Uncertainty Definition and 1000 Threads

Uncertainty refers to epistemic situations involving imperfect or unknown information. It applies to predictions of future events, to physical measurements that are already made, or to the unknown. Uncertainty arises in partially observable or stochastic environments, as well as due to ignorance, indolence, or both. It arises in any number of fields, including insurance, philosophy, physics, statistics, economics, finance, psychology, sociology, engineering, metrology, meteorology, ecology and information science.

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  1. Shreyas Shree

    Philosophy of the Uncertainty Principle

    what are the philosophical conclusion one can arrive at from the Uncertainty Principle?
  2. Misha Kuznetsov

    Uncertainty Principle of a high speed particle

    Hello everyone, Heisenberg's Uncertainty Principle states that the less uncertainty there is of a particles position, the more uncertainty there has to be of its momentum. Since mass is a constant in this case, we can refer to the uncertainty of the velocity instead. I was reading a physics...
  3. L

    Uncertainty For Multiple Measurements

    Homework Statement We needed to measure the temperature of a bucket of water using a thermometer which can be read to 0.1°C. Each group would do a single measurement, the data from five groups (including our own) was to be averaged with the uncertainty stated. The data collected was: 19.5...
  4. F

    Non-local uncertainty - does it make sense?

    Guys, I have been watching \ reading some introductory courses in QM for fun, and there's a thing I'd like to discuss. As you might expect, I was displeased by the seeming non-intuitiveness of QM and its interpretations, but one thing appeared to be more intuitive than people imagine. If you...
  5. B

    Quantum Coherence - Decoherence Question

    So I understand that as the number of entangled particles increases, observable quantum mechanical properties decrease to the extent that the mass of particles collectively loses its wave-particle character and behaves classically. In other words, the particles' collective position-space...
  6. N

    How does uncertainty apply to an electron's magnetic moment measurement?

    The electron paths in the path integral formulation of qm are in ordinary space-time. The end-points of the paths in the steady states must be in ordinary space-time as well. The electron's potential is exact or nearly exact either by measurement or by calculation. The electron's locations...
  7. mtnsrfr

    Uncertainty principle for time-energy & momentum-position

    Homework Statement 1) Very short laser pulses can be produced, on the order of a few femtoseconds. (look it up.) If a laser has a center wavelength of 800nm, and lasts for 20 femtoseconds, (2*10-14s) what spread of wavelengths must it have to be compatible with the time-energy uncertainty...
  8. A

    Uncertainty Principle cause infinite wavefunction solutions?

    Dear Physics Forum, Is the Uncertainty Principle the cause of the infinite solutions to Schrodinger's equation? I get the sense it is not. Could you elaborate a little? Thanks, Mark
  9. S

    Question on validity of Heisenberg's Uncertainty principle

    Hi, I have a question about the validity of Hiesenberg's principle when relativity is in action. Hiesenberg's principle tells us that simultaneous measurement of position and momentum can not be done accurately . But relativity tells us that simultaneity is relative , so simultaneous...
  10. C

    How Can I Choose the Right Career When Passionate About Math and Physics?

    Hi everyone. Sorry in advance for the long post.As much as I regret it, I didn’t spend as much time as I should have thinking about what I wanted to do for a career when I was in college. I graduated with a biology degree in May 2013, and entered a physical therapy program (a decision I had made...
  11. xyz_a

    How Do You Calculate Uncertainties in Physics Problems?

