it will take $100 s$ to stop. The average speed in that time is $500 m/s$, so the distance traveled is
$$500m/s*100s = 5*10^4m$$
Working through the same logic with an initial speed $v$ and a deceleration $a$, the final distance $d$ traveled before stoppi... | {
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Is causality a formalised concept in physics? I have never seen a “causality operator” in physics. When people invoke the informal concept of causality aren’t they really talking about consistency (perhaps in a temporal context)?
For example, if you allow material object velocities > c in SR you will be able to prove t... | In the axiomatic approach to quantum field theory, sometimes also called local or algebraic quantum field theory, pioneered by Araki, Haag, Kastler, Bogoljiobov et. alt., causality is formalized as an axiom, most often called the "locality" axiom.
The idea is this: To every bounded open subset of Minkowski spacetime we... | {
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Will tensile strength keep a cable from snapping indefinitely? Trying to secure a wall hanging using magnets; me and a coworker came up with an interesting question:
When the hanging is hung using 1 magnet, the weight of it causes it to quickly drag the magnet down and the hanging drops. Using n magnets retards this p... | Metals normally have crystalline, ordered structure. An atom moving from one appropriate site of the crystal lattice to the next one has to overcome a high energy barrier. If the tension is too small to distort the crystal structure, atoms will stay in their places and your weight will hang forever*.
* By forever I mea... | {
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Can Loop Quantum Gravity connect in any way with string theory? The one difficulty I see with LQG is that it requires an enormous number of degrees of freedom, e.g. these spin variables in the net. This is in contrast to stringy holographic theory where the fields in a space are equivalent to fields on a boundary or a... | I'm not sure anyone has tried (except possibly Smolin in some of his older papers). But it wouldn't be that hard: take a simple loop-quantum-gravity spin-foam-analog model in 25+1 dimensions (which is going to be rather more complex than the usual 3+1 dimensional spin foam), pick a ground-state-like solution for it tha... | {
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Renormalization and Infinites Measuring a qubit and ending up with a bit feels a little like tossing out infinities in renormalization. Does neglecting the part of the wave function with a vanishing Hilbert space norm amount to renormalizing of Hilbert space?
| No, those are two very different processes (as far as I understand).
*
*Renormalization: When you are calculating vacuum expectation values, for instance $\langle \Omega\mid T(\phi(\mathbf{p})\phi(0))\mid \Omega\rangle$, you discover that these values are infinite. However, you can interpret this infinity, in a cons... | {
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Why are there only derivatives to the first order in the Lagrangian? Why is the Lagrangian a function of the position and velocity (possibly also of time) and why are dependences on higher order derivatives (acceleration, jerk,...) excluded?
Is there a good reason for this or is it simply "because it works".
| There are implications for causality when a equation of motion contains higher than second derivatives of the fields, EM radiation from charged bodies goes over the derivative of the acceleration
i don't know the details of WHY but this book should give more details:
(Causality and Dispersion Relations)
http://books.go... | {
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Why beauty is a good guide in physics? Dirac once said that he was mainly guided by mathematical beauty more than anything else in his discovery of the famous Dirac equation. Most of the deepest equations of physics are also the most beautiful ones e.g. Maxwell's equations of classical electrodynamics, Einstein's equat... | BEAUTY =SYMMMETRY you only have to look the 'patterns' in nature (nautilus shell, flowers) etc.. also SYMMETRY means SIMPLICITY since you can generate beautiful figures from simple patterns
| {
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"source": "stackexchange",
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How to avoid getting shocked by static electricity? sometimes I get "charged" and the next thing I touch something that conducts electricity such as a person, a car, a motal door, etc I get shocked by static electricity.
I'm trying to avoid this so if I suspect being "charged" I try to touch something that does not con... | This happens to me all the time; I collect an electrostatic charge just sitting at the computer; earlier Sir Dumpty often was the medium for discharge - an audible zzzt as my accumulated charge discharged through his snout when he came to snuffle against my arm/hand/palm.
A simple solution would probably be to touch t... | {
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Why is the relationship between atomic number and density not linear? What are the factors that affect the density of an atom?
| Examine the densities of di-atomic gaseous elements ($\text{H}_2$, $\text{N}_2$, $\text{O}_2$) at STP. Compare to their respective atomic weights. Also look at the densities of the noble gasses at STP. Again, note how they scale roughly with the atomic weight.
By choosing materials that are more or less ideal gases I'v... | {
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Determining Maximum Velocity of an object traveling horizontally I'm in the process of working on a physics related game. I'm looking to find the maximum velocity of an object given it's mass and the force acting on it when it is traveling horizontally. I believe there must be a method of calculating this but I'm una... | Assume the object is moving on a frictionless surface in the absence of a gravitational field with a certain velocity or it is at rest. Calculate the kinetic energy of this object as a result of its uniform motion or rest. The formula for kinetic energy is:$K.E \ =\ \Large \frac{1}{2} \large mv^2$
Applying a force for... | {
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How to explain the weak force to a layman? I'm trying to explain in simple terms what the weak interaction does, but I'm having trouble since it doesn't resemble other forces he's familiar with and I haven't been able to come up (or find on the web) with a good, simple visualization for it.
| I like the history oriented approach, when explaining something to a layman. In this case you could start by briefly explaining the fundamental forces and how we needed a new force to model beta decay.
| {
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What would happen if $F=m\dot{a}$? What would happen if instead of $F=m \frac{d^2x}{dt^2}$, we had $F=m \frac{d^3x}{dt^3}$ or higher?
