1
vote
0answers
3 views

How to compute scattering amplitude $\gamma\pi^+\to\pi^+\pi^0$

I wish to find the amplitude for process $\gamma\pi^+\to\pi^+\pi^0$ at low energies. I am familiar with the basic concepts and techniques of QFT but have never dealt with the scattering processes ...
0
votes
0answers
10 views

Definition of 1 calorie

Why on defining 1 calorie its been taken as heating of water from 14.5 to 15.5 degree centigrade of 1gram of water at standard pressure? Any specific reason for taking the temperature from 14.5 to ...
2
votes
0answers
7 views

Why is a beam reach the fastest point of sail on modern sailboats?

I've heard that a beam reach (perpendicular to the wind) is the fastest point of sail on modern sailboats, but I haven't heard a satisfying explanation of the physics behind the claim. Triangular ...
0
votes
1answer
25 views

If a second is defined as a duration of 9192631770 periods of radiation - what is time?

Given the wiki definition of 1 second as: "the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 ...
0
votes
0answers
12 views

Why friction increases with increase in normal force?

Why is friction dependent on normal force and not the actual weight? I have also read that friction is horizontal component of contact force. Is this true?
0
votes
0answers
11 views

What does a scale accelerating on an incline read?

I was watching an online video lecture about dynamics, and then I came across this brain teaser, and I've been thinking it over for a couple of hours but can't seem to find the solution. I hope ...
0
votes
0answers
17 views

About the property of the mirror [duplicate]

It is actually said that left appears to be right and right appears to be left in a mirror. But when I stood in front of the mirror and raised my right hand, then according to this property my mirror ...
2
votes
0answers
11 views

Lifting capacity of superconductors

How does the strength of the magnetic field the superconductor is exposed to affect its ability to levitate/lock heavier objects? Or is there no relationship (for superconductors) between magnetic ...
0
votes
0answers
19 views

Sum of powers of complex exponentials

I encountered the identity $\sum_{j=1}^{N} {e^{ikja}} = N\delta_{k,0}$ when reading the section on phonon modes (2.4) in Lancaster & Blundell's "Quantum Field Theory for the Gifted Amateur". I ...
0
votes
0answers
8 views

Elementary question about global supersymmetry of a worldsheet

I'm reading chapter 4 of the book by Green, Schwarz and Witten. They consider an action $$ S = -\frac{1}{2\pi} \int d^2 \sigma \left( \partial_\alpha X^\mu \partial^\alpha X_\mu - i \bar \psi^\mu ...
0
votes
0answers
11 views

The derivation of canonical distribution: why does one linearize entropy (and not something else?)

I know that there are (at least) two ways to derive the canonical distribution. I am interested in the one where one considers the entropy of the reservoir (with which the system we are considering ...
0
votes
0answers
19 views

Facing a problem in Katrin Becker, Melanie Becker, John Schwarz's String Theory

In BBS's string theory book, in the equation (2.143), it says that $$\text{tr} \omega ^N=\prod _{n=1}^{\infty } \left(\prod _{i=1}^{24} \text{tr} \omega ^{\alpha _{-n}^i \:\alpha _n^i}\right)=\prod ...
1
vote
1answer
18 views

What is antimatter and its role in the universe?

As we know everything has its opposite. Like matter its opposite is antimatter. So why the universe is not made by antimatter instead of matter. And what is the main role of antimatter in the ...
0
votes
0answers
14 views

First fundamental form in the Gibbons-Hawking-York boundary term

Let me expose my problem, I am trying to perform the explicit variation of the Gibbons-Hawking-York boundary term, $$S_{GH}=\int_{\partial M} d^{n-1}x\sqrt{\left|h\right|}K$$ The problem I have is ...
-1
votes
1answer
29 views

Time dependent solution to infinite well

A particle of mass $m$ is confined within an infinite, one-dimensional potential well, $U(x)$, of width $a$. $$ U\left(x\right) = \left\{ \begin{array}{lr} \infty &\: x \leq ...
1
vote
1answer
14 views

Electric force between 2 rods with different lengths carrying different currents

What is the electric force between tow rods with different lengths that carry currents $I_1$ and $I_2$? Indeed, by the use of the Biot-Savart law I obtained a relation to calculate it, but there is ...
0
votes
0answers
4 views

What is normal fluctuation?

