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Supernovae May Not Be Standard Candles; Is Dark Energy All Wrong?
StartsWithABang writes: The accelerated expansion of the Universe — and hence, dark energy — was discovered by taking the well-understood phenomenon of type Ia supernovae and measuring them out to great distances. The results indicated that they were fainter than expected, and hence more distant, and hence the Universe's expansion must be accelerating. But new results have just come out, showing that supernovae may not be standard after all. Does this mean dark energy may not be real, or that it may just be slightly weaker than we previously thought?
"We" being nutcases, right?
No, the aether doesn't exist. If you're going to claim "the vacuum of empty space is the aether", then you'd be just as well calling it the FSM, and then claiming the same thing. Words are supposed to mean something. If you're gong to use a private language definition of the word, please stop talking to anyone.
According to Ethan Siegel, dark energy isn't written off, we just know a bit more about it.
"Money is a sign of poverty." - Iain Banks
On the internet, apparent aether refers to whatever people want when they want to sound disparaging about a particular idea they don't like. Within physics, it pretty specifically refers to a medium for electromagnetic waves, that for most of its versions in history was a fluid of some type. If people on the internet want to redefine it to mean anything permeating space so they can treat things like dark energy, they should at least be consistent then and acknowledge things like gravity and wavefunctions that also permeate space, among a whole bunch of other physics concepts. In that sense, we've known the "aether" to be real since components of Maxwell's equations started coming together with ever present electric and magnetic fields.
We've got the hubble expansion and cosmic background. Both of which point strongly towards an expanding universe with a point-like origin. Cosmologists hotly debate a lot of the details, but their agreement on the fundamentals is near-unanimous.
The summary has a link to a paywalled article (silly Ethan). The full article is freely available to all on the arXiv preprint server:
http://arxiv.org/abs/1408.1706
I'm peripherally involved with the supernova field, though I study only the nearby examples. There has been for years the understanding that IF a difference should arise between the nearby events that we can study well, and the distant events which appear dimly and vaguely, AND if we did not realize that such a difference existed, THEN we could reach incorrect conclusions.
Scientists in the field have worried about this for years. It's not a sudden new realization.
It's very pleasant to see that a space telescope -- SWIFT -- which was built to study one type of object (gamma ray bursts) has turned out to provide vital information on a different type (supernovae). Since it is in space, it can detect ultraviolet light, and so show us that some nearby supernovae emit different amounts of ultraviolet light, even though they appear similar in the optical region. This UV difference hints at differences in chemical composition between supernovae, which may indeed be significant when we try to study very distant events with other telescopes.
Fortunately, light from those distant events is redshifted into the optical regime, so we can use very large ground-based telescopes to see the same UV light and compare it to the nearby events.
It's a very interesting field to follow: things change on timescales of 3-5 years. And yes, we are more aware of the uncertainties in the business than some news articles might imply.
Michael Richmond "This is the heart that broke my finger."
mwrsps@rit.edu http://stupendous.rit.edu
*If* this result holds up, it doesn't sink dark energy - it will only be a small correction to the measured value using this particular probe. We have multiple, independent measurements of the existence of dark energy, from the early-universe Cosmic Microwave Background, to the late-universe feature in the galaxy distribution called the Baryon Acoustic Oscillation. In fact, for quite a few years supernova haven't been the principle method of measuring dark energy, because we've suspected issues such as this.
*If* this result hold up, and corrected measurements of dark energy from supernovae are in tension is all other measurements, then that will be interesting and require further study. However, despite having the confirmation of the existence of dark energy for several years, we haven't measured its exact properties very well yet. These corrections will probably shift things around inside known error bars.
For all the aether-claimers: we don't know what dark energy is. We've observed an acceleration to the expansion of the universe and called it "dark energy". This is a name given to an observed phenomena. The Nobel Prize was awarded to the original supernovae groups because it has been *repeatedly, independently* verified, using completely different sets of cosmological probes. This is like observing and measuring the observational reality of gravity without having a theory to explain it, but that doesn't mean that gravity doesn't exist.
You and whoever modded you up apparently don't have much exposure to the cosmology research community then. Both at conferences and local seminars, there seems to be a 1:1:1 split between talks on working out consequences of established theories, detailed checks of established theories against observation including assumptions they are based on, and people throwing out new ideas. I've seen plenty of talks in papers in the latter two groups with less data backing them up than this paper getting published, so I don't see what should be surprising about something like this one.
Dark energy can also be measured from the CMB radiation, through the angular size of anisotropies and through baryonic acoustic oscillations in the large scale structure.
And the constraints from these *independent* probes are consistent with the results from supernovae, all pointing to the presence of an acceleration of the universe at late times. It is not so that we rely on a single tool here!
Also, TFA states that their finding that a different class of supernova is dominant at high redshift does not attack the presence of dark energy, only its exact value (of energy density).
NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
The aether theories made some specific predictions, and even after several revisions to that, every single one was found to disagree with observation. Even if you attempt to rebrand some different new concept as an aether theory, that is just a semantics trick and doesn't change that original set of theories were found wrong.