Tagged Questions

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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Vacuum as a physical/chemical/material substance

Can the vacuum be understood as a physical/chemical/material substance? Remark: Vacuum has a density energy (so it has a density "mass" equivalence due to $E=mc^2$). Vacuum is quantum (but not ...
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4answers
629 views

Is it possible to create a vacuum ballon using concentric partially pressured spheres?

The old saying goes, nature abhors a vacuum, but that isn't exactly true. The universe is full of vacuum; what nature abhors large energy differentials. So for example, a vacuum chamber has to be ...
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3answers
4k views

What is meant by Vacuum?

What is the exact meaning of the word vacuum? Is it just a state of very low pressure or is it nothingness (as in there is nothing)? Also, when we say space is vacuum - it must be referring to ...
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1answer
162 views

Vacuum polarization in QCD and gluon bubbles

In analogy to QED, the following Feynman diagram is a diagram contributing to the vacuum polarization effect, leading to anti-screening, asymptotic freedom and running of the strong coupling constant. ...
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1answer
263 views

How could vacuum energy cause the expansion of the universe? [duplicate]

Is it by gravity? How could gravity produce a repulsive force?
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3answers
803 views

How should I clean a part before installing it in a vacuum system?

What are proven procedures for preparing a part that comes fresh out of the workshop for ultra-high vacuum (UHV) and extremely-high vacuum (XUV)?
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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 ...
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0answers
231 views

Is a venturi pump feasible at very low pressure?

I need assistance (or experience feedback) in estimating if a Venturi pump would work at low pressure. A boiler under vacuum (10% atmosphere) will produce steam (at a given speed depending on the ...
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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
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 ...
7
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1answer
222 views

Understanding multiple instanton contributions to vacuum tunneling in a double potential well

I'm trying to understand the method of calculating the transition probability of one vacuum state to another in a double well potential, using instantons. The reference I am following is Sidney ...
4
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1answer
213 views

de Sitter versus Minkowski QFT and cosmological constant

WMAP/Planck results confirm than we live in a de Sitter-like phase, i.e., a Universe with positive acceleration or positive cosmological constant! Therefore, I believe that a way to solve the ...
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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. ...
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2answers
106 views

How does a pierced vacuum move?

If a can of compressed air is pierced on the right, air pushes out, and the can moves to the left. If a vacuum container is pierced on the right, which way does it move? Right? Left? Not at all? ...
4
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1answer
180 views

How important is it, really, to clean vacuum parts?

In every lab I've seen, people are quite meticulous about cleaning parts that are to be used in ultrahigh vacuum, as well as the components of the chamber itself. The parts may be put in an ultrasonic ...
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1answer
328 views

How is it possible the speed of light is not constant?

I was reading this article recently, which summarizes a couple of new studies into the speed of light. In one paper, Marcel Urban from the University of Paris-Sud, located in Orsay, France and his ...
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1answer
565 views

How does the radius and length of a pipe affect vacuum performance?

Can I use Poiseuille's equation? Also If I have a vacuum pump which says that its performance is 30 cubic feet per minutes and I have two pipes (one is radius R1 and L1, the other one is 2*R1 and ...
3
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1answer
62 views

What would happen if a piece of matter, in our atmosphere, were to suddenly vanish?

What would happen if an object were to suddenly disappear? I mean actually disappear, as in, the space occupied by that object were now completely empty- and a vacuum was left. If I was holding a ...
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1answer
515 views

A water balloon in vacuum: does it boil?

If I put water in a vacuum it will boil. But what if I put this water inside a balloon ? I searched for answers and fount this video: http://www.youtube.com/watch?v=9q8F3ClUuV0 It seams that the ...
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0answers
241 views

Vacuum to vacuum transition amplitude

I have two questions about Vacuum to vacuum transition amplitude. Can any particle stay in $|0\rangle$? I was studying this topic from Srednicki's QFT book. He writes in eq.$(6.22)$ $$\langle0|0 ...
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1answer
200 views

Multiple vacua vs. vev's in qft

Take a (possibly supersymmetric) relativistic quantum field theory: when we construct it, we suppose that there is a unique vacuum state $|0\rangle$ which is Lorentz invariant, vector of some Hilbert ...
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1answer
490 views

Can electrons move through vacuum?

I studied that electronics is the branch of physics which deals with the practical applications of moving electrons through vacuum, semi-conductors and gasses. Can electrons move through vacuum?
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1answer
264 views

maybe the universe has already 'ended'? [closed]

I aks you if this reasoning has a base in what we know of universe. There are many articles about so called "vacuum metastability event". As I understand this happens (can happen) with an enormous low ...
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1answer
249 views

Spontaneous symmetry breaking: How can the vacuum be infinitly degenerate?

In classical field theories, it is with no difficulty to imagine a system to have a continuum of ground states, but how can this be in the quantum case? Suppose a continuous symmetry with charge $Q$ ...
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1answer
220 views

Influence of air resistance in space

Consider the following situation: You are locked inside a cylindric container allowing you to move around freely without being in contact with any of the items or surfaces aboard. The container is ...
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1answer
114 views

The equilibrium temperature distribution of a pan in vacuum

If a rectangular pan has a constant and uniform temperature $T$ first, then put it in a vacuum. Considering the effect of thermal radiation, the temperature distribution of the rectangular blackbody ...
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2answers
2k views

A hot object exposed to low temperature in a vacuum doesn't lose heat?

