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. G

    Calculating Percentage Uncertainty in Gradients

    Hello I was given following homework question. 2 gradients are given. gradient1 of the line is 0.503 gradient2 of the line intersecting the line above is 0.167. Find out the percentage uncertainty in the gradient. i thought you have to do (0.503-0.167)/0.503 is that right?Please help thanks...
  2. B

    The uncertainty principle

    Hi folks, I do read some of the interesting post on this forum particularly the discussions on the concept of uncertainty principle ie the more you know about the particle position the less you know about its momentum etc etc I am a complete novice and am trying to get the big picture here...
  3. C

    Time-Energy Uncertainty relation

    Homework Statement So I have this homework question and the answer that was given to me to check the answer that I have does not match with my answer. The question I have to complete is shown below: The answer given to me is D, 6.6eV Homework Equations \Deltat\DeltaE = h/2...
  4. B

    Finding the momentum uncertainty for a particle-in-a-box

    Homework Statement I'm looking at an electron-in-a-box with walls at x=0 and x=L; I want to calculate the uncertainty (delta p) in the measurement of its momentum: sqrt(<p^2>−<p>^2) for its nth excited state. Homework Equations The normalized wave function: psi_n(x)=sqrt(2/L)*sin(n*pi*x/L)...
  5. Z

    Thinking about the uncertainty principle.

    We all know that our universe is headed towards a heat death with maximum entropy and useless energy. However, we know that a vacuum of space will always have energy greater than its local minimum (potential well) due to the uncertainty principle. There must always be random fluctuations...
  6. A

    The Lorentz Transformations and the Uncertainty Principle

    Two observers A and B are in relative motion with a constant velocity[for example, along the x-x' direction].If A knows the the position of B accurately , the motion of B gets enormously uncertain[and vice verse] in his calculations/considerations.How is he going to derive the Lorentz...
  7. C

    Solution to uncertainty principle

    We all know that you can supposedly never know the exact position and momentum of a particle, because the very act of measuring disturbs it. Now, why can't we have two particles that start out and evolve the same exact way but separately and, using one of them as a dummy, perturb it, extract...
  8. F

    Uncertainty Analysis for $\pi$

    Homework Statement Find the uncertainty for pi using (a) the formulas (b) calculusHomework Equations \pi = (4/D^{2})(hw - m/(PL)) Uncertainty formulas: for products and quotients: Z = XY \deltaZ/Z = \deltaX/X + \deltaY/Y for differences: Z = X - Y \deltaZ/Z = \deltaX/(|X - Y|) +...
  9. E

    Heisenberg Uncertainty Principle homework

    Well first off, I am confused about what the book says earlier and what the actual answers are in the back of the book on homework problems. I thought I understood the book, but it seems like I don't. The book has: "Consider a particle whose location is known within a width of L along the x...
  10. M

    Estimating random uncertainty

    Homework Statement The value of the speed of sound obtained in an experiment is 327.76 ms-1. The result has an uncertainty of +-3% of the result. Which one of the following values is expressed to the correct number of significant figures? (A) 327m-1 (B)327.8ms-1 (c)328ms-1 (D)330ms-s...
  11. P

    Area & Uncertainty of Rectangular Concrete Floor

    4. A rectangular concrete floor is measured. Its length is (4.25 ± 0.05) m and width is (1.80 ± 0.05) m. Determine: b) the area and its uncertainty. This was the solution. However I got 6.65 x 10^2 as my absolute uncertainty. My questions are: 2. When finding the final uncertainty that...
  12. D

    Calculation of the velocity uncertainty

    Homework Statement I need to calculate the uncertainty for the velocity v_1=(cart length)/t_1. The cart length is constant. Homework Equations That is what I am not sure about. I need to use the rule "dividing by a constant" to find the uncertainty. Is that result q=B/x ,where B is...
  13. G

