1
vote
0answers
10 views

Why do people look for a field formalism for String Theory

String Theory was formulated originally from a perturbative description (using QM and replacing points by strings and doing path integral). Still, although QM has an upgrade to a field formalism -- ...
2
votes
1answer
23 views

Was the firewall paradox resolved?

For quite sometime there has been a claim that the firewall paradox has been resolved (via lasers). For instance, http://global.ofweek.com/news/Lasers-to-solve-the-black-hole-information-paradox-9867 ...
2
votes
2answers
23 views

Different results to a basic question ( Newton's law and perservation of momentum)

Trolley with mass of $m_0=1 \ kg$ is moving without friction on the railway track. It is raining so there is a constant mass flow of water $\Phi_m=0.1\ kg/s$. Constant force $F=0.1 \ N$ is ...
1
vote
0answers
19 views

Relationship between Connection and Material Derivative

Suppose $D\subset \Bbb R^3$ contains a fluid and that $f : D\times \mathbb{R}\to \mathbb{R}$ is a time dependent function defined on the fluid region. In that case, the material derivative along a ...
1
vote
0answers
14 views

String boundary conditions

I'm reading Polchinski and am confused about equation (1.3.13), $$\gamma_{\tau\sigma}\partial_\tau X^\mu-\gamma_{\tau\tau}\partial_\sigma X^\mu=0~~~~~\text{at}~~~~~\sigma=0,l.$$ It says that this ...
0
votes
0answers
16 views

Are photons travelling in future? Are they lifespan 0 (or close to 0)?

We know that if we are going closer to speed of light, we are travelling in future. Since the photons are travelling at the speed of light, that means that they are travelling into future? Also, if ...
0
votes
2answers
18 views

Does the coefficient of restitution matter in a collision?

Suppose two particles are colliding. Let initial velocities be $u_1$ and $u_2$ .Their final velocities are $v_1$ and $v_2$. Now $u_1$ and $u_2$ are known. By intuition I can understand that $v_1$ and ...
0
votes
1answer
17 views

Normal force on varying mass

A cart filled with a mass $m_0$ of sand leaks it at a constant rate of $\mu \ \mathrm{kg/s}$ through a hole at the bottom of the cart. Suppose that the cart is moving on rails. Find the ...
-4
votes
0answers
19 views

Capacitance of air capacitor [on hold]

Hi I'm currently working on the following question (image below), any help is much appreciated!
0
votes
1answer
17 views

Calculation of cable properties in parallel circuit

i am working on a simple program and need your help for a problem. I have a power grid circuit and between 2 nodes there are from 1 to many cables. But the program accepts only one cable between 2 ...
9
votes
1answer
177 views

Why do stickers curl?

When peeling a sticker off its base, the immediate reaction is that it curls; why is this? I am having trouble finding an answer to this. Could it be that the glued side expands upon contact with the ...
0
votes
1answer
28 views

A moving inclined plane with block problem

I'm trying to solve for a challenging problem : a moving inclined plane with a block I want to solve for the acceleration components for the block and the plane and the normal force acting on the ...
3
votes
2answers
179 views

Why do I always hear remote train horn at night?

This is definitely not an illusion, as many people have the same experience. I have usually lived in places miles away from train stations, which makes it unlikely to hear any train horns during the ...
0
votes
0answers
50 views

General definition of vector spinor and spin

I am looking for basic and exact definitions of fundamental physical consepts in graduate level. I reach this following definitions. Could you please help to improve these definitions. Spin: ...
-1
votes
0answers
22 views

what is the mean velocity of this? [on hold]

The Maximum velocity of a one dimensional incompressible fully developed viscous flow, between two fixed parallel plates, is 6 m/s. The Mean Velocity ( in m/s) of the flow is (A) 2 (B) 3 (C) ...
0
votes
0answers
12 views

How do you obtain the fluctuation spectrum of a tubular membrane?

I am reading through a paper. A tubular membrane, submitted to tension $\sigma$ acting as a Lagrange multiplier to conserve area, fluctuates around a cylindrical shape of length L and radius R. ...
1
vote
2answers
312 views

Why doesn't gravity bend everything equally?

