Choice Definition and 667 Threads

This set-theory theorem is very easy to prove: (*) if A≈B & C≈D & A∩C=∅ & B∩D=∅ then A∪C≈B∪D It seems intuitive that if one replaces the strong A∩C=∅ & B∩D=∅ condition by the weaker A∩C≈B∩D the implication (**) if A≈B & C≈D & A∩C≈B∪∩D then A∪C≈BD still holds. (**) does not seem to be much...

Hello everyone, thank you for taking your time to read this. I was assigned a homework task of multiple choice questions to do with gravitational fields. This is one of the last questions and I have been pondering over it for some time now. I don't understand how any sort of answer is...

Why meter bridge is chosen over post office box to measure low resistance?

Hi mates, I am working in computational physics for condensed matter. I have noticed that there are already some articles using deep learning for computational physics. I want to try this method but I do not have any experience with deep learning or machine learning. The first question is that...

Hi everybody. Some years ago I came across a video on youtube where they talked about an experiment with small and large envelops, when the small ones were placed into the large ones and then it resulted in something interesting. It might have been an instance of delayed choice, but I am not...

Hi Sorry about the stupid question. I am completely green on tv streaming. I have a limitation of 25MBPS internet connection. I know 4K video needs 25MBPS speed. That is I can ONLY run one tv. I really don't care about the clarity and resolution. I have modern smart tv, but I am still feeding...

Hi. I’ve seen a number of schematic diagrams for the Delayed Choice Quantum Eraser experiment. Some include a prism to make the two idler photon paths diverge. However, the prism is shown refracting the ‘idler rays’ in a way which contravenes Snell’s law. E.g. see prism marked ‘PS’ (not the...

I am entering into the 2nd year of my masters and I plan to do my phd in quantum chromodynamics. So for my specialization, would it be helpful if I choose nuclear and particle physics or quantum field theory?

A follow-up question from a previous thread: https://www.physicsforums.com/threads/is-entanglement-swapping-a-result-of-post-selection-or-a-result-of-a-quantum-operation-called-a-bsm.1047772/. So my point of view is this: there are systems 1-4 (which refer to photons 1-4 in...

My school's group project is to design a powered model flying wing that can fly for as long as possible. To make it stable in the longitudinal direction, we either have to use a swept wing design or an airfoil with reflex (like BR1). We are forced to use wing sweep because the airfoil with...

I am looking at a textbook solution to the following problem of finding the equation of motion of a half disk. In the solution, the author considers the half disk has a COM at the black dot, and to find the instantaneous translational velocity of the center of mass (he considers rotational...

Three non-concurrent and non-parallel lines divide an infinite plane in 7 parts. and four non-concurrent and non-parallel lines divide an infinite plane into 10 parts. Is this statement correct? If correct, we can proceed further to answer this question. If incorrect, suggest me the...

Under several historical experiments, measurement back-action has exhibited the ability the suppress a system's transitions to other states, especially when measurements are taken at a high frequency in time. This phenomena has become known as the Quantum Zeno Effect. In short, a quantum...

The variation with time t of the acceleration a of an object is shown What is the change in velocity of the object from ##t=0## to ##t=6##? A. ##6ms^{-1}## B. ##8ms^{-1}## C. ##10ms^{-1}## D. ##14ms^{-1}## So apparently the answer is B, which I am having trouble reconciling. Using methods...

Is data science in demand? Is data science hard? How many hours do data scientists work? Is it hard to find a job as a data scientist?

Hi, So say I have some data to process. I am trying, say, Linear/Multilinear Regression. I know how to do this within Python Pandas. I can learn how with Tensorflow (TF). Would TF produce the same output given the "right" choice of Activation Functions *? Or would it output a model that is...

Hey! 😊 A multiple choice test consists of 10 questions. For every question there are five possible answers, of which exactly one is correct. A test candidate answers all questions by chance. (a) Give a suitable random variable with value range and probability distribution in order to work on...

