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. bhobba

    A Interesting Paper On QFT and Quantum Measuremets

    I recently came across the following paper on QFT and Quantum Measurements. https://arxiv.org/abs/1311.0205 I have read it, but it may not be legit as it seems to accept the idea of virtual particles, which I find somewhat problematic, as discussed before. Before reaching any conclusions, I...
  2. keyzan

    Probability of the outcomes of ##J^2## and ##J_{z}##?

    Hi guys, I have a problem with point 2 of this exercise: The electron of a hydrogen atom is initially found in the state: having considered the quantum numbers n,l,m and epsilon related to the operators H, L^2, Lz and Sz. I am asked: determine the possible outcomes of a measurement of J^2...
  3. H

    A Repeated measurements and granular space time

    Hi Pfs, I would like to know if it would be possible for our known theories to derive conservation laws if space time was really granular. I think that entanglement is the only process which would succeed.
  4. flyusx

    What To Project Upon When Doing QM Measurements?

    I have read that if one measures the Hamiltonian and receives a value of h2, then the quantum state will be in ##|h2\rangle##. Finding the probability of a1 is done by projecting ##|a1\rangle## upon ##|h2\rangle## divided by ##\langle h2|h2\rangle##. In other words: $$\frac{|\langle...
  5. A

    Uncertainty Error and Significant Figures in this Force Tables Lab

    TL;DR Summary: I have a Force Table Lab and am not sure if the "percent error" is the correct way to express errors. I also need some help on sig figs for my results. Hello, I am working with the usual undergrad force tables apparatus. I would like to know how to express the results of...
  6. D

    Atomic diameter-scale measurements

    To be more precise: can we put two objects together so there will be a space with width of one (or some number below 10) atom's diameter(s) between them?
  7. M

    A Updated Hubble constant from TRGB measurements

    Scolnic et al have put out a new preprint with an updated value for the Hubble constant as measured from the Tip of the Red Giant Branch: https://arxiv.org/abs/2304.06693
  8. A

    I Repeated measurements on a quantum system interacting with other quantum systems

    In quantum mechanics if I repeat a measurement of the same observable in succession I get the same quantum state if it is not a degenerate state. If I make the system under consideration interact with another quantum system and meanwhile keep measuring it what happens? Does the system not...
  9. E

    I Error Propagation in Measurements

    I was imagining trying to construct a rectangle of area ##A = xy## If we give a symmetric error to each dimension ##\epsilon_x, \epsilon_y## $$ A + \Delta A = ( x \pm \epsilon_x )( y \pm \epsilon_y )$$ Expanding the RHS and dividing through by ##A## $$ \frac{\Delta A}{ A} = \pm...
  10. A. Neumaier

    I Can POVM measurements be explained by projective measurements?

    For the background of the discussion see my Insight artice ''Quantum Physics via Quantum Tomography'' and the posts #405 and later of the thread ''Nature Physics on quantum foundations''. Trying to translate your statements into precise formulas, and using ##\Pi## in place of ##E## (which to me...
  11. S

    Probability of Hypokalemia w/ 1 or Multiple Measurements

    TL;DR Summary: Finding the probability with one measurement and multiple measurements on separate days. Question: Hypokalemia is diagnosed when blood potassium levels are low, below 3.5 mmol/L. Let’s assume we know a patient whose measured potassium levels vary daily according to N(µ = 3.8...
  12. atyy

    I Relativistic Bohmian trajectories of photons via weak measurements

    I found out about this interesting paper through a Tweet by Steven Thomson. https://arxiv.org/abs/2108.05169 https://www.nature.com/articles/s41467-022-31608-6 Relativistic Bohmian trajectories of photons via weak measurements Joshua Foo, Estelle Asmodelle, Austin P. Lund, Timothy C. Ralph...
  13. T

    Understanding the Basics of VNA Measurements with an SMA Connector

    I have a VNA with an SMA connector for measuring reflection. If I connect only the center conductor of the SMA to a piece of metal, I get a spectrum. My question is, what should I be doing with the outer connector? I am trying to learn EE by reading and doing. I don't have a lot of intuition...
  14. Element13

    Construction Leveled Ceiling, Uneven Measurements - What's Wrong Here?

    Hi All, I received good insight from a previous post, https://www.physicsforums.com/threads/pulling-a-heavy-load.1015640/#post-6637181, now that I'm at the point of expanding the drawer support on the ceiling, I ran into the following. How is it that my level says it's leveled but the tape...
  15. A

    Inconsistent flow rate measurements of an engine diesel fuel

    I am measuring the volumetric flow rate of a diesel fuel using "Turbines" flow meter, both in the supply and return fuel lines of an industrial diesel engine (https://www.cat.com/en_US/products/new/power-systems/industrial/industrial-diesel-engines/18398034.html – coupled with a generator for...
  16. B

    I Isotope measurements in molecules

    Hello! Is there any measurement (can be from different papers/experiments) of a diatomic molecular isotopic chain (i.e. at least 3 isotopes of a given nucleus) where the ground state is ##^{2}\Sigma##?
  17. H

    I Can we determine the one way speed of light by combined measurements?

