Measurement Definition and 1000 Threads

A bit of physics history in this article. How Michelson (yes, that Michelson) measured the first stellar diameter (ok, except for the sun) at the Mt. Wilson Observatory. https://www.mtwilson.edu/wp-content/uploads/2019/12/50971-MtWilson-proof.pdf

Consider two entangled spin half particles given by the generic form of Bell Equation in Z-axis: ##\psi = (a\uparrow \uparrow + b\downarrow \downarrow)## where ##a^2+b^2=1## In a (2D) planer rotated (by an angle ##\theta##) direction the new equation can be given by: ##|\psi \rangle =...

Given a pair of Spin ##1/2## entangled particles created in the ##z^→## direction according to the following equation ##Ψ=1/√2(\uparrow\uparrow+\downarrow\downarrow)##. One entangled particle is sent to Alice and another to Bob. Now if Alice measures her particle in the ##z^→## direction she...

##\frac{1}{f}=\frac{1}{u}+\frac{1}{v}## ##f = \frac{u.v}{u+v}## Let: u + v = w → w = 250 mm ± 8 mm Percentage uncertainy of v = (3/50) . 100% = 6% Percentage uncertainty of u = (5/200) . 100%=2.5% Percentage uncertainty of w = (8/250) . 100% = 3.2% Percentage uncertainty of f = 6 % + 2.5 %...

In reading around, it seems that in the case of entangled particles, it is the measurement of one of the particles that causes the other one to be it's opposite spin and that there's some means of info transfer going on caused by the measurement. I'm not understanding why it would not be that...

Often a calibration certificate for an instrument has the error found during the calibration as well as the uncertainty associated calibration itself. I'm reasearching uncertainty calculations using the GUM 1995 method and I haven't found one yet that includes the uncertainty of the calibration...

The latest tau lepton mass measurement, from Belle II is 1777.28 ± 0.75 (stat.) ± 0.33 (sys.) MeV/c^2. The combined error is ± 0.82 MeV/c^2 (which is 0.38 sigma greater the the Koide's rule prediction). This is consistent at a one sigma level with the current Particle Data Group world average...

u is the aircraft speed. c is light speed f is the initial frequency λ is the initial wavelength λ' is the apparent wavelength λƒ = u +λ'ƒ λƒ = u + (c/ƒ')*ƒ c = u + (c/ƒ')*ƒ u = c(1-(ƒ/ƒ')) u = 1500m/s The answer is half of it, where is my error?

Hi, When a quantum entangled photon is measured to determine spin does it's spin stay in that orientation as long as it's measured it or does it immediately go back to a superpositioned state? In other words if you determined the spin of a quantum entangled particle at say 12:00 pm and...

If a non-commuting measurement is made on a quantum property (like spin), this can be seen as the wavefunction being prepared. So you can't tell if the outcome represents the property, or that the property is prepared. However, if the property is prepared, we can predict the correlation with a...

Can MWI account for the probabilities of outcomes? If MWI says all outcomes are realized, is the probability that an outcome occurs then not 100%? How is this explained with the entanglement of the measured object and the measurement apparatus?

If you look at the recent Wigner's Friend experiment, it seems to support Carlo Rovelli's Relational Interpretation which says there's no real measurement. Wiger's Friend carries out a polarization measurement. Before he does, the quantum system is in a superposition of horizontal/vertical...

Can someone explain this page to me please, Especially the part where it says (0.0390, 7.88). By the way, I am new here.

How do we know it;s redshift for certain? because unlike with stars the CMB doesn't have spectral lines nor other "similar" objects to compare to as it is everywhere and the same. From what I understand first came the theory and model of the Big bang, then Hubble saw that distant galaxies are...

I have an Textronics oscilloscope with 500 MHz sampling rate and using an 50 ohm cable for the measurement. I can’t find the measurement uncertainty in the manual or the calibration sheet. In the calibration sheet it says an ‘uncertainty’ for the used channel in divisions, for example 1m up to...

