# Tagged Questions

The result of sampling the property of a system

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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### Are there any industry usage for gas thermometer? [on hold]

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?
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### 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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### 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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### Can conductivity (or resistivity) value be assigned to 2D materials?

2D materials, such as graphene monolayer or graphene nanoribbon, don't really have a cross section. By definition, conductivity is $\sigma = \frac{J}{E}$, and $J$, the current density, is calculated ...
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### 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 ...
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### 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,...
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### Measuring force of a punch

I'm trying to build a device that can mesure the force of a punch. ​ My initial plan was to build a platform with 4 springs (one at each corner) and an accelerometer in the middle. But, if the ...
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### 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 ...
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### Non linear QM and wave function collapse

I heard that there have been some propositions about describing the collapse of the wave-function by adding non-linear terms, but I couldn't anything in any any textbooks or even articles (probably ...
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### 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 ...
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### 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 ...
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### How well can we localize gravitational wave sources?

A recent question cited a story about the recent gravitational wave detection saying that we can use the gravitational wave sensing to find supernova earlier in their process of collapse: [with ...
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### 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 ...
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### 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 ...