1
vote
3answers
52 views

How are the half life of particles mathematically related to the inverse square laws?

This video https://www.youtube.com/watch?v=K6i-qE8AigE&list=PL3B0924C6A0CB8B67 explains how forces are boson particles. It talks about the other non-force particles giving off and creating bosons, ...
4
votes
1answer
22 views

Calculating the angular power spectrum of a section of sky

To calculate the angular power spectrum $C_l$ of the whole sky, one uses the variance of the coefficients of the spherical harmonics in the temperature fluctuation field. I.e. $$C_l = ...
1
vote
0answers
45 views

BRST quantization of point particle

Suppose we have Lie algebra $\mathfrak{g}$ with basis $t_a$ with a representation $$ t_a \mapsto K_a: V \to V. $$ Denote by $c^a$ the dual basis. Chevalley differential is defined as $$ Q = c^i K_i - ...
1
vote
2answers
32 views

Would using a fan cause an air conditioning system to think it's cold?

Recently my office manager said this, after I requested a desk fan: ...using a fan causes a draught, which then leads the air conditioning to believe it’s cooler than it is and it then blows out ...
-1
votes
0answers
43 views

is this a good introduction to the standard model? [on hold]

I am not familiar enough with the subject matter to know if this is a good undergraduate/first course book. it is not cheap.
1
vote
0answers
33 views

Bose-Einstein condensation as a phase transition

1.How does a non-interacting system exhibit phase transition? 2.Is partition function of BEC is non-analytic (just like in the ordinary phase transitions)? 3.What is the order of BEC phase ...
1
vote
2answers
46 views

Why can't classical particles make Bose-Einstein condensate?

Where the quantum mechanics enters in BEC, why can't (non-interacting) classical particles condense?
0
votes
1answer
51 views

Why does accounting for direction give the wrong result for a bouncing ball?

This a conservation of momentum problem, gathered from an old textbook. I thought it would be simple, but I seem to be goofing up somewhere in my basic conceptual understanding. PROBLEM: A 1.0 kg ...
1
vote
1answer
16 views

Why is 0 $\nu \beta\beta$ decay often written with electron emission and not positron?

According to http://www.cobra-experiment.org/double_beta_decay/ I can see that double $\beta$+ decay is possible, but I often find neutrinoless double beta sources with the double $\beta$- decay ...
0
votes
0answers
23 views

Johnson Noise: Source of thermal fluctuations

I've read a lot online about Johnson noise being caused by thermal fluctuations, and the Wikipedia page of thermal fluctuations attributes this to the fact that particles don't all have the same ...
1
vote
4answers
33 views

Best way to heat something in aluminum foil? [on hold]

Let's say we have a wet piece of paper, wrapped in aluminum foil, that we need to heat up in the fastest and most energy efficient way possible (no flamethrower). What would that be? Details ...
3
votes
1answer
38 views

How does virtual particle become real particle in Hawking radiation? [duplicate]

I am new to black hole and general relativity and am just getting introduced to these concepts. According to my understanding, virtual particle that forms because of quantum fluctuation becomes real ...
1
vote
1answer
39 views

Why is the ground state energy of the Heisenberg XXZ Model unbounded for some values of $J$?

At the moment, I'm looking at numerically studying the Heisenberg XXZ model. The Hamiltonian is given below: $$ H=\sum_{j=1}^{N-1}\left(J S_j^z ...
0
votes
1answer
31 views

Finding the potential energy of a geosynchronous satellite above earth [on hold]

I am trying to find the gravitational potential energy of a 1kg geostationary satellite above the earth. So far: $E=mgh$, and $g=GM/r^2$ so substitution of $g$ into the energy equation gives: ...
0
votes
1answer
20 views

Why liquids in hydrostatic equilibrium stay at the same height? (open tubes)

This part of the book says that, because the two liquids have the same pressure at the same height (that's true), then if a liquid has a higher height, the liquid would have more pressure at a ...
0
votes
1answer
35 views

Eigen-state in a coupled Boson system [on hold]

What's the eigenstate of the coupled system like $$ H=a^{\dagger}b+ab^{\dagger} $$ The system is Boson system and $a,b$ are annihilation operators of fock states and they are commute. In my opinion, ...
0
votes
0answers
17 views

frequency shift in background radiation, where is the missing energy? [duplicate]

