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As the galaxy is moving and the solar system orbiting the galaxy and the Earth orbiting the sun. So how fast is each object moving and what is the fastest we move at?
Do we even know how fast the galaxy is moving that is not relative to another galaxy (although I guess velocity has to be measured relative to something)... |
First, what determines the strength of an RF signal?
Why is it said that a cellphones radiates more energy when the reception from signal tower is lower in strength.
Why is it said that RF gets transmitted along wires such as in wired headsets making them act as antennae?
Is it then safer to use bluetooth headsets ov... |
Recently I got the book "On the Shoulders of Giant" from Stephen Hawkings. It consists of more than 1000 pages of classical publications in physics. However 900 pages are given to the work of Copernicus, Galilei and Newton and 100 pages are given to the papers of Einstein. Therefore I think this books gives a wrong imp... |
Where/what is emitting cosmic background radiation, and when did it come into existance, was immediately after the big bang?
I know that the universe isn't 3D in the traditional sense, and I don't pretend to understand it. However if the big bang originated from a single point, and the cosmic radiation was emitted from... |
I have a top of unknown mass that has a moment of inertia $I=4\times 10^{-7} kg \cdot m^2$. A string is wrapped around the top and pulls it so that its tension is kept at 5.57 N for a distance of .8 m.
Could somebody help me derive some equations to help with this? Or to get me in the right direction? I have been tryin... |
This is a nice question when you find it out, and I am really looking for a proper answer.
Take quicksilver (Hg) in the periodic table. It has one proton more than Gold (melting point 1337.33 K), and one less than Thallium (melting point 577 K). It belongs to the same group as Zinc (692.68 K) and Cadmium (594.22 K). Al... |
I've come across this quote attributed to Misner, Thorne & Wheeler from their book, Gravitation:
Mathematics was not sufficiently refined in 1917 to cleave apart the demands for "no prior geometry" and for a geometric, coordinate-independent formulation of physics. Einstein described both demands by a single phrase, "... |
One of the curses of 2-liter bottles is that when carbonated beverages are stored in them for long periods (i.e. days between drinks) at least the last liter ends up being flat. However, if after every pour the bottle itself is crushed such that the remaining volume of air above the liquid is as small as possible, and ... |
This question is inspired by the following comment:
the strings in string theory are relativistic and on a large enough piece of world sheet, the internal SO(1,1) Lorentz symmetry is preserved. That's why a string carries not only an energy density ρ but also a negative pressure p=−ρ in the direction along the string.... |
recently I have had some exchanges with @Marek regarding entropy of a single classical particle.
I always believed that to define entropy one must have some distribution. In Quantum theory, a single particle can have entropy and I can easily understand that. But I never knew that entropy of a single rigid classical par... |
As we know, fermions are subject to exchange interactions that limit the densities they can achieve. However bosons (simple or composite) are not constrained by this, which implies physical phenomena like the Bose-Einstein condensate, where the main component is Helium-4
Question: Are there physical limits to the densi... |
On John Baez's website, http://math.ucr.edu/home/baez/entropy.html, he discusses the problem of how entropy increases when a cloud of ideal gas collapses gravitationally (no black holes - keeping it simple). But he doesn't give away the answer - instead he implies that, I presume, either gravitons or photons are relea... |
One of the main sources of subtlety in the AdS/CFT correspondence is the role played by boundary terms in the action. For example, for a scalar field in AdS there is range of masses just above the Breitenlohner-Freedman bound where there are two possible quantizations and which one you get depends on what boundary term... |
In the periodic table of the elements, only a few of the elements are gases at standard temperature and pressure. Those elements include the noble gases some of the halogens, and a few of the elements next to them, i.e. oxygen and nitrogen.
So why are these elements gases?
|
I've heard the claim that some aspects of string theory are used to improve Monte-Carlo simulations of lattice QCD, for example by people working at the LHC.
