0
votes
0answers
3 views

Is this the reason why acceleration is said absolute?

I've seem sometimes people saying that although uniform motion on a straight line cannot be detected and hence it is not absolute, acceleration is indeed absolute in Classical Mechanics (I don't know ...
0
votes
1answer
8 views

Converting $F^2$ to $C^2$

I'm trying to convert Fahrenheit squared $F^2$ into Celsius squared $C^2$. I know how to convert a value $x$ in $F$ into $C$ with: $\frac{5}{9}(x - 32)$ I also know how to convert a value $x$ in ...
0
votes
0answers
3 views

Form of the S matrix for interacting sclar field

The solution for the equation $ S^{-1} c_k^{in} S = c_k^{in} + f_ k $ is S= $ exp(f_k^{*}c_k^{in} - f_kc_k^{in*})$. Here $c_k^{in}$ is an operator and $f_k$ is a c number. This is the equation for ...
0
votes
0answers
3 views

First principle band structure calculation

In many literature, we see plots of the energy band structure from DFT simulation. How these eigen-energies are obtained as function of k within the DFT framework? Are they the physical quasiparticle ...
0
votes
0answers
5 views

Is density functional theory a mean-field theory?

Is density functional theory exact or just a mean-field theory?
0
votes
0answers
6 views

Fourier Transform and Canonical Transform

According to a book I'm reading, Fourier transform is a canonical transform. Anyone can prove that?
3
votes
1answer
22 views

Is there any evidence that the theory of everything exists?

I was reading a book and they were talking about Terra Australis. Terra Australis is a hypothetical continent first posited in Antiquity and which appeared on maps between the 15th and 18th ...
0
votes
1answer
13 views

Force and lions

Alright. So me and some other people right now need an answer to this. If you have 1 trillion lions traveling at 81 kilometers (top speed of a lion) towards the Sun in a pretty dense ball. (As dense a ...
-1
votes
0answers
15 views

What is the terminal velocity of a tungsten cylinder 20ft long and 2ft wide? (if it had a more aerodynamic end)

I read somewhere that the drag coefficient of a sphere is 0.5. so I tried calculating with that and got 4150 MPH. I don't know if 1 would be a flat end or not. However I would assume if you were ...
1
vote
1answer
17 views

Are nuclear processes the only processes that release more energy than is input?

Are the nuclear processes of fission and fusion the only known processes or events that release more energy than is input to create those processes? I know I am being a little vague; I do not know the ...
0
votes
1answer
13 views

Question about a car on a banked turn with no friction

A popular physics page explaining how a car can make a banked turn even with no friction : gives the following free body diagram and then says In the vertical direction there is no ...
0
votes
0answers
11 views

Behaviour of a degenerate classical harmonic oscillator

Solving the partition function for a system of N non-interacting particles with energy levels given by $E_{j} = j \epsilon $ and degeneracy g, $g_{j} = j$, and assuming the particles are ...
0
votes
0answers
23 views

Translation of the Mechanique analytique

Is there an English translation of the Mechanique analytique by Lagrange that is free? I have tried searching up online, however I only get French originals. The English translations seem all to be ...
1
vote
0answers
20 views

Vacuum has zero spin in Dirac theory

I have troubles trying to prove a statement made by Peskin-Schroeder in page 61, section 3.5 where he says that the "spin" operator $J_z$ given by the non numbered equation $$ J_z= \int d^3 x ...
1
vote
4answers
76 views

In circular motion, with a constant distance, why does the mass of the orbitting object have no effect on its revolution at all?

Using Newton's universal equation and some circular motion equation, the orbiting object's mass cancels out. But can someone please explain why this is without using pure algebra?
1
vote
1answer
16 views

Is gravitational time dilation the same for an object at $x$ radii from a black hole no matter what size the black hole is?

Assuming you have two non-rotating black holes. Black hole 1 is 1 meter in radius while black hole 2 is 10 meters in radius. If you are standing 10 meters from black hole 1, would you experience the ...
0
votes
1answer
35 views

In circular motion, what's preventing me from calculating the circumference of the circle, dividing it by time to find the speed of the object?

There are equations to solve for the speed in circular motion. However, is there anything preventing me from calculating the circumference from the given radius, and then divide that over the time to ...
-4
votes
1answer
49 views

Could dark energy be what we think is spacetime?

