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.

learn more… | top users | synonyms

0
votes
0answers
200 views

What properties does the vacuum have?

Once upon a time the vacuum was defined as "nothing". We now know it has all kinds of properties such as permeability, dimensionality etc. Is there a list of such properties anywhere?
7
votes
2answers
1k views

What happens to a body, initially at 300K, kept in isolated space? Will it's temperature drop to 0k?

With regards to Thermal Radiation, given a stable body initially at 300 Kelvin placed in isolation, after continuous Thermal Radiation will it's temperature gradually reduce to 0 kelvin asymptotically?...
3
votes
3answers
256 views

Propagation speed of photons when taking higher-order QFT corrections into account

In our group of experimental physicist who have nothing to do with and know very little about quantum field theory, we recently had a question concerning the propagation speed of photons in vacuum: ...
3
votes
2answers
130 views

Functional integral in spontaneous symmetry breaking

So, functional integral is defined to be (with $\lvert\Omega\rangle$ is the vacuum state): $$\frac{\langle\Omega\rvert ... \lvert\Omega\rangle}{\langle\Omega\vert\Omega\rangle} = \int \mathcal{D} \...
1
vote
4answers
474 views

Can I blow soap bubbles (of air) inside a vacuum chamber?

When I blow soap bubbles from a liquid dish soap mixed with distilled water at atmospheric pressure at ground level both internal and external air pressure nullify and the tension of the bubbles holds,...
0
votes
1answer
115 views

Can we generate electric current by injecting electrons into a copper panel

Suppose I take a vacuum tube and accelerate electrons in it by electric fields then collide it on a copper plate. Will the electrons then go inside it and generate an electric current by putting a ...
5
votes
3answers
3k views

What if you opened a door in a spaceship without a spacesuit?

In movies/cartoons you see astronauts and people in spaceships opening doors and closing them again with no suits on. Is it possible in "real life" or would you die immediately? Because consider this: ...
0
votes
1answer
55 views

Temperature in a vacuum made in the lab

Is the thermal energy of a vacuum 0? And, how close to a perfect vacuum can we make in the lab?
0
votes
0answers
57 views

Can a volume of N2 be more negative than -14.7 psi?

Ok. I’m getting -30 PSI on a gauge calibrated at 0 for 1 ATM. Let’s say I have a chamber with a volume of 20L of N2 at 1 ATM. A vacuum pump that can pump to absolute vacuum let’s say 1X10^-10mTORR. ...
10
votes
5answers
2k views

A cup of water in ZERO gravity

What will happen if I try to pour a cup of water in zero gravity, into another empty cup? Will the water come out of the cup? The adhesive force between the water molecules and the interior of the cup ...
0
votes
1answer
61 views

What happens if a free radical is placed in absolute vacuum?

I'd like to know what happens if a free radical has no material around to interact with. I have asked many people but I am not satisfied with their answer. I know there is nothing like absolute ...
17
votes
2answers
3k views

Bell in a vacuum, where does the sound energy go?

I'm not educated in physics, but I learned that a bell struck in a small vacuum chamber will not be heard by people around it (in a school science lab). If it had been surrounded by air, there would ...
0
votes
1answer
68 views

Repulsion of electric charges

If a take a vacuum tube and put electrons in it and put a negative ion strip or something like that outside the tube will the electrons inside the tube start moving due to the repulsion of charges of ...
1
vote
4answers
278 views

What is the meaning of Einstein's field equation in terms of source and its effects on curvature?

The Einstein's Field Equation is $$R_{\mu\nu}-(1/2)g_{\mu\nu}R=-8\pi T_{\mu\nu},$$ where the left hand side is the curvature term and the right hand side is the source term (see, Hartle). Now, in the ...
7
votes
5answers
1k views

Proving and demonstrating vacuum in container without breaking it

Let there be a hollow container made of glass or some other transparent material, roughly the size and shape of an apple. Let the walls be of sufficient thickness for the container to be safely ...
0
votes
1answer
99 views

Time in a perfect vacuum? [duplicate]

If we were able to make a perfect vacuum with no forms of energy in, including all forms of light would time still go on in that vacuum and if it doesn't how would we tell that it doesn't? Then if we ...
0
votes
0answers
134 views

What is the relationship between the Young's modulus of a material and the elasticity of a free fall collision