This is a follow-up video I made to a previous one on common misconceptions about the experiment. I'm interested in people's opinions here about how close the simulated experiment is to the real thing (e.g. there have to be some compromises due to the simulator not having free space propagation...

The line containing point A is rotated $90^o$ anticlockwise about the origin O $\begin{array}{ll} \textit{The y coordinate of point A } & \textit{The y coordinate point A}\\ \textit{before rotation} & \textit{After rotation} \end{array}$ a. The quantity on the left is...

Consider a region where a 25-volt-per-meter electric field and a 15-millitesla magnetic field exist and are along the same direction. If the electron is in the said region, is moving at a direction 20 degrees counter-clockwise from the direction of the magnetic field, and is experiencing a total...

At this point I recognize that it’s very common to doubt initial decisions or even to change your mind entirely two, three, four times but when did that stop for you. Did you have a problem between balancing what you’re genuinely passionate about versus other criteria such as a desire to...

This was my attempt at making an explanatory video discussing some of the misconceptions about the experiment. I'm looking for feedback on how it could have been better. In particular, based on some of the confusions in the comments on the video, it's clear to me that I should have e.g. gone...

Based on Wheeler's delay choice experiment, the following results of experiment1 can be achieved. Experiment 1, the light passed through the BS1, 50% of the light is transmitted on optical path A, and then passed through the polarizer P2(the polarization angle is 135°),and the polarizer P3 (the...

My attempt at a solution: Is my logic accurate/correct, and is my answer correct? I consider the forces acting to be: Restoring forces in springs parallel, and Force of the current-carrying conductor in the Magnetic field. I imagine a vertical displacement of y upwards ( direction determined...

Hi, I don't want to be too specific here, but specific enough for relevant advice. I'm finishing a Masters in Physics and am lucky to have been made offers by 2 excellent institutes: a Max Planck Graduate Centre (MP), and at Oxford UK. Both are in experimental condensed matter; Weyl...

It's a mod to a weather station which normally uses primary cells alone. There are four cells, connected as 2X2. I am providing dc power up there for another purpose so I thought it may as well supply the station as well. But I need to protect / isolate the batteries from the DC source with a...

I want to create multiple molecular dynamics simulations using LAMMPS which are different only in the initial velocity of the atoms. LAMMPS allows you to use a random seed to generate an initial velocity. I plan to just use successive numbers, so if there are 5 simulations, the seeds would be...

I recently saw this video by Sabine Hossenfelder on free will, which prompted me to re-watch and re-read a few different resources. One of those resources is a book called John S. Bell on the Foundations of Quantum Mechanics (by Bell, Gottfried, and Veltman). An Exchange on Local Beables - J.S...

I have space in a device about 3 1/2" across and need to get 12cfm of fresh air from this area via a reducing funnel with a ration of 15:1, into a 3/4" tube requiring cooling air inside it at a velocity of 4000fpm. How do I select a fan or drone propeller combination that will do this?

i. Rearranging the equation for kinetic energy in terms of momentum; 1/2mv^2=(mv)^2/2m=p^2/2m Inputting the values given KE=1^2/2*4kg = 1/8 J Kinetic energy of a body with twice the momentum; KE=2^2/2*2kg =1 J The ratio of the kinetic energy of the first body to the second body is therefore...

1. I believe that the gravitational field strength would decrease because it is inversely proportional to the square of the distance from the centre of the Earth, g∝1/r^2. Gravitational potential energy at large distances is directly proportional to the masses and inversely proportional to the...

Hi All, I finished my BS in physics last year and currently work full-time in engineering. I want to pursue my dream of being a research physicist, but I wasn't a stellar undergraduate student, so I'll have to be a self-funded, part-time masters student at first, and I chose to live near the...

I guess my question boils down to "Is choice of signature important when dealing with superluminal 4-velocities"? I wanted to show for superluminal velocities that ##\tilde{U} = \left( \frac{c}{\sqrt{\frac{u^2}{c^2} - 1}}, \frac{\dot{x}}{\sqrt{\frac{u^2}{c^2} - 1}}...