Intuitively, I have always seen a justification for $\sim 1/r^2$ forces as the "forces being divided equally over the area of a sphere of radius $r$".
But why $n=2$ in $F=m\frac{d^nx}{dt... | In statics, you can still have a force without acceleration so $F$ is independent of $a$. $F$ is the cause of the change in the position of an object initially at rest in some frame. To give it physical meaning, you have to define how it's to be measured and one way would be to define 1 unit of F causing one unit of co... | {
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Electromagnetic fields vs electromagnetic radiation As I understand, light is what is more generally called "electromagnetic radiation", right?
The energy radiated by a star, by an antenna, by a light bulb, by your cell phone, etc.. are all the same kind of energy: electromagnetic energy, i.e. photons traveling through... | Electromagnetic radiations are electromagnetic waves in the electromagnetic field. It is disturbance of the electromagnetic field propagated with the velocity of light. Electromagnetic field itself is a seat of energy. $u = 1/2 (\epsilon_0E^2 + B^2/\mu_0)$
Where $u$ is the energy density of the em field. Other symbols... | {
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What is the usefulness of the Wigner-Eckart theorem? I am doing some self-study in between undergrad and grad school and I came across the beastly Wigner-Eckart theorem in Sakurai's Modern Quantum Mechanics. I was wondering if someone could tell me why it is useful and perhaps just help me understand a bit more about ... | And if you are interested in "where" it might come useful: Some of the selection rules for optical transitions can be obtained from it, and I faintly recall that it helps rewriting the Hamiltonian for Spin-Orbit coupling into a much more convenient form.
| {
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Black holes in a head-on collision Assume two uncharged non-rotating black holes traveling straight at each other with no outside forces acting on the system. What is thought to happen to the kinetic energy of these two masses when they collide? Is the excess energy lost through gravitational radiation? What would th... | When two black hole collide the horizon area of the resulting black hole must exceed the sum of the areas of the two initial black holes. This places an upper limit on the amount of gravitational radiation which is produced. If the two initial black holes have equal masses $M$ then the finial black hole must obey
$$
... | {
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Bose-Einstein condensate in 1D I've read that for a Bose-Einstein gas in 1D there's no condensation. Why this happenes? How can I prove that?
| The claim is often that there is no condensation in $d<3$. The other answers are correct, but let's be clear, there are actually two assumptions present in the claim:
*
*Assume you have $N$ noninteracting bosons in $d$-dimensions in a hypervolume $L^d$
*Assume that these bosons have an energy-momentum relationship ... | {
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Mathematical background for Quantum Mechanics What are some good sources to learn the mathematical background of Quantum Mechanics?
I am talking functional analysis, operator theory etc etc...
| A good place to look for book recommendations for mathematical physicists is this page of John Baez:
*
*books, how to learn math and physics
I have to agree with the others that the best way to learn the mathematical background of QM is to learn QM, you'll see yourself what kind of mathematical tools you'll have t... | {
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Noether's theorem vs. Heisenberg uncertainty principle In continuation of another question about Noether's theorem I wonder whether there exists some kind of relationship between this theorem and the Heisenberg uncertainty principle.
Because both the principle and the theorem relate energy with time, momentum with spac... | Noether theorem is as valid in CM(*) as in QM(**). It deals with conservation laws and symmetries. In CM the variables are certain, in QM they may be uncertain.
HUP belongs to QM and gives a limitation on canonically conjugated variable uncertainties in a given state.
If some variable in QM is uncertain, it does not m... | {
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Gravitational and gauge-gravitational anomalies in ${\cal N}=1$ $D=4$ supergravity coupled to a SUSY gauge theory with chiral matter When people talk about the first superstring revolution they often mention the miraculous cancellation of anomalies via the Green-Schwarz mechanism. My question is whether such a string-t... | There are no purely gravitational anomalies in $D=4$. The one source of gauge-gravitational anomalies is a triangle diagram with one gauge vertex and two graviton vertices. This vanishes provided that ${\rm Tr}_L Q=0$ where the trace runs over all left-handed fermions and $Q$ is the gauge generator with the potential a... | {
"language": "en",
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Did spacetime start with the Big bang? Did spacetime start with the Big Bang? I mean, was there any presence of this spacetime we are experiencing now before big bang? And could there be a presence/existence of any other space-time before the big bang?
| I seriously doubt that.
There are quite a few theories trying to discuss "the beginning of the universe", and not all of them agree with having a "beginning" to the universe.
I don't have concrete facts to support what I'm about to say so consider it as "just another idea."
