Brownian motion is a stochastic process, continuous in space and time, used in several domains in physics. It is the motion followed by a point which velocity is a white Gaussian noise. This tag sould be used for questions concerning the properties of Brownian motion, white Gaussian noise and physical models using these concepts, like Langevin equations. It should not be used for questions about discrete random walks.
Questions tagged [brownian-motion]
272 questions
41
votes
2 answers
How loud is the thermal motion of air molecules?
In other words, given a magical room with walls that produce no vibration and transmit zero vibration from the outside, and nothing on the inside except room temperature air, what would be the noise level in dB SPL (sound pressure level) from the…
endolith
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5 answers
Do air particles "fly"? If not, how do they stay afloat?
I was reading my old physics textbook (from middle school), and it mentioned something about the idea of having non-existing attractive forces between particles like air. "We would live in a very dull world."
This made me wonder, what would've…
curiouslypink
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24
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7 answers
Does diffusion cause the bottle to move to the left?
There is a solution of solute and water inside the bottle, placed on a smooth horizontal surface with no friction, with the density of the solute greater than the density of the water, and the concentration of the solute on the left side of the…
dan
- 353
21
votes
4 answers
How can we experimentally confirm that atoms/molecules in a solid actually "move"?
The atoms in a solid are so attracted to each other that they "vibrate" and don't move past each other.
How do scientists "measure" that atomic vibration in a solid (let's say at room temperature)?
As a raw, uneducated person it is easy for me to…
Pavel Borisov
- 327
19
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7 answers
How does Brownian motion prove the existence of atoms?
I have heard many people say that the existence of atoms is proven by Brownian motion. Now, I understand how an atomic theory would suggest the existence of Brownian motion. However, who is to say that there is not another theory for what our world…
dts
- 1,004
17
votes
6 answers
Which experiments prove atomic theory?
Which experiments prove atomic theory?
Sub-atomic theories:
atoms have: nuclei; electrons; protons; and neutrons.
That the number of electrons atoms have determines their relationship with other atoms.
That the atom is the smallest elemental unit…
JohnAllen
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16
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What is the difference between solutions of the diffusion equation with an imaginary diffusion coefficent and the wave equation's?
The diffusion equation of the form:
$$
\frac{\partial u(x,t)}{\partial t} = D\frac{\partial ^2u(x,t)}{\partial x^2}
$$
If one chooses a real value for $D$, the solutions are usually decaying with time.
However, in some situations in physics, most…
Bloodworth
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15
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3 answers
How does a virus fall down in static air?
If we drop a virus from a height, in static air, will it fall to the ground like a lead ball, a balloon, or like a virus? How will it fall to the bottom? Like a Brownian particle? It will not float in the air, as its density is higher than air. But…
13
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3 answers
Is Brownian motion truly random?
We say that Brownian motion is caused by the random collisions of particles. But let's consider an ionized gas; in that case, there's a nonzero net charge on the atom. Doesn't this mean the electrostatic force determines the paths the gas ions take,…
Razz
- 441
12
votes
2 answers
Question about a Limit of Gaussian Integrals and how it relates to Path Integration (if at all)?
I have come across a limit of Gaussian integrals in the literature and am wondering if this is a well known result.
The background for this problem comes from the composition of Brownian motion and studying the densities of the composed process. So…
jzadeh
- 223
12
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4 answers
Diffusion coefficient for asymmetric (biased) random walk
I want to obtain a Fokker-Planck like equation by taking the continuous limit of a discrete asymmetric random walk. Let the probability of taking a step to the right be $p$, and the probability of taking a step to the left be $q$, with $p+q=1$. Let…
SarthakC
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11
votes
2 answers
Is the Navier-Stokes equation valid in $d=2$ spatial dimensions?
In the paper Asymptotic Time Behavior of Correlation Functions (1970), the authors study the time behaviour of the velocity-velocity correlation function of a particle in a gas. If the gas is in $d$ spatial dimensions, they find…
Quillo
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11
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1 answer
Renormalization and Brownian Motion
I've been reading about the renormalization group in QFT from Peskin & Schroeder, and wanted to consolidate understanding of "irrelevant operator" by connecting it to something more intuitive, aka Brownian motion. I'd be particularly interested in…
physicsdude
- 897
11
votes
5 answers
If particles get mass from the Higgs field, why do we not see Brownian motion?
If an electron would otherwise be moving at the speed of light if it weren't constantly interacting with the Higgs Field, how is conservation of momentum preserved if it's constantly bouncing off of virtual Higgs Bosons? Why does this not lead to…
Shufflepants
- 677
10
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Is Thibado’s Graphene Brownian Capacitor Charger Perpetual Motion of the Second Kind?
In Fluctuation-induced current from freestanding graphene (peer-reviewed version on Phys. Rev. E, note: behind a paywall) Thiabado, et al, report the extraction of work from brownian motion. The experimental set up involves graphene in close but…
James Bowery
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