Greetings - I have a question about observables and Quantum Mechanics. Let's say I want to measure the spin state of a particle. If I measure σZ (sigma Z), I will get either +1 or -1. That will then prepare the spin state accordingly. If I measure σX (sigma X), I will get either +1 or -1...

I work in research paper on medical isotope production. I need a software where i can measure the cross section and Irradiation Yield like TALYS and EMPIRE. If you ask me why i don't use TALYS then the reply is I can't install it on my PC. so i am looking for alternate software where i can do...

While reading a book "Physics and Philosophy: The Revolution in Modern Science." by Werner Heisenberg, 1958, I was much surprised by the following passage near the end of Chapter 3: "The measuring device deserves this name only if it is in close contact with the rest of the world, if there is...

The uncertainty principle tells us that there is no state that a particle can be in such that we can predict with certainty both what the result of a position measurement will be and what the result of a momentum measurement will be. This statement is not the same as saying we can't measure the...

I was reading about the general theory of relativity, and came to a chapter that the author start to talk about an invariant measurement by [TL] named interval square. It's the first time that i read about it, and i don't get it yet. An event, what he is calling, is anything? If I am thinking...

Hi I found this paper on the measurement of unknown velocity vector of a closed space. Does it mean that it is possible to measure the unknown velocity vector of a closed space ? Can someone explain it to me

[Mentors' note: Split from https://www.physicsforums.com/threads/is-there-a-thought-experiment-to-show-that-the-speed-of-light-is-constant.986641/] If I could provide you with a device to measure the speed of light, and the accuracy can reach 0.01 m/s, what would you do?

When a quantum measurement occurs under the Schrodinger picture, the wave function collapses to one of the eigenvectors of the operator-observable and the value measured is the corresponding eigenvalue of that eigenvector. What happens during a quantum measurement under the Heisenberg picture...

Assumption: Screen detector is much closer to the slits than in "standard experiment" and the small angle approximation can't be used to determine the interference fringe maxima, but the interference pattern still occurs. Is it possible to measure the time of detection in such setup accurately...

Hi Folks, I am exploring using Ultrasonic for LGP tank level measurement. I went through lots of readings, in particular use of SRF02 sensor. But, It's not conclusive. Anyone has been exposed to solving such problem? If yes, kindly share return on your experience. Appreciate!

Many times when i ask about test theories of SR, i am reminded by forum members, that equipment sensitivity, is equivalent to producing more extreme physical values. For example, you don't necessarily have to go faster in speed, in order to have a better measurement of time dilation, if you have...

Hi, Is it true that measurement proves the universe has inflated by 13.8 billion light years, and if so, how do we estimate the age or distance of those measurements? What's giving me pause is my assumption that the oldest light measured (furthest away) is 13.8 billion light years old, but...

You often hear this debate about the role of the observer in Quantum Mechanics. How you view this role is usually dictates the interpretation you prefer. If it's Copenhagen, then the observer is more robust and plays a crucial role in wave function collapse. If it's Many Worlds, then the...

In MWI, would you say that a measurement puts the observer in superposition of being in the various worldlines? If I said "yes" to that, would I be correct?

How did you find PF?: Google Is it true that the devices that quantify which slit do NOT produce wave collapse unless they actually record the light measurements rather than just detect them without recording?

This just occurred to me and I don't expect to be the first one to address it: It is said that in a specific measurement basis, the outcome of a measurement in this basis is determined by chance. But in how far is this the case, since if the eigenvectors are for example ##\overrightarrow{A}##...

What exactly is a measurement device and how does it carry out a measurement? For instance, in the double slit experiment, you always hear about particle/wave duality. When it's not being measured it behaves like a wave but when a measuring device is placed by the slits, it behaves like a...

I cannot post the science alert article where I saw this. Apologies, this put the study in layman's. @PeterDonis @vanhees71 et al will not need that. Is this significant? Could the wave function not instantaneously collapse?

If a proper time measuring clock goes along for the ride between events, then is such a clock physically possible as the scale factor changes / increases in the Friedman metric? How could any clock have zero spatial changes for that situation?

