April 13, 2015 | David F. Coppedge

Cosmic Ruler Flawed

Type 1a supernovae, vital to estimates of the size and expansion of the universe, are not uniform. This has cosmic implications.

A team from the University of Arizona has news of cosmic proportions. For many years, Type 1a supernovae have been considered “standard candles” at all distances. This allows astronomers to calculate cosmic distances, and in fact was used to deduce the accelerated expansion of the universe in the late 1990s that won three astronomers a Nobel Prize. Without a known cause for cosmic acceleration, astronomers have proposed some unknown kind of “dark energy” as the cause. All of this has relied on the assumption of uniformity of Type 1a supernovae (see 9/30/12, 3/15/08, and 11/01/06).

A UA press release now calls that assumption into question. Using data from the Swift satellite, which measures stars in ultraviolet light, the UA astronomers found that Type 1a’s fall into two classes. The nearest ones are redder than the more distant ones. Reporter Daniel Stolte titled his article, “Accelerating universe? Not so fast.”

“Since nobody realized that before, all these supernovae were thrown in the same barrel. But if you were to look at 10 of them nearby, those 10 are going to be redder on average than a sample of 10 faraway supernovae.”

The authors conclude that some of the reported acceleration of the universe can be explained by color differences between the two groups of supernovae, leaving less acceleration than initially reported. This would, in turn, require less dark energy than currently assumed.

The team is unable to put a number on how much the figures will need to be adjusted, saying further work is needed. Meanwhile, though, another mission is seeking to measure dark energy if it exists. The DESI spectroscope (Dark Energy Spectroscopic Instrument) will be fit at the prime focus of the Mayall 4-meter telescope at Kitt Peak (see photo) to measure 30 million galaxies’ worth of the universe in 3-D.

 

Mayall Telescope at Kitt Peak

Kitt Peak Mayall Telescope, c. David Coppedge

PhysOrg reports on the instrument built at University of Michigan:

Cosmologists suspect a mysterious property called dark energy. Although it is thought to comprise 75 percent of the universe, its nature and the physics behind it are still mysteries.

DESI will create a high-definition, 3-D map of a swath of the universe going back 10 billion light-years. By exploring how structure in the universe has evolved through time, scientists hope to uncover the tug-of-war between the forces of gravity and dark energy.

The UM astronomers need to talk to the UA astronomers.

If you win a Nobel Prize for a false conclusion, do you have to give the money back?

Note once again how assumptions play crucial roles in models that try to understand observations. Perhaps dark energy is real, though less than expected. There’s an outside chance though, if supernova populations are not as uniform as even the UA astronomers believe, that there is no dark energy at all.  This should be a lesson in assumptions and unknowns in science. Conclusions in theory are only tentative. They can always be overthrown by later findings.

 

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Comments

  • tjguy says:

    On Fox News today, there is an article about the asteroid collision that is said to have caused the dinosaurs to go extinct 65 million years ago. They are planning on taking a core sample from the crater to see if their models are accurate. Here is how they worded it:

    “Scientists think that, when a big rock smashes into Earth at high enough velocities, the collision causes the crust temporarily to act sort of like a liquid, first forming a so-called transient crater (like the indentation that forms on a lake surface after a rock is thrown in), and the center rebounds, or splashes, upward and then outward. “We think the peak ring is the record of the material that rebounded and splashed outward,” Gulick told Live Science.

    [Noticed what the article says next!]

    ALL OF THESE IDEAS ARE BASED ON MODELS AND AREN’T NECESSARILY WHAT HAPPENED. “We’ve never gotten a rock back from a peak ring to know if that’s correct,” Gulick said.”

    So, although their ideas are based on “models”, – which gives a scientific sounding authoritative ring to it, as the above article points out, it is really nothing more than a hypothesis that has not yet been tested.

    Often times, these hypotheses cannot be tested so they have no option but to choose what they think is the best model/assumption/belief/hypothesis and build their theories on top of it. How many of our current “models” are untested and possibly wrong?

  • St-Wolfen says:

    As we have seen so many times here in these pages, when a model or theory supporting evolution is rigourously tested, it is found to be false, or worse, it supports the creation account.

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