I heard somewhere that if the human body were exposed to outer space where the temperature is extremely low, the human won't actually feel cold because in a vacuum, the heat energy doesn't have ...
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5answers
3k views

Have we managed to make a perfect vacuum?

Have we managed to make a device without any atom inside it on earth? I was reading about vacuum here, and I found in the examples part here that even on the best man made vacuum devices, there are ...
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2answers
8k views

What exists in the Space between atoms

Apologies to all if this has been asked before, I searched but was unable to find one similar. This is a question that has been bugging me for a while that i haven't really been able to find a ...
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3answers
918 views

Can one heat up a vacuum?

I've got a question about heating a vacuum. If there were, say, a container in space, at 2.7 degrees kelvin (the typical temperature of space, if I'm not mistaken) and as empty as space (as close to ...
6
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1answer
306 views

Why does the echo for soundwaves hitting a vacuum come back out of phase? [duplicate]

Possible Duplicate: Phase shift of 180 degrees on reflection from optically denser medium I've read in a physics book for musicians that, when a soundwave hits a near-solid object, it ...
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2answers
493 views

What is the expectation value of the number operator when the vacuum has a VEV?

The number operator N applied to a field whose vacuum has zero VEV gives $N|0>=0$. What if we apply it to the Higgs field? The background of this question is that in popular scientific accounts, ...
5
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1answer
236 views

What happens when a piezo crystal is exposed to a vacuum?

Application of mechanical stress to a piezo crystal generates a charge. Quoting from wikipedia, a 1 cm3 cube of quartz with 2 kN (500 lbf) of correctly applied force can produce a voltage of 12500 ...
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2answers
433 views

Speed of light in a vacuum

I see many references to the speed of light in a vacuum implying that it is only truly a constant measurement in a vacuum. I can live with that, but what kind of vacuum? Are we still talking about ...
2
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1answer
781 views

Can traditional steam (water vapour) exist in a vacuum?

Can steam (water vapour) exist in a vacuum, and if so does it look and behave the same as in air? Let's assume the actual case is a kettle boiling in a vacuum. Note that I'm talking about a gas-less ...
2
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2answers
573 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 ...
2
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5answers
964 views

Is there perfect vacuum 10000 billion lightyears away?

Is there perfect vacuum about some 10,000 billion light years away? With perfect vacuum, I mean that there are no particles, not even virtual photons! I had this idea by assuming that all particle ...
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1answer
188 views

How long will our artifacts last in moon & space?

Given all the different space probes and equipment that have been either launched into space or lying on the moon. How long will they last before they get decayed into dust or some unrecognizable ...
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2answers
2k views

What causes the vacuum in my bento box?

I can't think of a good title for my post, sorry about that. I've got a lunch box (called a bento box) Basically it's a plastic box with a plastic lid with a rubber rim around the lid to create an ...
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3answers
663 views

Creation of particle anti-particle pairs

I was reading some QFT notes and there is one point that I don't understand, they are justifying why we need QFT saying that the number of particles is not preserved once we consider special ...
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2answers
173 views

How can thrust be generated in space which is a vacuum?

Since thrusters have no matter to push off of, how can a spacecraft generate thrust in the vacuum of space?
3
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1answer
663 views

How to properly bake a ultra high vacuum chamber?

I need to get rid of water excess in my vacuum chamber, and for that there is the procedure of baking. In order to do that there are several things that one needs to consider, the power, heat load, ...
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3answers
1k views

How can there be heat in a vacuum?

I keep reading in the Physics World focus issue on vacuum technology about scientists creating high temperatures in the vacuums etc. If heat is caused by thermal energy being radiated from particles ...
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2answers
950 views

can sound travel is space?

Everybody knows that sound cant travel through space, but is really valid? Here is my scenerio: Given the size of a football field's length cubed, there are two objects at two opposing sides. the ...
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3answers
684 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. ...
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1answer
74 views

Does reactive force require the two force involved have to have two different medium for reactive force to occur?

Does reactive force require the two force involved have to have two medium for reactive force to occur? I know the fuel-thruster is working on vacuum space, but we human could not use arm to swim in ...
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2answers
572 views

Why $\lambda\phi^4$ theory, where $\lambda>0$, is not bounded from below?

Why the following interaction, in QFT, $$\displaystyle{\cal L}_{\rm int} ~=~\frac{\lambda}{4!}\phi^4$$ where $\lambda$ is positive, represents a theory that is unstable (or unbounded from below as it ...
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0answers
136 views

How long must two surfaces be in contact for vacuum weld/cementing to occur?

Vacuum cementing apparently is far more likely in space than on a planetary surface in atmosphere. How long must two surfaces be kept in contact with each other in a vacuum for vacuum weld/cementing ...
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4answers
1k views

Is there an intuitive description of vacuum entanglement?

People often refer to the fact that the vacuum is an entangled state (It's even described as a maximally entangled state). I was trying to get a feeling for what that really means. The problem is ...
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1answer
1k views

Measured Higgs mass and vacuum stability

There is such a thing, called "stability bound" on mass of the Higgs boson. The basic idea (as I understand it) is that we take Higgs self-coupling, and calculate its renormalization running. And it ...