I don’t know the ratio of the CT. I’m just looking for an explanation on this. I thought in order to measure output voltage you need to pass the current through a resistor and read the voltage drop. A co worker put 400a through the CT and measured 130v. Something just seems off to me. Can you...

Using the above formulas, we can arrive at an unbiased estimate of the standard deviation of the sample, then divide by sqrt(N) to arrive at the standard deviation of the average. What I'm confused about it where the measurement uncertainty comes into the equation. Is it being ignored? Say I...

If we consider quantum wavefunction-collapse, when we end up in a world-thread with a specific value of the measurement outcome, has information got lost?

This thread is inspired by the statement of @vanhees71 in https://www.physicsforums.com/threads/books-about-interpretation-and-philosophy-of-physics.983540/post-6290970 : "What a measurement is, is not defined by philosophers (not even by theoretical or mathematical physicists) but by the...

I'm looking for a book about the theory of measurement in quantum mechanics. A book that goes deep into understanding different kinds and ways. thank you

Hello, I'm working with a thermal property measurement tool (KD2 pro). The manual provide the equations used to measure temperature but I'm not sure that I understand them correctly. Temperature during heating (equation 1) T= m0 + m2t + m3 ln(t) Temperature during cooling (equation 2) T= m0 +...

Considering Bell’s theorem and the expected correlations between entangled particles or photons. In a measurement setup e.g. Like Alain Aspect‘s with 2 entangled photons. If we could make a setup that guarantees that the measurement on both photons is done at exactly the same moment, what...

Hi I have collected data from a IMU on a boat. Currently I am using the angular velocity measurement vector ##\omega^b_{imu} = \begin{pmatrix} p\\q\\r\end{pmatrix} ## for use in kalman filter, where superscript ##b## is BODY frame. The BODY frame is given be x-axis pointing forward, y-axis...

I just placed my new paper Born's rule and measurement on the arXiv. It contains a self-contained discussion of the POVM generalization of Born's rule for quantum measurements. It is a much extended, polished version of my contributions to the thread How to teach beginners in quantum theory...

1. Kelvin - not the basic, but the derived unit of measurement? Modern physics believes that kelvin is the basic unit of measurement of SI (one of seven). At the same time, in all encyclopedias and textbooks it is written: T= Θ/k = Θ /1,380649x10е-23 Θ - is the energy of the molecule in...

I am reading this article now :http://www.cmp.caltech.edu/refael/league/thorne-morris.pdf. And i am a little bit confused about the Eq.(38a)and Eq.(38b), which means the time measured by traverller and people in the sataion, and I just think the time measured by traveller should be his proper...

Three related questions: (a) In a pair of entangled particles, after one is measured/observed/determined/collapsed, my understanding is that the measurement breaks the entanglement so that after the measurement, unless something happens to re-entangle them, they are no longer entangled. Correct...

Assuming the validity of the Heisenberg-von Nuemann cut, does the measurement problem influence the macroscopic nature of the macro world? Quantum effects, roughly speaking, 'lose' their quantum nature over the many degrees of freedom of many-particles systems(cars, chairs...) via averaging out...

Let us say that we have a stellar object so its total velocity is defined as $$ v_{tot} = v_{pec} + V_{rec}$$ Where $$V_{rec} = H_0r$$ and $$V(z) = \frac{cz}{1+z}[1+\frac{1}{2}(1-q_0)z - \frac{1}{6}(1-q_0-3q_0^2+j_0)z^2]$$ for small z.So my first question is what is the $z$ value here? Is...

(Edited with suggestions from Berkeman) After reading the original 1930 paper by Sawyer and Tower (link to original paper here), I noticed that their hysteresis loops are mirrored around the y-axis from many of the ferroelectric hysteresis loops reported today ( see FE examples here, here...

I am attempting to understand how POVMs fit in with quantum measurement, and I think I am getting tripped up in notation when it comes to multipartite systems. The situation is as follows: System: \rho_A Measurement instrument: \rho_B = |\phi\rangle\langle\phi| (pure state) The multipartite...