Measurement Definition and 1000 Threads

Summary: How does many worlds deal with the measurement of an electron's position in space? Hi all - I am reading Sean Carroll's book on quantum mechanics and reached the end of the section on "branching and splitting" without getting an answer. I will lay out my assumptions and then get to...

The probability that a measurement of ##L_x## will give zero for a given ##\psi## should be ##\vert \langle L_x = 0 \vert \psi \rangle \vert ^2##, I think. I found the eigenvalues of ##L_x## to be ##\lambda = -1, 0, 1##. Since it asks for the probability that the measurement will give zero, I...

Summary: Volts When measuring an electrical currents voltage, are you actually measuring the pressure emitted in electricity

An outcome of a measurement in a (infinite) Hilbert space is orthogonal to all possible outcomes except itself! This sounds related to the measurement problem to me, for we inherently only obtain a single outcome. So, to take a shortcut I posted this question so I quickly get to hear where I'm...

I'm trying to obtain the free carrier concentration vs depth profile from the CV (capacitance-voltage) measurements of a normally-on HEMT with the expressions used for a Schottky barrier, but I´'m confused about how to extract the values for depth. I found in textbooks and articles that the...

I find in the literature frequent reference to the "measurement postulate" and, sometimes, to the "von Neumann’s projection postulate". The difference, if any, seems to me subtle but I can't tell which. However, they are never mentioned both in the same context/paper, so I'm afraid that they may...

If we have a two dimensional measurementbasis, then we have two possible outcomes of the measurement. Now I figured: considering the law of conservation of energy, if one particle goes in, one and only one can come out. So outcome "both results simultaneously" cannot happen, for that would...

Is instantaneous limited to our in ability to continue to count time faster.

Publication News article It looks increasingly like something is wrong with the older electron-based results. The story of "with electrons you measure one thing, with muons another" doesn't work any more. Is that a good thing (there might be some conclusion what the radius is in the next years)...

[Moderator's note: Spin off from previous thread since this is a separate topic from that one.] It's hard to expect that it ever gets a standard interpretation, because it contradicts the very observations which lead to the discovery of modern quantum including Born's probability interpretation...

Summary: If a measurement outcome depends on the measurement setup, is de measured not real or the measurement? If the factual outcome of an electron-spin measurement depends on the orientation of the SG magnet, for instance up or down in one orientation and left or right in the other, does...

Hi, I'm reading Demystifier's article about an interpretation of quantum mechanics. One concept that seems important for this interpretation is that of what is perceptible by us human beings compared to what is not (non-perceptible). Demystifier says: A perception by a naked eye is direct, a...

Summary: A link to excerpts from a paper behind paywalls I just found this link featuring excerpts from a 2017 paper by Steven Weinberg on the measurement problem, which I couldn't read before, it being behind paywalls...

A new (short 3 pg) paper, making quite a grandiose claim, caught my eye last night: https://arxiv.org/abs/1908.07719 Abstract: We propose an experiment of two-path interference in which the optical path difference between the two interferometer arms is much larger than the spatial spread of...

I just saw a new paper on measuring the Hubble Parameter : https://arxiv.org/pdf/1908.06060.pdf It seems they are agreeing with Planck which I understand would speak largely against the idea of new physics from the Hubble tension. However it says +14 and -7 next to the estimate. I presume...

What is the most precise way to log temperature in the laboratory? I am concerned with resolution and precision here, not accuracy. RTDs don't seem to cut it. Almost all that I have looked at and tried only have a resolution of around 0.1 deg C. I was hoping for 10X better than that- Thanks...

Suppose you make a measurement of some particle. If you know it is entangled, you may have conditional knowledge of measurements that might be made at a spacelike distance (if the other observer does/has done x, they will/did get result y). Note, I am using local in the sense of special...

This is related to the thread "Is quantum theory a microscopy theory?" discussed mostly by Ph.Ds. I make this new thread so as not to disturb the experts discussions or even hijack or close it prematurely. In message #27 of...

Take 2 people P1 and P2. P1 claims that a Stern-Gerlach device collapsed an electron’s spin to + or - (mixed state if P1 doesn’t know which) while P2 may say it did not collapse, but instead remains in a pure, entangled state. If we continue this sort of thinking (2 people applying different...

Hello, This is my first post in this domain and I am fairly novice in this subject, so please bear with me. I have a GDS-20174A Digital Oscilloscope. I am trying to measure the delay between two BNC cables using a Square Pulse of 2V with an offset of 1 V using the oscilloscope. I am using...

Hello everybody! I have a question regarding my physics laboratory at the university. I am performing the measure of muon lifetime. The setup is quite standard (coincidence measurement with plastic scintillators). My question is about the time resolution. I have tried to see if the time...

Hello, I would like to start with an assumption. Suppose a system is in the state: $$|\psi\rangle=\frac{1}{\sqrt{6}}|0\rangle+\sqrt{\frac{5}{6}}|1\rangle$$ The question is now: A measurement is made with respect to the observable Y. The expectation or average value is to calculate. My first...

I'm a mathematician with a longstanding interest in physics, and I've recently been enjoying reading and thinking about Arnold Neumaier's thermal interpretation, including some threads on this forum. There's something that's still confusing me, though, and I'm hoping someone here can clear it...

Considering pilot wave interpretation, a singular particle measurements are fully defined (?) by knowing its wave function (a pilot wave) and the position of the "particle" (some hypotetical point particle riding on the wave). This should provide some sort of "realistic" explanation of how a...

calculate the moment of inertia of this I section about centriodal axis (##Y_{c}## = 108.4) Where does ##Y_{C}## measurement goes in this I section?

If I'm trying to solve the problem of a particle in free space (H = P2/2m ). the eigenfunctions of the Hamiltonian cannot be normalized. now assume I have a legitimate wave function expressed in terms of the eigenfunction of H and I want to measure its energy. what will happen to the...

