Vacuum Definition and 1000 Threads

In ΛCDM, H(t0) = 70km/s/Mpc, Ωd(t0) = 0.3, Ωr(t0) = 0 and ΩΛ(t0) =0.7, so that Ω(t0) = Ωd(t0) + Ωr(t0) + ΩΛ(t0) = 1and the universe is spatially flat. I want to know the t and z when the matter density equal to the vacuum energy density. By total energy density equation, I think Ωd(t) +...

common sense tells me that if an object can remain spinning in the vacuum of space for eternity, than placing that same object within a pressurised environment will cause the object to slow to a stop. is there a way for me to calculate the time in which it would take an object to stop rotating...

The Vacuum Permittivity of the classical vacuum seems to be for just conversion of units in Coulomb's Law, like Coulomb's Constant in disguise. Does the Electrical Permittivity of the Vacuum in classical electromagnetism have any real physical significance other than in the above context...

If you bring a pot of water to boil, you will notice that the bubbles form on the bottom surface of the pot. This seems to make sense intuitively as this is the hottest surface, so this would be where the boiling action starts. When I was in school during a thermo lab we pulled a vacuum in a...

Hi there, I have a small, few liter UHV chamber that frequently needs to be vented and rebaked. I want to shorten my bake time, so I’ve obtained a glove box to allow me to vent, work and close back up under inert gas. i’m curious if people have a preference between Argon and dry Nitrogen. I...

Einstein's vacuum solution metric: $$ ds^2 = -(1-\frac{2GM}{r})dt^2 +(1-\frac{2GM}{r})^{-1}dr^2+r^2 d\Omega^2 $$ which ##g_{\mu \nu}## can be read off easily. metric Killing vectors are: $$ K = \partial_t $$$$ R = \partial_\phi $$ How can I relate these to Maxwell equation?

trying to calculate the mass flow of Water vapour that is produced within a vacuum of 30 inhg when the water temp is 40 degrees. How is velocity calculated in this scenario. Also what boundary layer does the water vapour have.

I was wondering: what would be the value of Vacuum Permettivity in the case 1 meter (say 1m") would be defined as the distance we nowadays see as 1,10 meters. At first this looks easy: ##\varepsilon0 = 8.8541878128 \cdot 10{^{12}}## F / m with normal meters so ##\varepsilon0" = \varepsilon0...

Okay so for this one we can consider the Bianchi identity again$$\begin{align*} \nabla_{[\lambda}R_{\sigma \rho] \mu \nu} = 2 \nabla_{\lambda} R_{\sigma \rho \mu \nu} + 2\nabla_{\rho} R_{\lambda \sigma \mu \nu} + 2\nabla_{\sigma} R_{\rho \lambda \mu \nu} &= 0 \\ \nabla^{\lambda}...

I'm working on a project to replace a couple of vacuum pump skids for a lab campus. The existing pumps are water-cooled, liquid-ring pumps. Since they are water cooled, there is effectively no heat rejection into the mechanical room(s) except through un-insulated exhaust pipes. The new pumps...

1. If today vacuum and matter contribute 71 % and 29 % to the total energy density of the universe, at what redshift z were they contributing equally? 2. If today vacuum, matter, and radiation contribute 71 %, 29 %, and 0.01% to the total energy density of the universe, at what redshift z were...

Recently I saw an exercise on electromagnetics (plane waves) in which it was said that a plane wave was traveling through vacuum (ε0 and μ0) BUT with losses, i.e, σ ≠0. Is that possible? I think I have read in the past that it's OK in some texbook, but now, I have searched for it in a couple of...

Please forward to appropriate subforums as I wasn't sure where to post it.In the standard model there are the composite particles and elementary particles, for the elementary particles there is said to be an associated field and the particle is the excitation of that field. Apart from asking how...

Sean Carroll (in a video) claims that regions of empty space (vacuum) that are near each other must be highly entangled. He appears to argue that if they were not, there would be "a lot of energy contained there" which - my conclusion - would not be consistent with these regions being low energy...

