The result of sampling the property of a system

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1answer
67 views

Is the use of term Measurement appropriate in quantum physics [on hold]

It may not sound like a physics question, but I think, it is. When we measure spin of an electron in a certain direction, we are actually, setting it up in that direction. That does not sound like ...
0
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0answers
32 views

States after measurement

I am learing about quantum mechanics, and I am quite unclear about the the role of measurement and the density operator. Let $\mathcal H$ be a Hilbert space, $\psi(t) \in \mathcal H$, $O$ be a ...
3
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1answer
101 views

The Validity of a Heuristic Explanation of Black Hole Complementarity?

In one of the messenger lectures at Cornell in 2013, Leonard Susskind gave a heuristic argument for black hole complementarity. Suppose Alice is stationed far away from a Schwarzschild black hole and ...
3
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2answers
136 views

On Newton's discovery of the universal law of gravitation

I'm reading Peter Collier's book on relativity and was on the chapter where he describes how Newton figured out the law for universal gravitation. This is the cannonball referred to in the following ...
2
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1answer
32 views

Are there any industry usage for gas thermometer? [closed]

I've been searching on this for a while now. Are there any specific advantages and disadvantages for using gas thermometer? Are there any specific industry usage for this kind of thermometer?
2
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1answer
37 views

What are the tools used by Newton to measure motion?

I was wondering how did Sir Newton measured motion of objects (non celestial ones). What was his toolskit at the time?
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0answers
11 views

most efficient set of weights with whole number mass to n-power for balancing unknown mass on vertex of regular triangle

I saw this qustion: http://puzzling.stackexchange.com/questions/186/whats-the-fewest-weights-you-need-to-balance-any-weight-from-1-to-40-pounds Suppose you want to create a set of weights so ...
3
votes
3answers
69 views

Projection operators in quantum mechanics

I'm reading a book on quantum mechanics and a topic in there was not well explained. I couldn't find an answer on the web. Say $\psi(x)$ is a position wave function of a one dimensional free particle,...
0
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0answers
14 views

Using a magnetometer in a sub-sea application, how to get a good magnetic bearing?

Mechanical engineer here, getting in over my head concerning magnetic sensors, electronics and the like :-) Quick situation description:For a work-application I am looking at using a MEMS based 3 ...
1
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0answers
21 views

How to determine the three-velocity measured by a single observer?

In this question the issue of extracting the three-velocity of a test particle in some frame arose. The answer provided by @PaulT and in this paper (arXiv) seems to me to give rise to ambiguity when ...
1
vote
1answer
45 views

Entangled qubit measurement

I came across this while reading lecture notes and I have no idea how they got the $M_0$ and $M_1$. The way I see it, the matrix $U$ is a block matrix: $$ \left[ \begin{array}{ c c } P &...
8
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1answer
75 views

Have we measured the rate at which Jupiter is shrinking?

On most websites that I looked at, it says Jupiter is shrinking 2cm/year (for example wikipedia and Quora). However neither of these website say whether this rate is measurable (the latter says it is ...
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0answers
26 views

Antenna measurements and parameters calculation

Lets suppose we have some data collected from antenna measurement. For every theta and phi point in any coordinate system ( here refering to Ludiwg coordinate systems II and III) the data can be ...
-3
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0answers
21 views

Uncertainty principle-QM [duplicate]

I some trouble understanding the uncertainty principle. I understand most of the math derivation but not the physics. Is there any intuitive explanation of this idea, and why is the uncertanty does ...
4
votes
2answers
100 views

Does a measurement always require the exchange of energy?

Can you measure something about something without adding or removing energy from it? This comment has got me wondering if there is a way to measure a property or a quantity of something without some ...
3
votes
1answer
135 views

How to read numbers reported in this LIGO paper?

