Particles Definition and 1000 Threads

Hi everyone. Very orderly forum you have here. I'd like to ask a few philosophical questions which are very fundamental to QM. Firstly I assume we all agree that a fundamental particle - imagine an electron or quark - has multiple inherent properties which are all separable from each other, such...

Homework Statement Edit: Thanks to gneill for showing me the LaTeX ropes. Equations should work now. A perfect gas enclosed within a container escapes into vacuum through a small circular hole. The particle flux through the hole is ##\frac{nc}{4}## and the energy per particle escaping can be...

I had a quick question regarding particles touching each other. I know no one can really say for sure but inside a black hole where the gravity is astronomical would the particles be considered to be pressed up against each other? are the forces involved enough to compress atoms down into the...

Homework Statement A system has three non-degenerate energy levels with energies 0, ε, and 2ε. a) Calculate the entropy of the system if the three levels are populated by two distinguishable particles such that the total energy is U=2ε. b) Calculate the entropy of the system if the three...

It seems to me that we don't measure a particle because a particle doesn't have an objective existence independent of the wave function or does it? The wave function in this case would have to be real because you can't have probability without the underlying possibility of a specific outcome...

Supposed i wanted to do a relativistic simulation of charged point particles moving at different velocities and interacting with each other. My simulation would give me the x,y,z coordinates of each particle seen from an arbitrary observer's point of view, at a given t. The t given however, is...

From statistical mechanics in zeemansky's book . He states that it's easy to see that for a closed system the no. Of degenerate states ##g_i## for energy level ##E_i## is greater than the number of particles ##N_i##occupying that energy state. I can't find a mathematical proof for it. Can I...

As I understand it, the need for quantum field theory (QFT) arises due to the incompatibility between special relativity (SR) and "ordinary" quantum mechanics (QM). By this, I mean that "ordinary" QM has no mechanism to handle systems of varying number of particles, however, special relativity...

(Sorry for my bad English.) Suppose we choose the surface of the Earth at a point as having a zero potential energy. Now if there're two particles of equal mass at rest, one of them just an heigh above the another, the one which is at the ground will not have potential energy. Since the...

Particle accelerators use the electromagnetic field to accelerate charged particles. Would it be possible to build a particle accelerator for uncharged particles? Say we are given a narrow beam of neutrons. How could we accelerate them so that the accelerated particles were still in a...

Homework Statement [/B] 1 mol of gas at temperature T is contained in a cubic container of side L. Estimate the number of collisions per second between the atoms in the gas and one of the walls of the cubic container. My book gives this formula for that quantity \frac{N_A}{6L}\sqrt{\frac{3 k...

Hi all, Based on a previous post on Anderson Localization, I'm posting a more general question here: given that there is substantial disorder in many systems in general (e.g., the body, or the Earth), why do we not see effects like Anderson Localization more frequently - that is, why aren't...

I was looking at the diagrams from the lhc of the path of particles and notice that the path of the particles always craved parabolically not traveled strat outward from the point of impact. Why does this happen explachely when the particles are traveling at near light speeds thank you ahead...

I was referring a lecture series by Professor Hong Liu. In his first lecture on Emergence of gravity he says, "massless spin-2 particles (gravitons) can arise as bound states in a theory of massless spin-1 (photons, gluons) and spin- 1 particles (protons, electrons)". What does it exactly...

<Moderator's note: this is a spin-off from another thread> Matter isn't spreading out because of gravitational attractions between matter. If you took a bunch of gravitating particles and sealed them in container, the highest state of entropy is one where all the particles coalesce, which...

I could completely understand the fact it it was just a limit to our observations but how can it be a property of the microscopic particle itself? Here's how I understand about probabilities: Before a die is thrown, the probability of a certain number coming up is 1/6. But, it's before the die...

The question here is simple; would the existence of virtual particles make the universe an open system? And if not, why? I thank all who consider this question for their time and would love to hear an answer.

HI guys! I was thinking... What would happen if the atom were considered the smallest thing of the universe, or just that electrons, protons e neutrons were that? That would impact in semiconductors technologies? Or plasma? Or nanotech? How? Thanks in advance.

Ah. It was skepticism about publishing, not about giving a comprehensive account! Yes, I am preparing a book on quantum mechanics, which will contain an account of the thermal interpretation - but primarily to macroscopic, nonrelativistic reality, where it is obvious that it gives the correct...

The EM wave and the photon have two degrees of freedom. Their polarization directions and spin states, respectively. But they move in space, too. I mean light has the freedom to go in all directions in space. Like a macroscopic ball in 3-D space, which can go all three directions, if there are...

Let's say you have two particles that are the same in magnitude but have opposite charges like the equation down below: E1 = -q*k/r^2 E2 = q*k/r^2 ETotal = q*k/r^2 + -q*k/r^2 = 0 Does this mean that the electric field of both these charges cancel out each other? Then what is the electric...

Hi there ppl! I have a question ! I learned that neutral miuon ( μ0) is made of a quark and his anti quark (can't remember which) which explains it's very little lifetime(around 10-24s if I'm not wrong). Now i wonder how two particles ,that are meant to destroy each other,form for a little time...

Hi all, Following up on another post - for a layman, can someone describe the status of virtual particles in Loop Quantum Gravity models? Since LQG avoid UV divergences, and has a different structure from field-based theories, are virtual particles still talked about? (in the context of closed...

john baez submitted a new PF Insights post Struggles with the Continuum - Conclusion Continue reading the Original PF Insights Post.

john baez submitted a new PF Insights post Struggles with the Continuum - Part 7 Continue reading the Original PF Insights Post.

