6
votes
3answers
357 views

How would a realist interpretation of the Mermin-Peres square look like?

How would a realist interpretation of the Mermin-Peres square with counterfactual definiteness and the existence of states prior to measurements look like?
3
votes
1answer
299 views

How does a hinge affect the amount of a submerged material?

Suppose I have a rod that has a density of $X <1$. If I were to submerge that rod in water (density 1), I would expect $X$ of the rod to be below water and $1-X$ of it to be above water (simple ...
2
votes
2answers
286 views

Force and Torque Question on an isolated system [duplicate]

If there's a rigid rod in space, and you give some external force perpendicular to the rod at one of the ends for a short time, what happens? Specifically: What dependence does the moment of inertia ...
2
votes
0answers
122 views

Showing that the Ricci scalar equals a product of commutators

I have to compute the square of the Dirac operator, $D=\gamma^a e^\mu_a D_\mu$ , in curved space time ($D_\mu\Psi=\partial_\mu \Psi + A_\mu ^{ab}\Sigma_{ab}$ is the covariant derivative of the spinor ...
9
votes
4answers
3k views

Would a bicycle stay upright if moving on a treadmill and why?

I suspect not, because moving forward (or backwards for that matter) is an important part, but I would like to confirm. UPDATE: Clearly it's possible ...
-1
votes
1answer
340 views

Are the speeds of the different wavelengths of visible light different or varying in a medium such as air?

Are the speeds of the different wavelengths of visible light different or varying in a medium such as air? If so, please inform by how much? Also, even if the wavelength speeds vary minimally, please ...
3
votes
2answers
267 views

Does the Earth have a semi-solid body at its core because of lower pressure at the center of the Earth?

I have read that the Earth has a semi-solid iron body at its core, even though that object is surrounded by liquid magma.... I'm wondering if this is because of a pressure (and resulting temperature) ...
1
vote
1answer
246 views

Is it possible for an object to stop sinking after a while?

Suppose you drop an object into a body of fluid (on a planet with constant gravity). Suppose the fluid is pure (as in, there are no solid granulates or bubbles present in it), and finally suppose that ...
4
votes
1answer
261 views

Are new elements still being created?

Last I heard, there were 115 elements (natural and artificial, of course). Are there more still being made? If so, why? I thought this question would be more appropriate on the physics site rather ...
-1
votes
1answer
248 views

Suppose a hollow metal sphere filled with helium is dropped in a body of water

What are the conditions that would cause said sphere to sink or float? What if the sphere was full of ice instead?
6
votes
1answer
2k views

Why both yellow and purple light could be made by a mix of red, green and blue?

We see the mix of red light and green light as yellow light (#FFFF00). The wavelength of yellow light lies between red and green. But the wavelength of purple light lies outside of red and blue. ...
4
votes
4answers
647 views

Gravity from a singularity as distance approaches zero

If you had a singularity (that had mass but took up no space), what would happen to the acceleration of an object as it approached this singularity? I would assume that it would be infinite, since as ...
1
vote
2answers
1k views

Is all matter made of virtual particles?

This article in New Scientist says that all matter is actually virtual particles popping in and out of existence and nothing more. is this correct?
3
votes
0answers
189 views

What aspects of QFT do mathematicians find troublesome? [closed]

What aspects of "conventional" quantum field theory (i.e. what's used by most practicing physicists) are considered to be lacking mathematical rigor?
5
votes
1answer
232 views

Are isolated many-particle quantum systems always in a pure state?

I am trying to understand pure and mixed states better. If I have N quantum particles in an isolated system. The many-particle state is a superposition of the product of single-particle states by the ...
0
votes
2answers
910 views

Radiated power and energy density for a black-body

I am having an hard time trying to understand why the radiated power per unit area $P$ of a black body is given by $$P=\frac{c}{4} u$$ in terms of the energy density $u$ and the velocity of light. I ...
1
vote
1answer
626 views

Magnetic field of permanent magnet [closed]

Hi I am looking for some code to (computationally) calculate the magnetic field of a rectangular permanent magnet in 3D space. Preferably I could edit it to add in my own dimensions. Does anyone know ...
3
votes
1answer
331 views

Why aren't two systems in thermal equilibrium the same as one system?

