# All Questions

134,981 questions
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### Why is the transverse Doppler shift “difficult to measure”?

I'm currently reading a book on optics, and have encountered a curious section: $$\nu = \nu'\sqrt{1-\frac{u^2}{c^2}} = \nu'\left(1-\frac{u^2}{2c^2}+\ldots\right)$$ This is the formula for the ...
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### Is there a cosmological model where the observable universe is infinity bi-ended and also bi-limited

Is there a cosmological model where the observable universe continues to shrink as time decreases, and continues to expand as time increases, and such that at both directions it never reaches the ...
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### Quantum mechanics (Hamiltonian)

the wave function of a particle sci =1/√2×{phoi0+phoi1} is given by in terms of eigen state phoi0 and phoi1 corresponding to the ground state energy and first excited state energy E0 and E1 ...
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### What would happen if I put two identical particles close enough?

Is there a repulsive force between these two particles to prevent them from being in the same point? I mean, in order to obey Pauli exclusion principle?
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### Renewable energy resources

A butyl rubber bag of total volume 3.0 m3 is used as a biogas digester. Each day it is fed an input of 0.20 m3 of slurry, of which 4.0 kg is volatile solids, and a corresponding volume of digested ...
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### Charges in different mediums

Generally we read or solve problems about charges in the same medium. I wonder what would happen if the two charges were placed in different mediums. eg.) One is placed in vaccum and other is placed ...
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### Relation between quantum numbers $j$ and $\ell$

I'm given the following problem: "Consider an atom with orbital angular momentum $l$. What are the possible values of the total angular momentum quantum number $j$? Treat the case of $\ell = 0$ ...
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### What is the power dissipated in a conductance in the transmission line? [on hold]

The electric power dissipated due to a resistance is $P=RI^2$. What is the power due to a conductance?
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### two identical disc each of mass m(=4m) and radius r are rotating in opposite sense with equal angular speed w [on hold]

about vertical axes passing through their centres, (as shown in figure) .a person of mass m sitting on circumference of disc a jumps with tangential relative velocity u w.r.t one rotating disc A jumps ...
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### The transformations of Lorentz as a general case of the transformations of Galileo

Starting from the transformations of Lorentz, \left\{\begin{aligned} x&=\gamma (x'+\beta ct)\\ y&=y'\\ z&=z\\ ct&=\gamma (ct'+\beta x')\\ \end{aligned}\right. \quad \tag{*} I ...
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### Interpretation of rotating a quantum state

I'm currently taking an introductory quantum mechanics course, where the last covered topic was spin and identical particles. During some reading online, I stumbled across the term "rotating a quantum ...
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### Could light and heat reflecting off of surface ice on Earth have a noticeable impact on the sun?

If so, what could be the impact of these reflections on the sun during an ice age on Earth?
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### Is Everything Reducable to Geometry? [on hold]

Related to a previous post: Is there a Geometric Algebra for gravity? : I asked the question of whether gravity could be given a geometric interpretation though stated algebra. Because I first tackled ...
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### Acceleration as the logarithmic derivative of the redshift factor $U^\sigma \nabla_\sigma U^\mu = g^{\nu\mu}\nabla_\nu \ln V$

Let $K^\mu = V(x)U^\mu$ be vector proportional to the four-velocity $U^\mu$. (e.g. $K^\mu$ is a normalized time-like Killing vector for an observer at infinity). Then, $V(x) = \sqrt{-K_\nu K^\nu}$ is ...
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### Why the National Ignition Facility try to use 192 laser beams to trigger ignition without heat capsule?

In the discussion of the question "Nuclear Fusion with extremely high pressure and low temperature", the conclusion is only ultrahigh pressure cannot trigger fusion. But why does NIF try to use 192 ...
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### Energy-momentum vs charge-current

Is there a simple intuitive way to explain why energy-momentum density requires a tensor, while charge-current density is a vector? $\partial_{\mu} J^{\mu} = 0$ is a statement, in effect, that the ...