    Calculators Uncertainty+: uncertainty calculator

    To be honest, this is straight up advertising, but I think it'll be helpful to a lot of people. My friend has made an Uncertainty calculator app for the iPhone (android coming soon), and it has saved me tons of time. So I just want to support him. Here are the links and screen shots...
  14. Zarlucicil

    Uncertainty Calculation for Quantum Physics Lab | General Physics FAQ

    I'm in the process of doing a quantum physics lab and am having a bit of trouble with uncertainty. The specific things going on in the lab aren't relevant, I don't think, only the general procedure of my calculation. Also, I'm not certain where this question should be asked, so I decided to put...
  15. M

    Max/Min of Speed Uncertainty

    Homework Statement A baseball player friend of yours wants to determine his pitching speed. You have him stand on a ledge and throw the ball horizontally so that his release point is 3.6 m above the ground. The ball lands 29.0 m away. a. What is his pitching speed? b. As you think about...
  16. Z

    Heisenberg's 1927 paper on uncertainty

    Does anyone know if there is an online english translation of Heisenberg's paper on uncertainty "über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik" Z. für Phys. 43, 1927. I haven't been able to find it so far, all I can find is one's in German...
  17. 1

    Calculating the Volume of a Cylinder with Uncertainty

    Homework Statement 4 glasses of liquid must be transfferred into a beaker that has a cylinder shape without any markings. The teacher says that the glass will hold 250mL, but the uncertainty was 10mL in which this was determined. The radius and the height of the beaker was measured within an...
  18. 1

    Calculating Car Distances: Uncertainty in Car Gaps and Lengths

    Homework Statement Drivers that come to a stop leave different amount of gaps between their car and the car in front. It was found that the average gap was 1.45m, but as the values varied, the uncertainty was 25cm. It was also reported that the car is 5.1 ± 0.5m in average. What is the range...
  19. E

    Uncertainty Principle Equations

    I have a few questions regarding how/when to use which uncertainty principle formulas. I am not sure of the difference between them. I've checked my book and wiki and neither really helped. Here are the formulas in question. \Delta p \Delta x \approx \hbar \Delta p \Delta x \geq...
  20. N

    Uncertainty Principle: Explaining the Inequality Relation

    The Uncertainty Principle is an inequality relation but while its application, only the equality is considered. For example - to calculate the Mass/Energy of a particle produced during an interaction, the Life Time of the particle is used to divide the Constant (h/2). But in principle the...
  21. E

    Uncertainty - Finding Momentum and KE

    Homework Statement An electron is conned inside a cubic region of size an atomic radius L = 0.5 nm. Homework Equations What is the uncertainty in the momentum p of the electron? Remember that \Delta p \Delta x \approx h. The Attempt at a Solution I am confused when to use \Delta p \Delta x...
  22. Y

    Calculate 73.936 with Absolute Uncertainty

    Homework Statement Perform the calculation and report answer in proper scientific notation with absolute uncertainty 73.936(+ 0.19%) / [(0.00455+ 0.00096) + (0.011889(+0.73%))] Homework Equations Addition/Subtraction: Absolute uncertainty = square root(uncertainty1 + uncertainty2)...
  23. J

    Doubt regarding uncertainty principle

    I had a thought going in my head today about the uncertainty principle. Forgive me if it sounds too silly. Consider an electron in motion. Now, suppose that I'm measuring it's position with infinite accuracy. So, by the uncertainty principle, it's velocity is blurry. But what if I measure the...
  24. B

    Heisenberg's Uncertainty principle

    I am trying to understand fully the concept of this principle. But this uncertainty stuff confuses me. Can someone give me the link, or some material so I can work mathematics behind this mechanism. Its not that principle it self is the problem, I have glimpse what's going on, but the...
  25. G

    Finding Uncertainty of the Second Derivative

    Hey there, I have a problem to do, in which I need to determine the acceleration of an object and the uncertainty of the acceleration. The position vs. time equation is given by: s(t) = 0.205t2 + 0.3001t Therefore, after differentiation, I can state the the velocity vs. time equation...
  26. X

    PLEASE HELP Question regarding uncertainty principle

    Analogous to the uncertainty relation ΔpΔx > h/4π, there is an uncertainty relation for the time and energy, ΔEΔt > h/4π that stems from the methods usually used to measure the energy. The uncertainty in the time, Δt, can be interpreted as a lifetime. The excited state of an atom responsible...
  27. E

    Calculating uncertainty in data.

