Tuesday, May 4, 2021

The Cosmic Revolutionary's Handbook (Or: How to Beat the Big Bang)

This is a new book by two astronomers, Luke A. Barnes and Geraint F. Lewis, who live in Australia. I read it to update myself on the big bang theory, at least in an informal sense. Of course, the actual research in this area is quite abstruse, so books like this only give you a vague sense of what is going on. While there is an informal tone to the book, it is quite apparent that there has been an incredible amount of research, accompanied both by better telescopes and advances in physics, since Edwin Hubble first proposed the theory in 1929. One amusing aspect of the book is the continuous cautioning by the authors of how theories must be presented according to prevailing mathematical standards and provide experimental proof for their assertions; apparently this occurred because the authors wrote a book earlier and have been deluged with ideas and theories from people who have no conception of the scientific method. They were inundated with emails and letters, particularly from retired engineers, who thought that they had theories that explained everything. So the book is an attempt to provide them with some guidelines if they expect to be taken seriously.

As discussed in the book, the big bang theory is one of the great triumphs of modern science. It is still holding together, though various observations in recent years have raised questions regarding its validity. The main idea is still intact. The theory came about as new ways of measuring distance in space became possible. Cepheid variable stars were observed locally, and it was determined that their intrinsic brightness was the same no matter where they were located. Thus, a dim Cepheid is farther away than a bright Cepheid. Initially, the distance of Cepheids was measured by their parallax, using the earth's orbit to form the base of a triangle extending to a star. Hubble observed that the light from distant Cepheids was shifted toward the red end of the visual spectrum in the same way that the Doppler shift lengthens sound waves from objects that are moving away. He showed that the more distant a Cepheid star, the more its light had redshifted, indicating that it was moving away faster. This was the first indication that the universe is expanding. Later on, with the discovery of Type 1a supernovae in 1993, the measurements from objects at even greater distances became possible. The distance of nearby Type 1a supernovae can be determined when they occupy the same galaxy as a Cepheid variable, and this provides a distance scale for Type 1a supernovae that are well beyond any visible Cepheid variables. These supernovae have a predictable intrinsic brightness, which can be determined by the time it takes for the light to fade after the explosion. As it turned out, the more distant a Type 1a supernova, the more its light is redshifted, confirming Hubble's theory.

Most of the book discusses various findings that have occurred since Hubble and whether they are compatible with the expanding universe hypothesis. In the1980's, Alan Guth proposed the inflation theory in order to explain why we can't detect magnetic monopoles, as would be expected with a big bang. His theory was that the universe accelerated its expansion briefly very early in its existence. This does not necessarily contradict the basic idea of an expanding universe and is itself an unresolved issue. Another discovered phenomenon, the cosmic microwave background, seems to be compatible with the big bang. Then there are dark matter and dark energy, which, at this point, are theoretical entities used to explain galactic movement. They may be compatible with the big bang theory, but are not currently well understood. The discovery of quasars, which emit radio waves, has been useful for studying extremely distant objects and the matter between them and the earth.

The big bang theory is an important concept, because it summarizes all that we know about the early universe, which came into existence about fourteen billion years ago. It began very hot, expanded rapidly and gradually cooled down. The expansion that occurred was the stretching of space-time according to Einstein's theory of general relativity. At the particle level, the picture is far more complex and requires the use of the Standard Model of particle physics. It currently looks as if it may never be possible to know exactly what happened in the first moment of the universe or anything before that. There is a lot of speculation which may be impossible to prove. One person thinks that the universe began as the opposite end of a black hole: a white hole. There may never be a way to prove this. We may also never know whether there are other universes. Then there is the multiverse concept, in which new universes are created every moment: I find that theory unappealing. I think that future advances, probably with the assistance of AI, may produce some answers in these areas, though the theories may still be untestable.

The book is written in a light, humorous style, while the underlying ideas are quite complex, so the mental gymnastics can be strenuous. However, on the whole I found it highly instructive and it is probably better than the astronomy classes that I took in college.

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