Homework Statement Unstable particles cannot live very long. Their mean life time t is defined by N(t) = N0e−t/τ , i.e., after a time of t, the number of particles left is N0/e. (For muons, τ=2.2µs.) Due to time dilation and length contraction, unstable particles can still travel far if their...

In a thought experiment, there is a spin-0 source emitting particles. (I suppose you already know what is that experiment.) Two observers in opposite sides along the same axis measure opposite spin components. If one observer measure, say, spin up, then the second observer will certainly measure...

Homework Statement Unstable particles cannot live very long. Their mean life time t is defined by N(t) = N0e−t/τ , i.e., after a time of t, the number of particles left is N0/e. (For muons, τ=2.2µs.) Due to time dilation and length contraction, unstable particles can still travel far if their...

I'm in a deep discussion with a friend. He says that the Standard Model of particle physics is actually known by Standard Model of cosmology and that both are the same and that the SM of particle physics is in the Minkousky geometry... I disagree about this, I do think that the SM of particle...

First let me ask this: Consider a pair of entangled photons fired at a respective detector after passing respective polarisation filters. If a photon passes a polarisation filter, is it in a superposition of having passed and not having passed? Is the measuring device (that detects the...

My question is about system of infinite number of point like particles with gravitation interaction (classic Newtonian interactions). If the infinite system can be considered to be in equilibrium, uniform density, in 3D, did anyone analyzed this system with regard to propagation of density...

This is a common question asked but I can't find a good reference. Supposed the first generation particles (electron, quark up, down) vanish and we only had STABLE second generation particles composing of muon, strange and charm quarks that suddenly became stable (don't decay).. would they form...

I've discovered a potential treasure horde tucked away in the deep dark folds of the world wide web. A 1625 page mammoth on all aspects of quantum field theory by Prof. Hagen Kleinert. There's a draft ed. for free available here -...

Homework Statement We have got two particles with S_1=1 and S_2=1. We know that S_{1z}|\psi_1\rangle=\hbar |\psi_1\rangle and S_{2x}|\psi_2\rangle = \hbar |\psi_2\rangle. a) Find wave function |\psi_1\rangle in S_{1z} basis and |\psi_2\rangle in S_{2z} basis. b) We measure S^2 of total...

Homework Statement Two particles with spin S_1={1 \over 2} and S_2={1 \over 2} are at t=0 in a state with S=0. a) Find wave function at t=0 in S_{1z},, S_{2z} basis. b) Second particle is in a magnetic field B = (\sin\theta,0,\cos\theta), the Hamiltonian is H=\lambda \vec{S_2} \cdot \vec{B}...

When two electrons approach each other, there is a repulsion between them by the exchange of a photon as the electromagnetic force carrier. Is there a general range of wavelength of such photons? Does it depend on how rapidly these electrons are approaching each other?

I am relatively well versed when it comes to systems of spin, or doing the maths for them at least, but am unsure whether all of the {L2, Lz, (other required quantum numbers)} basis eigenstates for a general system of n particles of spins si, where si is the spin of the ith particle, can...

Why must photons, for example, that carry the EM force be virtual? Is it because they are tied to gauge invariance and that is not observable? Thanks in advance.

You have two electrons held at a fixed distance X from each other. You measure the opposing force is Y. Now you bring the electrons closer to each other, and then let them go so they can fly apart. As the electrons move apart and reach distance X, will the opposing force still be Y, or will it...

I've recently been reading a bit into the thermalisation of a system of particles and I'm unsure on a couple of concepts. Firstly, if a system of particles are out of mutual thermal equilibrium, does this essentially correspond to the particles in the system having randomly distributed momenta...

Hello, I hope this is not a stupid question as I am not a physicist. But I was curious about how contenders for the so-called Theory of Everything view the shape of the elementary particles. I know that the basic idea of string theory is related to the shape of elementary particles as one...

this was widely reported in the past, but not commented on here https://www.sciencedaily.com/releases/2016/04/160422115320.htm based on http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.161101 Search for Spectral Irregularities due to Photon–Axionlike-Particle Oscillations with...

Homework Statement Two identical charged particles, each of mass m and charge e, are intitialy far apart. One of the particles is at rest at the origin, and the other approaching it with velocity v along the line x=b, y=0 where b=e^2/2 \pi \epsilon_0 mv^2. Find the scattering angle in the CM...

mfb submitted a new PF Insights post LHC Part 4: Searching for New Particles and Decays Continue reading the Original PF Insights Post.

Homework Statement Three perfectly elastic particles A, B, C with masses 4 kg, 2 kg, 3 kg respectively, lie at rest in a straight line on a smooth horizontal table. Particle A is projected towards B with speed 15 m/s and after A has collided with B, B collides with C. Find the velocities of the...

Homework Statement Please refer to both figures. The result of the example problem was θ=33.2° Homework Equations ΣFn=man The Attempt at a Solution I am stumped. I thought you could solve the forces in the z direction, straight up from the car, and set that to zero since there is no...

Double-slit experiments have been done to death, Obtaining and preserving which-path information (or otherwise) for a particle or photon causes its entangled partner to show the probability distribution with or without the interference pattern, violating Bell's inequality and thus proving...

Homework Statement Refer to figure please. Homework Equations ∑Fy=0 before string is cut The Attempt at a Solution I tried summing the two forces in the y direction before the strings were cut which would be the two tensions at a sin40° and minus the weight of the ball(mg). That gave me T in...

Hi all, I've read a number of posts on virtual particles (including one of my own), but I'm still confused about one aspect - the interaction between real and virtual particles. Say we have an electron moving from position A to position B. As the electron moves, there should be virtual...

I've heard of photons being described as a wave/particle duality. But what evidence is there that individual photons behave like anything other than a particle? I can see how photons en masse can display wave/particle characteristics, but what evidence is there that any individual photon...