The Universe Might Be Expanding a Lot Slower Than We Thought | Hacker News Reader

The Universe Might Be Expanding a Lot Slower Than We Thought

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26 pointsDiabloD315 comments

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....

1 - http://arxiv.org/pdf/1408.1706v1.pdf

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

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

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.

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.

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.

> 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.

https://medium.com/starts-with-a-bang/five-reasons-we-think-...

While I'm not an astronomer, I think observations such as the the Bullet Cluster and the different position s for where the mass seems to be - including big changes in morphology, not just location - clearly indicates that something dark matter/energy-like must exist. The precise nature of this DM/DE is an a separate question.

I'm hopeful too, though I don't have any theories myself about how both ideas could be wrong, as I'm also just a layman. I do justify my hopes by pointing to Luca Lusanna's work[0], though, because I don't believe in using "Something Is Not Quite Right" feelings when it comes to physics, as quantum electrodynamics can initially have that feeling too but it's very well supported experimentally and I think one can get used to it.

[0] I've been vaguely aware of Lusanna (http://arxiv.org/find/all/1/au:+Lusanna_L/0/1/0/all/0/1) for some number of years now, who has an interesting (and mostly unintelligible to me as I'm sadly not familiar enough with conformal geometry nor most of the relevant physics) set of papers suggesting dark matter be thought of as a Relativistic Inertial Effect.

Since 'gravity of the universe' doesn't exist (because there is no center of mass of the universe) also its alleged counterpart 'dark energy' makes no sense. I described it in my article http://goo.gl/uQNo5L and in two PDF (links in the subtitle there).

Space itself expanding, ie inflation, doesn't require the universe to have a center of mass.

Exactly. Thanks for your affirmation. .. And space itself expanding doesn't require 'dark energy' and has nothing to do with momentum, acceleration etc.

> spdustin That's the uncertain part of the question. It's the same when you ask Does time require a force that drives it forward? The answer is We don't know yet. -- The certain part of the question is: scaling of space (in cosmic scale) can't be accelerated by 'dark energy' nor slowed down by gravity. It's not about mass, energy, momentum etc. - I really described it in my paper (see post above).

I had understood that time is a side effect of entropy.

Can you expand on why you believe that the expansion of space itself requires no energy?

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