I am not sure how to read the numbers in this excerpt from the abstract of GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence: Are the +/- small ...
2
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1answer
46 views

How to measure relative phases of quantum states

If I have a large number of identical systems in identical quantum state $\Psi$ and an observable $A$ whose eigenstates are $\alpha_n$: $$ \Psi = \sum_n c_n \alpha_n $$ I can get absolute values ...
1
vote
1answer
34 views

How the data or models given in physics or mathematics problems can be obtained in real life? [closed]

When ever there is physics or mathematics problem. we are already given a mathematical model. Can't we make own models from given diagrams or data collected from the problem? sometimes angle is given ...
3
votes
1answer
33 views

What are the effects of compositional changes in a thermocouple's junction?

We use thermocouples (type B) to measure the temperature of metals (Fe, Ag, Pd, etc) in a furnace under pressure. We weld two thermocouple wires together using an arc welder. This junction then comes ...
1
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2answers
74 views

Error Analysis involving random errors

The question goes like this: In an experiment, the time period of an oscillating object in five successive measurements is found to be $0.52$s, $0.56$s, $0.57$s, $0.54$s, $0.59$s. The least count ...
1
vote
1answer
40 views

How to find the covariance matrix after a partial homodyne measurement?

The Gaussian state of two modes, with quadrature operators $X_1,P_1,X_2,P_2$, is given by a displacement vector $d$ and covariance matrix $\sigma = \begin{bmatrix} Var(X_1,X1) & Var(X_1,P_1) &...
3
votes
1answer
74 views

How can I measure the amplitude of a light wave?

Suppose I have a light wave and I want to measure its amplitude, or check to see if it has an amplitude of a certain value: how would one go about doing this?
4
votes
2answers
62 views

Combining two data points with different uncertainties

I have two separate algorithms (call them "A1" and "A2") which reconstruct the $(x, y)$-position of an event in a particle detector. I can test both of these algorithms on simulated events from a very ...
0
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0answers
36 views

Does the definition of the metre have to take into account spacetime curvature?

The definition of the metre is: The metre is the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second Does this have to be modified in a ...
1
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1answer
30 views

Systematic+Random Uncertainty for velocity measurement

I have a question regarding systematic and random uncertainties. I have to measure the mean value of a velocity measurement in flow field at a point. I've recorded say 1000 samples in time, which I ...
1
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1answer
70 views

How to measure the mass and balance point of a human forearm?

I've been trying to find this out for about a month now. I'm usually met with humorous but not really helpful comments about chopping my own arm off. I'm preferably looking to do this on a budget ...
0
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4answers
99 views

Is there an official list of independent units of measurements?

When I say 'independent units', I mean those which cannot be broken down anymore, and simultaneously forms the basis for any more, complex measurements. For example, height, length, and width can all ...
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3answers
62 views

Is there a way to measure the thickness of a metallic plate of order of micrometers?

I have a $5 cm×5 cm×? \mu m$ copper plate. Where '$?$', the thickness of the plate, is really small (about 30um). Is there anyway using physics to calculate the thickness? Update: Sorry I forgot ...
68
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5answers
6k views

How do laser “tape measures” work?

There is a device available for about $\$40$, which fits in the palm of the hand, runs on two AA batteries, and can measure distances up to $50\,{\rm ft}$ to an accuracy of $\sim \frac{1}{8}''$ ($\sim ...
0
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1answer
28 views

making sense of measures in electronics

I am in secondary school in the UK, and at this point in physics the information we are given is very vague at a fundamental level. My main concern is with electricity and circuits, and the measures ...
5
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2answers
130 views

Is wavefunction collapse “global”?

I have the feeling that the premises of this question may not be coherent (so to speak), but here goes: Suppose we have a system $X$ in a quantum superposition between states $0$ and $1$, say, with ...
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0answers
46 views

Estimate heating wires temperature

Im design a power supply to work with heating wires and one of the task is to estimate the temperature of the bare wire for a given current or power consumption. I've tried to measure the ...
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1answer
60 views

Measurements in quantum mechanics

Why does measurement change things? I read that measurement changes things because we have to bounce photons off an object to 'see' it and that changes its position, momentum etc... But on the other ...
2
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2answers
65 views

Why doesn't precessing a spin cause a measurement?

When an electron is placed in a magnetic field, its spin precesses. Why doesn't this reveal the spin via angular momentum being transferred into the environment? Impractical Thought Experiment ...
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0answers
8 views

How can I measure radiance?

