What is Uncertainty: Definition and 1000 Discussions

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. A

    I Uncertainty of MonteCarlo Simulations: Weight and Error Bars

    Hello everybody, I need a help, primarly a confirmation about my reasoning. I have data from a MonteCarlo simulation of collisions between particles at LHC (made with Madgraph). I have plotted some variables, for example the angle between two final leptons. Then I have normalized the plot to a...
  2. S

    I Question about the uncertainty principle

    The uncertainty principle says that you can't know position and velocity of particle at the same time. So particular we can not say that the particle is at rest at some point because then we would know it is not moving and we would know exactly where it is. So my question is if we send the...
  3. M

    How do we find the uncertainty of v in the kinematics eqn?

    Homework Statement Given the kinematics equation v2 = u2 + 2as, find the uncertainty Δv. Given: Values of a, s, u, and their associated uncertainties. Homework Equations v2 = u2 + 2as The Attempt at a Solution I'm aware of the rules for uncertainty propagation, but what do I do in this case...
  4. D

    B Heisenberg's uncertainty principle

    Instead of just taking one measurement of the particle, you take a 2nd measurement in addition thereby gathering more information about the particle then the uncertainty principle allows?It would be possible to extend out to an arbitrary number of follow-on measurements thereby measuring...
  5. Ssnow

    I On Heisenberg's uncertainty principle

    Hi everybody, my question is a curiosity on the (generalized) Heisenberg principle: ## \sigma_{x}\sigma_{p} \geq \frac{\hbar}{2},## where ##x,p## are the usual quantum operators and ##\hbar## the Planck constant divided by ##2\pi##. If I understood correctly, Gaussian states that are solution...
  6. Sushmita

    "Uncertainity Product for Particle in 1-D Box

    Homework Statement For the ground state of a particle moving freely in a one-dimensional box 0≤x≤L with rigid reflecting end points, the uncertainity product (Δx)(Δp) is (A) h/2 (B) h√2 (C) >h/2 (D) h/√3Homework Equations The uncertainity principle says that - (Δx)(Δp) ≥ ħ/2 Ground state energy...
  7. A

    Can More Readings Reduce Fractional Error in Measurement?

    Why is fractional uncertainty not affected by systematic error? For example à vernier calipers measures the diameter of a coin: (5.06+-0.04) mm Can taking more readings, say 6, and taking average, reduce fractional error?
  8. Jerry Z

    Homework help: Uncertainty with negative power

    Question: A distance R is measured to be 3.400 ± 0.007m. What is the absolute uncertainty in R^−2? Attempted solution: Relative uncertainty: 2* (0.007/3.4) = 4.11E-3; R^-2 = 3.4^-2 = 0.0865 m^-2; Absolute uncertainty = R^-2 * relative = 0.0865 * 4.11E-3 = 3E-4 m^-2; Any help would be greatly...
  9. F

    I Significant figures and uncertainty in measurements

    Hello, I was recently pondering on significant figures and uncertainty reminding myself that there is no perfect measurement: every measurement involves an error caused by the instrument and/or the operator. A measurement should be executed as many times as possible and not just once. The...
  10. Krushnaraj Pandya

    Uncertainty in the energy of a laser beam

    Homework Statement The duration of a laser pulse is 10^(-8) s. The uncertainty in its energy will be? Homework Equations ## \delta x \delta p=\frac{h}{2\pi}## The Attempt at a Solution speed of laser beam=c, duration is given so distance can be calculated exactly-shouldn't that mean delta...
  11. Cardinalmont

    B Greatest Possible Uncertainty and Sig Figs

    There is something I seriously don't understand about uncertainty. Suppose there is an electric balance that reads 5.67g The limit of reading is 0.01g The greatest possible error is half of the limit of reading and is thus 0.005g By this logic, and assuming the very best possible situation, I...
  12. N

    Solve Uncertainty in "An Introduction to Error Analysis" by John R Taylor

    This isn't a homework question, but instead a question about an example in a book I'm reading, in prep for next semester. As such using the posting template is a bit of a miss. Hope that can be forgiven. 1. Homework Statement I'm reading "An Introduction to Error Analysis" by John R Taylor...
  13. Jozefina Gramatikova

