Measurement Definition and 1000 Threads

Hello Forum, I am taking a lab and we are learning about measurement and uncertainty. Suppose we have to measure the length L of an object. Once the data has been collected we can calculate the mean (average) and the standard deviation s. The resulting measurement would be expressed as [ mean...

I am taking a course in quantum information theory. In this theory, the state of a system is given by a density matrix, while a measurement is completely positive, trace preserving map of the form: Λ = ∑il i >< i l ⊗ Λi , where Λi is completely positive. Can anyone tell me how this is...

I was wondering about decoherence: Suppose a measuring apparatus measures a single quantum property (say, spin). After the actual measurement of the property has taken place, the result 'decoheres' into the apparatus until the apparatus shows the measurement result, after which it decoheres...

Homework Statement It's been a little while since I did one of these. My question is: We have to use http://phet.colorado.edu/sims/mass-spring-lab/mass-spring-lab_en.html to find the measurement of k, the spring factor using two different methods. For the method I am looking at, is the static...

What is an (the?) empirically demonstrable method used for determining a substance's state of matter? If a new substance was discovered and scientist A said it's solid and scientist B said it's a liquid, how would it be demonstrably proven to be one or the other? The books I have define states...

Whats the significance of Atmospheric pressure being refereed as 100kPa ? Does that really mean 10000 kg/m2 acting upon us ? If we are measuring only collision force on the surface and not the weight of the entire column of air above us, then why figure 100kPa (100000 N force/m2) which is huge...

Hello, Can anybody help me to understand the solved example as attached here. How can I follow that using dirac, bra notations. Regards

Homework Statement A horizontal Pitot tube (with one end open for airflow and another closed) is accidentally installed into an airplane askew, so that the tube is not horizontal. Instead the closed tube end is higher (in the y-direction of a xy-plane) than the inlet end. How does this affect...

I have a 3-axis accelerometer suspended on rubber bands inside a soccer ball and am wondering how to calculate the impact force of the ball with it. I have an intuition that the force will be proportional to the frequency of the oscillations of the sensor after a collision but I am having...

Considering the multiple universe view, if a measurement (or something else) makes visible which universe we are in, is it then also possible we find ourselves in one with (slightly) different laws of nature?

Hello folks, I'm looking for a way to measure core loss in RF transformers and inductors. I found a PhD thesis here: https://vtechworks.lib.vt.edu/bitstream/handle/10919/19296/Mu_M_D_2013.pdf which looks like just the ticket, but I'm having trouble understanding key parts. I've tried...

When we observe an electron it is always a localized excitation in the electron field. But when it's not being observed, does the excitation begin to spread through space and become a delocalized excitation?

I'm currently working with several No-Go-Theorems in Quantum Mechanics for my master thesis and there are two, which are confusing me: The No-Deletion-Theorem and the No-Partial Erasure-Theorem. This is what I found out: The No-Deletion-Theorem shows that "there is no quantum deleting machine...

Hey I am trying to tweak a Fighter jet game to make it more realistic. I am trying to the US Air Force AIM-120D AMRAAM missile like what it can do in real life. The question is what is the effective range of the missile against a maneuvering target or evading target, for a fighter let say 6Gs...

before measuring an electrons position, is it physically a smear,like a wave? Or is it just nothing?

I know the units of measurement for this are: MPa m^0.5 However a question I am working on has it as MPa m^-0.5 What is the difference and does it affect the way I calculate the answer? Would appreciate your insight. Thanks Pete

Hello, sorry if I created new thread that is already open, but I did not find answer. I would like to ask you about measurement problem (double slit experiment) and many worlds. When interference pattern is created, the dot on screen just show us in which branch or world we are. But if we...

A ket is expanded as \vert \nu \rangle = c_1\vert \nu_1\rangle+c_2\vert \nu_{2}\rangle . A measurement results in the eigenvalue a1. Is it possible to measure the other eigenvalue a2 at a time t after the first measurement? Could I write something like \vert \psi(t)\rangle = e^{-i \hat H t...

On separate lines list each measurement name, average value ±uncertainty (readability or reason for uncertainty) EXAMPLE: Displacement, 0.100 - 1.600 meters ± 0.005 meters (σ precision for start and final position reading.) Consider Displacement a measurement instead of startP and finalP. Here...

I have a formal lab due, and my idea is to use a bifilar pendulum, model its period using experimental data, and examine the effect of the length of the strings on the amplitude of the period. For anyone unfamiliar with it, here is a picture of the pendulum. This is how I plan on setting up my...

In 2012, experimenters showed that when two entangled photons separate and when one goes through the double slit, we can tell which slit it went through and see that they still created an interference pattern because the photon that it was entangled to tells us which slit it went through. What...

http://arxiv.org/abs/1507.02679 Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization Adi Zitrin, Ivo Labbe, Sirio Belli, Rychard Bouwens, Richard S. Ellis, Guido Roberts-Borsani, Daniel P. Stark, Pascal A. Oesch, Renske Smit (Submitted...

Why is impossible measurement of the magnitudes when his values are smaller than Planck units??

Hello, I have a question on the nature of vibrations due to thermal energy. Earlier today I read this article which talked about cooling a glass string to near absolute zero using feedback from a high precision sensor. http://phys.org/news/2015-08-smallest-vibration.html what I understood from...

As I understand, 'Einstein's mirrored light clock' shows us that a vessel (containing said clock) traveling at any speed greater than that of a duplicate, at rest will observe a slower passage of time. I understand that this is because of simple Newtonian physics that shows us that in the case...

