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. J

    Heisenberg's Uncertainty or hidden variable

    Intuitively it seems more plausible that there should be a hidden variable influencing the path of particles when they travel, than having a fundamental mechanism of nature be truly random, but what do I know. I just don't understand how you can ever completely rule out a hidden variable. I know...
  2. J

    Propagation of uncertainty from wavenumber to wavelength

    Hi, This is just a quick question. If wavenumber is a variable with some standard deviation Δk, how do I propagate this spread when converting from wavenumber to wavelength? Is it just 2π/Δk or is it more complex than that? Thanks
  3. X

    Heisenberg's Uncertainty Principle

    Hi Guys, Newbie question from a layperson so please don't beat me up! :D I know that Heisenberg's Uncertainty Principle relates to measurement/observation of particles with regard to quantum physics. My question is whether or not it applies to measuring anything in the observable...
  4. carllacan

    Neutrons and uncertainty principle

    Homework Statement Using the Uncertainty Principle show arithmetically that neutrons can't be formed by a proton and an electron. Homework Equations The Attempt at a Solution I can see that if neutrons were made out of a proton and an electron they would just attract each until...
  5. K

    Heisenberg Uncertainty Principle problem

    Homework Statement Explain, using the Heisenberg Uncertainty Principle, how classical physics is reached a a limit of quantum physics when (h-bar) tends to 0. Homework Equations ΔxΔp(x) ≥ (h-bar)/2 The Attempt at a Solution The only reasonable answer I can formulate is the fact that when...
  6. T

    Uncertainty Derivations/Calculation

    Homework Statement If F = aXn = f +- f +δf where a is a constant, show f = xn and \frac{δf}{f} = \frac{nδx}{x}. X = x +- δx x refers to the average and δx refers to uncertainty in x. Homework Equations The power rule for error propagation shows that the uncertainty is multiplied n...
  7. R

    Finding the Uncertainty of the Slope Parameter of a Liner Regression

    Finding the Uncertainty of the Slope Parameter of a Linear Regression Suppose I have measurements x_i \pm \sigma_{xi} and y_i \pm \sigma_{yi} where \sigma is the uncertainty in the measurement. If I use a linear regression to estimate the value of b in y=a+bx, I'm struggling to find a...
  8. F

    Uncertainty principle leads to superlumina ?

    According to the uncertainty principle Δp*Δx≥h/2pi, now suppose we measure a particle in a very tiny area(if x is tiny enough), s.t. Δp ≥ h/(2xpi) ≥ mc then v > c. But in fact, the velocity can not be faster than light. So how can we compromise these two statement?
  9. M

    Uncertainty significant digits

    When dealing with the intermediate value of example: 570 +/- 100, how do you put this into it's final form? If I'm not mistaken, doesn't the uncertainty only contain 1 significant digit? Doesn't the uncertainty digit have to correspond to the final significant digit on the actual value as well...
  10. D

    The uncertainty operator and Heisenberg

    In deriving the Heisenberg uncertainty relation for 2 general Hermitian operators A and B , the uncertainty operators ΔA and ΔB are introduced defined by ΔA=A - (expectation value of A) and similarly for B. My question is this - how can you subtract(or add) an expectation value , which is just...
  11. L

    Conceptual Question regarding Uncertainty Principle

    This could be one of those questions where I'm hindered by my lack of knowledge on the subject, being only a freshman in college, but recently we learned the uncertainty principle which states that: ΔE*Δt ≥ h/4π Given this, I'm assuming it'd be accurate to rewrite ΔE as Δm*c2, which would...
  12. F

    Uncertainty Help: Homework Statement on Measuring a Projectile's Range

    Homework Statement Students decide to measure a projectile's range for an initial projectile angle of 45°. This angle has many advantages, not the least being that since the expression for the range is proportional to the sine of twice this angle, errors in determining the angle do not...
  13. A

    Problem on Heisenberg's Uncertainty Principle

    The uncertainty in this principle is talking about uncertainty of measurement or particle itself?
  14. A

    How can uncertainties in measurement affect the estimation of g?

    Homework Statement Hi. I don't know if this is the right place to talk about my problem. Anyway, here it is: I've made a classic experiment to find g. For that I used a gravitational pendulum and measured several periods of oscillation for differentes values of L. After that, i made a...
  15. Quarlep

    The uncertainty when measuring time

    Does any uncertainty when measuring time? Can we measure time definitely(hundred percent correct)
  16. L

    Uncertainty Principle Question

    Homework Statement Laser can now be designed to emit pulses of light smaller than 30 microns wide in their direction of motion. (a) Estimate the uncertainty in the momentum of a photon in such a pulse. (b) The momentum of a photon is p=h/λ. Estimate the uncertainty in the...
  17. S

    Uncertainty principle and momentum

    if you know the position why can't you know the momentum isnt p=mv and v=dx/dt its the only doubt i have so far please help
  18. C

    Calculating Percentage Uncertainty for Measured Lengths

    Two lengths, a and b, are measured to be 51+/-1cm and 49+/-1cm respectively. In which of the following is the percentage uncertainty the largest? A a+b B a-b C a x b D a/b The answer should be b but I can't figure out why. I know that for / and x you add the percentage errors so if the error...
  19. liometopum

    Unusual uncertainty relations question

    What are the uncertainty relations for the following: 1. position and energy? 2. position and time?
  20. N

    Propagating Uncertainty for sets of data?

