Re: “An Imperfect Truth,” by David Orrell

“If it ain’t broke, don’t fix it.”  From where I sit, modern science is working pretty well, producing such near-magical  marvels as smart phones, nuclear power, and space travel. But Unger and Smolin’s The Singular Universe and the Reality of Time attacks the fundamental scientific notion that nature is governed by a set of immutable, mathematical equations, and proposes an alternative paradigm.

Science begins with a broad set of hypotheses and  proceeds by eliminating those that fail experimental or logical tests, leaving a core of as-yet unfalsified proposals that may be true, or at least useful approximations. The idea that there are immutable, mathematical laws of nature (such that experiments are repeatable with consistent results, and logic can be used to analyze theories) underpins this procedure. Like everything else in science, however, it can be falsified. Scientists are constantly probing natural law, searching for anomalies and exceptions. If the laws of nature change tomorrow or exhibit a feature that cannot be described mathematically, this will likely be discovered, and the discoverer will become very famous indeed. And even if natural law is found to change, quite plausibly the changes themselves would be governed by mathematical laws.

Smolin and Unger’s primary argument for radical change is what they call the “crisis” in modern cosmology. That cosmology is in crisis would come as a (pleasant) surprise to a majority of cosmologists, many of whom are somewhat discouraged by the success of the so-called “standard model of cosmology” that accurately predicted the flood of precision cosmological data that has become available in the last decade. For practicing scientists any anomaly is good news: it provides an opportunity for discovery, and is quickly exploited  by an army of eager researchers. In reality, the latest and greatest cosmological data sets show only faint hints of anything not predicted by the standard theory.

Smolin and Unger have no plausible explanation for the “unreasonable effectiveness of mathematics in the natural sciences” (the title of a seminal essay on the topic by Eugene Wigner). At one point they seek to justify it on the grounds that once collected, experimental data is unchanging and can hence be modeled with immutable mathematics (pp. 445-446).  But this misses the point entirely: as is well-known to all scientists, a theory is truly tested only when it makes predictions about future experiments with as-yet unknown results.

Let me turn to the “multiverse” or landscape of string theory: in Orrell’s review and Smolin and Unger’s book, the multiverse is presented as an example of how scientists’ faith in  immutable mathematics  leads to absurdity. If scientists accept such moonshine as multiple universes, does this not indicate something rotten at the core?

Unfortunately, this argument  is founded on a number of  basic misconceptions. In support of his incredulity, Orrell mentions Max Tegmark’s most radical (“level IV”) multiverse, an interesting but idiosyncratic philosophical speculation certainly not accepted by (or even familiar to) most scientists.

More to the point is the string landscape, a relatively concrete structure believed to follow from the mathematics of string theory.  However contrary to Unger and Smolin’s assertions, recent work indicates that current or near-future cosmological observations – specifically, the detection of positive spatial curvature – would falsify the landscape (if it is false).  Furthermore, the theory can be used to predict the signatures of cosmic bubble collisions:  violent events where two previously separate “universes” collide.  If these signatures are  detected (and cosmologists are actively searching for them) this will provide nearly irrefutable evidence for the existence of the landscape.  Hence the landscape is both falsifiable and makes positive and unique predictions that could  be observed – hardly the “radical departure from normal mechanistic science” Orrell describes. And it is not just string theory that predicts such a multiverse. Even the standard model of particle physics combined with Einstein’s theory of general relativity – two of the most well-established theories in physics – predict a  large landscape quite similar to that of string theory.

Those scientists (myself included) who take the multiverse seriously indeed do so because they believe it is mathematically predicted by the laws of physics.  Faced with a seemingly fantastical prediction, should researchers abandon these laws despite their tremendous success? The history of science is full of examples of scientific theories with seemingly absurd implications, often vigorously opposed by individuals who substituted their  personal notions of what nature ought to be for mathematical logic. But the conventional approach to science, using  mathematical laws to model physical phenomena, works too well to be abandoned. By contrast, rejecting science because one is uncomfortable with its implications has a decidedly poor track-record.

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