Vacuum Definition and 1000 Threads

So, a professor in class a about a year ago mentioned that opening a switch in a circuit that an inductor is providing power to would cause a breakdown in the air and a spark would jump across it because the current can't change instantaneously to zero in an inductor. Something just made me...

So this is a decent series of videos introducing QED http://www.youtube.com/watch?v=i8O_yQHxQos&feature=related At 7:05, the host starts talking about the force that a vacuum creates, but doesn't elaborate further. What force is this? Are they attracting the plates through electromagnetism? Or...

2 questions. 1. why vacuum is not used in hydro electric power plants and 2. why water under presure from big depths are not used for revolving turbines? 1. with vacuum you would need only small amount of water faling from a big altitude to revolve turbine. Turbine would revolve faster and...

Hi, I know the speed of light is the highest in vacuum. And in any other mediums is a bit slower. I just want to know... ...if a light passes through a medium (water let's say) and comes out in vacuum, will it retain the same speed as it had in the water, or will it increase back to its...

I was just thinking that if you set something spinning in space it keeps turning, so does this mean once you started an electrical generator turning would you get ‘free’ energy?? Will the force from the magnetic field eventually case the wire to stop spinning?

Hi everyone, I have a severe confusion about the notions of "expanding the theory around a classical vacuum" and "considering small fluctuations around a classical vacuum" which I find in QFT textbooks. My problem is: in the path integral \int D\phi e^{i S[\phi]} one doesn't integrate only...

I understand that the quantum vacuum is nothing with particles popping into and out of existence and I also understand that this has been in existence since the big bang but I am curious as to whether this type of nothing could exist before the big bang (not relying on a multiverse). I assume it...

Homework Statement A spherical black body with a radius r and a temperature T is placed in a spherical thin shell (radiation screen) with a radius R. The shell is also absolutely black on both sides. The space between the shell and the sphere and the space outer of the shell contain vacuum...

Can electron self energy diagram contribute to the vacuum polarization? Or is the question meaningful? What's the exact meaning of vacuum polarization? Does it necessarily involve some charged particle? For example, for the ordinary phi^4 theory, can I identify any diagram that can be called...

Argon gas is used in a lightbulb because it's not reactive, whereas air is. But why is it better than a vacuum?

I recently thought about using capillary action to power a generator (capillary action lifts water, right?) then researched it and learned that 1) I'm not the first one to think of it and 2) it wouldn't work anyways. Then I thought, why can't you use a vacuum to lift the water through a tube...

I recently learned about the possibility of the universe being in a false vacuum, but it seems really hard to find real information on it. I've looked at academic papers but they're well above my undergrad math. Does the acceleration of inflation imply that we do exist in a false vacuum...

Imagine a spacecraft containing a perfect vacuum, hurtling through space at 0.9c. This movement distorts the space the matter of the ship occupies. But what happens to the space inside the ship? It contains no matter. Is space irrelevant without matter?

1. why does gas expand to fill a container when there is no increase in temperature or any force applied to it? ( I am confused with the rising effect of gas in air and the expanding effect. how can we distinguis it?) 2. how can we determine the limitation of gas expansion when there is no...

Nikola Tesla observed that electrons transmitted through a near perfect vacuum in his vacuum tubes appeared as corona several feet through the air surrounding the tube. He thought that if there is nothing in the tube between the electrode and the glass then how do the electrons convey through...

When Einstein proposed the cosmological constant, it was regarded as an arbitrary constant having no connection with flat-spacetime physics (e.g. QFT to be invented later). IMHO the effective cosmological constant, in principle, should be the sum of QFT vacuum energy and Einstein's arbitrary...

Is the vacuum energy density, in case it exists which is the mainstream view, supposed to be continuously varying (decreasing) as the universe volume expands or is it really a constant (wich would be rather odd judging by what density and volume usually mean in physics)?

Will there be any change in buoyancy in bottle full of air and vacuum bottle?

I understand the basics of the double slit experiment. I'm trying to imagine what would happen if one slit could operate at a 180 degree phase shift, or nearly that. The obvious answer is not much except between the slits, and even less if the distance between the slits is near the wave length...

See followup for clarification and simplification of the question. I have a challenging question about electromagnetics, vacuum energy. I'd appreciate any leads on clearing up any of my misunderstanding. I presume if two antennas were designed to broadcast the same signal, but were designed...

Hello, Chitose here. First, I don't know which group should I post this but I put it here just in case. ........ As topic says, Can bomb still explode in vacuum area such as space? I heard that fire cannot lit without oxygen. but a lot of sci-fi movie show explosion scene in space...

If I understood well my professor, he showed that "playing" mathematically with Maxwell's equation \frac{\partial \vec E}{\partial t} = c \vec \nabla \times \vec B can lead to the result that \frac{\partial \vec E}{\partial t} satisfies the wave equation (only in vacuum). So what does this...

[b]1. Show that: electric field E(x,t) = [0, Eo, 0] * f(kx-wt) magnetic field B(x,t) = [0, 0, Bo] * f(kx-wt) (where k, w, Eo, Bo are constants) satisfy the Maxwell equations in a vacuum where charge and current densities are zero. What relation between k and w must hold for a...