I find it difficult to wrap my brain around how energy/matter, chemical reactions and resultant entropy or waste heat exist in abstract spacetime. First, how can a clock measure "time" without ...
1
vote
0answers
23 views

Quantum Gravity Singularity Question?

I am not a expert in QG (Quantum Gravity) or GR (General Relativity) for that matter so please forgive if I make any small mistakes, its just a curious question but I know that a singularity is a ...
0
votes
0answers
35 views

Deriving the Relativistic Mass Equation

Recently, I learned how to derive E = mc^2. However, to do so, one must accept the relativistic mass equation. How does one derive this?
1
vote
1answer
16 views

Topological invariant for interacting systems using single particle green functions?

Why Single particle green's function is (preferred) used to find topological for interacting systems? $N_1 =\frac{\epsilon_{ijk}}{24 \Pi ^2} \int dw d^3k G \partial_i ...
1
vote
1answer
15 views

COP of Stirling engine

If we consider the theoretical maximum of COP for a heat pump, we will see that it is possible to make it infinite by approaching the temperatures of each source to each other. Yet, in a real engine ...
1
vote
1answer
42 views

Physics involved in the DNA-structure discovery

In 1962 Francis Crick, James Dewey Watson and Maurice Hugh Frederick Wilkins won the Nobel Prize: For their discoveries concerning the molecular structure of nucleic acids and its significance for ...
7
votes
3answers
334 views

Is it possible that every single isotope are radioactive, and isotopes which we call stable are actually unstable but have an extremely big half-life?

I've read that tellurium-128 has an half-life of $2.2 \times 10^{24}$ years, much bigger than the age of the universe. So I've thought that maybe every single isotope of every single atom are ...
0
votes
2answers
51 views

Using Maxwell's demon alongside quantum mechanics to contradict 2nd law of thermodynamics

Suppose we have a steady state universe with a gas chamber resembling that of Maxwell's demon that is used to power this hypothetical heat engine as molecules transfer to their respectable sides based ...
1
vote
1answer
42 views

How can we prove this system is in a stationary state?

I'm having trouble using the given hint to solve the problem. The problem statement is as follows: At instant $t=0$, the probability distribution of a particle under a potential $V(x)$ is ...
1
vote
1answer
90 views

$\nabla^{\mu}\nabla_{\mu}$ in general relativity

I am trying to work out $\square=\nabla^{\mu}\nabla_{\mu}$ in the metric $ ds^{2}=-A(r)dt^{2}+B(r)^{-1}dr^{2}+r^{2}d\Omega^{2} $$ My work: when applying $\square$ to a scalar $\phi$, then $ ...
2
votes
0answers
8 views

Power spectrum calculation for simple inflaton potential

I am trying to obtain an expression for the power spectrum $\Delta (k)$ of cosmological perturbations, see for example eqn (148) from the following TASI lectures. Right now, I would like to use the ...
0
votes
1answer
29 views

How to solve infinite square well with exponential solution (of oscillatory type)?

Given a potential well of $V = 0$ on the interval $(0,L)$ and $V = \infty$ outside the well, I am working to solve the Time Independent Schrodinger Equation $$\dfrac{d^2}{dx^2} \psi= ...
2
votes
1answer
41 views

The g-force of common objects hitting the floor

At my friend's work they have an accelerometer which measures the force with which certain objects hit the ground. He claims that from four feet high, cell phones hit a solid metal surface with a ...
3
votes
1answer
31 views

Is it possible to directly pump a laser using sunlight?

Typically in the old days one would use a flash tube to pump a ruby crystal. Is there any way, or any lasing material, that could use concentrated sunlight directly for either continuous or pulsed ...
0
votes
1answer
22 views

Final charges on Capacitors connected in a curcuit

Capacitor C1 is charged to a Potential Difference of 10V. It's capacitance is 2 microFarad. Capacitor C2 is charged to a Potential Difference of 15V. It's capacitance is 4 microFarad. Now the ...
2
votes
1answer
29 views

Value of Planck scale

I read several times that the Planck scale is the energy scale at which the effects of gravity are comparable to the effects of the other fundamental forces. How can I show that this actually happens ...
1
vote
1answer
35 views

An inconsistency in Hamiltonian formulation for non-local Lagrangian: what am I doing wrong?

