What is Measurement: Definition and 1000 Discussions

Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. The scope and application of measurement are dependent on the context and discipline. In natural sciences and engineering, measurements do not apply to nominal properties of objects or events, which is consistent with the guidelines of the International vocabulary of metrology published by the International Bureau of Weights and Measures. However, in other fields such as statistics as well as the social and behavioural sciences, measurements can have multiple levels, which would include nominal, ordinal, interval and ratio scales.Measurement is a cornerstone of trade, science, technology and quantitative research in many disciplines. Historically, many measurement systems existed for the varied fields of human existence to facilitate comparisons in these fields. Often these were achieved by local agreements between trading partners or collaborators. Since the 18th century, developments progressed towards unifying, widely accepted standards that resulted in the modern International System of Units (SI). This system reduces all physical measurements to a mathematical combination of seven base units. The science of measurement is pursued in the field of metrology.

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  1. M

    I Decoherence references and a question about the measurement problem

    Couple questions here. 1. What do you think is the best source to read about decoherence, both from an intuitive/high level pov, but also with mathematical details. I'd partially read a recommended paper by Schlosshauer a while back, is that still the bible for this? 2. If probabilities in...
  2. nomadreid

    I Confused about the spectrum of an observable

    This is a very elementary question, from the beginnings of quantum mechanics. For simplicity, I refer to a finite case with pure states. If I understand correctly, the spectrum of an observable is the collection of eigenvalues formed by the inner product of states and hence equal to...
  3. The Baron

    I One way speed of light measurement

    Hi so to those of you who don't know the problem here is a video that explains it very well. - I have an idea on how to measure it, can someone please tell me if, and why it is incorrect. Thank you! Okay so we will have a timer, and a lot of mirrors, set up in a circle, a light beam is fired...
  4. graphking

    I Jordan Measurement: Accuracy You Can Trust

    nothing more need to be add(smiling face)
  5. G

    Pressure vessel thickness U.S. measurement

    Hi everyone, In purpose to estimate the corrosion degredation in pressure vessels it is recommended to measure the pressure vessel thickness using an U.S. device. My question is how to determine the number of test points on the shell/caps surface as a function of the pressure vessel size...
  6. nomadreid

    I "Filming" a quantum measurement

    The link is https://www.su.se/english/research/scientists-film-a-quantum-measurement-1.487234 How do they arrive at this distribution over time? It does not appear to be saying that this is the prediction (in it were, then why the "filming"?), and measurement of a single atom's superposition is...
  7. N

    Measurement of frequency deviation in FM signals

    Hi all Is there any way to measure frequency deviation in a recorded frequency modulated time domain data? The little research i have done on net mostly concerns with frequency deviation measurement using spectrum analyzer in real time i.e. data continuously received on spectrum analyzer while...
  8. R

    I Understanding Measurement Probability in Electron Spin: Explained by Susskind

    Susskind explains how if you prepare an electron along any axis n (with an electromagnet) and then measure it along any other axis m, the probability of finding the electron with spin up or spin down is given by the angle between the axis. I have left out the linear algebra, because my question...
  9. Hacker Jack

    Is there such thing as an absolute measurement?

    To want to know the exact quantity of an object whether it be it's length, width, weight etc... Doesn't an absolute measurement only exist in the math/our human Minds. Then go down to quantum scales and that gets even harder because from what point do we even measure from if there is no exact...
  10. BWV

    I Basic measurement theory question

    Trying to get my head around some basic points of measure theory So rational numbers are dense in the reals. I.e., if with , then there exists an such that . It follows that there are then infinitely many such. The Lebesgue measure of any single irrational (or rational number) is zero in...
  11. J

    I Exploring CV Bell State Measurement and Entanglement Swapping

    There is something I don't understand called CV Bell state measurement. In these two experiments they get two entangled beams "by overlapping phase-squeezed light with amplitude squeezed light with a phase difference of pi/2 at a 50-50 beamsplitter" See Figure 11...
  12. B

    B How is the measurement done for the double slit experiment?

    How is the measurement of which path the particle took done for the double slit experiment? When electrons are being sent through the slit. Or when photons are being sent through the slit. Is it an active process or a passive process? I haven't seen an explanation for this and perhaps this...
  13. F

    I Would circumnavigating the Universe allow one way measurement of light's speed?

    Suppose we're in a closed and non-expanding universe. You shine a beam of light in one direction such that it circumnavigates the universe and returns to its starting point from the other side. Now you put a detector at this starting point. Would this be a one way measurement of the speed of...
  14. ohwilleke

    B When Will Fermilab Release Its Initial Muon g-2 Measurement? [new update on August 10]

    Fermilab's E989 experiment is conducting the first precision measurement of the anomalous magnetic moment of the muon (muon g-2) since the Brookhaven lab did so fifteen years ago. It is currently collecting Run-3 data for this experiment, and said that it would be releasing preliminary Run-1...
  15. M

    Rotation angle measurement of pedal with ball and socket joint

    the device that I have is the same as the mirror of this truck.
  16. Someone_physics

    A Conditional time evolution entropy and the experimenter?

