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. In QFT, it signifies the ground state devoid of excitations/particles.

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32 views

What is the best possible explanation of Space and that its something we can interact with? [on hold]

i would like to know of Space which is the most important part of existence.What is the explanation for it.I see it as the most vital part of our existence in which other things exist. What is space ...
0
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1answer
34 views

Would a literal Air ship (boat) work?

If a set of very large airtight pontoons were made in the vacuum of space, would they float on top of the upper atmosphere? I thought about this while watching the last season of Mythbusters when they ...
14
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2answers
419 views
+200

An explanation of Hawking Radiation

Could someone please provide an explanation for the origin of Hawking Radiation? (Ideally someone who I have been speaking with on the h-bar) Any advanced maths beyond basic calculus will most ...
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1answer
48 views

What are the vacuum Einstein's equations? [closed]

I read on Wikipedia that if the Stress-Energy Tensor is set to zero in General Relativity's Field Equation that it makes the Vacuum Equations. What are these equations, and how are they used?
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2answers
36 views

Entropy and vacuums

If I have a vacuum (completely devoid of any particles; Q.M. effects aside), then turn a nozzle and let a gas freely expand into the vacuum, will I have increased the entropy of the vacuum? I get ...
3
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2answers
586 views

Producing gravitational waves in labs

Can gravitational waves be created on very small region of vacuum with quadruple movement of atom or subatomic particles?
0
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0answers
35 views

Why does the lack of pressure in outer space affect what's inside our bodies?

I have read multiple similar questions on this site, but none answer specifically the thing I am having trouble understanding. I have read repeatedly that a lack of pressure will cause the fluids ...
3
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1answer
35 views

Balloon of ideal gas suddenly pops in the vacuum of space - final average energy per atom?

My question is: is the following thinking pretty much correct? I'm interested hearing about anything here that is fundamentally wrong. Of course there is a bit of hand waving and approximation. If a ...
11
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5answers
252 views

How is the ground state chosen in a spontaneous symmetry breaking process?

This question is about how the ground state is chosen in a spontaneous symmetry breaking process. Say we have a Mexican Hat potential (e.g. the one for the Higgs field) and are sitting at the unstable ...
1
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1answer
74 views

How does Bremsstrahlung occur in a vacuumized particle accelerator?

In our electrodynamics course we have learned that accelerating a charged particle will lead to a loss of energy in the particle due to Bremsstrahlung. The exact amount of power radiated away is given ...
0
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1answer
30 views

effect of opening the barrier between a tube with one side pressurized and the other side a vacuum

What would happen when a tube with an air space pressurized to 500 atm by the water exerted at 5 km below the surface was opened into a vacuum chamber rising up 5 km to the surface? The bottom of the ...
0
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2answers
11 views

How to quantify the spreadness of beam of air molecules as they escape from a capillary to a vacuum?

Consider a tube from an oxygen cylinder attached into a vacuum chamber. When the cylinder is opened, the molecules escape out into vacuum chamber. What makes the molecules spread out when they escape ...
0
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0answers
8 views

What is the growth mode of thermal-evaporated aluminum on organic subtrates?

Does aluminum grow in an island mode or layer-by-layer mode on organic substrates which is amorphous? For example, on PMMA, fullerene or surfactant thin films. Can I predict the mode by comparing the ...
3
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1answer
57 views

Helmet to helmet in vacuum - can we talk?

Usual SciFi scene. In a spacesuit, in vacuum, with the comms out for some reason. They want to talk, so the butt helmets together so sound can pass through. Questions are: a) Would it really work in ...
0
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0answers
45 views

Questions regarding space

A difficulty I face is when I think of space. I haven't studied GR or SR yet, but I really want to know what it is. What is space? Is it just the empty place where things are in reality, or something ...
1
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2answers
57 views

Rising glass in xkcd what if

In http://what-if.xkcd.com/6/, Around this time, the glass on the left starts to visibly lift into the air. The air pressure is trying to squeeze the glass and water together. This is the ...
1
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0answers
22 views

Backing pressure for a turbo-molecular pump

It is known that turbo-molecular pumps are to be operated at already low levels of pressure. So the turbo is always backed by another pump (usually a scroll, rotary pump) that ensures this. One should ...
1
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1answer
60 views

Probability of finding vacuum?