Why do vacuum rocket engine always producing high thrust than sea level rocket engine ? for example spacex's merlin vacuum engine produce more thrust than merlin sea level engine. And it is due to the big nozzle with large area in vacuum engine because when the flow reaches mach 1 in the throat...

Following the method by Peskin and Shroesder 11.4 Trying to calculate the vacuum energy of a fermion. If my method is correct so far the next step is to find gamma function , the formula I have for gamma fuctions doesn't match this equation. Can anyone help with the next step? Starting with the...

Does it not raise question to be able to build two parameters with the same dimension and order of magnitude of two fundamental constants from five parameters (other fundamental constants and measured properties)? $$\sqrt{10\frac{\left(\varepsilon_0 e^{-2}\right)^3\left(k_B T\right)^4}{\rho_c}}...

What are the reasons X-ray vacuum tubes could not be replaced by solid state alternatives?

Gerard 't Hooft has been a renegade in Quantum Foundations for quite some time, insisting that there is natural order underlying the Quantum Mechanical mysteries. Essentially a local, deterministic hidden variable perspective. He has recently posted a new paper on arXiv where he lays out his...

Using the Einstein-Hilbert action for a Universe with just the cosmological constant ##\Lambda##: $$S=\int\Big[\frac{R}{2}-\Lambda\Big]\sqrt{-g}\ d^4x$$ I would like to derive the equations of motion: $$\Big(\frac{\dot a}{a}\Big)^2+\frac{k}{a^2}=\frac{\Lambda}{3}\tag{1}$$ $$2\frac{\ddot...

What does the phrase “Due to Lorentz invariance, only the Higgs particle can have a non-zero expected value in a vacuum” mean?

It has been hypothesized by quantum field theory that the vacuum is not empty due to the energy time uncertainity relationship. Instead it is filled with a sea of virtual particles popping in and out of existence and renormalized to the observed value we see today in experiments like the casimir...

Vacuum airships are a scifi idea where you evacuate the air out of a chamber to achieve lighter-than-air lift. I put this in scifi as it's just a curiosity at the moment. The issue faced with these designs is the chamber buckling with the pressure of the atmosphere around it, which puts pay to...

Hi, there. I am reading the article Relativistic quantum optics: The relativistic invariance of the light-matter interaction models by Eduardo Martin-Martinez el al (2018). Here he calculate the transition probability of a vacuum excitation for a detector. Suppose there is a lab where the...

If Evangelista Torricelli truly created a vacuum, then there would be nothing in it, yet you can see through it which means light is obviously still in there (and who knows what else), right? If there was truly nothing in it, and glass is a highly viscous fluid, and fluids conform to fill empty...

https://arxiv.org/abs/2002.04856 It's proposed that topological defects like cosmic string enhance vacuum decay. I do not quite believe it.

Hi all, I'm not sure if this is the correct space so please let me know if it belongs elsewhere. I've always been very interested in engineering. In my spare time, I tend to think about a lot of unconventional ways of doing stuff because I'm of the mindset that there's always new things to...

The point of the twin paradox in special relativity is that the traveling twin experiences a real, frame-invariant effect in which the time evolution of all moving matter is slowed down. If you read a hundred articles and textbooks on SR, you'll see a hundred variations on the message that the...

I have a question about interactions between matter and the vacuum, but I don't see a forum for that. Quantum field theory seems to be the most closely related subject. What would be the best forum for questions related to QFT?

Where, When and Who has performed the Double Slit Experiment in a Near Vacuum Environment Cannot find it anywhere on Line Thank You

Hello, I have got an integrated motor-fan unit of a Dyson DC04 vacuum. I don't know the motor speed (could not find from the manufacturer) but I guess, it must be well in excess of 10,000 rpm. Here is an image: https://www.espares.co.uk/product/es1562476 Now, I want to fit an axial, blower fan...

