zaterdag 28 februari 2015

The road to reality - or beyond?

I held Roger Penrose's book “Road to reality” popularizing physics highly but I changed my my view a bit. This was due to discussing his short article “On the second law of thermodynamics” (1994) with some philosophy of physics students.

The article deals with the second law of thermodynamics. This law states that the entropy - the amount of disorder - of a closed system on average increases with time. It implies that the entropy of the universe goes up in the future. But what about the past? Penrose's solution is his "Weyl curvature hypothesis". This hypothesis states that the Weyl curvature is zero (or at least very small) at the Big Bang, and with it the entropy. More important than knowing what Weyl curvature is, is understanding what it explains:
  1. The existence of the aforementioned second law.
  2. The observation that the universe is homogeneous and isotropic at large scales.
The far more popular and rivaling inflation theory explains only 2. 

From the discussion it became clear that entropy has different definitions. The well established definition by Boltzmann is suited for the computation of the entropy of a gas. But what about that of the universe as a whole? Cosmology seems quite speculative.

Penrose is a good popularizer of mathematics and physics. His accompanying illustrations are unique. However, the danger is that the uninformed readers (as his readers will generally be) are seduced to see his speculative theories as being main stream. This occurs because he starts out in his books with accepted mathematical and physical material, slowly introducing his own speculations after that. Like the hypothesis of above and also his twistor theory. 

The question is whether Penrose leads one to reality or beyond.

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