# All Questions

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### Maybe the difference between contextuality, nonlocality and retrocausality lies in where we draw the boundaries?

If the apparatus lies outside the boundary, we have contextuality. If the apparatus lies inside the boundary, but the measurement occurs after the "final time" boundary, we have retrocausality. If ...
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### Which number is bigger, -1 or -2? Discuss your answers by applying examples in Physics [on hold]

Which number is bigger, -1 or -2? Discuss your answers by applying examples in Physics. My answer: -1 is bigger than -2. \begin{align*} \ 3.4 \cdot\ 10 ^{-1} = 0.34 \\ 3.4 \cdot\ 10 ^{-2} = 0.034 ...
6 views

### The wave function of transverse one is different from longitude one for convinience?

I use the book Fundamental of Physics Hallidays&Resnick 10th Edition Jearl Walker to study in my physics class while I got myself University Physics with Modern Physics Sears, Zemansky 13th ...
31 views

### How can the electron be a wave?

I read Rutherford's failed attempt for describing atomic model. Then read the famous model of Bohr and his postulates. Ok, that was fine. But then my book dumbed before me a statement that shocked me: ...
17 views

### Difference between spin and polarization of a photon

I understand how one associates the spin of a quantum particle, e.g. of a photon, with intrinsic angular momentum. And in electromagnetism I have always understood the polarization of an EM wave as ...
14 views

### In which direction due to a polarizing grid the photon's electric field is oriented?

After a photon passes the slit, is it's electric field oriented perpendicular or parallel to the slit and why this is so?
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### Can we solve most of the cosmological questions using the Illustris universe simulation?

The Illustris project (http://illustris-project.org) attempts to simulate the universe in its most accurate form according to their website. With the simulation, they were able to predict the neutral ...
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### Quantum cloning of orthonormal states

If I understand correctly, for two orthonormal states $\left|\psi_1\right\rangle$ and $\left|\psi_2\right\rangle$ in the Hilbert space H, there must exist a unitary transformation $U$, such that: ...
29 views

### How can we take pictures of something billion of light years away?

I have had this question in my mind for a long time, I thought you guys might enlighten me easily. I am confused about some space photographs and claims like "this galaxy is 13 billions light years ...
10 views

### Conditions of friction on constant accleration

If a body is moving with constant acceleration, then what would the frictional force be? Zero In forward direction, In reverse direction all of above
26 views

### Why are position and velocity enough for prediction and acceleration is unnecessary?

In classical mechanics, if you take a snapshot and get the momentary positions and velocities of all particles in a system, you can derive all past and future paths of the particles. It doesn't seem ...
17 views

### Why is the Great Dark Spot so shortliving unlike the Great Red Spot?

The Great Dark Spot is an anti-cyclone in Neptune. But unlike the Great Red Spot of Jupiter which lasts for more than hundred years, the Great Dark Spot exists for only one year or so. Why is it so??
233 views

### What do units like joule * seconds imply?

I can easily understand what divisive units imply, but not what multiplicative units imply. What I mean is, when I read "12 eggs/carton", I mentally convert it to, "There are 12 eggs for each ...
27 views

### General Relativity: impact of acceleration on time, experimental setup

In What is relativity by Jeffrey Bennett (Amazon link), the author explains how acceleration/gravity impact time and causes time dilation. For this he takes an example of an accelerating space-ship ...
46 views

### Why is the Force of Friction Equation So Simple?

The general equation for the force of friction (static or kinetic) is $F_f = \mu * F_N$, where $F_f$ is the force of friction and $\mu$ is the coefficient of friction (its value is dependent upon the ...
30 views

### Why is friction independent of contact area, and why does it increase with surface smoothness?

Below there is a line from my book: The force of limiting friction is independent of the apparent area of contact, so long as normal reaction between two bodies in contact remain same. Why is ...
355 views

### How much heat from a fire actually warms your home?

A fire in a hearth disperses heat to, I guess, three places: the bricks of the chimney out the hearth (where the person tending the fire is standing) out the chimney, above the house How would you ...
45 views

### Is it possible to single out a proton, electron, neutron?

I've read that it's nearly impossible to take a proton from an element. But if it's "nearly" impossible then it is possible to some degree. If this has happened, what is exactly the process of taking ...
46 views

### Is placing a heater in the coldest part of a room the most efficient place to put it?

I've noticed that stores blow hot air in a "sheet" by doors and windows, which is "where cold air enters". I assume they do this because it saves money and/or keeps the store a uniform temperature. ...
82 views

### Are wave functions real physical objects? [duplicate]

Are wave functions (ex. electron waves) real physical objects or just mathematical tools. Some researchers say that they have proof that they are real objects. Here's the link. ...
390 views

### Why does heat lose its energy as we get further away?

Why does heat lose its energy dramatically as I move back? Say I have a fire around 0.5 meters in front of me, I can clearly feel the heat, however, as I move even very slightly back, say 1 meter ...
33 views

### Could we describe acids and bases using electromagnetism?

Why don't we use Maxwell's equations in acids and base theory? Surely the interaction between two charged species is readily described by this. The theory I have so far come across is HASB theory. ...
46 views

### How fast am I moving?

Given the speed of light is 299,792,458 meters per second and that it is constant through out the universe, (i.e a person who measures the speed of light while standing still will get the same result ...
25 views

### Predicting balls's movement in well due to fluid flow

I am a total newbie in fluid dynamics. In one of my experiments/open project, my experiment setup is as below: a small ball sits in a circular well (has mass density a bit heavier than water), with ...
43 views

