# Tag Info

### Why is Permittivity of free space or vacuum not Zero 0?

"Permittivity" is a bad name, I'd think, for just this reason - intuitively, you'd imagine a material which is less "permittive" of electric fields to penetrate it to weaken the ...
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### Why is Permittivity of free space or vacuum not Zero 0?

It was already stated but I couldn't comment as a reply. The simple answer is this: permittivity is inversely proportional to the (the square of) the speed of light. It takes time for electromagnetic ...

### Are the particles in the zero-energy Higgs field real or virtual?

Do not confuse the concept of a field in the quantum field theory of particle physics, the standard model, with the particles that creation and annihilation operators create and annihilate on those ...
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### Does the vacuum really have infinite energy density?

The energy of the vacuum is also known as "dark energy", or the cosmological constant. The value of this in Planck units is about $10^{-120}$, so not only is it non-infinite it is nearly ...
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### Does the vacuum really have infinite energy density?

Quantum field theory does not say that "the vacuum has infinite energy density" because part of our modern conception of quantum field theory is the idea of renormalization. Renormalization ...
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### Free energy from the vacuum?

As per energy conservation law (or "no free lunch theorem"),- whatever energy you'll put into a pair production - on annihilation it will return given energy back to the field, so that total ...
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### Is it possible the Black Holes to be pure deformations in the fabric of spacetime and not an effect of super-dense matter?

Your explanation in your comment: My definition is the absence of spacetime or vacuum space inside the event horizon will not work. If this were correct then the whole event horizon would be a ...
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### Is it possible the Black Holes to be pure deformations in the fabric of spacetime and not an effect of super-dense matter?

Is there any theory in the literature that supports this hypothesis that BHs in their center do not have a super dense matter singularity but are pure deformations in the fabric of spacetime itself or ...

### Free energy from the vacuum?

If the amount of charge on the electrodes producing the electric field doesn't change then I don't see how the electric field can lose energy in this process. Total EM energy (in the static case) ...
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### Questions regarding space

For your first question, you have asked what space is. Space is defined as the boundless three-dimensional extent in which objects and events have relative position and direction. (I don’t think the ...
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### How do we define a pure vacuum?

The vacuum is a theoretical concept of a state that does not contain any particles. As such, it can be defined as an eigenstate of the number operator of all particle fields with eigenvalue equal to ...
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1 vote
Accepted

### Electromagnetic wave in vacuum - Do we have always ${\bf E}\cdot {\bf B} = 0$ and $E = cB$?

Although $E\cdot B,\,E^2-c^2B^2$ are invariant (they're respectively proportional to $\epsilon^{\mu\nu\rho\sigma}F_{\mu\nu}F_{\rho\sigma},\,F_{\mu\nu}F^{\mu\nu}$), neither is $0$ for all solutions of ...
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The correct answer is $γ=NaN$. That is to say there's not exactly one correct value. Imagine you take a gas and then expand its volume to an astronomical degree. What you've created is effectively an ...