"Our whole universe was in a hot dense place,... | {
"language": "en",
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"source": "stackexchange",
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Resistance between two points on a conducting surface Suppose we have a cylindrical resistor, with resistance given by $R=\rho\cdot l/(\pi r^2)$
Let $d$ be the distance between two points in the interior of the resistor and let $r\gg d\gg l$.
Ie. it is approximately a 2D-surface (a rather thin disk).
What is the resis... | "Resistance between two points" is not a well-defined concept. If c is a curve connnecting point A to point B, the electromotive force V along c is a well-defined thing (it's the circulation of the electric vector field along c), and resistance would be the factor R such that V = RI when I is the inte... | {
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Should you really lean into a punch? There's a conventional wisdom that the best way to minimize the force impact of a punch to the head is to lean into it, rather than away from it.
Is it true? If so, why?
EDIT: Hard to search for where I got this CW, but heres one, and another. The reason it seems counter-intuitive ... | My guess would be that the objective is to reduce the amount of energy dissipated into a localised area, rather than reducing the force of the strike itself.
Consider that if you lean into a strike, your muscles will flex and become more rigid. The shockwave from the impact will then travel through the rigid muscle ins... | {
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Cooling a cup of coffee with help of a spoon During breakfast with my colleagues, a question popped into my head:
What is the fastest method to cool a cup of coffee, if your only available instrument is a spoon?
A qualitative answer would be nice, but if we could find a mathematical model or even better make the experi... | How about this:
Before putting the coffee into the cup, pour the hot coffee directly onto the spoon, allowing the excess to drizzle into the coffee cup. The goal here is to make the coffee flow downstream onto the spoon and then into the cup, with as much distance as possible.
The more distance there is between the spo... | {
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If Betelgeuse were to go supernova If Betelgeuse were to go supernova would the sky be twice as bright, or day time extended, depending on what time of year it happened in.
Basically when it does supernova how bright and large will it appear in the sky, and how do you work out the apparent brightness and size for somet... | Most models of type II supernovae expect that the explosion has a peak luminosity of around $10^8$ to $10^9$ solar luminosities. This gives it a peak absolute magnitude of -15.16 to -17.16. At a distance of 200 parsecs, this is an apparent magnitude of -8.652 to -11.15.
Okay, so how bright is that? Well, the full moon ... | {
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How fast does gravity propagate? A thought experiment: Imagine the Sun is suddenly removed. We wouldn't notice a difference for 8 minutes, because that's how long light takes to get from the Sun's surface to Earth.
However, what about the Sun's gravitational effect? If gravity propagates at the speed of light, for 8 m... | Since general relativity is a local theory just like any good classical field theory, the Earth will respond to the local curvature which can change only once the information about the disappearance of the Sun has been communicated to the Earth's position (through the propagation of gravitational waves).
So yes, the Ea... | {
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What does it take to become a top physicist? What does it take to become a top physicist?
Why do so many extremely talented young upstarts totally flop as they move to more advanced physics?
| A great brain and hard work are required to be a top physicist. To be an average or below physicist is possible through a deficiency in one and a surplus in the other (I would consider myself to be moderate intelligence but a very hard worker which makes up for it to some degree). As you can see, one of these traits is... | {
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Do extra-dimensional theories like ADD or Randall-Sundrum require string theory to be true? What I mean is could it turn out that the world is not described by string theory / M-Theory, but that nevertheless some version of one of these extra-dimensional theories is true?
I have no real background in this area. I just... | Well, we have to answer another question first: "Is there any complete or consistent theory of quantum gravity which doesn't arise from string theory?"
Constructing RS models and ADD models is "phenomenological model-building".
| {
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Electricity takes the path of least resistance?
Electricity takes the path of least resistance!
Is this statement correct?
If so, why is it the case? If there are two paths available, and one, for example, has a resistor, why would the current run through the other path only, and not both?
|
Electricity takes the path of least resistance. Is this statement correct?
YES
People often don't understand what the shortest path means. If I have a lightning rod connected to a wire which has a slight bend in it people still believe that the current will follow the wire to Earth and are astonished when the voltage... | {
"language": "en",
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What is Fermi surface and why is this concept so useful in metals research? What is Fermi surface and why is this concept so useful in metals research?
Particularly, I can somewhat appreciate the Fermi energy idea - the radius of Fermi surface which is a sphere. But is there any quantitative use of more complicated Fer... | I think what you might be interested in are Van Hove singularities or the critical points of the Fermi surface, where the density of states as given by $dN/dK_{|k=k_f|}$ diverges. Now $dN/dk$ is proportional to the inverse of the gradient of the energy $ dN/dk \propto 1/\nabla E $. The locations with the greatest d.o.s... | {
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Observation of cosmological topological defects Are there any projects/experiments running for the observation of topological defects (domain walls, monopoles, etc)?
Are there any past/canceled or future such projects?
| See e.g.
http://arxiv.org/abs/hep-ex/0302011
MoEDAL at CERN has survived since that time. This is about the magnetic monopoles. Domain walls may be too much stuff too wish for so I don't think that someone is looking for them and nothing else. Cosmic strings are being constantly looked for in the telescopes but so fa... | {
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Is it really possible for water to be held in a "cone shape" for a brief period of time? I just saw this "trick" where a cup of water is turned over onto a table without spilling (using a piece of cardboard. After removing the cardboard from underneath the cup, the person then removes the cup in a particular way (lif... | Its a trick.
