0
votes
1answer
21 views

An image in movement viewed by different cameras [on hold]

Why in the image the string looks like is in two places at the same time, what is the optical reason or is it because of how cameras work?
1
vote
0answers
13 views

Combining sound absorption coefficients

I am trying to predict the reverberation time in a room with different surfaces and different absorption coefficients (i.e. curtains, wood panels, carpet etc). My question is about how to calculate ...
0
votes
1answer
37 views

D branes Ns brane and p-branes

It is now a common knowledge that "D-p branes are equivalent to p-branes" due to Polchinski's work. Note that D-p branes are objects in string theory and p-branes are objects in blackhole theory. So ...
0
votes
0answers
24 views

How to parametrize off-shellness?

The energy of a massive on-shell particle of mass $m$ and three-momentum $\vec{p}$ satisfies $$E_\vec{p} = \sqrt{\vec{p}^2+m^2}. $$ What would be the analogous expression for an off-shell particle? ...
1
vote
0answers
30 views

Calculation of angular acceleration [on hold]

Hi I am doing a physics question and it's like this: Two identical blocks, each of mass M, are connected by a massless string over a pulley of radius R and rotational inertia I . When the system is ...
0
votes
1answer
41 views

Why 5D gauge theory is non-renormalizable?

My question is following "Why 5D gauge theory is non-renormalizable?" Here I treat $5D$ supersymmetric gauge theories. Also I heard Non-renormalizablity of $5D$ gauge theories implies the ...
0
votes
2answers
44 views

Thermodynamics : Work done on gas inside container by the force due to pressure exerted by external atmosphere

Suppose a container is fitted with a massless and frictionless piston lying on a table such that pressure due to gas is greater than pressure due to external atmosphere. Hence piston will move. Now ...
0
votes
0answers
18 views

Calculating the entropy of a monatomic ideal gas

I am looking at the start of the consider how to calculate the entropy of a monatomic ideal gas. We need to determine the number of microstates in $E \leq \mathcal{H}(\Gamma) \leq E+\Delta$. The ...
1
vote
1answer
51 views

Does anyone recognize the line element $ds^2 = ( 1 - \frac{2m}{r} )dt^2 + 2 dt dr$?

I've stumbled upon the line element $ds^2 = ( 1 - \frac{2m}{r} )dt^2 + 2 dt dr$. Obviously the corresponding metric tensor has components: $\begin{bmatrix} g_{tt} & g_{tr} \\ g_{rt} & g_{rr} ...
1
vote
1answer
44 views

How do i correctly go from a two variable function to a function of difference?

I would like to know how I can go from a two argument function $g(x_1,x_2)$ formally correct to a function of the difference of the parameters $g(x_1-x_2)=g(x)$ this seems to involve integration over ...
0
votes
0answers
39 views

Can a(n electro)magnetic field be amplified to overcome the residual strong force between protons-neutrons in a nucleus?

My knowledge of physics is cursory at best, I never studied it in high school but I enjoy reading about it as a layperson, especially the posts here on PSE. I don't understand any of the complex math ...
1
vote
1answer
38 views

EM radiation explanation [duplicate]

Why is it so that a charged particle when accelerated radiates energy? I tried to think if it might be violating the law of conservation of energy but the energy transferred by the external agent may ...
0
votes
1answer
40 views

Neutrino mass and the Majorana equation

I can't seem find this on the Internet. What does the Majorana equation predict neutrino masses to be (if they were their own antiparticle), and how? (I have little understanding of spinors, btw...) ...
-4
votes
1answer
32 views

I cannot find on the internet, what the roadblock is for this self-replicating robot idea [on hold]

Firstly, you can build a human robot with all the needed solid-state-memory sticks in it to make it build a duplicate human robot with the same amount of memory sticks inside, just that they cannot be ...
1
vote
3answers
74 views

Suppose $\phi(x)$ is a field, how should I interpret $\partial^\mu\phi$ and $\partial_\mu\phi$?

I am really confused by the sub and upperscript notation sometimes. It might be really trivial but I have a difficult time interpreting the following things in for example this Lagrangian ...
4
votes
3answers
92 views

What is the relationship between vibration of the field and quantum fluctuation?

