Virtual Definition and 565 Threads

If we can see a virtual image, why can't we obtain it on a screen?

In reading Feynman's "Lectures on Physics", volume 2 I have a question and have included a scan of a small section from the book. Feynman was a big fan of using the Principle of Virtual Work, but his explanation, as least insofar as how he used it is wanting, at least for me. The attached...

As I understand it, according to the Copenhagen interpretation of QM, nothing can be said to exist until it is observed. I have also read that it is impossible to observe virtual particles in an experiment. How is it then that virtual particles can be said to exist?

I am attempting to create a virtual host here on my machine. I assume the place to do this is in the /etc/apache2/sites-enabled/000-default file. The file currently reads this: NameVirtualHost * <VirtualHost *> ServerAdmin webmaster@localhost DocumentRoot /var/www/ <Directory />...

Why forces are modeled as virtual particles in quantum mechanics and how virtual particles can transmit force between two real particles?

Folks, I have a question about virtual particles. I recently read in a Scientific American article which says that "virtual particles are indeed real particles. Quantum theory predicts that every particle spends some time as a combination of other particles in all possible ways. These...

A mentioning about virtual particle problem in my other thread just reminded me of some thoughts, which I now succeeded putting together. When calculating cross sections in QFT, we encounter terms like this \langle 0|a_{\textbf{k}'} a_{\textbf{p}'} a^{\dagger}_{\textbf{p}_1}...

I've often heard the argument that vacuum is full of virtual particle pairs that get created and annihilated, but in fact the ground state of the harmonic oscillator is orthogonal to all excitation states, so shouldn't the vacuum, when in ground state, actually be empty of all particles? What is...

How do you go about solving an indeterminate beam for various deflections by virtual work? I'm kind of at a loss right now and can't proceed on my homework. I've attached a picture showing the problem I'm confused on - I don't know how to go about modeling the virtual model so I can find the...

Securing your virtual space: by implementing timed logins. (a space-time formatted entry) (A) User: {name,schedule} (B) schedule: {window of opportunity* } (C) window of opportunity: {recurrance, theHOUR, theMINITE, duration} (4) recurrance: {any, yearly, quarterly, monthly...

I'm very happy that I found this forum, hello everyone. I'm studying Lagrangian Dynamics and I can't figure out how to find the generalized forces in a setup like this: ____ ____ | | ___ | | | b1 |===|___|===| b2 | |____| |____| --->x...

hi everyone, I am having a tough time convincing myself about the virtual short concept in opamps, As i understand from texts, on the application of a voltage on one of the input terminals of opamp, the voltage at the other input terminal is also forced to match the voltage on the first...

Can they appear inside a black hole? Can they appear between an electron and the nucleus? Inside a nucleus? Can two sets appear at exactly the same place? What prevents them from appearing exactly where other existing matter is?

I don't have a CD or DVD burner. Is there a virtual DVD program that will recognize .daa files?

I have a few questions concerning opamps. First what is the big deal about infinite common mode rejection? It seems to me by looking at the open-loop gain equation A(V2 – V1) = V0 it is obvious that when V2 = V1 the output is zero (common mode rejection). This may be where I am confused …...

With some additional software and hardware modifications, this guy creates a virtual reality display using his Wii. http://www.youtube.com/watch?v=Jd3-eiid-Uw&NR=1 Okay, so when are the new VR shooters cooming out? I'm tired of trying to peek around corners in vain. The technology for...

It seems to me that the physics is the same they are all due to the exchange of virtual photons between two particles

Hi. I recently got my computer upgraded to have a 100G rather than 50G hard drive, and to have double RAM. However, I am having a different problem that is impacting my school. I take school online, and some of my courses are run off of disks. So I was working through one of the disks today...

Light travels slower in mediums like water than it does in the vacuum. Would it be even faster in the vacuum if the vacuum were "true" and there were no virtual particles popping into existence? Shouldn't light be slowed by them?

Homework Statement Assume that a high-energy nucleon is emitting a pion, i.e. the process N→N+π. Is the pion real or virtual or both? Motivate your answer with a calculation or a good argument. Homework Equations Virtual particles does not obey energy (and momentum) conservation. The...

At any given time, lots of them exist. I would expect this to produce a constant but rapidly changing gravitational force. How is this effect taken into account in cosmological theories?

Why are virtual photons and gravitons allowed to pass outwards through the event horizon of a black hole? Is it that it doesn't really make sense to assign a particular path to a virtual photon? This still isn't satisfying to me, as there is *no* path that allows a real photon to escape...

Hi everyone, I have some questions on the nature of virtual photons. Firstly, are they actually particles (in the sense that a normal photon is a particle), or are they just mathematical consequences...and if so, what is their nature? Secondly I have some questions still unanswered from a...

Hi, So, I'm confused about the difference between real and virtual images. Let's use a concave mirror for example. I understand that a real image is formed when the actual light rays reflect off the surface and converge to one point. A virtual image is formed when the rays don't themselves...

Are we sure about the existence of virtual particles?

Hello. Cant it be that the fabric of space-time continuum or space is transforming into the virtual particle and vice-versa?