Hi, I'm hoping this will be a fairly easy question for someone on here to answer. If I wanted to make a (small?) vacuum tank (basically a hollow cylinder capped with two similarly hollow hemispheres - like so: (===)), how thick would the walls of the tank need to be for it to withstand the...

This is an experiment I would have liked to do from the ISS, but an approximation could be done in a vacuum chamber on Earth. How big a soap bubble, polymer bubble, or glass bubble could you blow in the vacuum of space? How to calculate the evaporation rate in vacuum? A liquid exposed to vacuum...

In the book" The Quantum Theory of Radiation", Heitler derived the transverse self-energy of the electron(Chapter III, Section18, Eq.(23)) $$\frac{{{e^2}}}{{\pi m}}\int_{\text{0}}^\infty {kdk} $$ which is the energy of the electron under the action of the vacuum fluctuation of the radiation...

Hi everybody, I have a question with no clear answer so far. Does the rack and pinion mechanism work in UHV ? I have to translate an object in very confined scace (less than 10 mm), all in UHV. Any response is welcome :)

Hi everybody, this is my 1st post as I am a little stuck. I am putting together a short presentation for a job application and have built a Tool similar to the attached ( basic ) schematic, My question is What is the Purpose of the Active Inverted Magnetron ( AIM ) - ( on the chamber ) and the...

Hi, I have some problems with visualization (I'm trying to understand Jeff Steinhauer's experiment, but my questions are general). Why the quantum vacuum fluctuations are guaranteed by the underlying pointlike atoms composing a BEC? And if vacuum fluctuations generate excitations (i.e...

In theory, does an algebraic expression exist for the ground state of the Klein Gordon equation with \phi^4 interactions in the same way an algebraic expression exists for the simple harmonic oscillator ground state wavefunction in Q.M.? Is it just that it hasn't been found yet or is it...

Vacuum height of mercury

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Hi all, One more virtual particle question (sorry all!): for individuals who would take virtual particles as being 'real' (but unobservable), what is their understanding then of the content of the vacuum? For example, if I place a electron all by itself in the vacuum (thus making it no longer...

Has anyone heard of papers describing Brans-Dicke vacuum cosmology solutions? I'd be interested to know if the following calculations make sense. I assumed a constant mass density vacuum with equation of state ##p=-\rho##. I then plugged this equation of state into the Brans-Dicke equations...

In equation (3) of this article https://arxiv.org/pdf/astro-ph/0605418.pdf , on page 3, you can see an expression for the vacuum energy density of a field as a function of its particle spin, particle mass and the wave number k. It is fairly straight forward to derive the integral portion of...

Hi, I read various threads in PF about the concept of invariant speed and the speed of light in vacuum that in our universe happens to be the same as the 'invariant speed'. My doubt is about the speed of the light in vacuum as measured from a non-inertial frame (basically in the context of SR...

I probably haven’t thought this through. A sideview of a closed container filled with air consisting of two vertical cylinders (with radius ##r_1## and ##r_2##) are connected by two horizontal tubes. The container is separated by a small and a large lid (red) that are circular and can move up...

I’m self taught so I have a lot of holes in my understanding. I also have little to no mathematical understanding. Even though ironically, I tend to prefer to picture electricity as numbers rather than “water” in a pipe, etc. I’ve been studying displacement current recently and have a question...

I ran into something on a non-technical message board that is familiar to me - a poster, clearly without any scientific knowledge, saying that Relativity is wrong. Unfortunately, the point he used as a battering ram is one to which I don't know the answer. He suggested that the light...

Hello, Recently, I 'opened up' a Henry vacuum cleaner to trace the path the airflow takes - from inlet through to the outlet. The vacuum cleaner has 2 distinct sections: 1) A lower section with inlet pipe and the 'dust-bag' 2) and the upper section with the motor, fan and the outlet. Now, the...

Hi all! So recently me and a group of friends have begun working towards the construction of a cyclotron - and I was wondering, if anybody here would have an idea what kind of materials would be able to be used for the vacuum chamber that aren't specific Aluminium Alloys such as 7075 or 6061...