[♪ INTRO]
Maybe you’ve seen some of the headlines
over the last week or so:
“Mystery ‘dark fluid’ could make up 95% of the universe.”
“We might have finally discovered where
the missing 95% of the universe is.”
They’re referring to a paper published last
week in Astronomy & Astrophysics,
where a postdoctoral fellow from Oxford
proposed a hypothesis that identified
95% of the missing stuff in the universe.
According to the author, Jamie Farnes, the
missing stuff in question takes the form of
a fluid with quote-unquote “negative gravity,”
which permeates all of space.
And his work is based on the combination of
two older ideas in physics.
But that’s the thing: these are all just
ideas, nowhere close to proven theories.
And some of the coverage has been a little,
you know, over-hyped.
So here’s what the paper actually argues,
and how likely it really is.
Our current understanding of the universe
says that only about 5% of everything is the
stuff we can actually see, including regular
matter and light.
Another 26% is matter we can’t directly
observe; what we call dark matter,
which is not so much “dark” as “invisible.”
The other 69% or so is made up of dark energy,
which is basically the biggest mystery
cosmology has to solve at the moment.
All we really know is it’s a sort of pressure
that keeps the collapsing power of gravity
at bay, and even overpowers it on an intergalactic scale.
Right now, dark energy is making the universe’s
expansion accelerate.
Cosmologists have spent the past several decades
trying to figure out what either or
both of these actually are.
Sometimes it feels like they’re just throwing
ideas at a wall and waiting to see what sticks.
Or, rather, what the observed data don’t
contradict.
This new hypothesis claims to not just explain
what dark matter or dark energy is.
It tries to unite them both into a single
substance, called a “negative mass fluid,”
or “dark fluid,” which would be everywhere,
with more of it being generated all the time.
The idea incorporates two older, also-hypothetical
concepts: negative mass and matter creation.
Negative mass is basically like the gravity
version of a negative electrical charge.
As far as we know, there’s no reason it
shouldn’t exist,
we’ve just never seen any outside of special lab experiments.
As this new paper explains it, positive mass
attracts positive mass,
what we’re used to seeing from gravity.
On the other hand, if you pushed something
with negative mass away,
it would actually move toward you.
But Farnes also claims that two negative mass
particles should repel one another, which
runs totally counter to the established rules of general relativity,
the physics that governs much of the universe.
That’s one obvious problem some cosmologists
have with this hypothesis, especially because
Farnes put the repulsion idea in there because
he thought it made sense,
rather than getting it from mathematical equations.
But it’s a fundamental change that this
whole new model depends on,
so we’re just gonna have to take it as-is, for the moment.
Physicists have dismissed negative mass as
a potential dark energy candidate because
as far as we can tell, the density of dark
energy stays constant as the universe expands,
whereas the density of negative mass would
go down as it spread out.
So Farnes’ hypothesis includes matter creation:
the idea that this negative matter is continuously
created throughout the universe, keeping its
density constant.
This is actually an idea that early 20th-century
astronomers invoked for positive mass to
argue that the universe had an infinite
age and was always the same size,
meaning it didn’t start with the Big Bang.
Matter creation doesn’t jibe with observations,
though.
So Farnes only allows it for negative mass,
not for the regular positive stuff, and suggests
we could find evidence of it using future
telescopes that will map out the distribution
and movement of galaxies through the history
of the universe.
All together, he argues it’s a sensible
hypothesis because it simplifies two mysteries
into one, and introduces some mathematically
attractive symmetry to the matter in our universe.
But is all the regular matter out there really
just a bunch of rubber ducks floating along
in a universe-sized ocean of “dark fluid”?
I mean, it’s way too soon to declare an
answer to that question, but naturally, many
cosmologists have arguments against this proposal.
One problem is that if the vacuum of space
were capable of spontaneously generating negative
mass, quantum mechanics would dictate that
it, and therefore everything,
would become really unstable.
That doesn’t seem to have happened.
Then there’s the lack of evidence for matter
creation.
But one of the biggest problems with this
whole situation is that the published press release
failed to emphasize how preliminary it is,
and then some media outlets
just kind of ran with the hype.
Farnes has taken issue with that overhyping,
too, but then again,
he wrote a similar article himself.
Maybe this paper is onto something, and we
really do need to investigate the idea that
dark matter and dark energy are a single fluid
with negative mass.
But when you’re working with the biggest
mysteries of the universe, the answers are
never solved by a single piece of research.
Thanks for watching this episode
of SciShow Space News,
and thanks especially to our community
on Patreon for your support.
Because of you, we’re able to explore complicated
cosmology like this, and spread scientific
literacy and a passion for science with anyone
who wants to learn.
If you’re not yet a patron and want to learn
more about how you can join us,
just check out patreon.com/scishow.
[♪ OUTRO]
