# All Questions

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### Remnant of a supernova [duplicate]

i explain better A supernova remnant is the structure resulting from the explosion of a giant star . The supernova remnant is surrounded by an expanding shock wave that is formed from material ...
840 views

### Sound velocity in water

Conductivity, temperature, depth sensors are used by oceanography to calculate the velocity of sound at varying depths. These measurment values are used to comprise sound velocity profiles like the ...
734 views

### Neutral Pion Decay

While studying C-symmetry, a question about neutral pion decay came up. The most probable channels in which neutral pion $\pi^0$ decays are: $\pi^0\longrightarrow\gamma+\gamma$ (98%) ...
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### What are the implications for quantum gravity if the LHC sees no higgs?

Following the news in serious "non-hype" physics blogs I`ve learnd that as things are now one needs a lot of patience and more data to learn what happens in the higgs sector. There are already a ...
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### On what planar regions are the Earth, Moon.. for that matter, all astronomical bodies, placed in the Universe?

When we are on Earth, we look UP in the Sky to see the Moon. How do we have to look at Earth from Moon.. Is it the way ? If so, how are these bodies actually placed in the space? Are all astronomical ...
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### Quarks as preons for the whole standard model

This is a sequel to an earlier question about Alejandro Rivero's correspondence, the "super-bootstrap". The correspondence itself was introduced in his "Supersymmetry with composite bosons"; see the ...
397 views

### How much of the Earth would a spoonful of the Sun scorch?

How much of the Earth would a spoonful of the Sun scorch if held at ground level? I basically would like to conceptualize the heat of the Sun on a smaller scale, please.
866 views

### Why do electron-positron pair annihilate upon contact?

I'll a appreciate a layman's explanation, if there exists one, to this question that arose when reading an popular-science level article on Einstein and the $E=MC^2$ equation. What I mean is that, ...
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### Is building your own reflector telescope worth it?

I have always fancied building my own reflector telescope. I am wondering - For a certain budget, can you get better results with a home made rig? Or is this a folly, and really it would be better to ...
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### Are there Trojan family or Hilda family satellites locked in Earth's orbit?

Jupiter has many Trojan asteroids located at Lagrangian points L4 and L5 and Hilda asteroids dispersed between points L3, L4, and L5. Does the Earth have similar satellites? If so, how many?
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### Are there Trojan or Hilda asteroids locked in Earth's orbit? [closed]

Jupiter has many Trojan asteroids located at Lagrangian points L4 and L5 and Hilda asteroids dispersed between points L3, L4, and L5. Does the Earth have similar asteroids? If so, how many?
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### If the Earth didn't rotate, how would a Foucault pendulum work?

How does the Foucault pendulum work exactly, and would it work at all, if the Earth didn't rotate?
360 views

### Plenoptic camera and display

This is a two part question about the technology described here: Lytro's light field camera lets you choose focus later I'd love to get an explanation of the technology. What is the ...
1k views

### Tennis serving machine— How does a spinning ball bounce?

I have an idea of making a tennis serving machine. I will briefly describe what it is: The machine is configured to serve the ball at a fixed speed to the center of the left (or right) service court ...
245 views

### Is there a single metric for a given system?

Let imagine a tunnel that connect two distant places at the globe (eastern-western or north-south) There are a lot of posible "distances" or metrics, defined by maps, routes, "as the crow flies", ...
604 views

### Acceleration vector - deceleration vs direction

If acceleration of something $= - 10 \text{ m s}^{-2}$ And forwards is define as north. Does that mean the object is getting slower (decelerating) or accelerating in the reverse direction (south) ...
163 views

### The energy carried from one winding of a transformer to another, in quantum terms

I have read in wikipedia this statement "The energy carried from one winding of a transformer to another, in quantum terms is carried by virtual photons, not real photons" (wikipedia src: virtual ...
951 views

### Why is the string theory graviton spin-2?

In string theory, the first excited level of the bosonic string can be decomposed into irreducible representations of the transverse rotation group, $SO(D-2)$. We then claim that the symmetric ...
452 views

### Exactly how is the constant measured velocity of light deduced from Maxwell's equation?

For electromagnetic radiation the velocity of propagation is $c = 1/\sqrt{\mu_0 \epsilon_0}$. Since both $\mu_0$ and $\epsilon_0$ do not vary in any inertial frame, then $c$ must be constant in any ...
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### Equivalence of canonical quantization and path integral quantization

Consider the real scalar field $\phi(x,t)$ on 1+1 dimensional space-time with some action, for instance  S[\phi] = \frac{1}{4\pi\nu} \int dx\,dt\, (v(\partial_x \phi)^2 - \partial_x\phi\partial_t ...
1k views

### Heat exchange depending on coolant flow direction

Consider a simplest case of a heat exchanger - two parallel pipes of flowing liquids (say, hot and cold) that have physical contact along some part of their length. Hot water of a certain temperature ...
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### Compressing a fluid with arbitrarily large force in an infinitely strong chamber

Imagine I have an infinitely strong container of volume $v_1$, and I fill it with some monoatomic fluid like liquid hydrogen. I then proceed to compress the walls of the container to reduce its ...
863 views

### How long did inflation take to happen?

If inflation happened, it ended about 13.7 billion years ago. But how long was inflation going on before that? Was it just a short burst of time so that it's really okay to say that the age of the ...
896 views

### What effect does shape of dots on a household microwave oven door have on amount of EM radiation that escapes through the door?