It is known that the dilatation of the universe cause a shift in frequency in the background radiation toward lower frequencies. It is also known that photons with lower frequency have lower energy ...
3
votes
1answer
33 views

How much of a galaxy's mass is in stars? [duplicate]

I have been trying to find an answer for this question for a while without a success, so I guess it might not have a specific answer. But to make things easier, let's take the Milky Way galaxy as an ...
0
votes
2answers
87 views

Why can't we fly? [on hold]

Why can't we fly? It contradicts with our known laws of physics, but which one? Is it possible that once we know gravity better we would be able to fly using some sort of anti-gravity machines like ...
0
votes
0answers
26 views

3D harmonic oscillator problem [on hold]

I'm stuck with this problem, that says Find the angular moment $l $ that can be measured for the energy state $5/2 \hbar \omega$, providing the probability of each value. Also build the wave ...
1
vote
1answer
39 views

Can someone prove that the $\tilde{E}$ and $\tilde{H}$ fields in a waveguide looks as pictured?

Hi, I'm trying to use the solution to the wave's equation in a rectangular waveguide for $\tilde{E}$ and $\tilde{H}$ to show how I can get the above picture. For example, why is the magnetic field ...
0
votes
0answers
17 views

Is there uncertainity of position of the perfectly homogenous radiating body? [on hold]

I heard the standard interpretation of Heisenberg Uncertainty Principle: Just the measurement affects the position of the body because allways you want to see the body (=to measure the position), you ...
0
votes
0answers
9 views

Higgs field with pinwheel singularities

The Higgs field is a scalar complex field and the "only thing that matters" is the magnitude of the field. The field is at the lowest energy configuration at 246 GeV: If someone (somehow) created a ...
-1
votes
0answers
14 views

Different force vectors applied on a pulley [on hold]

All the pulleys are ideal. String is massless. Rate of work done by gravity at the given instant is (-x * 10^2) W, then calculate 'x' (refer to the diagram). By 10^2, I mean 10-squared.
5
votes
4answers
1k views

Are atoms made of protons, electrons and neutrinos?

If neutrons decay into proton, electron and (anti)neutrino of electron type, then is it safe to say that atoms are protons, electrons and neutrinos?
0
votes
1answer
46 views

Least Action Principle (Classical and Quantum Theory)

I) My first question would be "why should classical systems obey the principle of least action ?" When we find out the propagator in quantum physics, we find the amplitude to be equal to the sum over ...
0
votes
0answers
11 views

What does the Equation $E_s = -dF$ mean in terms of a Rydberg Atoms Dipole Moment and its Energy?

Could someone explain what the equation $E_s = -d$•$F$: Where, '$d$' is the Rydberg Atoms Dipole Moment, '$F$' is The Electric Field Strength and '$E_s$' is the Energy of the Rydberg Atom. In terms ...
2
votes
1answer
27 views

Why are laser pulses Sech Squared in temporal shape?

Ultrashort pulses from mode-locked lasers often have a temporal shape which can be described with a squared hyperbolic secant ($\mathrm{sech}^2$) function: $$ P(t)=P_0 \mathrm{sech}^2 \left( ...
0
votes
5answers
92 views

About the perception of the flowing of time

The user John Rennie suggested I ask the following as a new question: If time is continuous why would the perception of time being continuous or flowing be an illusion?
-1
votes
0answers
20 views

BIG source or lots of little sources [on hold]

source of any power eg audio in a speaker system for a concrete example or a car engine. you have 1000W. do I a 250W engine on each wheel or a 1000W engine under the hood and a transmission system to ...
0
votes
2answers
29 views

Power transmission loss in a large circuit

This is a followup question to this question Consider a large circuit like the german electric power transmission network. You have a lot of of people consuming power and a lot of power stations ...
-2
votes
1answer
52 views

If you are not given a metric, which one is more fundamental: a vector or a covector? [on hold]

If we do not have the metric $g_{\mu\nu}$ for a given spacetime, are vectors $x^\mu$ more fundamental than covectors $x_\mu$ or vice versa? Why? (if the metric were given we could just raise/lower ...
1
vote
0answers
37 views

Calculate Helmholtz Free Energy with Entropy, Work given [on hold]

it's my first time here and I hope the post complies with the general rules. My problem originates here: I'm doing a statistical physics task which unfortunately leaves me clueless atm. I keep my ...
2
votes
1answer
44 views

Why is the Carnot engine the most efficient?