If gravity is the curvature of spacetime it should bend everything equally. To clarify my point I would like you to imagine two scenarios. Think of a bird flying in the storm while the wind is blowing ...
3
votes
1answer
92 views

Glauber's Formula

In the Cohen-Tannoudji Quantum Physics book, Complement BII, says: [...] two operators $A$ and $B$ with both commute with their commutator. An argument modeled on the preceding one shows that, if we ...
-7
votes
0answers
41 views

Is {299,792,458^2 * (6.67384*10^-11)} the number that can be considered a moment of inertia? [duplicate]

Whence x is a variable, and given E=mc^2 and F=Gm1m2/r^2 and E/F=x, is approximately 59,981,482,620,609,230,385,376,000,000 the number that the equation (mc^2/Gm1m2/r^2=x) reduces to?
0
votes
2answers
34 views

Solar stills with Wine [on hold]

Is it possible to obtain more concentrated alcohol by using wine in a solar still instead of seawater? If yes, as I suspected, how does the concentration (of alcohol) of the distillate vary with ...
5
votes
2answers
111 views

Why is it so hard to mix spaghetti with meatballs?

When I cook spaghetti with a sauce that includes meatballs or chopped vegetables, those stay in chunks and won't get uniformly mixed in the pasta. Is there a simple reason for that? Has it been ...
0
votes
0answers
24 views

Orbital Speed and Centripetal Acceleration [on hold]

I need help in solving this A space station is in circular orbit around earth at an altitude of 5.0×10^5m. If the station makes one revolution every 95 min compute its; A. Orbital speed ...
-5
votes
1answer
50 views

Does the moment of inertia equal “the number attached to c (speed of light)” divided by “our most precise numeric value attached to G”? [duplicate]

Whence x is a variable, and when E=mc^2 and F=Gm1m2/r^2, and when E/F=x, can one reduce the equation mcc/gm1m2/r^2=x to a ratio of dividing the numeric value of the speed of light by our best ...
0
votes
1answer
69 views

What measurement of time is so small that it qualifies as quantum?

Quantum mechanics (QM; also known as quantum physics, or quantum theory) is a branch of physics which deals with physical phenomena at nanoscopic scales where the action is on the order of the ...
-4
votes
0answers
49 views

Does the moment of inertia equal “the number attached to c (speed of light)” divided by “our most precise numeric value attached to G”? [on hold]

Does the moment of inertia equal $4492053420519520995.4089399805809$? Considering the equation $E/F=x$ where $E=mc^2$ and $F=Gm_1m_2/r^2$, and whence $x$ is any variable... $c = 299792458\, ...
0
votes
2answers
37 views

equivalent spring constant for a drum floating in water

If I have a drum floating in water, how do I find the equivalent spring constant? I know that the water has density $\rho$, the drum has diameter $d$ and height $\ell$, and the positive direction is ...
3
votes
1answer
390 views

What is the meaning of this “let there be light” joke?

A middle school teacher across the restaurant is wearing this shirt, and I certainly don't get it.
0
votes
0answers
43 views

What does the behavior of the pair correlation function look like in the vicinity of the critical point?

What does the g(r) look like near the critical point? I know what the pair correlation function (radial distribution function) should look like for a solid, which has regular packing and therefore ...
0
votes
0answers
15 views

Clear view and good lighting of the x ray departments [on hold]

What is the benefit of clear view and good lighting of the x-ray diagnostic test department?
2
votes
2answers
95 views

Scientists observe the laws of the physics but, Where do they come from? [on hold]

Has anyone ever considered how the laws of physics that we study came into being.
0
votes
1answer
31 views

Deviation from 2D trajectory

I need to find out how far a ball is from the predicted trajectory in 2 dimensional space and I know the start and end position of the ball in both dimensions. Along with that I know the initial ...
1
vote
1answer
35 views

What's causing the effect of salt in voltage arcs?

I just came across this video demonstrating that salt increases length of voltage arcs. There is no explanation which leaves me quite confused. Does the salt decompose during the process?
3
votes
2answers
159 views

What is the difference between induced current and eddy current?

