# 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. ### A Teaching ideal quantum measurement, from dynamics to interpretation

A.E. Allahverdyan, R. Balian, and T.M. Nieuwenhuizen, Teaching ideal quantum measurement, from dynamics to interpretation, Comptes Rendus Physique 25 (2024), 251--287. https://www.researchgate.net/publication/380862732
2. ### AC gaussmeter in static magnetic field

When you shake back and forth AC gaussmeter ,he significantly increase reading(magnetic field), because device is moved in Earth static magnetic field. Does his acceleration or velocity cause increase in reading and why he even increase reading if magnetic field from Earth is static and...
3. ### I Cavendish balance and mass of objects

The Cavendish balance measures the gravitational constant G. To do so requires us to know the magnitude of the smaller and larger masses in the apparatus. However, mass is derived from the weight of an object, which is the gravitational force upon an object, which in turn requires the value of...
4. ### I Determining stellar mass independent of its gravity

What are the independent and accurate ways of determining stellar mass apart from its gravitational effect?
5. ### I How to enter measurement results into Bell inequality?

Hi. I can calculate the expectation values in the Bell (or in this case, CHSH) inequality and show that they violate it for entangled particles. But I'm confused about how to calculate them for an actual sequence of measurements, which could look like this ("Paar" is for photon pair): How do...
6. ### Measurements Calculation Problem

I have done this problem three times now, and keep coming up with an answer that is a factor of 10 off from the answer in the solutions manual. The way I'm doing it is MUCH different than how they did it, so I can't use their method to see where I'm going wrong. I want to find out what I'm...
7. ### I Feynman discussion of electron diffraction

Feynman, in the third volume of his Lectures on Physics, chapter 1, presents bullets and waves in two different diagrams, Fig 1-1 and 1-2 respectively. https://www.feynmanlectures.caltech.edu/III_01.html It is obvious that bullets are counted individually, the detector registering each hit...
8. ### Measure the transmission curve and wavelengths of colored mineral glass

hi , I want to measure the transmission curve and wavelengths of colored mineral glass , which is the simplest way or which instrument can I use ? thanks
9. ### Can You Convert Meters to Kilograms?

Distance and weight are two separate things so....the question cannot be answered?
10. ### Is zero of nothing nothing? If so, would you write units for nothing?

I stumbled over a datasheet of an old pentode where it says, in the english translation: I thought, wow, I am not sure if I wouldn't have written Ug3=0V instead. I am a theoretician in physics but work more as an engineer and teacher. What happens inside of me seems to be the following: The...
11. ### I Exploring Measurements in Quantum Field Theory: From Light Cones to Bell Tests

Hello, I'm interested in how measurement, entanglement, bell test etc are handled in QFT. It seems most QFT texts are being quite light on details on the subject. There would be is a preparation step as the start followed by some interaction and a measurement at the end. Interaction is usually...
12. ### A Putting upper bounds from a null result

Hello! If I have a measurement of a (dimensionless) parameter, ##a##, say 998 +/- 3 and the theoretical prediction of that parameter (assuming known physics) is 1000 +/- 4. Let's say that I want to set limits on a new parameter (not included in the theoretical calculations), call it ##\alpha##...
13. ### A Quantitative description of successive Stern-Gerlach measurements

I'm trying to understand how exactly we calculate the detection rate in this specific multiple Stern-Gerlach setup. As written on the image, an (unpolarized) atomic beam is sent through a three Stern-Gerlach apparatuses, and the detector supposedly clicks 25% of the time. When I try to...
14. ### B How to statistically calculate the final value?

My steps would be that I would first calculated ##a_1## and ##a_2##, determined by using that formula with partial derivatives its errors, and then I would made an arithmetic mean of ##a_1## and ##a_2##. I am not sure how to determine the final error, but I think I can use this formula ##\Delta...
15. ### Stargazing What is the maximum distance that parallax error can be used?

using the Earths orbit, what is the maximum distance that can be measured using parallax error?
16. ### B A thought experiment: Making astronomical measurements from different floors of a skyscraper

Bob lives on floor 500 in a 1000 meter high skyscraper. Bob has measured the time it has taken a star to orbit 1 round in the Milky Way relative to Earth. He started by measuring at the time when a single photon from the star was received exactly at the center of his telescope, and ended the...
17. ### Measuring changes in Earth's rotation

I read an article about the earth's rotation slowing due to redistribution of mass (probably mostly water). The headline indicated that Earth's rotation could slow to a rate of 25 hours per day, which seems rather large. This follows a publication announcing, Researchers improve measurement of...
18. ### A Does the Zeno effect freeze all the commuting observables?