It seems that the only condition used in proving that the Carnot engine is the most efficient is that it is reversible. More specifically, the Carnot engine can be run in reverse as a refrigerator. ...
3
votes
5answers
96 views

Confusion about Length Contraction (ex in Muon decay)

I am a bit confused about the implications of length contractions; For example, in the muon decay problem, we assume that the distance between the muon and the earth is contracted only in the frame ...
2
votes
0answers
19 views

Ray tracing a three-way intersection

I've been studying ray tracing in media with linear velocity-depth functions. One of the key concepts I've come across is the ray parameter, and in particular the idea that the ray parameter is ...
1
vote
4answers
133 views

Where do Newton's Laws not work? [on hold]

I'm working on high school level project about Newton's Laws and I picked topic that describes situations, where they dont work. Can you name any practical cases where they do not work? Why do they ...
1
vote
1answer
32 views

The Higgs field and spacetime intervals

The Higgs field imparts a rest mass to certain fundamental particles, but it also seems to do something more interesting. Particles that don't couple to the Higgs field, i.e. the rest-massless, are ...
0
votes
2answers
29 views

Kirchoff's loop law

Can any one provide me with mathematical proof of kirchoff's loop law? I am not able to understand from where to start.
0
votes
3answers
29 views

Power transmission in a circuit

lets say you have a battery and a resistance which form a circuit. The electrons flow through the resistance. How can you visualize the flow of energy. How do you visualize the energy field. I ...
0
votes
1answer
30 views

Why is energy of emitted particles negative?

recently I had one problem here, and in comments I got interesting thing written by user Sofia. Unfortunetly, the topic is in hold now and I can't ask her more. Here is the comment: Radio-activity ...
3
votes
0answers
27 views

Strong CP Problem

So, as far as I know, the Strong CP Problem in QCD results from the theta angle term in the action: $i\theta\int_X F_\nabla\wedge F_\nabla$ where $\nabla$ is the gauge connection and $X$ is a manifold ...
0
votes
2answers
42 views

How can we show that pressure is exerted sideways too?

We can show that pressure upward and downward in a fluid is caused by weight of fluid column or volume. A simple derivation of this: ...
0
votes
1answer
18 views

Thomson problem vs. maximizing sum of distance

Given $N$ equally charged points lying on the unit sphere ("electrons"), the Thomson problem consists of finding the configuration of these points such that the electrostatic potential energy $$ ...
0
votes
0answers
15 views

Gaze tracking with the pupil-glint response how does the geometry work?

I am struggling to understand the geometry behind the pupil glint response (see above) (With only one light source). I understand that you use the glint to find the corneal centre (Centre of corneal ...
0
votes
2answers
37 views

How come milk pours smoothly from a bag?

I have seen the commercial about the new beer can where it is vented by puncturing a whole on the can (air behind water). If you just pour normally with normal cans it will get bottle necked and the ...
0
votes
0answers
50 views

Show that there exists a Lorentz transformation such that two events are happening at the same time? [on hold]

I'm havin problems with the following exercise in a theoretical physics course: Show that there always exists a Lorentz transformation such that the two events $P$ and $P^0$ in the figure are ...
0
votes
0answers
32 views

How to find the Kinetic energy of a quarter of a wheel? [on hold]

A wheel of mass 'm' and radius 'R' is rolling on a level road at a linear speed 'V'. What is the kinetic energy of the upper right quarter part of the wheel , considering the wheel to be of the ...
0
votes
2answers
17 views

How velocity dispersion changes with change of inertial frame

I'm analysing a bunch of simulated galaxies, and one of the properties I'm looking at is their velocity dispersion (which is the same thing as the standard deviation of their speeds as far as I know). ...
5
votes
0answers
31 views

SciFi Stasis Field and the Quantum Zeno Effect

The Quantum Zeno Effect concerns the use of repeated measurement of a particle to prevent the time evolution of the wave function, and hence "freeze" it in the observed state. A Stasis Field is a ...

15 30 50 per page