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. Q

    Experimental uncertainty

    hi, just a simple question i have a linear graph y=mx+c lets say my y values have an uncertainty of ±1 . my x values don't have uncertainties. so what will my gradient's uncertainty be? PS: can i just use the linear least square fit function from microsoft excel? do they calculate...
  2. A

    Root Mean Square Uncertainty

    Root Mean Square Uncertainty [solved] My TA gave us a paper after this assignment regarding how to do Root Mean Square Uncertainty, however I can't read her handwriting... I think I get the gist of it, but It's written so strange I need to check. Is it sqrt(...
  3. A

    How Do You Calculate Speed and Uncertainty with Given Measurements?

    Homework Statement Hey there, I need some help with uncertainties and how to find the speed of a moving object. I have tried to solve the problem several times but my answer seems to be wrong. Formula for speed : v=d/t My uncertainties: 0.5cm (distance) and 0.5s for time. The uncertainties...
  4. S

    Quantum mechanics uncertainty principle

    Homework Statement If a neutron is confined to the nucleus, its wave function – and therefore the probability of finding it at a certain position – has a characteristic width, Δx, equivalent to the nucleus diameter. What is the uncertainty in the neutron momentum Δp as a function of...
  5. L

    Uncertainty principle, commutator.

    Homework Statement Calculate [x,px] = (xpx - pxx) Do this for a function f(x). Now calculate [x,py] for f(x,y) Homework Equations px is actually px hat, I'm just not familiar with latex code. px= -i (d/dx) The Attempt at a Solution I believe I got the first part, for...
  6. C

    Uncertainty Principle: Computing Δx & Δp for a Particle in a 1D Box

    Homework Statement The uncertainty ΔB in some observable B is given by a formula ΔB = √<B^2> - <B>^2. Use this formula to determine the uncertainty in position, Δx, and momentum Δp, for the ground state of a quantum-mechanical particle of mass m is a 1-D 'box' of length a, and show that the...
  7. A

    Exercise in propagating uncertainty in a simple calculation.

    YBa2Cu3O(7−x)(s) + ([ 7/2]−x)H2(g) → [ 1/2]Y2O3(s) + 2BaO(s) +3Cu(s) + ([ 7/2]−x)H2O(g) 35.937 ± 0.005 mg of solid YBa2Cu3O(7−x) reacts completely, according to the above equation, in a stream of hydrogen gas at 1000°C, leaving 33.242 ± 0.005 mg of solid residue. (For the purpose of this...
  8. H

    Use Uncertainty principle to find gound state energy?

    Homework Statement A particle of mass m is subjected to a potential V(x)=Kx.Use uncertainty principle in the form Δx.Δp≈h(bar)/2 to estimate ground state energy of the particle. The Attempt at a Solution I have no idea. :(
  9. C

    I get two different answers. Which one is correct?

    Homework Statement M = (a-b)/2 + a a = 15 b=5 What is the uncertainty in M if the uncertainty in a and b is ±0.7? Homework Equations for c = a + b Error in c =√[(error in a)^2 + (error in b)^2] The Attempt at a Solution Error in M = √[0.7^2 * 3] = 1.2124 The problem...
  10. B

    Uncertainty of coherent states of QHO

    Homework Statement What is the uncertainty in x and p of the coherent state |z> = e^{-|z|^2/2} \sum\frac{z^{n}}{\sqrt{n!}} |n> Homework Equations ... The Attempt at a Solution This seems pretty straight-forward to me. You just find the expected value of (let's say) x...
  11. N

    Uncertainty in ln(R) Calculation in R: Is (uncert in R)/R Correct?

    If I have the uncertainty in R and I want the uncertainty in ln(R). Am I right in thinking the uncertainty in ln(R) = (uncert in R)/R? Thanks
  12. C

    What is the Uncertainty in Wavelength for an Excited Atomic State?

    Homework Statement An excited atomic state has a lifetime of 1 ms. What is the uncertainty in its energy? The photon emitted during its decay is 550 nm in wavelength. What is the uncertainty and fractional uncertainty in its wavelength? Homework Equations ΔEΔt≥hbar/2 The...
  13. P

    Different significant digits in uncertainty and data?