NOTE: this is a programming exercise (Python). I started adding to ##x_{true}## an error related to a (for example) 10% relative error, obtaining ##x_{measurement}##. Then i computed ##y_{measurement}##. To find the precision, i calculated ##(y_{true}-y_{measurement})/y_{measurement}##. If it is...

Summary: 1.In the context of calibrating a scale to correlate volume change with temperature, my book states: "Since all substances change dimensions with temperature, an absolute reference for expansion is not available." What do they mean by an absolute reference in this instance? My...

The following two examples illustrate the differences between the thermal interpretation and Born's statistical interpretation for the interpretation of measurement results. 1. Consider some piece of digital equipment with 3 digit display measuring some physical quantity ##X## using ##N##...

Hello soon to be saviors, 😊I have two really simple questions that I have already answered but the teacher wants more info. I am really stumped and I am not looking for the answers so much as an explanation on how to better answer the questions. I will copy and paste the problems and my answers...

In https://arxiv.org/pdf/quant-ph/0203049.pdf, which is in the realm of Bohmian mechanics, Antony Valentini claims that by having a "non-equilibrium" particle with arbitrarily accurate "known" position, we can measure another particle's position with arbitrary precision, violating Heisenberg's...

I have two groups (expert & novice) that were tested on walking with stilts and without. The results were: walking velocity (cm/s) cadence (steps/min) stride length (cm) What would be the appropriate graph to run with RStudio to account for the three different measurements? Thanks, Dants

While trying to understand parallax and its use in measuring distances here, I had a few questions. (1) Parallax is defined as the apparent movement of an object with reference to another object in the background when one views it from different angles. As in the movement of a finger relative...

The digital CT (current transformer) operated energy meters are tested in field using consumer's load conditions by means of a parallel test equipment. It was observed that the reactive energy measurement has high accuracy mismatches on harmonic polluted loads. Some literature indicates that...

If we have a point charge of significant value, would osciloscope measure voltage if we just point the electrodes in two diffrent point in space?

Suppose we have a quantum object in superposition to some measurement basis, given by: ##\frac{\sqrt{2}}{\sqrt{3}}|a \rangle + \frac{1}{\sqrt{3}}|b \rangle##. (1) Suppose the measurement is made, and the system evolves, according to MWI, into ##\frac{\sqrt{2}}{\sqrt{3}}|a \rangle|W_a \rangle +...

Dear Sirs, After my theoretical post on vacuum diode electron flow, I decided to try and measure it physically. I didn't have a vacuum tube, so I improvised with some tungsten wire, aluminum sheets and some screws and the result was usable. Obviously the tungsten wire fails after some time due...

A physicist prepares a box and tells us that in the box there is a cat that is in a superposition of being alive and being dead. How can we be sure whether they're telling the truth? Is the state a superposition or a mixture? If we open the box and measure only whether the cat is alive, using...

Dear experts, I'm currently working my way through the paper Masanes, Galley, Müller, https://arxiv.org/abs/1811.11060. On page 3, they define what they call a bi-local measurement: If we have two systems a and b and we define an outcome probability function for some measurement f on system a...

If I want to measure my height, I need to find not only the location of the top of my head, but also the location of the bottom of my feet. The difference is my height. I make those measurements by placing the end of a tape measure against the floor, and then find where the top of my head is...

This thread is a direct shoot-off from this post in the Insights thread Against "interpretation" - Comments. I am usually not a big fan of Ballentine, but I tend to fully agree with him on the following issue (taken from this paper, credits to @bhobba) Decoherence theory is a pragmatic...

I was reading the free will theorem and it basically says that subatomic particles and observers have to have free will because there's nothing prior to measurement that predetermines the outcome. Here's more: The free will theorem states: Given the axioms, if the two experimenters in question...

If you prepare a particle with a “relatively precise” momentum by the act of filtering or measuring its momentum. It’s state will collapse into a momentum eigenstate and the measured momentum will be the corresponding eigenvalue. The position state will now be nearly uniformly spread out and...

The spacetime and energy momentum relations can be written as t2 - x2 = s2 P+P- = m2 Niels Bohr says that "the spacetime or energy momentum relations must be applied at least twice, otherwise they are not defined". Does anyone know what he means by this?

This question relates to the double slit experiment where measurement affects whether an interference pattern is generated. If an experiment were performed where electrons were sent through a double slit with another double slit behind the first double slit, and the measurement device measured...

Hi. Double slit experiments are being performed successfully with increasingly large molecules. Some physicists (e.g. Anton Zeilinger) believe it might work with viruses as well. Assuming it works with a system that qualifies as a measurement device (be it a virus or something else complex...

Given an ideal "box" as used by Schrodinger; - have a quantum event occur inside it, e.g. sudden cat death with 50% probability. - have a machine in it that sends out a qubit, fully entangled with the box' internal state, at regular intervals. - the qubit is a polarised photon - outside, use a...

Hello, I am trying to measure the time-varying electric field of a parallel plate capacitor using short dipole antenna, but my numbers are off by almost 100 times. I have a parallel plate capacitor, A=23cmx11cm, d=10cm. I apply 10sin(2pi*1KHz) and 10sin((2pi*1KHz)+180deg) to each plate. I am...

I have a graph measuring 1/3 octave sounds checking if they fall into a range so they are within a defined tolerance. If for example, I have 20 specific 1/3 octave frequencies I am looking at, I can figure out a percentage of which of the 20 frequencies fall in tolerance fairly easily...

Would not any real measurement taken on a complex state logically require that the results of the measurement have less information than the state? Although I’m just beginning in QM, it appears to me unsurpring that a real measurement on the complex wave function seems to collapse the wave...