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. L

    B Does Human Observation Affect the Double Slit Experiment Results?

    Let's say we do a double slit experiment with the standard laser/two slit setup with a screen to view the pattern. 1. In the first run, we just turn on the laser and observe the screen with our unaided eyes. We see an interference pattern consistent with the wave-like nature of light, correct...
  2. sergiokapone

    I Velocity measurement by a stationary observer in GR

    In almost general case, the space-time metrics looks like: \begin{equation} ds^2 = g_{00}(dx^0)^2 + 2g_{0i}dx^0dx^i + g_{ik}dx^idx^k, \end{equation} where ##i,k = 1 \ldots 3## - are spatial indeces. The spatial distance between points (as determined, for example, by the stationary observer)...
  3. 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...
  4. zonde

    B Dual meaning of "measurement" in QM

    Reading about collapse and Born rule it gives strong feeling that there is semantic mess in QM with the word "measurement". Wikipedia describes Born rule in following way: In its simplest form it states that the probability density of finding the particle at a given point is proportional to the...
  5. K

    I Wave function measurement question

    In Born interpretation of the wave function it notes that the matter itself cannot be measured however the square of its absolute value is measurable. I am lost as to why the product can be measured but not the wave function itself. Can someone provide clarity?
  6. 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...
  7. C

    B Is mass a measurement of energy?

    That's pretty much it. Are physical objects essentially clumps of energy, and that energy is measured as mass? And do objects become more massive as they receive more energy through push?
  8. 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...
  9. M

    How can i measure high magnetic fields?

    Hello! I've made a lot of research about measurement of high magnetic fields - such us 1T - 2T and I can't find sensors for this range. I'm looking for a hall sensor with which I will be able to measure 1T magnetic field with good accuracy - about 0.1 mT. Do you know about anything like that...
  10. J

    A Quantum measurement with incomplete basis?

    In page 9 of http://www.theory.caltech.edu/people/preskill/ph229/notes/chap4.pdf we can find simple form of Bell inequalities for three binary variables: $$ P(A=B) + P(A=C) + P(B=C) \geq 1 $$ which is kind of obvious: "This is satisfied by any probability distribution for the three coins because...
  11. B

    I Von Neumann measurement scheme

    I've been studying the von Neumann measurement scheme (and understanding the math part) where the system and apparatus are quantum in contrast to the orthodox where the apparatus is classical. I'd like to know the following. 1. Is the von Neumann measurement scheme 100% orthodox and believed by...
  12. E

    Understanding RF Power Measurement: Average vs. Composite Power

    What is the difference between average and composite power?
  13. H

    I Length-contraction time-dilation fallacy & length measurement

    Suppose an observer in the Earth frame set out to measure the length AB by measuring the time interval between the event "B coincides with D" (event BD) and the event "A coincides with D" (event AD), and then multiplying the time with ##v##. This observer argues that an observer in the train...
  14. mfb

    I Virgo joins the measurement of gravitational waves

    Finally... this month, Virgo and LIGO look for gravitational waves together (they started yesterday). The Virgo detector is a bit less sensitive than the LIGO detectors at the moment, but it is still a big improvement: It is an independent experiment, on a different continent run by different...
  15. FallenApple

    I How does measurement work in a two particle universe?

    Say that they are not entangled. Assume classical quantum laws still hold but that there are only two particles in this universe with nothing else. How would one of the particles measure the other? Both particle's location and momentum are nonexistent until a measurement occurs by one on the...
  16. 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...
  17. F

    I Understanding Measurement Uncertainty: Calculating Accuracy and Precision

    I have seen similar threads on here but not one with any detailed answer so I felt I would ask myself. I took a short undergrad module in measurement and uncertainty, intended to prepare for the numerous lab sessions and reports that would follow in the proceeding modules. In that particular...
  18. Q

    Phase shift measurement using phase modulated signal

    Hello everyone, I'm actually working on developping a phase shift sensor using one phase modulated signal, i know that the title is confusing beaucause the phase shift measurement need two signals , I'm trying to do this with the zero crossing method so if I could found the timestamps of the...
  19. N

    Wavelengths, Flux Density, Irradiance from a temperature measurement

    Homework Statement In my experimental setup I have a purpose built small aluminium tube that has a black layer on the inside to mimic a blackbody. The tube is heated so the inside emits as a blackbody. A separate temperature sensor attached to the tube gives the temperature of the tube. I...
  20. N

    I Using measurement to extract energy?

