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Posted 6 January 2008

Challenges to the Big Bang Theory

by Frikkie de Bruyn


This article is written in response to the ideas put forward by a group of scientists known as ‘alternative cosmology’. The analyses of the various theories have been done strictly in accordance with what a scientific theory is and in accordance with the positivist ideas of Karl Popper which means that a theory can be proved or disproved by observation. A good theory must be able to:

1. Describe what we see around us;
2. Make testable predictions such as General Relativity’s prediction that the path of light is bent by the curvature of spacetime near a massive body. This has been confirmed by the British scientist, Sir Arthur Eddington, during a total solar eclipse.

Note: Philosophical and religious reactions to the Big Bang Theory will not be discussed since that falls outside the scope of a scientific discussion. Galileo Galilei once said: “The Bible tells us how to go to Heaven, not how the heavens work.”

What is the Big Bang theory and what is it not?

There are so many popular misconceptions created by the unfortunate name of the theory ‘Big Bang’ that we should first look at what the Big Bang theory is not. It was neither big nor was there a bang. According to this theory the Universe originated from a primeval quantum object far smaller than an atom. There was no explosion as we understand it in everyday language, because an explosion presupposes the existence of space for the shock waves to disperse. There was no pre-existing space which made an explosion impossible. Rather it was an exponential expansion of space in terms of Guth’s inflationary universe which took place from 10-36 second to 10-33 second.

The Belgian priest, Georges Lemaitre, was the first to prove mathematically by using Einstein’s General Relativity equations that the Universe was born from an inconceivably small object and expanded to what we see around us today, in other words the Big Bang. This was followed by Hubble’s discovery in 1926 that the Universe is expanding which means if you follow the picture back in the cosmic history, everything we see in the Universe must have been together in the beginning in a very small hot and dense object. Roger Penrose and Stephen Hawking proved that the General Relativity equations predicted that the Universe was born from a singularity, a point of infinite density, gravity and temperature. The clincher for the Big Bang Theory was the discovery of the Cosmic Microwave Background Radiation (CMBR) by Arno Penzias and Robert Wilson of the American Bell Company. The argument was that if the Big Bang did happen, there must be a remnant of the radiation from such an event. The CMBR proved to be the relic from the Big Bang when the Universe was about 380 000 years old. Detailed studies of the CMBR are continuing.

There were many questions the Big Bang Theory could not answer: “What triggered the big bang? What forms of matter were created in the big bang? How did large scale structures such as stars and galaxies form?” In addition the theory could not explain why the Universe looks so smooth at very large distances. It could not explain why the Universe is flat (please not that all we can say is that the Universe is nearly flat). An important question was how stars and galaxies could form if the Universe was smooth at large distances? The Big Bang Theory alone could not explain this. Alan Guth’s theory of an inflationary universe answered at least most of the questions. The Big Bang as amended by the inflationary universe explains in detail what matter was created during the Big Bang Nucleosynthesis, known as the primordial abundances. It successfully explains the smoothness of the Universe at large distances, but it still could not explain what caused the big bang; what put the bang into the big bang. The exponential expansion of space would have smoothed out most irregularities but not all. The fluctuations of energy in the quantum sized universe in accordance with the theory of quantum mechanics would have ensured that tiny irregularities remain; the seeds from which stars and galaxies were formed. If we accept the quantum origin of the Universe, we must also accept the multiverse concept, the idea that there are not one but a multitude of universes. Leonard Susskind poetically described it as a “bubble bath of universes”. The parallel universes are so far removed from each other that we can never make contact with another universe. The Big Bang Theory has no problems in accommodating the multiverse idea. The exponential universe predicted a very ordered and smooth early universe, a prerequisite for the second law of thermodynamics, the proof which can be confirmed by observation.

Challenges to the Big Bang

The greatest challenge to the Big Bang Theory came from the Steady State Theory. This theory was devised in the late 1940’s by Hoyle, Bondi and Gold. They stated simply that the Universe had always been as it is now. This originated from the “perfect cosmological principle” and is an extension of the Copernican idea that there is nothing special about the Earth; it is not in a central special place in the solar system or in the Universe. To keep the Universe from having been denser in the past Hoyle said that new matter was continually being created to fill the voids left by ever-migrating stars. The theory was testable because young and old galaxies would be scattered around the Universe and so specifying the shape of the Universe. (The Big Bang Theory provides for a number of shapes).

The steady state theory was a good theory in that it made testable predictions which could be confirmed/not confirmed by observation. One of the predictions was that the number of galaxies or similar objects per given volume of space must be the same wherever we look. A survey of radio sources carried out by a group of researchers under Martin Ryle of Cambridge University showed that there were more weak sources (presumably far away galaxies) than strong sources, thus contradicting the steady state theory. We know now that if the Universe is indeed unchanging as the steady state theory stated, then the whole of the observable universe must have been ablaze with starlight by now. The only reason why the sky is dark at night is because the Universe is expanding. A more technical but very important point is that the disorder (entropy) in the Universe is always increasing in terms of Boltzman’s second law of thermodynamics. If the Universe is unchanging the whole of the observable universe must be in a state of complete disorder and chaos, making life impossible. The fact that we are here is observable prove that the steady state theory could not predict the second law of thermodynamics.