I am reading Molecular Driving Forces, 2nd ed., by Dill & Bromberg. On page 53, example 3.9, we consider why energy exchanges between two systems from the point of view of the 2nd law. We ...
2
votes
2answers
190 views

Forces involved in strapping something down

Say I have a hollow cylinder and I wanted to strap it down to the bed of a truck. I would tension the strap on one end, and it would exert a force on the cylinder. My intuition tells me that the strap ...
7
votes
3answers
4k views

Kinetic energy with respect to different reference frames

I'm having problems understanding the following situation. Suppose two 1-tonne cars are going with the same orientations but opposite senses, each 50 km/h with respect to the road. Then the total ...
3
votes
1answer
1k views

Where to find the current positions and velocities of the planets?

I've written a program which simulates the motions of planets and other bodies. I'd like to run it on our own solar system, but to do so I need to know the current positions (preferably in ...
0
votes
1answer
197 views

How would it be to look at the sky if the earth were near the edge of the universe?

By looking at this picture: http://earthspacecircle.blogspot.com/2013/01/earths-location-in-universe.html The earth is near the center of the universe. I've read that the universe look the same no ...
3
votes
1answer
2k views

why is orbital moment quenched while atoms forming solid

atom has well defined spin(up and down) and orbital(s,p,d,etc) momentum, but when forming crystals, why the spin degree continues to be good quantum number while orbital momentum is quenched?
1
vote
1answer
1k views

Explanation of energy levels in molecules, atoms, nuclei and their relationship

Why are the energy levels of molecules, the atoms that form them and the nuclei inside the atoms considered separately? Or phrased in a different way- what is it that makes their energy levels so ...
-2
votes
1answer
215 views

Photoionization equation

I really need help understanding this equation ,i am new to quantum mechanics and i cant understand the math, so i need every single symbol to be explained or given a value if it is a constant , ( ...
2
votes
2answers
600 views

Is 't Hooft's Determinism based on the holographic principle?

Does 't Hooft's determinism work need the holographic principle in order to work or is it just an extension of his work?
1
vote
2answers
1k views

Bowling ball on a rubber sheet analogy - what pulls the ball down [duplicate]

Possible Duplicate: Does the curvature of spacetime theory assume gravity? Since I read Cosmos long ago, I see the same analogy about the balls rolling on a rubber sheet used to explain how ...
2
votes
2answers
1k views

Orthogonality of modes

I want to know what it exactly means when it is said the modes of vibration are Orthogonal.I understand what it means mathematically but what is its physical interpretation?
0
votes
1answer
2k views

Estimate the damping coefficient of my car

I was wondering how I can estimate the damping coefficient of my car by doing the hand bouncing the car body and watching the motion of the car? I just need a rough estimate of the damping ...
0
votes
6answers
676 views

Relation between field strength and potential?

In terms of gravity and electric fields, I'm not sure what the difference is between field strength and potential is and how they are related? Both using maths and not.
1
vote
2answers
701 views

What is 'past null infinity'?

For example, in the sentence "there is no incoming radiation at past null infinity".
-3
votes
1answer
778 views

Spectral radiance unit conversion [closed]

I have spectral radiance data in SRUs (spectral radiance units), as a function of wavelength: $$a = \mu W cm^{-2} sr^{-1} nm^{-1} $$ However, I am working with software which requires my data in the ...
2
votes
1answer
478 views

Electrodynamics and the Lagrangian density

Could anyone tell me what equations can I obtain from the Lagrangian density $${\cal L}(\phi,\,\,\phi_{,i},\,\,A_i, \dot A_i,\,\,A_{i,j})~=~\frac{1}{2}|\dot A+\nabla\phi|^2-\frac{1}{2}|\nabla \times ...
2
votes
2answers
260 views

locality vs non-locality

Suppose we have a circular loop of wire, and we put a long perfect solenoid inside it which is connected to an AC voltage source so that the magnetic field inside it starts to vary by time, does this ...
2
votes
3answers
9k views

Entropy Change During Reversible Processes

I'm confused about the Second Law of Thermodynamics. The Second Law of Thermodynamics prohibits a decrease in the entropy of a closed system and states that the entropy is unchanged during a ...
8
votes
4answers
553 views

If quantum computation is reversible, what is the point of Grover's search algorithm?