I know a bit about Monte-Carlo methods in lattice QCD, but have no idea of how string theory ideas are applied to QCD at all, so I'd like to ask for
a short exp... |
Here :
http://www.newscientist.com/article/dn20084-neutron-star-seen-forming-exotic-new-state-of-matter.html
are news on superfluidity in a neutron star. The necessary bosons they say are pairs of neutrons. So far, so good.
But then they postulate the production of neutrinos in the formation of those neutron pairs.
... |
Why is the amount of energy transferred to a driven mechanical oscillator largest when the drive frequency is the same as the natural frequency of the oscillator? Why are they exactly out of phase by π/2?
Clarifying example experimental setup: http://av.ph.tum.de/Experiment/1000/Grafik/b1605.gif
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Taking off from the Rutherford-Bohr model,
Figure 1. Rutherford-Bohr model.
when an electron absorbs energy (from light, heat, or otherwise) it jumps to a higher energy level, or shell. Then when the electron loses that energy, it reverts back to a lower-numbered shell.
Now that the atomic orbital model is now more wi... |
I have been reading Hawking's 'A Brief History of Time' and it has gotten me thinking about Einstein's theory of relativity, in that it assumes that an object must have infinite mass if it is to be traveling at the speed of light (please correct if I'm wrong in my beginner's knowledge of physics).
But, do light waves h... |
[Question suggested by @Lawrence B. Crowell's answer to the question on T-duality]
There are three parts to my question:
A. What is the action for ${\cal N}=4$ SUSY Yang-Mills and what is the physics of the various terms in the action?
B. Give a simple explanation for the origin of Montonen-Olive duality in this theor... |
Should they be taken out of the wrapping and stored as single units, or should I leave them in the package?
EDIT to add I mean, the package is 24 bottles bundled together. Should I just leave them in the crate, or disperse them around the fridge?
|
How the Green's functions and the Quantum Mechanics are related? Do they can be used to solve the Schrödinger equation of an particle subjet to some potential that is not a Dirac's delta? And the proprieties of some Green's functions that are symmetrical, i.e. $ G(x|\xi) = G(\xi|x)^{\ast} $, has some relation with the ... |
Today I saw the derivation of the wave equation in class, and I did not understand the following step.
We are modeling a uniform-density string as being made up of tiny masses spaced a small amount $h$ apart connected by springs obeying Hooke's law. Let $y_i(t)$ be the vertical position of the $i$'th such particle. Th... |
Is it correct to say that kinetic energy is a scalar?
|
It is always told as a fact without explaining the reason. Why do two objects get charged by rubbing? Why one object get negative charge and other get positive charge?
|
The increasing water pressure as you go deeper is generally explained in terms of the weight of the water column above the observation point pressing down. The question, then, is what would happen if you had a big blob of water in free fall, say 100m in diameter-- not big enough to produce large gravitational forces on... |
If I have a vector A=4i+3j and B=5i-2j, how can I find the vector product AxB? I know that given the angle, its C=AB sin theta, but how can I solve this without the angle?
|
The usual way to model a vibrating membrane is by using the wave equation. Is it possible to do that from "within"? Probably the answer is yes, but where can I see it done explicitly. What I mean is can we model the membrane as a two dimensional Riemannian manifold without any specific embedding in $\mathbb R^3$ plus e... |
I'm trying to solve a problem where I have an object resting on an inclined plane, with the angle of the plan being alpha, and the weight being w. I'm having trouble figuring out how I can calculate the component of the weight parallel to the plane. I also want to find out the weight component perpendicular to the plan... |
I premise that I haven't yet studied General Relativity, but in Relativistic Electrodymaics I have knowed impulse-energy tensor of Electromagnetic Field.
I know in Einstein's equations there is impulse-energy tensor $T_{\mu\nu}$ too:
$$
R_{\mu \nu} - {1 \over 2} g_{\mu \nu} R + \Lambda g_{\mu \nu} = \frac{8 \pi G}{c^... |
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 space.
So far, so good? (if not please clarify)
On ... |
According to this picture
the light emitted by an object depends on its temperature.