I'm coding a 2D physics simulator based around the Newtonian physics principles with some alterations due to computation limits and I am at the stage of creating a collision event between a planetary ...
0
votes
1answer
55 views

Creating vacuum in a glass by acceleration

Suppose we have a cylindrical glass at atmospheric pressure. The glass is put in a horizontal position such that the bottom of it (the closed end) is at the right side and the open side is on the left....
2
votes
4answers
1k views

Why do we theorize that the Big Bang created space? [duplicate]

I just asked this astronomy question about how far away the light is that would show us the beginning of time, the Big Bang. Some answers claim that the light I ask about doesn't exist, because "The ...
31
votes
5answers
5k views

What physical evidence is there that subatomic particles pop in and out of existence?

What physical evidence shows that subatomic particles pop in and out of existence?
69
votes
7answers
16k views

What is the speed of sound in space?

Given that space is not a perfect vacuum, what is the speed of sound therein? Google was not very helpful in this regard, as the only answer I found was 300 km/s, from Astronomy Cafe, which is not a ...
0
votes
4answers
429 views

Can this container withstand a vacuum? [closed]

I am putting together a piece of equipment that will involve a vacuum pump pulling up to 10 Torr / 13 Mbar.  I need to use a container for liquid within the equipment and have found a stainless steel ...
2
votes
3answers
3k views

Why is it impossible to have a perfect vacuum?

In another question someone mentioned that it couldn't happen. Why not? For example I asked about the speed an object would have to move at sea level to create a vacuum behind it; in the comments ...
4
votes
1answer
1k views

How fast would an object have to move to create a vacuum behind it?

When an object moves, I assume that the air above it, instead of remaining at the same general height, is pulled downward as it is passed in order to fill the low-pressure area behind the object where ...
7
votes
4answers
15k views

How do electromagnetic waves travel in a vacuum?

This is perhaps a total newbie question, and I will try to formulate it the best I can, so here it goes. How does an electromagnetic wave travel through for example, the vacumm of space? I usually ...
1
vote
2answers
280 views

Could a really tall tube suck garbage in to space?

When I was around 10 years old, I had this idea that was supposed to solve our waste problems; I imagined having tubes miles high that would stretch in to space. Every tube would have a door at the ...
0
votes
4answers
261 views

What happens when I place an object of certain temperature in space ? Does it loose its entire heat energy?

Can i obtain absolute zero temperature this way? And let's assume there is no cosmic microwave background and also assume that there is a way to shield the object from any heat source, such as the ...
1
vote
2answers
974 views

Does spacetime have a “mass” value? or What is “Spacetime” made out of?

When measuring the MASS within the Universe, does "space" or "spacetime" have a value? I only ask, because when speaking of expansion, space is expanding. Could it be possible, to reverse the process,...
0
votes
2answers
69 views

Can energy be “subtracted” from vacuum?

It probably sounds absurd, but I heard such expressions as "subtracting a particle from vacuum", or from squeezed vacuum, in the context of quantum experiments, or quantum optics, (not black holes). ...
0
votes
3answers
343 views

Can you stop an electron in vacuum?

If we shoot an electron in vacuum tube, then stop it with electromagnetic field, and switch off the field, what will happen with electron? Will it continue its movement? If there is a gravitational ...
12
votes
4answers
14k views

Why is space a vacuum? [duplicate]

Why is space a vacuum ? Why is space free from air molecules ? I heard that even space has a small but finite number of molecules. If so, won't there be a drag in space?
2
votes
2answers
120 views

Can the vacuum energy be made finite with quantized space

From what I know the reason we have infinite vacuum energy is because according to Quantum Field Theory at every point in space we have something analogous to a harmonic oscillator but since the Zero ...
5
votes
1answer
118 views

Which assumption is less plausible, “action at a distance”, or that “virtual particles” can exist for a short time?

It is understood that virtual particle appear in Feynman diagrams as a tool of calculus. And it is understood that they are problematic about their mass, and cannot be detected (is that sure indeed?). ...
2
votes
0answers
184 views

Help with derivation of the Casimir Effect?

I am at the very last part of a relatively long derivation of the Casimir effect, and I just don't understand the final step D: So far, I have derived the ground state energy to be $$\langle 0| \hat{...
0
votes
1answer
88 views

Why is the storage ring of a synchrotron a vacuum?

