Fully covariant radiation force on a polarizable particle
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| Number of Parts | 63 | |
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| License | CC Attribution 3.0 Unported: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.5446/39024 (DOI) | |
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00:00
Electric power distributionParticleRadiationParticle physicsPlain bearingVideoElementary particlePolarisierte StrahlungForceVideoPaperRadiationComputer animation
00:03
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00:20
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00:38
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01:28
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01:43
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01:48
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01:59
Lecture/Conference
02:14
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02:42
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02:58
ParticleForceFahrgeschwindigkeitLecture/Conference
03:05
Angeregter ZustandSpantReference workPhotonTemperatureGround stationLecture/Conference
03:22
SoundElementary particleLecture/Conference
03:28
Doppler-VerschiebungOptical aberrationParticleCosmic distance ladderReflexionskoeffizientPresspassungLecture/Conference
03:43
FrictionTemperatureForceLecture/Conference
03:50
TemperatureParticleForceLecture/Conference
04:00
TurningLecture/Conference
Transcript: English(auto-generated)
00:03
Hello, welcome to a video abstract. In our paper we wrote about the radiation forces on polarisable particles. Friction is a very common phenomenon. Actually it is very complicated to understand and this is why we studied in our paper a system that is reduced to the max.
00:22
Now consider the simplest possible situation, a single particle moving through empty space. There is no friction force. And there can't be, because there is no preferred reference frame, as Newton had thought. This is the principle of relativity due to Einstein. What if we would fill space with thermal photons?
00:43
Now there is friction. The particle sees blue-shifted photons from the front and red-shifted photons from the back. In addition there is angular aberration, as known from these hyperspace pictures from the Star Trek series. All this has been calculated already in 1917 by Albert Einstein in his paper Zu Quanta Theorie de Strado.
01:03
A well-known example from modern times is the cosmic microwave background, as measured by the COBE spacecraft. In one direction, as the Earth is moving, we see the microwave photons with a slightly higher temperature, a bit of free-carbing. While in the opposite direction it appears to be colder. Thermal photons define thus a preferred reference frame, with respect to which we can measure motion by blue-shift and red-shift.
01:28
Consider another way to break the symmetry, a solid surface at a particle moving above it at constant speed. In this case, excitations are created pairwise inside the media. This carries energy away and dampens the motion of the particle.
01:44
We developed a covariant formulation of radiation forces. Let's come back to relativity. Take for example the frequency and the weight vector of a single photon. These two can be combined into a single 4-vector.
02:00
If we have two observers at relative motion, they will see different k-vectors, k' and k. These two are linked by a Lorentz transformation, which is a 4x4 matrix. Not all vectors are part of the 4-vector. Consider the electric field with components E123.
02:21
To construct a covariant object, we have to combine it with a magnetic field into this array that is called the Faraday tensor. Two different observers see tensors F1 and F' that are linked by applying twice a Lorentz transformation on each of the two indices. This encodes the mixing of electric magnetic fields.
02:42
We are set to present you the final formula of our paper. The first line gives the force density on a polarizable particle. It is given by the product of the Faraday tensor and the magnetization and polarization tensor that gathers the dipole moments of the particle. In the second line, you can see the force on a particle moving a constant velocity above a surface.
03:05
I will talk you through the features of it. You will recognize the temperature of the field and the temperature of the atom. These two functions are Bose functions, which give you the average photon number in the reference frame of the field and the average excitation number of the atom.
03:22
This is the particle's polarizability, evaluated at the comovian frequency. This entails the Doppler shift and the aberration. This gives you the features of the surface, where Rzigma are the reflection coefficients and the distance of the particle is encoded in ZA.
03:43
So where do we go from here? This expression could be the starting point to clarify the discussion on friction forces at zero temperature. Finally, these forces could be a fancy way to measure the temperature of the surface by watching the force on an atom or a small particle that is moving at high speed above it.
04:00
So thank you for watching our video abstract. Thank you!