Why are they dots and not squares, triangles, or some other shape?
783 views

### How do Leptons arise from Lambda decay?

I have a question for an assignment: Use your understanding of the quark model of hadrons and the boson model of the weak nuclear interaction to explain how leptons can arise from lambda decay, ...
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### Knowledge needed to study and understand general and special relativity theory [duplicate]

Possible Duplicate: What are the prerequisites to studying general relativity? I'am 27 now and i have a burning desire to study math and physics from the ground up and I strongly prefer ...
597 views

### I found it strange in case of an egg omlette

Its known to everyone that when a solid is heated up to its melting point it turns into a liquid. What happens when a liquid is heated? Simple, it tends towards becoming gaseous. While making omlettes ...
439 views

### simple test/measurement to quantify water opacity

I am performing some measurements on liquid surfaces and I want to quantify how these mesures depend on the liquid opacity by performing it with different concentrations of colorant. To allow ...
712 views

### Nonlinear dynamics beneath quantum mechanics?

Yesterday I asked whether the Schroedinger Equation could possibly be nonlinear, after reviewing the answers and material given to me in that thread I feel like my question were adequately answered. ...
7k views

### What is Energy made of?

We have the famous equation $E = mc^2$, and we also believe that matter is made of particles. Then, What is the energy made of? If the two are interchangeable, there must be some common building ...
170 views

### How do some substances “get wet”?

For example, paper's structural integrity decreases when it comes into contact with a liquid. What happens at the time of contact?
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### Confusion with infinity and time [closed]

I have some confusion between with resolving the following situation. I know that no measurable quantity can have a value of infinity. For example, I just wrote something out, but clearly this ...
247 views

### Since the universe is expanding, does anything ever occupy the same point in space?

Let's say we can observe expansion in a supercluster. We define origin of our frame of reference at the center of the supercluster. We observe an object/atom at point A at time T. The object is ...
2k views

### How do you prove $S=-\sum p\ln p$?

How does one prove the formula for entropy $S=-\sum p\ln p$? Obviously systems on the microscopic level are fully determined by the microscopic equations of motion. So if you want to introduce a law ...
25k views

### Can the “Milky Way” galaxy be seen by the naked eye in a clear sky?

Is this photo "real"? Are the stars not super-imposed in the image?
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### Does anisotropic expansion of the universe imply quintaessence?

a Recent paper establishes under solid grounds anisotropy in the expansion acceleration rate in the universe. My question is very simple: can this anomaly be explained entirely in terms of a ...
3k views

### Focusing light into an optical fiber cable

I'm trying to focus light from a flashing light lamp throught two lens into a optical fiber cable which is around 0.8cm in diameter. flashing light: a bulb and then covered by a glass of 7.5cm x 7cm ...
241 views

### Equation of Motion in a Non-Inertial (Rotating) Frame

Let me preface my question by informing you this is for an assignment, so I would rather not have explicit answers but rather be given guidance in arriving at the correct solution. The question is ...
1k views

### Formula for Rotation curves of Galaxies

To ask a more specific one for the rotation curves of elliptical galaxies, and hope from there to later understand the dynamics of spiral galaxies. Treating the galaxy as an isothermal ...
198 views

### false false beliefs in physics [closed]

Reading Common false beliefs in Physics I feel that there are also "fake false beliefs", ie, that the "false belief" does not actually exists, it is a rhetorical argument or just a basis for ...
132 views

### K3 gravitational instanton

Could you please recommend a sufficiently elementary introduction to K3 gravitational instanton in general relativity and the problem of finding its explicit form? Under 'sufficiently elementary' I ...
258 views

### Inelastic nucleon-nucleon cross section at LHC energies

I am trying to reproduce the number of participants $N_{part}$ in Pb-Pb Collisions at LHC using a Glauber Monte Carlo simulation, specifically aiming to reproduce the values given in Phys. Rev. Lett. ...
637 views

### Changing magnetic flux graph?

In regards to a graph of the changing magnetic flux in a generator such as this one: a) The equation of the graph should be $\Phi = BA \cos \theta$. As $\theta=\omega t$ (angular velocity*time), ...
530 views

### Can one canonical conjugate variable be considered to be the “frequency” of the other one? (which could be a “wavelength”)?

So, from http://en.wikipedia.org/wiki/Conjugate_variables#Derivatives_of_action, we have... The energy of a particle at a certain event is the negative of the derivative of the action along a ...
1k views

### Diffraction through one slit?

When Thomas Young first conducted his double slit experiment to prove the wave nature of light, he shone light through two slits, creating an interference pattern. Apparently he then covered up one ...
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### How does a pressure difference cause a force?

One more thing that's bothering me, could somebody clarify a little bit? I think it has something to do with being in the state of lowest energy state, what instigates that change? Perhaps even ...
392 views

### $P=ρgh$ - intuitive understanding of the equation?

I've come across this equation recently which relates pressure with the product of density, gravitational acceleration and height difference in a medium. I understand that $P = ρgh$ expands to ...
337 views

### AQFT and the Standard Model

The German physicist Rudolf Haag presented a new approach to QFT that centralizes the role of an algebra of observables in his book "Local Quantum Physics". The mathematical objects known as operator ...