    I'm writing the paper on this experiment I just did. Basically I took sets of data for two variables (x,y) and I fit the points to a line in Origin to extract the value that I was trying to measure (J). *Using generic variables here* I found a value for J where J = [8*∏*x*a(b+c)] / y I...
  21. Suwailem

    Uncertainty Principle and the Second Law

    For those who read carefully the paper by Esther Hänggi and Stephanie Wehner: "A violation of the uncertainty principle implies a violation of the second law of thermodynamics": 1. Can you elaborate how extra work can be extracted if the UP is violated? 2. Does the paper implies that...
  22. J

    If you have any further questions, feel free to ask.

    So I am a little confused about how to calculate the error uncertainty of a slope. Let's say I have data points (1,2), (2,2.75), (3,3.75), (4,4.7), (5,5.5) which when put in excel gives me a slope of .895. Let's say the error uncertainty for every point is +/-0.1. What I used to do is subtract...
  23. B

    Derive a formula from the uncertainty principle

    Homework Statement Derive from the uncertainty principle a formula for the relative spread of the spectral line that corresponds to the longest wavelength of the Lyman series. Homework Equations uncertainty principle: σxσp≥\hbar/2 planck constant \hbar=h/2pi h=λp Lyman series...
  24. J

    Error uncertainty for power law

    So I have a series of 5 data points let's say that they are (1,1),(2,3),(3,4),(4,4.5),(5,4.75) that create a power function that has the equation y=1.2x^.97. Let's also say that the error uncertainty for every number is 0.1. I know that for a linear line you can take the uncertainty of the...
  25. W

    Uncertainty and entanglement relationship

    Is there a hard and fast relationship between uncertainty and entanglement? In other words, if you have one phenomena, you have to have the other. I would think so because of the following example, but I wanted to make sure I understood the relationship. Please let me know if there are better...
  26. H

    Can heisenberg uncertainty principle be beaten by fast measurements?

    I don't know much about physics but just had this idea: As I understand it the HUP prevents good accuracy of a small object's momentum and position at the same time. Assume trying to measure the momentum and position of a single atom. In theory, can't we get a very good idea of both of...
  27. J

    Calculating Kinetic Energy Uncertainty

    Homework Statement An object of mass m = 2.3±0.1 kg is moving at a speed of v = 1.25±0.03 m/s. Calculate the kinetic energy (K = 1 mv2) of the object. What is the uncertainty in K? Homework Equations k=1/2mv^2 The Attempt at a Solution I have figured out that the kinetic energy...
  28. P

    Is Uncertainty intrinsic property or a consequence of measurement ?

    Hello friends, Most people that I heard put uncertainty as an intrinsic property of the universe which is evident when we make a measurement. But to me it seems that intrinsic property and making a measurement are two entirely different things. If uncertainty were to be just(purely)...
  29. M

    Uncertainty Analysis Homework: Vel Calc from Line of Best Fit

    Homework Statement Hey everyone, I've data for some oscillatory motion. I used MATLAB to find line of best fit for the data. I got a line of the following form y = A*sin(2*pi*f*t + ø) I got the root mean square error between my data and the line of best fit (call it u_y) Now I want to...
  30. S

    Heisenberg Uncertainty Principle Derivation

    I know I have seen this before a few time done a few different ways/starting points and I am always blown away when I see it worked out. Don't know why but I love seeing this derivation. Does anyone want to post the derivation for all to see, it being done a few different ways would be great.
  31. E

    Heisenberg's Uncertainty Principle

    My source is the high school chemistry textbook: General Chemistry, 2nd Edition, by Donald A. McQuarrie and Peter A. Rock, published 1987 (This is not for a high school homework assignment.) According to Heisenberg's Uncertainty Principle, the product of the uncertainty in the momentum...
  32. B

    Heisenberg's uncertainty principle

    Homework Statement So here's the question An electron is confined within a region of width 1 X 10^-10 meters. Estimate the uncertainty in the x component of the electrons momentum Homework Equations ΔPΔx\geq(1/2)(h/2pi) The Attempt at a Solution The problem appears pretty...
  33. J

    How Do You Calculate Error Uncertainty for ln(x)?

