What is Spontaneous: Definition and 157 Discussions

By Spontaneous emission it is said that the electron jumps to the higher energy state and then after some time "spontaneously" falls to the lower state. It is still not clear to me, what makes the electron to "fall" back to the lower state, if higher state is also allowed state and excitation...

Does entropy increase during spontaneous emission? If not, how is the information about the emitted photon mode encoded into the initial state of the atom (and/or environment)? If so, where does the extra information come from?

Hi, I am trying to understand what keeps getting referred to as "super radiance". So this has led me to R. H. Dickes 1954 paper "Coherence in spontaneous radiation processes". http://dx.doi.org/10.1103/PhysRev.93.99 . On the first page Dicke presents a "simple example", that is not simple at...

I'm a novice in SUSY and I'v got a question concerning spontaneous supersymmetry breaking and goldstinos. In Martin's review on page 68 there is a proof of a statement about existence of massless particle when one of ##F_i##'s or ##D_a##'s VEV is not zero. The thing I don't get is why vector...

Spontaneous symmetry breaking refers to the solution of a system loses some symmetry in its Lagrangian. Consider a Simple Harmonic Oscillator, its lagrangian is time translationally invariant but its solution is periodic in time, thus not time-translational invariant. Is this Spontaneous...

I would like some help understanding some parts of spontaneous parametric down conversion (SPDC).In the Wikipedia article on the topic…http://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion…the third figure from the top is labeled “An SPDC scheme with the Type II output”. The figure...

How to change the upper step to lower step on the figure? Why does N2(0) change to N2(t) the exp(-t/21) will be missed? Thanks.

Hi everyone Is there anyone who can explain when does Spontaneously generated coherence(SGC) happen and how? Thank you in advance Vahideh

I read somewhere that gauge symmetry prevents the photon from acquiring a mass. The argument seems to go that the 1-loop correction to the photon won't contain a term independent of the external momentum due to gauge invariance, so there is no need for a bare mass counter-term. So should that...

Hi, this may seem like a noob question for you geeks out there, but I can't wrap my head around this. The formula for a spontaneous reaction is \DeltaH-T\DeltaS < 0 Basically, since the reaction between hydrogen and oxygen gas has a negative change in enthalpy it must mean that if the...

Hi, I am looking into symmetry breaking and how it (may have) affected the photon/baryon ratio in the primordial universe. I found this wonderful encyclopaedia of cosmology which relates the grand unified theory to an orthorhombic crystal, making analogies for symmetry, spontaneous symmetry...

I'm trying to understand inflation (in the cosmic sense). I know that ultimately that's a subject that involves both quantum field theory and General Relativity, but I'm wondering to what extent it can be understood from the point of view of classical (non-quantum) GR. If you have a classical...

I'm considering applying for some internship/job this summer if my plan A doesn't pan out. Listings are utterly sparse, though. I'm sure there are opportunities out there, but from what I've heard, the smartest thing to do is contact the companies you're interested in directly instead of sitting...

In the standard model, the Lagrangian contains scalar and spinor and vector fields. But when we consider spontaneous symmetry breaking, we only account for the terms contain only scalar fields, " the scalar potential", in the Lagrangian. And if the scalar fields have vacuum expectation value...

Hi there, In regards to the Spontaneous Emission of a photon from an atom, after that process occurs, is it possible according to the reversibility of the laws of Quantum Mechanics that the photon is re-absorbed by the atom? According to the reversible equation governing the process, would that...

I have a quantum harmonic oscillator at energy level n_1, and I want to know how much time will pass before it spontaneously drops to energy level n_2. I know about the position operator, momentum operator, energy operator, and angular momentum operators. Is there a "time until a system...

I am confused about spontaneous fission. My basic understanding is that like α-decay the tunnel effect is responsible. We have a potential barrier caused by the superposition of surface tension energy and coulomb potential through which an energised nuclear fragment can tunnel with a certain...

I'm studying spontaneous emission and I'm in trouble to understand the following: In a hydrogen atom we have distinct energy levels with different energy values associated to them. E1 = -13,6 eV E2 = -3,4 eV E3 = -1,51 eV To go from the first to the second energy level we need a photon...