Other reactions

What follows can hardly be described as scientific theories. They were rather specific ideas to specific problems. We are all aware that there are unanswered questions which cannot be explained by the Big Bang Theory. Some claim that the theory is wrong. Some attack the idea of a Universe which is expanding, a very important aspect of the amended Big Bang Theory. How do we know the Universe is expanding? Light (photons) reaching us from distant galaxies is red shifted; the wavelength of the photons are stretched by the expansion of the Universe. This is also known as the Doppler Effect. Observations show that the Universe is not only expanding, the expansion is accelerating. A problem for those who accept the idea of an accelerated expansion is the assumption that the laws of physics remain the same everywhere. One of the best known attacks on the expansion of the Universe (well known to me, because I had to answer so many questions about it) is the tired light hypothesis. If light has to travel such large distances to reach us, perhaps subjected to unknown strong gravitational fields, wouldn’t the light loose energy, therefore appearing redder since the light’s wavelength is stretched? In other words, are we being fooled? Fortunately the speed of light, which forms an integral part of general relativity, has been measured to an accuracy of one part in a million. General relativity has been proved correct hundreds of times, such as the bending of light, and since it explains the working of the Universe so accurately, most scientists reject the idea of ‘tired light’.

Another rejection of the red shift idea came from Halton Arp of the Max Planck Institute for Astrophysics in Germany. Arp had been studying irregular galaxies very carefully and he noticed that many of the quasars (which are at very large distances from Arp’s galaxies as measured by the red shift of light) appear to cluster right in line of sight of the irregular galaxies. Many of these quasars had red shifts very different from each other. Arp concluded that the irregular galaxies appear to be connected to some of the quasars. If Arp’s suggestion is correct it means that the idea of red shifting of a photon is wrong. Arp believes that stars and galaxies have an intrinsic red shift and it has nothing to do with whether the stars are moving away from us. Most scientists reject Arp’s ideas. Unfortunately no one else, other than Arp has ever study these irregular galaxies rigorously. He argued, maybe correctly, that his ideas have not been accepted, because scientists resist any ideas contrary to their own, he found it al most impossible to publish contradictory ideas. Red shifts have become a very important tool not only to determine the velocity of recession of an object, but also how old and how far away it is. If Arp’s ideas are correct then the idea that the Universe is expanding falls away and our understanding of how the Universe works is simply wrong.

The expansion of the Universe is accelerating

Scientists have always thought that the expansion of the Universe would be slowed down by the matter and energy in it. In 1998 a group of scientists under Saul Perlmutter discovered that the expansion is accelerating. This had forced scientists to rethink their understanding of the Big Bang Theory and, to the dissatisfaction of many, had to bring back Einstein’s cosmological constant as part of Einstein’s equations. Remember Einstein described the cosmological constant as his “biggest blunder”. The cosmological constant has been incorporated into the big bang and many regard this as an explanation for the anti-gravity force thought to be responsible for the expansion of the Universe and to explain the nearly flat Universe we see.

The Ekpyrotic Universe

This new theory, presented to the scientific world in 2001 by Paul Steinhardt, a physicist from Princeton University, is perhaps the only viable alternative to the inflation theory. (The word “Ekpyrotic” comes from an ancient Greek term describing a universe periodically destroyed by fire, a possible end for our Universe in this theory.) It comes from the M theory which is an extension of the string theories or supersymmetry theories. In terms of this theory particles are made up of thin membranes. The membranes, simply known as branes, describe a pre-big bang universe which consisted of vacuous cold space with four spatial dimensions and one of time. Two four dimensional branes, describing our Universe and a parallel universe, floating in this cold space would move towards each other, accelerating and slamming into each other, releasing enormous amounts of energy, called the big bang. These collisions between branes would happen from time to time, creating new universes from big bangs.

In the Ekpyrotic universe the flatness problem is solved in a different way since the branes were already nearly flat. The same temperature problem is also solved since, given the amount of time, it is reasonable to understand that a situation of thermal equilibrium would be reached. In this universe stars and galaxies were seeded from the inherent quantum fluctuations present in the primordial branes as they crashed into each other. How viable is the Ekpyrotic theory. At this stage it is a very new theory and it is too early to say. It is still not fully understood. It is testable in the sense that the collision of branes will create enormously strong gravity waves. Once scientists can detect gravity waves experimentally we might know more about this aspect of the theory.

Conclusion

Without predictions being tested we cannot say much bout the Ekpyrotic Universe Theory. Much more research will have to be done. Until then the Big Bang Theory is our only viable theory, tested successfully in many experiments. My own feeling is that a fully fledged Theory of Quantum Gravity will shed more light on many problems we cannot understand at this stage.

Frikkie


Bibliography

Technical but a very good book on general relativity and the quantum theory

Wald, Robert M. General Relativity. Chicago: University of Chicago Press, 1984.

More general books

Barrow, John D. Impossibility: The Limits of Science and the Science of Limits. Oxford: Oxford University Press, 1998.
Davies, Paul. The Last Three Minutes: Conjectures about the Ultimate Fate of the Universe. New York: Basic Books, 1994.
Hawking, S. W. and Ellis, G. F. R. The Large-Scale Structure of Space-Time. Cambridge: Cambridge University Press, 1973.
Hawking, S. W. and Penrose, R. The Nature of Space and Time. New Jersey: Princeton University Press, 1996.
Kaku, Michio. Parallel Worlds: The Science of Alternative Universes. London: Penguin Books Ltd., 2005.
Penrose, Roger. The Road to Reality: A Complete Guide to the Laws of the Universe. London: Jonathan Cape, 2004.
Rees, Martin. Before the Beginning: Our Universe and Others. Reading, Mass.: Helix Books, 1997.
Smolin, L. Three Roads to Quantum Gravity. New York: Basic Books, 2003.
Thorne, K. Black Holes and Time Warps. New Haven: W. W. Norton and Company
Weinberg, Stephen. The First Three Minutes: A Modern View of the Origin of the Universe. Second ed. New York: Basic Books, 1993.
Zee, A. Einstein’s Universe: Gravity at Work and Play.
New York: Oxford University Press, 2001.





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