0
votes
0answers
4 views

Conceptual questions on the path integral formulation of QFT

I'm currently trying to teach myself the path integral formulation of QFT (having studied the canonical approach previously), but I'm having some conceptual difficulties that I hope I can clear up ...
0
votes
0answers
2 views

Quasi-fermi niveaus in a solar cell?

I was wondering, if my fermi niveau splits up due to n and p type doping into two fermi niveaus, one for the p type one for the n type, and now due to light radiation my fermi niveaus split up into 2 ...
2
votes
1answer
6 views

Why exactly do sometimes universal covers, and sometimes central extensions feature in the application of a symmetry group to quantum physics?

There seem to be two different things one must consider when representing a symmetry group in quantum mechanics: The universal cover: For instance, when representing the rotation group ...
-2
votes
0answers
20 views

Can atoms exist [duplicate]

Can an atom be created from 2 top and one bottom quark together with a tau selectron? How would its properties differ from a hydrogen atom? What combinations of quarks and selectrons are possible to ...
2
votes
1answer
36 views

Can atoms with top / bottom quarks exist?

Do we have examples in nature or the lab of atoms constructed of 2 top and 1 bottom quark and a tau selectron? How would its properties differ from a hydrogen atom?
2
votes
4answers
147 views

Squaring a Vector?

So this one is basic. And should be pretty quick. Lets say that I have a vector $\vec{r}$: $\vec{r} = \vec{x} + \vec{y} + \vec{z}$ Is this true: $\vec{r}^{2} = \vec{x}^{2} + \vec{y}^{2} + ...
1
vote
1answer
28 views

How can we obtain equations of motion from $\iota_{X_{H}}\omega =dH$?

I don't know if this is an obvious result and I am just missing a trick, so please forgive me, but how do we obtain equations of motion from the following equation. \begin{equation} \iota ...
0
votes
1answer
17 views

Allowed Virtual Displacements

I am having trouble understanding the kinds of virtual displacements which are permitted for a given constrained system. I have a specific example in mind: A block of wood resting on a table parallel ...
0
votes
0answers
14 views

Does motion with constant proper acceleration, in a flat region, necessarily mean straight hyperbolic motion?

Is motion of a participant with constant proper acceleration, in a flat region, necessarily straight, hyperbolic motion (with respect to members of any inertial system, in that region)? Or is for ...
-1
votes
0answers
6 views

Plane color shift

Please explain this phenomenon. In google earth, type in these coordinates: 26.07712027, -80.17626934 This is I'm assuming captured by some sort of radar, and this shifts the color spectrum in motion ...
0
votes
1answer
16 views

Why do so many galaxies in clusters have a near zero velocity?

I'm looking at a velocity chart of the Coma Cluster: And the question occurred to me: why are there so many galaxies that have a zero velocity (relative to the core of the Coma Cluster which is ...
-1
votes
1answer
18 views

Lifting a block or sliding a block- Which will consume more energy?

A box with mass m units resting on a table with smooth surface (slightly oily). A to B : d units Action 1 : Slide the box from Point A to B. Action 2 : Lift the box from A to B in an arc fashion. ...
0
votes
0answers
16 views

Regarding synchronization of clocks in special relativity

I am trying to read of synchronization of two clocks in same inertial frame in special relativity. Suppose we have two synchronized clocks in an inertial frame placed at positions $x_1$ and $x_2$ in ...
3
votes
2answers
172 views

Two Point Universe

Imagine a universe consisting of only two point masses, neither of which are in motion. Would they be drawn towards each other? Does there need to be motion for the curvature of spacetime to affect ...
0
votes
1answer
18 views

When a neutron star accumulates enough mass, does a black hole start at its center?

With less dense bodies, such as the earth and the sun, the center has less gravity/density (since there's an equal amount of mass surrounding the center, pulling out on it from all directions). Does ...
2
votes
0answers
25 views

Complex / real representations of the Lorentz group

In Michele Maggiore's book "A Modern Introduction to QFT" he describes the spinorial representations of the Lorentz group as The representations are in general complex. I always thought the ...
2
votes
0answers
38 views

Polarization Sums in QCD

In the case of a Spin 1 massive particle it's possible to demonstrate that $$\sum_{\lambda=0,\pm1}\epsilon_{\lambda}^{* \ \mu}\epsilon_{\lambda}^{\nu}=-g_{\mu\nu}+\frac{q^\mu q^\nu}{q^2}$$ for a ...
0
votes
0answers
33 views

What is a “Quantum Network” in this context?