A positive lens has a focal length of 12cm. An object is located a distance of 3 cm from the lens. How far is the lens from the image? Is the image real or virtual, erect or inverted? My attempt f = +12cm o = +3cm i =? 1/o + 1/I = 1/f 1/i = 1/f – 1/o = 1/12cm – 1/3cm = 1/12 – 4/12 =...

I often read that particle-pairs that are created in the vacuum consists of a particle and it´s antiparticle which both have an positive energy that is "borrowed" from spacetime according to Heisenbergs Uncertainty principle. But when it comes to Hawking radiation one often refers to one of...

Homework Statement A transparent photographic slide is placed in front of a converging lens with a focal length of 2.44 cm. The lens forms an image of the slide 13.2 cm from the slide. How far is the lens from the slide if the image is virtual? nearer possible distance = Homework...

Homework Statement Im having real trouble with drawing diagrams for virtual work. Can someone please, please help me! We were asked, in the diagram i posted, to find 1)vertical reaction at F, 2) all reactions at A, 3) bending moment and shear force at B using virtual work. i think i...

Quarks are smaller then electrons? I read that when a electron moves from a higher energy level orbit to a lower energy level orbit it emits a "real" quark... So are other quarks virtual?

I'm a novice here..but in virtual neural networks, does adding more virtual neurons improve the performance of the network in terms of recognizing patterns? Has this been experimentally verified anywhere? Can you then make an analogy that the same would happen in a biological neural network? Or...

You guys are smart and give good replies so i thought i would run this by you folks. Theoretically communism is the best for of government we have thus far, in praksis however that changes dramatically. Democracy is the current leader when it comes to ruling the masses... but is it not time...

Has anyone seen the software/demos for this project made by the U.Iowa?It looks pretty sweet. edit: you it would've helped if i posted the link also. http://www.digital-humans.org/santos/SantosPhotos.htm http://www.digital-humans.org/main.htm

I was just reading the Feynman Lectures on Physics when Feynman discussed virtual work. Unfortunately, I found his explanation somewhat confusing. The following are the three examples Feynman uses in order to illustrate the principle of virtual work. 1. 2. 3. I'm trying to...

1. The radius of Earth is 6.40 x 10³ km. The moon is about 3.84 x 10^5 km away from Earth and has a diameter of 3475 km. The Pacific Ocean surface, which can be considered a convex mirror, forms a virtual image of the moon. What is the diameter of that image?2. 1/p + 1/q = 1/f M = h'/h = -q/p...

what the term "virtual particles" referred to I wanted to know what the term "virtual particles" referred to. I found many "descriptions" of them on webpages. Fine. Then I went to the index of many advanced QM books, and the term "virtual" doesn't really show up as prominently as I thought...

Hi, I am writing a visual basic program and used MSComm for testing communication ports of PC. It is working well. At company, we have a game machine using two standard ports (com1 and com2 which can use MSComm to test) and virtual ports (com3 and com4). Of course, the program cannot test...

Sad i know but it is just a thought that, the ratio of real to virtual particles that are present at anyone time may have some outcome for QG, if anyone could even calculate such a thing.

we used a concave mirror and a candle for an experiment when the candle wa placed between the vertex and the focus of the mirror (f=12.7cm) a virtual image appeared behind the mirror. We measure the image distance approximately by pointing a finger towards where the image might be and got...

magnetic field is made of photons? i've been researching photons and i discovered on http://http://van.physics.uiuc.edu/qa/listing.php?id=414" and http://en.wikipedia.org/wiki/Photon" both resources state that all mangetic fields are made of photons. soooooo, this brings up a lot of...

How can one readily determine that the reality one experiences is real, not virtual - perhaps through Turing machine logic?

i know that virtual particles are a result of the uncertainty principle and that most of the time they are annihilated but i also think i read that sometimes they come into being when they receive an energy boost? I am thinking maybe an errant photon? also I've read about velocities of...

Perhaps someone can explain virtual particles. My intuitive notion of them is that particles come in and out of existence to communicate to other particles how to behave and if you try to observe them they disappear. How is the Higgs mechanism responsible for particle masses? What is a Higgs...

Hi, I'm a newbi when it comes to physics, but i read something last night that made me wonder: I read that an electron can send out "virtual photons" that "goes back" to the electron if it doesn't find anything to interact with, my question is now, when are these photons sent out? Is there...

In the "Beyond the Standard Model" forum there is a thread entitled "What causes gravity?" https://www.physicsforums.com/showthread.php?t=123380 In the discussion Yogi writes: What is the thinking among most physicists today on this issue? Are virtual particles considered certainly...

There's a lot of talk about "virtual particles" and of energy conservation within a normal perturbative approach to QM. I'm struck by the fact that there are precious little concrete examples or illustrations or gedanken experiments to support all the arguments, which go around and around and...

Hi I was wondering if somebody could kindly tell me what the difference between a real and a virtual image is. The way I which I know them apart is that in a real image the light rays actually intersect, while a virtual image the light rays diverge , thus never actually intersect. Is this...

According to what I have read, virtual particles are those which are intermediate photons in interactions, which cannot be directly observed. If my understanding is correct that would mean that they consist of (in low order perturbation theory), (among other things) u and t channel photons. But...

What is the Virtuality for a virtual photon (Q^2). How's it defined? What is the virtual photon's frequency then? Any relations between them? Thanks. :!)