    The idea is to have 2 clocks at position A and B. The clocks are synchronized by sending a light pulse from position S over 2 equal distances x. The receiver is at position R at a distance y rectangular to the direction AB and exactly in the middle between A and B and right below S. for proofing...
  18. H

    A Exploring Quantum Measurements and Unitary Operators

    Hi Pfs I read this answer in https://quantumcomputing.stackexchange.com/questions/136/if-all-quantum-gates-must-be-unitary-what-about-measurement Quantum measurements are special cases of quantum channels (CPTP cards). Stinespring dilation states that any quantum channel is realized by...
  19. nuclearsneke

    I Uncertainty in measurements of the thickness of a pile of pellets

    Howdie! We have been playing around with melting and molding HDPE pellets recently. After that, we measured their diameter and thickiness 5 times each to get an uncertainty. In our experiments we put one pellet between gamma-source and detector and measure its attenuation. After that we place...
  20. entropy1

    I MWI and interpretation of measurements

    I was wondering, if we have a measurement of, say, spin of an electron, which can yield spin-up and spin-down in the context of MWI, then the electron gets entangled with the measurement device, yielding the wave function ##|Measurement_{spin-up}, Value_{spin-up} \rangle +...
  21. gxa

    Measurements with the CsI(Tl) detector

    I made an experiment in the lab. I took some measurements with the CsI(Tl) detector by placing the cobalt at a distance of 5 cm. I have attached the measurement result. I need to find the count for the peak energies. How can I do it? Any idea?
  22. greg_rack

    Engineering Exploring the Confusing Impact of Compressibility on CL Measurements

    This situation is really confusing me. First of all, does accounting compressibility affect the measurements for CL? If yes, how does CL change as a function of the increasing mach number? Back to the problem, above is the "in-flight" lift curve for a plane traveling at high speeds, so the CLs...
  23. J

    I Do measurements modify angular momentum and energy?

    While physics is generally believed to be CPT symmetric, there are processes for which such symmetry is being questioned - especially the measurement. One of examples of (allegedly?) going out of QM unitary evolution is atom deexcitation - we can save its reversibility by remembering about...
  24. F

    Instrument accuracy and comparison measurements

    Hello, All measurement instruments have a finite accuracy. For example, a thermometer may provide a temperature measurement that is +-2F from the "actual" and true temp value. For example, if the reported measurement is 70F, the actual temperature may be between 72F and 68F. That said, let's...
  25. B

    Light Transmission Measurements: What Else Can You Find?

    If you measure the light transmission over time of the human thumb you can get the heart rate. Is there another thing you can get by using light transmission ? like the Heart rate? can you find bacteria in water using light transmission ?is light transmission measurement even the right word ?
  26. K

    I Advantage of having more measurements

    Hello! I have some points in the plane, with errors on both x and y coordinates. The goal of the experiment is to check if the points are consistent with a straight line or not i.e. if they can be described by a function of the form ##y = f(x)=a+bx## or if there is some nonlinearity involved...
  27. Ghost Quartz

    I Simultaneous measurements of 1 observable

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  28. fluidistic

    Quantum Schwinger's Quantum Mechanics: Symbolism of Atomic Measurements

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  29. L

    I Quantum Measurements with Gravitational Waves

    Would using gravitational waves to measure (it's obviously a gedankenexperiment!) position and momentum of, say, an electron in a specific state, disprove HUP since the quantum of energy of grav. waves does not exist? Would it be possibile to have an arbitrarily small uncertainty in position...
  30. M

    I Constraints on BSM from EDM measurements

    Hello! I see that the experiments looking for electric dipole moment (EDM) of fundamental particles (especially for the electron) are able to place constraints on new BSM particles with masses of around 10 TeV or even more, in a model independent way i.e. we just need to measure a non-zero...
  31. S

    What is zero error of a measuring instrument ?

    Is this correct? "The systematic error in a measuring instrument due to non-uniform or wrongly marked graduation due to which a measurement may be less or greater than actual measurement is called zero error of the measuring instrument". Another one: The measuring instruments are combination...
  32. C

    I Low p_t cuts in experimental measurements

    Just few questions based on experimental presentation of results: In (semi-)inclusive measurements (say, p + p -> Y + X), producing some well defined state Y and the rest, X, summed over, is there typically a minimum cut made on the p_t of the state Y? If so why? What is the reason of...
  33. ORF

    Lab Experiment: Estimate the error in these measurements of Ohm's law

    Hi, I have measured a set of V-I values, and I have to provide the value of the resistance. I have used ac and dc current. The circuit was quite simple: power supply -> ammeter -> resistance -> [power supply] wave generator -> ammeter -> resistance -> [wave generator] Voltage was measured...
  34. Omega0

    B Measurements - How can it be that precise?

