

The Universe Might Be Expanding a Lot Slower Than We Thought - DiabloD3
http://motherboard.vice.com/read/the-universe-might-be-expanding-a-lot-slower-than-we-thought

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brittonsmith
To see what this means for the cosmological parameters, the best place to look
is Figure 15 of the journal article [1]. The effect of the distance bias
pushes for a higher value of Omega_M (the fraction of the energy density of
the universe in matter) and a lower value of w (a term which characterizes the
equation of state of dark energy). The currently accepted values for these two
parameters are roughly Omega_M = 0.3 and w = -1. If w = -1, it means that dark
energy is consistent with a cosmological constant, which is more-or-less the
simplest form of dark energy (not that we really know what it is). Going to w
< -1 is interesting because it means that the acceleration of the expansion of
the universe will itself also increase, resulting in a Big Rip. If these
findings are correct, it would mean the universe is more exotic than
previously thought.

Also, here is a nice discussion of the equation of state of dark energy:
[http://ned.ipac.caltech.edu/level5/March04/Carroll/Carroll4....](http://ned.ipac.caltech.edu/level5/March04/Carroll/Carroll4.html)

1 -
[http://arxiv.org/pdf/1408.1706v1.pdf](http://arxiv.org/pdf/1408.1706v1.pdf)

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raverbashing
This will probably reflect in a lower estimate to the amount of dark energy in
the universe, if it's confirmed

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scarygliders
I'm hoping this whole "dark energy" and "dark matter" thing will go away
entirely.

I highly suspect that both theories are the result of an "error cascade" \-
i.e. erroneous but at the time quite legitimate assumptions/thought/theory
made early on, subsequently create errors in later assumptions/thought/theory.

The article mentioned is a case in point.

I'm a layman when it comes to astronomy and maths with no formal
qualifications in astronomy - but I do like reading articles on the subject -
and to me, Something Is Not Quite Right about the concepts of dark energy or
dark matter

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antognini
I'm a graduate student in astronomy and I think it's extremely unlikely that
dark energy or dark matter will go away. The concern of an "error cascade" was
legitimate when these ideas were first proposed and many astronomers were
skeptical of both dark matter and dark energy for long while. But over time
there have been a number of independent lines of evidence pointing to the
existence of both dark matter and dark energy. It's possible some comedy of
errors could have lead to the spurious detection of dark matter or energy
through one of these measurements, but very unlikely that it would be mimicked
in other, independent measurements.

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GravityWell
Care to share some examples of dark energy evidence? If the evidence is a
measurement of expansion, then it doesn't necessarily support the existence of
dark energy.

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antognini
One of the other major pieces of evidence for the existence of dark energy is
the observation of baryon acoustic oscillations. The basic idea is that as the
universe was forming, there were concentrations of dark matter. Standing sound
waves of photons and baryons (ordinary matter) formed around these
concentrations. After decoupling, the photons streamed away, but the baryons
remained and eventually formed galaxies. This results in a characteristic
pattern seen on the sky, where there are clusters of galaxies observed, and
then rings of galaxies around them.

It is possible to calculate the physical size of these rings from first
principles. Since you observe how big these rings appear on the sky, you can
figure out how far away they are, and from this determine the expansion
history of the universe.

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vorg
> as the universe was forming, there were concentrations of dark matter.
> Standing sound waves of photons and baryons (ordinary matter) formed around
> these concentrations

You make it sound like "dark matter" is normal matter and the "ordinary
matter" is the abnormal stuff, since ordinary matter formed afterwards and has
more complex interactions in that it supplements gravitation with
electromagnetism and what not. And of course there's far more dark matter than
ordinary.

