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. 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?
  2. 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...
  3. 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...
  4. L

    Can Ultrasonic Sensors Accurately Measure Gas Tank Levels?

    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!
  5. R

    B Scale of Measurement vs Equipment Sensitivity: Does Symmetry Always Hold?

    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...
  6. N

    Inflation and measurement of cosmic bodies

    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...
  7. Quantum Alchemy

    I Wigner's Friend shows the difference between Observer and Measurement

    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...
  8. entropy1

    I Observer superposition in MWI?

    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?
  9. UnderstandingQT

    B Questions about measurement devices in the double slit experiment

    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?
  10. entropy1

    I What does it mean to influence a quantum measurement's outcome?

    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}##...
  11. Quantum Alchemy

    I What exactly is a measurement device and how does it work?

    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...
  12. pinball1970

    A Quantum measurement of a Strontium ion

    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?
  13. E

    A Time Measurement in Friedman Metric: Physically Possible?

    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?
  14. K

    Voltage measurement on a Current Transformer (CT)

    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...
  15. bluemystic

    Standard deviation vs measurement uncertainty

    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...
  16. entropy1

    I Does information get lost by measurement?

    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?
  17. Demystifier

    A Is theory of measurement an oxymoron?

    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...
  18. Jamister

    Quantum Book for quantum measurement theory

    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
  19. carter7gindenv

    Decoding Thermal Measurement Equations with KD2 Pro

    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 +...
  20. P

    I Collapse of the wave function under simultaneous measurement

    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...
  21. H

    Rotate IMU data to obtain correct measurement data

    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...
  22. A. Neumaier

    I What is the POVM generalization of Born's rule for quantum measurements?

    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...
  23. Piotrovskiy Yury

    B Kelvin - not the basic, but the derived unit of measurement?

    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...
  24. W

    A Time Measurement in MT Traversable Wormholes - Help Needed

    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...
  25. nomadreid

    I Entanglement after measurement

    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...
  26. E

    I Macroscopicity and the measurement problem

    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...
  27. Arman777

    I Which redshift value is used in the velocity measurement of distance

    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...
  28. R

    Orientation of the Ferroelectric Hysteresis Loop -- Why is it different now?

    (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...
  29. beefbrisket

    I Taking a partial trace of a multipartite state for measurement

    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...
  30. entropy1

    I Can we accurately determine the trajectory of an electron using a SG detector?

    Would this be an accurate portrayal of measuring the spin of an electron with a SG detector?: The electron is in a superposition of spin-up and spin-down; Upon entering the magnetic field of the SG detector, the electron enters a superposition of an upward trajectory and a downward trajectory...
  31. phyzguy

    I New measurement of the Hubble constant is consistent with the CMB value

    This paper just came out with a new measurement of the Hubble constant based on the technique of gamma ray attenuation. The result is consistent with the lower (CMB-based) value. Interestingly, they also do a joint analysis of several non-CMB techniques (BAO+BBN+SN+γ-ray attenuation), and find...
  32. P

    Many Worlds and the Measurement of an Electron

    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...
  33. T

    Probability of Measuring ##L_x = 0## for a Given ##\psi##

    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...
  34. F

    Is Voltage a measurement of pressure?

    Summary: Volts When measuring an electrical currents voltage, are you actually measuring the pressure emitted in electricity
  35. entropy1

    I Orthogonal eigenvectors and measurement

    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...
  36. B

    How to calculate Carrier Concentration vs. Depth from a CV measurement?

    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...
  37. A

    B Measurement postulate = von Neumann’s projection postulate?

    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...
  38. entropy1

    I Conservation of energy and measurement problem

    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...
  39. H

    Speed measurement -- Limitations to "instantaneous" measurements?

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

    I New proton radius measurement with electrons favors "muon value"

    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)...
  41. vanhees71

    A The thermal interpretation and measurement

    [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...
  42. entropy1

    I Does a measurement setup determine the reality of spin measurement outcomes?

    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...
  43. microsansfil

    A Bohmian mechanics for instrumentalists and quantum measurement

    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...
  44. A. Neumaier

    A Weinberg on the measurement problem

    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...
  45. C

    I "Spatial Width," "Coherence Length," and the Measurement Problem

    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...
  46. W

    I New measurement of the Hubble Parameter

    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...
  47. fsonnichsen

    Precision Temperature Measurement

    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...
  48. P

    I Can you locally tell that a measurement you made was entangled?

    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...
  49. L

    I Is the Measurement Apparatus made up partly of electrons? Perhaps not.

    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...
  50. M

    I Can ambiguity in the word "measurement" allow contradictions in QM?

    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...
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