That makes perfect sense when we heat a metal. As its temperature raises we see it red at first, then orange, then yellow... and then?
If we heated it even more should we see the metal turning green? and then blue?
|
Many equations of motion can be derived from a variational principle. To take a simple example, the wave equation $h^{ij} \partial_i \partial_j u = 0$ (where $h^{ij}$ is the Minkowski metric $\mathrm{diag}[-1,+1,+1,+1]$) can be derived from the Lagrangian density
$L = \frac{1}{2} h^{ij} (\partial_i u) (\partial_j u)$ :... |
A local FM radio station transmitting at 89.3 MHz recently announced that it would be running at 50% power due to freezing weather and a forecast of ice accumulation, as "when ice is forecast ... it can damage our antenna if we run at full power."
What is the effect of ice on (the electrical properties of) an antenna?
|
How do we know that dark matter is dark, in the sense that it doesn't give out any light or absorb any? It is impossible for humans to be watching every single wavelength. For example, what about wavelengths that are too big to detect on Earth?
|
Am I correct it remembering that unless a pulsars beams plane faces earth we can not detect them. And that similarly inbetween the pulses we can't see them either?
If so how does this differ from dark matter? Isn't it possible that there are a lot more pulsars that we just can't see them because they are pointing the w... |
So I am studying for my exam on monday for analytical mechanics. I am kind of stuck on a question, so wondering if someone can give me a pointer. I am actually looking for some pointers and some techniques (hints and tips) to get me through this. the topic is just simple velocity as a function of time, velocity as a fu... |
Can you provide a list of the most important discoveries/breakthroughs in physics recently?
By recent, I mean the past decade or so. All branches of physics are welcome.
Basically, I am interested in major physics breakthroughs/discoveries which haven't become well-known yet outside their narrow specialties. Most break... |
There has been some heated debate as to whether the laws of physics allow for traversable wormholes. Some physicists claim we require exotic matter to construct wormholes, but then others counter the Casimir effect with ordinary matter is sufficient. But these same physicists seldom come up with an explicit solution or... |
Perturbation theory presumes we have a valid family of models over some continuous (infinitely differentiable, in fact) range for some parameters, i.e. coupling constants. We have some special values for the coupling constants characterizing the unperturbed model, which presumably, is relatively easy to solve. We also ... |
Inspired by How do we know that dark matter is dark? and What is the temperature of the surface and core of a neutron star formed 12 billion years ago now equal to?
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Where exactly does CMB come from. I've seen it in documentaries as a huge sphere with Earth in the middle. But if all this radiation was ejected from the start of the universe some time after the big bang; why can we see it? Surely the radiation should be travelling away from us? Just like every galaxy is?
|
Most string theory compactifications analyzed so far have as backgrounds a conformal field theory corresponding to a nonlinear sigma model with a Calabi-Yau target space, or some relatively classical background, possibly with orbifolding. But as long as the central charge of the Virasoro algebra is right, and worldshee... |
For $S$ and $S'$ in standard configuration, the Galilean transformations are :
$x' = x - vt$
$y' = y$
$z' = z$
$t' = t$
From the Lorentz transformations for $v << c$ :
$x' = x - vt$
$y' = y$
$z' = z$
$t' = t - v_x/c^2$
So it looks as if the Galilean transformations become increasingly accurate for :
$v_x \implies 0, v... |
Why can't photons have a mass? Could you explain this to me in a short and mathematical way?
|
This question is directed mostly at people giving lectures on black holes, but input by other physicists or students is very much appreciated.
Do you know a good (home)-experiment with a black hole analog (such as water in a bathtub) that allows to discuss most of the pertinent concepts and features of a black hole?
To... |
If I poured water into my tea, would I see more or less of the bottom of the tea-cup?
Intuitively, there would be as many particles blocking as many photons, and so I'd see the bottom just as clearly as before.
|
Im a writing a school report regarding the electric energy and potential of a capacitor.
