# All Questions

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### Capture reflecting image

Suppose you have following installation: ...
230 views

### What does the decay constant mean?

In my curriculum, the decay constant is "the probability of decay per unit time" To me, this seems non-sensical, as the decay constant can be greater than one, which would imply that a particle has a ...
138 views

### Inexact measurement and wavefunction collapse

As is usually said, measurement of an observable $q$ leads to collapse of wavefunction to an eigenstate of the corresponding operator $\hat q$. That is, now the wavefunction in $q$ representation is ...
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### Would a cone shaped Stirling engine work?

A Stirling engine evidently functions by heating and cooling air, thus making the piston move up and down. What if the heated side of the cylinder were shaped as a sort of cone with a gentle slope, ...
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### How fast does the water travel down river when the discharge gates of a large dam are opened?

How fast does the water travel down river when the discharge gates of a large dam are opened? Can the discharge-wave travel downstream faster than the water? Is this likely to occur for a real river ...
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### Most particles that have ever been modeled

Two billiard balls collide. Consider the two balls only, how many particles are in that system? Have particle systems of that size been modeled with each individual particle before? What is the ...
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### Where is a closed form also exact?

I'm not very familiar with exterior derivatives. I've some trouble following argument (which is a part of a proof that if the Riemann tensor vanishes, $R^{\,\rho}_{\;\,\sigma \mu \nu}=0$, iff there ...
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### Foucault pendulum explanation, rotating earth or rotating universe?

If we start from the assumption that all frames of reference are valid for describing motion, how can a foucault pendulum either prove or disprove that the earth rotates or is stationary? Couldn't ...
495 views

### holographic projection in thin air?

from where I come from ,they taught us in high school that it is possible to project holograms in thin air simply by illuminating the hologram with the "correct light" , and having a semi transparent ...
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### Paradox Regarding Time Dilation at the Speed of Light

Consider the following scenario: On earth, I pulse a laser focused at a far away mirror such that the time it takes for the light to reflect off the mirror and arrive back at me is at least a few ...
831 views

### Photons and phonons

A few months ago I asked about phonons. I got some very good answers but I still have difficulty getting an intuition for phonons, while somehow photons, which in many ways are similar and which I ...
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### Do two photons traveling in opposite directions emit gravitational waves?

Do two photons traveling in opposite directions emit gravitational waves? If so, does it mean that any volume filled with photon gas will eventually degrade into graviton gas? In other words, if flat ...
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### Why Sun light can reach us if Time is dilating?

I understand that if something is moving with constant speed in respect to an observer, the time of the moving one runs slower, so the more your speed is, the more your time ticks slower. Which ...
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### Question about gravity in 1 dimension

Consider 2 pointmasses in 1D space. More specific ; object $A$ with mass $m_a$ and object $B$ with mass $m_b$. $A$ and $B$ are a distance $d$ away from eachother. Let these pointmasses $A,B$ have no ...
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### Is there a probability that an electron in an atom change its energy level due to emitting gravitational wave?

Is there a probability that an electron in an atom change its orbital by emitting a quantum of gravitational radiation instead of photon?
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### Why doesn't a particle's velocity effect the strength exerted on it by an electric field?

Here is what I know: $F = E q = m a$ so $a = \frac{E q}{ m}$ and we can increase the acceleration ($a$) of a particle in an electric field ($E$) by either decreasing its mass ($m$) or ...
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If water is cycled through a thin pipe by a pump, and a certain spot on that pump is made of thin copper that is being heated by a 1000 C source, will the water, as a whole, attain a heat of 1000 C ...
Wikipedia says that Nordstrom theory with equations of motion of the test particle $$\tag{1} \frac{d (\varphi u_{\alpha})}{d \tau} = \partial_{\alpha} \varphi$$ and field equation $$\tag{2} \varphi ... 0answers 48 views ### What speed should have an alone planet to have a habitable zone due to relic radiation? What speed should have an alone planet to have a habitable zone due to relic radiation, without any star involvement? How much time the planet will be able to remain in the habitable zone before the ... 1answer 293 views ### Partially polarized light with jones vectors? I have read that polarized light is treated by Jones vectors and that to treat partially polarized light you have to use Stokes vectors and mueller matrices. Nonetheless, the optics notes that my ... 0answers 108 views ### Off-shell corrections to massive vector boson propagator in polarization form As an exercise for myself, I have been working on rewriting the massive vector boson propagator (unitary gauge). I have run into a problem interpreting some of the terms that stick around when the ... 5answers 2k views ### Trouble with classical mechanics self-learning (How to avoid going down the Physics rabbit hole?) [duplicate] I'm a retired police officer trying to learn classical mechanics on my own. I have gone through many links on the Internet including the classical mechanics quick reference textbooks from Physics ... 2answers 74 views ### Irradiance at surface point due to lighting from point light source I'm reading through a computer graphics paper and author says that the radiant intensity emitted by an infinitely small surface point p with normal  n  into direction  \omega  is$$ I_p(\omega) ...
I'm looking at torque-free precession, occurring when the angular velocity isn't aligned with a principal axis of an object. I've looked at some Euler arguments, some decompositions of $\vec{\omega}$ ...