0
votes
0answers
7 views

Loss of interference in single-photon Mach–Zehnder interferometer with detector in only one arm

I have read that if you have a Mach–Zehnder interferometer (doing a single-photon experiment) and put a detector in only one of the two arms (connected to the first beam splitter), you lose ...
3
votes
4answers
253 views

Could there have been two “Big Bangs”?

A couple of years ago, I remember seeing a documentary on the big bang theory. The theory presented was that to explain the cosmic microwave background radiation, there needed to have been two big ...
3
votes
1answer
477 views

Hubbard Model Hamitonian

$H = -\sum\limits_{i,j} A_{ij} c_i^{\dagger} c_j + \frac{U}{2} \sum\limits_i(c_i^\dagger c_i)(c_i^\dagger c_i -1)$ is defined to be a Hamiltonian for modeling quantum random walk of identical ...
0
votes
0answers
6 views

density of states with changing potential floor

I wish to calculate the density of states for a 1D finite potential well, for the scattering states, meaning $E>0$. I have a potential of the form: $$ V(x)=\begin{cases} -V_0 & |x|<a\\ 0 ...
1
vote
1answer
72 views

What am I doing wrong while proving time dilation using Minkowski space-time diagram?

Consider two events A and C. They have same value of x' and time interval between them is $\triangle \tau$. This is the proper time interval between the events. ...
0
votes
1answer
15 views

Reduced Pressure and Cooling

Hi Knowledgeable folks, Since boiling point of a liquid can be reduced via pressure reduction. I was wondering whether this is possible: Add some liquid (alcohol or Water) in a container, reduce the ...
1
vote
2answers
195 views

Is the center of mass in general relativity equal to the center of mass in newtonian gravity?

Consider 2 point masses $A,B$ a distance $d$ away from eachother without velocity or rotation spin. Is the center of mass in general relativity equal to the center of mass in newtonian gravity ? In ...
4
votes
2answers
133 views

Why are nonrelativistic methods used in binary pulsar systems (gravitational waves)?

Although gravitational waves are a subject of the General Relativity, why do most books use Newtonian equations of motion for power radiated and rate of change of eccentricity calculations? In most ...
0
votes
3answers
30 views

When we write that F = -grad V , what if would happen if we ommit the (-) minus sign

I have had this question for a long time. In classical mechanics, if we choose $\mathbf F = -\mathbf \nabla \, V,$ with the minus sign, we can proof the work - kinetic energy theorem. What are the ...
1
vote
0answers
26 views

Understanding the $\phi^4$ phase diagram

I'm having trouble making sense of this phase diagram. The model is a $V(\phi)=g_2 \phi^2+g_4\phi^4$ scalar field theory. Here's what I think I understand: the capital letters represent different ...
3
votes
1answer
101 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? ...
3
votes
0answers
25 views

How can a bowling ball curve in both directions?

There is a popular video on facebook that I just don't understand. A man spins a bowling ball very fast then slightly taps it down the lane. Somehow it does half of a figure eight, curving around two ...
0
votes
1answer
19 views

Why don't eye lenses alter depth perception?

What it is going to do is bend the rays so that light from infinity "appears" as though it is coinciding with a person's far point. In doing so, it allows the person to see a clear image, without ...
0
votes
1answer
24 views

How Much Weight Would This Put On The Legs Of A Desk?

first time on this site and I need help with this, I got 2 stands 1 is longer and goes top of the other. The top of the stand will have 70 lbs on it and I want to know how much pressure (if that is ...
1
vote
1answer
224 views

What happens to gas molecules after ionization?

I know that gas molecules conduct electricity after they get ionized but what will happen if we keep increasing the voltage even after ionization? Will it explode? If it will then how much energy ...
0
votes
1answer
16 views

In the orthonormal tetrad method, what is the relation between basis one forms and commutation coefficients?

If $\omega_i$ are dual basis one forms corresponding to an orthonormal tetrad basis $e_i$, and given that the commutation coefficients $C_{ij}^k$ are defined by \begin{equation} [e_i,e_j]=C_{ij}^k ...
0
votes
0answers
9 views

solving for diameter of a glass tube to hold water

I am trying to solve the diameter as a function of the length of a tube, 'l', when it is turned upside down. Note that the glass tube is closed at one end. This is similar to a question I recently ...
1
vote
1answer
17 views

Can electrons within a positive ion absorb and reflect light?

