2
votes
1answer
47 views

Nahm's theorem and related with SYM ;other theories

To study $S$-duality in more detail, i tried to read, Electric-magnetic duality and the Geometric Langlands Program. In section 2.1, there is a comment about 10d SYM. Excerpt from the paper above, ...
0
votes
0answers
18 views

Work power and energy question, circular path [duplicate]

Suppose when someone travel in a circular path and covers 2 pie r distance. Is he done some work or not.(here r is radius of circle). work done is only force times displacement or force times distance ...
0
votes
0answers
34 views

How to derive friction laws?

How do I derive the laws: $$F_s = \mu_s N, F_k = \mu_k N$$ For static and kinetic friction? It was one of the very first things I was ever taught in a physics lesson, and yet to this day I still ...
1
vote
1answer
45 views

Can you see Bose-Einstein condensates with the naked eye?

In this article it is said that "A BEC is a group of a few million atoms that merge to make a single matter-wave about a millimeter or so across." Does this mean that when they make a matter wave ...
1
vote
1answer
93 views

Direct Sum representation of multiple particles in Quantum Mechanics

Suppose that I have three non-interacting spin-1/2 particles such that I can represent the combined system in a basis of \begin{align} D^{(1/2)}_1 \otimes D^{(1/2)}_2 \otimes D^{(1/2)}_3 & ...
3
votes
0answers
86 views

Renormalization confusion

I'm starting to read about renormalization in the case of scalar field theory. I have some confusions. I will consider momentum renormalization. First, consider a theory with a coupling constant ...
0
votes
1answer
63 views

Calculus of Variations - Virtual displacements

I am currently reading "The Variational Principles of Mechanics - Cornelius Lanczos", in which the author talks about the variation of a function $F(q_1, q_2, \dots q_n)$ where $q_1, q_2, \dots q_n$ ...
-1
votes
3answers
212 views

Can rotating disk clocked at its center at the speed of light have an outer edge that travels faster than the speed of light? [duplicate]

I have been running this through my head for a few days and I understand I am probably missing something very simple here. If a wheel is spinning the outer edge will travel at a speed that is greater ...
1
vote
3answers
108 views

How does the tuner really work in a crystal set?

I would like to know how and why the tuner works in a crystal set radio. I already know all the theory and the "formal definitions" (this creates a resonant circuit which responds to an alternating ...
3
votes
4answers
137 views

Can a die be made unfair without changing the center of mass or the exterior?

This question came from trying to design some 3d printed dnd dice. I think it's possible to make a die unfair without changing the center of mass or affecting the exterior shape*, but I'm not sure ...
0
votes
1answer
76 views

Laser-induced electrical discharge

Attracting lightning with an ion beam has been done in a lab but how strong of a laser is needed to reach the clouds to redirect the lightning bolt?
0
votes
1answer
30 views

If I pass light through a conducting ring will I get an emf induced in the ring? Also if I do get an emf would that not violate energy conservation?

Here is what I think should happen. Light being an electromagnetic wave should have an oscillating magnetic component which should constantly change the flux linked with the conductor. Hence an emf ...
1
vote
5answers
249 views

Can we speed up the evaporation of black holes manually by accelerating it?

If we throw an object to pass near a black hole, to bypass it, it will change the speed of the black hole, just like gravitational assist for a space probe. Does an accelerating black hole evaporate ...
0
votes
1answer
24 views

Pressure Change in Supersonic Wind Tunnel [closed]

As far as I know, the total pressure changes across a shock wave. How is this possible if you are in the atmosphere and atmospheric pressure isn't changing? Is energy lost due to entropy in ...
0
votes
0answers
27 views

Entropic forces in Brownian motion

Reading Entropic forces in Brownian motion I'm having trouble to understand how the author makes a computation. He needs to calculate the number of ways a particle that is released from the origin can ...
-2
votes
1answer
95 views

Do photon inside event horizon exceeds speed of light?

Event horizon is a region of space whereby nothing with information can escape, so I imagine that a photon falls into this region of space does it accelerates toward the singularity if it exists? Do ...
0
votes
0answers
28 views

Considering rolling without slipping using axis at contact point with surface

For a ball rolling down a ramp without slipping, we can use $\Sigma \tau = I \alpha$ about two axes: an axis through the center of the ball, and an axis through the contact point with the surface. The ...
1
vote
1answer
118 views

Why is it so hard to explain that the Brownian Ratchet doesn't work?

