A region of space devoid of any fluid molecules resulting in a zero pressure in ideal cases. In practice, even space has a small but finite number of molecules.

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3answers
891 views

Anti-laser: How sure we are that energy is transported?

Reading this PE question can-we-transport-energy-over-infinite-distances-through-vacuum-using-light, a related question arises naturally: Is energy transported (by light)? -- (I did believed in this ...
4
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2answers
125 views

Why should energy have a lower bound but not an upper bound?

This question seems to be naive, but I really want some intuitive way of understanding the reason. Neglecting some trivial explanations, I have only one idea about this: the vacua state. Consider ...
9
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5answers
2k views

What causes the permittivity and permeability of vacuum?

When light travels through a material, it gets "slowed down" (at least its net speed decreases). The atoms in the material "disturb" the light in some way which causes it to make stops on its path. ...
0
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1answer
95 views

How do objects outside a spacecraft fall “around” the earth?

Now I get what microgravity is, how spacecrafts (even moon) fall around the earth to keep up themselves in their orbits and other related concepts after reading ...
0
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2answers
321 views

What is space made of?

General Relativity posits that matter curves spacetime, such that geodesics point towards the object in question, hence, gravity. Now, how does matter do this? What is spacetime "made of", anyway, ...
5
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1answer
51 views

Vacuums and free space

Do physicists use the terms "vacuum," "quantum vacuum," and "free space" synonymously? For example, I have read that based on conservation arguments, the spontaneous splitting of a photon into an ...
4
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1answer
109 views

The relation between classical and quantum vacua

First let me clarify what I mean by vacuum. Suppose we are concerned with a theory of fields $\phi ^i$ defined on a stationary globally hyperbolic spacetime $M$ (I want the spacetime to be stationary ...
4
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1answer
90 views

Vacuum polarization of dark matter candidates

Can a dark matter particle (axions, for instance, but the question applies to any valid candidate for dark matter) induce QED vacuum polarization effects even if being electrically neutral and with no ...
4
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1answer
114 views

Tadpole diagram and vacuum

This statement may be well-known. For many massless theories, these tadpole diagram graphs vanish in dimensional regularization (by dimensional analysis and the absence of any inherent mass scale in ...
0
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0answers
31 views

Help with vacuums?

Okay, here is my understanding. Please correct me if anything here is incorrect. Suppose I have a cube with a side length of ten inches. It has a surface area of 600 square inches, and at an ...
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0answers
96 views

Space between particles [duplicate]

I am a high school student, and I am just wondering what is the space between each particle, like what is the gap around each atom? I have found no text book cover this topic. Is it a vacuum?
15
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2answers
234 views

What would happen to wet laundry in the vacuum of space?

Imagine for a second that I was in a college dorm room frustrated that all the dryers were broken or in use. I'm impatient and not a jerk so I don't wait or take out someone else's laundry, I shoot it ...
18
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0answers
293 views

Finding the vacuum which breaks a symmetry

I will start with an example. Consider a symmetry breaking pattern like $SU(4)\rightarrow Sp(4)$. We know that in $SU(4)$ there is the Standard Model (SM) symmetry $SU(2)_L\times U(1)_Y$ but depending ...
2
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1answer
94 views

How can a vacuum have a breakdown voltage?

This question (What is the capacitance between the Earth and Moon?) on EESE makes me wonder: How can a vacuum have a breakdown voltage? If electrons can find the shortest path through a vacuum, ...
5
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0answers
107 views

Could energy be stored into (not extracted from) the quantum zero point field (like a battery)?

In order to explain the question clearly, I will make a short introduction. In 1962, Josephson predicted that for a sufficiently thin insulating layer, it should be possible for Cooper pairs to ...
0
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0answers
30 views

Can you clean the air in a small room using a vacuum cleaner?

You can use a vacuum cleaner to vacuum the floor but if you tried to vacuum the the air in a small room would this work or will the laws of physics stop this from working in any way? In what way would ...
1
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2answers
272 views

Balloon, lighter than air and vacuum?

