From A Storehouse of Knowledge

The Big Bang is the currently-popular theory that the universe began in a very dense, hot state, and has expanded and consequently cooled through the continual creation of new space between its particles. The remnant of the original "flash" of the Big Bang is now identified by supporters with a cold microwave hum- known as the cosmic microwave background or CMB - corresponding to a black body radiating at a temperature of 2.7 degrees above absolute zero. This radiation, as well as Edwin Hubble's discovery that galaxies appear to recede from us at velocities proportional to their distance, are the two chief discoveries that support the Big Bang theory. Additional and independent evidence is seen in the relative abundances of the isotopes of hydrogen, helium, and lithium, and in the large scale distribution and apparent evolution of galaxies.^[Fact?] Especially detailed are the measurements of the fluctuations of the cosmic microwave background radiation, whose complex spectrum can be very well fit within the Big Bang model using only a few free parameters.^[Fact?]

Contents 1 Limitations 2 Timeline 3 Alternatives 3.1 Quasi-steady state 3.2 Halton Arp's proposal 3.3 Cosmological General Relativity 4 References

Limitations

The Big Bang is a theory of how space changes over time given its contents. In its most general form it does not specify what those contents are. One component is ordinary matter and radiation, whose properties are well-known from laboratory experiments.

Another component, known as dark matter, is modeled as particles that interact through gravitation but in no other way. These particles have never been observed in the laboratory, possibly on account of their weak interactions or large mass, nor is there any theoretical consensus on what they should be. Nevertheless, proponents claim that something of this sort is required to explain gravitational lensing and the motions of stars in galaxies and galaxies in clusters, independent of the Big Bang theory. The leading alternative theory to dark matter is Modified Newtonian Dynamics (MOND), which is able to model some of the observations, especially the galactic rotation curves.

To explain a variety of observations from supernovae to the flatness of space and details of structure formation, a third component, known as dark energy, has become widely accepted in the last ten years, although its characteristics are even more mysterious than those of dark matter. It is most simply modeled as a cosmological constant, essentially a constant energy density of the vacuum, but there are a number of alternative ideas. In most cases there is not enough observational evidence to rule out these proposals.

Critics describe both dark matter and dark energy as "fudge factors" required to make the Big Bang work^[1] and see other explanations (see below) as being viable alternatives.

Timeline

The current Big Bang theory begins just after the beginning of the universe. In the words of Brian Greene,

A common misconception is that the big bang provides a theory of cosmic origins. It doesn't. The big bang is a theory ... that delineates cosmic evolution from a split second after whatever happened to bring the universe into existence, but it says nothing at all about time zero itself. And since, according to the big bang theory, the bang is what is supposed to have happened at the beginning, the big bang leaves out the bang. It tells us nothing about what banged, why it banged, how it banged, or, frankly, whether it really banged at all.^[2]

There are a number of highly speculative theories about the origin of the state of the universe that expanded in the Big Bang. Some of the currently popular theories propose that uncountable new universes are constantly bing created, perhaps with different laws of physics, or even different numbers of dimensions.

• Up to 10^–43 seconds - Planck epoch, unknown physics because gravitation and quantum mechanics are not compatible at this energy
• Between 10^–36 seconds and 10^–32 seconds - inflationary epoch
• Between 3 minutes and 20 minutes - nucleosynthesis
• 377,000 years - "recombination", the origin of the cosmic microwave background
• 150 million to 1 billion years - the first structures (quasars and stars) form from gravitational collapse
• 8 billion years - formation of our Solar System
• 13.7 billion years - today

Alternatives

The Big Bang has been criticised by a number of cosmologists, both on grounds of the evidence and because dissent is stifled. A number of these cosmologists wrote a letter complaining about alternative views being suppressed, but could only get it published—in New Scientist—as a paid advertisement.^[3] The letter^[1] started as follows:

The big bang today relies on a growing number of hypothetical entities—things that we have never observed. Inflation, dark matter and dark energy are the most prominent examples. Without them, there would be a fatal contradiction between the observations made by astronomers and the predictions of the big bang theory. In no other field of physics would this continual recourse to new hypothetical objects be accepted as a way of bridging the gap between theory and observation. It would, at the least, raise serious questions about the validity of the underlying theory. But the big bang theory can’t survive without these fudge factors.

The letter was signed by 30 scientists, with more adding their support later.

Various alternative cosmologies have been put forward.

Quasi-steady state

The Quasi-Steady State model is the successor to the Steady State model proposed in 1948 by Bondi, Gold, and Hoyle. The Steady State model was based not only on the assumptions that the universe looked the same in every direction and from every point within the universe, but also at any point in time. As the universe was expanding, this meant that new matter had to be continually created as the universe expanded.

However, the discovery of the cosmic microwave background radiation (CMBR) appeared to favour the Big Bang model, so the Steady State model lost favour. Hoyle didn't give up on the idea, though, and about 20 years later proposed a different mechanism to explain the CMBR, based on a proposal by E. L. Wright that metallic or carbon "whiskers" might be behind infrared emissions from gas clouds.

This led to the Quasi steady state model of Hoyle, Burbidge, and Narlikar, which incorporated Halton Arp's idea of matter being generated from galactic centres (see below). This model postulates the creation of matter only (no antimatter).

Almost all cosmologists today believe that steady state models are not compatible with the latest cosmological observations.^[4][5]

Halton Arp's proposal

In conventional cosmology, quasars are supposed to exist beyond the observed galaxies, as inferred by their large redshifts, which are interpreted as being an indicator of their vast distance from Earth. However, in the 1960s astronomer Halton Arp published evidence that many quasars are actually associated in pairs with closer galaxies, so that their redshifts would have to be explained differently. Arp's proposal is that the quasars are actually new matter being ejected from the centres of galaxies, and that these balls of new matter will eventually become new galaxies. His proposal includes that the new matter is initially massless, but gradually gains mass, and that the initially-massless matter produces light that is highly redshifted, with certain values preferred ("quantized redshifts"). Arp's idea also explains the clustering of galaxies, in that the new galaxies remain gravitationally bound to their parent galaxies. The idea is based on Mach's principle, an idea put forward by Ernst Mach in the 19th century, and which formed a basis for Einstein's now well-accepted general theory of relativity.

Almost all cosmologists today reject Arp's proposals, citing advances in observations and theory in the intervening decades, including models of quasars as very distant but very active galaxies, observations of normal galaxies at very high redshifts, and large scale surveys that show "no evidence for a periodicity at the predicted frequency in log(1+z), or at any other frequency".^{[6][7][8][9][10]}

Halton Arp was the first of the signees of the letter complaining about suppression of dissent of alternatives to the Big Bang,^[1] and has been a victim of that discrimination.^[11]

Cosmological General Relativity

In Einstein's special relativity, the speed of light is constant and space and time are combined into "spacetime" which can be different depending on who is observing and how fast they are travelling. Moshe Carmeli, a theoretical physicist, developed an alternative in which space and velocity are combined into "spacevelocity". He then extended this by including matter and derived his "Cosmological General Relativity". He used this model to predict the accelerating universe in 1996, two years before it was verified from observations. His model also says that the universe is spatially flat. Although popular among creation scientists, Carmeli and his ideas have received little notice from secular cosmologists.

References