Thursday, March 5, 2015

The scientific work of Stephen Hawking

The scientific work of Stephen Hawking has been quite productive, although the media, influenced by his sad personal situation, tend to exaggerate its importance, putting him sometimes at the level of Einstein. His most renowned works are the following:
  • The singularity theorems, published in 1970 in collaboration with Roger Penrose, proved that the application of the equations of Einstein’s General Relativity to the entire universe requires at least one singular point in that universe (a point where all the geodesics in the universe converge). As a consequence of this theorem, in the book The Large Scale Structure of Space-Time (1973, written with George Ellis), Hawking unequivocally embraced the theory that the universe began at a point of infinite density (the Big Bang).

  • The analysis of the dynamics of black holes and the discovery in 1974 of Hawking radiation, an application of quantum mechanics in the vicinity of a black hole. If this radiation exists (for the time being we can’t verify it experimentally) black holes won’t last indefinitely, as previously thought, but will eventually evaporate.
  • The first theory of quantum gravity, formulated in 1983 with J.B. Hartle in a paper published in the scientific journal Physical Review D, titled The wave function of the universe, where Hawking changes his mind about the existence of a singularity at the beginning of the universe and replaces it by something different. Unfortunately, this article contains a mathematical error: the solutions proposed for the wave function in equations (6.14) and (6.24) do not match the graphic representation in Figure 4. In fact, the error is so glaring that I saw it the first time I read the paper. Later I found that (as could be expected) others (Claus Kiefer, for instance) had noticed it before. As this problem could not be corrected, the theory of Hartle and Hawking has been abandoned.
In this situation I ask myself a question: what is the use of the reviewers of scientific journals, if they were unable to find a mistake that a non specialist detected in the first reading of a paper that was supposed to revolutionize the current scientific theories by denying the existence of the Big Bang as it was understood at the time? Did the magazine decide to publish the article without reviews, based on the prestige of the author? Or were the reviewers blinded by his name, skimmed it over and advised its publication? I cannot answer these questions.
Roger Penrose
Hawking relied on his quantum gravity theory to write his famous book A Brief History of Time, the biggest seller ever in the field of popular science. I have not seen, in the book or later, any public reference to the fact that this theory has been abandoned. True, there have been later attempts to build theories of quantum gravity more or less similar to Hawking’s, such as string theory, Bojowald’s loop quantum gravity, Penrose’s twistor theory, and a few more. But none of them has been verified experimentally, and all of them must be considered for the time being as scientific speculations.

Manuel Alfonseca


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