    I have a question about statistics or measurement technology. Let be ##K## and ##N## natural numbers. We measure a variable ##x_{kn}## where ##k\in\{1,K\}## and ##n\in\{1,N\}##. Let us say that you have ##K## measurement series to measure ##N## values ##x_{kn}## No matter how big ##N## is...
  35. C

    I Correctly Scaling the Standard Deviation for Scaled Measurements

    We're working on a project that plots flux density of a light curve with respect to time. To do this, we had to scale data from different wavelengths so we had just the one variable for the flux. Essentially we took each value for flux density and multiplied it by three over the frequency raised...
  36. U

    B Calculating Uncertainty of Mean for 0.5 mm Ruler Measurements

    I am following this: avntraining.hartrao.ac.za/images/Error_Analysis.pdf I have a ruler with an uncertainty of ± 0.5mm. I made a calculation subtracting one measurement of the ruler, from another measurement, making the uncertainty for the data ± 1.0mm. As I have four trials, I calculated the...
  37. E

    How Do Measurements Affect GHZ States?

    Here's what I think I understand: First off, the GHZ state ##|GHZ \rangle = \frac {|000\rangle+|111\rangle} {\sqrt 2}##, and ##\sigma_x## and ##\sigma_y## are the usual Pauli matrices, so the four operators are easy to calculate in Matlab. I'm thinking the expectation values of each operator...
  38. E

    Projective measurements of quantum processor

    Am I correct in thinking that the system measures the probability |<f|1>|^2 for some state <f|? Then the probabilities for each of the six states would be: |<0|1>|^2= 0 |<1|1>|^2= 1 |<+x|1>|^2= |(1/√2)|^2 = 1/2 |<-x|1>|^2= |(-1/√2)|^2 = 1/2 |<+y|1>|^2= |(-i/√2)|^2 = 1/2 |<-y|1>|^2= |(i/√2)|^2...
  39. Tone L

    Optical Measurements of the Sun's radiance and ray tracing

    Summary: This is a hobbyist project I am working on. I am building an instrument to measure radiance from the sun at 500 nm, using optically filtered photodetector with bandwidth ± 10 nm. This type of science can be called Sun Photometry, so let's get to it! Geometry for Optics: The sun has an...
  40. K

    Uncertainties in a set of measurements

    Suppose I measure the distance between two objects for three trials. The two objects then get farther away, and I measure the distance between them again for three trials. I repeat this for 3 more different distances, getting a total of 15 measurements (3 trials for 5 distances). I then compute...
  41. D

    Find distance using map measurements

    Summary:: That is the problem down there. The scale on a map is 1 inch (in.) ? 80 miles (mi). If two cities are 2 & 3/4in. apart on the map, what is the actual distance between the cities? So what I did was convert the scales 80/1 mi per in. and multiplied it to 2 & 3/4in which I got an answer...
  42. A

    How to calculate the 3D straight line distance between 2 GPS measurements?

    This seems like a trivial question at first, but I am struggling how to get it right. If I have 2 GPS (lat, lon, height) observations P1 and P2 taken at some height from the Earth's surface, how do I calculate the straight line distance between them? I am using the picture below to illustrate...
  43. G

    I Is there a reason eigenvalues of operators correspond to measurements?

    Given a wave function \Psi which is an eigenstate of a Hermitian operator \hat{Q}, we can measure a definite value of the observable corresponding to \hat{Q}, and the value of this observable is the eigenvalue Q of the eigenstate $$ \hat{Q}\Psi = Q\Psi $$ My question is whether it's a postulate...
  44. O

    Electromagnetic radiation measurements

    What does a measure of 2000 µW/m² electromagnetic radiation by "Hf35c Rf Analyze (800mhz – 2.5 Ghz)" radiation meter mean? Is it too high? see this link: https://www.electrahealth.com/hf35c-radio-frequency-meter.html it shows that “1000 or more µW/m²” in the meter is “Extreme Concern”, does it...
  45. K

    I Exploring Photo-Sensor Measurements for Brightness Change Evaluation

    Hello, I'm using photo-sensors from commercial and industrial cameras to document an experiment. Afterwarde I evaluate the change in brightness during the test of a fixed segment of every image I took. The ambient light condition is stable and the images are in raw files, but I'm unsure how raw...
  46. Michael Price

    A Measurements and electroweak gauge invariance/transformations

    Most gauge transformations in the standard model are easy to see are measurement invariant. Coordinate transformations, SU(3) quark colours, U(1) phase rotations for charged particles all result in no measurable changes. But how does this work for SU(2) rotations in electroweak theory, where...
  47. H

    Speed measurement -- Limitations to "instantaneous" measurements?

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

    B Calibrating measurements from scratch

    Assuming you are in the field and don't have any device to weigh, measure volume, or measure time. How would one establish accurate measurements? Where does one start?
  49. E

    B Confusion over spin measurements

    I will refer to the spin example outlined in the opening chapters of the Theoretical minimum. Suppose we prepare a spin with a z component of +1. If we rotate the apparatus about 180 degrees, the ‘classical component’ of the prepared spin vector along the new axis of the detector is -1, so...
  50. Marilyn67

    A Influence of strong measurements in a Two Slit Interferometer

    Hello, I am interested in weak measures since I discovered this paper: https://arxiv.org/ftp/arxiv/papers/1206/1206.6224.pdf I understood that retro-causality is only an interpretation and that's not more exploitable than the famous experiments of quantum gum delayed choice. In fact, we...
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