    Homework Statement Remember: all answers (including uncertainties) must have three significant digits. For all problems: use the value of g given: g = 9.802 m/s2 0.0005 m/s2. Look at the diagram in the above image. Suppose the total mass of hook 2 is m2 = 951.0 g 2.3 g, and θ = 31.90o...
  12. T

    About the Uncertainty Principle

    If I understand correctly, this very important principle in quantum theory says that the more precise you know the position of a particle, the less precise its momentum can be known. So this raises several questions to my mind: 1) Does this principle applies to photons? Isn’t a photon source...
  13. S

    Uncertainty principle presentation

    Hi all. In my physics class I have to give a 15 minute blackboard lecture on a topic in modern physics. I chose the uncertainty principle because I feel there is a tendency (at least at the undergrad level) to just accept what it is without proof or intuition. I would like to go into greater...
  14. U

    How to quantify relatively simple experimental errors

    Homework Statement For my coursework task, i am to quantify and discuss errors associated with an experimental procedure. This involved a thyristor control unit which allowed the firing angle of two thyristors (in a half controlled bridge rectifier) to be varied with a rotary dial or pot/rheo...
  15. D

    Scaling - Inverse relationship between uncertainty and mass

    Scaling - Inverse relationship between uncertainty and mass I’m trying to express Heisenberg's Uncertainty Principle in a simplified formula that is not boundary unlimited and still capture what I believe is an inverse relationship between uncertainty and mass - the "scaling hypothesis". I...
  16. S

    How Do You Properly Round in Error Analysis?

    Hi, to start with my questions I will show you what I have done so far. (23.56+/-0.05) km/h x (56.3+/-0.4) h So I ended up with (1326.428+/-12.234) km But I know the real answer is (1330+/-10) km What I don't understand is how I would round to that answer. I do not know what I have to look...
  17. B

    Uncertainty principle and relativity

    Consider a particle and you measure the position with a relatively small uncertainty in a box Δx2 . And then you measure the momentum very precisely, let's say with infinite precision. Is the position then completely undetermined or is it still in a large ball of 4/3π(cΔt)3? Does the wave...
  18. S

    Confusion About Quantum Uncertainty

    From what I have heard, it is impossible to know the exact position and the exact velocity of any particle, but what I don't get is why. Does one of those values just not exist at any given point, or does measuring one change the other, or is it maybe something completely different?
  19. Rajkovic

    Is Everything Connected by Quantum Entanglement?

    Hi, I have 16 years old, I am planning to be a physicist in the near future, and I have 3 doubts, could you guys answer to me? 1. Does quantum entanglement proves that everything is connected? http://phys.org/news/2015-01-popper-againbut.html#nRlv 2. 'The Observer Effect' and 'The Uncertainty...
  20. B

    Wave function with a certain wavelength

    I have a number of questions about the wave function - 1. Do photons have wave functions like the one in Schrodinger equation? 2. If they do, when you send out a wave function with a certain wavelength, then because you know the momentum with no uncertainty the uncertainty of the position...
  21. H

    Exploring the Connection between Uncertainty and Relativity in Physics

    I'm still pretty much a virgin when it comes to the serious study of physics, so I apologize if this question is a bit ridiculous. Is the lack of specificity of velocity and position according to the uncertainty principle somehow related to the lack of meaning of velocity without an independent...
  22. Palpatine

    How to devise an experiment that violates uncertainty principle

    Lets suppose device A measures the position of a particle very accurately. Device B now cannot measure its momentum to high accuracy due to the uncertainty principle. But let's suppose that neither A nor B can ever communicate their findings to the rest of the world. Now the uncertainty...
  23. CKaiL

    What is fractional uncertainty mean?

    When we calculate fractional uncertainty , we get a percentage of the uncertainty but what does it mean? For example 5% .
  24. B

    Finding uncertainty for index of refraction

    Homework Statement In an experiment to find the index of refraction, n, of a block of glass, the angle of incidence, θi , and angle of refraction, θr , were measured a number of times as follows: θi 10◦ 20◦ 30◦ 40◦ 50◦ θr 7.0 ◦ 13.5 ◦ 20.0 ◦ 25.5 ◦ 31.0 ◦ calculate the index of refraction n...
  25. CKaiL

    Need help on how to find the uncertainty in this question

    Homework Statement To find the acceleration of a glider moving down a sloping air track, you measure its velocities (v1 and v2) at two points and the time t it takes between them, as follows: v1 = 0.210 +/- 0.05m/s v2 = 0.850 +/- 0.05m/s t = 8 +/- 1 second What should you report for the...
  26. S

