What is Quantum physics: Definition and 723 Discussions
Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.
Classical physics, the description of physics that existed before the theory of relativity and quantum mechanics, describes many aspects of nature at an ordinary (macroscopic) scale, while quantum mechanics explains the aspects of nature at small (atomic and subatomic) scales, for which classical mechanics is insufficient. Most theories in classical physics can be derived from quantum mechanics as an approximation valid at large (macroscopic) scale.Quantum mechanics differs from classical physics in that energy, momentum, angular momentum, and other quantities of a bound system are restricted to discrete values (quantization), objects have characteristics of both particles and waves (wave-particle duality), and there are limits to how accurately the value of a physical quantity can be predicted prior to its measurement, given a complete set of initial conditions (the uncertainty principle).
Quantum mechanics arose gradually from theories to explain observations which could not be reconciled with classical physics, such as Max Planck's solution in 1900 to the black-body radiation problem, and the correspondence between energy and frequency in Albert Einstein's 1905 paper which explained the photoelectric effect. These early attempts to understand microscopic phenomena, now known as the "old quantum theory", led to the full development of quantum mechanics in the mid-1920s by Niels Bohr, Erwin Schrödinger, Werner Heisenberg, Max Born and others. The modern theory is formulated in various specially developed mathematical formalisms. In one of them, a mathematical entity called the wave function provides information, in the form of probability amplitudes, about what measurements of a particle's energy, momentum, and other physical properties may yield.
Homework Statement
For this question, h= 6.63×10–34 J.s, c = 3×108 m/s, me= 9.11×10–31 kg, e=1.6×10–19 C. Electrons are accelerated from rest by a voltage of 78.0 V. After that acceleration their speed is 5230000 m/s, their linear momentum is 4.77×10-24 and their De Broglie wavelength is...
Homework Statement
Let \phi (k) be the Fourier transform of the function \psi (x). Determine the Fourier transform of e^{iax} \psi (x) and discuss the physical interpretation of this result.Homework Equations
(1) \tilde{f} (k) = \frac{1}{\sqrt{2 \pi}} \int{f (x) e^{-ikx} dx}
(2) \psi...
Homework Statement
Give the full designation (e.g. 3P0) for all possible singlet, doublet, triplet and quartet S, P and D atomic states.
The Attempt at a Solution
I don't understand this question at all!
Up to which values does the angular momentum (supscript) and multiplicity...
hi i resently read about Schrödinger's experiment called the Schrödinger's cat experiment which states that things don't exist if not mesured and then exist when they are mesured so then that should mean we can minipulate space and time. As i get it, it would be like somone says there are three...
Homework Statement
A system of 20 neutrons are confined in the region
0<x<3L
0<y<L
0<z<2L
With L=10^{-15}m
If each eigenstate can accept 2 neutrons (corresponding to the 2 possible spin states) what is the total kinetic energy of the system?
Homework Equations
I found the...
In one of Feynmans messenger lectures he proved that relativity implies local conservation of energy using the lagrangian (energy can't jump from one place to another). In the atom of quantum theory the electron jumps around in various discrete orbits. This seems like a contradiction.
Is this...
Hi, this is my first thread, and my question is; to witch degree can an autist thinker(comprehending via association through different fields such as music) learn quantum phyisics without math?
Homework Statement
An energy level of a certain isolated atom is split into three components by the
hyperfine interaction coupling of the electronic and nuclear angular momenta. The
quantum number j , specifying the magnitude of the total electronic angular
momentum for the level, has the...
I want to double major in AstroPhysics and Quantum Mechanics. But considering the two work on different scales (Sizes of matter- One Celestial, the other, Sub Atomic), is it an unrealistic goal? The two fields are at odds at the moment, so I'm starting to have doubts as to whether or not it's a...
Hi, I have a question which I've been pondering over and would like to have an anwser to. I'm not schooled in physics so I may be using bad terminology which you're welcome to point out of course.
Anyway my question mainly has to do with the randomness in quantum physics.
I know that the...
hello everyone.i need you ppl to recommend a quantum physics or modern physics book for reference.i stay in india. Wiley publication and Pearson Education are two publisher which i knw.u can suggest any other but good ones.
Hello, I was hoping someone can help with some information. I was in my last year, and I needed to pass quantum mechanics to graduate. Unfortunately, I got a failing grade and will have to wait till next spring to retake it. I was wondering if anyone knows a college that offers a quantum...
Are there any theoretical applications of quantum physics that could in the future lead to weapons in the same way that special relativity led to nuclear weapons?
Hello, world. This is my first post here...and an ambitious one it is indeed. I'm 15 years of age (I don't know how that is proportionally to the main contributors here, but anyway) and it has occurred to me that there exists a mysterious ether in the non-quantum literate world that it is an...
Quantum physics, I believe Lz is the term for angular momentum.
I have a one dimensional system with a particle with mass M and it's moving a long a circle with radius R.
a)Use Lz=MvR to express the particle kinetic energi with help of Lz. Then use the substituion that L_z\rightarrow...
Homework Statement
A particle of charge q and a mass m, moving with a constant speed v, perpendicular to a constant magnetic field B, follows a circular path. If in this case the angular momentum about the center of this circle is quantized so that mvr_n = 2nh, determine the allowed radii for...
I don't understand how matter can be transformed to light and light can be transformed into matter?
Also, how exactly does this happen when something happens to one particle and something equivalent happens to another particle of the same type on the other end of the Earth instantaneously...
I have seen the movie 'The Secret Law of Attraction'. It seems to remind my of quantum physics a bit. However, I read about the concept behind the creation of the movie and have come across a lot of controversy. Some people are saying the law of attraction usually does not take the function of...