In short:
An experiment was carried out where we charged a capacitor, and then decharged it with an electric engine, lifting up a predefined weight. We then measured how high the weight was lifted with different voltages.
i then fo... |
A damped harmonic oscillator with
$m = 10$kg, $k = 250$N/m, and
$c = 60$kg/s is subject to a driving force given by $F_0\cos(\omega t)$,
where
$F_0 = 48$N.
(a) What value of $\omega$ results in steady-state oscillations with maximum
amplitude?
(b) What is the maximum amplitude? What i... |
Hey guys,
while learning thermodynamics i wondered how a the principle of a heat pump would look at a microscopic level, not on a quantum mechanical level.
I learned that when a hot and a less hot body are in direct contact, the heat is transferred by the kinetic energy of the atoms, so to speak the vibrating atoms of ... |
1.In classical mechanics, using Newton's laws, the ellipticity of orbits is derived. It is also said that the center of mass is at one of the foci.
2.Each body will orbit the center of the mass of the system.
My question is : Are the assumptions in 1 and 2 correct?
Follow up question : Assuming the distance from the ... |
As you may have seen, a small asteroid had a near miss with the earth a few days ago.
As a physics teacher teaching momentum, I think this could be an excellent problem for my students, however, I don't know how to determine the mass or velocity of this object. I could get a decent estimate of the mass simply by assum... |
Last month I asked about a 27-dimensional origin of the heterotic string. Now I'm looking at Witten's "Three-dimensional gravity revisited", where he proposes that pure gravity on AdS3 is dual to the "monstrous moonshine" CFT, which is bosonic string theory on a "Leech lattice" orbifold. Wouldn't that mean we were also... |
Why massless particle can't exceed speed of light?
|
I had earlier also asked a question about super conformal theories and I am continuing with that, now with more specific examples. I am quite puzzled with it given that I see no book explaining even the basics of this. I am merely picking this up from stray notes and papers and mostly discussions. So for ${\cal N} = 2... |
I read this report and summarise here but my question is - if quantum mechanics will make glass melt at temperatures near absolute zero and it is near absolute zero then wouldn't this be a huge issue for satellites and space shuttles?
http://www.sciencedaily.com/releases/2011/02/110202102748.htm
Scientists Use Quantum... |
Why is there a deep mysterious relation between string theory and number theory (Langlands program), elliptic curves, modular functions, the exceptional group $E_8$, and the Monster group as in Monstrous Moonshine?
Surely it's not just a coincidence in the Platonic world of mathematics.
Granted this may not be fully an... |
A lot of physics, such as classical mechanics, General Relativity, Quantum Mechanics etc can be expressed in terms of Lagrangian Mechanics and Hamiltonian Principles. But sometimes I just can't help wonder whether is it ever possible (in the future, maybe) to discover a physical law that can't be expressed in terms of ... |
What happens in string theory when the temperature exceeds the Hagedorn temperature? Is that even possible? If yes, what is the nature of the phase transition and the phase beyond that? What happens to spacetime in the new phase?
|
I would like to know how important the cosmic censorship conjecture is? Should/must a quantum theory of gravity obey this? It was never rigorously proved in classical GR too. What would be the consequences if it turns out that CCC (weak) does not hold?
|
The hotter something is glowing the more white/blue it appears. A dying medium sized star expands, cools and becomes a red giant for a while, but eventually it is going to gravitationally collapse (once enough Iron (Fe) is accumulated in the core). Then it blows the outer layers away and what is left collapses into a w... |
a fight from east to west, (e.g. Australia melbourne to perth) takes longer than travel backwards. (west to east).
What's the reason?
|
Wikipedia article on deuterium says this:
The deuteron wavefunction must be
antisymmetric if the isospin
representation is used (since a proton
and a neutron are not identical
particles, the wavefunction need not
be antisymmetric in general).
I wonder why does the wave function need to be antisymmetric when... |
I'm working on an AI for a pinball-related video game. The ultimate goal for the system is that the AI will be able to fire a flipper at the appropriate time to aim a pinball at a particular point on the table. We are using an engine that will handle the underlying physics interactions when the ball is hit (Unreal). ... |
One thing I've heard stated many times is that "most" or "many" physicists believe that, despite the fact that they have not been observed, there are such things as magnetic monopoles.
