Physicists have devoted enormous amounts of effort to supersymmetry and string theory, but let us ask the provocative question: is the evidence for either of these theories better than the evidence for ESP?
First, let us look at the current evidence for ESP (which stands for extrasensory perception). The standard party line of reductionists and materialists is that ESP is quackery and pseudoscience. However, you will be surprised if you objectively examine the evidence for ESP, which is much stronger than one would imagine it to be, given the scorn which many have for ESP.
Serious systematic university research into ESP started with lengthy work done by J. B. Rhine in the 1930's at Duke University, one of the top US universities. Rhine's experiments suggested that the ESP phenomenon is real. In 1940 Rhine published the book Extra-Sensory Perception After Sixty Years summarizing his own work and numerous similar studies. According to the wikipedia article on ESP, “61% of these independent studies reported significant results suggestive of ESP.”
The most compelling evidence for ESP comes from what are called ganzfeld experiments. A ganzfeld experiment is one in which a test for extra-sensory perception is combined with sensory deprivation achieved through methods such as cutting a ping-pong ball in half and taping it over someone's eyes, and having someone wear an earphone transmitting white noise. In these ESP experiments, the expected chance hit rate (matching of a user's selection and a random target) is 25%. But as wikipedia reports here, “In 2010, Lance Storm, Patrizio Tressoldi, and Lorenzo Di Risio analyzed 29 ganzfeld studies from 1997 to 2008. Of the 1,498 trials, 483 produced hits, corresponding to a hit rate of 32.2%.” That success rate of 32.2% is hugely above the expected by-chance success rate of 25%. The review article can be found here. The probability of such a hit rate occurring by chance is incredibly low. The Law of Large Numbers dictates that whenever you do a huge number of trials, there is only a very low chance of exceeding the result expected by chance.
Although I am not familiar with the math for exactly calculating the odds of getting the success rate above, it was easy for me to whip up a "Monte Carlo" computer program that tells me there is less than 1 chance in 500,000 of getting more than 482 successes out of 1498 when there is a 25% chance per trial.
When skeptics heard of the ganzfeld experiments, they suggested ways in which the experiments could be made more rigorous. The experimenters made the suggested improvements, and continued to get the same results, with hit rates very far in excess of what chance would produce.
In this review article the author states, “The review is followed by a basic assessment of 59 ganzfeld ESP studies reported in the period following the publication of a stringent set of methodological guidelines and recommendations by R. Hyman and C. Honorton in 1986. The assessment indicates that these 59 studies have a combined hit rate of approximately 30%, which is significantly above the chance expected hit rate of 25%.” The probability of that occurring by chance, according to my computer program, is roughly 1 in 175,000.
How can we explain away these findings without accepting that some actual extra-sensory perception is occurring? One way is to postulate a kind of conspiracy theory, and to imagine that there is simply widespread fraud occurring in these tests. But there is a reason why such a theory is highly implausible. While it may be that true that certain types of paranormal accounts make lots of money for some of the people who tell them, ESP researchers reap no big financial bonanza from their research. ESP books are not big sellers (people just aren't that interested in reading about things like card matching). The average ESP researcher could just as easily be making as much money doing other types of psychological research, so why should he bother to falsify his results? Plus we have no cases of any major ESP researchers confessing to have falsified results. Given that ESP research has been carried on systematically for at least 80 years, one would think there would be quite a few deathbed confessions of fraud if fraud had been widespread.
Given the abundant experimental evidence that has accumulated for many decades, and the lack of credibility in any theory that it is fraudulent, it seems that the evidence for ESP is actually surprisingly substantial. The commonly made claim that experiments suggesting ESP cannot be replicated does not seem to be correct. There actually seems to be a quite significant degree of replication. ESP may or may not exist, but there seems to be a large, rather consistent body of experimental evidence to support the claim that it does exist.
Now, let's look at the evidence for supersymmetry (SUSY) and string theory. Both of these theories have gobbled up countless research dollars in recent years, so surely the evidence for them must be much greater than the evidence for ESP, right?
Wrong. It's actually the other way around. The evidence for either supersymmetry or string theory is actually weaker than the evidence for ESP. This is because there is basically no evidence for either supersymmetry or string theory.
In the case of string theory we have a theory that is so exotic and extravagant (and has so many different variations) that some scientists say it will never be possible in the future history of mankind to produce evidence that backs up string theory. We know that a major discovery a few years back (that the expansion of the universe is accelerating) caused huge problems for string theory, requiring string theorists to almost tie themselves into knots patching up the theory to reconcile their theory with this observational fact.
In the case of supersymmetry, it's a different situation. There was a golden opportunity to get evidence for the theory when the Large Hadron Collider started operating a few years back. The problem is that the evidence did not materialize. None of the particles predicted by the supersymmetry theory were found. Quite a few people now say that the supersymmetry theory is on life-support given the results from the Large Hadron Collider.
Large Hadron Collider. Credit: CERN, 2001
But as described here, some physicists are very reluctant to give up the supersymmetry theory, having spent decades working on it. This seems to be an example of "stick to your guns no matter what" thinking that psychologists call escalation of commitment.
The Large Hadron Collider findings which cast doubt on the SUSY theory (supersymmetry) seem to do pretty much the same thing for string theory, since the wikipedia article on string theory says, “All consistent string theories are supersymmetric.”
For books critical of string theory, look at Not Even Wrong by Peter Woit and The Problem With Physics by Lee Smolin. Smolin (a physicist who worked quite a bit of time on string theory himself) has a chapter mentioning sociological explanations for the popularity of string theory, in which Smolin comments on the cliquish groupthink tendencies of string theorists.Woit has a very popular blog which regularly exposes the excesses of string theory and “multiverse mania” as he calls it.
Many people regard scientists as godlike impartial judges of truth. But I think this assessment is wrong. Scientists are just ordinary people like you and me, and are subject to the same obsessions and cognitive biases as ordinary people, biases that may derive from psychological, sociological, and economic factors. Just as people are not objective judges of other people who they have fallen in love with, scientists are not objective judges of theories that they have fallen in love with. We seem to have too many physicists who have intellectually fallen in love with extremely speculative theories that are not supported by evidence.