Fields Definition and 1000 Threads

Intuitively, I'd say that adding a 4-divergence to the Lagrangian should not affect the eqs of motion since the integral of that 4-divergence (of a vector that vanishes at ∞) can be rewritten as a surface term equal to zero, but... In some theories, the addition of a term that is equal to zero...

Summary: The quantum fields stem from the quantum mechanical wavefunction, which in the standard QM is epistemological (amplitude of probability). How can they be then considered ontological? The quantum fields stem from the quantum mechanical wavefunction, which in the standard QM is...

As a prior physics major (had to stop at my 3rd year of undergrad due to children and financial difficulties), there was something I was always extremely passionate about - finding feasible ways to travel faster than light. Obviously, the only feasible way seems to be to bend space-time, but I...

In this question, I would have to calculate the force in respect to time. However, the question gives me the value of the mass of the electron. In my attempt, I didn't take that into account. I just replaced ##v## with ##\frac{d}{t}## and made the Lorentz force undergone by the particle...

I'm just going to post this image now since my tablet won't render the latex. This is a free response question.. But my experience is that the methods of solving are more focused here at mhb saving many error prone steps.. Mahalo ahead...

I'm reading on Wikipedia about quantum field theory and read this: "Quantum field theory naturally began with the study of electromagnetic interactions, as the electromagnetic field was the only known classical field as of the 1920s". Why wasn't Newtonian gravitation regarded as a classical...

the image is given here along with some numerical information: Now I know that the formula for the electric field in a capacitor is given as: $$E = \frac{V}{d}$$ which I can use to obtain the three following fomulas: $$E_1 = \frac{V_1}{d}$$ $$E_2 = \frac{V_2}{d}$$ $$E_3 = \frac{V_3}{d}$$ where...

[Moderator's note: Spin-off from another thread.] You need the structure of a topological vector field K with 0 as a limit point of K-{0}. The TVF structure allows the addition and quotient expression to make sense; you need 0 as a limit point to define the limit as h-->0 and the topology to...

So I have managed to derive the magnetic field of a current carrying wire, however, I seem to have some enquiries on deriving the one for the loop. In the formula where ##\frac {ds * r} {r^2}##, I know that it will become ##ds sin \theta.## However compared to the theta in the wire, the theta...

Can someone provide me intuitive visualization of how E or H field can be longitudinal in a waveguide (TM/TE)? TEM is easy to visualize, but how EM wave can behave like sound in a waveguide (constant phase and amplitude plane in the same direction)? [Moderator: large bold font removed. In the...

Is it true, what he's saying from 04:28 to 04:56 ? I have my doubts, but I thought I'd better ask here.

It seems that QED treats the matter and EM fields as independent yet coupled fields. On the other hand the EM field equations emerge immediately under local change of the phase of the matter field, exactly as required to reestablish local (gauge) invariance. From that perspective it almost seems...

Sorry in advance if this question doesn't make sense. Anyway, I am reading a paper about quantum field theory and the Whitman Axioms (http://users.ox.ac.uk/~mert2060/GeomQuant/Wightman-Axioms.pdf), and it describes a field (Ψ) as Ψ:𝑀→𝑉⊗End(𝐷) where 𝑀 is a spacetime manifold, 𝑉 is a vector...

I know that the field inside sample is a combination of the demagnetizing field and whatever applied field you may have. So these two fields together influence how big a field you need in order to magnetize the sample.

Hello everyone. My question is how can I use databases like scopus to know which areas of physics are the "hot" today or which are still in development.

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In a simple example of two current carrying wires, there are mutual forces. Do we speak of the forces on each wire as action-reaction or as someone I'm debating with, each wire and the fields from the other wire as action-reaction? Or both? Thanks.

How would it be possible to fluctuate one magnet between two magnets? Thanks

Following up on @A. Neumaier's excellent series of articles on virtual particles, I'm confused about one thing (well of of several). If you pop over to the discussion of virtual particles on Matt Strassler's page, he mentions that, for example, an excitation in the photon (em) field will also...

Lets say we have a Direct Current (not an alternating current) going through a wire ; so there is a steady-state magnetic field created around the wire. Then let's say we move some object into the magnetic field that disturbs the field. . My question is : How do we/they get information...

Summary: I need to build an asymmetric capacitor, but the mathematics of electromagnetics become too tough, do you have any info that can help? Appreciate it! Hello, I am an undergraduate student in engineering and I want to build an asymmetric capacitor, so I need electromagnetics which I...

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Summary: What is the relationship between paramagnetic field strength at a given distance from the source? Apologies if I have put this in the wrong topic. And apologies if the question is unclear, I am a biologist by background attempting to do some physics here! Basically I am looking to...

Electromagnetic waves are oscillations of the electrical/magnetic field which propogate through space. So one might predict that the presence of a magnet/charged particle would effect their propogation somehow, like distortion or interference (eg, light might get refracted in a magnetic field or...

Premise: everything that follows is done in the frequency domain. Boundary conditions If there are superficial currents (electric and magnetic) impressed on the boundary between two media, we have these discontinuities for the tangential components of the fields...

I am currently studying QFT from this book. I have progressed to the chapter of QED. In the course, the authors have been writing the Lagrangian for different fields as and when necessary. For example, the Lagrangian for the complex scalar field is $$\mathcal{L} \ = \ (\partial ^\mu...

I am studying QFT from A First Book of QFT. It is a very well-written book. However, due to some personal reasons, I cannot buy the printed book at this moment. So I borrowed this book from a person (who, in turn, borrowed it from his university library), and scanned it. Everything is fine...

