# All Questions

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### Fluctuation spectrum of lipid bilayer membranes

I am interestend in calculating the fluctuation spectrum of a thermally fluctuating 2d membane which is only subject to a surface tension $\sigma$. ($\mathcal{H}=\sigma\int\mathrm{d}A$) Depending in ...
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### Which is stronger, wire rope or chain?

Assume they are the same material with the same weight, which is stronger?
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### What's wrong with this experiment showing that either FTL communication is possible or complementarity doesn't hold?

The assumptions are: Alice and Bob have perfectly synchronized clocks Alice and Bob have successfully exchanged a pair of entangled photons The idea is simply to have Alice and Bob perform the ...
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### Is gravity just electromagnetic attraction?

Recently, I was pondering over the thought that is most of the elementary particles have intrinsic magnetism, then can gravity be just a weaker form of electromagnetic attraction? But decided the ...
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### What is the rebound angle of a circle striking a concave surface?

First, pardons to all because I don't have a physics background and I'm probably using laymans terms. What is the rebound angle of a circle striking a concave surface? Assume the simplest case: ...
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### Atomic physics - photoelectric emission

I understand that when photoelectric emission occurs: $$h\nu = h\nu_o + K.E.$$ Where $\nu_o$ represents the threshold frequency. What I don't understand is what happens if the frequency is just equal ...
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### Connection between the Big Bang and Black Holes [closed]

So... this is my first question here after a little while of lurking; so be gentle. I've been thinking lately about trying to wrap my head around the concept of spacetime and how it can be affected ...
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### Problems book recommendation on supersymmetry, supergravity and superstring theory

I'm learning supersymmetry, supergravity and superstring. I want some problems books to have some idea in this area. Is there this kind of books? Or are there some papers that have many solved model?
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### Does sign convention in geometric optics fail to explain the cases of image formation by virtual objects?

Here is an example of Cassegrain telescope: Parallel rays from a distant object get reflected by the concave mirror forming an image at its focus behind the convex mirror. This image acts as a virtual ...
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### Relativity Question Fireworks explosion

A firecracker explodes at the origin of an inertial reference frame. Then, 2.0 microseconds later, a second firecracker explodes 300m away. Astronauts in a passing rocket measure the distance between ...
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### Why is charge not taken as a fundamental unit? [duplicate]

According to the definition of electric current, it appears to be a derived quantity. Charge on the other hand seems more fundamental than electric current. Then why is current taken as fundamental ...
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### Collision of a heavy charged particle with an electron at rest - Deduction

When I was studying Nuclear Physics I saw this formula about interaction of radiation with matter. The book mentioned that when considering a elastic collision of a heavy charged particle of mass $M$ ...
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### $\langle TT\rangle$ correlator of the boundary CFT from metric fluctuations in the bulk gravity

Is there a reference which explains how the $\langle TT\rangle$ correlation of the boundary conformal field theory (CFT) can be holographically calculated from the bulk gravity? (..I am often getting ...
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### Using the loop rule while charging circuits

We know that in an LC circuit the voltage across the capacitor is the same as the voltage across the inductor (the emf induced in it). This is a direct conclusion of KVL (Kirchoff's Loop Rule) applied ...
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### Why is the Earth shaped like a sphere and not any other shape: cube, prism? [duplicate]

Why is the earth shaped like a sphere and not any other shape: cube, prism?
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### Is the Earth round?

Imagine you are a common man and want to prove that the Earth is Round, how would you prove it without any mathematical derivation or without the theory of the ships.
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### Lift a weight with a pulley system

I have two weights, weighing one ten times the other. I should figure out a way to make a pulley system that can lift the heavier mass with the smaller one. I would like to use the least number of ...
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### Initial condition for Fourier transformed Schrödinger equation

I asked in this thread Time-dependet Schrödinger equation how to solve the Time-dependent Schrödinger equation. One of JamalS' recommendations was the Fourier transform, which is why I want to quote ...
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### Why is solar eclipse so important for sunlight spectrum analysis?

People wait for decades to catch the chance of a solar eclipse to observe the sun. Why cannot they do it every noon?
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### Optimal speed for the water wheel

The hydroelectricity plants extract the potential energy of highly deployed massive object (water) as it falls down. Without turbine, all that energy would be converted into speed (kinetic energy) at ...
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### Need an analytic model for describing a region with fast transition of magnetic field from a constant value to zero

I would like to describe analytically the electromagnetic fields in a region with the magnetic field changing rapidly from a constant value to zero. It's more or less like the fringe region of the an ...
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Why do the propellers on helicopter appear to be so slow when the propellers is going at full speed? Can you please explain this particular optical illusion to me?
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### What happens when some asteroid comes in the way of warp drive?

Recently Harold white, NASA scientist shared his knowledge and the things he is working on. That is Warp drive for interstellar navigation. This spaceship compresses the space in front of it and ...