Measurements Definition and 397 Threads

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. J

    I Eigenstates and repeated measurements

    A measurement X collapses the wave function randomly into an eigenstate of X. Then if a different measurement Y is made the wave function will randomly collapse into an eigenstate of Y. So for example if you measure position, the wave function will collapse into a narrow peak. Now if you measure...
  2. A

    I Does the Compton wavelength put a limitation on position measurements?

    I have read on Wikipedia (https://en.wikipedia.org/wiki/Compton_wavelength) that we cannot measure the position of a particle more precise than half of its Compton wavelength, since the photon we would need will be so energetic to produce electron-positron pairs. How does the creation of...
  3. J

    Open-Wire Feedline Measurements

    When investigating 600 ohm ladder line, a few questions come up that I hope some of you can answer. It appears this type of feedline can operate with significant vswr because of its extreme low loss characteristics. On the other hand, impedance matching between the feedline and antenna feed...
  4. C

    How to compare two measurements with uncertainties in terms of sigma?

    Perhaps that statement is just saying how big the t-value is. Like, in this case: t = (1.0 - 0.98) / 0.1 = 0.1 So we can say that our measured value is within 1 sigma from the other measured value. In this case, do we just ignore the uncertainties of the other measured/reference value? It's...
  5. nineteen

    B Defining a Vernier Caliper when a reading is already showing....

    Hey, there was an MCQ question in our term test paper regarding measurements and it was about what the reading was of a vernier caliper. But the least count of it wasn't given. As it was already showing a reading, I was kinda confused on how to define it. Is there any method to define a vernier...
  6. Raschedian

    Information on Different Systems of Units and Measurements

    Hello everyone! I would like to ask a rather comprehensive question. I would appreciate it if you could help me with this. I have started reading a chemistry textbook recently and typically in the first chapter of any basic chemistry course, you come across, measurement, unit conversion, etc...
  7. X

    B Special Relativity: Time Measurements on Two Systems - Mike's Question

    I saw this question on special relativity on the internet: "A spaceship traveling to Alpha Centauri, at 0.95C it takes 4.5 years to get there as measured on Earth.how long does it seems to the spaceship passengers?" the answer was 1.4 years (Lorentz factor of 3.2). this answer makes no sense...
  8. pellman

    I How can one know the initial state from measurements?

    Theoretical problems often begin with "given a system in state ψ0" For example, the 2-slit experiment begins with the assumption of a plane wave incident on the slits. I had always understood to this mean some prior set of measurements had been made to determine the initial state. But how can...
  9. R

    A Finding E_J Value of a Qubit: Step-by-Step Guide

    Hi everyone, I’ve performed microwave measurements on a 3D transmon and want to find the E_J value of the qubit. I’ve tried searching through many papers, particularly Koch et al, about how to do this, but I am stumped. Could someone please help me out? Thanks in advance.
  10. G

    I Photoelectric Measurements & the Nature of Surfaces

    Why are photoelectric measurements sensitive to the nature of the photoelectric surface?
  11. E

    Uncertainty of measurements & significant figures

    Homework Statement This conversion factor 1m = 39.3701 inches was used, when measuring a tape that had inches on it to a full meter. The measuring tape increased by 0.0625 inch increments, so the 1 meter (39.3701) was estimated to be in between the 39.3125 and 39.3750 on the actual measuring...
  12. J

    B Help with Bell states and measurements

    Hi everyone! Sorry for the bad english! I'm trying to understand the "delayed choice entanglement swapping" (avaliable in https://arxiv.org/abs/1203.4834 ) and (long story short) , in the article we have pairs of photons that are entangled in the ## \phi \pm ## Bell state and the photons...
  13. 0

    Simple lift/drag measurements in a wind tunnel

    Hi everyone, I will be conducting wind tunnel tests of a NACA 0012 airfoil to obtain values of lift and drag in a low-speed wind tunnel (approx M = 0.1). I am looking for a really simple way of measuring these forces. Does anyone know of ways to achieve this? I am aware of force balance...
  14. ohwilleke

    I How Much Better Will Top and Higgs Mass Measurements Get?

    The ATLAS and CMS experiments at the Large Hadron Collider (LHC) recently released joint annual review papers regarding their measurements of the properties of the top quark and the Higgs boson, including their masses, respectively. The most recent mass measurement of the top quark are 172.51 ±...
  15. A

    Can More Readings Reduce Fractional Error in Measurement?

