# All Questions

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### Long string model of black hole

I wonder if anyone can advise me literature about " long string model" of black hole. I've tried google, and of course arxiv.org. Still I couldn't find anything about this theme. I would be also very ...
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### What is the difference between negative acceleration and decreasing acceleration?

According to Reisnick and Halliday, retardation is the acceleration in the negative direction of time axis ie. opposite to the motion. Decreasing accleretion is the decrease in the magnitude of time ...
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### What is the linear and rotational motions generated by a force not on the CG?

Given a force that is applied to a free body, not directly towards, or away from the centre of gravity, how would you calculate the amount of linear and rotational velocities generated, as the farther ...
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### If virtual particles have negative mass why do they contribute positive mass to atoms?

According to Lawrence Krauss, atoms containing in our body consists of merely 10% (if I remember correctly) of our total mass. The rest come from virtual particles popping in and out of existence from ...
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### Reflection from multiple thin films: accounting for lost light due to small surface area

I have a problem similar to reflection of multiple thin films. I have light coming in from medium 1 and I want to find the total reflected intensity after being reflected inside 2 layers. However, I ...
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### Is it possible to design a large permanent magnet that creates a multi-Tesla field?

Is it ever possible to create a LARGE magnet (in meters wide/long) that could potentially create a powerful magnetic field?
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### supersymmetry vs multiverse

I'm a complete noobe in physics and quite honestly need help. My question is simple, based on CERN's tentative findings stating the Higgs boson at a mass of ~125 GeV: Is the physics community leaning ...
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### How to actually use the BB84 protocol?

I have read how the BB84 protocol could work. However, I couldn't see a way to implement it in the laboratory, so that I could make a demonstration in the university's quantum optics laboratory. ...
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### Efficiency of reversible engines

I'm a little confused about something. All reversible engines have the same efficiency, or one could drive the other to move more heat in the reverse direction. Also, no engine has an efficiency ...
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### Suggested reading for classical field theory

I am reading a marvelous book Classical Field Theory by E Soper, but it is mathematically too compact and sometimes I am unable to follow the equations. Can anyone suggest a side book for solution of ...
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### How to define the thermodynamic temperature

I've been reading derivations of the thermodynamic temperature scale. I'm assuming these are using Kelvin's method. I follow the math and the conclusion of the argument, but I don't understand how it ...
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### Canonical transformation that contains the time as an explicit parameter

On the Page 385 of Goldstein's Classical Mechanics book (third edition), it starts to talk a bout the canonical transformation with time as an explicit parameter. But I don't quite under understand ...
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### Transmission/Equilibrium Question

Suppose there are two wheels linked by some kind of apparatus with a transmission, in a vacuum. Wheel A is spinning, wheel B is not. Is it empirically possible for the transmission to transfer the ...
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### Shallow water wave question from Acheson's book

I am learning Fluid mechanics by reading Acheson's book entitled "Elementary Fluid Dynamics". Admittedly, you will need to have the book to respond to my question. I did this problem 3.1, which deals ...
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### Why no thermal expansion for camping tents?

I know that solid materials expand when heated, which is called thermal expansion. But what is happening to tent square or tent canvas of (plastic?) camping tents? I have noticed, that during the ...
205 views

### Why does earth cool?

This question is boggling me for some time. We know that heat can be transferred from matter to matter and heat is nothing more than tiny atoms vibration intensity (correct me if I'm wrong). But space ...
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### Rotating a Gaussian Beam

I need to see how the phase fronts of two gaussian beams interact when they intersect with each other. The two beams are tilted towards each other so that they intersect each other at their respective ...
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### Steam Turbine Inlet Velocity

Consider an ideal steam turbine. The power generated by a steam turbine comes down to the torque and the angular velocity, which is ultimately dependent on the velocity at which the flow enters the ...
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### How can individual photons have different amounts of energy?

If photon is an elementary particle, how can different photons have different energy, if E=mc^2 and all photons have(or don't have) the same mass and the speed of photon is constant shouldn't it mean ...
23 views

### Does supercavitation create vacuum?

While reading the amazing things that the mantis shrimp can do, such as moving two of their limbs so quickly that the water around them 'supercavitates', a friend of mine told me that those limbs were ...
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### Why is baryon or lepton violation in standard model is a non-perturbative effect?

The baryon number B or lepton number L violation in the standard model arise from triangle anomaly. Right? Triangle diagrams are perturbative diagrams. Then why the B or L violation in Standard model ...
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### How can we see that there is superconductivity/superfluidity in the boundary theory in the holographic principle?

For example in the models for holographic superconductors we can calculate the conductivity. Also there is an energy gap. I can understand that it describes a superconductor. However I have also heard ...
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### Determine the acceleration in a double Atwood machine

Trying to solve the following double Atwood machine: Suppose there is a mass of 12kg hanging on an ideal rope that wraps around an ideal pulley, and that the other end of the rope is attached to ...
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### How to measure trajectory regularity?