    I've just read an article (link to the discussed paper at the end) talking about a newly proposed Maxwell's demon where they use a quantum measurement to extract energy from the system, which made me think, isn't energy conserved in QM as well (at least in the average sense)? and seeing that a...
  21. P

    I Concerning the Nature of Quantum Measurement....

    I'm well aware of the common adage and quantum fact that, until a particle is measured by some sort of instrument, it exists in a state of superposition, can interfere with itself, etc. My questions pertains to the definition of "measurement". In order for something to qualify as a measurement...
  22. hilbert2

    A Field strength measurement and continuity

    Something about the theory of quantum measurement/collapse in the case of quantum fields... Suppose I have a field, either a scalar, vector or spinor, that I want to describe as a quantum object. For simplicity let's say that it's a scalar field ##\phi (\mathbf{x})##, where the ##\mathbf{x}## is...
  23. Danny Boy

    A Forming a unitary operator from measurement operators

    If we consider a measurement of a two level quantum system made by using a probe system followed then by a von Neumann measurement on the probe, how could we determine the unitary operator that must be applied to this system (and probe) to accomplish the given measurement operators.
  24. S

    I QM: Measurement & Wave Function Change

    <Moderator's note: two essentially very similar threads merged.> Hello! I am a bit confused about the idea of measurement in QM. As far as I understand, if you measure the position of a particle, the wavefunction of that particle changes into a delta function, and thus the particle gets...
  25. arpon

    I Does measurement change the energy of a system?

    Suppose, the energy of a particle is measured, say ##E_1##. So now the state vector of the particle is the energy eigenket ##|E_1>##. Then the position of the particle is measured, say ##x##. As the Hamiltonian operator and the position operator are non-commutative, the state vector is changed...
  26. Radiosan

    Uncertainty analysis of 2 port measurement

    I analyzed uncertainty analysis of 2 port measurement. I referenced 2 book "Transmission Reflection and Short Circuit Line Methods for Measuring Permittivity and Permeability" at pages 31 equation(2.83) "Transmission and Reflection and SCL Permittivity Measurements" at pages 44 equation(2.67)...
  27. R

    I Shor Algorithm - Post measurement state

    Hello! So I'm working to try to understand shor algorithm and I have some doubts. So, after the hadamard gates we apply the unitary gate that construct the function yk mod N. Next we do a measurement in the second register to get some function value. So, when I do this measurement on the...
  28. O

    A Measurement and error (error estimation and propagation)

    Description of the situation I have measured the incident number of electrons in a channel electron multiplier at different light polarization angles (a photoelectron angular distribution measurement). The events follow a poisson distribution and as far as I know the number of electron counts in...
  29. Paul Colby

    Signal measurement ~50 pico volts

    Hi, my question may be too open ended in which case some help defining it would be helpful. The signal I wish to measure is estimated to be ~50 pico volts in amplitude generated in an HF AT-cut quartz crystal. Basically all the signal power will be at the fundamental mode resonant frequency...
  30. C

    B First Direct Measurement of Brown Dwarf Mass Limit: 6.7% Sun

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  31. R

    Selective Incident Headlight Intensity Measurement

    Hey guys, I am trying to come up with an idea to measure incident intensity of headlights from an oncoming car for one of my uni projects. This wasn't specifically assigned project topic, we get to choose what we want to do. It's my Instrument and Measurement unit, and I had this idea thought it...
  32. S

    I Possible to estimate the location of a measurement point?

    Hi guys, I am just wondering if it is possible to calculate/estimate the location of measurement point on a rigid body? For example, let's say we have a rigid body that is in motion. We attach a sensor, say an accelerometer on the surface of the rigid body. Now can we estimate the location of...
  33. E

    I General Questions Related to Quantum Measurement

    I've recently been wondering about the notion of measurement in quantum mechanics. While I'm aware that understanding and precisely defining the concept of a quantum mechanical measurement is at the heart of interpreting the subject, I would like some feedback on some aspects of this topic I...
  34. B

    Preparation of murexide indicator for Ca measurement

    I want to prepare murexide indicator for Ca measurement using EDTA titrimetric method. I am following the procedure set by the American Public Health Association (APHA), however, I only have murexide diluted with K2SO4 (1:250). I want to know if I can use this as a substitute, and if yes, how...
  35. S

    B Double slit experiment - doesn't measurement affect photons?