There are 2 vessels:
the outer that we saw, and an inner one, transparent and soft.
Stopt it at 1:48 you will see the water move out from the bottom. Under atmospheric pression the vessel merge down. The image after this moment is truncated and we can not see the remnants in the table.
The water was previo... | {
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How to build a laser in the garage? So I wonder if it is any how possible to build laser at home. A powerful one to melt brick.
| Yes. 100W CO2 laser is doable at home, and some in fact did that.
100W one will BURN really well.
No other types of power lasers are doable at home. (well, probably there is also killing 200 DVD-RW drives and collimating them all - I am actually doing that, I have 45 RW drives ;-) )
The only problems is that you still ... | {
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meaning of an integral in the continuity equation This is about continuity equation. What does the last integral mean?
$$\frac{\mathrm{d}Q_V}{\mathrm{d}t}=\iiint_V \mathrm{d}^3x \,\frac{\partial\rho}{\partial t}=-\iiint_V\! \mathrm{d}^3x\,\operatorname{div}\,\mathbf{j}=-\iint\limits_{\partial V}\!\!\!\!\!\!\!\!\!\!\!\... | Note that the range of integration has changed from $V$ meaning over the volume to $\partial{V}$ and that the variable of integration has changed from $\text{d}^3x$ to $\text{d}S$.
It means an integral over the surface that bounds the volume.
The closed curve over the integration signs implies that the surface must be ... | {
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Are elementary particles ultimate fate of black holes? From the "no hair theorem" we know that black holes have only 3 characteristic external observables, mass, electric charge and angular momentum (except the possible exceptions in the higher dimensional theories). These make them very similar to elementary particles... | This is indeed a tempting suggestion (see also this paper). However, there is a crucial difference between elementary particles and macroscopic black holes: the latter are described, to a good approximation, by non-quantum (aka classical) physics, while elementary particles are described by quantum physics. The reason ... | {
"language": "en",
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Special Relativistic Time Dilation -- A computer in a very fast centrifuge Ok, I've stumbled onto what I think is a bit of a paradox.
First off, say you had some computer in a very fast(near light speed) centrifuge. You provide power to this computer via a metal plate on the "wall" of the centrifuge's container, so it... | One thing to be aware of is that the principle of relativity would not apply to this computer--rotating reference frames are not inertial, and therefore, will not be related to 'stationary' reference frames by simple Lorentz transformations. Also note that if there are any capacitors or anything along those lines in t... | {
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List of freely available physics books I'm trying to amass a list of physics books with open-source licenses, like Creative Commons, GPL, etc. The books can be about a particular field in physics or about physics in general.
What are some freely available great physics books on the Internet?
edit: I'm aware that there... | Structure and Interpretation of Classical Mechanics Sussman, Wisdom, Mayer
A No-Nonsense Introduction to General Relativity, Sean Carroll
| {
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Paradoxical interaction between a massive charged sphere and a point charge Suppose we have a sphere of radius $r$ and mass m and a negatively charged
test particle at distance d from its center, $d\gg r$. If the sphere is electrically neutral, the particle will fall toward the sphere because of gravity. As we deposi... | The statement that the gravitational attraction will eventually dominate the coulomb repulsion as n increases is correct.
You probably think the restmass of the electrons will invoke gravitational attraction, but that part is neglible for high electrondensities on the sphere. The gravitational attraction by (the curva... | {
"language": "en",
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Why are all-Sky images drawn as a filled ellipse? There is some convention? how is this 3d to 2d mapping done?
here an example
| The ellipse is a particular way to draw the surface of a sphere - like the sphere of the skies around us, or the surface of the Earth - on a flat piece of paper or screen (because of the curvature of the sphere, it cannot be "flattened" without distortions). This one is called the Mollweide projection and it preserves ... | {
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Does hot air really rise? "Heat rises" or "warm air rises" is a widely used phrase (and widely accepted phenomenon).
Does hot air really rise? Or is it simply displaced by colder (denser) air pulled down by gravity?
| "Hot air" is just air molecules (M) moving faster (F); "cold air" is M moving more slowly (S). The collisions between the FMs and SMs force both Ms in all directions (SM faster than before, FMs slower than before, but still faster than most SMs). The space below them, however, is crowded with SMs, so those FMs knocked... | {
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I need help with finding distance traveled How do I find the distance traveled of an object if the speed is not constant?
| You can use a simple way it does include calculus.First find the maximum value of s(distance/displacement).By using the differentiation formula :ds/dt.Then add the time (t) value to the s equation.
