2
votes
1answer
39 views

Au, Ag nanoparticles plasmon peak position?

Is the interaction between metallic nanoparticles (~ 20 nm) and light in the UV-Vis-NIR range governed by Mie theory or by Rayleigh scattering theory? Where are the Au and Ag plasmonic peaks located? ...
1
vote
0answers
17 views

To what fraction of the speed-of-light has any multi-atom molecule (or polyatomic ion) been accelerated?

Of course photons go 'c' in a vacuum, and seems there's data on electrons getting to 0.999999999976c and protons to 0.99999912c. For the twins paradox to be plausible, one of the twins must reach ...
0
votes
0answers
8 views

Would our universe seemed static from outside?

As the time we experience does not exist outside our universe and all the change we experience are measured with respect to the time, how our universe would seem from outside? Will be like an static ...
0
votes
1answer
36 views

Energy conservation of permanent magnets engine

How to explain the fact that magnet can attract an object (apply a work W) without losing a (significant) part of its internal energy? How to apply the energy conservation principle? Please think to ...
3
votes
1answer
65 views

How can one reasonably theoretically model polycrystalline materials?

Many techniques are taught in advanced solid state courses but they are almost all derived for perfectly crystalline materials. For example, band structure really only appears theoretically when you ...
0
votes
0answers
34 views

Can energy be extracted indefinitely from a mass dipole/mass negative mass pair in perpetual motion?

Some days ago I have read this short piece of article by Hammond which caused me to revisit the theoretical properties of negative mass. It is known that a pair consists of ordinary mass and negative ...
0
votes
0answers
6 views

What is the correct theoretical formula of the Hyperfine transition of neutral hydrogen (21cm line)

I found two different expressions to express the energy split of the Hyperfine transition of neutral hydrogen (21 cm line, HI) that are not equivalent, imo. from Wolfram: $$\Delta\ ...
0
votes
2answers
66 views

Why liquids in hydrostatic equilibrium stay at the same height? (open tubes)

This part of the book says that, because the two liquids have the same pressure at the same height (that's true), then if a liquid has a higher height, the liquid would have more pressure at a ...
2
votes
3answers
276 views

Are length contractions limited by Planck length?

While we are getting closer to speed of light our length in the direction of the movement is according to Lorentz transformation getting shorter. But we can not (even theoretically) consider length ...
1
vote
2answers
44 views

Would it be possible to make a space elevator only in the atmosphere?

I wonder if with current day technology we could make a "floating platform" which hangs from a satellite by a space elevator. This could allow a "launch process" involving floating a balloon to the ...
0
votes
0answers
9 views

Why is space (almost) flat? Is it because masses are approximately homogeneously distributed?

The question I have is: Why is space (almost perfectly) flat in our neighbourhood? (I am disregarding the deviations due to the sun and the planets.) Is it correct to say that space is (almost) flat ...
2
votes
1answer
58 views

Is my diagram of spacetime curvature valid (relatively)?

I've been wracking my brain trying to understand what "curved spacetime" really is, and I think replacing one dimension with the time dimension then drawing the world-lines through time was the "aha!" ...
-3
votes
1answer
17 views

How does the solar cell work?

As of i know that a solar cell consists of a transistor(NP) .First step it creates a barrier between the n type and the p type junction.Then following that the sunlight i.e,(the photons) supply ...
-1
votes
1answer
26 views

Integral calculation

I do some calculation in QED, but I can not calculate such integral $$ I(a_1,a_2,m_1,m_2)=\int\frac{ d\mathbf{x} d\mathbf{y}}{(1+x^2)(1+y^2)((\mathbf{x}+a_1 \mathbf{y})^2+m^2_1)((\mathbf{x}+a_2 ...
0
votes
1answer
114 views

Does Graphene have a honeycomb lattice?

In my grand ignorance I would state that graphene has a honeycomb lattice. Some tend to agree with me and some others do not. I'm curious to know what members of the SE community think is the right ...
0
votes
1answer
21 views

Is it possible to tell time within a steady state?

