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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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 ...
10
votes
3answers
487 views

What is the difference between $|0\rangle $ and $0$?

What is the difference between $|0\rangle $ and $0$ in the context of $$a_- |0\rangle =0~?$$
8
votes
1answer
2k 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 ...
-2
votes
3answers
924 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 ...
17
votes
2answers
4k views

How does space affect the human body (no space suit, no space craft)

How does "outer space" affect the human body? Some movies show it as the body exploding, imploding or even freezing solid. I know space is essentially a vacuum with 0 pressure and the dispersion of ...
6
votes
1answer
226 views

How do instantons cause vacuum decay?

From what I read about on instantons (Zee, QFT in a Nutshell, pg 309-310), an instanton is a vacuum solution that maps $S^3 \rightarrow S^3$ (the boundary of Euclideanized spacetime), which comes from ...
3
votes
4answers
3k views

How is a vacuum able to propagate light?

We say that sound waves need a medium to propagate and we know that light doesn't need such a thing. But is that really how that works? There's no such thing as "nothing" according to Quantum ...
10
votes
6answers
3k views

Does anything exist in the intergalactic space?

I am a part time physics enthusiast and I seldom wonder about the intergalactic space. First, it is my perception that all(almost all) the objects in the universe are organized in the forms of ...
10
votes
3answers
2k views

What are the calculations for Vacuum Energy?

In wiki the Vacuum Energy in a cubic meter of free space ranges from $10^{-9}$ from the cosmological constant to $10^{113}$ due to calculations in Quantum Electrodynamics (QED) and Stochastic ...
22
votes
4answers
3k views

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

What is space? It seems to be everywhere in the equations of physics, as some sort of postulate or hidden hypothesis. We also have a direct experience of it, but is it "real"? The fact that we ...
1
vote
6answers
7k views

Does vacuum (empty space) exist? [closed]

Added: 5 times down vote for now! Down voter is this religion or physics, please try to explain your decision. I'm confused about this. In physics we know for a vacuum, but I think that there is a ...
5
votes
2answers
10k 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 ...
2
votes
5answers
2k 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 ...
50
votes
5answers
8k 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 ...
16
votes
6answers
1k views

Do all massive bodies emit Hawking radiation?

It is known that any accelerated observer is subject to a heat bath due to Unruh radiation. The principle of equivalence suggests that any stationary observer on the surface of a massive body should ...
9
votes
1answer
561 views

The vacuum in quantum field theories: what is it?

In Section 10.1 of his textbook Quantum Field Theory for Mathematicians, Ticciati writes Assuming that the background field or classical source $j(x)$ is zero at space-time infinity, the presence ...
7
votes
3answers
729 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. ...
4
votes
3answers
753 views

Vacuum and repulsive gravity

How can one show from General Relativity that gravity is attractive force, and under which conditions it becomes repulsive, also why positive energy vacuum drives repulsive gravity?
6
votes
1answer
277 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 $Q$ ...
10
votes
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. ...
8
votes
4answers
340 views

Direct exposure to the vacuum of space

I was watching a few sci-fi movies and was wondering the real science explaining what would happen if you were to be subject to the conditions of outerspace. I read the wikipedia article on space ...
4
votes
1answer
195 views

After using annihilation operator on vacuum state, why it is $0$ instead of vacuum?

For bosonic systems, why $a|0\rangle=0$ and not $a|0\rangle=|0\rangle$?
2
votes
2answers
524 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
votes
2answers
499 views

Beryllium Vacuum Sphere Boat/Aircraft

Is it possible to make a solid rigid evacuated "balloon" out of Beryllium or other elements or alloys? The critical buckling pressure at which an evacuated sphere is given as $$ ...
0
votes
1answer
91 views

Does time pass fastest in isolated, resting space?

While it is fairly established that both fast movement and the presence of gravity make time pass slower as compared to a system at rest / free of gravity, does that mean that there is no way for time ...
16
votes
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 ...
12
votes
2answers
2k views

Are we living in a false vacuum? Is there any way to tell?

I was thinking of the noted 1980 paper by Sidney Coleman and Frank de Luccia--"Gravitational effects of and on vacuum decay"-- about metastable vacuum states that could tunnel to a lower energy "true ...
5
votes
4answers
2k views

Water in vacuum (or space) and temperature in space

So, water in vacuum will boil first and then freeze. I don't know how the freeze happens. As pressure lowers to zero, what happened to freezing point? (I know heat taken by vapor, and the water cool ...
4
votes
1answer
175 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? .
1
vote
2answers
595 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, ...
12
votes
1answer
1k views

How to interpret vacuum instability of Higgs potential

If the Higgs mass is in a certain range, the quartic self-coupling of the Higgs field becomes negative after renormalization group flow to a high energy scale, signalling an instability of the vacuum ...
8
votes
5answers
739 views

Does time exist in a vacuum?

Imagine a perfect vacuum devoid of all matter and radiation. Irrespective of whether such a space can even exist, my intuition tells me that time would not exist within such a space. What this thought ...
4
votes
3answers
714 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 ...
3
votes
0answers
126 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 ...
4
votes
2answers
1k views

If I put a ping pong ball in a vacuum, would it pop?

If I put a ping pong ball in a vacuum, would it pop? If so, at what point would it happen? Any standard table ping pong ball is acceptable.
4
votes
1answer
305 views

What are the current (popular(ish)) approaches to modelling the quantum nature of spacetime at the Planck scale?

My guess at a list of them would be: spin foams, casual sets, non-commutative geometry, Machian theories, twistor theory or strings and membranes existing in some higher-dimensional geometry... ...
2
votes
5answers
448 views

Can computers survive bubble nucleations?

According to string landscape theory, our vacua with a cosmological constant of $10^{-123}$ is a metastable vacua which can decay to a supersymmetric vacua with either a zero or negative cosmological ...
1
vote
2answers
137 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 ...
1
vote
1answer
154 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
vote
0answers
213 views

How fast is a true vacuum bubble going to expand?

If a true vacuum bubble will occur in our universe, how fast is it going to expand?
0
votes
4answers
1k views

Atoms pop out of nothing/vacuum/pre-big-bang?

I saw a great documentary last night about 'nothing'. It's about vacuums, and how if you have a total vacuum atoms will pop out of nowhere! Pretty crazy stuff. Atoms literally coming out of ...
6
votes
2answers
904 views

Wheeler-Feynman theory, QED without fields, vacuum polarization

Initially Wheeler and Feynman postulated that, the electromagnetic field is just a set of bookkeeping variables required in a Hamiltonian description. This is very neat because makes the point of ...
4
votes
1answer
144 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
votes
1answer
665 views

Why does Hauksbee's electrostatic machine produce light?

I'm reading on the history of the discovery of electricity and the electron, and I've went from reading about Rutherford's gold leaf experiment all the way back to Francis Hauksbee's spinning glass ...
2
votes
2answers
653 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 ...
1
vote
2answers
542 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, ...
1
vote
2answers
457 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?
1
vote
4answers
1k 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 ...
1
vote
2answers
194 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?
0
votes
1answer
114 views

Difference between $|0\rangle$ and $0$ in the context of isospin

I know this has been asked before, but I am confused having read it in the context of isospin, where the creation operators act on the "vacuum" state (representing no particles) $$a^\dagger_m|0\rangle ...