Vacuum Definition and 1000 Threads

As much as I have understood, virtual particles keep appearing and disappearing in a vacuum state. This leads to zero-point energy, Casimir effect etc. Now, I want to know if there is a lifetime (i.e. a time limit) for which these virtual particles can exist before disappearing. Also can there...

When a field is quantized on the light front, there is no possible pair creation from the vacuum energy. This is because kinematic operator P^+ generates only a positive spectrum ( https://en.wikipedia.org/wiki/Light_front_quantization#Spectral_condition ). So there is no "particles popping out...

A. Neumaier submitted a new PF Insights post The Vacuum Fluctuation Myth Continue reading the Original PF Insights Post.

My background is in Health Physics and as such, I have had only rudimentary instruction in quantum mechanics, so my understanding (such as it is) is largely conceptual. With that in mind, this may be a very ignorant question, so I apologize in advance. I understand the theoretical basis for...

Hello I needed to know a logical answer to the question that whether the time of flight of the objects in air increases or decreases as compared to vacuum? Why?

Homework Statement So suppose there is a chemical rocket operating in the vacuum of space (assume it's a perfect vacuum). It generates a hot gas with a total enthalpy of h. What's the final speed of the rocket exhaust, in terms of h? Homework Equations The energy equation seems to be useful...

https://en.m.wikipedia.org/wiki/Vacuum_energy And it is this type of energy dark energy or a form of it?

Hello folks, I have two simple questions and some ideas about it:1. Why is it harder to create a vacuum and takes more time to evacuate the chamber when the air inside is humid? Humid air is lighter than dry air. So I have no idea why it takes longer...2. Why do you use nitrogen to vent the...

If we look Einstein equation ##G_{\mu\nu}=0##, which nontrivial aspects it can gives? One phenomenon is gravitational wave. I suppose that we are also free at initial conditions for this equation, thus we can begin with curved space time? What else?

Imagine a hole drilled through the Earth from which all air has been removed thus creating a vacuum. Let a cluster of test particles in the shape of a sphere be dropped into this hole. The volume of the balls should start to decrease. However, in his article "The Meaning of Einstein's Equation"...

Hi all, I am learning about the vacuum Rabi frequency for the first time in Metcalf's book Laser Cooling and Trapping (Section 2.2). I am trying to make sense of the following two equations Metcalf gives: $$\hbar \Omega_{S} = -\vec{\mu} \cdot \vec{E_{\omega}}$$ and $$\vec{E_{\omega}} =...

So, I know this isn't entirely an Engineering question, but I am an EE and I wanted to get a few opinions on my planned project. I have had a central vacuum in the past three homes I have owned. I have always installed the unit and all plumbing myself, but the units are still $500-$1000 just...

Hey all, I'm a bit of a food geek and a DIY nut and I'm looking to build my own vacuum sealer for as cheap as possible. My question to you guys, is what is the cheapest material I can use that will still withstand the pressure as well as maintain the airtight seal needed? I am looking to get a...

When I was taking a look at this page, I noticed that she is "known for proving the local existence and uniqueness of solutions to the vacuum Einstein Equations". But this doesn't make sense to me(the uniqueness part). Just consider the Minkowski and Schwarzschild solutions. They're both vacuum...

I know that you couldn't extract work from vacuum fluctuations without violating the laws of thermodynamics, but what if there was a gradient in the vacuum energy. If you did work on the vacuum by applying some field you could then extract this work from the gradient, but if the gradient was...

Hi all, Silly question perhaps: I had understood that the energy density of the vacuum is constant throughout spacetime. But, with the Casimir effect, for example, the geometry of (real) matter (i.e., parallel plates), changes the vacuum energy density in between the plates - is this correct...

I often wonder about how little I understand vacuum, and only recently I've been paying attention to this "vacuum energy" hypothetical. I see it being associated with things as small as spontaneous emissions to things as large as the expansion of the universe. This is a huge range of length...

Is the capability to apply force dependent on the medium.Suppose two human beings are placed in vacuum.Now, can they apply forces on each other? Also, can force fields such as gravitational and electrical fields exist in vacuum and if so then why?

Recently I came across an excellent video that brings to life an age-old physics teaching theme... The world’s largest vacuum chamber is NASA’s Space Power Facility in Ohio, pictured below. They remove around 30 tons of air from the chamber in order to test equipment during in-space conditions...

I read on the net that the moons gravity is one sixth that of Earth's so if I could jump 12" off the ground on Earth it would be 72" on the moon. I also see (you tube) that in a vacuum (akin to the moons surface) if you drop a feather and kilo weight simultaneously they reach the ground at the...

How do I calculate glass thickness on a bottomless aquarium where air pressure is holding the water up. Example: 18"x18" by 36"' high closed top. 6" of the aquarium is submerged in a pond. Thanks.

This is my first try at building everything myself. Programming the G Code to cut the chassis on my old Linux computer took a bit of thinking...lol Here is a short video. A few photos so far. I will post the schematic when I finish it. Cheers, Billy

Please excuse my ignorance, I am 11years old. I have been wondering will magnets work in a vacuum A.K.A SPACE. Thank you for any and all answers.

I am looking for guidance on how to successfully measure vacuum using a device similar to a pirani gauge, my device however is a tungsten filament which is heated electrically to about 90*C, and it's current draw is a measure of vacuum.The problem I am having is how to relate specifically the...

I am getting confused as to which experiment proved that the speed of light was invariant in a vacuum. At first I thought it was the Michelson-Morley experiment but that does not have a moving observer.

Hello! I am designing a vacuum chamber made of a vertical glass cylinder free of contact from any other structure, except by the top and bottom where aluminum disks seal the device. Temperature is the same inside and outside. I found on several books the following formula for the hoop stress...