This question is based on a previous question I asked, Q. [1] In this question, I proposed an example of a non-local Lagrangian (functional), I'm revisiting it here: $$\mathbb{L}=\frac{1}{2}\int^t_0 ...
0
votes
0answers
22 views

Water as heat source in a heat pump

Consider we have water flowing in a pipe, which is working as a hot source for a heat pump. We are able to know the temperature of the water in both ends of the pipe, yet we don't have information ...
2
votes
1answer
35 views

Rindler and Minkowski space future/past infinity

In my black holes course, we are looking at the Penrose diagram for 1+1 D Minkowski space. My notes don't specifically describe $i^{\pm}$ (future/past timelike infinity) but do say all timelike curves ...
1
vote
0answers
20 views

Vertex of gauge boson interaction in an arbitrary gauge

Let's have interaction between some gauge boson (for example, $W$ boson) and some other field, for example, let assume $\bar{u}\gamma_{\mu}(1 - \gamma_{5})d W^{\mu} + h.c.$. Let's then use gauge ...
0
votes
1answer
42 views

Can an Atom be negatively as well as positively charged simultaneously?

For example there are three atoms- atom A, atom B, atom C. Atom A has 3 electrons, atom B has 4 electrons and atom C has 2 electrons. If we bring together atom A and atom B, in this case atom A is ...
0
votes
0answers
47 views

What happens if the big bang occurs once again?

according to string theory every universe is a large brane and big bang is a event which takes place when two branes collide with each other. if our universe brane collides with another brane there ...
0
votes
0answers
21 views

Simultaneity hypersurface, local rest frame in special relativity

I am reading the book "Special Relativity in General Frames" by Eric Gourgoulhon for its more axiomatic approach to flat Minkowski spacetime geometry. In this book, the author defines something called ...
0
votes
0answers
26 views

Accuracy of quantum mechanical algorithms

Is it possible for a quantum mechanical algorithm to ensure when the wave function collapses that the right answer will be obtained 100% of the time? For this, I am excluding processes such as ...
0
votes
0answers
7 views

How to specify boundary conditions as function of curvature in dynamic elastic beam pde?

In this article (already mentioned in this question) the dynamics of a planar elastic beam with "cantilever constrains" (one clamped end and one free end) is modeled. Using the Euler-Bernoulli Beam ...
1
vote
2answers
56 views

The equivalence between Heisenberg and Schroedinger pictures

In quantum mechanics, the two pictures of Schroedinger and Heisenberg are taken as equivalent, where in the former wavefunctions are time variants and operators are not, and in the latter it is the ...
-1
votes
0answers
24 views

Forces between neutrons and protons [on hold]

The nature of the electrostatic force and nuclear force between a proton and a neutron inside a nucleus is: (a)repulsive and attractive or (b) zero and attractive
0
votes
0answers
16 views

SR: vector field and change of reference

If $U$ and $V$ are vector fields, then the derivative of $U$ along $V$ is the vector field $\nabla _V U$ with components $$\nabla _V U=V^b \frac{\partial U^a}{\partial x^b}.$$ I would like to verify ...
0
votes
1answer
18 views

Combination of current sources

Most books say that to connect sources in series, the current sources will be equal in magnitude. I really don't understand the meaning of this statement. What happens if you connect current sources ...
1
vote
0answers
27 views

In the Leidenfrost effect why dropplets of water can travel uphill?

The Leidenfrost effect is a phenomenon in which a liquid, in near contact with a mass significantly hotter than the liquid's boiling point, produces an insulating vapor layer keeping that liquid from ...
19
votes
3answers
1k views

Why doesn't light affect a compass?

In our daily life a lot of photons of visible light, infrared and radio etc move around us. We know that light is an electromagnetic radiation. So why doesn't that electromagnetic radiation affect a ...
1
vote
0answers
44 views

Chern Simons theory

I have a one question. i am studding Higher spin Theories Part 2(Gomez)http://arXiv:1307.3200.in section 1.2.2 of this he describes gauge algebras and about ISO(D-1,1) tells me:it admits a ...
0
votes
1answer
39 views

Does a photon travel in all directions?

For example i am standing and a beam of light is passing in front of me. I am able to see that beam of light so does it mean that photons are travelling in all directions other than the photons which ...

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