A student asked if the labs need to be written in pen. Apparently, the lab instructions say to do so. Actually, I forgot that was in there. It’s kind of a hand-me-down set of instructions from ancient times (a few years ago). I should probably take it out, but it's worth a short discussion. The...

Object: Black Plastic Lid $C$ = Circumference (cm) $D$ = Diameter (cm) Ratio $= \frac{C}{D}$ Ratio $= \frac{30.75}{9.46} = 3.25$

Suppose we define the measurement of an observable A by v(A) v being an 'algorithm giving out one of the eigenvalues each time it is called' (we accept the axiom of choice) In this context we have in particular v(A)≠v(A) since when we call the left hand side and then the right handside the...

2 basic questions from a non-physicist (sigh!). Is decoherence essentially a measurement? And if so is the system of quantum particles set into the classical world forever? Or is there a mechanism by which it will evolve again into a superimposed state? Secondly, if the particle (as in the 2...

I think entanglement swapping shows the difference between measurement and observation. A measurement isn't as important as observation at least to subatomic particles. Here's some key points...

Lets assume that a human colony wants to reform time measurement units for more practical. Reasoning: -circadian rhythm a bit exceeds 24h, so perfect day would be around 24h and 10 minutes ( http://www.circadiansleepdisorders.org/info/cycle_length.php ) -readjusting year zero, somewhere...

This is a variant associated with the Scully and Druhl signal-idler photon delayed choice experiment, as described and discussed in Brian Greene's Fabric of the Cosmos. The commentary notes the "delay" may be configured to happen a very (years) long time after the photons pass the two...

The experiment is described at p26 of http://arxiv.org/abs/quant-ph/0402001 In this experiment we see that we sum measurement results and not measure the sum. Is then the quantum measurement operator not : $$S=A\otimes B\otimes\mathbb{1_{64}}-\mathbb{1_{4}}\otimes A\otimes...

A system at absolute zero (ground state) can't be be divided into observer and observed, can it? I'm struggling with the relationship between superposition, decoherence and temperature. Decoherence requires information. Information requires energy. Though multiple basis of "information" can...

Hi all, I am working on electronics material (using metal oxide as an active layer in TFTs). Currently, I'm trying to measure the sheet resistance (Rs) of CuO thin film (~100nm in thickness). My lab uses Agilent B1500 device for measuring the Rs. I met some problems when carrying out the...

Hello All, I am having some issues with calculating the measurement uncertainty when there is a mismatch in the index of refraction between a fluid and an interface. If am using an unobtrusive measurement technique such as Laser Doppler Velocimetry, how would I be able to quantify the...

Hey guys and gals, clearly I'm new here, not only new here but new to QM (relatively speaking). I've read a few threads here pertaining to a thought I've been pondering on but the answer doesn't seem clear. In the Copenhagen interpretation, what qualifies as a "measurement", and/or what...

[Mentor's Note: Thread moved to homework forums from another forum] Figure shows a potentiometer circuit for comparison of two resistances. The balance point with a standard resistor R = 10.0 Ω is found to be 58.3 cm, while that with the unknown resistance X is 68.5 cm. Determine the value of...

Most presice measurement to date done by MINOS of neutrino time of flight through Earth published two days ago, once again found neutrinos slightly faster than light speed within statistical errors. Only when they extend the band with systematic errors doesn't neutrinos surpass light speed...

What is the differences between inclusive and exclusive B-meson measurements? I think the inclusive is that in the case eg of a B\bar{B} mesons creation, we use the one ##B## meson as a tag (and measure all its products) while we don't measure the mesonic decay of the other ##B## but only the...

I read yesterday about a double-slit experiment in which the researchers set up the device ready to make the measurement, but didn´t make the measurement and the wave function collapsed. Then they did it by taking the measurement and it also collapsed. What does it mean that just by setting up...

What is current density

What is the effect of air bubble in transmission line when measuring differential pressure by the using an electronic transducer? Purging is a must before measurement, however if we still have some bubble inside the transmission line or in front of transducer diaphragm, how it may effect to my...

I have read, and seen it claimed in another old thread, that Galileo was the first to measure the free fall acceleration near Earth's surface. I have not found any source that explains how he did so or what his result was. I've skimmed through most of his Discorsi and have not seen it there...

I keep hearing about things like "quantum decoherence" and the notion that measurement doesn't need a conscious observer. However, I haven't really seen these topics discussed in any of the textbooks I've used (mostly on the level of Griffiths and higher). I haven't even seen a reference to...

Homework Statement You make a measurement of two variables with 100% correlated systematic uncertainty: x_1 \pm \Delta x_1^{stat} \pm \Delta x_1^{sys} = 1.0 \pm 0.1 \pm 0.1 x_2 \pm \Delta x_2^{stat} \pm \Delta x_2^{sys} = 1.2 \pm 0.1 \pm 0.2 The average is taken by: \bar{x} =...

What is the effect of transmission line while measuring pressure value? I want to learn difference between big and small diameter of measurement line (transmission line).

Hi everyone, I am interested in measuring stellar aberration as a challenge to myself; I am more of a physicist than an astronomer. I have a fair knowledge of telescopes and imaging. I would appreciate if somebody can give me instructions or point to some references on: which star to select...

What is the relation between classical from quantum vs measurement problem. On one hand they seem to be related on the other they seem to be of different nature. We always see our screens on front of us and not 100 meters away, that we say is classical object although the screen is a quantum...

Hello, I was reading an article the other day regarding measurement and 'Quantum Wierdness' and it made me think about this whole deal with measuring stuff in QM. [EDIT: Article: http://www.anu.edu.au/news/all-news/experiment-confirms-quantum-theory-weirdness ] The thing is I regularly work...