(Inspired from this question (A) which unfortunately the link in the selected answer is now 404 broken (which might have contained my answer), thus cannot read any deeper than that) From the above ...
0
votes
0answers
11 views

Notion of distance in a Conformal Field Theory

I'm confused about the how the notion of distance is used in Conformal Field Theory. Let's take for example the Operator Product Expansion (OPE). In a conformal field theory, due to the scale ...
3
votes
2answers
58 views

Simplest example of spontaneous breaking of time reversal symmetry

Consider a two-dimensional fluid flow, confined to a square, where the bottom is held at a higher temperature than the top. With appropriate choices of the parameters, this will form a single ...
1
vote
0answers
22 views

How did special relativity change physicists views on the two prominent inverse square laws (ie Newton grav and Coulomb's law)?

On page 107 in Hartle's Gravity -- An introduction to Einstein's General Relativity, he says the following With the success of special relativity it became apparent that the Newtonian theory of ...
0
votes
1answer
74 views

Superconducting electromagnets?

Is it true that superconducting electromagnets don't need any power? So... energy to created a magnetic field via a superconductor would be zero? Since resistance is zero, does that also mean that ...
4
votes
2answers
147 views
+100

Is there an exact formal definition of the Universe?

I've read several articles about observable Universe, Universe and Hubble volume, including Wikipedia article and references on it, and I wondered: Is there a formal, rigorous definition in physics of ...
1
vote
2answers
63 views

Capacitance and voltage drops

Let's say that Switch $S$ is closed. I have a conceptual question: If a stream of particles acquire a potential difference upon exiting the battery, why will they lose some of that potential ...
-4
votes
1answer
15 views

Uncertainty of energy for harmonic oscillator at ground state and first excited state

How does one calculate the energy uncertainty of the harmonic oscillator in the ground state and first excited state?
0
votes
1answer
59 views

How does one normalize this wavefunction? [on hold]

Here is the question: So I could write $ N = \dfrac{1}{{\sqrt{<Ψ|Ψ>}}} $, right? Considering the parentheses in the exponential term, it looks like a good idea to switch to spherical polar ...
0
votes
0answers
25 views

How can I replace the Euler method by RK4 to determine the free fall time? [on hold]

How can I replace the Euler method by Runge-Kutta 4th order to determine the free fall motion in not constant gravitional magnitude (eg. free fall from 10 000 km above ground)? So far I wrote simple ...
0
votes
2answers
24 views

Using a charged capacitor to charge two others

Here is the homework question in question: The figure (below) displays a 13.1 V battery and three uncharged capacitors of capacitances C1 = 4.08 μF,C2 = 6.19 μF and C3 = 3.30 μF. The switch is thrown ...
1
vote
2answers
89 views

How does electrostatic force affect electronic devices?

How does electrostatic force generated by two seperate plates having opposite charges affect electronic devices? I know that magnetic fields have some harmful effects to electronic devices but I am ...
2
votes
3answers
138 views

Why is the scalar product of four-velocity with itself -1?

My GR book Hartle says the scalar product of four-velocity with itself $-1$? Consider the definition of four velocity $\mathbf{u} = \frac{dx^{\alpha}}{d\tau}$. Suppose I take the scalar product of ...
1
vote
2answers
41 views

How holes conduct current?

I had questions about holes in semiconductor, when i checked the net it is said holes are said to be equivalent positive charge and they say because the hole moves from one place to another when it is ...
2
votes
1answer
22 views

Non-degenerate or degenerate perturbation theory for a non-degenerate level of a system with other levels degenerate?

To decide whether I have to use non-degenerate or degenerate perturbation theory, I have to look only on whether the energy level I am calculating corrections to is degenerate, the degree of ...
1
vote
1answer
102 views

Upper limit to electric charge confinement?

The following questions are not intended for conventional capacitors (which stores excess charge on the outside surface), rather a type of hypothetical capacitor which is designed to confine charge by ...
2
votes
2answers
84 views

How to accurately mark with arrows an electric circuit

As I understood, we choose to mark the current with arrows going from the plus pole to the minus pole (even though we know that in reality it is the contrary). As I'm looking at electric circuits, I ...
1
vote
1answer
23 views

SU(3) irreducible representations with tensor method

I am dealing with the tensor product representation of SU(3) and I have some problems in understanding some decomposition. 1) Let's find the irreducible representation of $3\otimes\bar{3}$ we have ...
2
votes
1answer
45 views

Can observations of cosmic super voids teach us anything about time, dark energy, or dark matter?