EXAMPLE:Lets say t=2 then apply the vale to the s equation say : s=20t-5t^2
... | {
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Snell's law starting from QED? Can one "interpret" Snell's law in terms of QED and the photon picture? How would one justifiy this interpretation with some degree of mathematical rigour? At the end I would like to have a direct path from QED to Snell's law as an approximation which is mathematically exact to some degre... | In regard to the single photon aspect of the question, I speculate that the explanation is similar to the Mossbauer effect, ie the photon is absorbed and re-emitted by the entire mirror/crystal rather than a single atom. If you insist on thinking of a single photon being absorbed and re-emitted by a single atom, you a... | {
"language": "en",
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Fresnel transform How is it possible to encrypt multiple images using fresnel transform and inverse the operation to de-multiplex those images?
| The particular application the OP is asking about might be better on Theoretical Computer Science or Math, but the long and the short of it comes down to three properties of the transform
*
*The Fresnel transform is a special case of the Linear Canonical Transform (and also of the Generalized Fresnel Transform (here... | {
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Are water waves (i.e. on the surface of the ocean) longitudinal or transverse? I'm convinced that water waves for example:
are a combination of longitudinal and transverse. Any references or proofs of this or otherwise?
| I will just say what I think I know:
In the open ocean or great lakes the waves are transverse: the water goes up and down. They are originated by the winds in the surface.
Near the shore the waves become also longitudinal: the small distance from the the surface to the bottom of ocean make the difference.
added:
I d... | {
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Why are Saturn's rings so thin? Take a look at this picture (from APOD https://apod.nasa.gov/apod/ap110308.html):
I presume that rocks within rings smash each other. Below the picture there is a note which says that Saturn's rings are about 1 km thick.
Is it an explained phenomenon?
| If one could assume that the ring is a continuous distribution of mass, we could try minimizing the total energy of the system (self energy + energy of interaction with Saturn). These two conditions along with the condition that total mass of the disc is a constant, would (I think) leave us with a unique geometry (inne... | {
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Why is the decibel scale logarithmic? Could someone explain in simple terms (let's say, limited to a high school calculus vocabulary) why decibels are measured on a logarithmic scale?
(This isn't homework, just good old fashioned curiousity.)
| It's a historical accident which has left us a lasting pain in the ass. There's no reason to express sound as decibels: writing the pressure level in Pascals in scientific notation is just as convenient as writing a level in decibels relative to some reference pressure level. And it's often MORE convenient for calcul... | {
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dynamic casimir effect A few years ago, when i studied the casimir effect interpretation as the filtering out of vacuum modes with appropiate boundary conditions, i had the following dilemma; supposedly the derivation of the force between the walls was entirely equivalent to just calculating Van der Waals forces. This,... | A friend recently brought to my attention that this experiment was actually performed 6 months after i posted the question in this site:
http://blogs.nature.com/news/2011/11/light_coaxed_from_nothingness.html
http://www.chalmers.se/en/news/pages/chalmers-scientists-create-light-from-vacuum.aspx
Christopher Wilson from... | {
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Coriolis effect on Tsunami The Japanese tsunami, moving at about 700 km/h, affected areas as distant as Chile's coast, 20 hours after the earthquake. How does the Coriolis force affect tsunami? Also, I saw an image of a boat caught within a large whirlpool. Is the whirlpool's rotation due to Coriolis force?
| The Coriolis effect is proportional to velocity:
$\boldsymbol{ F}_C = -2 \, m \, \boldsymbol{\Omega \times v}$,
where $\boldsymbol{\Omega}$ is the angular velocity (of the earth).
As waves, tsunamis have very high velocities, you would think it would be enough to see the Coriolis effect, but in fact there is little eff... | {
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Why does Fukushima pressure rise?
Possible Duplicate:
Why didn't the control rods in Fukushima shut down the reactor?
They say that pressure rises and that this can be dangerous. But why does this happen if the reactor is shutdown ?
| Because even if reactor is not-critical, there are lots of radioactive materials in the fuel which decays and produce some heat. You cannot stop that process. Although it gives much less heat than nuclear fission, it is still significant and can cause meltdown.
The same reason is why spent nuclear fuel is stored under ... | {
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Uses of the 'Golden Ratio' in Physics 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 questi... | In general, no, the golden ratio is not used often in physics. As a graduate student in experimental physics, I have never encountered the golden ratio in my work, except in toy problems.
| {
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Can a nuclear reactor meltdown be contained with molten lead? 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 reac... | A problem that seems to have been overlooked is the atomic mass of lead.
Lead, although heavier than all non radioactive elements, is lighter than all
radioactive elements. The result of injecting molten lead into a molten core
would be a layer of molten lead floating on top of the molten fuel.
Further, depending on t... | {
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What are the reasons to expect that gravity should be quantized? 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... | For the sake of argument, I might offer up a plausible alternative. We might have some quantum underpinning to gravitation, but we might in fact not really have quantum gravity. It is possible that gravitation is an emergent phenomenon from a quantum field theoretic substratum, where the continuity of spacetime might... | {
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For an accelerated charge to radiate, is an electromagnetic field as the source necessary? 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?
| Your question is somewhat abstruse, but here's what I think you're asking:
Put a charged particle in a uniform external magnetic field. The particle will move in a circular orbit, but since it's accelerating, it will radiate and its orbit will decay.