I understand that in a crystalline metallic structure, such as one making up a bar of gold, there are one, or more, valance electrons of each atom that have left their outer shell (became free ...
4
votes
4answers
22k views

Why is stainless steel a poor conductor of electricity?

I recently had a metal plate put in my shoulder and was wondering why stainless steel isn't a good conductor (At least I hope it isn't). Does the alloy just lack free electrons? Why is that?
4
votes
7answers
875 views

How can a product of Bra and Ket be a scalar if they are matrices?

I am trying to teach myself Quantum Mechanics and am currently on Complex Vector Space Arithmetic. According to Wikipedia, product of a Bra and Ket is a scalar (which, I think, means a complex ...
0
votes
2answers
25 views

Damped Pendulum (generalised)

I know the differential equation for the swinging of a simple pendulum: $\displaystyle\frac{\partial^2\theta}{\partial t^2} + \left(\frac{g}{L}\right)\sin\theta = 0$ where: $L$ is the length of ...
0
votes
1answer
17 views

Calculating Rolling friction of a car's wheels (NOT ON AN INCLINE)

I'm dealing with a small toy car consisting of a bottle that has a small hole in the back, covered by a thumb tack. The bottle is filled with pressurized air then the thumb tack is released, releasing ...
-1
votes
0answers
19 views

Gravity/Newtons Law

You are explaining why astronauts feel weightless while orbiting in the space shuttle. Your friends respond that they thought gravity was just a lot weaker up there. Convince them and yourself that it ...
-1
votes
1answer
33 views

When travelling in the direction of light, what is my relative velocity?

If suppose I am traveling in the same direction as that of light, the relative velocity I am traveling with is speed of light + my speed in the direction of light. Is this correct? Does this have ...
0
votes
1answer
169 views

Rigorous proof of Ampère's law from the Biot-Savart law

Let us assume the validity of the Biot-Savart law for a tridimensional distribution of current:$$\mathbf{B}(\mathbf{x})=\frac{\mu_0}{4\pi}\int_V ...
0
votes
1answer
19 views

Question on the degeneracies of a thermodynamic system

I think I have a basic understanding of what degeneracies are: Two or more different states of a quantum mechanical system are said to be degenerate if they give the same value of energy upon ...
0
votes
1answer
18 views

Can charge flow to a neutral body?

If an electrically positive object is kept with a neutral object, in which direction will charge flow? Will charge flow from positive to neutral until both have equal charges, or will nothing happen ...
0
votes
1answer
20 views

The dot product integral in the proof of the Parallel axis theorem

The first picture is a question about proving the Parallel axis theorem and the second is the solution. I have no problem with the solution except for the part which says that $$ \int 2\vec h ...
1
vote
2answers
146 views

How does exciting an electron's surrounding electromagnetic field cause 'electron excitation'?

In more meaningful words than the ones above, how does adding energy to the EM field cause the electron to to change orbitals or oscillate in a different pattern.
4
votes
1answer
91 views

Help needed to understand “On the reality of the quantum state”

I am having trouble to understand the reasoning in the following paper, On the reality of the quantum state. MF Pusey, J Barret and T Rudolph. Nature Phys. 8, 475–478 (2012); arXiv:1111.3328. ...
1
vote
1answer
5 views

dry adiabatic lapse rate

Adiabatic lapse rate is defined as $$ \Gamma_a \equiv -\left(\frac{dT}{dz}\right)_{\rm parcel}=-\frac{R_{\rm a} T}{c_p \,p}\left(\frac{dp}{dz}\right)_{\rm parcel} = \frac{g}{c_p} $$ $R_a$ is gas ...
1
vote
1answer
57 views

Information Preservation and Weather Forecasting for Black Holes

Referencing Stephen Hawking's recent paper Information Preservation and Weather Forecasting for Black Holes and this question. I understand concept of holding the information on the apparent horizon ...
0
votes
3answers
768 views

Does light color change when refracting? [duplicate]

When light refracts from a medium to a second one, its frequency stays the same, and its wavelength changes. If this is true, why we see the refracted light ray's colour is the same as the incident ...
-2
votes
2answers
56 views

Is there a natural source of Antimatter in this universe?