    Hi, I've just got a question about uncertainties that came up while doing a lab report. I have a set of data for currents required to cancel the deflection of an electron beam caused by the Earth's magnetic field: 0.195 A 0.220 A 0.250 A 0.251 A 0.239 A Because of the difficulty in...
  14. S

    Uncertainty in Energy-Time Relation for Atomic Transitions

    If an atom transitions from an initially excited state emitting a photon E=hf and going to the ground state, and since ΔxΔk=1 show that ΔEΔt = hbar. So I know Ephoton=hf=hbar*sqrt(k/m) = hbar * sqrt(1/Δx*m) and since E=pc and p=hbar*k=hbar/Δx but I am not sure what to do from here? Any...
  15. A

    How Do You Calculate the Absolute Uncertainty of One Rotation Time in a Dryer?

    Homework Statement Lab 1: Question 6. (Note: each time you do this problem, the numbers will be different.) I want to measure accurately the time it takes for the drum of my clothes dryer to make one rotation. Since the door on the dryer is made of heat resistant glass, I can see the...
  16. Z

    Heat death, quantum uncertainty and Feynman's Path Integral

    Hi all, as a complete noob, I must first ask that people understand that I have only a layman's understanding of cosmology. However, after watching a few of Brian Cox's lectures on entropy and the heat death of the universe, I had a rather interesting thought (although as I am not a...
  17. S

    Generalized optimization under uncertainty problem

    Hi, I have formulated what I believe to be a generalized(to some degree) optimization under uncertainty problem. The write up is included in the attached file. I would appreciate any and all input, help or guidance as to how this problem could be solved. If you have any questions please feel...
  18. B

    Simple average question using sig figs within ± 0.0 of uncertainty?

    Simple average question using sig figs within ± 0.0 ? Homework Statement Consider the following measurements of mileages: 23.8 mph, 20.1 mph, 26.5 mph, 20.7 mph, 21.7 mph, 27.6 mph, 30 mph, 28 mph, 27.4 mph, 34.3 mph, 26.5 mph, 32.7 mph. What is the average mileage (using...
  19. X

    Quantum Mechanics: Uncertainty and Commutation relation

    I am stuck on one part of my Quantum Mechanics HW. Above the question it says "Try and answer the following question." So I can only assume that he isn't looking for something incredibly detailed. (Ill explain why after the question is given.) Homework Statement What is the meaning of the...
  20. A

    Another Uncertainty with Equations question

    Homework Statement A useful kinematic equation is (vf)^2 = (vi)^2 + 2ad You drop a ball (with zero initial velocity) from the top of a building to measure the acceleration due to gravity. If you measure the final velocity to be vf ± ∆vf, and the height of the building to be d ± ∆d...
  21. A

    Uncertainty with Equations Question

    Homework Statement You would calculate the average velocity of the ball bearing in the fluid as v = h/t How would you calculate the absolute uncertainty on v? a) h(Δh/t) + (Δt/t2) b) (Δh/t) + h(Δt/t2) c) (Δh/h) + (Δt/t) d) h(Δh/t) - (Δt/t2) e) t(Δh/h) + h(Δt/t) Homework...
  22. X

    Large Uncertainty Became Unsignificant After Calculations?

    Homework Statement Calculating focal lengths of lenses. s = 144.7 ± 5.52 mm s' = 86.0 + 0.71 mm Homework EquationsFocal Length f = (s)(s') / ( s + s' ) Adding/Subtracting two numbers with uncertainties A + B ± root [ (±A)^2 + (±B)^2 ] Multiplying/Dividing AB ± root [ (±A/A)^2 + (±B/B)^2)...
  23. binbagsss

    Quick Uncertainty Problem - atom energy levels

    Two quick problems, not sure whether the 2 are related or not: 1) The question is: A sodium atom in one of the states laveled 'lowest excited lvels' remains in that state, on average, for 1.6 x 10^-8 s before it makes a transition to the ground level, emitting a photon with wavelength...
  24. P

    Relationship Between Uncertainty and Emergence (neuroscience)?

