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.
Hi I'm currently pursuing electronics and communication degree in India. I'm confused whether to get another bachelors degree in physics or i can directly do my masters. Most of my friends suggested to directly carry masters in any US colleges so that professors would be knowing what i lack and...
Description
1. Prove that operators i(d/dx) and d^2/dx^2 are Hermitian.
2. Operators A and B are defined by:
A\psi(x)=\psi(x)+x
B\psi(x)=d\psi/dx+2\psi/dx(x)
Check if they are linear.
The attempt at a solution
I noted the proof of the momentum operator '-ih/dx'...
So what is the implication of time-reversal asymmetry in relativistic physics, now that we know that quantum mechanics is not time-reversal symmetric to 14 standard deviations?
Why do we say that classical physics is a lot different from quantum physics?
The laws that determine the macroscopic world should be derivable from quantum laws. So in a way the Newtonian or classical laws are basically quantum laws( maybe a bit approximated)
So why differentiate between...
I want to self study quantum mechanics so that I can apply it in both physics and chemistry. However I don't want one written for a layman without any mathematical equations.
I want one book that will cover everything that will be taught in an introductory undergrad quantum physics course(and...
In the book "The Quantum Story", by Jim Baggott, we find the following:
"[...] Many physicists, including Planck and Bohr, dismissed the light-quantum. They preferred to think of quantization as having its origin in atomic structure, retaining Maxwell's classical wave description for...
Hello!
As my title suggests, I want to know about the difficulty of quantum mechanics and several of the prerequisites I should know before I begin such a venture. The following is the path of college courses that I will be taking over the next two years.
Year 2013-2014
Mathematics: S1...
1. A p-n junction is a double layer of opposite charges separated by a small distance and has the properties of a capacitance. The resistivity of a semiconductor can be controlled by doping. Thus the elements in the trasistor circuit of Figure 13-24a can be manufactured on a p-n-p semiconductor...
Homework Statement
Observable \widehat{A} has eigenvalues \pm1 with corresponding eigenfunctions u_{+} and u_{-}. Observable \widehat{B} has eigenvalues \pm1 with corresponding eigenfunctions v_{+} and v_{-}.
The eigenfunctions are related by:
v_{+} = (u_{+} + u_{-})/\sqrt{2}
v_{-} =...
what i want to know is why classical physics does not work on quantum level particles?
what are the consequences of using classical physics on quantum level particles?
Hey, I haven't been here for awhile but I would like to know if anyone has some good links or free pdf books, to help me learn and excel in quantum physics and calc. I so far have not taken any calculus and it will most likely be completely foreign to me but, I understand that and since I'm...
I was originally an applied math major and about 2 years ago doubled up with a major in physics... Being an applied math major, I have had quite a few courses in mathematical modeling, and there was always something that bugged me about quantum physics. I figured that I would figure it out once...
Dear folks,
Under the aalaniz blog, I just posted step-by-step notes starting for ODEs and PDEs both linear and nonlinear, of the type you will see in grad physics programs. The notes connect Lagrangian, Hamiltonian and Poisson Bracket methods in classical physics to the various approaches...
Hello everyone!
I recently have transferred to a 4-year institution from a 2 year community college. Unfortunately, my community college did not offer Modern Physics and so I did not take the course. I am currently trying to pursue a B.S. in Physics and it requires me to take Quantum Physics...
I am fairly new to quantum physics, I don't know much more than the double slit experiment and schrodinger's cat paradox. Can anyone tell me what would be a good subject to read about to be able to "understand" quantum physics? Superposition? Entanglement? Also, if anyone has any good...
hey, I'm physics student, doing my quantum physics exam soon, was wondering if there is any textbooks you recommend.
any kind of information that will help me understand the subject in theory and mathematically..
thanks a lot
Hey everyone,
I know that quantum mechanics is a sub topic of quantum physics and is the most general also, but I'm having trouble finding an article that is recent, detailed, and accurate. So if you guys could explain the basics and go into detail when you feel necessary. Thanks.
As I watched a documentary lately on an experiment by Aaron O'Connell, that "proved" that quant exist in two points in space at the same time I couldn't help but wonder why that was the result derived from such an observation.
I am not a physics specialist but have a background of physics and...
Hello.
I have this problem at hand:
Homework Statement
A quantum mechanical system has a hamilton operator \hat{H} and another, time independent operator \hat{A}_{0}.
Construct a time dependent operator \hat{A}(t) so that:
<ψ(t)|\hat{A}_{0}|ψ(t)> = <ψ(0)|\hat{A}(t)|ψ(0)>
for all states...
Well, am an Alevel student... Edexcel.. I just find quantum physics a really really confusing topic.. My question is particularly in black bodies. If we consider the sun as a black body, where did the radiations of the sun initially come from. I don't mean the emitted radiation we see, i mean...
talking about ψ-epistemic, ψ-ontic and ψ-complete models.How would the world appear to us if its ontology was that of classical mechanics but every agent faced a restriction on how much they could come to know about the classical state?
http://arxiv.org/pdf/1111.5057v1.pdf...The success of this...
Hey everybody,
I have to give a talk in our seminar on invariant theory of Lie Groups. And I'm now looking for
easy applications of invariant theory to quantum physics. I want to present them to
motivate the discussion.
I would be lucky if someone of you has an idea where I can found...
Homework Statement
The nuclear processes obey certain rules. I.e.
Conservation of energy and mass
Conservation of charge
Conservation of spin
Conservation of momentum
Conservation of lepton and baryon numbers
Use the following examples to discuss these various rules in the following...
This question bothers me a long time and finally I decided to ask here.
The classic theory fails to deal with electron orbiting around atomic nucleus because energy has been emitted if we assume electron continuously orbits which leads to the collapse of the electron-nucleus model. But in real...
