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Old July 15th 18, 10:04 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Default Missing matter found in the cosmic web

In article , "Bruce D. Scott"
writes:

| "Dark energy" is really a stupid term, modelled on "dark matter" (which
| does make at least some kind of sense). Substitute "cosmological
| constant" as there is no evidence at all against the idea, and much for
| it, that "dark energy" is just the good old cosmological constant.
[...]

Yes, but can't they simply call it "vacuum energy" as in "vacuum"
displacement or polarisation when talking about eps_0 in EM?


As Jonathan noted, this makes an assumption about its origin.

(I confess to be a little motivated by Carlo Ovelli "Reality Is Not
What It Seems: The Journey to Quantum Gravity")


I'm reading that myself at the moment. :-)

[[Mod. note -- To clarify, the following 7 quoted lines were written
by me (Jonathan Thornburg), not Bruce D Scott. -- jt]]
(On the other hand... calling it "cosmological constant" is also
making an implicit statement that it's trully *constant*, i.e., that
it enters into the Einstein equations in a certain way, with NO terms
involving the spacetime derivatives of the "cosmological constant".
We don't know that, either. About all we know today is its average
value over the past 10^10-or-so years. We probably won't know much
about its time variation or lack thereof for another decade.)


True. On the other hand, there is no evidence that it is not constant,
and people have looked for such a deviation. Obviously, one can put
only upper limits on such deviations. The traditional cosmological
constant was there long before observations made it clear that it or
something like it actually exists. As long as a constant value fits the
data, there is no reason to assume otherwise, unless someone has a
really convincing theory (which should predict variation at some level
which could, at least in principle, be confirmed). However, one should
be open to a more complicated form, not repeating the mistakes of
assuming it is zero until forced otherwise by the data, as happened 30
or so year ago.