    A huge common misconception about brain function is that function can be localized to "very" specific locations. However, reductionism falls apart when speaking about emergent phenomenon such as higher order brain functions (e.g. feeling of knowing, consciousness, visio-spatial processing). Just...
  25. A

    Calculating Uncertainty in Spring Period Measurement

    I want to calculate the uncertainty in the period for a spring, when I have measured the extension of it under the influence of gravity. Call that x and say I got: x=0.10m ± 0.01 And we know that: T = 2∏√(x/g) Is it then correct to use the following formula for the uncertainty σT: σT =...
  26. G

    Uncertainty principle and single slit experiment

    hi my concern is, that there is a huge amount of equations that are somehow related to the uncertainty principle and it is not straightforwardly obvious to me, when i have to use which of them. let me put it this way: as far as i see, there is this overall applicable equation that says ΔxΔp ≥...
  27. O

    Uncertainty of a non linear least squares fit

    Hi, I have some experimental data as a function of time t and temperature T. I have done a least squares fit of the data with a function f=f(a1,a2,t,T) (the function is non linear in a1 and a2!). Optimization of e^2 = sum((yi-f(a1,a2,ti,Ti)^2) with Matlab's fminsearch gave me a1, a2 and the...
  28. A

    Question on uncertainty principle

    If I understand correctly, the uncertainty principle works, because in order to measure the position accurately, you need a smaller wavelength. But observing with a particle with smaller wavelength means observing with a particle with larger momentum. Therefore, when the observation is made by...
  29. M

    How Do You Calculate Uncertainty in Amplitude Readings from a Sound Sensor?

    I used a sound sensor in my experiment and hooked it up to the computer and used it to plot a graph of amplitude against time. I then too readings straight off the graph. How would I go by giving a value for the uncertainty in the amplitude?
  30. I

    Computing Heisenberg Uncertainty Value

    Homework Statement Consider a particle in a one dimensional box of length L, whose potential energy is V(x)=0 for 0<x<L, and infinite otherwise.Given the wave function at ground state ψ=sqrt(2/L)sin (pi*x/L) Compute ΔxΔp where Homework Equations Δx=sqrt(<x^2>-<x>^2) and...
  31. A

    Electron and the uncertainty principle

    I completely understand the uncertainty principle and why we can't pinpoint the exact location of an electron. but what if we could?? would it be important that would could find the location of an electrom? would we know more about atoms?
  32. ShayanJ

    Proof of uncertainty principle

    Is there a mathematical or physical proof for uncertainty principle other than the one that says if you want to observe a particle you should collide with it,a photon and blah blah blah ? I can't accept that as a proof.Because It falls if you find another way of measuring the position of the...
  33. A

    Violation of uncertainty principle?

    Suppose I have an electron gun that shoots electron with momentum p (no uncertainty) at t=0, then at t=t0 I can calculate the exact location of my electron, with no uncertainty. Violation of uncertainty principle?
  34. S

    Calculating Uncertainty With A Sine Function

    Homework Statement I am doing this calculation in my lab: h = sin(24.0°)[(180.0cm)(1m/100cm)] The uncertainty on the angle is ±0.5° and on the length it is also ±0.5cm. How can I go about calculating the uncertainty? If you know the answer, do you mind putting it in terms of a...
  35. L

    Uncertainty propagation for Normalising Signals

    I am measuring an average signal through a range of filters and compute the standard deviation of that signal over a certain range on my image plate. Now I want to normalise all of the signals to an arbitrary filter signal - does the standard equation of uncertainty propagation hold...
  36. A

    Is the Uncertainty Principle affected by the number of particles in a system?