Hi Pfs Take a two level system up-down in its up level, There are other observables that commute with that. is it true that applying the Zeno's effect by fast repeated measure of that observable will also freeze the system on up? thanks.
19. ### I Results of measurement using a magnetic sensor

Hello. I am seeking some advice or information regarding a measurement I made using a magnetic sensor. Essentially, to summarize, I measured the socket for a ceiling light using a magnetic sensor, taking the necessary safety precautions. In so doing, in the immediate proximity of the socket, I...
20. ### I Need help understanding the first single attosecond pulse measurement

In the 2001 paper Attosecond Metrology, the authors presented the first attosecond pulse setup and explained the measurements. This paper cites another paper quite often to mention similarities in the setup, but emphasized that they chose different observables: and only the choice made by...
21. ### Alternate ways to measure surface roughness?

I am trying to compare the surface roughness of 3D printed specimens for a school project, but I am realizing I don't have access to any of the standard equipment that would be used to measure it. Are there alternative measurements I would be able to use that would yield similar results, using...
22. ### I Are Real Numbers Essential in Scientific Measurements and Models?

A couple of weeks ago we had an interesting thread where a tangent developed discussing whether real-valued measurements were possible. I would like to generalize that discussion a bit in this one and discuss all scientific purposes, not just measurements. 1) What is a measurement anyway? Is it...
23. ### B Why can only the electric field (E) be measured?

I would like to consult with you about something. Mobile phone towers transmit at relatively high frequencies. From a health perspective, on the internet :) all measurement values are interpreted in microteslas. However, with the Wavecontrol probe (WPF8) I have, only the electric field (E) can...
24. ### I How was electronics propagation delay measured historically?

Hi, I know in todays world we have more sophisticated equipment to measure the propagation delay of electronics equipment, but for my own curiosity i want to know how historically the propagation delay was measured for electronics device such as transistor.
25. ### B Can Dark Flow Be measured, based on Special Relativity?

Let's assume Dark Flow is real. If so can't we measure it based on 2 atomic clocks. Dark Flow occurs presumely in a southerly direction. One atomic clock must start at the time the earth's rotation begins to bring the first atomic clock in a slightly southerly direction, (due to the earth's 23.4...
26. ### I Measurement and Thermal Effects Similar?

A weak (one photon at a time) beam of laser light strikes a double slit. In case 1 the barrier forming the double slit is a mirror. In case 2 the barrier is flat black. An array of detectors surround the experiment and can detect the photon whether it goes through the slit or is reflected. In...
27. ### An example of state determination (Ballentine Problem 8.4)

I've given the question as an image as some of the formatting was difficult for me in the small window given: My work is below. I got (a), but cannot get (b): (a) It was a theorem proved in the text that any measurement on one subsystem will always be fully determined by the reduced state...
28. ### How much of an approximation are power measuring tools for martial arts?

For instance this Power Cube device. Is it capable of reporting EXACTLY how hard Francis Ngannou punched, or will it be biased towards mass or speed and overestimate one of the components? How "off" from the actual physics of reality do you expect such a tool to be? 5%? 10%? 20%?
29. ### Medical BP measurement : is it ok to re-inflate gently around threshold?

Is it ok to gently squeeze the bulb just after crossing the systolic or diastolic threshold, just to make sure of the exact value?
30. ### I Can We Accurately Measure Momentum in the Lab?