Now remove the magnetic field. Grab the charge and forcibly swing i... | {
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CPT violation and how could quark masses differ from anti-quark masses? 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... | I suppose it will be a painful wait for the 5 sigma. Well, quarks are confined, so maybe it's OK for them to exhibit genuine CPT violation, whereas the neutral particles need renaming according to the mirror picture. But on the other hand, the quark braids have neutral strands, and if we mix (say for the proton) the uu... | {
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What is the most energy efficient way to boil an egg? 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 ... | "Energy efficient" usually means "with minimal production of entropy". For that you need, 1) a well insulated (on the sides) pot, 2) minimal loss from heating element, 3) the smallest possible (and practical) amount of water amount that can boil an egg (i.e. conver its whole surface) and 4) put the egg at the beginning... | {
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Quaternions and 4-vectors I recently realised that quaternions could be used to write intervals or norms of vectors in special relativity:
$$(t,ix,jy,kz)^2 = t^2 + (ix)^2 + (jy)^2 + (kz)^2 = t^2 - x^2 - y^2 - z^2$$
Is it useful? Is it used? Does it bring anything? Or is it just funny?
| There is a book:
"Quaternions, Clifford Algebras and Relativistic Physics." by Patrik R. Girard. Find this if you want to learn more -- very good reading, not very complex and not very long. I'll just cite the first paragraph of chapter 3.
From the very beginning of special relativity, complex quaternions have been us... | {
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Can electricity transfer radioactivity? If a cable used to power something is exposed to a radioactive source will it over time make the entire cable radioactive?
| Are you worried that the cables that go to the Fukushima reactors will carry radioactivity out?
The answer is No. You should read up a bit on radioactivity and educate yourself, since it is one of the facts of life. In the article you will see that it is atoms that are responsible for radioactivity whereas the current ... | {
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What properties do you need for building a tower? When I was a boy I used to daydream about building a tower so tall that the top of it would project into near space.
There would perhaps be a zero gravity area in the penthouse where my friends and I could bounce around and play space versions of various earth-based gam... | Rather than using material, perhaps magnetic fields configured in stages. Imagine a stack of plates separated at a distance on the order of a meter. Magnetic fields, from superconducting magnetics repeal the plates above or below. Sensors and an electronic system dynamically adjust the fields. I wonder if the fields wo... | {
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Do cosmological and Doppler redshift produce different patterns? For a given black body radiation curve, would the changes to the spectrum resulting from cosmological expansion and those from Doppler effects be distinguishable on the basis of the shapes of the resulting curves alone? Or, put another way, starting from ... | This addresses the comment to Professor Bunn's answer more than the original question:
Any spacetime described by the FLRW metric, where objects are static in comoving coordinates and redshift is due to expansion of space, can in principle be also described, via an appropriate change of coordinates, by a spherically-sy... | {
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Will Earth Hour do damage to power supply system? There is always a debate around Earth Hour every year, and the opposite side of Earth Hour usually claims that
The (sudden) decrease and increase of the power usage in the start and end of Earth Hour will cause much more power loss (than the save of power), and even do... | As the vast majority of people aren't stupid enough to fall for the scam/hoax, the effects will be miniscule.
And of those who do, as said, their electric lights are only a small percentage of their total power consumption (and most likely they'll compensate by turning to other electrical appliances that consume more e... | {
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"source": "stackexchange",
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What future technologies does particle physics and string theory promise? What practical application can we expect from particle physics a century or two from now? What use can we make of quark-gluon plasmas or strange quarks? How can we harness W- and Z-bosons or the Higgs boson? Nuclear physics has given us nuclear p... | Cultural enrichment.
Let me explain. String theory is a work of art. Art has no practical application, you say? No! It is practical in enriching culture and uplifting the emotions of mankind. So is string theory. The emotional satisfaction that you get out of it. Shout it out to the whole world!
We fund art, so why not... | {
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Definitions and usage of Covariant, Form-invariant & Invariant? 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 quant... | These words do have different meanings, this is a general guide to their differences. In different fields they may have slightly varying definitions. I would recommend looking them up to be certain.
Invariant means does not change at all. Everything is the same (whether physical law, quantity or anything). In terms of ... | {
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Why there's a whirl when you drain the bathtub? 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.
| Since you want to explain it to your daughter, take a plastic bottle, cut the bottom open, turn it upside town, hold the top closed and fill it with water. Give her that bottle and have her release the top (which is on the bottom now, sorry for the bad phrasing). The water will whirl in different orientations whenever ... | {
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"source": "stackexchange",
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Why does Venus spin in the opposite direction? 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... | There seems a lot of conjecture in any event. Venus could have been a meteor, with an innate spin, that swung by the Sun and have been captured into our Solar systems anticlockwise orbital arrangement. Retaining her original spin momentum, clockwise relative to the others.
| {
"language": "en",
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"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "14",
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How might a resonant antenna and black body radiation interact? 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 whe... | OK, the simple answer:
When there is a resonance in the antenna you have a coherent phenomenon. All the bands of electrons of the antenna are marching in tune.