    To my understanding Heisenberg Uncertainty Principle, states that we do not exist due to the fact that atoms("what we are made of") are not present, when they are not consciously observed. Please elaborate.
  37. S

    Uncertainty and significant figures

    Homework Statement A student makes measurements from which she calculates the speed of sound as 327.66ms–1. She estimates that her result is accurate to ±3 %. Which of the following gives her result expressed to the appropriate number of significant figures? A 327.7ms–1 B 328ms–1 C 330ms–1 D...
  38. H

    Existence and the interpretation of infinite uncertainty?

    The trade off in uncertainty in momentum vs position in the HUP leaves me confused. In the context where the momentum is measured to increasingly greater precision and consequently position becomes less refined, is any logical inference made about the existence of the object i.e. is it...
  39. C

    Heisenburg's Uncertainty Principal and the definition of randomness

    I started this thread to continue a conversation from another thread. Does HUP imply randomness? What really is the definition of randomness? I would say that HUP does not imply randomness, but just tells you the relationship between how the state vector is spread out along the basis of two...
  40. P

    Confusion about how to work out the uncertainty in my final calculated value

    Homework Statement So basically I have plotted two variables I measured on a graph, which gives a simple linear relationship, and have found the gradient and standard error of the gradient (1.21251 and 0.03275 respectively). Now my problem is that this gradient is equal to a constant divided...
  41. Q

    Uncertainty Meaning: Definition & Difference from Error

    hi this is my first physical post , i hope i find the right help i just want to know the meaning of uncertainty and the difference between unceratinty and errors any explanation would help
  42. P

    Putting uncertainty on a scatter

    Hi, first of all, sorry if my English is not perfect I'm from Quebec City and English is not my first language. I'm trying to make a scatter plot with average of numerical data. But now I also want to put the standard deviation on the scatter. Exemple, I have a point (x,[y ± σ]) and I...
  43. G

    Comparing Uncertainty of Two Results in Conclusion

    I am trying to figure out how to refer to two overlapping uncertainty results. I have to write a conclusion and I find it difficult to explain. Even now it may seem unclear as to what I am referring to so I will provide an example. This is directly from my conclusion. 'The 72 rated golf ball...
  44. G

    I am trying to figure out how to refer to two overlapping uncertainty

    I am trying to figure out how to refer to two overlapping uncertainty results. I have to write a conclusion and I find it difficult to explain. Even now it may seem unclear as to what I am referring to so I will provide an example. This is directly from my conclusion. 'The 72 rated golf ball...
  45. D

    Uncertainty principle, virtual particle pairs and energy

    I'm a bit confused about how the uncertainty principle allows for the spontaneous creation and annihilation of virtual particle pairs. I can understand that energy conservation can be violated for a very short time as per delta_e*delta_t > h_bar/2. However, when the virtual particle pair...
  46. S

    Use Uncertainty Principle to estimate the size of the H atom

    Homework Statement In Bohr model of the hydrogen atom, the max. kinetic energy that an electron can have is around 13.6 eV, as it would otherwise not be confined to the atom. Uncertainty Principle: ΔxΔy ≥ h/2π a) Find the max. momentum of such confined electron. b) Use Uncertainty Principle...
  47. J

    Uncertainty should be called as unpredictability

    it should be called as unpredictability rather than uncertainty principle because the event is certain but we cannot predict it.
  48. C

    How to use Heisenberg Uncertainty Equation/Principle?

    I'm working on a few problems involving the Heisenberg Uncertainty Principle and I'm a little confused as to how the equation works and what to plug into the equation. The equation I'm using is: (delta(x)*m*delta(v) = h/(4pi). In one of the problems I'm working on, I'm given the mass of a...
  49. M

    Energy time uncertainty principle

    how Energy time uncertainty principle account for the broadening of a level? thanks in advance
  50. U

    Calculating Energy Uncertainty for a Particle Described by a Wave Function

    Homework Statement Determine the energy uncertainty \Delta E = \sqrt{<E^2> - <E>^2} for a particle described by a wave function \Psi (x) = c_1 \psi (x)_1 + c_2 \psi (x)_2 where \psi_1 and \psi_2 are different (orthonormal) energy eigenstates with eigenvalues E_1 and E_2. Homework...
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