    Question --- So I've done a calculation which seems to suggest if I combine the system of a measuring apparatus to say an experimenter who "reacts" to the outcome of the the measurement versus one who does not. Then the change in entropy in both these situations is bounded by: $$ \Delta S_R...
  17. J

    B Implicit error margins based on significant figures

    WARNING: Topic is very pedantic. I have used a set of different physics books over the years, and they have all had a focus on the topic of significant figures, error margins and measurement. I have never quite understood these concepts fully and the relationships between them. One aspect I...
  18. S

    Applying least squares to measurement of nuclei masses and Q-value

    Consider the problem in the attached image. The difference between A and B is 0.0020(20). How does one use the least squares method, particularly in matrix form, to find the best value of the masses of A and B respectively, as well as the Q-value? Aren't more measurements needed for the masses...
  19. J

    I Are all processes CPT symmetric like measurement, stimulated emission?

    https://en.wikipedia.org/wiki/CPT_symmetry says "CPT theorem says that CPT symmetry holds for all physical phenomena" - e.g. we could imagine decomposition of given phenomena into Feynman diagrams and apply CPT symmetry to all of them. However, for some o processes such reversibility seems...
  20. H

    I Bell measurement of distant particles

    Hi Pf I am looking at the figure in wiki about quantum teleportation. https://en.wikipedia.org/wiki/File:Quantum_teleportation_diagram.PNG A wants to send a qubit to B . She receives another qubit from a spdc. so she has to make a Bell measurement on them. Has these qbits to be close in space...
  21. Mr_Allod

    Commutation and Measurement of Observables

    Hello there, I am having trouble with part b. of this problem. I've solved part a. by calculating the commutator of the two observables and found it to be non-zero, which should mean that ##\hat B## and ##\hat C## do not have common eigenvectors. Although calculating the eigenvectors for each...
  22. danHa

    B How do we know that the measurement affects the result?

    how do we know that measuring effect the result . how can we know weather quant would behave differentially if we wouldn't measure it . and if we do know the difference between quant that had been measured for example one quant can interference with it self if it haven't been measured in some...
  23. LCSphysicist

    Calculating the uncertainty with this measurement

    It is supposed to find it with the uncertainty propagation, so i tried by it. $$\delta _{n} = \delta_{\theta}\frac{dn}{d\theta}=\frac{\delta _{\theta}\pi sec(\theta )^{2}}{180} = sec(59,3)^2*\pi*1.2/180$$ $$n = 1.68 \pm 0.08$$ But this uncertainty is quite low, so i am trying to understand if i...
  24. bland

    I Is the measurement problem equally as vexing as entanglement?

    Maybe I've got this wrong, because from what I've been able to glean, how a particle measurement affects another particle which can be on the other side of the Universe in principle is agreed to be 'spooky' and it seems that everyone is happy to simply say, yes this is very mysterious and...
  25. Buzz Bloom

    I Consequences when a measurement is destroyed?

    I would much appreciate it if someone can help me find a source discussing this topic. I tried a search on the Internet with several alternative ways to express the question, but nothing worked. I have in mind a particular example, but I do not know if it is applicable to this question as a...
  26. V

    Finding the probability of making a measurement E1

    Summary:: How to solve this? See attached. This is from Griffiths 3rd edition quantum mechanics textbook, problem 2.7: This is the solution for an infinite square well. I am to find the probability of obtaining E1 where En = n^2pi^2hbar^2/2ma^2. E1 = hbar^2pi^2/2ma^2 When finding the...
  27. DaveE

    Art Article - The first measurement of a star's size

    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
  28. R

    I Measurement of an entangled Particles in two Different Bases

    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 =...
  29. S

    I A query regarding Spin Entanglement Measurement

    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...
  30. S

    Uncertainty in the measurement of the focal length in this experiment

    ##\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 %...
  31. CarawayBlossom

    I Measurement of Entangled Particles causes up or down spin?

    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...
  32. F

    When does the calibration uncertainty contribute to a measurement uncertainty?

    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...
  33. ohwilleke

    I Latest Tau Lepton Measurement Consistent With Koide's Rule

    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...
  34. LCSphysicist

    Doppler radar measurement by an aircraft

    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?
  35. F

    B Quantum Entanglement spin measurement

    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...
  36. entropy1

    I Ontology of measurement and correlation

    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...
  37. entropy1

    I Compatibility of MWI with probability of outcomes

    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?
  38. allisrelative

    Doesn't Wigner's Friend Experiment solve the measurement problem?

    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...
  39. Anonymous1

    B Measurement and Uncertainities

    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.
  40. A

    I CMB creation, distance measurement question

    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...
  41. N

    How to estimate the measurement uncertainty of an oscilloscope ?

    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...
  42. M

    I Question about simultaneous measurement

    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...
  43. Rifat amin

    Software for nuclear cross-section measurement and Irradiation yield

    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...
  44. MichPod

    I What did Heisenberg know about the measurement problem?

    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...
  45. SamRoss

    B Uncertainty versus impossibility of measurement

    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...
  46. LCSphysicist

    Exploring the TL Interval Square Measurement

    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...
  47. W

    B Measurement of an unknown velocity vector of a closed space

    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
  48. T

    B Accurate measurement of the speed of light

    [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?
  49. LarryS

    I Quantum Measurement under Heisenberg Picture?

    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...
  50. Marcin

    I Time measurement in a double slit experiment with single photons

    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...
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