    All these videos and articles about the Double Slit Experiment say that if we "look" where the single photons go, they act like particles and if we don't "look" they act like waves, creating the interference pattern... BUT What does it mean to "look"? We're not using our eyes or any camera...
  36. Martin Pecha

    How van der Pauw measurement is influenced by the size of the sample

    Dear all, I am trying to use Van der Pauw method to measure some samples, however I cannot get where in calculations van der Pauw method includes size of the sample. F.e. if I have circle with diameter of 2 cm or 5 cm there must be a difference right? Can anyone explain to me why or why not...
  37. LarryS

    I Entanglement correlations vs. timelike measurement events?

    The experiments that have been done to demonstrate that entangled particles are correlated (or anti-correlated) have been designed so that Alice and Bob's measurement events are intentionally space-like separated. Thus demonstrating that the "ghostly action at a distance" is supraluminal or...
  38. Lafith

    Measure Entropy: Can Absolute Entropy be Zero?

    Can we measure 'absolute entropy' of a system. Also can entropy become zero at 0 kelvin.is it possible only theoretically?
  39. B

    Problem about measurement and probability of energy

    Homework Statement Homework Equations I solve the (a) , using even,odd function. So, C=1/a The Attempt at a Solution I don't know how to approach (b). I think that 'total energy of the system' doesn't mean expectation value, how can i get total energy and probability of them?
  40. C

    I Measurement precision question

    Supposing we have 2 circles in a 2 d space that can bounce off each other like balls. These circles are made of an infinite number of points. We put the centre of each circle on a line and send them towards each other along the line. Are they going to bounce off keeping their trajectory on the...
  41. S

    Is light speed limit an artifact of the math of measurement

    A delightful video here A lecturer derives special relativity in a world of bats and echo location using a bat (sound) clock. All communication is limited by the speed of sound. (so a parallel of our world and light speed communication) He ends up observing that in no cases for any observer...
  42. O

    B Basic question about double slit interferance

    I am new here so I will start with a warming up question :) My question is very trivial here we go: In double slit experiment when shooting one photon at a time, we get interference pattern. Then when we put a sensor at one of the slits the interference pattern disappears because we now know...
  43. R

    I Measuring Vectors: Defining Direction and Magnitude

    On wiki measurement is defined as: Measurement is the assignment of a number to a characteristic of an object or event, which can be compared with other objects or events. So a number. For scalars, I agree because they are described by a single number. But what about vectors? They have...
  44. G

    I Commuting observables vs. exchanging measurements

    Hi. I'm afraid I might just be discovering quite a big misunderstanding of mine concerning the meaning of the expectation value of a commutator for a given state. I somehow thought that if the expectation value of the commutator of two observables ##A, B## is zero for a given state...
  45. L

    I Measurement Science: True Magnitude, Error & Accuracy

    Hello. So one of the axioms of measurement science is that every measurement we make is an approximation and can never reflect the true magnitude of a physical phenomena. We would then go on to teach that there is a certain "true" magnitude which is something that experts or majority would...
  46. A

    Measurement of grinding wheel waviness

    I have done experiements on a grinding machine and have collected the data of grinding wheel profile (using a laser sensor). The raw data consists of info on grinding wheel profile, waviness and roughness (because of abrasive grains). I would like to process the colelcted raw data. I want to...
  47. F

    Measuring AC current with an oscilloscope.

    I have a technical question, for research purposes. I have LED that we probe in AC mode. To measure the applied voltage in AC and the light-response in AC is no problem. However I would like to measure the current going through the device as well and I would like to link it to an oscilloscope...
  48. N

    SR830 lock-in amp measurement problem

    Hello I am currently have difficulties trying to measure dc-modulated voltages while applying a dc current, via Sr830 Lock-in Amplifier (LIA). Basically, I apply an 2 GHz ac current (amplitude modulated@10kHz and referenced to the LIA for lock-in measurement) and a dc current to my DUT...
  49. M

    Finding thermal expansion problems for measurement technique

    I am trying to find examples problems on thermal expasions related to the subject of measurement technique Google but I can't find them.. I don't know exactly what could be asked but the problem will be related to: "expansion of measurement device" is given, and "expansion of measured...
  50. I

    Repeating measurement of observables?

    I have a question on my homework set and I'm not sure the principle behind it: 1. Alice measured an observable F (a matrix) and passed the measured system immediately to another experimentalist, Bob, who is going to measure another observable G. Alice claims that she can deduce the experiment...
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