I was reading Statistical Mechanics (second edition) by Kerson Huang. On page 146, after equation 7.14, there is a reference to normal fluctuation. What is it?
1
vote
1answer
16 views

Sequential Stern-Gerlach Experiments

Suppose a beam of particles is prepared with spin in the $+z$ direction (e.g. by a Stern-Gerlach apparatus). Suppose this beam then enters a Stern-Gerlach apparatus with orientation theta relative to ...
0
votes
2answers
21 views

Which materials absorb heat?

Which are the materials that absorb heat? and can i somehow convert that absorbed heat into a different form of energy? I am looking into trying to absorb the wasted heat dissipated by laptops,severs ...
2
votes
2answers
44 views

What counts as information?

What counts as information? In e.g. the EPR experiment why is one entangled particle knowing instantaneously the state of the other not counted as 'information'.
5
votes
3answers
51 views

True randomness?

I am a physics high-school student so my knowledge is not very deep on the subject. We started learnning about quantum mechanics and on some processes that my teacher described as random. I began to ...
-3
votes
1answer
41 views

How do I normalize this wavefunction?

I need to find the normalisation constant $A$ for the wave function: $$ \psi\left(x\right) = \left\{ \begin{array}{lr} A &\: \frac{-a}{4} \leq x \leq \frac{a}{4}\\ 0 &\: ...
2
votes
1answer
17 views

Energy levels in molecules

I apologize in advance if this turns out to be a duplicate question. As far as I can understand, if you bring two or more atoms together their wave functions begin to interfere and, since there ...
1
vote
3answers
22 views

Calculating the probability of a given energy

Given a normalised wavefunction say $\psi(x) = A\sin(n\pi x)$, (where $A$ is a normalisation constant) I can calculate the probability of finding the particle being between a position $x$ and $x + dx$ ...
1
vote
1answer
46 views

With the LHC about to restart as max energy, are there absolutely no hints or tantalizing signs of Supersymmetry in previous data?

Over the last couple of years I've seen several articles talk about hints or bumps in the data that might point to Supersymmetry. An article in NewScientist from Summer 2012 discussed the discovery of ...
1
vote
2answers
83 views

Are photon energies conserved in general relativity?

As I understand it, both Maxwell's wave equation and the null geodesics of general relativity are scale invariant. Thus an electromagnetic wave can be shifted along a null geodesic without changing ...
0
votes
1answer
23 views

Is there a word for all the particles in an atom?

That is to say, is there a word that picks out protons, neutrons, AND electrons, rather than just saying "nucleons plus electrons"?
-3
votes
0answers
9 views

What is the energy levels of 1d hydrogen by using WKB?

I need to find the energy levels of 1d hydrogen using WKB and $V(x)=-1/x$? can you help me please?
0
votes
1answer
18 views

Notation of polarization of light

Upon my research of polarization of light I stumbled upon the following formula: What do the three dots mean? I have never seen them before. Edit: Found this notation in the book "Nonlinear fiber ...
1
vote
0answers
16 views

Polchinski equation 11.2.7

In Polchinski's string theory volume 2, when discussing the GSO projection for the heterotic string he says: In the IIA and IIB superstrings the GSO projection acted separately on the left- and ...
-1
votes
1answer
19 views

Central Force - Trajectory [on hold]

There is a central force $\vec{F}(\vec{r})=f(r)\vec{e_r}$. 1.1.: The trajectory/flight path is defined by $r=r(\phi)$, compute $f(r)$. 1.2.: The path is defined by $u=u(\phi)$ with ...
0
votes
2answers
32 views

Is the light from the stars within our galaxy redshifted?

I know that metric expansion does not happen within a galaxy. But is the light from stars in our galaxy somehow redshifted? Also, everyone says that our galaxy isn't expanding. But is there a slight ...
2
votes
1answer
45 views

Minimizing the Lagrangian action of an impossible problem

I'm working my way through Structure and Interpretation of Classical Mechanics (SICM), and am stuck on an exercise in Section 1.4: Exercise 1.6. Minimizing action: Suppose we try to obtain a ...
-1
votes
1answer
26 views

Time dilation: reference frame

So I'm calculating how long it will take for half of some muons to decay for in a stationary observers frame of reference. They have a half life of 2.2 * 10^-6 and are moving at a speed of .98c ...
1
vote
3answers
19 views

How can we be sure that a new frequency standard is better than the old one?