    Uncertainty in spin on multiple axes

    In my quantum mechanical studies, I came across the information that if you know an electron's spin on one axis, then you can not know its spin on another axis. For example, if you know that an electron is spin up on the z-axis, then apparently due to the Uncertainty Principle, you can not know...
  27. rpthomps

    Heisenberg's Uncertainty Principle using Linear Algebra

    I am working through linear algebra from MITs MOOC online courses. One of the question refers to the uncertainty principle. It states: AB-BA=I can happen for infinite matrices with A A=A^{ T }\\ and\\ B=-B^{ T }\\ Then\\ x^{ T }x=x^{ T }ABx-x^{ T }BAx\le 2\parallel Ax\parallel \parallel...
  28. P

    Time-energy uncertainty and derivative of an operator

    Homework Statement I would appreciate feedback on the following two problems: (1) For a given operator A with no explicit time dependence I am asked to show that d/dt(eAt)=A(eAt) (2) A free wave packet of width Δx is traveling at a constant velocity v0=p0/m. I am asked to estimate the...
  29. nomadreid

    Diagonalizabilty versus spread for uncertainty (discrete)

    I have seen two characterizations of the problem in measuring a discrete variable of a state ψ exactly with each of two non-commuting Hermitian operators A and B: (1) that the product of the standard deviations ( = √(<ψ|A2|ψ>-<ψ|A|ψ>2), & ditto for B) ≥ 1 (2) that one cannot simultaneously...
  30. Ahmed Abdullah

    Equivalence of waveparticle duality to uncertainty principle

    http://www.sciencedaily.com/releases/2014/12/141219085153.htm It says "Here's a nice surprise: quantum physics is less complicated than we thought. An international team of researchers has demonstrated that two peculiar features of the quantum world previously considered distinct are different...
  31. P

    Alpha Particle Spectroscopy - Is My Method Correct?

    Homework Statement Hey, first time poster here, I'm current writing up a lab report I just wanted to check my method is correct. I'm doing alpha particle spectroscopy using a cloud chamber setup. Most published reports seem to vary pressure (so the mass thickness varies). Our chamber let us...
  32. S

    ? connection between uncertainty and wave-particle duality

    After reading these recent articles on proof of the theory that merges the "duality" of .. " The connection between uncertainty and wave-particle duality comes out very naturally when you consider them as questions about what information you can gain about a system" Can someone point me to a...
  33. A

    How do we know uncertainty principal isnt ignorance?

    what if there's a way to measure speed and direction at the same time and we haven't found it out yet? does it have to do with information theory?
  34. Ahmad Kishki

    Why is Energy Conservation Not Guaranteed?

    please explain energy time uncertsinty principle, and how does it imply that energy conservation is not guaranteed?
  35. A

    Possible sources of error/uncertainty in bifilar pendulum?

    in my AH physics investigation - measuring acceleration due to gravity, I used the bifilar suspension pendulum btw a light gate was used for the errors/problems section so far I have problems in making the rod level and keeping the two strings parallel, also all the random, calibration and...
  36. A

    Possible sources of error in compound pendulum experiment?

    completing my advanced higher physics investigation - measuring acceleration due to gravity for the oscillating mass on a spring experiment so far I have included friction between the nail & oscillating rod as a possible source of error can anyone think of anything else? thank you very much...
  37. A

    General Uncertainty Relation -- Why drop anticommutator?