    Homework Statement This is from a laboratory exercise. I was asked to measure the time it took for a pendulum to cover 3 periods. I repeated this 25 times, to get 25 measurements for as many trials. I also calculated the standard deviation from the measured data (calculated for different...
  28. A

    Absolute Uncertainty of a Volume

    Determine the absolute uncertainty of the prism's volume. The uncertainty of each measurement is +/- 0.5mm. The length of the prism is 142mm, width is 86mm and the height is 151mm. Thank you!
  29. T

    Does Time-Energy Uncertainty Violate Energy Conservation?

    Hi folks, I am new to physics forums , an engineer by profession, I have newly developed some interest for pure physics, can someone please enlighten me on the violation of energy conservation by the time energy UP? The way I understand it the principle only puts a LOWER bound. Is...
  30. maverick_starstrider

    What's Really so Quantum About Heisenberg's Uncertainty?

    What's Really so "Quantum" About Heisenberg's Uncertainty? I've never really understood what was so interesting and strange about Heisenberg's Uncertainty (or Robertson's Inequalities). If we take as axiom that particles exist as wave functions that satisfy schrodinger's equation then what is...
  31. V

    Calculating Electron Energy with Uncertainty Principle: Homework Example

    Homework Statement Using the uncertainty principle, estimate the minimum energy in electron volts of an electron confined to a spherical region of radius 0.1nm. Homework Equations delta-x * delta-p = h-bar / lamda delta-y * delta-p = h-bar / lamda delta-z * delta-p = h-bar /...
  32. V

    How to Calculate Uncertainty of an Operator with Known State

    Given the state and an operator I know the uncertainty of this operator can be calculated via (see next post latex is being weird, sorry)
  33. H

    Determining Uncertainty in XRD

    I am new to XRD and want to know the best way to measure uncertainty. Any help would be greatly appreciated.
  34. brainpushups

    Uncertainty in the parameters A and B for a linear regression

    I'm working through John Taylor's An Introduction to Error Analysis and so far this is the only problem I haven't been able to solve. I was hoping someone could lend me some insight. The problem asks you to use error propagation to verify that the uncertainties in A and B for a line of the...
  35. M

    Uncertainty in the presence of quantum memory

    I am looking at the paper "The uncertainty principle in the presence of quantum memory" by Berta and others. It states that if Bob maximally entangles a particle P with a quantum memory M then he can beat the bound of the uncertainty principle on P. The argument is that, if Bob gives P to...
  36. F

    I2 Gas Molecules: Uncertainty in the Double Slit Experiment?

    If buckyballs display uncertainty in the double slit experiment, shouldn't iodine gas molecules as well? An I2 molecule is certainly less massive than a buckyball. Yet why can we see I2 gas as a purple haze? I can see it, almost in the same way I can see my pencil, which has a very small...
  37. T

    Uncertainty Principle: Misconceptions & Justifications

    Hi together ... In many textbooks on particle physics i encounter - at least in my mind - a misuse of the Heisenberg uncertainty principle. For completeness we talk about \Delta p \Delta x \geq \hbar/2 For example they state that the size of an atom is of the order of a few Angstroms...
  38. soothsayer

    Mass Uncertainty: Position, Velocity & Mass

    Whenever I hear the Uncertainty Principle used, It's always to talk about how a particles' momentum can only be known to a certain range if it's position is known too precisely, and in problems I've encountered, or vice-versa. In problems I've encountered, often times I'll be asked to find the...
  39. M