Consider a free field like the KG equation. I see that why $$\tilde \phi(\mathbf{p},t)$$ a momentum-dependent quantity, is an oscillator, vibrating at a frequency because when we apply the Fourier ...
3
votes
3answers
85 views

Average surface temperature of Earth [duplicate]

I had a question in my school exam. Will the average surface temperature of the Earth be lower or higher, if there was no atmosphere? Now, the answer expected is "The avg temp will be lower, because ...
0
votes
0answers
14 views

What are the conditions of wave function continuity when solving for Dirac Spinors as done in “Klein paradox” paper by Novoselov?

In the paper "Chiral tunneling and Klein paradox" paper by Katsnelson, Novoselov, and Geim, they use the wave function for Dirac spinors. What are the conditions for continuity of the wave function ...
0
votes
0answers
14 views

Equivalent force–couple system STATICS Meriam 6th exer. 2/71 [on hold]

I need a bit of help to clarify what I couldn't see here. 2/71 The system consisting of the bar OA, two identical pulleys, and a section of thin tape is subjected to the two 180-N tensile ...
5
votes
1answer
233 views

How to tell if a star is in a galaxy?

An astronomer is studying a star that appears to be in a galaxy. How does the astronomer know the star is actually in the galaxy and not just on the same line of sight as the galaxy? I'm guessing ...
-4
votes
0answers
24 views

What formula gives the solunar periods of the Solunar Theory? [on hold]

Challenge Find a general formula that: Given latitude,longitude and date finds (at most) two major solunar periods for that day. Given A table of daily solunar periods for a given month at a given ...
-2
votes
0answers
42 views

What is the most general form for a plane wave?

In the context of electromagnetism, what is the most general form of a plane wave. My suggestion is: $$E=\sum_i{\vec E_ie^{i(\omega t+\vec k \cdot \vec r+\phi_i)}}$$ where $\vec E_i$ are constant ...
1
vote
2answers
77 views

If we can see a galaxy can that galaxy see us?

This is a question about the properties of the expansion of the universe. I can't say it any better than: If we observe a primordial galaxy that existed soon after the Big Bang, does it follow that ...
0
votes
1answer
31 views

can a wave on rope placed away from gravity go on forever?

we can make waves on a rope like we produce waves on a whip. assume that my rope(which is pretty long) is in space and i produce a wave on it at a point the rope is connected at the two ends. would ...
2
votes
2answers
56 views

Proper length in GR

What meaning/use is associated with the notion of proper length in general relativity? Do you know an example of any quantity that depends on it? I have so far found statements like "the length ...
0
votes
0answers
25 views

Has galaxy merger and universe expansion been proven?

I understand the basic argument for hierarchical merging of galaxies during expansion of the universe. I also understand peculiar motion and the Hubble flow. So I understand what's going on with ...
0
votes
0answers
27 views

When does a balloon burst? [on hold]

I'm working on a project and I need to know something. and that's : When does a balloon burst? I mean, does it have any relation to its internal pressure or its volume? for example can we say a volume ...
1
vote
0answers
44 views

Analytical solution to Maxwell's equations in 3D

I'm working on solving Maxwell's equation numerically and have implemented Yee's algorithm in Matlab. In order to check if the algorithm is implemented succesfully, I need an analytical solution to ...
2
votes
2answers
44 views

Is there a difference between Weight and Force of Gravity?

Is there a difference between Weight and Force of Gravity or they just mean the same thing? My textbook does not clarifies this point. Thank you in advance for your help!
1
vote
1answer
52 views

Relation between scattering matrix and an effective Hamiltonian

Could somebody provide the proof (or reference to some accessible literature) of relation $$S(E) = 1 + 2πiW^{†} (H_M − E − iπW W^{†} )^{−1} W \tag{2}$$ of arXiv:0806.4889, which relates $S$-matrix to ...
-2
votes
1answer
34 views

Is there a difference between velocity and drift velocity? [on hold]

While I do know that VELOCITY is displacement in time ,I read something about the DRIFT VELOCITY of electrons. What is DRIFT VELOCITY?
0
votes
0answers
13 views

Find the length of time for which the direction of motion is between 20 degree above and below the horizontal [on hold]

A particle is projected with speed $65\, m s^{−1}$ from a point on horizontal ground, in a direction making an angle of $\alpha$ above the horizontal. The particle reaches the ground again after $12\, ...
-4
votes
0answers
22 views

Perceived solution to grand unification theories and more specifically the TOE [on hold]

My question is doesn't the fact that escaping Earth's atmosphere significantly reduces gravitational attraction lead one to agree with Einstein's original intuition that aether is everywhere and ...
4
votes
2answers
292 views

Reflected and refracted light have same frequency as that of the incident light frequency. Why?

