It is of course true that we cannot know anything for certain. For all we know, we may be living in "The Matrix", and everything we see is mere computer simulations. Likewise, we can never know for sure that a theory is true in an objective sense. I consider these two statements as uncontroversial, however, when relativists go one step further and argue that all theories are equivalent since no theory can be proven, that is when I must disagree…
People who use this reasoning have completely forgotten about the concept of evidence and prediction. Though a theory can never be proven in the absolute sense it can be better or worse at describing reality. Just as simple example there are people who claim that the world is spherical (or almost spherical), and there are those who claim that it is flat (based on religious reasoning I might add). What predictions does each of these two theories make? Well, one very simple prediction is that a round earth should cast "round" or banana shaped shadows on the moon when the earth is between the sun and the moon. If the earth was flat on the other hand, the shadow should be flat as well. Everyone who has ever gone out to watch the moon knows that the round earth theory gives the more accurate prediction. We cannot know for certain that the earth is round, but the predictions it makes agree with what we see. When a prediction is correct we can call that evidence. My point is simply that people do not walk around and think that the earth being flat and the earth being round are two equivalent theories just because neither can be proven. Almost everyone believes that the earth is round because there is so much evidence in favor of that theory.
I have previously argued that in fact it does not really matter whether a theory is true in the objective sense. As long as a particular theory is very good at predicting the world as we see it, it is a good theory and we should simply act as if it was true. It is this mentality together with the scientific method, which reduces the risk of seeing evidence where there is none that has brought us to where we are today. Here it is important to remember that if a theory is true in the objective sense, then all predictions derived from that theory would have to be true as well.
Relativists also like to point fingers at the scientific method. One frequent argument that you hear from relativists is that throughout history there has been paradigm shifts in almost all sciences. In astronomy for example we have gone from the Copernican system, to the Newtonian, to Einstein's relativity. Furthermore they claim that these paradigm shifts occur, not because latter theories are more accurate, but due to cultural factors. Relativists who use this argument, first of all, forget that history is also a science. They are using evidence which has been produced using the scientific method – the very same method which they are criticizing. Clearly hypocritical...
Besides, it is clear to me that all shifts in astronomy have been progressive. The details of the various paradigm shifts may have been influenced by sociological factors, however, the main reason for all the shifts have been that they make better predictions. Newton's theory of gravitation gives a better description than Copernicus theory, and Einstein's theory of relativity make better predictions than Newton's theory. Old theories are exchanged with new ones when the new ones are better at describing the world as we perceive it.
This will be all I write about relativism for now, but check back later if you want to read more. For some reason I end up in discussions about relativism very often, and therefore I also have many thoughts on the subject. Many of the arguments that I present here have been influenced by this book (see picture above), which I recommend to everyone.