Why is the storage ring of a synchrotron a vacuum? I know that when the accelerated particles get to the storage ring they lose energy, releasing synchrotron radiation, but how does the vacuum make ...
1
vote
3answers
320 views

How does air in a water balloon act in space?

I was making an analogy with gravity and water and it went like this. When air is trapped in water as a bubble, water is pushing towards the inside and like Newton's law equal and negative forces ...
0
votes
0answers
328 views

Thermal conductivity in vacuum

It is my assumption that material objects preserve/gain heat via: 1) material contact (air or other touching material/object) and/or 2) absorbing radiation / electromagnetic waves So, imagine that ...
1
vote
2answers
166 views

Moving frames - a blow on “virtual particles”?

There is a polemic about whether virtual particles EXIST, or are only a tool for making our calculi easier. Here is a doubt about their existence, and on the other hand, an argument in support of ...
3
votes
3answers
761 views

The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?

There is no "action at a distance" in nature. Attraction of a piece of iron by a magnet, attraction between distant electric charges of opposite sign, have to be mediated by something. The virtual ...
1
vote
2answers
172 views

If the vacuum is not “emptiness” why the speed of the electromagnetic wave is independent of the frame of reference?

If the vacuum were "emptiness" it were easy to accept that there is no "preferred frame of coordinates" and the light velocity is the same in any inertial frame of coordinates. But the vacuum is an ...
3
votes
1answer
191 views

Inexplicable Results in a Vacuum Experiment

We've been doing the following experiment in our Physics Lab course and are coming up with some strange results which we're at a loss to explain. The purpose of the experiment is to determine the ...
9
votes
1answer
1k views

What is the difference between quantum fluctuations and thermal fluctuations?

Start with a simple scalar field Lagrangian $\mathcal{L}(\phi)$ at zero temperature $T = 0$, which has a hidden symmetry and spontaneously break it. By the standard procedure a field $\phi$ is ...
12
votes
3answers
394 views

Are vacuum fluctuations really happening all the time?

In popular physics articles and even some physics classes I've been to, the vacuum of space is described as being constantly full of quantum fluctuations. Supposedly, all sorts of particle-...
3
votes
0answers
229 views

Is everything made of space? [closed]

I had been studying quantum field theory for a while now, and how there had been many efforts in physics to finally create a "Theory of Everything" (TOE). But while I was learning about all this, I ...
1
vote
1answer
559 views

Different density objects falling on Earth's atmosphere?

So I finally understood why 2 objects with different masses, free falling from the same distance reach Earth's surface at the same time (due to the objects Inertia). Now when the objects fall in the ...
2
votes
3answers
219 views

What is the physical meaning of $a_{\vec{p}} \! \mid \! 0 \rangle$

$a^\dagger_{\vec{p}} \! \mid \! 0 \rangle = \mid \! p \rangle$ is interpreted as a creation of a particle with momentum $p$ from the vacuum. $a_{\vec{p}} \! \mid \! p \rangle = \mid \! 0 \rangle$ is ...
3
votes
2answers
639 views

masslessness of Goldstone boson, Effective action, and functional-integral measure

I have difficulty in understanding the path-integral formalism of SSB, and that of Effective Action. Let's say a complex scalar field theory has the global $U(1)$ SSB, $$L(\phi)=(\partial^\mu \phi)^2-...
1
vote
2answers
315 views

Vacuum to vacuum transition amplitude using functional integral

The vacuum to vacuum transition amplitude for a free particle with source $J$ is given by $$Z_0[J]=\int D\phi \mathrm{exp}\{-i\int [\frac{1}{2}\phi(\square +m^2-i\epsilon)\phi-\phi J]d^4x\}$$ Let $P=\...
0
votes
1answer
471 views

2 vacuum pumps in parallel [closed]

I have a problem with a vacuum pump that cannot generate enough vacuum to grip an uneven item. There is a spare vacuum pump in parallel which I will turn on and run at the same time to try and get ...
5
votes
1answer
235 views

How fast until you feel wind in space? [duplicate]

I couldn't find this question asked anywhere else, so I thought I would ask it here: does anyone know how fast you would have to be traveling in space to feel 'wind' from the particles in front of you?...