I'd like to measure radiance in order to see how accurate the Lambertian, Phong models are and maybe to measure the "shininess constant" of a material (which appears in the Phong Model) on some ...
13
votes
2answers
967 views

How precise can current technologies measure the mass of an object?

Masses of various objects are listed on this wikipedia page: Orders of magnitude (mass). For example, mass of an HIV-1 virus is on the order of 1 femtogram. Are these data actually measured (which I ...
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0answers
25 views

Why does't the use of the same number of significant digits result in consistent result?

Here is a table: $ \begin{array}{ c c c c c c c } Trial number & Time for 20 cycles & Period & Frequency & Wavelength & Velocity (wavelength*frequency) & Velocity (wavelength/...
3
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1answer
89 views

Measuring very long half lives accurately

There are already some questions about long half life times for radioactive elements, explaining how to calculate the half life time. Now I am wondering: When you have some radioactive material and ...
0
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1answer
62 views

Measurement on two Qubits

Assuming I have two Qubits, i.e. a four-dim. Hilbert space. In the following, I choose the basis {|11>,|10>,|01>,|00>}. I want to have a look on the non-diagonal part <11|$\rho$|00>. How can I ...
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0answers
25 views

Total uncertainty of multiple stereo camera depth measurements

I have a stereo camera that measures depth for a rectangular area of pixels in a single image. Each depth measurement is obtained independently (this goes back to the stereo matching algorithm used). ...
4
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0answers
60 views

Calculating statistical significance of peak over background in counting experiment

I histogrammed the invariant masses of particular events in a counting experiment. There is a specific peak which towers over the expected exponential background. How can I give the statistical ...
2
votes
1answer
28 views

Correction for uncertainty of multiplications and divisions

The conventional means of obtaining uncertainty of $c$ where $c = a \cdot b$ is adding percentage uncertainty of $a$ and $b$. This method seems to have a flaw as shown below (please excuse me if I am ...
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0answers
12 views

Rarefaction/compression events detection using time resolved sound measurement

I had a question about sound measurement in air using a B&K condenser microphone. In the acquired time resolved sound measurement signal I can see both negative and positive voltages/ pressure ...
3
votes
2answers
37 views

Why the Du Noüy ring method does not depend on the material the ring is made of?

Du Noüy ring method is a way to measure surface tension. Why the measured force, $$F= 2\pi \cdot (r_i + r_a) \cdot \gamma$$ does not depend on the material the ring itself is made of? Wouldn't a ...
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0answers
37 views

Terminology for 'inferring the current state of a quantum system as it evolves and gets measured out of your control'

Suppose I hand you a quantum computer in an unknown state, but running a known program. You know the program and which part of the program is currently being executed. The program tells the computer ...
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0answers
18 views

Frequency combs measurment

How is a frequency comb actually used to measure something? For example: I don't know the length of my pen, so I take a ruler and measure it -- it reads 10 cm, so now I know my pen is 10 cm. From my ...
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1answer
35 views

How to quantify the level of non determinism / randomness in the universe

I recently read a little about the Bell test (I'm not a physicist, but reasonably well educated) and I started wondering if there is a way to express the level of non-determinism as a single number ...
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3answers
55 views

Finding the random uncertainty of a set of values [closed]

Ok, for the switch-on voltage of a red LED I have the readings as follows, all in volts: $$ 1.45, 1.46, 1.46, 1.44, 1.45 $$ The mean of these readings, in volts, is $1.45$ (I rounded up to $2$ decimal ...
4
votes
1answer
72 views

Decoherence Free Subspaces and how they stay this way, using the Zeno Effect

I am currently reading papers discussing the Zeno Effect, which discuss how measuring a system at high frequencies can almost freeze the state of a system, or keep the system in a specific subspace of ...
3
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1answer
46 views

How is the total spin of a particle actually measured?

Say I have a fermion whose total spin I do not know. I then use a stern gerlach setup to measure $S_z$. If I find +1/2, I could say that the total spin is $1/2$. But it could also be the eigenket $|3/...