What is the methodology for concluding accelerated expansion?

[Cosmo_Ken]

I saw an article on the internet within the past week about a scientific paper that was published on November 22 in the Astrophysical Journal by Swiss astrophysicist André Maeder, raising the question does Dark Matter really exist and proposing an alternative theory to fit the observations, interesting, see:

https://www.space.com/39001-dark-matter-doesnt-exist-study-suggests.html?utm_source=sdc-newsletter&utm_medium=email&utm_campaign=20171208-sdc

And on the subject of Dark Energy, is it real or is there something fundamentally wrong with the assumptions.  What was the exact methodology that the astronomers used to conclude that the expansion of the universe is accelerating, not slowing down?

[Strange]

There was some discussion of this already: http://www.scienceforums.net/topic/111856-no-dark-matter-and-dark-energy-needed/

 

 

[swansont]

2 hours ago, Cosmo_Ken said:

 And on the subject of Dark Energy, is it real or is there something fundamentally wrong with the assumptions.  What was the exact methodology that the astronomers used to conclude that the expansion of the universe is accelerating, not slowing down?

!

Moderator Note

This thread will remain open to discuss this question. The Maeder paper can be discussed in the other thread, that Strange has linked to above.

 

Thread title edited to reflect this.

 

[mathematic]

An overly simplified description of the methodology.  The distance to far away galaxies can be measured two ways, red shift or standard candles (1A supernovae).  The distances didn't match when assuming a uniform or slowing down expansion.  They matched for speeding up.

[Strange]

There is a bit more detail on the Wikipedia page: https://en.wikipedia.org/wiki/Dark_energy#Evidence_of_existence

Note that the original work has been confirmed with much larger samples of supernovae.

[Mordred]

A key methodology that doesn't rely on distance measurements is the thermal history. As the universe expands it also cools down

[T. McGrath]

The original 1998 paper that paved the way for the existence of Dark Energy set out to calculate how quickly the universe was slowing down.  They were not expecting the results that they got.  Using 30 Type Ia SNe observed at z = 0.5 and 10 Type Ia SNe observed at z = 1.0 they erroneously assumed all Type Ia SNe had the exact same absolute magnitude of -19.46.  We have since discovered not only a whole new class of very dim Type Ia SNe (known as Type Iax SNe) that range between -14.2 and -18.9 absolute magnitude, but also superluminous Type Ia SNe with absolute magnitudes exceeding -20.  The "Standard Candle" they thought they had in the 1990s proved to be not so standard after all.

At the very least it brings into question the SNe data that was used to calculate the age and acceleration of the universe.  Edwin Hubble made the exact same mistake in 1927 when he used Cepheid variables as his "Standard Candle" and erroneously calculated that the universe was only ~2 billion years old.

Just as a side note:  I find it rather difficult to comprehend why people have no problem accepting the fact that we have confirmed the existence of exoplanets based upon the gravitational effects the exoplanet has on its parent star (without ever seeing the actual exoplanet), but they have difficulty accepting the existence of Dark Matter even when it is those very same gravitational effects that tell us something must exist.  Very odd.

Sources:
The High-Z Supernova Search: Measuring Cosmic Deceleration and Global Curvature of the Universe Using Type Ia Supernovae - The Astrophysical Journal, Volume 507, Number 1, 1998 (free preprint)
Type Iax Supernovae: A New Class of Stellar Explosion - The Astrophysical Journal, Volume 767, Number 1, March 2013
Analytical Expressions for Light Curves of Ordinary & Superluminous Type Ia Supernovae - The Astrophysical Journal, Volume 809, Number 1, 2015
Hydrogen-Poor Superluminous Stellar Explosions - Nature 474, 487-489, June 2011 (free preprint)

 

Edited December 14, 2017 by T. McGrath