Hi, Between the choices given below, which one is going to be more in demand and helpful in landing a good job. My general impression is that MS in Computer Engineering or MS in Electronic Design are good but you could only aim to be hired by selective companies. On the other hand, MS in...

How do we verify whether a condition on the magnetic vector potential A constitutes a possible gauge choice ? Specifically, could a relation in the form A x F(r,t) be a gauge , where F is an arbitrary vector field?

In a previous thread it was concluded that both torque and angular momentum are taken about a chosen origin, and these quantities are generally not invariant under translations of the origin (since ##\vec{r}## changes but ##\vec{v}## does not, etc.). The moment of inertia tensor doesn't...

[Moderator's note: Thread spun off from previous discussion due to topic change.] Does the observed quadrapole moment change over time when considering a relatively moving object, for certain choices of observer coordinates? My suspicion is that it does (Terrell-Penrose rotation implies...

Hi all; This goes under the heading of experimental predictions... gone awry. Let me say from the start that I think I've got something wrong, and would have no problem having it pointed out to me. I'm a newbie, and I've been boning up on basic quantum physics phenomena on Youtube, and...

I need to use some property of the relalation between the coordinate systems to prove that g_{hk} is independent of the choice of the underlying rectangular coordinate system. I will try to borrow an idea from basic linear algebra. I expect any transformation between the rectangular systems to...

Hello everybody, I am a master student in Theoretical Chemistry and I am working in the DFT realm. Both TDDFT and DFT applied to extended systems (eg. using QUANTUM ESPRESSO). Of course I work with these softwares from a end-user point of view, not as a developer. But anyway, even if some of...

From Wikipedia entry on the Axiom of Choice: [1] What about a finite set of indistinguishable things (e.g. identical socks)? Do we need to invoke the axiom? [2] Is there any physical consequence of this axiom, i.e. is there any physics experiment where the calculations to predict the result...

Homework Statement:: Consider an electron trapped in a one-dimensional finite well of width L. What is the minimum possible kinetic energy of the electron? A) 0 B) Between 0 and h^2/8mL^2 C) ≈h^2/8mL^2, but it is not possible to find the exact value because of the uncertainty principle D)...

This is purely for fun, as it won't affect my plot direction whatsoever. Which of my scifi created humanoid races would you prefer to work with and why? Which would you not want to and why? Based on their behavior only? Race 1: Take a positive view most all the time of situations, but can...

ok just posted an image due to macros in the overleaf doc this of course looks like a sin or cos wave and flips back and forth by taking derivatives looks like a period of 12 and an amplitude of 3 so... but to start I was not able to duplicate this on desmos altho I think by observation alone...

i've been offered a place where the supervisor's phd students tend to publish at least four times before graduating with their PhD, however it's not a university I would have selected for my undergrad studies, to put it that way. But I've noticed a lot of such places, including this one, seem to...

Summary: Is Baby Rudin a good choice for first Real Analysis textbook for someone without strong pure math background? I've completed 2 semesters of college calculus, but not "pure math" calculus which is taught to math students. I'm looking for introductory text on Real Analysis and I've...

Hi All, I am setting up a WMWare15 Virtual Machine (VMWare Workstation 15 Player, more accurately). It requires the use of an OS. I have a copy of Win7 Pro which I already used successfully _except_ that it was a 32-bit version. Someone who knows more than I told me that it is possible for...

Hi all, I'm entering the last year of my PhD on the interface of quantum optics and condensed matter (theoretical) in Europe. At this point, I am happy to have started it and now love doing research (even when being stuck on a problem-because this usually means something interesting will appear...

Hi, As the summary says, I'm trying to design a simple gearbox with an approximate ratio of 20:1. I have two preliminary designs, one using a worm gear and another using a train of 5 spur gears. Both designs give me the desired ratio, but I really don't know which one I should choose. The...