The Brownian Ratchet stood up to a lot of scrutiny before it was finally shown why it would not work as a perpetual motion machine, but it seems weird to me that all of that was necessary. If the ...
0
votes
1answer
50 views

Fundamentally speaking, what are all the essential factors for waves (of any nature) to exist?

Considering all systems in which waves can exist, from atomic scale (such as DeBroglie Waves for example) to cosmic scale (gravitational waves for example), and those that require media for transport ...
3
votes
1answer
190 views

Unbounded perturbed geometry due to analyticity

I have an interesting mystery for you, loosely inspired on work related with this question. I have a certain Ansatz for a gravitational wave perturbation of the metric $h_{\mu \nu}$ that is nonzero ...
4
votes
1answer
533 views

Are there weak force waves?

In the same way as there are electromagnetic and gravitational waves that update the information on their respective field, is there an analogue for the weak and strong forces?
1
vote
0answers
46 views

History of Renormalization Group

I want to study from an historical point of view the renormalization group (starting from statistical mechanics). Are there any historical (but also technical) books about this? Thanks.
0
votes
1answer
62 views

Possible inconsistency of mixed index tensor notation

I am posting this here, because in my experience, this sort of thing exists in physics-related works only. Given a local frame $\{e_{(i)}\}$ on some $n$-dimensional manifold $M$, and given a local ...
2
votes
0answers
66 views

Is the equivalence principle Machian?

There is a lot of discussion on the subject of Mach's principle, and whether it has any place in the theory of relativity. But it seems to me that one could argue that Mach's principle is at the heart ...
0
votes
1answer
42 views

In golf, is there a rotational mechanical advantage of using a thicker grip?

I was asked to migrate this question to the physics exchange. Ok, so many professionals are now using the new SuperStroke golf grips. I am basically thinking about the concept of a bigger grip, but ...
0
votes
1answer
74 views

Can conductivity (or resistivity) value be assigned to 2D materials?

2D materials, such as graphene monolayer or graphene nanoribbon, don't really have a cross section. By definition, conductivity is $\sigma = \frac{J}{E}$, and $J$, the current density, is calculated ...
1
vote
1answer
46 views

What is the underlying transport mechanism of electron drift in metals?

The equations involving drift speed, mobility and conductivity, $v_d=\mu E$ and $\sigma=\mu e n$, treat electrons in a Newtonian way. This model works well in practice (at least in macro scale), but I ...
1
vote
1answer
81 views

Understanding Vaidya metric and pure radiation stress-energy tensor

I am following Vaidya metric and how it is related to pure radiation from Wikipedia. But when it reaches the line where stress-energy tensor is equated to product of two four-vectors, I cannot follow ...
0
votes
1answer
42 views

What is the underlying transport mechanism in “ballistic transport”?

From Wikipedia: Ballistic conduction or Ballistic transport is the transport of electrons in a medium having negligible electrical resistivity caused by scattering. Without scattering, ...
1
vote
1answer
68 views

How to increase/decrease laser pattern size

I have a laser pointer with a diffraction grating lens that creates a cross-hair, like the one seen below. I'd like to be able to increase or decrease the size of the cross-hair so that it may ...
1
vote
3answers
114 views

What is wrong with this method for FTL communication? [duplicate]

I've seen the other questions, but almost all of them deal with manipulating quantum states so that the other person reads a message in the data. However, you cannot force a quantum state on ...
0
votes
0answers
26 views

Curved light cones converge at big bang

Space has expanded manyfold since the big bang, presumably even 1090x since the CMB. Thus our light cones which start out straight must curve inward to theoretically meet at the single point of the ...
1
vote
0answers
30 views

Asymptotic expansion with stationary phase

I am reading Rudolf Haag's book on "Local Quantum Physics", and on page 89 he writes that the following function $f(t,\vec{x}) = \int ...
1
vote
2answers
129 views

Classical physics in curved space

I'm trying to learn General Relativity. As a stepping-stone between classic (Newtonian) physics and complete relativity, imagine a universe where space is curved, but time is perfectly flat. Also, the ...
4
votes
0answers
77 views

Why are so many relationships in physics described by equations? [closed]

Consider $f$, some mapping between two ordered subsets of the natural numbers, $A$ and $B$. I see two ways $f$ can be expressed. The first way is an equation that defines $f$ (i.e. $f(A) = 2A$). ...
0
votes
0answers
62 views

Size of the universe from CMB?