The black body radiation is an incoherent phenomenon coming from the individual atoms of the antenna. Even if the peak of the black body radiation were sitti... | {
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Dangerous dose of I-131? I was searching a lot and could only find dosages for curing cancer and allowed emission, but no Iodine-131 dose that could be connected with increased thyroid cancer risk (like, 10mSv is the radiation dose resulting with measurable increase of cancer).
The Central Laboratory of Radiological Pr... | It's difficult to get hard figures without exposing people and seeing how many die! Then the problem is that for low levels of exposure you have to workout how many extra people have died
The Nation Cancer Institute has some calculators and papers based on US nuclear testign exposure
| {
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"source": "stackexchange",
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Measuring the spin of a single electron Is it possible to measure the spin of a single electron? What papers have been published on answering this question? Would the measurement require a super sensitive SQUID, Superconductive Quantum Interference Device?
| I was browsing old questions and noticed this one. I think I ought to take issue with the idea you can measure the spin of a single electron. Suppose I prepare an electron in a definite spin state and send it into another room; I don't think there is any way someone else can tell what state I prepared the electron in. ... | {
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What are the conditions to be satisfied by a theory in order to be a quantum theory? This is in continuation to my previous question. It is not a duplicate of the previous one. This question arises because of the answers and discussions in that question.
Can we call a theory, quantum theory, if it is consistent with HU... | *
*.NET is a framework
*Software that is built using languages supported by .NET is called .NET software.
*That software may or may not break if some part of .NET breaks.
*It is necessary to have .NET in place for the software to work.
Now replace .NET with QM and software with theory. :-D
| {
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What reflective media do laser shows use? I am having a hard time in finding out what exact light media laser shows use. I am trying to build a laser show myself. I know that the laser light is reflected off these particles in such a way that that it makes the laser line "viewable" in all directions
Can somebody explai... | http://en.wikipedia.org/wiki/Theatrical_smoke_and_fog describes the methods used to create smoke. Also I think, in a room filled with people (like at evening parties), the humidity gets high enough to make light beams visible.
| {
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How to measure the spin of a neutral particle? If a charged particle with charge $q$ and mass $m$ has spin $s \neq 0$ we can measure an intrinsic magnetic moment $\mu = g \frac{q}{2m}\hbar \sqrt{s(s+1)}$. This is how spin was discovered in the first place in the Stern-Gerlach Experiment.
But for a neutral particle $\mu... | Also the neutron has a magnetic moment. Check this out. The reason is that the neutron is not an elementary particle but built up from quarks which have charge...
| {
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What is the difference between $|0\rangle $ and $0$? What is the difference between $|0\rangle $ and $0$ in the context of $$a_- |0\rangle =0~?$$
| You may consider 0 as an eigenvalue and write $a|0\rangle = 0|0\rangle$.
Any eigenvector $a|\alpha \rangle = \alpha |\alpha \rangle$ is of different "length" than the corresponding normalized vector $|\alpha \rangle$. In your particular case the vector $0|0\rangle$ is of zeroth length.
| {
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Can a disk like object (like UFO's) really fly? UFOs as shown in movies are shown as disk like objects with raised centers that emit some sort of light from bottom. Can such a thing fly?
My very limited knowledge in physics tell me that a disk like object may not be able to maneuver unless it has thrusters on sides and... | In mid 2010, Japan Aerospace Exploration Agency launched IKAROS, a spacecraft that is pushed by the radiation of the Sun.
Explanation: If you consider relativistic effects, light (photons) have no mass, but they can carry momentum $p=h/\lambda$ per photon particle, where $h$ is Planck's constant and $\lambda$ is light'... | {
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"source": "stackexchange",
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Making a "heavier-than-air" craft float How big would a hollow rigid object need to be to float, (not in water but in air) if all of the air was vacuumed out and the container sealed?
| Just to flesh out Jim's answer.
