Is dark energy
related to
gravitational
waves?
Gravitational waves need to be
dense and very fast to create
ripples in spacetime we can
measure. The kind of objects
we are capable of detecting,
are colliding black holes.
Scientists looked to see if black
holes are dark matter, but
black holes are collapsed stars,
so essentially atoms. Very
good evidence from our
understanding of formation
chemical elements from the
early Universe suggest that
dark matter is not made of
atoms.
So long story short, if black
holes were dark matter, the
black holes would have to be
primordial black holes. This is
an issue, because the amount
of matter that these black
holes would have would
probably not have escaped our
notice.
We just need to keep testing
and disproving theories.
Is the acceleration of
gravities the only
evidence for dark
energy?
Not entirely, evidence comes
from range of sources. We only
see its effect on something we
can observe. For example, dark
energy slows down collapse of
structures such as stars, pulling
it apart as gravity pulls it
together.
https://cosmosmagazine.com/society/improbable-feats-and-
useless-discoveries-a-public-lecture
So, it’s almost an
anti-gravity?
Yes, in a way. It has its origins
in sci-fi. Michael Turner and his
colleagues back in ‘91 thought
‘Oh we’ll call it dark energy’.
They even wrote a paper on
phantom energy, something
even more influenced by Star
Wars Episode 1 coming out.
So anti-gravity would be a
good a name as any. The
effect of it is basically anti-
gravity. Our best guess of
what it is, is a manifestation of
the natural energy scale of the
vacuum of empty space, which
in quantum physics isn’t
actually empty, but rather a
sea of virtual particles
popping in and out of
existence; Not for very long,
the more energetic a particle
is, the less time it would take
for the Universe to notice and
the uncertainty principle to
say, ‘Oh no you can’t last any
longer than that’.
But somehow this is sticking
around. The universe finds a
way to keep these quantum
fluctuations going and pulling
everything apart.
How can dark
energy explain the
accelerating of the
Universe, if there is
no dark energy
appearing…?
I’ll stop you there. It is. There is
a term appearing in Einstein’s
equations, a cosmological
constant relating to the vacuum
of empty space. He thought he
needed the term to keep the
universe static, but it turns out it
isn’t static. He later said this
term might be his biggest
blunder. This constant and an
expanding universe may coexist,
but the constant cannot be the
same value. Instead, it can
represent an energy density. If
the universe gets bigger, to
keep energy density constant,
energy is created.
If space expands, vacuum
energy associated with that
space is created. That is
essentially dark energy. The old
idea that energy cannot be
created and destroyed doesn’t
really work in a quantum sense.
That idea is Newton’s view of
physics within a closed system
and really when you’re looking
at an expanding universe, you
can’t explain things in those
terms.