The CMB is almost 13.8 billion light years away in every direction so the diameter of the visible universe as we actually observe it is 27.6 billion light years, twice the distance light traveled over ...
0
votes
0answers
27 views

Explanation of example of ergodic movement

I was presented with the following question in as part of an introduction to ergodic movement: A man walks on a circle of radius 100 meters. Each man’s step is equal precisely 1 meter. There is a ...
1
vote
2answers
77 views

Attracting lightning with an ion beam

Can an ion beam be strong enough to create a path for lightning to travel to the ion machine? This is what I found in a lab that may help: An ionization factor jτi (the product of electron beam ...
1
vote
4answers
113 views

Force required to send ball in set trajectory

If I have a desired 2D trajectory where I know the desired speed of my ball and desired path, and a ball that starts at (x=0,y=0), how can I calculate the required force / point at which the force ...
0
votes
2answers
50 views

Travel by Earth rotation [closed]

why we can't go outside the atmosphere and travel with earth rotation .. and can we travel in the opposite direction of atmosphere by the same speed of atmosphere it’s moving at about 1,000 miles an ...
0
votes
0answers
54 views

Different Signs in Yang Mills Gauge Transformations

I have seen the Yang-Mills Gauge Theory be constructed in many books and papers, however I have seen pretty much equal disparage of + and minus signs in the following equations, the definition of the ...
-1
votes
1answer
146 views

how to calculate diameter and length change from volume change for a hollow cylinder?

I have a cylindrical material with a hole going through its center all along the larger dimension (length). I know the dimensions and the volume of the cylinder at temperature T1. Now, if I heat it up ...
1
vote
1answer
67 views

Wave equation with spatial damping

I would like to understand "spatially damped wave equation", $$\frac{1}{v^2} \frac{\partial^2 u}{\partial t^2} = \frac{\partial^2 u}{\partial x^2} + \beta \frac{\partial u}{\partial x}.$$ I am ...
1
vote
2answers
64 views

Light and mirrors [duplicate]

When I shine a beam of light at a mirror why does the ray go in the exact opposite direction (tested with protractor). Why does it not go back in exactly the same direction? The beam is of an ...
0
votes
0answers
41 views

Density matrices & spin correlation

So I have two 1/2 spin systems A and B in a singlet state $|ψ>=\frac{1}{\sqrt{2}}(|\uparrow \downarrow>−|\downarrow \uparrow>)$ . The question is: If I measured B and got $S_{Bz}=\hbar/2$ . ...
0
votes
1answer
52 views

spin representations and polynomials

I'm reading Group Theory and General Relativity by Moshe Carmeli and his discussion of spin representations of SU(2) and the isomorphism to the space of homogenous polynomials is confusing me. I'll ...
0
votes
0answers
27 views

Resistance used to get maximum illumination with proper security

In which way a resistance is to be connected with a bulb labelled 120V-60W when it is connected with 220V DC source so that maximum illumination with proper security is maintained? What is the ...
3
votes
2answers
84 views

What exactly is an arbitrary parameter?

I was reading the article Turning Points: A meeting with Enrico Fermi by Freeman Dyson (available e.g. here), and I had a question about Dyson's use of the term 'arbitrary parameter'. More ...
3
votes
2answers
92 views

How is light related to photons? [duplicate]

This may seem like a duplicate but I do not understand other explanations. I have read that light is an electromagnetic wave (a fluctuation or disturbance in the electric and magnetic field). How ...
3
votes
0answers
60 views

Why isn't $G=1$ as common as $c=\hbar=1$? [closed]

It is standard practice in theoretical physics to use a system of units in which $c=\hbar=1$. However, even though you could also set $G=1$, most physicists prefer not to. For example, in my cosmology ...

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