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astronomy Cosmology Physics

Now the expansion of the universe is not accelerating

In 2011 the Nobel Prize in Physics was awarded to three astronomers for their discovery, as part of two separate teams which published their results around 1998 that they claimed showed that the Universe is expanding at an accelerating rate. Also they claimed the existence of some sort of mysterious ‘dark energy’ that was driving the expansion at a faster and faster rate.

Hubble image of supernova remnant N 49 in the Large Magellanic Cloud. Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Hubble image of supernova remnant N 49 in the Large Magellanic Cloud. Credit: NASA and The Hubble Heritage Team (STScI/AURA)

The interpretation of the 1998 data depended heavily on the big bang cosmological theory they applied and the assumption that it was the correct theory to describe the structure and time evolution of the Universe. It also depended heavily on the assumption that the type Ia supernova explosions that they used are reliable standard “light bulbs”, i.e. that those stellar explosions all were accurately chosen to have the same characteristic intrinsic absolute brightness.1 The latter, however, we now know is not the case.2

It has been shown that the stellar masses of the stars that result in the type Ia class of supernova are not so well-defined that they all fall within a narrow range as to give a clear standard in terms of the intrinsic brightness of the resulting explosions and hence the type Ia are not a uniform reference. Also as I have previously indicated circular reasoning was employed in the choice of the candidate supernova to be considered.2,3 The cosmology under test was used to choose the candidate Ia supernovae and then those chosen were used to test the same cosmology.

A new study, published in the Nature journal Scientific Reports, on a data set ten times larger than the original studies used (5 years ago) has been carried out.4

Now, a team of scientists led by Professor Subir Sarkar of Oxford University’s Department of Physics has cast doubt on this standard cosmological concept. 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. (emphasis added)

Categories
astronomy Cosmology Physics

Is the Universe really expanding — the evidence revisited

3d expansion question markThe Hubble law, determined from the distances and redshifts of galaxies, for the past 80 years, has been used as strong evidence for an expanding universe. In 2011 I reviewed various lines of evidence for and against this claim. It included the lack of evidence for the necessary existence of time dilation in quasar and gamma-ray burst luminosity variations, angular size tests for galaxies as a function of redshift, the Tolman surface brightness test which is sensitive to expansion of the Universe, evidence that the CMB radiation is not from the background, which it should be if from the big bang fireball as alleged, intergalactic absorption lines due to hydrogen clouds and Lyman-α systems, and what they do tell us. Here I present that information again in light of my current understanding.

This review concluded that the observations could be used to describe either a static universe (where the Hubble law results from some as-yet-unknown mechanism) or an expanding universe described by the standard Λ cold-dark-matter model. In the latter case, the imposition of size evolution of galaxies is necessary to get agreement with observations. Yet the simple non-expanding (i.e. static) Euclidean universe fits most data with the least number of assumptions. I made a straw table comparison with the various lines of evidence to see how they stack up. It was found not to be definitive and hence the result equivocal. From this review it became quite apparent that there are still many unanswered questions in cosmology and it would be a mistake to base one’s theology on any particular cosmology. Far better to base you cosmology and theology on the clear narrative historical prescription in the Genesis account and elsewhere in the Scriptures. (This was first published in two parts in the Journal of Creation 25(3):109-120, 2011.)

Introduction

Ever since the late 1920s, when Edwin Hubble discovered a simple proportionality1 between the redshifts of the light coming from nearby galaxies and their distances, we have been told that the Universe is expanding. This relationship—dubbed the Hubble Law—has since been strengthened and extended to very great distances in the cosmos. Nowadays it is considered to be the established dogma of the expanding big bang universe. This means that the space that contains the galaxies is expanding and that the galaxies are essentially stationary in that space, but being dragged apart as the universe expands.

Hubble initially interpreted his redshifts as a Doppler effect, due to the motion of the galaxies as they rushed away from our location in the Universe. He called it a ‘Doppler effect’ as though the galaxies were moving ‘through space’—the space itself is not expanding but the galaxies are moving through space, and that is how some people, especially astronomers, initially perceived it. This is different to what has now become accepted, but observations alone cannot distinguish between the two concepts. Later in his life Hubble varied from his initial interpretation and said that the Hubble Law was due to some hitherto undiscovered mechanism, but not due to expansion of space—now called cosmological expansion.

The big bang expanding universe model essentially offers a coherent paradigm or explanatory framework which can, in principle, provide answers to a wide range of key cosmological questions; examples are the origin of extragalactic redshifts, the dynamical state of the Universe (i.e. not apparently collapsing under gravity), Olbers’ paradox (why is the night sky dark?), the origin of the cosmic microwave background (CMB) radiation, the origin of galaxies, and the origin of the elements. The fact that its answers to some questions are currently unsatisfactory or unconvincing does not change the basic point that such a model will always be preferred to a more limited model such as a static Euclidean universe, which does not attempt to address such questions. In this sense the big bang model is necessarily preferable regardless of one’s theological position.

Categories
astronomy Cosmology Physics

Accelerating Universe: Standard ‘light bulbs’ not so standard

I once wrote about one of the problems of determining distance using the so-called standard ‘candle’ of the type Ia supernovae.1  That method is considered to be the gold standard in cosmic distance determination and hence in testing of the expanding universe paradigm. From those measurements, by two independent teams, an accelerating expansion of the Universe was claimed in 1998, for which the Nobel Prize in Physics was awarded in 2011.

That same galaxy in a NASA Swift image is shown, with bars indicating the location of supernova SN 2011fe. The Swift image is a false-color image with UV emission blue and optical emission red. Credit: NASA/Swift
An optical image of the galaxy M101, with bars indicating the location of supernova SN 2011fe. This NASA/Swift image is a false-color image with UV emission shown in blue and optical emission shown in red. Credit: NASA/Swift

Type Ia supernova were (are) believed to be a class of stellar explosions that resulted from progenitor stars with a very small range of masses and chemical properties. It was (is) believed that these could be accurately modelled and therefore they could be relied upon to produce the same intrinsic brightness in their explosions. It was believed therefore that they varied only by a very small degree in a distribution around a well established intrinsic brightness or absolute magnitude near MB ~ -19. That means they were believed to all have the same intrinsic brightness.