So I went to St. Andrews University with the unbelievably stupid idea that I would be able to "handle" their physics. My university, reading only the course description, thought that fourth semester physics was equivalent to Baylor's second semester physics. I soon realized that they only...
Hello, I was wondering if a person majoring in physics takes quantum physics classes too, and if a person with a BSc in physics get a doctorate without having an MSc in physics.
Thanks for the help. :D
Hi, I am just a teenager but I am very interested and dedicated to learning quantum physics, i want to be a theoretical physicist or astrophysicist, something like that. But I am trying to learn as much as I can using books, tv, and the internet mostly. Sometimes i have a hard time...
According to Einstien's theory, energy of one photon is absorbed by one electron. Is this photon is smaller than electron? If not, why energy of photon is not absorbed by other subatomic particles.
Hello people, its been a while since i used physics forums. My assignment is basically a comparison between classical physics and the Quantum physics and to explain why we don't use classical physics. While surfing on the web, i came across a text implying that the definitions of light, energy...
Homework Statement
For a certain system, an observable A has eigenvalues 1 and -1, with corresponding eigenfunctions u_+ and u_-. Another observable B also has eigenvalues 1 and -1, but with corresponding eigenfunctions:
v_+ = \frac{u_+ + u_1}{\sqrt{2}}
v_- = \frac{u_+ -...
The discussion about the existence and importance of experimental study of the strong time noninvariance in quantum physics lasts more than 10 years (see arXiv:hep-ph/0002084, physics/0612089v2 and others). Its essence is that the inequality of forward and reversed processes is quite usual in...
Hey Guys and Gals!
This is my first post ever!
I would like to discuss something i have recently thought about.
If classical physics is deterministic and allows us to create laws, since quantum physics is probabilistic can we ever create any quantum physics laws? (i don't think there...
Homework Statement
The four antennas are arranged in a square with side length d and each of the antennas has an adjustable phase of the radiation emitted. The intensity of radiation emitted by each antenna is I1 with wavelength λ. A receiver is placed at locations A (at the center of the...
I want a clarification in the idea of superposition principle.Perhaps,I should rather say that the distinction of superposition principle in QM and in classical physics.
Few weeks back,I was spending time with Gottfried's book. He explains the novelty of superposition principle with the help...
Quantum Physics Help!
Homework Statement
The spring constant for a particle in the ground state of a simple harmonic oscillator changes by a factor a^4 instantaneously, what is the probability that the particle is observed in the ground state of the new potential immediately following the...
If gravitational waves have such tiny amplitudes (typically several orders of magnitude smaller than a proton), then why do we model them entirely in terms of general relativity? Aren't quantum effects important at this scale?
I read some articles, where equivalence principle is no more valid in quantum area. One example are neutrinos, changing colours (electron, muon, tauon neutrino). But formulae are not derived from fundaments, so I do not understand, where it is the catch.
I read also about COW experiment...
I'm not sure if this is the right forum for my question so here it goes. If not, let me know and I'll be happy to move on.
I've been reading information written by Fred A. Wolf and J. Sarfatti and I think that I'm getting carried away with how I'm interpreting their information. According to...
Why is it that more physicists aren't looking at possible connections between quantum physics and consciousness like Wolf and Sarfatti ? Seriously... is there no money in it? Not testable? Is it considered career suicide? What is it? Just curious...
I just want to make sure I understand some of the greater implications of discoveries made by quantum physics experiments and theories like the double slit experiment and Schroedinger's cat.
Because observation effects results, it becomes clear that an observer cannot extract themselves from...
What is the correct way to use the term trajectory in physics when discussin path integral forumaltion calculations. Here is the sentence i am trying to complete and am unsure if i may use the term trajectory:
So the wavefunction offers a much more simplistic and perhaps more beautiful way to...
Homework Statement
a particle of mass m is in the groundstate of a 1D box with width a. the box then expands rapidly and symmetrically to width 2a. i). What is the probability that the particle is in the new groundstate immediately after the expansion? and ii). how rapid must this expansion be...
Does anyone know of any books on the history of quantum mechanics? I'd ideally like an in depth coverage of the experimental results and theoretical developments, with references to original papers. A complete treatment of non-relativistic quantum mechanics (from pre-Planck to Dirac) would be...
anyone read or have opinions on The Quantum Physics of Time Travel by David Deutsch and Michael Lockwood?
He talks about closed time like curves and if we followed them it would end up taking us to the past to participate in events, shake hands with former selves etc
I was a little...
I have recently been doing research and have found that The Theory of Relativity is not accurate enough to predict paths of the planet's orbit. I would also like to call to attention that gravity and quantum physics are flawed in one way or another. So in turn I would like to have some ideas...
As a novice to Quantum physics and as a working physicist in the oil industry this may be a stupid question but I find the whole subject of quantum physics fascinating.
I have been pondering the missing mass in the universe and particle vs wave argument and came across a nice description...
Homework Statement
Hi
I am new to this forum and offering quantum physics at A level. Can anybody help with the following problem:
The rest energy of an electron is 0.511MeV. A positron created in a cloud chamber has 0.158MeV of kinetic energy. It collides with an electron at rest...
Hello all,
I have a quantum physics question which is more conceptual and mathematical than anything. Here's the question:
Explain why ψ and its derivative have to be continuous and finite.
I'm doing the frank hertz experiment and in preparation I'm trying to get a few questions answered.
any help would be greatly appreciated,
8.
Considering that the energy of the 1st excited state of the mercury atom is ~4.8eV above that of the ground state, what is the maximum amount of...
I'm doing the frank hertz experiment and in preparation I'm trying to get a few questions answered.
any help would be greatly appreciated,
8.
Considering that the energy of the 1st excited state of the mercury atom is ~4.8eV above that of the ground state, what is the maximum amount of energy...