Astronomers Probe Origin of Planet 9 --"Captured By Our Sun?" (WATCH Today's 'Galaxy' Stream)
Strange Pitch-Black Exoplanet Observed by Hubble Space Telescope

"Acceleration of Our Universe May Not Be Real" --Royal Astronomical Society

 
Dark-energy-depiction

 

The accelerating expansion of the Universe may not be real, but could just be an apparent effect, according to new research published in the journal Monthly Notices of the Royal Astronomical Society. A new study—by a group at the University of Canterbury in Christchurch, New Zealand—finds the fit of Type Ia supernovae to a model universe with no dark energy to be very slightly better than the fit to the standard dark energy model.

Dark energy is usually assumed to form roughly 70% of the present material content of the Universe. However, this mysterious quantity is essentially a place-holder for unknown physics.

 

Current models of the Universe require this dark energy term (image above) to explain the observed acceleration in the rate at which the Universe is expanding. Scientists base this conclusion on measurements of the distances to supernova explosions in distant galaxies, which appear to be farther away than they should be if the Universe's expansion were not accelerating.

 However, just how statistically significant this signature of cosmic acceleration is has been hotly debated in the past year. The previous debate pitted the standard Lambda Cold Dark Matter (ΛCDM) cosmology against an empty universe whose expansion neither accelerates nor decelerates. Both of these models though assume a simplified 100 year old cosmic expansion law—Friedmann's equation.

Friedmann's equation assumes an expansion identical to that of a featureless soup, with no complicating structure. However, the present Universe actually contains a complex cosmic web of galaxy clusters in sheets and filaments that surround and thread vast empty voids.

In the graphic below, the difference in the magnitudes of supernovae in the ΛCDM and Timescape cosmologies and the magnitudes the supernovae would appear to have in an empty universe (horizontal dashed line). Both models show recent apparent acceleration following earlier deceleration. In the Timescape model this is not a real effect, however, and the curve is flatter than the ΛCDM case. (Lawrence Dam, Asta Heinesen and David Wiltshire).

 

Newsupernova


David Wiltshire, who led the study from the University of Canterbury in Christchurch, said, "The past debate missed an essential point; if dark energy does not exist then a likely alternative is that the average expansion law does not follow Friedmann's equation."

Rather than comparing the standard ΛCDM cosmological model with an empty universe, the new study compares the fit of supernova data in ΛCDM to a different model, called the 'timescape cosmology'. This has no dark energy. Instead, clocks carried by observers in galaxies differ from the clock that best describes average expansion once the lumpiness of structure in the Universe becomes significant. Whether or not one infers accelerating expansion then depends crucially on the clock used.

The timescape cosmology was found to give a slightly better fit to the largest supernova data catalogue than the ΛCDM cosmology. Unfortunately the statistical evidence is not yet strong enough to rule definitively in favour of one model or the other, but future missions such as the European Space Agency's Euclid satellite will have the power to distinguish between the standard cosmology and other models, and help scientists to decide whether dark energy is real or not.

Deciding that not only requires more data, but also better understanding properties of supernovae which currently limit the precision with which they can be used to measure distances. On that score, the new study shows significant unexpected effects which are missed if only one expansion law is applied. Consequently, even as a toy model the timescape cosmology provides a powerful tool to test our current understanding, and casts new light on our most profound cosmic questions.

The Daily Galaxy via Royal Astronomical Society

 

Comments

Whoa?? whats that you say? There is no need at all for dark energy... Well now I guess that would mean there is no need at all for dark matter....

Wow, I have been saying the exact same thing for years and years now....

I guess sometimes it takes the really smart scientists to catch up with those that can look at something and clearly state the obvious.

"... just how statistically significant this signature of cosmic acceleration is has been hotly debated in the past year...". Am curious as to the statics numbers.

"Dark energy is usually assumed to form roughly 70% of the present material content of the Universe. However, this mysterious quantity is essentially a place-holder for unknown physics."

That's not really true. The current data is well fitted by a cosmological constant (the Lambda in Lambda CDM), which is entirely standard General Relativity.

Threshold filter for evaluating potential signal sources was set at S/N 5.5. Full statistical treat based on Fourier Transform analysis is at [http://iopscience.iop.org/article/10.1088/1538-3873/128/969/114201].

Oh hey LOOK - the first comment - a couch scientist! Bill, might you present your hypothesis (just as this is from actual scientists) and provide your research evidence that you worked on that helped you to reach this conclusion - as Daily Galaxy shared from these actual 'paid to be' scientists?

No? Just a 'gut feeling' you got from reading something online that seemed to 'jive' with how you 'felt' things were?

Yah, go back to the 1400's with that shit..

wow, just wow. that's something unexpectable. "Dark energy is usually assumed to form roughly 70% of the present material content of the Universe. However, this mysterious quantity is essentially a place-holder for unknown physics."
it actually left me confused. is this something to be real?

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Working...
Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.

Working...

Post a comment

Your Information

(Name is required. Email address will not be displayed with the comment.)