I was reading today about electromagnetic induction and eddy currents. But while reading I was unable to differentiate between induced current and eddy current. What is the difference?
5
votes
0answers
59 views

Is there a way to obtain an RG flow equation for Quantum spin systems using MERA

We restrict ourselves to ground states of translationally invariant 1d quantum systems. I understand that there is the scale invariant MERA(multiscale entanglement renormalization ansatz) which ...
2
votes
0answers
60 views

Integral over a product of two Green's functions

Need some help here on a frequently encountered integral in Green's function formalism. Forgive me since I am a junior student. I have an integral/summation as a product of a retarded and advanced ...
-3
votes
0answers
27 views

Solve the following linear second order circuit [on hold]

I am not able to solve for the second part of the question (when v(t) = 0)
3
votes
3answers
224 views

Negative energy levels in the diagram for a hydrogen atom

The higher the number of the shell (n), the higher is the energy level of the electron. However, why was it necessary to have negative values. So for example, when $n=1$, the energy could be $5 eV$ ...
-9
votes
0answers
70 views

The explanation of the mass of the photon [on hold]

Actually, I'm not asking a question, I am answering to people who don't understand why they say that photon has no mass and exists at the same time! I am a popularizer of science, specialized in ...
-4
votes
0answers
75 views

Corrected Lorentz transformations [on hold]

The standard Lorentz transformations are not correct because in their derivation a logical contradiction is involved: namely in the derivation is assumed that for any value of the velocity, the ...
3
votes
3answers
255 views

How would normal matter behave under conditions found in the core of the sun?

Considering how low the power density is at the sun's core, I seem not to be able to expect what would happen to matter in case it was thrown inside the sun's core. For example, let's assume an ...
0
votes
2answers
124 views

Who foots the (magnetic) energy bill?

Gravitational attraction and electrostatic attraction/repulsion are intrinsic properties of matter, any particle (electron, proton) for some unknown reason can produce KE at a distance. But magnetic ...
0
votes
0answers
32 views

Quantum chaos in interacting discrete time quantum walk?

I have situation where I am simulating discrete time quantum walk (DTQW) for various graphs. I have two quantum walkers on the graph and they can interact with each other by the fact that where the ...
2
votes
1answer
31 views

Can an Ergodic dynamical system approach equilibrium?

An ergodic dynamical system $(\Omega,\phi^t,\mu)$ is such that the time average $\bar{f}$ of every function $f\in L_1(\Omega,\mu)$ equal the space average $\langle f \rangle_\mu$, i.e. the system ...
1
vote
1answer
22 views

How to find the required inlet velocity/pressure to achieve 0.5 m/s in one part of the underground tunnel? [on hold]

I have this problem here related with tunnel and ventilation. As you can see at the picture below, it is a top view of the tunnel. The tunnel has an inlet and an outlet. The air flows from the inlet ...
1
vote
1answer
20 views

How to calculate the differential scattering cross section?

I am doing some simulations with the Meep code to study some properties of a metal nanoparticle. The situation is this: an incident electromagnetic wave on a metal nanoparticle. By now I know how to ...
0
votes
0answers
18 views

Calculate object displacement with a radial/centripetal acceleration [on hold]

What i want to do is calculate the displacement of a object with a certain radial acceleration in a moment of time. The object has a velocity, radial acceleration and a tangential acceleration. For ...
2
votes
2answers
73 views

Expanding universe and the speed of light [duplicate]

When physicists talk about the expanding universe they often say that the distant galaxies are not really "moving" away but instead the space itself between us and them is expanding. If this is true ...
-2
votes
1answer
29 views

What formula connects the moment of inertia and angular velocity? [duplicate]

I need to determine angular velocity of a disc when a man with given mass and speed whacks on the edge of it. I calculated the total moment of inertia of disc and body, how do I calculate the ...
5
votes
2answers
320 views

The acceleration vector of a simple pendulum

In this picture the acceleration vector $\vec{a}$ points upward when the pendulum is halfway Click To see animated GIF But according to this picture, the force acts tangentially: Which means the ...
1
vote
0answers
42 views

Hermiticity of the quantum field

The quantum field resultant from the quantization of a real classical field is hermitian, but why the quantum field corresponding to a complex classical field should be non-hermitian?

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