1
vote
0answers
15 views

2-to-2 vs 2-to-N with N>2 QCD processes

In high energy particle physics, what is the rough ratio of 2-to-2 hard scattered QCD processes to 2-to-N hard scattered processes with N>2. How can it be calculated? For example, in LHC, two protons ...
-1
votes
1answer
37 views

Can quantum entanglement work like this?

Lets say you have two entangled particles (A,B) and you already measured theirs spins and know that A has z+ and B has z- What will happen if after the measurement you will set the spin of B to z+ ...
1
vote
1answer
9 views

heating elements and arc welding?

In a water heater stove or arc welder, the most basic electric circuit is formed when one has a source (AC or DC) and 2 wires going to and from the heating element, in the case of the heater and ...
-1
votes
0answers
17 views

finding the unknown values of x and y in terms of base units in an equation [on hold]

express the following correct equation in terms of base unit to find the value of powers x and y ::: T=Kl(l with the power of x)g (g with the powers of y) find the values of x and y ?
1
vote
3answers
51 views

With respect to the Casimir effect, why can't the wavelengths of the virtual particles between two plates just “pass through” the plates themselves?

I've read over the years that the suppression of many of the possible wavelengths between the two plates in a Casimir experiment is what causes the phenomenon (top comment on this Askscience thread is ...
0
votes
1answer
51 views

Can anyone think of any astronomical phenomenon that could be due to engineering projects of an advanced civilzation? [on hold]

It has always seemed to me that there could very well be evidence of advanced civilizations in other parts of the galaxy/universe that are staring us in the face. Within a thousand years, heck, maybe ...
0
votes
0answers
5 views

What exactly is an integral kernel? [migrated]

I am not sure if I have seen integral transforms in the right way, but given a transform like fourier transform - its actually a basis transformation right ? $$ F(y) = \int K(x,y) f(x) \text{d}x $$ ...
2
votes
3answers
29 views

Shielding of electric and gravitational force on particles inside a spherical shell

A cavity inside a conductor is shielded from outside electric influences. But, if you put charges inside the cavity, the exterior of the conductor is not shielded from the fields by the inside ...
0
votes
1answer
18 views

Using fiber optics to focus quartz tungsten halogen light

Our purpose is to make 1 mm spot size of quartz tungsten halogen light with 100 mm working distance for spectral imaging of wavelengths of 350-2000 nm. With some QTH light source and adapter on the ...
1
vote
1answer
58 views

Periodicity of function as a result of superposition in Quantum Mechanics

Say we add infinitely many waves (states of definite momentum) so as to produce a function that gives a very well-defined position, does that addition(using Fourier series) make that function ...
0
votes
2answers
57 views

Superposition of waves with different initial phase in Quantum Mechanics

In Quantum Mechanics, if a particle's state is a superposition of many states of definite momentum, then we say that it's position is well-defined (by the Heisenberg uncertainty principle, because ...
0
votes
0answers
19 views

Dipoles in an external rotating field?

Consider a bunch of magnetic dipoles in $x-y$ plane in an external magnetic field $B(t)=B_0 \hat{z}+B_1(\cos\omega t~\hat{x}+\sin\omega t~\hat{y})$. The dipoles are rotating around $z$ axis and of ...
0
votes
2answers
35 views

Manometer & pressure

I have trouble with a homework question in understanding how the manometer liquid responds to pressure changes. Any help will be much appreciated. The problem goes like this: A cylinder of diameter ...
0
votes
2answers
21 views

total vorticity generation in 3D

In 2D flows, the total vorticity generation for an impulsively started plate can be found by measuring the circulation of the flow. This gives the vorticity generated per unit length. I would like ...
0
votes
0answers
8 views

How to obtain a lower mass bound for a unstable (or stable) particle from Poisson statistics?

Imagine you have a particle (stable e.g. if some R-symmetry or similar does exits) heavy or not so heavy... Question: how to guess a lower (upper bound as well) with the aid of Poisson statistics, ...
2
votes
0answers
34 views

Why does ice fall from the top of the ice tray first?

