New answers tagged

-2

@Zeldredge, your first equation which is supposed to define a total hamiltonian of a certain system is not accurate at all. You used the pauli sigma Z out of context. the Pauli Z operator is diagonal with a negative sign at the last matrix entry so if we shifted the zero point energy of our system we can actually represent the Atomic (internal) hamiltonian ...


5

Let me preface by saying that "coupling" is a favorite physicist word that is perhaps best described linguistically than rigorously; it's deployed in a few different situations. In general, we say that a coupling exists in quantum mechanics if the evolution of one part of the system depends on another quantity, which could be either classical or quantum. I'...


-2

I think Entanglement may answer your question. Two systems are said to be entangled(coupled) if we cannot assign an independent and separate wavefunctions for each system, instead we define a composite system which is simply the tensor product of the original constitutes. To be precise, in the general case the wavefunction description of any quantum system ...


2

In optics a "ray" is the direction of propagation of the classical electromagnetic wave. The term "ray' used for particles, as "cosmic rays" , and "gamma rays" are associated with this directional definition, from the times when it was clear that the phenomena followed straight lines like optical rays, before the differentiation into the particles we know ...


0

Lasers are termed as beam. Maybe the reason behind this terminology is the finite and easily characterizable size of the laser. Laser can propagate in a in a defined direction without diverging appreciably, on the other hand the term ray refer to something that propagate in a straight line. However, the parallelism is not necessary property.


0

Light is an electromagnetic wave. And for example gamma rays are electromagnetic waves. So the visible and near-visible light produced by most laser is like gamma rays but with a different frequency (wavelength). Thus saying ray and beam is roughly the same. Scientific convention is to say laser beam when the emitted electromagnetic waves are strongly ...


1

An internal symmetry is a transformation acting only on the fields, therefore not transforming spacetime points, and leaving the lagrangian or the physical results invariant. Example of internal symmetries are gauge symmetries. These are local symmetries, which means the transformations are in general spacetime dependent in the sense they are, in general, ...


0

"Normal" in this case refers to their orthogonality, although the terminology is somewhat ambiguous. For example, you may sometimes see modes, or more generally basis vectors of some abstract function space, labelled as "orthonormal". This indicates that they are both orthogonal and "normal" in the sense that they are normalized such that the inner product ...


1

I think "normal" means also "proper to the system", i.e., existing after the system ceased to experience an external force.


3

"Normal" in the context of oscillators simply means "periodic" – periodic solutions and the frequencies and other aspects associated with them. It's like in "he breathes normally" – the breathing seems to be periodic. "Quasinormal ones" are those whose time dependence is $\exp(-\Gamma t) \sin (\omega t)$, i.e. they have some exponential decrease aside from ...


4

Pseudoscalar and vector are terms that indicate the total spin and parity of the resonance. Pseudoscalar particles have spin 0 and parity -1, while vector particles have spin 1 and parity -1. The Particle Data Review lists your particles as: $D^\pm\qquad\qquad\qquad\quad 0^-$ $D^0\qquad\qquad\qquad\quad 0^-$ $D^*(2007)^0\qquad \qquad 1^-$ $D^*(2010)^\pm\...


0

After searching I find these "closing operators" defined by the authors correspond to particular sets of operators mentioned in a part (on quantum regression theorem) of the book Statistical methods in quantum optics 1.


3

There is something famously called "Feynman's famous formula", which comes up in QFT calculations, which I imagine must be the second FFF referred to in Welton's account. It reads: $$\frac1{a_1 a_2 \ldots a_n} = \int_{x \in \Delta^{n-1}} \frac1{(\sum_{i=1}^n a_i x_i)^n} d\sigma$$ where $\Delta^{n-1}$ denotes the simplex $\{x = (x_1, \ldots, x_n) \in \...


0

It's explained here in a lecture from the Clay Mathematics institute: https://www.youtube.com/watch?v=pCQ9GIqpGBI Because Area grows like $r^2$. So the classical "field lines" in a $1/r$ potential aka $1/r^2$ force get less dense, but integration over the surface at all distances still yields a constant. A short range potential gets damped with distance. ...


0

Strength and Toughness Image source: Materials Group - University of Cambridge We need the separate words "strength" and "toughness" because sometimes materials with high toughness and high strength are very different, like rubber and ceramic. Let's say you are designing a chair so that can support a person of a certain weight. Why not build it out ...


0

I have never heard that the non intrinsic greek-written points (mainly $\Gamma$, $\Delta$, $\Lambda$ and $\Sigma$) has been written or spoken as the corresponding greek letters. Might this be a sub-community thing?


4

Online data analysis is cursory analysis done as the data is collected. It is often used for the purpose of selecting which events to save to disk or tape to be analyzed later (an event "filter"). Given that the current CERN experiments will be taking, in the next run, data at rates exceeding a terabyte per second, this notion is essential. In fact, the ...


1

For the simple hydrogen atom there exists a ground state, then there are energy levels where an excited electron can reside, and then there is the zero energy level, so yes, there is a name in this case. From the zero energy level the maximum energy is given up, when the electron falls to the ground state, so it is the highest potential energy state.


0

The main issue in your question is that it assumes that motion is absolute. Which it is not. As far as I know only photons are considered to have no rest-mass. In common words when it doesn't move it 'disappears'. Wrong conclusion. It just always move. There is no reference frame where a photon does not move at speed $c$. Electrons and quarks ...


0

Rest mass means the mass which would appear if a paricle were at rest. Do not confuse between particles and photons. These particles are metarialistic particles behaving as energy in some circumstances. Being matter they possess rest mass. While photon is a bundle of energy behaving sometimes as a particle and hence can not possess a rest mass or more ...


6

The term rest mass is a poor one because it implies it's the mass measured in the rest frame. But photons have no rest frame, and indeed any particle subject to some form of confinement has a $\Delta p\gt 0$ so its rest frame is somewhat poorly defined. The modern term is invariant mass, which is simply the mass in the equation for the total energy: $$ E^2 ...


2

That's the Gertsenshtein effect. It is the theory that light passing through a strong magnetic field will produce a gravitational wave.


-1

In mechanical systems, I would say the difference is whether the forces involved are due to static or quasi-static situations in which the forces are due to weight/gravity, springs, etc. If the forces result from accelerations then we have a dynamic system, whereas the former would be a kinematic system. In the transmission of light example of the original ...


3

By an incoherent state (relatively to a basis, and it must be specified), they simply mean a mixed state described by a diagonal density matrix (in this basis). The word "coherence" refers to the usual thing in the discussion of "decoherence" (indeed, it has no simple relationship with the coherent states of harmonic oscillators). Coherence is the ...


0

It just means that the energy (e.g. in the GR language, the ADM energy) is minimized among all configurations with the same boundary conditions. It means that there are no gravitational or electromagnetic or other waves inside the space. In practice, it just means that the geometry is a Cartesian product $M^4\times Y$ where $Y$ is the manifold of compact ...



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