Vacuum Definition and 1000 Threads

Hi everyone, here's the situation: Everyone knows that you can simulate artificial gravity by rotating a space ship. Usually these scenarios include an atmosphere with regular air inside. I know that the inclusion of air has an influence on the effects inside by way of friction. How different...

Hi, Can someone give me some guidance on how to calculate the work or energy required to create a vacuum. For example, I would like to create a 2.5psi vacuum in a tube of a specific length and diameter using a pneumatic cylinder to remove the air. How would I go about calculating the...

Hi Folks, Could someone please help me?:blushing: I want to work out the power requirements for the torque or wattage required in an electric motor when evacuating a vacuum to a certain level. The tube to be evacuated is 200 mm x 50 mm and the evacuation would be done using a pneumatic...

I have noticed that some of my tube amp power tubes are glowing slightly blueish. Why? It has been explained to me that this only means that the tube is ok. However, I find it fascinating! Because what is this blueish glow, really? To me it sounds like secondary emission of either the anode...

In chapter 10 of Robert D. Klauber's excellent QFT book, there's a nice overview of different concepts occurring in the context of vacuum fluctuations. Inspired by that chapter I ask: If one would state that there is no such thing as vacuum fluctuations, what counter arguments are there? In...

Homework Statement EM Waves propagating through vacuum towards the x-direction approaches a conducting surface at x = 0. Part (a): Prove the following relations. Find the boundary conditions for E and B if charge density σ and current density s exists on the surface. Part (b): Find B in...

Suppose we consider a proton where we set the electric charge of the three quarks towards zero. At this point I assume we still would have the three quarks bound together? Now reduce the strength of the strong force by say ten times. I was told in posts that the radius of the proton depends on...

I learned that work done by gas is zero when a gas expands in vacuum. But the volume and pressure of the gas change.Then how work done by gas is zero?

In various other threads we have been kicking around various equations for a spherical shell and discussing the implications. In this thread I would like to present what (I think) I have worked out about how the shell metric relates to the vacuum metric inside and outside the shell. I hope to...

So I was looking through the internet on how one could improve the efficiency of a vacuum system (with a diffusion pump). Lots of websites describe systems with, cold traps to remove condensable vapors such as water. If I am not mistaken, cold traps also help prevent back streaming, similar...

Hi, Similar to the position-momentum uncertainty principle, there is a time-energy uncertainty of the form $$\Delta E \Delta t \geq\frac{\hbar}{2}\enspace .$$ However, since time is not an observable, the derivation and interpretation of this inequality is somehow different compared to...

I'd like to understand better the connection between Hal Haggard's September ILQGS talk http://relativity.phys.lsu.edu/ilqgs/ http://relativity.phys.lsu.edu/ilqgs/haggard091713.pdf http://relativity.phys.lsu.edu/ilqgs/haggard091713.wav and the talk he gave at PI two days ago...

The quantum vacuum is said to be the ground state of the combination of all virtual particles contributions from all particles and forces. How about in deep space where there is only CMB... so the virtual particles present is only from contribution from the CMB or complete particles meaning the...

Let's say I have an unbreakable pole. Let's also say I'm in an infinite vacuum. This pole is 240,000,000 meters in length. You are at the other end of the pole. I move the pole to the right 1 meter over the course of 0.9 seconds. Does the other end of the pole move immediately? If so, does it...

Hi all, i was pottering away at work yesterday and realized just how little i truly understand about vacuum! So i have a question, i have a piston in a cylinder, the piston is fully in the cylinder so there is very little air space and the cylinder port is blocked off, the piston has an area of...

First of all, I understand that an EM wave is created by a charged particle that is moving. What I don't understand is how it propagates itself when traveling through a vacuum as there is no medium for it to interact with. Can this be explained by anything other than photon theory? I really...

