Tag Archives: Hubble Constant

“One of the greatest discoveries of the century is based on these things and we don’t even know what they are, really.”

The uncertainty of science: New research suggests that astronomers have little understanding of the supernovae that they use to estimate the distance to most galaxies, estimates they then used to discover dark energy as well as measure the universe’s expansion rate.

The exploding stars known as type Ia supernovae are so consistently bright that astronomers refer to them as standard candles — beacons that are used to measure vast cosmological distances. But these cosmic mileposts may not be so uniform. A new study finds evidence that the supernovae can arise by two different processes, adding to lingering suspicions that standard candles aren’t so standard after all.

The findings, which have been posted on the arXiv preprint server and accepted for publication in the Astrophysical Journal, could help astronomers to calibrate measurements of the Universe’s expansion. Tracking type Ia supernovae showed that the Universe is expanding at an ever-increasing rate, and helped to prove the existence of dark energy — advances that secured the 2011 Nobel Prize in Physics.

The fact that scientists don’t fully understand these cosmological tools is embarrassing, says the latest study’s lead author, Griffin Hosseinzadeh, an astronomer at the University of California, Santa Barbara. “One of the greatest discoveries of the century is based on these things and we don’t even know what they are, really.”

The key to understanding this situation is to maintain a healthy skepticism about any cosmological theory or discovery, no matter how enthusiastically touted by the press and astronomers. The good astronomers do not push these theories with great enthusiasm as they know the feet of clay on which they stand. The bad ones try to use the ignorant mainstream press to garner attention, and thus funding.

For the past two decades the good astronomers have been diligently checking and rechecking the data and the supernovae used to discover dark energy. Up to now this checking seems to still suggest the universe’s expansion is accelerating on large scales. At the same time, our knowledge of supernovae remains sketchy, and thus no one should assume we understand the universe’s expansion rate with any confidence.

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Expansion rate of the universe might not be accelerating

The uncertainty of science: A new review of the data suggests that the expansion of the universe might not be accelerating as posited based on research done in the 1990s.

Making use of a vastly increased data set – a catalogue of 740 Type Ia supernovae, more than ten times the original sample size – the researchers have found that the evidence for acceleration may be flimsier than previously thought, with the data being consistent with a constant rate of expansion.

The study is published in the Nature journal Scientific Reports.

Professor Sarkar, who also holds a position at the Niels Bohr Institute in Copenhagen, said: ‘The discovery of the accelerating expansion of the universe won the Nobel Prize, the Gruber Cosmology Prize, and the Breakthrough Prize in Fundamental Physics. It led to the widespread acceptance of the idea that the universe is dominated by “dark energy” that behaves like a cosmological constant – this is now the “standard model” of cosmology.

‘However, there now exists a much bigger database of supernovae on which to perform rigorous and detailed statistical analyses. We analysed the latest catalogue of 740 Type Ia supernovae – over ten times bigger than the original samples on which the discovery claim was based – and found that the evidence for accelerated expansion is, at most, what physicists call “3 sigma”. This is far short of the 5 sigma standard required to claim a discovery of fundamental significance.

I am not surprised. In fact, I remain continually skeptical about almost all cosmological theories. They might be the best we have, based on the facts available, but they are also based upon incredibly flimsy facts.

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Universe’s expansion rate contradicts dark energy data

The uncertainty of science: New measurements of the universe’s expansion rate, dubbed the Hubble constant, contradict theoretical predictions based on previous data.

For their latest paper, Riess’s team studied two types of standard candles in 18 galaxies using hundreds of hours of observing time on the Hubble Space Telescope. “We’ve been going gangbusters with this,” says Riess.

Their paper, which has been submitted to a journal and posted on the arXiv online repository on 6 April, reports that they measured the constant with an uncertainty of 2.4%, down from a previous best result2 of 3.3%. They find the speed of expansion to be about 8% faster than that predicted based on Planck data, says Riess. [emphasis mine]

I highlight the number of galaxies used to get this data because I think these scientists, are being a bit over-confident about the uncertainty of their data. The universe has untold trillions of galaxies. To say they have narrowed their uncertainty down to only 2.4% based on 18 is the height of silliness.

But then, the lead scientist, Adam Riess, recognizes this, as he is also quoted in the article saying “I think that there is something in the standard cosmological model that we don’t understand.”

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Using data from the Spitzer Space Telescope astronomers have narrowed the universe’s rate of expansion to about 74.3 kilometers per second per megaparsec.

The uncertainty of science: Using data from the Spitzer Space Telescope astronomers have narrowed the universe’s rate of expansion to about 74.3 kilometers per second per megaparsec.

The importance of this number, also called the Hubble Constant, is that it allows astronomers to extrapolate more precisely backward to when they believe the Big Bang occurred, about 13.7 billion years ago. It also is a crucial data point in their effort to understand dark energy, in which this expansion rate is actually accelerating on vast scales.

Back in 1995 a team led by Wendy Freedman, the same scientist leading the work above, announced that they had used the Hubble Space Telescope to determine the expansion rate as 80 kilometers per second per megaparsec. Then, the margin of error was plus or minus 17 kilometers. Now the margin of error has been narrowed to plus or minus 2.1 kilometers.

Do I believe these new numbers? No, not really. Science has nothing to do with belief. I do think this is good science, however, and that this new estimate of the Hubble constant is probably the best yet. I would also not be surprised if in the future new data eventually proves this estimate wrong.

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