# All Questions

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### How could the multiverse theory be disproven?

Theorists (physicists) suggest that there is the term/entity, the Multiverse that contains a huge number of universes not necessarily like our own. I personally find this theory very elegant because ...
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### Difference between single mode and multi mode optical fibres?

What is the difference between single mode and multi mode optical fibres? First off, I guess that by modes we mean the spatial modes of the electric (or magnetic?) field right? Now: what makes a ...
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### Why the electric field $\vec{E}$ is constant (=position independent) for an infinite 2D sheet of constant charge?

So I'm reading a text on electricity and it talks about using the integral to compute the total charge of a collection of points, which I mostly understand. But then we get to finding the electric ...
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### Why does decay of correlations imply absence of order?

In a few articles I have read, a two-point correlation function $\langle g(x)g(y) \rangle$ is shown to decay with increasing distance of $x$ and $y$, and this is then taken to imply an absence of the ...
746 views

### How does the speed of electrons change around a circuit?

I have been thinking about ways of teaching electronics and I'm wondering if the following is true... For starters, when we talk about voltage as energy per unit charge, is this energy manifest ...
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### Drake's equation

Some years ago i read about this equation that helps us estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. Now, i am wondering if there are results ...
204 views

### Any difference between thermodynamic double-derivative and derivative “at constant” value?

Reading about the Maxwell relations has left me confused, and I want a basic sanity check regarding the notation. The Wikipedia article breezes over the following switch of notation without really ...
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### Methods for quantifying a network of coupled oscillators

I usually am more on the statistics part of things, so pardon my misuse of the terminology. I am simulating a network of non-pulse coupled non-linear oscillators ( I am not sure what the correct term ...
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### Why are these periods the same: a low earth orbit and oscillations through the center of the earth?

Related: Why does earth have a minimum orbital period? I was learning about GPS satellite orbits and came across that Low Earth Orbits (LEO) have a period of about 88 minutes at an altitude of 160 ...
146 views

### Fourier expansion of the Klein-Gordon field

Is there a reason(both physical and mathematical) why the Klein-Gordon field is represented as a fourier expansion in the second quantization as opposed to other mathematical expansions? Be gentle ...
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### Polarization selection rules

So, I am just reviewing some of my physics stuff, and I have read something about polarization selection rules in inter-band-transitions in quantum wells. If I calculate them, I get a strength of 1/2 ...
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### Why is capacitor used?

I don't quite get the practical use of a capacitor. The theory is fine, but in simple words please explain how, why and where capacitors are used? Is there any other equivalent circuit for capacitors? ...
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### Free Particle Path Integral Matsubara Frequency

I am trying to calculate $$Z = \int\limits_{\phi(\beta) = \phi(0) =0} D \phi\ e^{-\frac{1}{2} \int_0^{\beta} d\tau \dot{\phi}^2}$$ without transforming it to the Matsubara frequency space, I can ...
187 views

### Is the pH of antimatter the reverse of the pH for matter?

If it does have a pH, I mean. Though I don't see why it shouldn't have it. Both the Brønsted-Lowry and Lewis definitions of acid have to do with the ability of a substance to accept, or provide ...
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### Is a lens with a focal point that doesn't shift as sun shines from different angles possible? [closed]

My question: Is it possible to manufacture a lens whose focal point doesn't shift in any direction during the day when the sun shines from different angles? It is understood that the focused energy ...
62 views

### What is the deepest cause of the such high specific heat capacity of water?

Yes, I know about the hydrogen bridges. But I think, it isn't the deepest cause. Anyway, they are only second-order bindings, although quite strong. I think, somehow should have the water a ...
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### st. venant shallow water equations for pipe flow

As far as I know from the fluid dynamics class, St. Venant equations (the shallow water equations) are derived by depth-integrating the Navier-Stokes equations. This depth-integrating is done with the ...
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### I still don't understand how a gas with an equation of state f(T,p,V)=0 can change if 2 state functions are fixed?

Just like classical potential, it's stated that equilibrium is obtained when the corresponding thermodynamics potential reaches the minimum. Explicitly, according to Wikipedia, in particular: ...