Already I'm taken aback by the somewhat ridiculous afterword written by Richard Dawkins when he says that "If On the Origin of Species was biology's deadliest blow to supernaturalism, we may come to see A Universe From Nothing as the equivalent from cosmology." Are we really going to compare what was arguably the most crucial publication in the advancement of biology ever in its history, with a book that doesn't propose anything original or new and that dabbles in speculative and untested (possibly untestable) physics? Well I guess we are.
This is the best part of the book, it both recants much of the history of cosmology–from the viewpoint of what Krauss was working on–and some quantum mechanics. This much is largely well written and I commend these chapters to anyone interested in astronomy and astrophysics.
The book starts out as a nice popularization of many aspects of cosmology, it describes the evidence Cosmologists have that convince them that our universe is filled with dark matter (Tyson's simulation weighing galaxies with gravitational lensing, Fritz Zwicky's calculations in the 1930s and the observation of galaxy rotation) and dark energy (largely from the BOOMERanG experiments and the observed acceleration of the universe). It also ties in well with the modern discoveries about the local topology of the universe, which at times Krauss understandably but wrongly equates to the geometry of the universe.
These discoveries accumulate to what cosmologists refer to as the "LCDM model" of cosmology and its so far stood up against all the data we have, including the most recent test, that being the 2015 Planck data published after Krauss' book.
Chapter 8 is roughly when Krauss makes the transition from known physics, to what he thinks is the best explanation for the initial conditions of the LCDM model, namely eternal inflation. Unfortunately Krauss' description of the universe which emerges from a false vacuum as 'nothing' is set up for confusion; a lot of people who read this description are likely to go away confused or disappointed when they realize he hasn't actually addressed the subtitle of his book. Namely 'why does something exist, rather than nothing?'
Krauss Wrong About "Nothing"
Rather than using the term "nothing" as a negation, which is what almost everyone means by the term, Krauss insists on treating it as the subject of a sentence or perhaps the object of a statement. This is just a semantic quibble not a very impressive argument and Krauss manages to draw it out to fill in the last three chapters of the book.
On the one hand Krauss uses nothing to refer to particles popping out of "empty" space in several physical theories, e.g. Hawking radiation, the quantum processes which produced the dominance of matter over antimatter, the casimer effect, inflationary theory where energy density is conserved instead of mass-energy.
- $E(t) = \rho V(t)$
While on the other, he argues that even this vacuum can arise from a deeper kind of 'nothing'. Referring to speculative models in quantum cosmology, like the Hartle-Hawking model or Vilenkin's tunneling model. It's simply wrong to refer to the Harlte-Hawking model (which is eternal) as coming from nothing. I've tried to explain in some way both of these proposals on this blog already, so I won't repeat myself here. In short, Krauss' remarks to have solved Leibniz's quandary are dead wrong and his religious critics who fight over the issue are absolutely right, the question is unanswered and probably unanswerable.
You can explain the evolution of the quantum state at one time with fields and no particles, to a state with particles perfectly well and consistent with a set of known laws but that still leaves a lot of questions unanswered. Referring to that prior state of space, time, fields, laws of physics and so forth as "nothing" doesn't help much.
Whether you refer to "something" as "nothing" it only misleads; it doesn't answer the problem of why anything at all exists. One can still ask why do the laws of quantum mechanics exist, why does the quantum vacuum exist, or why does the wave function 'exist'?
Krauss continues that inflation, which could have produced a multiverse may also vary many of the constants, parameters and masses of fundamental particles in accord with the $10^{500}$ possible variations of those parameters in string theory. Eternal inflation is a sensible proposal but most cosmologists aren't as a certain about the multiverse as Krauss appears, the model is not based on known physics.
There's no global description of eternal inflation like there is of our local universe in the FRW standard model; Friedman's equations assume large scale homogeneity which is violated in eternal inflation. Moreover eternal inflation is a quantum process, it can't happen in ordinary general relativity, the quantum effects which drive inflation carry energy and therefore must alter Einstein's background solution, how do you correct this back-reaction effect? I don't believe either of these questions can be answered without postulating some new physics.
It seems also to have a pretty serious measure problem $P= e^{S}$ where $S =1/\Lambda$ and this is largely neglected in the book, and for what its worth, its certainly not the only game in town, as far as string cosmology goes, other models like pre-Big Bang inflation or the Ekpyrotic Cyclic scenario are at least still possible.
In the last section of the book, Krauss speculates more about a quantum origin of 'eternal' inflation but doesn't go much into the history of quantum cosmology, he only briefly mentions the field in chapter 11 but the history is fascinating. The foundations of the field were set by John Wheeler and Bryce DeWitt in the 1960s and seminal ideas about the quantum origins of the universe (or rather its material content) began as early as 1973 with Edward Tryon.
More speculative ideas about the quantum origins of spacetime itself began emerging in 1982 by Atkatz and Pagels and 1982 by Vilenkin, and then the famous Hartle-Hawking proposal in 1983.
I'm also now tempted to comment on the preface of Krauss' book, therein includes the unpleasant ad hominem that "philosophers and theologians are the experts on nothing". In my experience its only a relatively small number of physicists who disparage or derogate entirely, in their way of thinking from philosophy and those who do are apt to misunderstanding.
Philosophy is the science of all things, it is in essence the use of reasoning and rational thought to come to conclusions about a conceptual space of ideas which are not open to empirical testing. If all you're interested in is science, the study of the empirical world, then no, you probably don't need philosophy.
However, if you want to understand the way the world is, or even many of the physics-related problems we have today like the nature of the wave function, the interpretation of quantum mechanics, the problem(s) of time, then philosophy is important.
Scientific theories are often filled with philosophical questions and its wrong to judge the philosophy of science by what contribution or advancements it makes to science (as Krauss does). Philosophers of science are largely not even attempting to address scientific problems any more than historians of science or sociologists of science. Their discipline is to advance the philosophy of science, not science itself.
My main objection to this book however isn't that its anti-philosophy, speculative or even sometimes draws conclusions which are overstated, or even that its off centered for a science book it talks relatively, a lot of ammeter theology. The problem is the main edifice of the book, to explain "why" anything at all exists in terms of scientific theories, is not even wrong. If what Krauss says is true he's only explained one physical state in terms of some prior physical state. The fundamental mystery indicated in the subtitle of the book remains at large.
Comments
Post a Comment