    Why is fractional uncertainty not affected by systematic error? For example à vernier calipers measures the diameter of a coin: (5.06+-0.04) mm Can taking more readings, say 6, and taking average, reduce fractional error?
  16. T

    B The Dependence of Angular Acceleration on Moment of Inertia and Mass

    Hey guys, Forgive my ignorance on some of these things. I'm having a bit of trouble understanding the meaning of this question. In a previous question, the angular acceleration was found to be given by α=mgr/(I+mr^2) where I is the moment of inertia for a disk. So, question 6, I figure...
  17. F

    I Significant figures and uncertainty in measurements

    Hello, I was recently pondering on significant figures and uncertainty reminding myself that there is no perfect measurement: every measurement involves an error caused by the instrument and/or the operator. A measurement should be executed as many times as possible and not just once. The...
  18. Alex Torres

    B Entanglement and delayed choice measurements

    A laser gun pumps one photon at a time that goes thru an SPDC process and two entangled photons are generated...photon A and photon B... Photon A is sent to Bob who has a standard DS setup located a couple of meters away from the laser pump... since the photon is in superposition of states he...
  19. Felipe Lincoln

    Basic doubts about measurements and fitting

    Homework Statement Let's say I'm doing a experiment in order to measure a resistance of a single resistor of 200 ohm by its V against I graph, where V is the voltage in the resistor's terminal given by and voltmeter and I the current of the circuit, given by and ammeter. The angular coefficient...
  20. F

    Is there an optimal distance between measurements for regression

    Suppose I am trying to approximate a function which I do not know, but I can measure. Each measurement takes a lot of effort. Say the function I am approximating is ##y=f(x)## and ##x \in [0,100]## Supose I know the expectation and variance of ##f(x)##. Is there a way to compute the confidence...
  21. A Alex P

    B How do scientists measure mass, radius, and distance in astronomy?

    We know mass, radius, distance of Sun and other stars. We also know size, number of stars in our galaxy or others. But, how do scientists measure these parameters ?
  22. Danny Boy

    A Measurements of multipartite entanglement

    Hi I am interested in finding a good measure of multipartite entanglement for pure quantum states represented in the Dicke state basis. Any recommendations of notes or texts in this regard would be appreciated. I am looking to start with the most basic measure of entanglement for states...
  23. M

    I Error of a measurements taken with a multimeter

    Hi, normally when we take a measure with a multimer we consider the error given by this type of tables: http://www.transcat.com/media/pdf/mete35xp.pdf Do you know how these errors are calculated?
  24. binbagsss

    A What is the importance of EM measurements in astrophysics?

    I was asked this in a PhD interview and hit a blank, it seemed to open...
  25. A

    Uncertainty/error of a volume is greater than the normal volume

    Homework Statement I have an empty cylinder with an external diameter of (23.0 ± 0.5) mm, an internal diameter of (22.5 ± 0.5) mm and a height of (60.0 ± 0.5) mm. I need to calculate its volume with its uncertainty/error. Homework Equations The Attempt at a Solution I do it like this...
  26. W

    Stern-Gerlach: Measurements of spin

    Homework Statement Hi all, here's the problem I need help with: Compare the following situations : A beam of atoms has half of them preselected having spin up along z and the other half having spin down along z. This beam is sent through a Stern-Gerlach (SG) apparatus that sorts in the z...
  27. LarryS

    I A Closer Look at the Randomness of Quantum Measurements in QED

    In all Quantum Physics experiments, the sequence of measurement results is inherently random. Consider just the position observable. In the Schrodinger picture of non-relativistic QM, in each measurement-event, nature steps in and randomly selects one of the observable's eigenvalues/vectors to...
  28. Danny Boy

    A Fundamental Theorem of Quantum Measurements

    The Fundamental Theorem of Quantum Measurements (see page 25 of these PDF notes) is given as follows: Every set of operators ##\{A_n \}_n## where ##n=1,...,N## that satisfies ##\sum_{n}A_{n}A^{\dagger}_{n} = I##, describes a possible measurement on a quantum system, where the measurement has...
  29. Danny Boy

    A How Do Quantum Measurements Impact System Coherence?

    The following, regarding quantum measurement, is stated in the paper "Limitation on the amount of accessible information in a quantum channel" : "Our discussion of measurement will be based on a specific physical model of measurement, to which we now turn. Suppose we have a quantum system ##Q##...
  30. Danny Boy

    A Quantum measurement operators with Poisson distribution

    The following is a somewhat mathematical question, but I am interested in using the idea to define a set of quantum measurement operators defined as described in the answer to this post. Question: The Poisson Distribution ##Pr(M|\lambda)## is given by $$Pr(M|\lambda) =...
  31. Paul Colby

    Can Two Cheap SDR Radios Accurately Measure RF Noise Correlation?

    I'm trying to measure correlation between two RF noise sources and as usual trying to do it on the cheep. I've purchased 2 SDRPlay RSP2pro radios. These operate from 500kHz or so to 2 GHz with sampling rates from 2 to 10 MHz. Not bad for $200 and they work well as radios. The RSP2s have in and...
  32. G

    I Spin Measurements: Up vs Down | Gf

    I’ve been watching the Susskind lectures on utube and already confused. Measurement of spin in up state gives up ( in sig z) while measurement of down gives minus down. What experimentally is the difference between down and minus down? Gf
  33. Q

    A Measurements of the Self-Interaction of the Higgs

    Hello Everyone, Hope you are all enjoying learning more and more about this wonderful world of Physics! Is it that I am missing something somewhere, but when I searched the ATLAS site to find out what experiments were planned to measure the self-interaction of the Higgs, I could see...
  34. A

