# What is Measurements: Definition and 394 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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7. ### 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...
8. ### 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...
9. ### 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...
10. ### 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...
11. ### 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...
12. ### 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...
13. ### 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##?
14. ### 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...
15. ### 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...
16. ### 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...
17. ### 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 +...
18. ### 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?
19. ### 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...
20. ### 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...
21. ### 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...
22. ### 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 ?
23. ### 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...
24. ### I Simultaneous measurements of 1 observable

Hi. I'm new to the forum and and I am currently studying quantum mechanics. According Sakurai, page 24, "When the measurement is performed, the system is" thrown into" one of eigenstates of observable". This raised some questions for me: Is possible two measurements simultaneous of one...
25. ### Quantum Schwinger's Quantum Mechanics: Symbolism of Atomic Measurements

I had never heard of Schwinger's Quantum Mechanics: Symbolism of Atomic Measurements until very recently. I wonder what you people think about that QM textbook. Is it a good introduction to QM? A reference? Or, possibly an outdated and bad book? At first glance, it seems a masterpiece to me...
26. ### 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...
27. ### 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...
28. ### 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...
29. ### 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...
30. ### 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...
31. ### 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...
32. ### 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...
33. ### 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...
34. ### Measurements of GHZ state

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...
35. ### 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...
36. ### 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...
37. ### 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...
38. ### 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...
39. ### 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...
40. ### 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...
41. ### 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...
42. ### 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...
43. ### 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...
44. ### Speed measurement -- Limitations to "instantaneous" measurements?

Is instantaneous limited to our in ability to continue to count time faster.
45. ### 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?
46. 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...
47. ### 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...
48. ### 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...
49. ### 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...
50. ### 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...