In the lab, how accurately can we measure momentum? What is the max value of the uncertainty in position as the uncertainty in momentum approaches zero? Or vice versa. What experiments do these types of measurements?
31. ### Questions from Quantum Measurements

[Mentor Note: Two similar thread starts merged] The questions are from MIT OCW. First of all, I cannot understand what is the meaning of the measurement outcome being 0. How can an eigenvalue be 0? I tried doing the problems guessing that by 0 they mean the posterior state will be |0>. The only...
32. ### I Mass measurement of galaxies with non-gravitational means

What are the non-gravitational ways of determining mass of galaxies, and how accurate are they?
33. ### The increase of Fidelity after non-selective measurement

The above question is adopted from the exercise of Preskill's quantum information lecture note My attempt: (a) From the condition, ## p(\theta)\propto \sin^{(2N-4)}\theta \cos\theta ##. Normalizing the probability distribution would give the answer. This is because the weight of the phase of...
34. ### I Confusions I have regarding Measurements in Quantum Mechanics

Hi. This is Annwoy Roy Choudhury. I have just completed my first-year undergraduate studies in Physics. I am new to Quantum Mechanics. There are certain confusions I have regarding Quantum Measurements. It would be really kind of you to help me out. Postulate 3 states, An example is, Let's...
35. ### Calculate the voltmeter reading for this circuit with 2 sources and 2 resistors

I find the current first, which is 2 A. Then the voltmeter reading would be 10 V - 1 x 2 = 8 V. But the answer is 12 V. I don't understand why it should be 10 + 1 x 2 = 12 V Thanks
36. ### How many branches are possible after measurement/splitting?

Say you have a simplified 1d Gaussian wave function describing location of a particle. Many worlds says that every outcome is a separate branch. Copenhagen says you will get one of those branches. So how many distinct positions, imaginary or real, can you generate from a fixed segment of a...
37. ### Setting Up a Mechanical/Electrical Inertia Measurement of Propellerarm

Hello Everybody I'd like to set up a mechanical or electrical inertiameasurement of a Propellerarm that is in rotation, while the thrust (rpm of propeller) is rising. Maybe with a forcespring, a pendulum, camera (timer)... Not sure how to set it up nicely. Any suggestions? Best George P.
38. ### A Measurement uncertainty due to thermal noise

I have a charged particle in a Penning trap. The particle motion is non-relativistic and the energy is high enough such that we can assume it is not in the quantum regime. For the purpose of the question I am interested only in the axial motion of the particle, so basically this is a classical...
39. ### I Exploring Microscopic Particles: Interactions & Measurement

1.How is that possible for us to say that a non-interacting microscopic particle can have numerous values of a physical parameter in a given instant? the mixed state of a microscopic particle is simply the probability distribution of the particle having those values of a given physical parameter...
40. ### I Measurement of a superposition and Born's rule

Let be a superposition ##|\psi\rangle=\sum_j a_j|j\rangle## with one amplitude ##a_x## much greater than the others, where ##x## is not known. For example, ##|\psi\rangle## may result from the quantum Fourier transform of a periodic wave function with an unknown period. I expect a measurement of...
41. ### I (extended) Page-Wootters formalism

Hi Pfs, I am beginning to read this short paper https://arxiv.org/abs/1504.04215 (quantum time) i read things like that on first page: Ht is the space of a system T (we call it the clock system) isomorphic to a Hilbrt space of a particle on a line. this space is equipped with coordinates T and...
42. ### B How to calculate measurement error by using other quantities?

Let's say I have ##F=mg \tan \alpha## and want to calculate ##F##. I know ##m=(1.0 \pm 0.5)\,\mathrm{kg}## and ##\alpha=(20.5 \pm 0.5)° ##. How to calculate ##F=( 3.7 \pm ?)\,\mathrm N##? What is the general method of determining a measurement error in these cases?
43. ### B Does the bomb experiment do a measurement?

In short, the Elitzur–Vaidman bomb experiment consists of a Mach–Zehnder interferometer, where a bomb is placed in one of the paths (I used the wikipedia description https://en.wikipedia.org/wiki/Elitzur%E2%80%93Vaidman_bomb_tester, and Sabine Hossenfelder's video: ) The bomb can be live or a...
44. ### Building an Affordable OD600 Sensor for Cell Concentration Measurement

Hi all, I'd like to make an home-built OD600 sensor for measurement of cell concentration in suspension by Optical Density. There are several spectrophotometers in the market, indeed quite expensive, so I am interested in realizing a cheap device with standard components. Here's an example on...
45. ### B How to calculate a random measurement error?

I have seen this formula $$\sigma=\sqrt{\frac {\sum_{i=1}^{N}{(X_i- \bar{X})^2}}{N(N-1)}}$$ but also this formula $$\sigma =\frac{\sum_{i=1}^{N}{|X_i- \bar {X}|}}{N}.$$ Which of them is correct?