So if space is a vacuum, how can we have dark matter? What does it contain that means that space still acts like a vacuum?

Hi, Here is the schematic link: http://www.classictubeamps.com/schematics/Mesa/Mesa%20Boogie%20Solo%2050%20Rectoverb%20schematic.pdf The 12AX7 inverter tube has a measured plate voltage of 416 VDC just like the schematic indicates. V1a rail voltage is 394VDC with a 200K plate resistor and a...

I know that the nth order tadpole equations give you the value of constant field configurations for which the first derivative of the nth order effective potential is 0, but what does this have to do with the tadpole graphs?

Hi, Here is a typical data sheet for a commonly used 6l6GC tube. http://www.drtube.com/datasheets/6l6gc-jj2003.pdf Under typical characteristics (in this data sheet) a value of Ra and Ra-a are given. I assume Ra-a means Za-a and it could also be written as Zout. Is this a correct assumption...

Homework Statement Given an electric field in vacuum: Find the magnetic field under condition that |B| -> 0 as t -> infinity. Homework Equations I clearly have to use Maxwells equations to obtain the electric field here. Our equation for B has to satisfy them. More specifically Faraday's law...

When the cathode emits electrons which are accelerated towards the grid, usually on its way it will ionise a molecule in the vacuum. However at a certain low pressure there are too few molecules and therefore the electron will hit the grid and emit an x-ray. My question is, wouldn't electrons...

Hi All, Once in the past I have heard that the vacuum in quantum mechanics, having its energy given by ## \sum_n \frac{1}{2}\hbar \omega_n ## was also obtained by methods of Einstein's relativity, through the claim that the vacuum should be a field which is invariant under a boost...

If vacuum energy has a non-zero value, is the vacuum energy density (vacuum energy over a given volume of void space) being reduced over time due to the expansion of the Universe? If so, is there any consequence on the particle-antiparticle creation/annihiliation process? Will there ever be a...

I was asked how you can lift the water up to 5 meter but you are not allowed to use any kind of pump. What I thought; seal the container from where water is being lifted. Connect it with a pressure vessel at some height which is containing steam and water with valve in between them. By default...

Hi, My name is Rodrigo and I need to achieve a permanent seal for a vacuum chamber in the high vacuum range (I’ll be working between 1x10-4 and 1x10-torr). We were thinking of using a cold-weld sealing of an annealed copper tube to separate the chamber from the vacuum pump once the vacuum level...

Its said that if there are different pocket universes made by inflation then this solves the alleged fine tuning of dark energy. My question is this: can the idea of different values for the vacuum energy density in these different pockets be derived from quantum field theory or does it need...

hi ...this is may be stupid question citing that there is so much information about the subject.. i understand that friction is possible in space...ie rub two things together and a resisting force will create drag on both surfaces and heat will be produced... But can space vacuum create drag...

Good morning, I am new to the forum, so let me get straight into the problem. I am working on an old scooter with small displacement (150cc, with about 9.6:1 compression ratio). After rebuilding the engine, I figured I have to put in a much bigger piston 60mm compared to the original 58mm...

As far as I understand it, the non-zero vacuum energy attributed to a quantum field (at each point in space-time) is precisely due to the Heisenberg uncertainty principle (and the fact that the energy of the quantum field at each space-time point is quantised). Accordingly (in order to satisfy...

i work at a cavern attraction and one of the parts in the speech we say is that a section of the cavern was once filled with a naturally occurring vacuum until it was punctured and destroyed. we explain in the speech that the vacuum was created when a river packed in that area with mud and clay...

I'm building a vacuum filling system for charging liquid inside heat pipe. I am using 1/8 inch stainless steel tubing for system connecting construction and swagelok ball valve 1/8 inch for regulating the pump down flow from heat pipe to vacuum pump. The fluid regulate with micro metering valve...

Hello all! I understand the concept of the TOKAMAK vacuum chamber, but can someone explain to me how I can actually calculate the pressure in which I need the chamber to be evacuated? I know it should be in the range of approximately 10^-7 or so but more specifically, is there an equation to...

Please look at the wikipedia article about thermal coherent states. We can only consider the states centered at the origin (##\alpha## = 0). If i understand what is written the vacuum is a pecular thermal state in the limit of a null temperature. I can understand that no energy can be borrowed...

Hello Physics Forums, After about one year of research and construction, I have nearly finished building a functioning inertial electrostatic confinement fusion reactor. Just to be clear, I do not wish to discuss the dangerous activities that are involved with my project as I know such topics...

Cant seem to find a kv/mm for waterglass/sodium silicate. I was thinking of using it as an electrical insulator for vacuum feedthroughs, expecting an easy seal as I hear it expands when heat cured, therefore pushing against the chamber wall and the wires to prevent leaks and also seal by its...

I am looking for a very simple and specific vacuum tube. It doesn't have to be high power. I only need a plate that completely surrounds the cathode. No grids would be ideal. Anyone have a parts number or link for something similar to this?

To get bubbles out of plastic resin that's to be used in casting, the uncured resin can be put in a vacuum chamber. However, I notice that a pressure chamber is also advocated for getting out bubbles (e.g. http://www.smooth-on.com/faq_display.php?faq_id=81 ). Are bubbles in a plastic resin...

I have a flexinol wire, and it has a resistance of 0.11 ohms/inch and it requires 4000mA for a 1 second contraction. I was wondering how much energy was required for a 1 second contraction and if I were to heat the flexinol under a vacuum, how much less energy would be required. The flexinol is...

Why does the free space permittivity has the value it has?