Can Physics Be Too Speculative?

Imagination and creativity are the heart of science. But look at the headlines in the popular science media and you can’t shake off the feeling that some physicists have gotten ahead of themselves. Multiverses, dark matter, string theory, fifth forces, and that asteroid which was supposedly alien technology. These ideas make headlines, but are then either never heard of again – like hundreds of hypothetical particles that were never detected, and tests of string theory that were impossible in the first place – or later turn out to be wrong – all reports of fifth forces disappeared, and that asteroid was probably a big chunk of nitrogen. Have physicists gone too far in their speculations?

The question how much speculation is healthy differs from the question where to draw the line between science and pseudoscience. That’s because physicists usually justify their speculations as work in progress, so they don’t have to live up to the standard we expect for fully-fledged scientific theories. It’s then not as easy as pointing out that string theory is for all practical purposes untestable, because its supporters will argue that maybe one day they’ll figure out how to test it. The same argument can be made about the hypothetical particles that make up dark matter or those fifth forces. Maybe one day they’ll find a way to test them.

The question we are facing, thus, is similar to the one that the philosopher Imre Lakatos posed: Which research programs make progress, and which have become degenerative? When speculation stimulates progress it benefits science, but when speculation leads to no insights for the description of nature, it eats up time and resources, and gets in the way of progress. Which research program is on which side must be assessed on a case-by-case basis.

Dark matter is an example of a research program that used to be progressive but has become degenerative. In its original form, dark matter was a simple parameterization that fit a lot of observations – a paradigmatic example of a good scientific hypothesis. However, as David Merritt elucidates in his recent book “A philosophical approach to MOND”, dark matter has trouble with more recent observations, and physicists in the area have taken on to accommodating data, rather than making successful predictions.

Moreover, the abundance of specific particle models for dark matter that physicists have put forward are unnecessary to explain any existing observations. These models produce publications but they do not further progress. This isn’t so surprising because guessing a specific particle from rather unspecific observations of its gravitational pull has an infinitesimal chance of working.

Theories for the early universe or fifth forces suffer from a similar problem. They do not explain any existing observations. Instead, they make the existing – very well working – theories more complicated without solving any problem.

String theory is a different case. That’s because string theory is supposed to remove an inconsistency in the foundations of physics: The missing quantization of gravity. If successful, that would be progress in and by itself, even if it doesn’t result in testable predictions. But string theorists have pretty much given up on their original goal and never satisfactorily showed the theory solves the problem to begin with.

Much of what goes as “string theory” today has nothing to do with the original idea of unifying all the forces. Instead, string theorists apply certain limits of their theory in an attempt to describe condensed matter systems. Now, in my opinion, string theorists vastly overstate the success of this method. But the research program is progressing and working towards empirical predictions.

Multiverse research concerns itself with postulating the existence of entities that are unobservable in principle. This isn’t scientific and should have no place in physics. The origin of the problem seems to be that many physicists are Platonists – they believe that their math is real, rather than just a description of reality. But Platonism is a philosophy and shouldn’t be mistaken for science.

What about Avi Loeb’s claim that the interstellar object `Oumuamua was alien technology? Loeb has justified his speculation by pointing towards scientists who ponder multiverses and extra dimensions. He seems to think his argument is similar. But Loeb’s argument isn’t degenerative science. It's just bad science. He jumped to conclusions from incomplete data.
It isn’t hard to guess that many physicists will object to my assessments. That is fine – my intention here is not so much to argue this particular assessment is correct, but that this assessment must be done regularly, in collaboration between physicists and philosophers.

Yes, Imagination and creativity are the heart of science. They are also the heart of science fiction. And we shouldn’t conflate science with fiction.