    Fractional uncertainty of g on the surface of the Sun

    Homework Statement Homework Equations The Attempt at a Solution it looks like I got too big numbers for the uncertainty
  14. JessiLim

    Static and Kinetic Friction vs Normal Reaction Graphing

    How do i suppose to determine the uncertainty for the slope of my Static friction against normal reaction graph? My data for static friction and normal force has the uncertainty of +/- 0.0001 The uncertainty is too small for me to draw airbox/bar in the graph to draw the max and min slope...
  15. F

    I Heisenberg - Uncertainty principle - lifetime of a particle

    I have seen that the more a particle has a high energy, i.e ##E##, the more its lifetime is short, respecting so the uncertainty principle. But by the definition of this uncertainty principle : ##E\,\Delta t \geq \dfrac{\hbar}{2}##, I can write : ##\Delta t \geq \dfrac{\hbar}{2E}##, then...
  16. S

    I Uncertainty of coefficients after a least square fit

    Fitting data to a linear function (y=a0+a1*x) with least square gives the coefficients a0 and a1. I am having trouble with calculating the uncertainty of a0. I understand that the diagonal elements of the covariance matrix C is the square of the uncertainty of each coefficient if there are no...
  17. Sandeep T S

    Uncertainty and the speed of light?

    By Uncertainty Principle speed of a particle cannot be constant. then speed of a single photon not?
  18. B

    I Reconciling Spacetime & Quantum Uncertainty

    These two ideas seem to be categorically opposed. The concept of an event as a point in spacetime seems to not square with uncertainty and the concept of quantum intrinsic randomness seems to not square with unchanging spacetime... Assuming it is unnecessary to explain further why this is a...
  19. J

    I Does the Uncertainty Principle imply a linear cosmology?

    If the uncertainty in the age of the Universe is ##\Delta t## then the Uncertainty Principle implies that it has an uncertainty in its energy ##\Delta E## given by $$\Delta E \ \Delta t \sim h.\tag{1}$$ If this energy fluctuation excites the zero-point electromagnetic field of the vacuum then a...
  20. J

    A Classical uncertainty principle

    What assumptions underlie the classical uncertainty principle? The principle doesn't seem to apply when I want to know the precise pitch of a tone from a bowed violin string, since I can measure the duration (as precisely as I want) of the beats produced when I interfere it with a sine wave of...
  21. dRic2

    I How Does Measurement Affect Uncertainty in Quantum Mechanics?

    I'm having trouble trying to remember this: suppose I have an operator ##A## and an eigenfunction ##\psi = c_1 \psi_1 + c_2 \psi_2## for ##A## so that $$ A\psi = a\psi$$ The expected value is ##\langle A \rangle = \langle \psi|A|\psi \rangle = a## After a measurement ##a## can be ##a_1##...
  22. E

    I The energy-time uncertainty principle

    I'm watching a freshman-level lecture trying to take students through the energy-time uncertainty principle. (They've covered the position-momentum uncertainty principle). In the lecture, the professor starts by saying that we have a particle with some momentum, but that we can't know the...
  23. S

    I Uncertainty relation derivation

    Hey guys , my lecturer introduced a new concept with reference to the commutation of two operators.He claimed that if two commutators commute then they can be simultaneously measured.I can clearly see how this works.He then went on and state if they don't commute they can't simultaneously be...
  24. C

    Uncertainty Principle and the lifetime of an excited state

    Homework Statement [/B] Estimate the lifetime of the excited state of an atom whose natural emission line width is 3.00 × 10−4 eV. Homework Equations $$ \Delta E \Delta t = \frac{1}{2} \times \frac{h}{2\pi} $$ $$ \Delta E \Delta t = \frac{h}{2\pi} $$The Attempt at a Solution I think all I...
  25. e2m2a

    I Cosmological Redshift and Heisenberg Uncertainty Principle

    Has anyone conjectured that the redshift associated with Hubble's constant can be explained by Heisenberg's uncertainty principle? Another words, the further in space away from us a photon is emitted from a galaxy, the longer in time it takes for the photon to reach us. Since the photon has a...
  26. J

    I What happens if B measures the x-axis spin in an entangled pair?