    QM: Purity, two-outcome measurements

    Homework Statement Homework Equations in addition to those provided in the questions, I used the following: Tr(B) = sigma<x_j|B|x_j> purity = Tr(rho^2) The Attempt at a Solution [/B] I find calculating trace and purity very confusing. Am I on the right track with question 1? With...
  35. S

    A Electron's Roundness measurements at JILA

    Just came across this report by Science Magazine about research findings at JILA concerning the measurement of the electric dipole moment...
  36. Auto-Didact

    A Falsifications and constraints due to GW measurements

    This thread is to serve as - a collection of theories that have been falsified by and/or have had new constrained placed on them by the ongoing gravitational wave measurements. - a place to discuss the further constraining/falsifying of still existing models using GW data. I'll start by posting...
  37. D

    Probability that two measurements have the same true value

    Homework Statement I am in a lab course studying Brownian motion. I have gathered data for for movement in two dimensions. I currently have a fairly large data set for ∆x and ∆y and have taken the mean and standard deviation of each. The lab asks what is the probability that these two sets of...
  38. 1977ub

    B Understanding Measurements / Collapse

    I'm trying to understand the impact of past measurements, and when measurements occur. As I understand it, in the simplest case, you've got a particle emitter in the center of a circle, and a measuring plate around the circle. Here in the ideal case the particle is emitted and has equal...
  39. S

    MHB Convert blueprint measurements to usable feet and inches.

    I have to read house plan blueprints and convert the measurements on the plan to usable feet and inches to do layouts in feet and inches.
  40. morrobay

    B Entangled Photon Measurements: A(t) = d/c and B(t) = 5d/c

    Entangled photons in superposition state : | Ψ} = (|HV} - | VH})/1/√2 are sent from source to polarizers and then to detectors A and B ( in this setup distance from source to detectors is equal). If A measures vertical photon she knows immediately that B photon must be horizontally...
  41. I

    More questions about 2 state system measurements

    Homework Statement Homework Equations I know that there are two eigenstates of the operator C: |B> = (1 0) as a column vector with eigenvalue 1 |R> = (0 1) also a column vector with eigenvalue -1 The Attempt at a Solution I'm attempting to solve part c (second image). My initial...
  42. A

    I Calculating expected number of measurements

    In my Physics lab, we divided into groups and our task was to throw darts on a target containing 13 bins. The ultimate goal is to hit bin 7. The bins look something like the image below. At the end, our class combined each groups average, standard deviation, and standard error (located below)...
  43. K

    I Preamplifiers in radiation measurement systems

    In the radiation detection, it's of common use pulse-type systems, which have a preamplifier between the detector and the amplifier. I have read that the preamplifier primary function is reduction of attenuation of the signal that exits from the detector by matching the impedance of the detector...
  44. R

    I How does sequential measurement affect observable data in molecules?

    I'd like to understand and know actual examples of how sequential measurements of different observables (position, energy, charge, etc.) in the same molecules can affect them giving rise to changes in the IR and Raman spectroscopy data. For example.. when you sequentially measure the molecules...
  45. J

    A Discrete measurement operator definition

    Consider the Gaussian position measurement operators $$\hat{A}_y = \int_{-\infty}^{\infty}ae^{\frac{-(x-y)^2}{2c^2}}|x \rangle \langle x|dx$$ where ##|x \rangle## are position eigenstates. I can show that this satisfies the required property of measurement operators...
  46. T

    Weight measurements and gravitational acceleration

    Hi all, Since the gravitational acceleration varies depending on location, then how do you know if your scale is precisely calibrated? If I use a calibration weight (e.g. 100.000000 g) that was manufactured and tested around at equator where g=9.780 m/s^2, in my lab at the north pole where...
  47. FallenApple

    I Measurements at the Cosmological Horizon?

    Under the holographic principle, the physical description of the 3d world at a particular location in spacetime is encoded on the two dimensional cosmological horizon that encapsulates it. Does that imply that the "measurements" taking place on a 2d shell that is the horizon is creating new...
  48. ohwilleke

    B The Latest Higgs Boson Mass Measurements

    It is summer conference season for physicists and one of the highlights this time around is the first set of new Large Hadron Collider Run-2 measurements of the Higgs boson mass. The Status Quo At the end of Run-1 at the Large Hadron Collider (LHC), the combined estimate of the Higgs boson...
  49. A

    B Measurements on the entire universe

    I can not claim that I fully understand my own question, but I feel it is worth sharing. Suppose there is a physical system composed of MxN degree of freedom where M is the number of the states and N the number of particles. When a measurement is undertaken, the physical system collapses to...
  50. Johny Boy

    A Using feedback in quantum measurements

    If we consider an efficient measurement performed on a system in a pure state. How would we use feedback (by applying to the system a unitary operator that depends upon the measurement result), to prepare the system in the same final state for every outcome of the measurement (this can be done...
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