Hi, If we took the blood of all people here on Earth and made a ball of it (r=200, T = 310 K) how long would it take for it to cool down to ~ 285 K in vacuum (absent of sunglight)? How long would it take to cool down in air, with reasonable conduction speeds?

Air typically has a very high but non zero resistance. Given that air is just a medium, and that space is also just a medium, does the vacuum of space have a fundamental constant of electrical resistance, or is the electrical resistance of space truly infinite? How is this proven one way or the...

It's a theoretical study. I would like to understand how the sum of forces can be at 0 if I put an object (vacuum in it) in a big liquid disk (disk is fulled with liquid), the disk is big enough for agglomerate liquid (like this works with a planet, matter is agglomarate with gravity). There is...

I did a demo for my students, using a simple vacuum pump and a vacuum chamber. I put a burning candle in the vacuum chamber. This generates numerous CCNs (cloud condensation nuclei) (I believe) and perhaps some larger-than-normal CCNs. A cloud forms in the vacuum chamber for a few seconds, then...

Why does Tesla coil detects vacuum leaks?

I have been interested in constructing a vacuum chamber for quite some time, but I am not completely certain on what the structural specifications need to be so that it can hold up to the immense external pressure. My main motivation for building a chamber like this is in the hope that I will...

I wish to design a two chamber stainless steel vacuum system where the two vacuum chambers are connected via a flexible tube with a valve. The system needs to be able to be pumped down to 6 torr and must be able to maintain that vacuum for at least a year without pumping. The size of the...

Homework Statement In 1654 Otto von Guericke, inventor of the air pump, gave a demonstration before the noblemen of the Holy Roman Empire in which two teams of eight horses could not pull apart two evacuated brass hemispheres. (a) Assuming the hemispheres have (strong) thin walls, so that...

What operator acting on the vacuum state (vacuum state of the box?) gives a m^3 box of cosmic background radiation at 2.7K? As the temperature 2.7K slowly drops (wait a million years) must our operator above change in time? Do photons scatter via gravitions so that their energy changes...

It could be possible for a driven vacuum bubble (like an Alcubierre drive,assuming that it could be possible to realize ) to travel not only many order of magnitude faster than light but even trough different vacuum phase ? like for example region of false vacuum ?

Why doesn't a mercury barometer containing vacuum get crushed by the atomospheric pressure? Here is what I think might be the reason. Although there is vacuum inside a mercury barometer, that vacuum is pressurized by the atmosphere that pushes mercury from the reservoir. That pressure is...

Greetings, I am thinking of ways to make a parabolic dish. If you apply vacuum to one side of a flat circular elastic sheet, will it make a parabolic or spherical shape? Thanks

I have a hand vacuum pump I'm using to evacuate air out of a container and hold the vacuum for a long period of time. This pump came with a valve that eventually failed. I bought a few more just like it and those failed as well. I guess the diaphragm inside the valve is too weak to hold a vacuum...

The general field equation for GR is Rab - 1/2 gab R = 8πTab where I am setting G = 1 and c = 1. Also, the vacuum solution is Rab = 0 But it seems to me that this "vacuum" solution must hold even when there is matter present. Pick a point within a planet. Then excavate an...

I was wondering on what parameters the vacuum generated by a fan in a vacuum cleaner depends. How can I calculate the vacuum created and the density of materials that it can suck in? Thanks

Hello forum members and thank you for letting me post. My question refers to how rocket thrust works in a vacuum. I know this question has been posted before, but I am still confused about how it works. My understanding is that rockets do not move by pushing against air but move by pushing...

I'm reading a paper by Art Hobson called "There are no particles, there are only fields" and had a question about something in there. (http://arxiv.org/abs/1204.4616) (Page 20-21) He basically says that since the vacuum in QFT has energy and non-vanishing expectation values, it is ultimately...

Would a piezoelectric crystal create a negative voltage if held within a vacuum? Perhaps it's my misunderstanding of the materials properties, but it seems that if there is zero net output within the "creation"(0) atmosphere, and any slight elastic deformation shows itself in the form of an...