Sorry if this was already addressed in the other Windows 10 thread. What do the different check mark fields (round and square) mean in the icons on my new Windows 10 laptop's desktop? My Google search only turned up results on "green checkmarks" that related to Office 365 synching? Thanks <<...

Summary: Mathematical and Physical queries in regards to Electromagnetic Fields and their manipulation of Space-Time. I recently started looking into Einstein's Field Equations, to get a better understanding of how mass distorts and curves the plane of Space-Time, however from doing this I...

I have came across a term "coherence length of velocity field ##\lambda## ",tried to search in the internet but doesn't find any result...will anyone please give a brief summary of this in this context..

I am curious about the case where two electric or magnetic fields cancel each other out (I'm assuming this is possible). If a charged particle travels through the region where the cancellation exists, I am assuming the particle behaves as if no field exists. Does that area still have electric...

I am assuming the answer is NO. I realize that the electric field of any charged object has an energy density, but I was curious to know it that same field has it's own 'charge density' so to speak, and that it would have a small secondary electric field of it's own. This would imply that...

I understand that the energy of an electric field arises from the work put into gathering the electrons together to create the field. Bringing electrons close together requires energy because they naturally want to repel. This potential energy is stored in the field itself and the field has an...

Can anyone explain why an artificial magnetic field may or may not promote an increase in cellular metabolism?

Dear everyone. I'm doing an assignment on vectorfields and for most of the assignment I have to deal with tensors and tensornotation. The first assignment asks me to express the following vector and matrixproducts in tensornotation. $$\overline c = \overline a + \overline b \\ d=(\overline a +...

In dealing with rotating objects, I have found the need to be able to transform a vector field from cylindrical coordinate systems with one set of coordinate axes to another set. For eg i'd like to transform a vector field from being measured in a set of cylindrical coordinates with origin at...

Hi, I want to plot the vector field ##\vec F = ye^x \hat i + (x^2 + e^x) \hat j + z^2e^z \hat k## The code I have tried: # The components of the vector field F_x = y*e**x F_y = x**2 + e**x F_z = z**2*e**z# The grid xf = np.linspace(-0.15, 2.25, 8) yf = np.linspace(-0.15, 2.25, 8) zf =...

Personally, I have trouble visualizing a flock of birds without the birds. I have the same trouble trying to visualize an EM field without the photons. More than once, I have been hounded off of the ham radio forums for mentioning the word "photon". As one ham radio operator put it, "We don't...

I'm trying to derive the electric and magnetic fields of a plane wave from the four-potential ##\mathbf{A} = (A^t , \mathbf{a}) ## in the Lorenz gauge. Given: ##\mathbf{A}(\mathbf{R}) = \Re \left( \mathbf{C} e^{i \mathbf{K} \cdot \mathbf{R}} \right)## for constant future-pointing lightlike...

I've had a lot of problems that involve a segment of current carrying wire, for example when you have a square loop of wire. I have a formula for "long" wires that is B = μ0 * I/(2 * π * d). Can I use this for shorter wire segments, and if not, what formula can I use?

I figured that we would simply add up the forces acting on the electron (the electric force Fe and the magnetic force Fb) and then equate this to the given acceleration multiplied by the mass of the electron like so. vector Fe + vector Fb = (mass of electron) (vector acceleration) since vector...

I am a master student in theoretical physics from Italy and I would like to know more about fields related to "Quantum Information". I've been to some seminars and I think that these fields are very interesting, but I need to understand before applying for a PhD. What should I do?

If you calculate the uncertainty of a scalar field in the vacuum state, i.e. ##\langle0\left| \phi^2\right|0\rangle##, you get a divergent integral that comes out to something like $$\frac{1}{4\pi^2}\int_0^\Lambda \frac{k^2 dk}{\sqrt{{m^2}+{k^2}}}$$ Where ##\Lambda## is some momentum cutoff...

The videos from Veritasium explaining permanent static magnets and electromagnets were quite good I thought… But they have me a little confused with regard to the origins of magnetic fields generated by an electric current as opposed to a permanent static magnet from say iron. 1. An...

at a point they become plain waves, how much will they be attenuated when 'received' by a spiral log periodic antenna Vs another dipole? Would an H field created by a loop antenna have less attenuation?

My paper "Classical states, quantum field measurement", arXiv:1709.06711, has been accepted by Physica Scripta, https://doi.org/10.1088/1402-4896/ab0c53. The version as submitted to Physica Scripta on November 4th, 2018 is available as arXiv:1709.06711v5. I believe that anyone who puts some...

For light it is said it has no volume and also it it waves of electric and magnetic field. But for electric and magnetic field you need space? So can they both be at the same time?

hello, i have a doubt i bought some small neodimium magnets 8x3mm and now i would like to try some experiments with them i have a doubt: if i rotate one of these magnet around one of its parallel axis, very fast , near 1000000 rpm, what happens to the magnetic field produced by the magnet? if...

After learning that QFT describes particles as excitations of underlying fields, I've been trying to gain a more definite understanding of what it means; I came across this paper: https://iopscience.iop.org/article/10.1088/1361-6404/aaa032 Does the author say anything that is misleading? If...

I found this interesting article https://blogs.ams.org/matheducation/2019/02/14/mathematics-gatekeeper-or-gateway written by Mark Saul So the question is: What is mathematics: A necessary evil or the universal language physics is written with? If you tune in on a random tv quiz show and wait...