Consider a real scalar quantum field $\varphi (x)$, interacting with a classical real scalar field $J(x)$ : $$ \mathcal{L} = \frac{1}{2}(\partial \varphi)^2 - \frac{m^2}{2} \varphi^2 + \varphi J$$ ...
1
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1answer
47 views

The Space Between Atoms And Sub-Atomic Particles And More [closed]

I was wondering what the space between atoms or electrons is called. Is it Vacuum ? And what is in there ? Is it really free or empty space ? And if so, how can nothing exist ? It is a bit of an odd ...
0
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1answer
139 views

Is space really empty? [duplicate]

This guy here says space is not empty.. It explains how space inside nucleus is Full of fields. Does it mean to say gluons are present everywhere, even outside nucleus? Consider a region without any ...
0
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0answers
23 views

What is meant by a “change in volume of a system”?

I keep getting confused when my professor talks about the change in volume of a system. Sometimes it seems as though he's talking about the volume of the gas and at other times he might be talking ...
1
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2answers
37 views

Does eq. of continuity hold in vacuum too?

When a streamlined flow of water flows down through an ordinary tap, it's cross-sectional area decreases according to eq. of continuity due to atmospheric pressure. If the same apparatus were to be ...
1
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0answers
40 views

Imaginary part of the stress-energy tensor

I just encountered in an article of D. G. Boulware ("Quantum Field Theory in Schwarzschild and Rindler Spaces", Phys. Rev. D 11, 1404, 1975, in the last paragraph of the Introduction) the statement ...
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1answer
46 views

How does water height in a vacuum chamber effect pressure

I am testing for package leaks in non-porous packages. Quick details are: 1) Package is sealed at atmospheric pressure. There is some headspace inside the package which is just air. 2) A small hole is ...
3
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1answer
85 views

Vacuum has both zero four-momentum and nonzero vacuum energy?

I have heard that in QFT, the vacuum has zero four-momentum: $$P^\mu |\Omega \rangle = 0.$$ However, I also know that the vacuum has vacuum energy, i.e. $$ \langle \Omega | H | \Omega \rangle = E_0 ...
0
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1answer
48 views

Balloon in a vacuum

What arrangement will a mixture of low density gas and high density gas take inside a balloon (in a vacuum chamber) in zero gravity? FYI: water boil then freeze's in a vacuum. which one will stick to ...
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2answers
31 views

Can we enhance a thermal gradient by combining a dark surface and a shiny surface with an external glass layer?

I refer to the article at this site: http://solarcooking.wikia.com/wiki/Solar_Kettle-Thermos_Flask As we know, dark surfaces absorb radiation (eg. solar water heater), while shiny surfaces reflect ...
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3answers
98 views

Thinking about the properties of 'nothing' [closed]

If a certain identifiable part of space that has no type of measurable energy fields manifesting 'in it' for a given duration ; is such a totally empty space the same as 'nothing'? Anything with any ...
0
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2answers
54 views

why is there no total vacuum condition on earth? [duplicate]

I know that Bell jars are often used in laboratories to form and contain a vacuum but not total vacuum like space.So i don't understand why can't human make vacuum bell jar a total vacuum state?
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2answers
38 views

what would happen to flowing electrons in a vacuum if they are not giving any exit point?

Lets say theoretically electron flow is captured in a vacuum and not allowed to exit then where would they go? I do not want to know the practical impossibilities of it. And also what would happen if ...
0
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1answer
19 views

HV Vacuum seals

I have a vacuum port that is 8.75" in diameter, it was attached to a block of aluminum. I am machining a piece of stainless steel to make a blank for it since it is a non-standard size. What are my ...
2
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2answers
58 views

Vacuum is not really empty

Vacuum should contain something in it. Because nothing is perfectly empty that's what I feel, but what is there left in it? Is there any matter or its just enegry. Can energy be pulled out of some ...
1
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3answers
85 views

Why would we freeze in space if there is no matter to conduct the heat away from us?