My text book says- When a monochromatic light is incident on a surface separating two media, the refracted and reflected light both have the same frequency as the incident frequency. Can anyone ...
0
votes
0answers
24 views

Why don't we consider cubic terms in the Higgs potential? [duplicate]

In the Standard Model scalar potential, we only consider quadratic and quartic terms, why not cubic terms though? I've noticed also in BSM theories with one extra scalar singlet, only quadratic and ...
0
votes
0answers
19 views

In the Standard Model Lagrangian, why does every term's mass dimension have to be less than four?

In the Standard Model Lagrangian, why does every term's mass dimension have to be less than four? I know that the Lagrangian has to be renormalizable, I guess my question then translates into why ...
1
vote
0answers
50 views

How do you visualize a quantized electromagnetic field?

Quantizing the EM field gives you the standard sum of all quantum harmonic oscillators as given by this hamiltonian: $$ \hat{H} = \sum_k \hbar\omega_k( \hat{a}^\dagger_k \hat{a}_k + 1/2) $$ ...
-2
votes
1answer
32 views

Bounce height of ball on Mars vs Earth

I understand that if a ball is dropped on mars and on earth the ball will bounce back to basically the same height on both planets thanks to the law of conservation of energy. But can anyone prove ...
0
votes
1answer
29 views

Why does negative energy imply that a system is bounded? [duplicate]

I wanted to know why "negative energy" of a two particle system implies that it is bounded. That is what happens in the case of a hydrogen atom; my textbooks say so, but they do not give any reason ...
1
vote
0answers
20 views

The standard textbook on supernovae?

This is a straightforward question: What is considered to be the standard treatment of supernovae? Could be a textbook, lecture notes, review article, etc.
-1
votes
0answers
15 views

Numerical Estimates for the fermi Energy [on hold]

The question is to give the numerical estimates for the Fermi Energy of electrons in a typical metal, nucleons in a heavy nucleus and $He^3$ atoms in a liquid $He^3$ and compare the results. I know ...
1
vote
3answers
52 views

What is meant by a “sodium line”?

What speed should a galaxy move with respect to us so that the sodium line at $589.0\ \mathrm{nm}$ is observed at $589.6\ \mathrm{nm}$? In the above question what's meant by a sodium line? The ...
0
votes
1answer
22 views

Conformal group and stereographic projection

In Ginsparg's Applied Conformal Field Theory (http://arxiv.org/abs/hep-th/9108028, on the bottom of p. 5) the following remark is made: Indeed the conformal group admits a nice realization acting ...
2
votes
0answers
45 views

As an older student, is it better to finish my degree or go straight into studying physics now? [on hold]

I'm a 23 year old going through a very early mid-life crisis, and considering a career change to physics. I would be very greatful for any advice :) I'm currently studying medicine, but I've realized ...
0
votes
0answers
24 views

Acceleration of an incompressible fluid along a conical pipe [on hold]

I've been reading Theory of Flight by Richard von Mises and early on I came across this problem. The full text of the problem is as follows: "Show that along a conical pipe the acceleration of an ...
0
votes
1answer
42 views

Scientific Laws for Engineering Materials [on hold]

I have a conceptual question. There is a law in science for every phenomenon in nature, like gravity or electric field. But also there are laws for springs or capacitors etc... I mean the ...
0
votes
2answers
28 views

Pendulum point in polar coordinates for Lagrangian

So I'm really stumped with this. I have a particle in a cone, like pictured. The particle orbits the z axis on the dotted line for $r$. So knowing that $\alpha$ and $r$ remain constant in this ...
0
votes
1answer
19 views

Spectroscopy - Absorption lines

Let's say we run a light source (a strong torch) with full spectrum light through a big, transparent, glass box filled with neon. Will we be able to see any Fraunhofer lines on the spectral analysis ...
2
votes
2answers
92 views

Hamiltonian mechanics really useful for numerical integration? Lagrangian can become 1st-order

(I'm talking about the classical mechanics.) Many texts say that Euler-Lagrange equations are difficult to treat numerically because they are second-order ODEs, ${f_i(\boldsymbol{q, \dot{q}, ...
0
votes
1answer
35 views

How can Bernoullis be solved without Vectors [duplicate]

Some time ago I asked a question why Dynamic pressure is considered scalar. Why is the dynamic pressure not a vector quantity? This still puzzles me so I hope to give a scenario that doesn't make ...

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