My understanding is that when a fan begins spinning, a partial vacuum is created. Physically, what creates this partial vacuum? Does the motion of the blades create a void in which there are fewer air molecules than in the ambient air and thus the pressure is lower than the ambient pressure?

Consider the vacuum state that is hypothesised to precede the moment of inflation in classical inflationary theory. The theory assumes that quantum fluctuations in this vacuum are magnified because of the process of inflation and have gone on to form the real energy structures that we witness...

i understand why there can be no breakdown, however "arcing" is just the transfer of electrons. a breakdown in air just provides a path for the electrons to take. But if you have two sharp surfaces, like a needle, pointing towards each other, separated by some distance d, let's even say that d...

According to the third law of thermodynamics, one could argue that a vacuum has zero entropy, since it has only one ground state and a temperature at absolute zero. However, assuming the accelerated expansion of the universe to result in a 'heat death', i.e. a state of absolute thermal...

I'm a bit confused by vacuum "fluctuations" (I know there is nothing fluctuating since vacuum is lorentz invariant) and their interpretation/representation by Feynman diagrams. In a normal Feynman diagram, you have energy conservation at each vertex, so overall energy conservation is ensured...

Why 299,792,458 m/s? Why does light travel at the speed that it does?

Hi , well we all know that the speed of light in vacuum is measured at c and it slows down when it enters other mediums. Now we always say speed of light is c in vacuum but hence I believe the speed is c there because there is nothing in the way that could slow light down like there is in other...

I have a 6500 litre or 6.5 m^3 tank. A vacuum pump (40000 litres per minute) creates a 90 % vacuum inside the tank. The vacuum is used to suck in water. The climb the water has to make is 6m. How much time will it take to fill the tank, given that the pump is kept on all the while...

Hello! I was hoping somebody may be able to help me understand something much beyond the physics I have learned so far. I need to complete an assignment that I believe is asking me to find the Higgs potential function? 1. My professor mentioned the following: minimization at the origin...

According to QM the ground state of the quantized empty space is not considered to be empty but as a fluctuating sea of virtual particles creating and annihilating continuously. In the case of virtual particles with mass I have a problem with this. According to which reference inertial frame are...

I'm tutoring a high-school level student where one of the questions is asking why fitting a vacuum pump to a popcorn maker would cause the popped kernels to get bigger. For those unfamiliar with popcorn :), it's modeled as a sealed hulled with starch and moisture inside. Heat causes the moisture...

Ok again I'm thinking some things but a simple question, You have two metal spheres , one inside the other.Now we know long ago from Faraday that closed metal spheres or cages or etc that are at some potential above ground tend to have their charge at the outside of the conductor in this case...

A cylinder with a piston to seal it starts empty. The are of the piston give a force of about 100 pounds. Lift the piston till there is 100 liters of vacuum. Now 2 cases: 1) release the piston, it slams down almost instantly. Since 1 atmosphere is about 10 Newtons per centimeter, and 1 liter is...

This is my 'virgin' attempt at intercourse in this venue, so please be roughly gentle. (I.E.; this is my first post, I'm a bit slow (intellectually) but willing to learn. I tend to be somewhat playful in how I use words. I hope you will forgive me if I step outside the boundaries of...

I was reading a paper by Geroch and I was confused by the following: given a scalar field ##\omega## satisfying ##\nabla_{a}\omega = \omega_{a} = \epsilon_{abcd}\xi^{b}\nabla^{c}\xi^{d}## and the scalar ##\lambda = \xi^{a}\xi_{a}##, where ##\xi^{a}## is a killing vector field, can someone prove...

Why vacuum tubes can not be made small sized ? I'm talking about millimeter to micrometer or maybe even nanometer size ranges ? Or can they be ? This way electronic devices, for example computers, could be made they way they were made in the past but much smaller.