Is this graphic wrong, see, http://en.wikipedia.org/wiki/File:Spontaneous_Parametric_Downconversion.png Shouldn't k_s + k_i be less than k_pump in the top graphic because |k_s| + |k_i| = |k_pump|, as energy is proportional to momentum? If so is momentum transferred to the crystal after the...

Homework Statement Our quantum system has two levels: ψ1 = (1/\pi)1/4 * e-x2/2 ψ2 = (4/\pi)1/4 * x * e-x2/2 The energy of the ground state ψ1 is 0; the energy of the excited state ψ2 is \hbar * \omega0. What is the spontaneous emission rate for this system when it is in the excited state...

Is there a reason why we have to expand a field ψ about the true vacuum |Ω>? Can't we just do field theory about ψ=0 instead of about ψ=<Ω|ψ|Ω>? Also, I'm a bit confused about other fields. For the E&M potential, under the true vacuum, wouldn't we need to expand about A=<Ω|A|Ω> instead of...

Spontaneous symmetry breaking: the vacuum be infinitly degenerate? In classical field theories, it is with no difficulty to imagine a system to have a continuum of ground states, but how can this be in the quantum case? Suppose a continuous symmetry with charge Q is spontaneously broken, that...

Today in AP Chemistry we started learning about entropy and spontaneous reactions. Could someone explain on an undergraduate level (preferably not using calculus) how, if the universe has a fixed amount of mass and energy, that reactions can be spontaneous and create their own energy? Thanks!

Hi, In quantum optics, the interaction between light and atoms is described by a Hamiltonian of the form d.E where d is the dipole moment of the atom. The picture given is basically that this is a vector and we take the the dot product with this and the electric field vector (whose direction...

I'm not sure what people meant about this. Heisenberg hamiltonian is ##O(3)## invariant. H=-J\sum_{\langle i,j \rangle} \vec{S}_i \cdot \vec{S}_j ##\langle \rangle## denotes nearest neighbors. It has ##O(3)## symmetry. If I understand well ground state is infinitely degenerate. But system...

dear all, I want to confirm whether there is spontaneous polarization in the piezo materials. I know the piezo materials need to be poled under high temperature and electric field before applications. So if there is spontaneous polarization, comes my following confusing. Given a piezo disk with...

Hi! I wanted to check if I have got the correct interpretation of stimulated vs spontaneous emission. It seems like stimulated emission is defined as a process for which an excited atom/electron spontaneously relaxes down to a lower energy level. Stimulated emission on the other hand...

what is the relationship between unstable equilibria and spontaneous symmetry breaking? Would this qualify as an example of spontaneous symmetry breaking? Take a (perfectly round and unlabeled) pencil standing upright on its eraser so there is a U(1) symmetry on its original position...

I know about all those so-called water to ice scams out there but this is NOT one of those this weird thing happened to me and I am trying to figure out what happened. I normally make my own soda drink by carbonating water and adding a liquid mixture for sweetness and flavoring many have...

For a chemical reaction we have, ΔH=-114.1kJ and ΔS=-146.4J/K ---> ΔS=-146.4·10^{-3}kJ/K. Question: Determine the temperature range at which the reaction is spontaneous. A reaction is spontaneous when ΔG is negative in the equation ΔG=ΔH-TΔS, so I do: ΔG=ΔH-TΔS 0>ΔH-TΔS -ΔH>-TΔS...

The Higgs mechanism is often explained (both here at PF and in many physics sites including wikipedia) as an example of spontaneous symmetry breaking, but the Nobel winner physicist 't Hooft says in his "for laymen" book about particle physics, "In search of the ultimate building blocks", that...

Homework Statement At 2600 K, ΔG° = 775 kJ for the vaporization of boron carbide: B_{4}C (s) ⇔ 4 B (g) + C (s) Find ΔG and determine if the process is spontaneous if the reaction vessel contains 4.00 mol of B_{4}C (s), 0.400 mol of C (s), and B (g) at a partial pressure of 1.0 x 10^-5...

Okay I found some references and the equation I am after is Q = 2 * C * (D * t / ∏)^(1/2) where Q is the weight of drug released per unit area (hence unit is mg/cm^2) C is the initial drug concentration D is the diffusion coefficient (unit of cm^2 min^-1) and t is release time in...

