Road to Reality: New Perspectives
In this book, mathematician Roger Penrose provocatively suggest that the community of theoretical physics has engaged in promoting fashionable ideas, that have deep conceptual problems, as frontiers of new physics. The principles of quantum physics and string theory and predictions in cosmology are done recklessly. Penrose calls string theory a “fashion,” quantum mechanics “faith,” and cosmic inflation a “fantasy.”
Penrose observes that quantum physics has deep conceptual problems despite its success in predicting phenomenon in chemistry and physics. Quantum physics governs the behavior of matter and energy at the level of fundamental particles (quantum reality). In many-particle system such as biomolecules, living cells, planets, stars and galaxies, the quantum reality cease to exist; it can only be explained by the laws classical physics. Penrose thinks there is a threshold mass at which gravity (spacetime curvature) destroys the quantum phenomenon. In one of his interview, Penrose said that “you have to give up the idea of spacetime as we know it from Einstein.” The fact that an object can exist in many states at once contradicts the real world. The reason is that the mathematics of quantum physics has two parts. One is the evolution of a quantum system is described extremely precisely and accurately by the Schrödinger equation. In terms of physical reality, if you know what the state of the system is now, then you can calculate what it will be doing 10 minutes from now. However, there is the second part of quantum physics, which happens when you want to make a measurement. Instead of getting a single answer, you use the equation to work out the probabilities of many possibilities. The equation should describe the world in a completely deterministic way with certainty as we experience in real world, but it doesn’t. Penrose suggests that that the fundamental principles of quantum physics have not yet been found. Perhaps this is the reason that the full integration of classical gravity into quantum physics into a testable theory have not been successful. Penrose’s main concern is that the success of quantum physics have made physicists insensitive and treat that as the canonical gospel of physical reality. In an interview Penrose commented that his “own view is that quantum mechanics is not exactly right.”
Penrose expresses major concerns about string theory in particular which tries to present a unified picture of quantum gravity and sell it as the theory of everything. But this theory is without its usual problems, like the six hidden dimensions that has not been experimentally verified. The fact that strings are suggested to propagate in ten dimensions, and only four are large dimensions (including one time-dimension), and the rest are small, curled-up and decoupled with the larger dimensions intimidates Penrose. He would not compromise on decoupling these degrees of freedom with two sets and observes that causes instability; hence a stable ground state with four large spacetime dimensions would not be possible. Many predictions of the theory are not testable within the realm of available technology.
Penrose illustrates the inflationary cosmology as an example of fantasy since it does not explain what set the initial low entropy condition of the universe. Inflationary cosmology, which suggests that the universe inflated exponentially within a small fraction of a second after the Big Bang is a big fish observes Penrose. In fact it is sacrilegious to attack it, and even more sacrilegious is quantum physics which has become a faith. People don’t want to question it.
Penrose also discusses his “twistor” theory in which he explains how particles move and interact in spacetime, but spacetime themselves are secondary constructs that emerge out of a deeper level of reality. The conventional wisdom is that spacetime geometry fluctuate on quantum scales, altering how events relate to one another. Hence an event that was supposed to cause another may not happen creating paradoxes such as those found in time-travel. In twistor theory, causal sequences are primary and do not fluctuate. Instead the location and timing of events fluctuate. String theorists showed that an event of ambiguous location and time is nothing more or less than a string.
Many string theorists dismiss Penrose’s criticism. They claim that their theory has mathematical beauty and it has the ability to include the classical theory of gravity and it is the only theory of everything. Despite his criticism, he was invited by the Princeton University in 2003 where some of the most important proponents of string theory work. The ideas for this book was developed from these lectures.
Roger Penrose is a mathematician and firmly believes that understanding math is fundamental to the understanding of physics and physical reality. In his 2005 book, “The Road to Reality” math was extensively used as a concept learning tool even though that book was written for a general reader. This book also has math but less extensive than his 2005 book. Some sections are written for wider choice of readers but other parts require significant knowledge in mathematical physics. It will make it easier for a reader to know that Roger Penrose, in his 2009 interview with “Discover” magazine, admitted he was “bad” in math in school and in his own words he “was at least twice as slow as anybody else.” Eventually I would do very well. You see, if I could do it that way.” This is a great source encouragement for readers who did not have significant physics and math while they were in school. I recommend readers to skip the part of the book that is too intense but focus on main arguments of the book. One can still appreciate the efforts of Penrose’s masterful way of communicating his ideas.
No comments:
Post a Comment