I was just asking if there is an natural source of Antimatter in this universe capable of creating simple molecules/compounds? So, any good answers?
0
votes
2answers
28 views

Some Clarifications about Electricity

In the diagram below (ignoring the text), does the $V$ mean that there is some electric field outside of this system which results in a potential difference of $V$ between $a$ and $b$ or does it mean ...
0
votes
1answer
271 views

How to find the least count of a normal scale

Well suppose i have a normal measuring scale how do i find its least count?I have just been introduced to errors in measurement and our professor was giving us least counts of different instruments ...
-4
votes
0answers
10 views
1
vote
1answer
31 views

Tornado Vortex Low-pressure Force

If a tornado forms not contacting the ground and then moves over a large flat roof and contacts that surface, producing low pressure above that surface and having normal, higher atmospheric pressure ...
1
vote
1answer
43 views

How do I remove the negative sign from this derivation?

A homework problem required me to show that the first equation below can be written in the form of the second equation. It was all fairly simple except for the negative sign. I'm not sure how this is ...
0
votes
2answers
21 views

Why is the intensity of an alpha ray constant along a material?

I'm taking a course in radiation physics and I've come across the following problem: A thin beam of alpha particles of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity ...
3
votes
1answer
22 views

shape formed by a stiff string with ends pinched together

Suppose I have a string of length $L$ with a bending energy given by $$E=\frac{1}{2}\epsilon \int_0^L ds\, (\mathbf{R}''(s))^2 $$ Let's say I form a bight with it by pinching the ends together, ...
2
votes
2answers
36 views

Is Planck’s proof of Kirchhoff’s Law of Thermal Emission false, and if not why not?

In his book ‘The Theory of Heat Radiation’, Max Planck adduced his theoretical proof of Kirchhoff’s Law of Thermal Emission. It was recently shown that Planck’s proof is false: “The Theory of Heat ...
1
vote
0answers
23 views

Identifying Lorentz Covariant Equations

Statement: $\phi , A^{\mu}, T^{\mu \nu}$ are a Lorentz scalar, vector, and tensor. Which of the following equations are Lorentz covariant. a. $\phi = A_{0}$ b. $\phi = A^{\mu}A_{\mu}$ c. $\phi = ...
-3
votes
1answer
52 views

Do you say it right? [on hold]

If someone asks you your WEIGHT what would you answer in SI Units. My weight is x 'kilogram' My weight is x 'Newton'. As we know that weight is a force due to local acceleration and still most ...
2
votes
1answer
166 views

What are phase conventions in angular momentum and rotation calculations?

I work with complicated angular momentum calculations related to atomic physics; nevertheless, I never need to use anything related to a phase convention (apparently because it's taken care of in a ...
0
votes
0answers
24 views

Obtain an exact expression for the heat capacity of the system

Before anyone mentions it, yes I did my research and found this question on this site. My question is his exact question, but I'd like some clarification or maybe a bit more explanation than the one ...
1
vote
1answer
39 views

Why is it difficult for 2 black holes to merge?

Apparently as part of the merger of galaxies, sometimes the central supermassive black holes of colliding galaxies get really close, however once they come to a distance of about <1 parsec, it ...
2
votes
6answers
73 views

Is QM something that belongs to all relative small particles or only to subatomic particles?

For us human beings subatomic particles like elektrons are described by the laws of QM. But imagine their is a very huge giant looking on the universe. For him all the planets and stars are so tiny ...
1
vote
1answer
17 views

How can I change the divergence angle of a single mode fiber

For my project I use the end of a single mode fiber as a "transmitter". I need to set the divergence to 20 micro radians. Is there an equation how to calculate the divergence and the necessary optics ...
1
vote
0answers
11 views

Density parameter (cosmology) as a function of redshift

Hopefully I'm missing some very basic algebra for this question. In essence, I need to derive the following: $$ \Omega=\Omega_{1}\frac{(1+z)}{1+\Omega_1{z}} $$ Now, I proceeded from the Friedmann ...

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