If a near perfect vacuum is assumed to be in space, how can heat leak around from our body for example? Although theoretically energy wishes to spread equally all around, it still needs a medium to ...
1
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3answers
48 views

Motion in vacuum [closed]

If we have a hollowed sphere in a vacuum, and its hallow space is filled with vacuum. In the center of the hollowed space inside the sphere is a ball. If we push the sphere does the ball move? (prior ...
1
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1answer
46 views

Methods to solve a vapor pressure equilibrium question with water on the moon? [closed]

"Imagine a tall column of water on the Moon, maintained at a temperature of 50°C and left to the open vacuum at the top. Up to what depth will the water continue to boil? The Moon's radius is 0.273 ...
1
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3answers
91 views

Is the empty space really empty? [duplicate]

I've come across another article in "list verse" which says that the empty space is not actually empty at least for a while. I've tried to find about this, so I googled it .It also quotes a word ...
3
votes
2answers
108 views

Gases Expanding and Bonding in the Vacuum? Frozen Clouds

Why do gasses expand in space rather than attract forming a liquid? Do some gasses attract or bond when they get colder and what would be the characteristics of it in space? Would it be like powder ...
1
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0answers
55 views

Could a perfect vacuum exist at the boundary of the universe?

Space is not truly a vacuum because of our observation of quantum foam, but if causality does not exist outside our universe, could that mean that quantum foam cannot exist outside our observable ...
0
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0answers
26 views

acrylic vacuum chamber design

I want to build a vacuum chamber for experimentation from acrylic sheets, ideally a cube $60~\textrm{cm}$ on each side. Assume that the chamber can be pumped down to theoretical perfect vacuum. How ...
-3
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1answer
129 views

Atoms, Gravity and Electrostatic Charge [closed]

How close do 2 atoms of any type the have can be together before gravity with an electrostatic charge that repulses?
0
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0answers
17 views

What result would I get from series-mounted vacuum assist? (hydraulic vacuum assist)

If I install two inline vacuum assist devices (such as VH44) on my clutch line, what will change in comparison to having a single boost? Will it decrease pedal travel? Tension? Both? Neither? Lest ...
2
votes
2answers
181 views

What happens with liquids in vacuum? [closed]

I am wondering what would happen in a situation where there is some liquid in a closed container A is vacuum and B is the liquid. I am also interested if there are any differences in behaviour ...
3
votes
0answers
86 views

Angular momentum of the vacuum

I'm studying quantum field theory from "An introduction to Quantum field theory" by Peskin and Schroeder and from "A modern introduction to quantum field theory" by Maggiore. I've read from "An ...
3
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0answers
28 views

Baryonic operators in ${\cal N}=1$ $U(N)$ SQCD in four dimensions

Seiberg's duality is usually considered as a duality for $SU(N_c)$ theories with $N_f$ flavors. In his case, the vacuum for $N_f \geq N_c$ is parameterized by mesons $M$ and baryons ${\bar B}$ and ...
5
votes
2answers
549 views

Why does the QCD vacuum have zero momentum?

Today in the hadron physics tutorial we were talking about the Fabri-Picasso theorem where one step in the proof involves $\hat P |0\rangle$ which is the four-momentum operator on the vacuum. And from ...
0
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0answers
20 views

How to Calculate Pressure From Earth up to Space at Certain Height? [duplicate]

https://en.wikipedia.org/wiki/Vacuum#Measurements_relative_to_1_atm https://en.wikipedia.org/wiki/Pressure_measurement#Thermal_conductivity I wonder if there's a clear equation for this calculation. ...
1
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1answer
37 views

Cryogenic (LN2) gas vs liquid for cooling

For cooling, would you recommend using gas over liquid or vice-versa? What is the temperature differential between gas and liquid? In other words, at standard volumes and pressures from a gas ...
1
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1answer
105 views

What happens to a sound wave going from air to vacuum?

Let's say you are in a space ship. The inside is filled with air, a medium in which sound waves can exist and travel. Then there's a wall, still a medium in which sound waves can exist and travel. And ...
1
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1answer
34 views

What is the temperature of a vacuum? [duplicate]

what is the temperature of Vacuum since temperature of a system is related to the average of the molecular kinetic energy and there is no molecule in a vacuum? i know there could be radiations but i ...
0
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0answers
22 views

Can we lock electric charges in dielectric cells?

Suppose next. We using Wimshurst machine and gathering charges in dielectric cells such as mica .Before discharge we put whole machine in vacuum chamber.Question is next. Can we storage those charges ...