However, I've never really heard a good argument for why this should be the case. The explanations I've heard tend to limit themselves ... |
What causes gravity? Why is there attraction between masses? Is it due to time or space distortion?
|
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 it. I have had two years of undergrad mechanics and ... |
How are photons counted?
What is the experimental setup used to count photons from a laser or even a lamp? Of course, in the case of the lamp, I would be able to count only the photons that pass through an area sensor in a particular observation point.
If at all possible, a setup that can be done at home is preferred--... |
I was reading a post about space mining, specially lunar mining. I was thinking about what would change in Earth's orbit if we start bringing tons of rocks to it? I mean, in a huge scale.
So, would space mining change Earth's orbit in a way to produce any dangerous effects?
If the system in question is not a planet/sat... |
A useful way of thinking (not only) oceanic waves is to consider them as a superimposition of linear modes: the elevation η of the sea surface is given by:
1: $\eta({\bf x}, t) = \int_{-\infty}^{\infty} \hat{\eta}({\bf k}) e^{i({\bf k \cdot x} - \omega t)} d{\bf k}$
where $\omega$ and ${\bf k}$ are related by a dispers... |
Quantum electrodynamics based upon Euler-Heisenberg or Born-Infeld Lagrangians predict photons
to move according to an effective metric which is dependent on the background electromagnetic
field. In other words, photon trajectories are curved in presence of electromagnetic fields,
meaning that an effective gravity is a... |
I recall from my undergraduate statistical mechanics and QM classes that Planck's Law may be derived fairly straight-forwardly by considering the density of states of EM radiation in thermal equilibrium with a particle inside a cubic box. Indeed the derivation on this wiki page is just the same and appears (IMO) to be ... |
Is 89MHZ station emitting photons of 89MHZ frequency? (I mean $\nu$ in $E=h\nu$).
|
A photon emitted from a receding source (Doppler redshift) has less energy when detected at an observer's location. Please explain the energy loss from the perspective of energy conservation.
|
I have a ball attached to a spring and the spring is attached to a wall. There is no gravity for simplicity. In the rest RF the oscillating ball energy is conserved: T + U = const. In a moving RF it is not conserved. I would like to see the shortest answer to the question "Why?".
| <-- -->
|/\/\/\/\/\/\/O
|
... |
First, I should point out that this question was raised by a particle physics Professor whose lessons I attended last year. I don't recall exactly how the question was phrased so if anyone would like to suggest an edit feel free.
So, here are some statements that to the best of my knowledge are correct:
In QM and the ... |
Give me a lever long enough and a
fulcrum on which to place it, and I
shall move the world.
-Archimedes
How long would that lever have to be?
That is to say, how long a lever would be needed on Earth, to lift a sphere with the mass of Earth if a human of average size were to sit on the other side ... |
I was wondering, within a static train, for a fly which is currently floating in the air and not moving at all, what will happen if:
The train starts to accelerate and move forward. Will the floating fly experience inertia and being pushed backward?
If the train is completely evacuated (without air), will the floating... |
I am aware about different interpretations of quantum mechanics out there but would mostly like to see an answer from the perspective of Copenhagen interpretation (or relative quantum mechanics if you wish).
Let an observer being a man with brain consisting of molecules and atoms. According the basic principles of quan... |
We've previously discussed why it is that spinning tops do not fall over, see: Why don't spinning tops fall over?
However, as the highest rated answer notes, the angular momentum of the spinning top is "quite high". On the other hand, I know that if the angular momentum of the top is zero it will, in fact, fall over. T... |
As I read in The Road to Reality by Roger Penrose, the Joukowsky transform $$w(z) = \frac12\left( z + \frac1z \right)$$
after Nikolai Zhukovsky (transcribed in several versions from Никола́й Его́рович Жуко́вский) can be used to calculate the flow of a non-viscious, incompressible and irrotational flow around an airfoil... |
I am in a debate with a friend about the value of string theory in physics. He is concerned that we are wasting valuable intellectual and financial resources on a path that is fanciful and can't ever hope to be verified by experiment and evidence (11 - 20 dimensions etc).