Wikipedia et al say the following about Grover's algorithm: Although the purpose of Grover's algorithm is usually described as “searching a database”, it may be more accurate to describe it as ...
0
votes
0answers
671 views

Entalpy and entropy role in freezing-point depression phenomena

There's this "atomic" explanation of the freezing-point phenomena on Wikipedia that leaves me really intrigued. Consider the problem in which the solvent freezes to a very nearly pure crystal, ...
2
votes
2answers
136 views

Eutectic systems behavior near 100%-0% composition and low temperature

I can't understand why in this phase diagram , in the area where the system is approaching the 100% $\alpha$ or 100% $\beta$ composition, the state is just a pure solid. I mean, where does the ...
2
votes
1answer
196 views

Construction of the supersymmetric Faraday tensor

When I first learned gauge theories in my introductory quantum field theory course, I was taught that the Faraday (field-strength) tensor can be constructed by computing the commutator of the ...
1
vote
1answer
3k views

What is the electrical conductivity (S/m) of a carbon nanotube?

I have been searching around for a while for this but I am having trouble finding any actual figures, all I can seem to find is that it is "very high". So I am wondering, does anyone have any figures ...
12
votes
3answers
4k views

Gravity in other dimensions than 3 and stable orbits

I have heard from here that stable orbits (ones that require a large amount of force to push it significantly out of it's elliptical path) can only exist in a three spatial dimensions because gravity ...
3
votes
1answer
547 views

How does one write the Einstein field equations in terms of Ricci tensor?

How can I go from the 'standard' Einstein equations $R_{\mu\nu} - \frac{1}{2}g_{\mu\nu}R = \frac{8\pi G}{c^4}T_{\mu\nu}$ to these equations: $R_{\mu\nu} = \frac{8\pi G}{c^4}(T_{\mu\nu} - ...
0
votes
0answers
139 views

How to convert a hologram into an image?

Suppose one knows in full detail the phase and intensity of monochromatic light in a plane. This is basically what a hologram records, at least for some section of a plane. By using this as the ...
3
votes
1answer
294 views

Rutherford's Gold Foil Experiment

Can anybody explain how Rutherford bombarded a 0.0004 cm thick gold foil? How did he put it in a photographic sheet? Wasn't the foil too thin to be held? How did he know that the atoms were deflected ...
2
votes
1answer
70 views

Rosenberg-Coleman effect

I know only that it states some variations of the Sun's magnetic fields. What is the Rosenberg-Coleman effect specifically?
4
votes
1answer
305 views

Trying to understand “recursion at the lowest level of matter”

I'm reading the book Gödel, Escher, Bach: an Eternal Golden Braid and on Chapter V, Hofstadter talks about different examples of recursive structures and processes. By page 142 of the 20th anniversary ...
1
vote
2answers
445 views

Was the early Earth radioactive?

I've been reading of the (surprising) fact we are uncertain on whether there is nuclear fission in the center of the Earth or not (yet we know so much detail on structures at the other end of the ...
1
vote
1answer
480 views

Does mass concentration affect the torque induced by a force?

If you had two bodies with the same weight but one having mass concentrated more in the center, while the other had most mass concentrated on the outside, but both had the same center of mass and ...
0
votes
1answer
264 views

If there was no Earth, what would be the acceleration of gravity from here from the Sun?

Suppose there were no Earth to pull us back and we're hanging in the solar system. Assuming no other force of gravity from other bodies, what would be the $g$ from the Sun?
0
votes
1answer
1k views

If 2 charges have the same sign, the coulomb force is positive but repulsive, while with 2 masses the gravitational force is positive but attractive

If you have two point objects both the same positive charge and both of the same mass at a distance $r$ from each other. The force between them due to gravity is $F_g=\frac{Gmm}{r^2}$ and $F_g$ is ...

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