Measurement Definition and 1000 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. D

    B A tilted container with water inside - how to calculate the distance A?

    We are trying to control a container with water inside. The container has two phases of operation. In one phase, the container is tilted. In this tilted state, the distance from the observation point (red dot) to the surface of the water (distance B) is known from a measurement device. However...
  2. A

    Measurement of Angles and Lengths With Length Contraction

    I'm having a hard time since the angle is being measured in frame ##S##. What I have put together so far is ## l_y = l_{y0} = 1m(sin(\theta_\circ)) ## And ## l_x = l_{x0}/\gamma ## Where ## l_{y0} ## and ## l_{x0} ## are the respective x and y values of the meter stick in the proper lengths...
  3. Sagittarius A-Star

    I Understanding the Equivalence Principle

    Alan Macdonald claims in "4 Appendix: The Equivalence Principle" of his text "Special and General Relativity based on the Physical Meaning of the Spacetime Interval", that his calculation regarding a 2D-surface of a sphere proves, that the equivalence principle is violated. He defines the...
  4. Kyuubi

    I von Neumann Measurement Scheme

    Greetings, I would like to ask something about the von Neumann measurement scheme in the context of Time~symmetric QM and weak measurements in the popular Aharonov, Bergmann, and Lebowitz (1955, ABL) paper and the Aharonov, Albert, and Vaidman (1988, AAV) paper. Particularly in the latter...
  5. DaTario

    I Is there a gravitational effect on spatial measurements

    Hi All, We often read that the gravitational field acts by slowing down clocks. Is there any statement that, with the same simplicity, reports on the action of the gravitational field on lengths measured by observers which are close or far from Earth, for example? Best wishes, DaTario
  6. H

    I What is the meaning of "same direction" for spin measurement?

    Hi Pfs, I read that pairs of entangled particles were measured on earth along a same direction and that the distance between them was greater than 1000 kilometers. What is the définition of a "same direction" on earth? is Is it related to the direction of a very distant galaxy or somethig like...
  7. I

    B What I don't quite get about entanglement...

    I have watched videos on Bell's Theorem and quantum entanglement. What I don't quite get is: if a pair of particles are created and separated and then we measure one we already know the other particle has the opposite orientation. How do we know for sure that the first particle we measure does...
  8. rocketwaveuk

    I Matter Anti-Matter Annihilation

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  9. KjUy

    I Measuring Second-Order Correlation Function with Start and Stop Signal

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  10. F

    Ruler measurements and knowing how many decimal places to include

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  11. C

    Will an Encoder Measure Correct Rotation with Shaft Movement in X and Y?

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  12. A. Neumaier

    A Teaching ideal quantum measurement, from dynamics to interpretation

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  13. U

    AC gaussmeter in static magnetic field

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  14. Ranku

    I Cavendish balance and mass of objects

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  15. Ranku

    I Determining stellar mass independent of its gravity

    What are the independent and accurate ways of determining stellar mass apart from its gravitational effect?
  16. G

    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...
  17. A

    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...
  18. elou

    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...
  19. MR v

    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
  20. M

    Can You Convert Meters to Kilograms?

    Distance and weight are two separate things so....the question cannot be answered?
  21. Omega0

    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...
  22. D

    I Exploring Measurements in Quantum Field Theory: From Light Cones to Bell Tests

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  23. K

    A Putting upper bounds from a null result

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  24. Garlic

    A Quantitative description of successive Stern-Gerlach measurements

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  25. Lotto

    B How to statistically calculate the final value?

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  26. D

    Stargazing What is the maximum distance that parallax error can be used?

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  27. M

    B Why Do Bob and Alice Disagree on Astronomical Measurements?

    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...
  28. Astronuc

    Measuring changes in Earth's rotation

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  29. H

    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.
  30. C

    I Results of measurement using a magnetic sensor

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  31. genxium

    I Need help understanding the first single attosecond pulse measurement

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  32. Quietrabbit

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  33. Dale

    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...
  34. A

    B Why can only the electric field (E) be measured?

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  35. Muhammad Usman

    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.
  36. M

    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...
  37. bushmonk

    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...
  38. E

    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...
  39. Username34

    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%?
  40. S

    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?
  41. D

    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?
  42. ARoyC

    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...
  43. Ranku

    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?
  44. NeophyteinPhysics

    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...
  45. ARoyC

    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...
  46. S

    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
  47. L

    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...
  48. G

    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.
  49. K

    A Measurement uncertainty due to thermal noise

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  50. S

    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...
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