    Watching an old (2012) youtube video (), the narrator says (time 10:38) that if A measures the y-axis spin of an entangled pair and communicates his finding to B, then B "cannot" measure his x-axis spin, because doing so would give him knowledge of the spins along both axes, which uncertainty...
  27. F

    A What are the typical uncertainties of data in Astophysics?

    Hello, everybody. I'm conducting an investigation in planetary sciences. Specifically in exoplanet detection by the radial velocity method and I'm stuck because I need to know how to defend the data that I'm using. I'm using the data from http://exoplanet.eu/catalog/ and I have found some data...
  28. S

    How do you find the uncertainty of an average?

    Homework Statement I used a spectrometer in class and obtained 6 angles in which and found the angles. I needed to find the average of the angles and account for the uncertainties here is what I did: Center (A): 179.58°±.26 Center (B): 359.35°±.26 Purple(RA): 194.95°±.66 Purple...
  29. olgerm

    I Calculate measurement uncertainty? I made one measurement....

    How to calculate measurement uncertainty of m. I understand I should use these formulas to calculate it if I had data of many measurements, but when have only measurement then it becomes undefined, because of 0/0 in standard deviation formula. ##u(m)=\sqrt{u_a^2(m)+u_b^2(m)}##...
  30. S

    I How does the equation for experimental uncertainty work?

    We have been using the equation attached as in image to calculate experiment uncertainty in my class, can somebody explain exactly how this works? Let’s say we have a value y which is equal to 1/x, where x is some measured quantity with some uncertainty, and let’s say that that value of x is...
  31. D

    Multiple choice on uncertainty

    1. A student measures the density of a metal and calculates answer to be 8543.2kgm^-1 . The result is accurate to +- 1.1% Which of the following states answer to an appropriete number of sig figs? A 8.543x10^3 B 8.5x10^3 C 9x10^3 D 8.54x10^3 2. Relative Uncertainty = Absolute Uncertainty/...
  32. Derek P

    I Heisenberg Uncertainty vs Measurement Error

    Spun off from https://www.physicsforums.com/threads/is-quantum-physics-retro-deterministic.945431/#post-5984157. @Gerinski said: if we measure a particle's position at time X (not caring about its momentum) and we measure it again at a later time Y and we find it at some other position (again...
  33. A

    Time Uncertainty Propagation - Stoke's Law & Average Time

    Homework Statement [/B] So basically I am calculating the terminal velocity for a small sphere falling in a measuring cylinder filled with glycerine. The distance traveled is 20 cm (0.20 m), and I have conducted 3 trials for each temperature. I have measured the displacement of the ball using...
  34. Derek P

    I The inequality in the Heisenberg uncertainty relation

    I was musing about why the HUP is an inequality. If you analyse a wave packet the spatial frequency spectral width is inversely proportional to the spatial width. So there should be an equality such as Heisenberg's equation 3 in this paper. Has anyone got a simple explanation of where the...
  35. J

    B How Do You Properly Calculate Uncertainty in Measurements?

    I've come across it it at least half a dozen classes in my life but I never really learned how to do uncertainty calculations properly. Right now I am torn between what is taught and what makes intuitive sense. In every book or website there is a different explanation of this concept with...
  36. CricK0es

    Uncertainty of a chosen value

    Homework Statement I have taken 5 sets of readings of voltage against angle for an experiment to determine specific rotation. (I'm using the maxima to determine the phase shift) So, having averaged these values and determined the maximum, I can then trace back to the angle at which this...
  37. SuchBants

    Uncertainty larger than the plotted value

    Homework Statement I'm determining g by the extension of a spring. I used a PASCO motion sensor to record the displacement of the spring towards the sensor since it is more accurate than myself using a ruler. The uncertainty in the distance on the sensor is 0.8%. I get the uncertainty in...
  38. F