I have two animal running trajectories. A regular one with repeated back and forth running between point A and B, like the one on top in the figure. The other one is very irregular, animal paused and ...
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### XCrysDen Structure file

Does anyone know how to directly convert a .cif file to a Xcryden structure file(.xsf) ? I know how to extract the lattice vectors and the atom positions from a .cif file, but don't whether the .cif ...
21 views

### What is the relation between photoelectric current and frequency of incident light?

I googled it a bit and found that photoelectric current is independent of frequency(of incident light).Some further look revealed that actually "saturation current" is independent of frequency.I could ...
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### Temperature of a neutron star

In our everyday experience termperature is due to the motion of atoms, molecules, etc. A neutron star, where protons and electrons are fused together to form neutrons, is nothing but a huge nucleus ...
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### Effective Potential of experienced by a particle with contact interaction in an optical lattice

Suppose i have an optical lattice with particles loaded onto it, the potential due to the optical lattice is $V_{0}Cos\left(x\right)$. Assume that the particles interact with eachother through contact ...
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### Amateur thoughts on QM theory at celestial scale

Some amateur scientist asked me that why can't one just simply apply the entire theory of QM at atomic scale to "quantize" celestial system with a different choice of $\hslash$, which he believed can ...
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### Can an underdensity in space act as a negative matter density powering a warp drive?

Consider a homogeneous isotropic universe filled with a perfect fluid with density $\rho$ and pressure $P = \rho/w$. E.g. for $w=-1$ we get a universe equivalent to one with "vacuum energy" or with ...
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### Why is binding energy $\Delta mc^2$?

As we know the mass-energy equivalence relation $E=mc^2$ originally came from special relativity. And the binding energy is $\Delta mc^2$. How do we know that the extra mass coming from theoretical ...
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### What are the linear maps which preserve the time-like cone?

I'm looking at the set of forward pointing time-like vectors: $\mathcal{T}_+ = \{ x \in \mathbb{R}^4 \mbox{ s.t. }x_0 \geq 0, x^T \eta x \geq 0 \}$, where $\eta = \mbox{diag}(1, -1, -1, -1)$. I ...
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### Is the “Force” of Gravity Simply Hamilton's Principle on a Curved Spacetime?

It's my understanding that General Relativity abstracts away the concept of gravity as a force, and instead describes it as a feature of spacetime by which massive objects cause curvature. Then it ...
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### Birds inside of a closed box [duplicate]

Suppose there's a closed box with birds inside, on top of a scale. If the birds started flying inside, would the box get lighter?
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### Quantum Mechanical States

What can be the precise answer to the question that Quantum states are complex and infinite dimensional. Why is this so? Is it because they belong to the complex Hilbert space? Even if they ...
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### Time difference in clocks of an accelerated frame [on hold]

If we have two inertial frames $S$ and $S'$ and $S'$ is moving to the right w.r.t. $S$ with a velocity $v$. Suddenly $S$ undergoes negative acceleration (no longer being inertial) and after some time ...
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### Transmission of porous membrane with vertical cylindrical pores

There is some porous dielectric membrane with strictly vertical cylindrical pores. I would like to find theoreticaly optical transmission spectra of this membrane, depending on the bulk material ...
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### Can Light Cones be Local Event Horizons for the Causal Universe? [on hold]

I propose that massless bosons are quantum entities unbounded by speed. They are simply bounded by the local boundary of the casual universe. The casual universe is locally bounded by light cones. ...
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### Is the subadditivity of quantum entropy valid in the infinite-dimensional case?

Does the subadditivity (and strong subadditivity) of quantum entropy hold for infinite dimensional quantum systems as well? Unfortunately the books in my hand give proof for finite dimensional cases ...
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### Double dot product in Cylindrical polar coordinates - Strain Energy

I'm working with a problem in linear elasticity, and I have to calculate the strain energy function as follows: $$2W=σ_{ij}ε_{ij}$$ Where σ and ε are symmetric rank 2 tensors. For cartesian ...
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### Is it possible to shield a camera so as to record from the inside of a running microwave oven?

Would it be possible to create shielding for a camera, allowing it record food being cooked from the vantage point of the inside of a consumer microwave oven without the camera being damaged? ...
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### Calculating force of a car

I'm simulating car cruise system and my results are not making any sense. I have been told that my force formula is wrong but I don’t understand why it is wrong and how I can fix this. Does anybody ...
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### Geffen's Ladders Distance [on hold]

The Geffen Mage Guild decided upon some touch-up repairs to the Geffen Tower, and contracted with the Alberta Mercantile Guild for work. While setting up, the Merchants placed two ladders ...