Hello forum, I have a question about photonic crystals. From Wikipedia: "photons (behaving as waves) propagate through this structure - or not - depending on their wavelength. Wavelengths of light that are allowed to travel are known as modes, and groups of allowed modes form bands...

Hello Forum, when a wavefield is incident of an atom and the photon have the right energy (equal to the band gap energy), the photon is absorbed and disappear... But isn't the photon re-emitted later on and allowed to propagate through the material or does all its energy get lost into heat...

Could someone demonstrate to me how in Landau's Mechanics book, he gets from equation (16.5) tan θ = (v_0 sin θ_0) / (v_0 cos θ_0 + V) to equation (16.6) cos θ_0 = -(V/v_0) sin^2 θ ± cos θ √[1 - (V/v_0)^2 sin^2 θ] I am using the quadratic formula, and the first term on the right...

Hi,all My problem is following this picture! http://mykomica.org/boards/shieiuping/physics/src/1325318780058.jpg If the system is isolated, dQ is always zero. Sb-Sa ≥0 And it satisfies the requirement of spontaneousness in isolated systems. So ,I do wonder if irreversible process is always...

What happens then if one has applied a static magnetic field to a heat conductor? Could the temperature increase as a result of reducing the degrees of freedom, increasing the ability for heat to be transferred from that body to others?

http://www.bbc.co.uk/news/world-europe-15032614

Homework Statement What is the Q value in units of MeV in each of the following processes? i) The spontaneous fission of 232U92 to 145La57 and 87Br35 ii) The neutron induced fission of 232U92 to 146La57 and 87Br35 Explain why heavy nuclei such as 232U92 do not usually undergo fission...

On an exam I got this question: [PLAIN]http://img849.imageshack.us/img849/5732/spontaneity.png but at the time I had no idea how to answer it. I still don't really know if I can answer it. I can explain it mathematically with the equation: ΔG = ΔH - TΔS seeing as a spontaneous reaction...

Homework Statement a) A hollow magnetic sphere of internal radius a and external radius b, has a uniform spontaneous magnetization M per unit volume. SHow that the field strength in the internal cavity (r<a) is zero, and that the external field strength (r>b) is the same as that of a dipole...

Hi I am currently reading through a semiclassical approach to nonlinear optics. I learned about effects of second-order nonlinear optics like second harmonic generation and three wave mixing. I understand three-wave mixing as a process in which you send two (or three) monochromatic beams...

I'm trying to get a basic picture in my head of particles having mass. I always seem to come across the ridiculously vague statement that "the Higgs mechanism gives particles mass", and a passing mention of "spontaneous symmetry breaking". There is a lot of stuff confusing me at the minute so...

Homework Statement The spontaneous fission rate for U-238 is roughly 1 fission per gram per 100 seconds. Show that this rate is the equivalent to a half-life for spontaneous fission of ~5.5x1015 years Homework Equations none that I can find in my book The Attempt at a Solution I'm...

Supercooled water freezes. Is this a spontaneous process?? Homework Statement "one mole of supercooled water at -10degC freezes reversibly to ice at -10degC at constant P of 1500atm. The system is at chemical equilibrium. Assume that ΔH_fusion is independent of temperature. Also assume that...

random question just wondering what would happen if an object were to Spontaneous appear. not like multiplying but not existing then suddenly coming from nowhere. like you look at a wall all you see is the wall then bam TV pops from nowhere. what would happen to the atoms ect that were in that...

Hi, If I have a Lagrangian of complex scalar field (just U(1) local invariance). And I know that phi^star describes field with -e electric charge and phi describes field with e electric charge. How do I apply "charge issue" when I write Lagrnangian after spontaneous symmetry breaking in...

It seems that many top scientist, mathematicians, composers etc speak of the moment of insight, including Feynman and Bohm, and it seems to come down to when the brain is silent. Being clever as Feynman was, he sought to figure out if there was some mechanical process, some pattern that could...

This question came to me during my reading of "A Brief History of Time" and learning of Mr. Hawking's statement of the universe arising spontaneously from chaos as a result of the law of gravity, which would preclude a God's role in creation. ABHT states that "one could still imagine that God...