    Homework Statement What would be the error uncertainty when you take ln of a number. For example ln(10) and the error uncertainty for 10 is ± 1 Homework Equations The Attempt at a Solution Is the error uncertainty just (1/10)*2.3? (2.3 is the answer to ln(10))
  34. L

    If i have a=exp x, and i know that my uncertainty in a is 3% ( at all

    if i have a=exp x, and i know that my uncertainty in a is 3% ( at all points). At a point where a=2, how do we calculate the uncdrtainty in x. is the absolute value = (3% of ln 2)/ln 2, which equals 0.03mm, which equals 1% (if x is 3mm) thanks
  35. G

    Time-energy uncertainty and vacuum fluctuations

    Hi, Similar to the position-momentum uncertainty principle, there is a time-energy uncertainty of the form $$\Delta E \Delta t \geq\frac{\hbar}{2}\enspace .$$ However, since time is not an observable, the derivation and interpretation of this inequality is somehow different compared to...
  36. L

    Trying to calcualte the uncertainty

    if i have two repeat measuremetns, A and B, is the following correct? I am trying to calcualte the uncertainty... I know there are easier ways to do this but i need to have the uncertainty of the mean in terms of δ(A-B). from pairs of measurements A and B at each setting we have...
  37. Y

    Fourier Transform, and the uncertainty principle

    Hello, Recently I've learned about Fourier Transform, and the uncertainty principle that is arose from it. According to Fourier Transform, if there is only one pulse in a signal, then it is composed from a lot more frequencies, compared to the number of frequencies that are building a...
  38. L

    Heisenberg's Uncertainty - ΔλΔx

    So we have a light bulb emitting through a small slit. I read somewhere that a blackbody shining through a small slit acts like a perfect emitter, and I wanted to know why. I figured it must have something to do with Heisenberg's Uncertainty. Here's how I went about it: \Delta x\Delta p \geq...
  39. edguy99

    Is Heisenbergs uncertainty principle valid?

    An article at physicsworld.com suggests that arbitrarily small measurements can be made. Ozawa: "My theory suggests if you use your measuring apparatus as suggested by the maker, you can make better measurement than Heisenberg's relation" Regarding his opposition: "They now prove that if...
  40. F

    Feynman Lectures and Uncertainty Principle

    I read the Quantum Physics section of the online version of Feynman lectures http://feynmanlectures.caltech.edu/I_02.html#Ch2-S3 and I don't understand how he can deduce electron momentum from the Uncertainty Principle. I agree that the momentum is uncertain but how can he deduce that it is very...
  41. B

    Uncertainty principle asymmetric with respect to time?

    We take for granted the fact that we can infer more about the past than the future. Considering the only difference between past and future is entropy, I wonder if the reason it is possible to have records of the past and not the future is entropy related. At the quantum level is the...
  42. arivero

    Sommerfeld uncertainty principle

    Ok, I http://en.wikipedia.org/wiki/Academic_genealogy_of_theoretical_physicists#Arnold_Sommerfeld that Heisenberg had studied under Arnold Sommerfeld, but I have just now learned that Sommerfeld proposed a sort of uncertainty principle in the first Solvay meeting. That was 1911. It seems...
  43. D

    Uncertainty of Sample skew and kurtosis

    What is the uncertainty of a samples skewness and kurtosis? Such as the uncertainty of the standard deviation is SD/sqrt(2*(N-1)). I was able to find what someone is calling the Standard Error of these but they both only depend on N which doesn't make sense to me. Skewness Standard Error...
  44. N

    Uncertainty on entangled electrons

    We know that can't measure both position and momentum simultaneously whether both are orthogonal. If i measure position one entangled electron and momentum on other electron for single state then how Heisenberg's uncertainity princple works?? so We may know the both parameter.
  45. B

    What Uncertainty Principle actually is?

    What Uncertainty Principle actually is? I searched on the internet and got an amazing answer that the energy could form out of thin air. Who could explain more specifically to me, who is in year 11.
  46. D

    Triangle wavefunction - position uncertainty and probability amplitude

    Homework Statement Hey guys. Basically I have a wavefunction that looks like this http://imageshack.com/a/img843/3691/22r3.jpg I have to find: (a) The normalization constant N, of course by normalizing it (b) Find <x> and <x^2> and use this to find Δx. Homework Equations I'm just...
  47. M

    Quantum uncertainty after passing through a slit

    Homework Statement A given particle is confined to a certain potential. At a given instant that potential is turned off and the particle is accelerated by gravity. In the initial instant t = 0, when the potential is turned off, it has an initial speed of vz = 1 m/s. In the instant t = 0...
  48. H

    Use uncertainty principle to obtain the result of Bohr's Model

    Problem Find the minimum energy of the hydrogen atom by using uncertainty principle a. Take the uncertainty of the position Δr of the electron to be approximately equal to r b. Approximate the momentum p of the electron as Δp c. Treat the atom as a 1-D system My step 1. Δr Δp ≥...
  49. D

    Uncertainty principle for electron in nucleus

    Hello, I have this exercise and want to check if what i did is correct Homework Statement Nuclei, typically of size $10^{-14}$ m, frequently emit electrons with energies of 1-10 MeV. Use the uncertainty principle to show that electrons of energy 1 MeV could not be contained in the nucleus...
  50. S

    Percent uncertainty for noobs (like me)

    I KNOW this is going to be a very basic question for most of you but I am new to PF which seems awesome by the way and generally new too physics too. My question that my teacher went over on the practice questions for home was determine the percent uncertainty of the number 1.56. I know...
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