I haven't found an answer for this anywhere, so hopefully this community can help. It's not important at all that I know this but I'm curious. If you take a plastic tray of ice from the freezer and ...
0
votes
1answer
29 views

Spontaneous radiative decay due to electric dipole radiation

In my textbook, we calculated the rate at which an electric dipole radiates energy to be $Pwr = \frac{1}{4\pi \epsilon_0}\frac{2}{3c^3}\left(\frac{d^2 p}{dt^2} \right)^2$ where p is the dipole ...
-2
votes
1answer
54 views

Is time a finite resource?

I am struggling to find an answer for this question because time as we know it would end when we reach the heat death of a universe. Which would imply that is the end of time. I think I have a ...
0
votes
1answer
62 views

The EFE - The 'Mother' of all equations of motion in the universe?

This question addresses the scope of general relativity. Scientists and engineers solve all sorts of physical problems in all sorts of fields and often to solve these problems a 'system' is defined ...
-2
votes
2answers
56 views

Electricity from vacuum

Can I generate electricity in complete vacuum without using any conventional sources? Using Casimir theory, according to him, he kept two plates nanometers apart in a vacuum. According to the law of ...
2
votes
0answers
24 views

Scale-covariant decomposition of capacitance

I'm wondering if there is any good insight of how to evaluate a given capacitive geometry in such a way that it would be expressed as a function that depends only on two components: as a geometric ...
1
vote
0answers
33 views

Locality defined in terms of the Lagrangian density

I've been reading through Matthew Schwartz's book "Quantum Field Theory and the Standard Model" and in chapter 24 there is a section on locality (section 24.4). In it he defines locality in terms of ...
1
vote
1answer
31 views

Question about what a simultaneous measurement of entangled spins means

I was working through a problem I found online and ran into something that is confusing me. We have a system of three spin-1/2 particles, in the state $$ |\psi\rangle = ...
1
vote
1answer
54 views

Why do people wear black in the Middle East?

I have read various dubious explanations as to why people often wear black in the heat, from cultural to somehow encouraging the evaporation of sweat (unconvincing). So, does anyone know what, if any ...
1
vote
1answer
39 views

All possible photons wavelengths [duplicate]

As far as I know all photons come from electrons loosing their energy. I remember from physics and chemistry classes, that electron can loose or get only certain determined amount of energy. Also I ...
12
votes
1answer
1k views

Confusion I have regarding Einstein's 1905 derivation of LT

In his 1905 paper, Einstein derives the Lorentz transformation using the two postulates of SR;constancy of $c$ for all inertial frames and the Invariance of the laws of physics for all inertial ...
2
votes
0answers
35 views

Why are WZW models interesting?

I realise this is a very broad question, but when I was studying for my thesis I randomly came across WZW models for a few times and I never quit understood them. So I understand that these models ...
0
votes
0answers
35 views

Addition of spins and projection

This is a calculational question but is not a homework question (rest assured I'm past that stage). Still, I don't quite know how to show the following. Say we have two $SU(2)$ spins $\vec{S}_1, ...
-2
votes
2answers
30 views

How do I calculate the energy produced in a beta decay reaction? [on hold]

How do I calculate the energy produced in this reaction: Masses of subatomic particles: proton=1.007276u neutron=1.008665u electron=0.000549u Don't know if these are also relevant: Rest mass ...
1
vote
1answer
42 views

How does a Pulsed Plasma Thuster work?

My friend was describing a Pulsed Plasma Thruster (PPT) to me, and we couldn't figure out how it actually worked. The setup involves two conducting plates with a potential difference and a solid, ...
-1
votes
0answers
19 views

Quantum mechanics Hermitian problems [on hold]

how to determine its non zero Eigenvalues and eigenfunctions how to prove A is hermitian in problem 2
2
votes
2answers
61 views

The action of a relativistic point particle, the meaning of its parametrization invariance and possible potential terms

i am currently toying around with the behaviour of a classical relativistic point particle a bit. For a free one we get the action \begin{align} S =\int_\tau - m\sqrt{- \dot X_\mu \dot X^\mu}. ...
2
votes
3answers
87 views

Why do electric shocks send you flying?

One question which has recently been interesting me is: Why exactly do people get thrown back when they are shocked by electricity. I have done some research to find the answer to this, and i am yet ...
0
votes
0answers
31 views

Is it possible to “leech” a usable amount of current from a 220V line?