Just found this at Quanta Magazine (click the interactive show 3 times, or send slider to "Quantum Network") and I'm not able to find out what is meant by Quantum Network -- According to this ...
0
votes
0answers
10 views

Data on the period of large amplitudes

Can you give me a link where I can find the results of real and accurate experiments concerning the period of pendulums from 0 to 90°. I once found one, but in spite of long research and google ...
-2
votes
0answers
8 views

Bandlike vs. Excitonic Semiconductors

What is the different between 'bandlike' semiconductors and 'excitonic' semiconductors and how does this relate to whether they are organic or inorganic? I also wonder how such bandlike or excitonic ...
1
vote
0answers
10 views

Hypermultiplet as BPS particles

In the third paragraph of page 7 of the paper arxiv:1112.3984 it mentions that we form a basis out of hypermultiplets on the charge lattice $\Gamma$. My questions are: In what sense do we form such ...
0
votes
1answer
27 views

Final temperature of water+ice+water Mix

I found this physics question: In a container there is a mixture of water at $ T = 0°C$, mass $m_w = 300g$, and ice, mass $m_i = 600g$. More water is added into the container, mass $m = 1100g$ at ...
0
votes
2answers
25 views

Would a magnetic needle standing on it's point on a magnet be more stable than the same needle stood on a non-magnetic surface?

So I was watching MinutePhysics' video 'How long can you balance a pencil?' and it turned out to not be for very long. Would introducing a magnet to the equation make for different results? We can ...
-1
votes
0answers
24 views

Why do electrical charges given to a conductor come to the surface?

It is said that any charge given to a conductor comes to its surface. Should all the protons come to the surface? Should all the electrons come to the surface, or should all the free electrons come ...
2
votes
2answers
70 views

Could a civilisation contact us by laser from 50 light years away?

The Kepler Space Mission has discovered over 1,000 planets. These discoveries may increase the confidence of some people that other civilisations exist. That is an opinion issue, and not what I want ...
0
votes
1answer
30 views

Is this the reason why a circuit with no components (except wire) would discharge the battery faster?

I read that if I simply connect two ends of a battery it would discharge really quick and it would last longer if the circuit contained e.g. a light bulb. I wondered why is this happening and my ...
0
votes
0answers
27 views

So, whirling around a neutron star in which the centrifugal force counteracted the gravity exactly, one could slow time considerably?

My apologies if, once again, I have repeated a previous question. But, I really looked at all of the "may already have your answers". I deleted the last one and I can do it, again! Anyways, if it ...
0
votes
0answers
29 views

Reason for strange magnetic ball movement

I was playing with a set of those neodymium magnet spheres and noticed a couple of strange behaviors (which I believe are related so I'm only positing a single question) and I was hoping to get an ...
0
votes
1answer
31 views

Can capilliary action move liquid against gravity?

I was wondering if it was at all possible to very slowly suck up water from a cup with a rope, and then deposit the water into another cup on a 3cm thick book or similar object. Here is an example ...
6
votes
2answers
171 views

Shaken vs stirred, is there a difference? [on hold]

I was looking up tequila Drink recipes for the up coming holiday, and I kept seeing ones calling to be shook and other to be stirred. So I wondered: is there really a difference? does stirring provide ...
0
votes
1answer
21 views

Body that both cools (proportionally to temperature difference) and heats with constant power

This is almost more of a math question, and a simple one, but I can't figure it out, and I haven't been able to find a solution online since I don't really know what words to search for. There is a ...
-3
votes
0answers
50 views

Why photon have zero rest mass?