As I understand, in a balloon/air balloon, a gas burner is used to heat air or using some lighter atom like helium. Since helium or hot air is lighter and less dense than the cool air around the ...
0
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1answer
29 views

Can low end hepa vaccums still clean near all of the air?

In the US HEPA filters will remove 99.97% of particles sized 0.3 microns. In Europe HEPA filters do not have to meet this exact figure and there are different classes of HEPA filters e.g. h10(removes ...
2
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1answer
101 views

Can a vacuum cleaner be used to purify the air in a small room? [closed]

A hepa vacuum cleaner will pick up fine dust from the floor, filter it and send the clean air out through the exhaust. However with movement in the room fine dust will also be goinng up in the air ...
7
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3answers
696 views

What really goes on in a vacuum?

I've been told that a vacuum isn't actually empty space, rather that it consists of antiparticle pairs spontaneously materialising then quickly annihilating, which leads me to a few questions. ...
6
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2answers
851 views

Does water have surface tension in a vacuum?

I could be totally wrong here but I was thinking about water surface and what creates that. My thought is it is the thin mixture of water and air separating the two. This mixture creates the boundary ...
3
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3answers
383 views

why cannot fermions have non-zero vacuum expectation value?

In quantum field theory, scalar can take non-zero vacuum expectation value(vev). And this way they break symmetry of the Lagrangian. Now my question is what will happen if the fermions in the theory ...
1
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2answers
223 views

How electromagnetic fields travel through vacuum?

How electromagnetic fields travel through vacuum is it right to say that they propagate or travel? do they alternately form each other by charged particles?
0
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1answer
180 views

If empty space is not really empty, what does the space between an atomic nucleus and its electrons consist of? [duplicate]

I'm currently reading Brian Greene's The Elegant Universe and have also picked up his other book - The Fabric of the Cosmos. In The elegant universe Brian makes up an interesting point that empty ...
5
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2answers
88 views

Does space have a “radiation pressure” caused by subatomic particles?

If space is not actually a void, then there's something shooting around in it, I'm guessing a lot like molecules in a gas. Could we apply a $(PV/T = k)$ -like gas law to it. Obviously we're not ...
4
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1answer
91 views

Is nuclear fusion via underwater vacuum possible?

An under water explosion creates a bubbly which quickly collapses on itself. The action takes less that 1/100 of a second for bubbles less than a foot across. This creates a point of extremely ...
13
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7answers
1k views

Can energy be taken out of the QFT vacuum?

There have been recent questions about the vacuum. In my simplified knowledge the vacuum is like a ground state energy level, and also that there might even exist other lower energy levels than the ...
4
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0answers
196 views

Is the double-slit experiment typically carried out in a vacuum?

It is my understanding of the double-slit experiment that when a measuring device is activated, to measure which of the two slits a particle is travelling through, this measuring is responsible for a ...
2
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2answers
132 views

What exactly does vacuum contain?

Does vacuum or outer space contain any gases? Recently i watched a video on youtube,in which NASA installs a camera on a spacecraft.The footage shows some dust particles or some matter floating over ...
0
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0answers
40 views

What is the perturbative vacuum?

Will someone please supply me with a good definition of the perturbative vacuum vis a vis quantum cosmology?
2
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0answers
58 views

Conservation laws in vacuum phase transition

Let's consider a bubble nucleation phase transition between different vacua via quantum tunnelling .For my understanding a particle must penetrate the potential barrier and find herself in an another ...
0
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0answers
89 views

How do you calculate the air and water pressure inside the bell siphon during and after the vacuum is formed?

I am interested in the math/physics behind the simple bell siphon. In this YouTube video, the presenter says that the space in the top of the bell becomes a vacuum when the water flow eventually fills ...
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2answers
1k views

Are quantum fluctuations completely uncaused events?

I read here that particles/antiparticles appear and annihilate each other spontaneously in empty space. Since particles appear and disappear in empty space, it would seem that empty space has some ...
8
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2answers
176 views

What are the current experimental limits on the polarizability of the vacuum?

