I've often read that the speed of light more about the speed of events than light specifically. I wonder if this implies that spacetime has some base viscosity, or mathematically similar mechanic.

To restate, I'm not really asking if there is a literal, physical viscosity. For a simulation, I am considering whether or not I can relate the cosmological constant to a viscosity property with some special treatment in a similar algorithm to what's used for handling refraction depending on type/density of materials.

The main goal is to get a pretty accurate speed of light as an emergent property rather than a hardcoded limit.

  • $\begingroup$ If you are not asking about "literal, physical viscosity", then what is your definition of viscosity here? Without knowing what you're talking about we cannot determine whether spacetime has that property or not. $\endgroup$
    – ACuriousMind
    Feb 25, 2017 at 18:08
  • $\begingroup$ Literal viscocity would be OK or anything fairly close, but what I'm talking about is more generally "piecewise" / piece-by-piece drag or ability to calculate drag per cm^3 for example. A little tricky to call it drag since in materials slower propagation time isn't drag but when computing distance traveled in a simulation it works close enough for conversation. $\endgroup$ Feb 25, 2017 at 18:10
  • $\begingroup$ @ACuriousMind hopefully that is clearer; yeah I'm not completely sure how to ask the question tbh. Is there anything physically similar to viscosity related to the energy density of space? $\endgroup$ Feb 25, 2017 at 18:18
  • $\begingroup$ The Higgs mechanism, en.wikipedia.org/wiki/Higgs_mechanism but the model assumes special relativity, so c is fixed in all frames as the velocity of light and masslss particles. $\endgroup$
    – anna v
    Feb 25, 2017 at 18:35
  • $\begingroup$ @annav yeah I get a bit confused thinking of whether or not to include a Higgs field for this effect. plausibly the best idea really but at the same time does it really count as a supposed true vacuum still? maybe since it's the Higgs field and this is sort of its job that's alright. I don't have enough domain knowledge. $\endgroup$ Feb 26, 2017 at 4:10

1 Answer 1


It is the permittivity and permeability of vacuum that determine the speed of light. Those two come from how strong an electric field is created by charge in vacuum and similarly a magnetic field. C is the inverse square root of those two multiplied. Nowadays those are considered simply part of defining the units one uses, with c more basic.

See in Wikipedia at https://en.m.wikipedia.org/wiki/Maxwell%27s_equations

In materials those are typically larger and the equivalent effective speed of light then goes down.

If ones of those were 0, or both, which makes no sense, infinite electric or magnetic fields would be induced in an electromagnetic wave and it would propagate infinitely fast, which of course makes no physical sense, only that's what Maxwells equations would lead to.

So in essence the speed of light is the best measure of how resistant the vacuum is to creating electromagnetic waves. Maybe this could represent your undefined viscosity, but it won't do anything to explain why c is what it is, and the fact that it is finite. It's that if it was infinite all effects in the universe would be instanataneous, there would be no localization.

  • $\begingroup$ Thanks. I think this will put me on the right track but I don't totally understand what you mean this wont explain why C is what it is? Anyway thanks again this helped me aim my perspective. Will leave question unanswered for just a juday or two in case of other potential feedback. Thinking in terms of permeability and permittivity is a better way of looking at this, I'll try to think of a better way to phrase my question without making your answer redundant lol $\endgroup$ Feb 26, 2017 at 4:07

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