If photon have zero rest mass then the term E=hf should also be zero because if rest mass is zero then relativistic mass is also zero and so on by Einstein mass energy relation energy shoud be zero ...
0
votes
0answers
28 views

Data on Nuclear Fusion

I'm currently doing a detailed project on Nuclear fusion and it's future. I've found some great books on the subject so thats not a problem. What i'm struggling to find is data more specifically ...
0
votes
1answer
22 views

Change of temperature in liquid when it is pressurized fast to high pressure

Here's one question I've been thinking for some time: Let's assume that certain volume of water (or any other normal liquid, I'm just thinking how these kind of things should be calculated) is ...
0
votes
0answers
16 views

Distance between first maxima and first minima in Young double slit experiment

While calculating distance between first maxima and first minima in Young double slit experiment, I used formula for maxima and minimx taking $n=1$ as shown. For first maxima, distance from central ...
-2
votes
1answer
76 views

Are black holes in a binary system with white holes, and are they both wormholes? [on hold]

What is a black hole? The general explanation is that a black hole is small region in space with such strong gravitational effects that nothing can escape and even light is trapped inside of the event ...
-4
votes
0answers
15 views

Show that boundary layers diffuse out from the plate with speed $\sqrt{\frac{\nu}{t}}$ [on hold]

I was wondering if someone could help me with this problem. I think it's quite simple, but I'm not sure how to do it! An infinite horizontal plate moves with speed $U$ in its on plane relative to ...
1
vote
1answer
32 views

How does the mass affect the fall time of a parachute?

Why do parachutes with a heavier load fall faster than a parachute with a lighter load?
0
votes
0answers
12 views

What is Frequecy Pushing/ Pulling in Laser Physics

I heard the term "Frequency Pushing/Pulling" in combination with phenomena like in homogeneous broadening and hole burning but I didn't understand what Frequency Pushing/ Pulling is supposed to mean. ...
1
vote
0answers
15 views

Calculating collapse factor in the crater equation [duplicate]

In the Crater Equation $$ D=0.07C_f\left(\frac{g_e}{g}\right)^{1/6}\left(E \frac{\rho_a}{\rho_t}\right)^{1/3.4} $$ where $\rho_a$ is the density of the impactor, $\rho_t$ that of the object, $g_e$ ...
0
votes
0answers
55 views

Why is this 4x4 tensor a 16-dimensional representation of SO(3,1)?

In his QFT book "A Modern Introduction to Quantum Field Theory" (http://www.nucleares.unam.mx/~alberto/apuntes/maggiore.pdf, pages 20-21), Michele Maggiore describes the tensor product of the ...
2
votes
0answers
69 views

The tested scale of classical mechanics

I was reading this, but I was wondering actually how good an approximation is classical mechanics in very large chosen scales? Which makes me would like to ask a question here: to what scale, order ...
-3
votes
0answers
26 views

Motion on a rolling Body [on hold]

How can an object can continue to run on a rolling circle along the X direction and maintain a balance with specific acceleration.
2
votes
1answer
15 views

internal torques

In translational motion, for an isolated system, the net internal force acting on the system is zero according to Newton 3 law. But for rotational motion of an isolated system, does the internal ...
0
votes
0answers
12 views

About to purchase a 3d-printed Keppe Motor Kit for art project - what should I test for? [on hold]

I'm about to apply for art-grants in order to purchase a educational student toy called a 3d-printed Keppe Motor Kit. Says on their page "Designed with educators and students in mind".. So.. It is ...
0
votes
1answer
14 views

Diffraction of light around an object & human perception

A wave exhibits diffraction when it encounters an obstacle that bends the wave or when it spreads after emerging from an opening. Diffraction effects are more pronounced when the size of the ...
0
votes
0answers
23 views

Why does increasing/decreasing the distance between two fringes, decrease/increase the fringe-width in interference pattern?

I am talking about this equation $$w= \frac{D\lambda}{d} \\\ \text{where}\; D= \text{separation between the slits & the screen}\\\ d= \text{separation between the slits}\\w= \text{fringe-width}$$. ...
0
votes
4answers
93 views

“FTL” Communication with Quantum Entanglement? [duplicate]

Can quantum entanglement make sending a message, whether audio, video, or even Morse code, instantaneous between two points (faster than it could travel normally at the speed of light)? Let me first ...
2
votes
0answers
53 views

Continuum analogue of $ \langle \psi | \psi \rangle = \sum _i a_i^* a_i$

I'm learning Dirac notation, and I found the following exercise: Verify that if $$|\psi \rangle=\sum_i a_i |i\rangle, \tag{1}$$ (where $a_i=\langle i|\psi \rangle$), with $$\langle i|j ...
-2
votes
0answers
20 views

Equation for centripetal acceleration in terms of R, alpha, delta theta [on hold]

Find an expression for the centripetal acceleration. Express your answer in terms of the variables $R$ = radius, $α$ = angular acceleration, and $Δθ$ = angle. I can't find the answer to this at all. ...

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