# What is Quantum phyics: Definition and 57 Discussions

No Wikipedia entry exists for this tag
1. ### I Understanding the dynamics of a perturbed quantum harmonic oscillator

I'm trying to understand how quantum systems behave when they are perturbed, and I'm using the quantum harmonic oscillator as a model. I start by implementing a symmetric gaussian shaped bump in the middle of the harmonic oscillator, and then i propagate the wave functions in time. the...
2. ### I How is spin exchange interaction generalised to many electrons?

In solid state physics or statistical physics, the many-body spin Hamiltonian is written as ##\sum_{i,j} \hat{S}_{i}\cdot \hat{S}_j##. I referred to many textbooks, and most of them just generalised this from the two-electron case ##\hat{S}_{1}\cdot \hat{S}_2##. While this seems natural, it is...
3. ### B Can objects in nature store light information on the quantum level?

In the 1934 novel by John Taine, Before the Dawn, scientists are able to retrieve images of the past by accessing the light absorbed by stones throughout history. While this is fictional, 1934 was really before the dawn of quantum physics. In the far future, could we retrieve images from light...
4. ### I Conservation of energy in quantum gravity

is conservation of energy present in our current theories of gravity? more specifically string theory and loop quantum gravity?
5. ### I Why is there no single slit interference when one slit is closed in a double slit experiment?

When two slits produce an interference pattern, and one slit is closed, then the interference pattern disappears. But one slit interference should still be possible. What should be the measurements of each slit for this to occur? That is, that, starting with a double slit, closing one slit does...
6. ### Given the potential find the eigenfunction

Hi, this was one of the oral exam questions my teacher asked so i tried to solve it. Consider y>0 the energy spectrum here is continuous and non degenerate while for y<0 the spectrum is discrete and non degenerate because E<0. for y>0 i thought of 2 cases case 1 there is no wave function for...
7. ### I TISE solutions should be combinations-of-eigenstates, why this is not?

I would really appreciate some help with a question I have aboute the TISE (Sch. tipe indipendent equation). This is a linear equation and linear combination of the solution should be solution too. The problem is that for the free particle, which solution can be written like exp[-ikx], a linear...
8. ### I What Is Bell's Theorem and Why Does It Matter?

Hi everyone, I need some help getting the gist of Bell’s theorem and his notion of inequalities. How would you explain it to someone with limited knowledge of mathematics? What are the potential implications?
9. ### I Does the Photon Exist? Exploring Its Necessity

I am wondering why the photon is necessary at all. Is there experimental evidence of its existence? My understanding is that it experiences no time or distance. So if this is true why do we need it at all? Why not just say that a particle here interacts with a particle there. Do we use the...
10. ### I Do atoms recoil when emitting a photon?

Hello! I have some questions regarding the photon emission and whether the atom recoils or not. When an electron in an atom emits a photon. One can calculate the energy of the photon by the difference between the energy levels from where it left to which it returned. Let’s say it jumped from...
11. ### I Other ways of finding expectation value of momentum

Apart from the usual integral method, are there any other ways to find expectation value of momentum? I know one way is by using ehrenfest theorem, relating it time derivative of expectation value of position operator. Even using the uncertainty principle, we might get it if we know the...

13. ### I Exploring Electromagnetism & Quantum Mechanics

In classical electromagnetism I think I have understood the following(please correct me if something is wrong): A charge produces an electric field, a charge moving with constant velocity produces a magnetic field, an accelerating charge emits electromagnetic radiation. In radio antennas this is...
14. ### How do I normalize a wavefunction with Cn instead of Ci and Cj?

I ran into this question in my problem sheet. Does anybody know how to work it out?
15. ### I Zero spin of Higgs boson? Is it really zero?

Zero spin of Higgs boson? Is it really zero? Where is the spin (intrinsic angular momentum) of the Higgs boson on so small that we quantify it as having zero spin?I am aware of the reduced plank constant. But I we sure there is nothing in between the reduce Planck’s constant and the zero spin of...
16. ### I Mass of Water Increasing with Heating

Suppose we heat up a sealed container of water (no vapour escape), will it mass increase according to E=m.c^2 ?
17. ### B Missing mass in atomic systems

Hi! My name's Logan Knox and I'm aspiring to eventually understand the physics and nature of the quantum world in its totality, and I have a LONG way to go, but I have to get there by asking the right questions, and I think this is the first step to finding the right question to ask for this...
18. B

### What is the role of local realism in quantum mechanics?

I studied at UBC, U of Leiden, in quantum statistical mechanics and kinetic theory. I worked in chemistry at McGill University for many years doing the theory of NMR which involves spin theory. In 1997 I gave up NMR and started to study the EPR paradox. I do not follow the party line because I...
19. ### Quantum Is "Quantum Physics for Dummies" a good textbook for starting QP?

I've been reading about Quantum Mechanics for years now and I think it's time I bought a textbook and really learned the math. I'm 15 y.o. and have a working understanding of Derivitives, Integrals and Vectors. Is this textbook a good one to start with or is it too complex? Which one would you...
20. ### Rotational partition function for CO2 molecule

Hello fellow physicists, I need to calculate the rotational partition function for a CO2 molecule. I'm running into problems because I've found examples were they say this rotational partition function is: ##\zeta^r= \frac T {\sigma \theta_r} = \frac {2IkT} {\sigma \hbar^3}## Where...
21. ### I Properties of a unitary matrix

So let's say that we have som unitary matrix, ##S##. Let that unitary matrix be the scattering matrix in quantum mechanics or the "S-matrix". Now we all know that it can be defined in the following way: $$\psi(x) = Ae^{ipx} + Be^{-ipx}, x<<0$$ and $$\psi(x) = Ce^{ipx} + De^{-ipx}$$. Now, A and...
22. ### I Calculate a spin state as a function of the base spin states

Practically it is said that, given two spin states |u⟩ (up) and |d⟩ (down) - which are the spin measured along the +z and -z semiaxes - such that they are orthogonal ( ⟨u|d⟩ = ⟨d|u⟩ = 0), it is possible to write any other spin states using a linear combination of these two (because they are a...

49. ### Quantum Book on quantum electrodynamics

Can anyone suggest me a book on quantum electrodynamics for beginners? Thanks in advance
50. ### Exploring Electron Scattering in Crystalline Nickel Foil

Homework Statement A beam of electrons with kinetic energy 50 eV is fired at a 100 nm thick crystalline nickel foil. (a) Calculate the speed of the electrons in the beam.(b) Based on your answer to part (a), state, with justification, whether classical (Newtonian) mechanics correctly...