Inspired by wireless charging technology and "current clamp" type meters - I've been wondering if one could "leech" a small amount of power (say ~2.5W) from a 220V line carrying ~2200W using a wire ...
3
votes
3answers
88 views

4-vectors in special relativity and spacetime interval

In one of my vector mechanics lectures, the lecturer said the the space time interval was the dot product of the four position vector. But then he proceeded to show it was this: $s^2$ = $\Delta r^2$ - ...
0
votes
0answers
38 views

Is there an intuitive explanation for the fact that the Lorentz algebra contains SU(2) twice? [on hold]

The Lie algebra of the Lorentz group contains "two copies" of $SU2)$. I mean it's kind of obvious that one instance of $SU(2)$ is there, because $SU(2)$ is the Lie algebra of $SO(3)$ and $SO(3)$ is a ...
2
votes
2answers
55 views

Why are racing catamarans' hulls not teardrop shaped? [on hold]

Looking at the America's Cup 72 class catamarans, I was wondering about their hull shape, which has a sharp wave piercing bow. My question is: since an airfoil shape experiences less drag than a sharp ...
0
votes
0answers
19 views

how much heat will be produced when air is compressed to liquid air [on hold]

I understand about 700 litres of ambient air becomes 1 litre of liquid air. I want to know how much heat will be dissipated when this happens. I appreciate any help.
2
votes
0answers
29 views

Why would an alpha-beryllium neutron source generating a radioisotope not produce controllable net power?

I have a question. I was looking through the table of nuclides and noticed that the energy needed to produce certain radioisotopes was less than the energy given off by the radioactive decay of that ...
1
vote
1answer
39 views

Is it theoretically possible to prevent or deter a star from becoming a black hole?

Suppose NASA decides too many black holes are being produced in a year, so it decides to do something about that. Given our current scientific knowledge, is there theoretically any way NASA could ...
0
votes
0answers
17 views

Why do high altitudes have larger diurnal temperature variation than lower altitudes?

It seems like the lack of atmosphere should not be playing a role in the diurnal temperature variation because that's what makes it colder. Mountains are not that dry, usually.
1
vote
1answer
28 views

Why does moving the source-slit closer to the double-slit plane decrease the sharpness of the interference-pattern?

Thomas Young used a single-slit plane before the two-slits plane in order to make the light source coherent. My book (NCERT Physics II) presents the above query and writes: Let $s$ be the size ...
1
vote
5answers
139 views

Why isn't momentum conserved in this pulley problem?

I have some conceptual doubt about method of solving this problem. 24. A block of mass $m$ and a pan of equal mass are connected by a string going over a smooth light pulley as shown in figure ...
0
votes
1answer
42 views

Does Schwarzschild metric have cosmological horizon?

Since the space is not expanding in the Schwarzschild metric does that mean that there is no cosmological horizon? Also, what if the Schwarzschild metric was not asymptotically flat and we replace ...
58
votes
1answer
3k views

Where is the flaw in this machine that decreases the entropy of a closed system?

I was thinking about a completely unrelated problem (Quantum Field Theory Peskin & Schroeder kind of unrelated!) when the diagram below sprang into my mind for no apparent reason. After some ...
4
votes
2answers
70 views

Do individual rays of light lose energy via the inverse square law?

We've all heard of the inverse square law, but apparently that refers to the flux or intensity or number of photons hitting an imaginary surface area. This is not exactly what I want to ask about. ...
-1
votes
1answer
36 views

Compton's formula for change in wavelength

I want to measure the shift in wavelength predicted by Compton's formula. I find that I cant measure a shift of less than 5% and that I also cannot measure at angles greater than 150 degrees. What is ...
-2
votes
0answers
27 views

gravity and inflation [on hold]

Looking at the interaction between mass and the higgs field. Could gravity be a result of the topographical distortion of the fabric of space-time as the universe accelerates under inflationary ...
2
votes
2answers
26 views

Galvanic Cells and Electric Potential

In a battery or a galvanic cell, the electric potential of the battery is due to a difference of charges between the two cells like in a capacitor? So it is the electric field due to this separation ...
3
votes
2answers
35 views

how can $\frac{kqq_o}{r}$ be $U$ for both a particle and a system of two particles?

If there is a charge $q$, at a distance $r$ from it there is a voltage and the potential energy of a test charge $q_o$ would be $\frac{kqq_o}{r}$. Now if I construct a system of two charges a ...

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