Tag Info

20

The energy is borrowed from the Heisenberg Uncertainty Principle to create virtual particles and has to be paid back in a very short time. $\Delta{t} \geq \frac{\hbar}{2\Delta{E}}$ This is why virtual particles live for very short times (i.e pop in and out of existence). We cannot manipulate this energy.

13

Whether you can extract energy from this or not (and I strongly suspect not) the Casimir effect is a consequence of vacuum fluctuations. Essentially when two metallic plates are very close to each other, the wavelengths of virtual particles that can be created between the plates is restricted and hence there are fewer particles between the plates and ...

11

1) Most materials you use in everyday life contain far more moisture than you might believe. This is a major reason materials meant to be exposed to space are specially designed and tested. In a general vacuum, most fabrics and many plastic will outgas - all of the absorbed moisture and oils will work their way to the surface and boil off - which is a major ...

8

I think the key conceptual hurdle is that the vacuum state is not nothing. Quantum field theory describes matter as excitations in quantum fields. These quantum fields are very strange things, and I don't know of any easy way to explain to a non-physicist what a quantum field is. The key thing is that the quantum fields fill all of spacetime. So a vacuum is ...

7

This creates a point of extremely focused energy at the middle point where the bubble collapses. In theory, this point focuses enough energy to trigger nuclear fusion. It is not currently accepted mainstream science to say that collapsing bubbles focus energy enough to cause nuclear fusion. Temperatures over 10,000K can be acheived, but are still well ...

7

Let's consider the simplest case of a quantum harmonic oscillator, with creation and annihilation operators $a^{\dagger}$ and $a$ respectively. The ground state of our system is, $\lvert 0 \rangle$ which has energy, $$E_0 = \frac{1}{2}\hbar \omega$$ Every time a creation operator acts, the state $\lvert n \rangle \to \lvert n+1 \rangle$, modulo some ...

6

You're right that the vacuum is the state that minimizes the energy. In the classical limit this is easy to do. Let's take $\phi^4$ theory for example. Then the Hamiltonian is $\dot{\phi}^2/2+(\nabla \phi)^2/2+\lambda \phi^4/4!$. The lowest energy configuration is thus the one where $\phi$ is constant sitting at $\phi=0$, the bottom of the potential. ...

6

Assuming you're willing to accept General Relativity as a valid theory, your question has a well defined answer because we can solve the equations of GR for an empty universe. The result (well, the simplest result) is Minkowski spacetime. You might think that nothing much can happen in an empty universe, but even though no matter or energy is present there ...

6

Both the free and interacting vacuum are invariant under translations, assuming that translation invariance isn't spontaneously broken. Usually we expand around spatially homogeneous and time-independent field configurations, so that you don't have to worry about spontaneously breaking translations. There are some cases where translations are broken in the ...

5

The phrase is a translation of a quote from Democritus, an ancient Greek philosopher. The quote is not intended to refer literally to the details of modern physics. It is simply an example of an early expression of the naturalistic viewpoint. Carroll's general philosophy is that the universe can be understood in terms of natural laws. There is nothing ...

5

The speed of any object is constant if there are no forces acting on the object. This applies to light and all other matter. Without forces (e.g. friction), an object that is moving will never stop moving. By "perpetual motion" people usually mean a machine that can produce more work than the work required to run it. It's hard to think of an everyday ...

5

Yes, water still has surface tension in a vacuum. Water/vacuum surface tension is 72.8 dyn/cm experimentally according to Zhang et al. J. Chem. Phys. 103, 10252 (1995). Surface tension is caused by the fact that water molecules in the bulk (not at the surface), are surrounded by other water molecules with which they interact through intermolecular ...

5

I assume you are asking why we are not drawing air out of a balloon like container so as to create the lower density that helium or hot air gives us. The answer is that it is hard to maintain a vacuum with a thin enough, so as to be almost weightless, rigid contaning surface. A balloon with gas inside equalizing the atmospheric pressure with the gas ...

5

The image of space being bent is just an analogy, it is not meant that anything is actually being deformed. Gravity distorts the notion of distance on spacetime, i.e. the presence of matter somehow causes the metric to change. A way to visualize this is to think of spacetime being bent, as you say, but really, spacetime is not made of anything, the idea of ...

4

But as I understand it, the fields in QFT are not operators, I'm not sure where you heard that, but quantum fields are operators. Or more precisely, operator-valued functions of position: a quantum field $\psi$ maps every point in space, $\mathbf{x}$, to an operator, $\psi(\mathbf{x})$. The VEV $\langle 0\rvert\psi\lvert 0\rangle$, or (perhaps more ...