Lets assume for this question that at one point in scientific history everyone was running along well with their cesium frequency standards, and someone has a brilliant idea and builds an active ...
-1
votes
0answers
8 views

What voltage is induced between the endpoints of bar, if we swing it by an amplitude [on hold]

After a long horizontal conductor carrying current of 10 A is vertically suspended 2m long insulated conductive rod. We swing it by an amplitude of 10 cm. (a) in the direction of the wire; (b) in ...
0
votes
0answers
10 views

Rigorous definition of superselection sector/quasiparticle type in anyon systems

The systems I have in mind are for example Kitaev's toric code model (arXiv:quant-ph/9707021) and Kitaev's honeycomb model (arXiv:cond-mat/0506438). What I'm looking for is a mathematically rigorous ...
4
votes
3answers
324 views

Explaining a quote by Weinberg about the signifcance of symmetry groups in physics

When skimming through a book, I found this quote: The universe is an enormous direct product of representations of symmetry groups. —Steven Weinberg I am a mathematician (so I know only basic ...
-1
votes
0answers
5 views

With what frequency triangle swings if it shuns from equilibrium? [on hold]

Guide V-shaped is with no friction in the swivel bearings A and B (see Fig.) Of the magnet with a vertical magnetic field of 0.8 T. The weight of the guide is 50 g, the length AB 4 cm, and the length ...
0
votes
2answers
39 views

How do vinyl records work?

I know that vinyl records save the sound as ups and downs on the record plate surface. Let's say two people with different voice timbers say "I like vinyl records" with the same level of voice. It ...
1
vote
2answers
85 views

Speed of light paradox

If I send two rockets from the Earth in opposite directions, at, say, 60% of the speed of light relative to the Earth, then relative to each other they are travelling at 120% of the speed of light. ...
0
votes
0answers
10 views

Calculating curvature of spacetime when energy is present

I am only about half-way of studying SR and GR and I am not yet familiar with a formula to calculate the curvature of spacetime when energy is present. To be more specific, I want to calculate ...
2
votes
1answer
14 views

What is the value (order of magnitude) of electric charge density of the atom and the nucleus?

The mass density of the nucleus is constant. But what is the electric charge density of the nucleus and the atom (any order of magnitude)?
0
votes
0answers
19 views

How to count the symmetric wavefunctions made by 6 (u, d, s, $\bar{u},\bar{d},\bar{s}$) quarks to form Baryons (i.e., 3 particle state)?

Peskin said 6 (particles + Anti-Particles) guys make (6($\Rightarrow $particles) x7x8)/(3x2)= 56 total symmetric state. How?
1
vote
1answer
10 views

does the internal energy and enthalpy of the GAS changes in a free expansion process?

when a balloon kept in an evacuated room is punctured and the ideal gas in the balloon goes on to fill the entire room,does the gas perform any work in this expansion, and is there in any change in ...
2
votes
2answers
36 views

'Doppler redshift' Vs 'Cosmological redshift'

It is not difficult to understand the differences between 'Doppler redshift' and 'Cosmological redshift' conceptually. But how do astronomers distinguish them when doing observations?
4
votes
2answers
919 views

How much is if my internet provider says “we have increased your WiFi connection by 2 decibels”?

I understand the definition of decibel as a logarithmic unit for intensity of anything. I just cannot imagine its "actual size" when comes to the wireless connection. Can you provide something ...
0
votes
0answers
22 views

Why wouldn't any Emission Theory work?

http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/origins_pathway/#Emission Here, at the Emission theories of light, I loved the discussed theory. There seems to be a contradiction right ...
0
votes
0answers
9 views

Reverse polarity vs falling in Millikans experiment

There are multiple methods of hot to perform Millikans oil drop experiment. One of them lets the drop rise through an electric field (and measures the velocity) then lets if fall (without an electric ...
0
votes
1answer
29 views

Acceleration of uncharged particles

Following on from this comment - do uncharged particles radiate under acceleration? (no offense to the commenter, just clarifying as I've not heard of this before) Why is this? I vaguely recall a ...

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