    Uncertainty product of infinite square well

    For the ground state of a particle moving freely in a one-dimentional box 0\leqx\leqL with rigid reflecting end-points, the uncertainty product (del x)(del p) is 1 h/2 2 sqrt{2}h 3 >h/2 4 h/sqrt{3} I used (del x)^2 =<x^2>-<x>^2 and (del p)^2 =<p^2>-<p>^2 Using the wavefunction of...
  40. E

    Minimum uncertainty wave packets energy interpretation

    I am having trouble understanding (not for homework) what a wave packet is in terms of the correspondence of the idea of a wave packet to a "point like" particle. I'd like to focus on the 1d wave packet ultimately, but in order to describe my consternation -- let me detour to a well defined...
  41. C

    Uncertainty in Multiplication: Significant Figures vs. Rate

    Why do we use significant figures in calculations instead of the rate of Uncertainty? (2,5\pm0,4000)*4,000=(10\pm1,6). The number 2,5 has 2 significant figures, which is the same as we will write in the answer, while it should be only one significant figure in the answer if we take the rate of...
  42. snoopies622

    Confirming Uncertainty: Electromagnetic Fields in Hilbert Space

    I think this is right, but could someone confirm (or deny) this for me? While a particle like an electron - or a finite set of particles for that matter - is represented by a single normed vector in Hilbert space which is acted on by operators such as ones for energy, position and momentum...
  43. L

    Heisenberg's uncertainty principle

    in Heisenbergs uncertainty principle, how do you know when to use hbar, h, h/2 or hbar/2? thanks
  44. N

    Uncertainty Principle Hypothetical question

    Ok hey forum. I thought it might be a neat idea to contemplate this idea, and perhaps regurgitate some thoughts back on to this thread. So, as the Heisenberg uncertainty principle states, one can not know both the velocity and position of a particle or electron. I was curious to hear thoughts...
  45. M

    Uncertainty in measurements and epsilon delta definition of a limit

    does the epsilon delta definition of the limit connect to the uncertainty in measurements like this? like if we measure a quantity time with value a with error of + or - delta then my formula will give me v with value L +or - epsilon or is it unrelated?
  46. P

    Quantum variance (uncertainty)

    Homework Statement N=a^+a a=\frac{ip+mwx}{\sqrt{2m\hbar w}} \quad a^+=\frac{-ip+mwx}{\sqrt{2m\hbar w}} |z>=e^{\frac{-|z|^2}{2}}\sum^{\infty}_{n=0}\frac{z^n}{\sqrt{n!}}|n> where <n|n>=1 Show that the variance (uncertainty) in N, \Delta N is |z| i.e. calculate (\Delta...
  47. E

    Heisenberg Uncertainty Principle

    Homework Statement A beam of 50eV electrons travel towards a slit of width 6 micro metres. The diffraction pattern is observed on a screen 2m away. Use the angular spread of the central diffraction pattern (+/- lambda / slit width) to estimate the uncertainty in the y-component of momentum...
  48. E

    Uncertainty Principle beam of electrons

    Homework Statement A beam of 50eV electrons travel towards a slit of width 6 micro metres. The diffraction pattern is observed on a screen 2m away. Use the angular spread of the central diffraction pattern (+/- lambda / slit width) to estimate the uncertainty in the y-component of momentum...
  49. E

    Finding Uncertainty of # Cans in Pool

    What is the volume of the pool? 165 m^3 What is the uncertainty in the volume of the pool? Express it in terms of cubic meters. 20.6 m^3 Joe's supervisor says, "Okay, Joe, your first job is the fill the pool. We used to use a hose, but it sprang a leak. Instead, you'll have to fill...
  50. P

    Standard deviation from measures with different uncertainty

    Homework Statement i have a few results of measurements, with different measurement uncertainty: L=5\pm0,2, L=5,1\pm0,1,L=5,2\pm0,3,L=5,3\pm0,1,L=5,4\pm0,2 and how can i count standard deviation and final result of measurement with uncertainty? The Attempt at a Solution i counted arithmetic...
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