How/Where to begin studying Quantum Physics? Please Help!
Hello, (Very sorry for the length, but please help!)
I'm currently a grad student studying transnational security. Problem is, I'm worried that I've chosen the wrong field to study! Like all of you, I find quantum theory absolutely...
just thinking cross sections here. a neutron that is freed as a result of a fission of pure U235. travels @c/10(fast!) will its trajectory be perturbed by the gravitational force emitted by a nearby nucleus, or do things on the quantum level work differently?
Is this right about the double-slit experiment and quantum physics??
Well I'm trying to understand the double-slit experiment (and quantum mechanics), so could you tell me if this is correct?
A photon is fired through two slits at a plate behind the slits. As long as it isn't observed it...
I am a young adult writer, and my current WIP involves parallel universes. My main character is from another universe.
I have read about worm holes and black holes. Quite frankly, just when I think I am beginning to remotely comprehend I hit another brain cramp. I realize this is all...
Hello all,
Homework Statement
I’m trying to derive a result from a book on quantum mechanics but I have trouble with bra-ket notation and operators…
Let’s say we have a photon moving along the cartesian z-axis. It is polarized and its state is
Psi(theta) = cos (theta) x1 + sin(theta) x1...
Hi everyone I'm having a little trouble in my class and part of the reason is because my book is very confusing to me. The book is:
Quantum Physics: A Fundamental Approach to Modern Physics by John S. Townsend
What sidebook would anyone recommend for me so I can get a better grasp of the...
Homework Statement
A laser produces light of wavelength 540 nm in an ultrashort pulse. What is the minimum duration of the pulse if the minimum uncertainty in the energy of the photons is 1.0%?
Homework Equations
ΔEΔt ≥ hbar / 2
The Attempt at a Solution
Now I tried a couple ways...
One; how to determine a wave function of a particle ( let's use the muon as an example)
Two; an explanation of wave particle duality with reference to the Airy experiment and the fact that a particle is a wave until observed by a human.
Hello,
I am writing an appendix to my thesis where i try to explain how nmr works but i am having trouble understanding something.
Suppose that we have a sample with many nuclei with 1/2 spin precessing around an external magnetic field \vec{B_0} aligned with the z axis. At Boltzmann...
Hi, I am a 16 year old high school student. I am really interested in Maths and its my passion.
I am also really interested in Quantum Physics and I would just like to know a list of what type of Maths (eg. Differential Calculus) I would need to learn to understand it.
I just need a list...
Hi, that's my frist post here, I just made my registration. I'm 21 yaers old and I'm studying for a lowyer so my knowage on physics is quite poor. Anyway I watched a documentary on quantum physics today and my mind got messed up !
Here are my questions:
Quantum entanglement- Is it true that...
Homework Statement
Use the Bohr quantinization rules to calculate the energy states for a potential given by
V(r)=V_0 (\frac{r}{a})^k
with k very large. Sketch the form of the potential and show that the energy values approach E_n \cong Cn^2
Homework Equations
The Attempt at a...
I came across a discussion on net recently, where projectile motion was solved using the quantum mechanical approach.
http://www.physics.csbsju.edu/QM/fall.14.html"][/PLAIN]
I have already seen solution of the vibrations in string using quantum mechanics.
I want to ask can i use quantum...
The titular question is quite straightforward. I'm going for an honours bachelors in physics and I'm considering going for a masters in one of those fields. I don't know how well Hbsc Phys transfers to aerospace engineering, and I'm also unsure what type of branches of quantum I could go into...
Hi,
I know very little about quantum physics so I need some help here, but recently I have seen lots of new agers claiming work on Quantum physics "refutes" materialism and either supports dualism or that mind is the basis of reality, they cite people like gowami or even Bohr or Heisenberg...
hello guys,
currently i am a pediatrician, i am still 27y old, it has always been my dream to study quantum physics, this branch is not available in egypt
can anybody give me any tips on where i can study quantum physics ?
i am just going to give my exams after two months. After that i will be free for 2-3 months, before i join any other institute.
I have done classical physics in detail in past two years.(not of engineering level, as i still hav to join a college)
i like physics very much.
Quantum world looks...
I am a high school senior who is new to these forums. So far, I have found them intriguing, but I do have a question that I have asked many of my teachers, but sadly, had no real response.
What are the basics of quantum physics? Basic concepts, theories, equations for example. I haven't been...
If you have a degree in mechanical engineering, can you do an M.A in quantum physics? is it about your previous certificate? or simply your ability to handle the following field?
a. What do we know about any quantum-physical law, dictating 8 electrons in the outer atomic shell + the other shells' populations, including the 2 electrons in the innermost. Any physical theory behind these numbers, or just an empirical reality ?
b. How reacting atoms 'choose' between...
Recently I have been looking into Fuzzy Theory which is a relatively new subset of logic and is closely related to probability theory. Fuzzy Theory right now is practically a "taboo science" with not many scholars too interested in it. However, I see this as a grand opportunity to jump into a...
Greetings,
This evening as I write this post, I can not be more humble of a person. I am writing because I am on a quest for more knowledge. Early in the middle of 2009 I stumbled across a documentary with a couple well known physicists that peaked an old, long-let-go dream. What started...
Homework Statement
Given a wire with length a and square base b x b (where a >> b), show that the first 1700 (approximately) levels of the electron in the wire are identical for the one dimensional box, when a = 1m and b = 1mm.
Homework Equations
I know that the allowed energies of...
Homework Statement
A rectangular corral of widths Lx = L and Ly = 1.94L contains seven electrons. What multiple of h2/8mL2 gives the energy of the ground state of this system? Assume that the electrons do not interact with one another, and do not neglect spin.
Homework Equations
Enx,ny =...