    In the derivation of the generalized uncertainty principle (as pgs 1-2 of here), there is an anticommutator term that is dropped at the end, leaving just the commutator part...this is said to "strengthen" the relation, as both terms are positive. I don't understand this. So we basically have...
  38. O

    A very basic question about Heisenberg Uncertainty

    So I understand that Heisenberg Uncertainty states that we cannot know the position and velocity of an electron at the same time. Although I haven't go through its proof and assumptions, I have read on couple place that that's because if we are able to observe it, that means it have to reflect...
  39. A

    Time Energy Uncertainty Question

    I would appreciate if someone could help figure out this thought experiment: Lets say I have two detectors named A and B. They both want to detect system C. For my naming convention I will say that C.B is the perturbed state of C after interacting with B Ok so both A and B decide to measure...
  40. D

    Determining the mass of a beam and using percent uncertainty

    Homework Statement An astronaut exerts a 110-N force pushing a beam into place on the International Space Station. The beam accelerates at 0.40m/s2 . What is the percent uncertainty in your answer? The uncertainty of the force is 10 N and the uncertainty of the acceleration is 0.01 m/s2...
  41. R

    How to Estimate Expanded Uncertainty in Absolute Humidity Calculations?

    Homework Statement The Magnus formula is used for calculating the saturated water-vapour pressure Ew at temperature t. The average of the 10 repeated measurements of air temperature is 22.27 ˚C with experimental standard deviation s(t)=0.09 ˚C. The permissible error of the thermometer is ±0.3...
  42. throneoo

    Uncertainty Principle and single-slit diffraction

    Homework Statement A beam of 50eV electrons travel in the x direction towards a slit of width 6 micro metres which is parallel to the y direction. The diffraction pattern is observed on a screen 2 metres away. Use the Heisenberg uncertainty principle to estimate the minimum uncertainty in the...
  43. D

    How to find the uncertainty of a slope (using software)?

    I've just done an experiment and need to calculate the slope of the best fit straight line, but I'm having some trouble with it. First, let me briefly describe the experiment. I need to vary the distance two metal plates and find the capacitance of it. I tried to record the value a few points...
  44. R

    Wave Particle Duality & Uncertainty Principle: Which Came First?

    Which of them comes first,(I mean the concept or the theory)? Did Heisenberg come up with the idea of uncertainty principle because of the discover of the wave particle duality? Thanks for paying attention~
  45. B

    Path Integral From Heisenberg Uncertainty?

    Two questions about the path integral: a) Intuitively, how does one (as Landau does) start quantum mechanics from Heisenberg's uncertainty principle, which states there is no concept of the path of a particle, derive Schrodinger equation i \hbar \tfrac{\partial \psi}{\partial t} = H \psi the...
  46. G

    Can I Accurately Measure Temperature with 3 1/2 Digit Equipment?

    In an attempt to determine how the temperature varies over a distance of 100m, I have taken five temperature measurements for every 10 meters, for a total of 55 measurements. I have then, for each dataset of N=5, calculated the mean value, standard deviation and standard error. Finally, I've...
  47. O

    Calculating Emitted Photon Properties for Excited Atoms | Homework Help

    Homework Statement Atoms of a certain material are in an excited state 1.8eV above the ground state and remains in that excited state for 2.0ms before to the ground state. Find 1) The frequency of the emitted photon 2) The wavelength of the emitted photon 3)The uncertainty in the energy of the...
  48. V

    Expecting the possible event of zero probability

    Consider a potential well in 1 dimension defined by $$ V(x)= \begin{cases} +\infty &\text{if}& x<0 \text{ and } x>L\\ 0 &\text{if} &0\leq x\leq L \end{cases} $$ The probability to find the particle at any particular point x is zero. $$P(\{x\}) = \int_S \rho(x)\mathrm{d}x=0 ;\forall\; x \in...
  49. P

    Energy Uncertainty and expectation value of H

    Homework Statement A particle at time zero has a wave function Psi(x,t=0) = A*[phi_1(x)-i*sin(x)], where phi_1 and phi_2 are orthonormal stationary states for a Schrodinger equation with some potential V(x) and energy eigenvalues E1, E2, respectively. a) Compute the normalization constant A. b)...
  50. S

    Calculating Uncertainty of an intrinsic function

    Homework Statement I need to calculate the value and the uncertainty of the equation \begin{equation} S = 2d \sin(\theta) \end{equation} (one side of the Bragg formula), however, the final answer is strange, so I would like to know what I'm doing wrong. Homework Equations My $\theta$ value...
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