Assume you made a cube (makes the math easier!) 1m x 1m x 1m
Aluminium has a density of 2700kg/m^3
And you need the cubeto have a mass of less than 1.2Kg
- so can use (1.2/2700) m^3 of material
The surface area is 6m^2 then you can have a thickness of (1.2/2700)m^3 / 6m^2 = 70um
Or abo... | {
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Have CMB photons "cooled" or been "stretched"? Introductory texts and popular accounts of why we see the "once hot" CMB as microwaves nearly always say something about the photons "cooling" since the Big Bang. But isn't that misleading? Don't those photons have long ("cool") wavelengths because space expanded since the... | I will use most of @Ted answer to describe 'hot' but I will ask a more basic question:
I think the best way to think about it is that the sentence "the
photons have cooled" is simply describing a fact, not explaining that
fact. At early times, the photons at any given location had a thermal
(blackbody) distrib... | {
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Alcubierre Drive - Clarification on relativistic effects On the Wikipedia article on the Alcubierre drive, it says:
Since the ship is not moving within this bubble, but carried along as the region itself moves, conventional relativistic effects such as time dilation do not apply in the way they would in the case of a ... | Spacetime is constructed in such a way that the travellers own proper time is equal to the coordinate time of the external, distant observers. Thus, there is no time dilation. This is clear from Alcubierre's original article:
Of course, other kinds of warp drive spacetimes also need to be checked individually, i.e. wh... | {
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Supergravity calculation using computer algebra system in early days I was having a look at the original paper on supergravity by Ferrara, Freedman and van Nieuwenhuizen available here. The abstract has an interesting line saying that
Added note: This term has now been shown to vanish by a computer calculation, so tha... | I don't know about this particular paper, but I do know that several early supergravity computations were checked using a computer algebra program 'Abra' written in Pascal by Mees de Roo. You could do gamma matrix algebra and Fierz transformations with it (among others), and it had a quite clever method to interactivel... | {
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"source": "stackexchange",
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Why does a rotating tire use the static, rather than the dynamic coefficient of friction? The explanation I have heard of the difference between static and dynamic friction is that static friction is stronger because bonds form when one object is put on top of another object and these have to be overcome to get the mov... | A car drives at 20 m/s. The circumference of the wheel is 2m, so the rotation rate is 10 Hz. A reasonable percentage of the tire is in contact with the ground - maybe around $5\%$. That would give a contact time of $5\times 10^{-3}$ s.
This is a pretty long time in molecular terms. The distance between molecules divi... | {
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Why do they store gold bars with the narrow side down? I watched on TV as they where showing gold bars stored in bank vaults and I noticed that they always stack them with the narrow side down and the wide side up. Like this:
So there has to be a mechanical reason why is that. Any ideas?
| They do not always seem to be that shape. For some cuboids which are not designed to be moved regularly, see this picture from Fort Knox.
But for bullion bars in the world market (about 10.9-13.4 kg of gold) which have the standard sort of trapezium cross-section, the top when casting is the wider area to get them out... | {
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"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
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Relativistic space-time geometry What subject (suggest book titles, etc.) should I study to get a clear grasping of hypersurfaces, 2-surfaces, and integration on them, mostly in special relativity (I'm not messing with general relativity yet).
| As others mentioned, special relativity (by definition really) doesn't have anything to do with curved surfaces! Special relativity has a particular metric (minkowski metric) which has no curvature. If your interested in manifolds (particularly integration on them, since integration in minkowski space is pretty trivial... | {
"language": "en",
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What is meant by positive and negative gravity/energy/spacetime-curvature? I have recently come across some cosmological assertions (based on empirical data) about the universe being self contained in the sense that it is entirely capable of coming into existence from a zero-energy initial state. This is based on the o... | This is a very misleading claim which keeps being touted in popular science books and the media.
I asked about this earlier over here.
Total energy of the Universe
From what I can see, there is a lot of controversy over what total energy even means in the context of general relativity, so claims about "negative energy ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/9201",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
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Laplacian of $1/r^2$ (context: electromagnetism and Poisson equation) We know that a point charge $q$ located at the origin $r=0$ produces a potential $\sim \frac{q}{r}$, and this is consistent with the fact that the Laplacian of $\frac{q}{r}$ is
$$\nabla^2\frac{q}{r}~=~-4\pi q~ \delta^3(\vec{r}).$$
My question is, w... | The electric field from your potential is:
$$E(r) = {2\over r^3}$$
Using Gauss's law, the total charge in a sphere of radius R is:
$$Q(r) = \oint E \cdot dS = 4\pi r^2 {2\over r^3} = {8\pi\over r}$$
The total charge is decreasing with r, so there is a negative charge cloud of density
$$ \rho(r) = {1\over 4\pi r^2} {dQ\... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/9255",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
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Is dark matter repulsive to dark matter? Why? I think I saw in a video that if dark matter wasn't repulsive to dark matter, it would have formed dense massive objects or even black holes which we should have detected.
So, could dark matter be repulsive to dark matter? If so, what are the reasons? Could it be like the o... | Lubos Motl's answer is exactly right. Dark matter has "ordinary" gravitational properties: it attracts other matter, and it attracts itself (i.e., each dark matter particle attracts each other one, as you'd expect).
But it's true that dark matter doesn't seem to have collapsed into very dense structures -- that is, thi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/9302",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
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What is the smoking gun signature of string theory? What is the smoking gun signature of string theory? Suppose we have a complete and consistent model of quantum gravity with a zero or negative cosmological constant, but all we are given is its complete S-matrix. Using only this information, how do we figure out wheth... | I ( an experimentalist) will wade in where angels ( theorists) fear to tread :).
There exists this great in length report by CMS where you will see in the introduction part of the motivation for the experiment as :
Various alternatives to the Standard Model invoke new symmetries,
new forces or constituents. Furt... | {
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Anti-matter repelled by gravity - is it a serious hypothesis?
Possible Duplicate:
Why would Antimatter behave differently via Gravity?
Regarding the following statement in this article:
Most important of these is whether ordinary gravity attracts or repels antimatter. In other words, does antihydrogen fall up or do... | The only problem with this is that antimatter has the same mass as its matter counterpart. So this means that is effected the same way by gravity as normal matter.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/9375",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
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