Falsifiability in Modern Science

It appears that science and, in particular, particle physics has reached a point where one of the most foundational requirements of science is coming under spot light. For any theory to be science it has to be falsifiable. In other words, we should be able to devise an experiment to test whether the theory is correct or not. This modern view of science was put forward by Karl Popper. 

I am not sure about other fields of science but in physics this question is very relevant these days. There are fields of physics, such as condensed matter and plasma physics that relate to low energy phenomena but then there is particle physics which addresses phenomena at high energies. In particle physics, string theory, supersymmetry and grand unification are examples of theories that appear to be very elegant mathematically but have not yielded any experimental signatures. The late Stephen Hawking wrote in his book "A Brief History of time" that to truly test grand unified theories we would have to build an accelerator the size of our Universe. To test string theory we need an even bigger accelerator. Experiments have been conducted to test the indirect signatures of these theories but to date no evidence have been found. For example, one of the predictions of grand unified theories is proton decay which the Super-K experiment has been testing but no signatures have been found. 

So the question arises whether we should call these theories science or not and should we continue investing money and effort in trying to test these theories. I think we have come across a decisive point in the history of science as we did at the time of Ludwig Boltzmann. During Boltzmann's time, the popular approach in science was that of the "positivist" [1]. Positivism was based on Ernst Mach's philosophy that we cannot introduce any variable in physics that cannot be directly tested or observed. In Boltzmann's famous equation "S=k log W", the variable "W" [2] is not directly observable so he was confronted by the scientists of his time. It is said that the opposition to his ideas was one of the reasons he went into depression and committed suicide. Luminaries like Einstein and Heisenberg were deeply influenced by Mach's philosophy which is why there is so much emphasis on observables in their theories. So a lesson that we can learn from this part of history is that we may have to broaden the definition of science as Karl Popper did.

The fact that most of the senior particle physicists have spent their lifetimes on these theories makes things even more complicated. So, it appears that we are dealing with not only a complicated philosophical question but a difficult social issue as well. They continue to emphasize on making bigger experiments to test these theories. But is it worth it? I recently wrote about the proposal of an even bigger collider here.

So, are we reaching an era where we need a post modern view of science? If we are not able to truly test these theories should we reject them as science and instead invest in theories that are accessible with our current technologies. These are tough question that the scientific community has to think about.  Maybe when we get to the level II or III civilization on the Kardashev scale, we can think of directly testing these theories but for now let's spend on what we can afford.

[1] I remember reading a great concise article about logical positivism in Roger Bowley and Mariana Sanchez's book on Statistical Mechanics which I strongly recommend.

[2] The variable W measures the number of accessible states in a system. So in a way it is a measure of entropy of the system.