Many (all?) materials are polarizable at some level; meaning that when we apply an electric field across the material, there is an induced dipole moment $$ \vec{p}=\alpha(\omega)\vec{E}, $$ where ...
2
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2answers
592 views

What is the best tool for simulating Vacuum and Fluids together?

I require a software to simulate Fluid simulation with the capability of supporting vacuum simulation. My requirements are that all numbers must reflect their real counterparts almost exactly. For ...
4
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1answer
170 views

Vacuum energy extraction: What happens to the cosmological constant?

If the vacuum energy is extracted, then what will happen to the cosmological constant? Will it remain the same? .
3
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5answers
816 views

Does it take infinite energy to create a perfect vacuum?

Question is inspired by a recent burst of perpetuum mobile-type questions. It would be nice if one could simply discard them all by an argument that shows it's impossible to create a perfect vacuum. ...
0
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1answer
65 views

Container in a Vacuum in a Container Problem

My friend puzzled me with this: Say I have a container that contains a vacuum and another container inside. And this inner container contains air. Also the outer container material is just barely ...
4
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1answer
139 views

Does $\langle\Omega|\mathrm{e}^{\mathrm{i}Px}=\langle\Omega|\mathrm{e}^{\mathrm{i}0x}$? $(\langle\Omega| =$ ground state of the interacting theory)

Let $\langle\Omega|$ be the ground state of an interacting theory, just as Peskin & Schroeder(PS) describes on page 82 and page 213. On page 213 PS do the following ...
3
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1answer
67 views

Why apply voltage on an Si detector only on atmosphere or high vacuum

The general instruction when using a silicon detector is to either apply voltage only in atmospheric pressure or in high vacuum. Not in between! I can't find a physical answer to it. Why is it so ...
4
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1answer
119 views

Definition of vacuum in field theory; Connection between the classical definition and the connection to QFT

I am a bit confused by what is defined to be a vacuum in field theory. Classically a vaccum state is defined to be the state where the field sits at some minima of the potential $\frac{\partial ...
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5answers
1k views

Nothing vs. empty space

This question quotes Hawking saying: [...] you enter a world where conjuring something out of nothing is possible (at least, for a short while). That's because at this scale particles, such as ...
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2answers
90 views

Would a beam of light moving through a vacuum be considered an example of perpetual motion? [closed]

I have a very limited understanding of Physics but if the beam of light was moving through a vacuum like space and had saw no obstuctions during its path, would that be perpetual motion in action?
-1
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1answer
66 views

Loss of atmosphere to a vacuum

I'm working to craft a space-horror themed RPG a la Dungeons & Dragons and I've run into a situation I can't resolve on my own. At what rate is atmosphere lost to space through various sized ...
1
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1answer
99 views

gas pressure outside nozzle in vacuum

I'm currently trying to figure out the following in the simplest possible way: Say we have a nozzle in a vacuum environment. A gas of a certain pressure is emitted through the nozzle, which has a ...
1
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1answer
146 views

Expectation values in QFT?

What is the meaning of different expectation values in QFT? For instance: $$\langle 0|{\cal O}(0)|q,s\rangle$$ or $$\langle 0|{\cal O}(0)|0\rangle$$ with ${\cal O}$ being some operator and ...
1
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3answers
109 views

Can the vacuum be filled with virtual micro-black holes?

Since the vacuum is thought to be virtual particles, is it possible that there might be virtual micro-black holes with virtual horizons and virtual hawking radiation which form and evaporate at a rate ...
20
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4answers
2k views

Is space “real”, or is it some sort of accepted postulate?

sorry for this very naive (layman) question. What is space? It seems to be every where in the equations of physics (as some sort of postulate or hidden hypothesis). We also have a direct experience ...
0
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0answers
25 views

Question on the Electroweak vacuum decay

Is there any current estimate of the electroweak vacuum lifetime based on the recent measurement of the Higgs boson and the top quark masses?
0
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1answer
625 views

Lawrence Krauss' Theory of Origin

I don't understand how a vacuum, the absence of matter, can hold energy. How can it hold energy when Einstein proved that matter is energy? And a second related question; how does the energy in a ...