# All Questions

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### Meaning of the discrete Fourier transform in condensed matter

I'm in a CMP course now and I think I'm taking for granted what it means for a creation/annihilation operator to be Fourier transformed. I understand what a Fourier transform is for some function, but ...
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### Could Planck Relics prevent a contained particle of anti-matter from interacting with exterior matter?

The need for some quirky asymetry to exist in the way matter and antimatter cancelled out to result in the universe having matter seems... well, weird. During the big bang, a bunch of microscopic (...
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### the constants of the matrix 4*4

I have the following matrix $$A= \begin{pmatrix} 0 &1 &0 &0 \\ 1 & 0 &0 &0\\ 0 &0&0&1\\ 0&0&1&0 \end{pmatrix}$$ The ...
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### Why is Sellmeier's equation an even function of $\lambda$?

According to Sellmeier's formula, the dispersion formula of a transparent material can be written as $$n^2(\lambda) = 1 +\sum_i\frac{B_i \lambda^2}{\lambda^2 - C_i},$$ where $B_i$ and $C_i$ are ...
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### Need help with understanding the equation below. Here $h$ is the film thickness of fluid left behind in a fluid fluid displacement

A simple equation for the evolution of the interface described by $$r=R(z,\phi,t)=a-h(z,\phi,t)$$ where $a$ is the radius of the cylinder and $h$ is the typical film thickness – can be found in terms ...
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### Testing space-time warp on a smaller scale, “Breaking the Warp Barrier: Hyper-Fast Solitons in Einstein-Maxwell-Plasma Theory”

So according to this paper it creates a warp drive without the need of negative energy to operate which many think does not exist in reality. So my question is what would you do to experimentally ...
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### Exceeding the Kerr black hole spin limit

It is well known that the limit on the angular momentum for a Kerr black hole is given by $$0 \leq a^* \leq 1 \quad \text{where} \quad a^* \equiv \frac{cJ}{GM^2}$$ and $J$ ...
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### How does time dilation apply at the centre of a black hole?

At the direct centre of a black hole, you have $0$ GPE, and the net gravitational force is $0$. So how does time dilation work there (or is this another physics mystery)? Specification: I refer to how ...
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### Are chaotic systems examples of complex systems?

I am struggling to find a proper source or reference where examples of complex systems which are chaotic are given. Based on my understanding, complex systems consist of interacting components, each ...
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### Positional is not equivalent to conservative in dimensions greater than one

I've just started writing dynamical systems and I was trying to find an example to show that if we are in a $2$ or $3$ dimensional real space "positional do not implies conservative". In ...
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### Why the Warp-drive uses a 3D shape to distort space instead of a 4D shape?

I know that warp-drives are just a theory and that they would require exotic mass (that is also a theoretical material), but, as said in this video, after some re-calculations, it was theorised that ...
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### Speed of electromagnetic wave in a medium

Speed of electromagnetic wave in a medium (for example air) is different for different frequency (for exmaple red light is faster in air than blue light). So how can we calculate the speed of light ...
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### A question about collisions and probability, from an élite university admission test [closed]

Good afternoon, I have come across this question, from a recent admission exam to my country's top physics university, which I have found particularly interesting as the text seems to be deliberately ...
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### Cosmology - The Geodesic Equation Derivation

My question relates to the derivation of the Geodesic Equation given on pages 121-122 of Baumann's cosmology. $$\frac{d^2x^i}{d\tau^2} = -\partial^i \Phi (dt/d\tau)^2 + O(\Phi^2). \tag{A.2.43}$$ On ...
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### Why is the SI unit of Magnetic Pole Strength Ampere-meter?

Till now I was silent because I thought the SI unit of pole strength to be Ampere-Second and due to everything in analogy with electrostatic, it was ok, but when I looked closely, it changed to Ampere ...
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### ISO an elegant derivation of the Geodesic Equation from the Einstein Equation

Assuming a particle filled with perfect pressure-less fluid can the Geodesic Equation be derived from the Einstein Equations?
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### Coefficient of thermal expansion

Is the coefficient of thermal expansion of a particular material under constant pressure constant?
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### Ideal gas partition function

I am studying how to calculate the density of states and the partition function of $N$ non-interacting particles. My question is why the integral of the momentum, in the density of states calculation, ...
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### Low energy strong coupling asymptotic

The low-energy behavior ($Q^2<\text{1GeV}^2$) of the strong interaction coupling constant predicted by LFHQCD, $\alpha_S = \pi \exp(-Q^2/4\kappa^2)$, where $\kappa=M_\rho/\sqrt{2}$, is in ...
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### Why is volume of gas independent of its molecule size?

According to the ideal gas law: $pv = nRt$ My question is, why is the volume $v$ independent of the volume of individual components of the gas, i.e. molecules? As the sizes of individual molecules ...
29 views

### SUSY Kinetic and $W$ potential terms: RG flow — free or interacting

In this Seiberg's SUSY lecture, the professor said that the following theory with Kinetic and $W$ potential terms: $$K=|\phi|^2$$ $$W=m\phi^2+g \phi^3$$ "It is not a valid theory in $4d$, ...
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### How to perform experiments near absolute zero temperature when the background temperature of the universe is 2.7 K?

The cosmic microwave background (CMB) radiation as a remnant from an early stage of the universe (Big Bang) is filled all space and has a thermal black body spectrum at a temperature of \$2.72548±0....