4

There is a video on YouTube of such an experiment. The corresponding paper is as follows: Can a Siphon Work In Vacuo? Adrian L. Boatwright, Simon Puttick and Peter Licence. J. Chem. Educ., 2011, 88 (11), pp 1547–1550. DOI: 10.1021/ed2001818 After watching the video (but not reading the paper), my first thought was that the liquid in question has unusually ...

4

Creating a vacuum above carbonated drinks causes the CO2 to outgas faster--simply because there is no CO2 above the drink to diffuse back into the liquid. In physical terms this means there is no vapor pressure of CO2 above the liquid, so net movement of CO2 is from the drink to the space above it. If you leave a closed carbonated drink bottle long enough, ...

4

There are lots of related questions on this site but I couldn't find one that answered your question exactly. If you're interested try searching the site for boiling vacuum or something similar. The boiling point of a fluid depends on the external pressure. Specifically a fluid will boil when its vapour pressure is greater than or equal to the external ...

4

I just realized what the problem is. It actually doesn't have anything to do with the detector. When working in vacuum systems you have to worry about the dielectric breakdown of the air as the pressure is reduced. It turns out that the breakdown voltage hits a minimum around $\sim 1$ Torr depending on the species of the gas (see the curves below). This ...

3

First of all, classically (neglecting loop corrections), we obviously want to expand around the true minima that are found in the vacuum, which means around one of the states $|0_\pm\rangle$ – these two are really equivalent to one another due to the gauge symmetry. The state around $\phi=0$ is a maximum of energy, not a minimum, so Nature doesn't spend much ...

3

It has nothing to do with action at a distance the way you talk about it. There is some sort of instantanious action at a distance to the particles knowing where are holes to go ? Not quite. Consider that case of the barrier with vacuum inside. From one side, the air atoms are constantly colliding with the surface, and exerting a force on the barrier ...

3

We have the functional of the external source $J$, which gives us v.e.v.s of field operators, by functional differentiation: $$e^{-iE[J]} = \int {\cal{D}}\phi\, e^{iS[\phi]+iJ\phi}$$ $$\phi_{cl}=\langle\phi\rangle_J = -\frac{\delta E}{\delta J}$$ Where $\langle\phi\rangle_J$ is the v.e.v of $\phi$ in presence of external source $J$. That could be ...

3

Expectation values in QFT mean the same thing as they do in quantum mechanics. It's just that certain of these guys, the so-called vacuum expectation values (VEVs) $\langle 0|\rm{operator}|0\rangle$ turn out to be especially useful and important in QFT. In particular, the correlation functions (aka Green's functions) of the QFT, which for the theory of a ...

3

The vacuum is polarizable. The polarization can be with respect to electric charge or color charge. In the presence of an electric field, virtual electron-positron pairs briefly exist (created from virtual photons of sufficient energy). The virtual pairs act as dipoles and orient with respect to the field. For example, near a proton, the virtual electron ...

3

The answer kinda is "You can, but why would you". It is indeed possible to extract energy from the vacuum. It has been studied, both theoretically and experimentally, using a variety of metal plates and other Casimiresque gizmos. The problem is just that it basically acts like a spring. To put the Casimir effect in action, you must first approach together ...

3

No. Just like in Chemistry and Thermodynamics, we never get anything for free. On a mechanistic level, it's important to recognize that zero-point (vacuum) energy represents the lowest energy state waveform. I remember thinking that because the EM fields are everywhere and quantized, that there was some sort of magic taking place. Realistically, ...

3

Why can't fermions have a non-zero vacuum expectation value (VEV)? Lorentz invariance. If anything other than a Lorentz scalar has a non-zero VEV, Lorentz invariance would be spontaneously broken. For example, suppose we have a Lorentz invariant term in a Lagrangian for a vector $$\mathcal{L} \supset m^2 A_\mu A^\mu.$$ Now suppose the vector obtains a ...

2

A high vacuum will also break down under a sufficiently high DC field. Under an increasing DC voltage, small projections on the negative electrode (called "asperities") begin to experience a localized electric field that is sufficient to initiate field emission, often accompanied by intense localized heating, thermoelectric emission, or even explosive ...

2

You need to be a little careful with your definition of vacuum. For instance inside a spherical shell of matter spacetime is flat, however time still runs more slowly than it does outside the shell. I'm assuming you have no such trickery in mind, and by vacuum you mean the usual concept of far (effectively infintely far) from any matter. To a good ...

2

After reading quiet a few dozen articles on this subject, the math seems to fall into two catagories: 1. People who claim that the physics disallows vacuum spheres of ANY size: http://en.wikipedia.org/wiki/Vacuum_airship 2. Others who claim that a larger sphere's volume being greater in proportion to it's surface area respectively, affords buoyancy ...

Only top voted, non community-wiki answers of a minimum length are eligible