My point is not to agree with string theory bu... |
Does polarized light interfere?
|
I'm looking at Jeans (thermal) escape of hydrogen from the early Earth's atmosphere. I understand how to calculate the rate in (g cm^-2 s^-1) using the number density, average particle velocity, and integrating the tail of the boltzmann distribution, but those units are frustrating me.
How would I convert to mass per ... |
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 the effect of these gravity waves be ... |
I am becoming familiar with the Geometric Optics approximation in General Relativity which (to summarise) says that EM waves follow null geodesics under the geometric optics approximation. In the context of General Relativity the Geometric Optics approximation amounts to the assumption that:
$\lambda << R$ where $\lamb... |
Lets say you're an undergrad physics student with a lot of "sense" for technology and limited theoretical abilities. Now you need some kind of a career advice about the specific field of physics to specialize in. So you ask your senior colleagues: what is the current area of research that is promising most technologica... |
I want to calculate stress matrix in a cube with two faces parallel to x axis and perpendicular to z axis (sorry I don't know how can I put a picture in this post).
There are two force uniform distributions (that we'll indicate with p) over this two surfaces: the superior is in the x direction, the inferior in the -x d... |
I'm looking for the most readable quantitative explanation, with the least amount of difficult mathematics. Rather than an answer with just a number, I'd like to see the derivation from the CKM matrix.
|
what are the conditions to check point type singularity in a bianchi type model ?
bianchi type model are of Type I,II,III,IX,IV or u can say we use different Bianchi type models having some specific metric or line element as i know .
|
I know that it must have something to do with (gauge?) theories with N=2 supersymmetry, BPS states and even black holes, but most papers on the subject are too technical for me. So what is wall crossing?
|
In the early days of quantum electrodynamics, the most popular gauge chosen was the Gupta-Bleuler gauge stating that for physical states,
$$\langle \chi | \partial^\mu A_\mu | \psi \rangle = 0.$$
However, this gauge is practically never used now. Why? Is there anything wrong or inappropriate with the Gupta-Bleuler gaug... |
In several papers (including a recent one by Banks and Seiberg) people mention a "folk-theorem" about the impossibility to have global symmetries in a consistent theory of quantum gravity. I remember having heard one particular argument that seemed quite reasonable (and almost obvious), but I can't remember it.
I have ... |
I've been wondering about this question for a while. If you have alpha and beta particles released from a radioactive core, how do they ionise surrounding particles?
|
Okay, so I just read through huge sections of http://gordonwatts.wordpress.com, which I found quite interesting. There are some questions that really came to my mind.
Do a lot of particle physicists use windows computers? (relative to other physicists?) And why? In most other academic departments, the professors seem t... |
If the universe is spatially infinite (and assuming, if it makes a difference, that we don't have eternal inflation), what actually happened 13.7 billion years ago? Was the energy density infinite (or "very large") at each point in R3? Or did R3 itself collapse to some other structure?
|
Why do Faddeev-Popov ghosts decouple in BRST? What is the physical reason behind it? Not just the mathematical reason.
If BRST quantization is specifically engineered to make the ghosts decouple, how does this engineering work?
|
I've read some papers recently that talk about gapped Hamiltonians or gapless systems, but what does it mean?
Edit: Is an XX spin chain in a magnetic field gapped? Why or why not?
|
Does Wick rotation work for quantum gravity? The Euclidean Einstein-Hilbert action isn't bounded from below.
|
Does a relativistic version of quantum thermodynamics exist? I.e. in a non-inertial frame of reference, can I, an external observer, calculate quantities like magnetisation within the non-inertial frame?
I'd be interested to know if there's a difference between how to treat thermodynamics in a uniformly accelerated re... |
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