### What topics do I need to study electromagnetism on the quantum scale? [on hold]

What topics do I need to study (in order) so that I can study electromagnetics on the quantum scale? What is the name of the discipline studying electromagnetism on the quantum scale? Do I need to ...
37 views

### How are the Lorentz force, Maxwell's third law and Faraday's law of induction clasically related?

Faraday's law of induction can be used in any situation where the magnetic flux is changing through a closed conducting loop. While giving the correct answer, it seems to me that for the following ...
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### Lightning strikes causing nudity [on hold]

Klutz's Zap Science states on p. 62: Ever Had Your Sweat Explode? A few survivors of lightning strikes — after recovering consciousness — have found themselves lying on the ground, groggy, ...
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### Where does light go when you switch it off? [duplicate]

I have a lamp. When I switch it on, it immediately illuminates the surroundings. When I switch it off, the light goes away in an instant. Why is this? Where do the light particles go? Do they quickly ...
13 views

### Cartoon shape cutout at high velocities

I was recently reading this, and Floris's answer confirmed my knowledge that the information of an collision travels at the speed of sound. While I was thinking about that, my mind wandered and I ...
33 views

### Measuring the pressure in a container without altering it

Let's say I have a closed, non-transparent metal container with pressurized gas and I'd like to measure the pressure inside without altering it (the pressure should stay the same), is thatpossible ? ...
41 views

### What does the relation between mass and energy of a free particle mean?

What does the Hamiltonian for a free particle mean? Does it mean that the kinetic energy of the particle is in reverse relation with mass? $H$ or $E=\hbar^{2}k^{2}/2m$. Or, what's the relation ...
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No Nobel prizes at stake, but just an idle thought and an idle question. How could one calculate the probability of a flipped coin landing stable on its edge, instead of heads or tails? I assume ...
58 views

### Why $D^{\mu} D^{\nu} F_{\mu \nu}=0$ ? (Noether Identity) [on hold]

I have to show that: $$D^{\mu} D^{\nu} F^A_{\mu \nu}=0$$ vanish identically. This is the generalization to non Abelian groups of $\partial^{\mu} \partial^{\nu} F_{\mu \nu}=0$, apparently called ...
17 views

### Calculating buoyant force of air experimentally

I'm planning a physics project to submit at school and since it has to be something where we experimentally determine some value, previously known theoretically, I had this following idea but I want ...
407 views

### Exploring beyond event horizons

In the expanding universe the velocity of separation between galaxies depends upon how far they are. If they are much far away will they have relative velocity of separation greater than speed of ...
35 views

### Understanding the advantage of using integration over summation for finding COM for a continuous body?

My book (NCERT) writes: In a rigid body, such as a metre stick, the number of particles is so large that it is impossible to carry out the summations over individual particles. Since the spacing ...
198 views

### Wave function in quantum mechanics

I was wondering about something while studying quantum mechanics. If the wave function collapses when measuring a particle and assumes a single position, how do we know that it was a wave in the first ...
151 views

### Making precise the statement “particles are excitations in a quantum field”

I've been trying to self teach QFT lately. I find that the basic physical idea makes sense, and I can keep up with the mathematical formalism without too much trouble, but I'm having trouble ...
31 views

### What are some good physics websites for learning in general? [duplicate]

As a 17-year-old who is interested in physics and especially in the laws of the universe, what are some good websites that are clear explanations and straight to the point?
28 views

### Independence of thermodynamic variables

A given thermodynamical system has a number of state variables, not all of which are independent. Suppose that we have a system which can be specified by $k+1$ extensive variables: $U,X_1,\cdots,X_k$. ...
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### Why two-particle wavefunctions are separable and their corresponding particles are indistiguishable at the same time?

If the wavefunction $\psi(r_1,r_2)$ doesn't represents an entangled state, it is separable: $$\psi(r_1,r_2)=\psi_a(r_1)\psi_b(r_2)$$ In this treatment, we ignore the interaction between two particles ...
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### If I kept getting closer and closer to the speed of light, what would be the gravitational effects appearing like to an observer? [duplicate]

Now, with special relativity applied to the scenario of me getting closer and closer to light speed, my mass would increase with respect to the observer, and also my length would contract in the ...
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### A modern version of Landau theoretical minimum? [duplicate]

Can anyone point to me any modern books that are similar to Landau's book in scope and depth, these books used to serve as the backbone that determines one’s level of scientific culture, and since ...
19 views

### Better gas mileage going fast or slow [duplicate]

In an automobile, do you get better miles per gallon when going faster or slower? Is this question answerable without more information? If more information is needed, assume the following: ...
766 views

### Physics & derivatives written in a weird way

I was always taught that $\frac d {dx} (\ln x) = \frac 1 x$. No derivative had as a result any $dx$ words. In a physics book I encountered something like this (error discussion) [there might be a ...
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### How to derive the Bhatnagar-Gross-Krook collision integral from Boltzmann one?

Let's have Boltzmann collision integral: $$I_{coll} =\int d \sigma d^{3}\mathbf p_{1}(ff_{1} - f{'}f{'}_{1})|\mathbf v_{rel}|.\tag{1}\label{1}$$ How to transform $\eqref{1}$ to BGK collision ...
I came across a question regarding linear momentum $L$ and it's conservation, however I tried and got confused. It reads: A $40kg$ girl stands on the very edge of a rotating disc of mass $50kg$ and ...