Now this may seem a stupid question, but as my old dad said there are no stupid questions only stupid answers! I am distilling some liquid which has a boiling point of about 190 C, I have put the liquid under vacuum of -1bar and the liquid now boils at about 160C, I would like the liquid to...

I know the ideal gas law applies, but how?

I understand that the purpose of a vacuum pump is to remove the gas molecules from a sealed volume to create a partial vacuum, but just what is actually happening to the gas molecules throughout this process? I have been researching online, but have not found any guides that clearly explain the...

I was wondering, since vacuum energy is supposed to have some energy density,according to standard comology equating it to dark energy and cosmological constant , does this energy gravitate? I mean it looks like according to GR its stress-energy tensor with negative pressure should generate some...

A liquid in a vacuum environment has a lower boiling point than when the liquid is at atmospheric pressure Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. Water, when heated to well over 2000 °C, decomposes to its constituent elements: could a a...

Do atoms exist in a vacuum?

Homework Statement A 200 g oscillator in a vacuum chamber has a frequency of 2.0 Hz. When air is admitted, the oscillation decreases to 60% of its initial amplitude in 50 s. How many oscillations will have been completed when the amplitude is 30% of its initial value? Homework...

i have searched the web over looking for some kind of chart for hydrous pyrolysis. im not extremely smart but i grasp the concept. but still not real sure, know water boils in a vacuum at lower temps, so is that the same for most organics. say i create a vacuum tank, containing water and...

what kind of a pump is used in creating vacuum in vacuum flasks or thermose. Diffusion pump, Roots Blower, Rotary vane pump

So I am in an intro E&M class and the topic of Van de Grraaff generators came up. The instructor said that when there is enough charge on the surface then there is corona discharge. But what would happen if the generator was in a vacuum? Then there would be no corona created. So would the amount...

Hi folks, I have a question that I so far haven't been able to locate an answer to - it's mostly for curiosity. If virtual particles are continually popping in and out of existence in the vacuum, why do they not produce a frictional force on objects moving at constant velocity through...

Say we have a maglev train traveling i a vacuum. The only thing limiting its speed is the g-force tolerance of the passengers. The train would therefore accelerate at a certain rate until halfway, and then decelerate until it reached its destination. What would be the traveling time of...

Hey all, I've been puzzling about this one for a while, and can't intuitively reach a conclusion about it. Although perhaps some law would provide a definite ruling... In short: How can a system floating in vacuum lose angular momentum? Longer, fun mental illustration: You awake to find...

Place a guitar floating in the vacuum. Once one string start to vibrate it would not stop since there is no air and contact. So any object vibrating in the vacuum would continue to vibrate indefinitely or the energy would become heat and radiation?

Why do air "rush" into vacuum I was reading the quite enjoyable "Physics for Superheroes" By J. Kakalios. At some point he explains what is entropy and give an example of air molecules rushing into a previously sealed and empty room (no air either) It was explained how the molecules would get...

Hi, Quantum Mechanics has so many Interpretations like Many Worlds, Bohmian, etc. How come we seldom hear about Interpretations in Quantum Field Theory? Is there something in the quantum vacuum ontology that cancel out all the Interpretations? Or is it also valid? For example, in Many Worlds...

Homework Statement Hi I was wondering what happens to a car accelerating in a vacuum? Homework Equations Newtons 1st Law of motion: A Body continues at uniform speed or in a state of rest, unless acted upon by an external force The Attempt at a Solution Outside a vacuum, cars will...

Hi, Is Spacetime inside the Quantum Vacuum or is the Quantum Vacuum inside or fill up Spacetime?

If you have a vacuum within a piston say and compress its volume what happens to it? I am trying to understand how a vacuum that is 'nothing' - no molecules / energy within it can have properties such as Volume and a sort of existence that obeys physical laws. I guess I am ultimately thinking...

I heard somewhere that some materials and devices need to be manufactured in a vacuum environment. I heard superconductors was one of them, but I'm wondering what else there is?

By my understanding, the cosmological constant problem is that the computed vacuum energy by quantum field theory (in the form of virtual particle pairs) is far larger than the measured vacuum energy density. Would it not seem to solve the problem with dropping the proposed mass of "virtual...

Some physicists are giving up on physical particles and talking about quantum fluctuations in a vacuum. So, what exactly is a quantum fluctuation in a vacuum?

Assume that both light and an observer are traveling through water with a refractive index of 1.33. Without getting my calculator out, I think this means that the light would be traveling at about 0.75c. The observer is traveling in the opposite direction at about 0.25c (it is only a thought...

Layman here Is the notion that our universe derived from a fluctuation which took place in a quantum vacuum scientific theory or just a hypothesis? I tend to believe the later, yet there are many scientists(particular motivated atheists) who talk about it as if it is scientific theory. Can...

Does a vacuum have a temperature?

Does anyone know of a good source for small electron guns? Just a simple one. I was using a TV CRT gun but the filaments don't last when exposed to atmosphere. I obviously operate under vacuum but I have no way to store my device in a vacuum for a long period.

Although I've yet to see any device that actually works I don not understand how the principle of extracting ZPP or vacuum energy from the vacuum and turning it into mechanical energy violates the 1st law of thermodynamics BECAUSE energy is just being transferred from one place(where it EXISTS)...