Can observations of cosmic super voids teach us anything about... Time - If gravity affects time is there a chance we could gain any further information from studying a region with lower than ...
2
votes
1answer
89 views

Mode groups in an optical fiber

I know what modes in an optical fiber mean but what are exactly mode groups in an optical fiber? From what I read until now, I have the impression that modes that have close propagation constants ...
0
votes
0answers
17 views

What justification is necessary for convolutional variational principles to be considered legitimate?

I recently asked a related question and was interested in why/or why we cannot use convolutional variational principles in practice or in theory. Summarizing the points I made in the earlier post: ...
2
votes
4answers
121 views

Are empty black holes possible

When just considering GR without evaporation nor QM, is an empty (containing no matter or anything) black hole possible ? Let's say that there is only GR and nothing else (no matter or boson fields), ...
0
votes
1answer
98 views

What arguments and examples did Newton give in support of Absolute time and space?

As everyone knows, Sir Newton advocated the Absolute Space & Time theory. But what examples and arguments did he confer to establish his theory? I read the wiki page where it was written that he ...
0
votes
1answer
20 views

Why does this derivation of the dependence of free energy on pressure not work?

It is well known that the Gibbs Free Energy of a gas depends on the pressure via the following formula: $$G_m(p) = G^\circ_m + RT\ln{\frac{p}{p^{\circ}}}$$ Where $G_m$ is the molar gibbs free energy ...
1
vote
1answer
32 views

Working out the penetration of radioactive decay products

From my understanding of the products of radioactive decay (alpha particles, beta particles, and gamma are all I know of), the particles (or energy I guess?) are stopped by a medium according to it's ...
6
votes
2answers
103 views

Ambiguity in Asymptotic Perturbative Series and Instantons

I know there are a number of questions about the asymptoticity of perturbative series and about instantons on StackExchange (e.g. Instantons and Non Perturbative Amplitudes in Gravity from user566, ...
0
votes
1answer
35 views

How do you accelerate atoms/particles?

So I'm in 11th grade, and I'm writing a theory for my Physics professor and I need help. I need to know how you can make atoms/particles travel faster. For example, making sound travel a little bit ...
0
votes
2answers
49 views

Balancing a pencil

I came across this equation for balancing a pencil while solving some problems: $$ml\ddot { \theta } =mg\theta $$ Where $l=$the length of the pencil, and $\theta$ is the angle it makes with vertical. ...
0
votes
1answer
17 views

What frequencies will get lost/diminished when you listen to a colloidal speaker without the backside

I was checking the connections of my colloidal speakers, so I had to listen to music without the backside of the speakers. There was clearly a difference in the quality of the music, but I couldn't ...
0
votes
0answers
34 views

Are there any equations describing solid, liquid, or plasma containing the gas constant $R$? [on hold]

The gas constant $R$ relates so much to Boltzmann constant $k_B$. Boltzmann constant= gas constant divided by the Avogadro constant. For example, $R$ can be used in Nernst equation. So, $R$ is not ...
0
votes
0answers
18 views

Can we prove that zero point energy exists everywhere and not just locally around individual particles or our universe as a whole?

If zero point energy only exists locally around the particles that we are using to observe it and not globally then the zero point energy would have to rise in value when we put two particles close ...
1
vote
1answer
17 views

Laser cutting - ignition

How is that sometimes laser cutting by burning material or "flame cutting" causes ignition of the whole material like here where the whole paper starts to burn and sometimes doesn't allowing precise ...
2
votes
1answer
94 views

Calculate the mass of a Schwarzchild black hole with Komar integral

In Wald's GR, Komar integral is Eq. (11.2.9): $$M=-\frac{1}{8\pi}\int_S\epsilon_{abcd}\nabla^c\xi^d$$ $S$ can be chosen as a 2-sphere, the boundary of a spacelike hypersurface $\Sigma$ such that the ...
1
vote
2answers
65 views

Is there a portable method of preventing all IR radiation from being emitted?

Me and some friends were recently disuccing "How cool it would be to be invisible", from a military viewpoint, I said that Camouflage, when done correctly, works surprisingly well, so invisibility was ...
1
vote
0answers
13 views

Compute $Z_2$ Invariant of 2D Topological Insulators without Computing the Eigenstates

For 2D Time-Reversal Invariant systems ($T H(\vec{k}) T^{-1} = H(-\vec{k}) $), there is a formula by Fu-Kane-Mele in order to determine whether the system belongs to either one of distinct topological ...

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