    I Making sure about the spreads in the Uncertainty Principle

    Hello Forum, Going through Griffith's book last night, I read a good paragraph on page 111 about the canonical uncertainty principle for position and momentum in the x direction: $$\sigma_{x} \sigma_{p} \geq \frac{\hbar}{2}$$ If we could make 100,000 identical copies of a system in exactly...
  39. SuchBants

    Uncertainty in the intersection of two lines with error bars

    The only thing I wish to take from this graph is the intersect of the two lines of best fit. How can I get the uncertainty in this point? While the points appear to have the same uncertainties, they actually each have their own distinct % uncertainty. Would the maximum uncertainty in the X...
  40. P

    I Why is the Uncertainty principle inherent to particles?

    If we have a particle, say, an electron and we shoot it straight through an empty box. This box is surrounded by light sources on its two sides: So, if you consider the above cube, if we shoot a particle in a straight line such that it crosses the face ABEF and it crosses the face HGDC through...
  41. A

    Uncertainty/error of a volume is greater than the normal volume

    Homework Statement I have an empty cylinder with an external diameter of (23.0 ± 0.5) mm, an internal diameter of (22.5 ± 0.5) mm and a height of (60.0 ± 0.5) mm. I need to calculate its volume with its uncertainty/error. Homework Equations The Attempt at a Solution I do it like this...
  42. K

    B Uncertainty Principle: Velocity, Position and Energy

    If velocity is delta position vs delta time and you know the velocity and change in time exactly why is it impossible to find the exact position of the electron? Same question for energy and position.
  43. T

    Calculating uncertainty for a small sample

    Homework Statement I am currently doing a lab experiment on viscosity. Basically placing a glass ball inside a tube full of sugar solution., and recording the times for the ball to travel a distance of 100mm. My issue is for such a small data set i.e 3 trials how do I calculate the uncertainty...
  44. G

    Uncertainty for a particle diffracted through a single slit

    Homework Statement A horizontal beam of laser light of wavelength 486 nm passes through a narrow slit that has width 0.0590 mm . The intensity of the light is measured on a vertical screen that is 2.90 m from the slit. What is the minimum uncertainty in the vertical component of the momentum...
  45. K

    Calculate the minimum uncertainty

    Hello, can anybody help me with solving the problem. Homework Statement :[/B] Calculate minimum uncertainty? A horizontal beam of laser light of wavelength 604 nm passes through a narrow slit that has width 0.0600 mm . The intensity of the light is measured on a vertical screen that is 2.40...
  46. heavystray

    B How do you calculate the uncertainty in T using graphs?

    i have an equation like this: Given m(B-V)= 1.2 +- 0.2 How do you calculate the uncertainty in T? (btw, I solve T using graphs by finding the intersection point) My idea was first to calculate T when m(B-V) =0.2, and I then calculate T when m(B-V)= 1.2 + 0.2(its uncertainty). and then find the...
  47. J

    Young's modulus and uncertainty

    Homework Statement Homework EquationsThe Attempt at a Solution Y = (F/A)/(∆L/L) = FL/A∆L Putting values of F , L , A and simplifying Y = 2×109/∆L I don't know how to proceed . I also don't understand what is uncertainty in length and uncertainty in strain . Is uncertainty the same thing...
  48. MichPod

    B Where is the mistake -- violation of Heisenberg uncertainty

    The following is kind of a semiclassical reasoning which goes along the style of the discussions between Bohr and Einstein in Solvay Conference. Suppose we have a single slit from which a particle may be emitted and, on a very large distance from it, a thin cloud chamber CC, which we use as a...
  49. P

    I Field operators and the uncertainty principle

    Hi, I am reading QFT by Lancaster and Blundell. In chapter 4 of the book the field operators are introduced: "Now, by making appropriate linear combinations of operators, specifically using Fourier sums, we can construct operators, called field operators, that create and annihilate particles...
  50. N

    How to appropriately assign sigma values (uncertainty)

    First let me preface this by saying, I'm not a native english speaker. I'm not sure "uncertainty" is the word I'm looking for it might also be deviation, however it is the translation of what its called in Danish, my native tongue. I'm doing a lab report about rolling objects on a slope, for my...
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