Not too long ago, I had a conversation with a friend of mine about the dichotomy between science and religion. His position was that we can’t rely on certainty in anything, since our understanding of the universe is constantly changing. Because of this, he reasoned, faith in the supernatural is just as valid as the use of scientific evidence. I had a similar conversation with another friend a few months later, who was trying to convince me that medical woo-woo might be validated someday because the nature of science was “constantly changing”.
This position is, at best, only trivially true if you consider all forms of change to be exactly the same. Even though I walk 5 km towards work every morning, I will never end up 10 km away from work. Even though my position is “constantly changing”, I’m not jumping all over the place at random, hoping eventually to land at my office. Our understanding of the universe and the processes that hold it together similarly does not fluctuate at random – it is modified by progressively better evidence. So while the statement “science is constantly changing” is true, it is true only in one specific way.
My first friend brought up our understanding of physics as an example of how things might be completely different in 25 years (this was after many drinks, so I’m going to go easy on him). His position was that while we “know” that F=ma today, we might have an entirely different understanding of the relationship between force, mass, and acceleration. He cited the re-orientation of the world once quantum physics was better understood as an example of how science can be replaced with newer understandings.
“Bullshit,” I replied. “Einstein didn’t ‘replace’ Newton; he showed where the limitation of Newton’s mathematics were, and provided a guide for how to overcome them.” In order for Einstein to ‘replace’ Newton, he would have to provide sufficient evidence of events or occurrences where F did not equal ma – in other words, there would have to be overwhelming evidence to show that F only coincidentally equals ma. What Einstein did was show that Newton is true within a specific range of phenomena. The fact is that Einstein’s equations had to continue to describe the phenomena that Newton’s did; the fact that they agree perfectly is a testament to Einstein’s genius.
Perhaps a better illustration of this is the competing theories of evolution in vogue 160 years ago – those of Darwin and Lamarck. Darwin’s theory is familiar to us all – environmental changes favour the survival of certain individuals in a population to survive and breed. Lamarck’s theory was that environments imprinted changes on individuals, who passed traits on to their offspring – for instance, giraffes have long necks due to stretching to reach tall leaves. While it sounds ridiculous now, it certainly fit the available evidence (DNA or modern genetics were not understood, and heritability of traits was well-documented). Presented with two competing theories, biologists of the day looked to see which one matched the evidence best (Darwin, of course, had the advantage of basing his theory on years of carefully-collected evidence).
Since then, many developments have been made in biology. The discovery of the structure of DNA, for example, led to a greater understanding of where variation in species came from, and how mutations occur. Advances in technology have enabled us to measure climate changes and global events that happened millions of years in the past. The tree of life has been re-drawn (one of the few examples of a time when science has been completely re-understood, but the old tree of life wasn’t based on rigorous science, simply some guy looking at things and giving them names) to reflect new understandings in the common ancestry of all life. Changes have been made to Darwin’s original theory in light of evidence that wasn’t available to him at the time. None of this means that evolution has been replaced, any more than the 26 year-old version of me is going to “replace” the 25 year-old version of me on my birthday (which is coming up soon – please give me many presents). It is a development that refines and build upon the understandings of the past.
Hence my objection to the idea that science is “constantly changing”, and therefore is only selectively valid. This attitude comes from a fundamental misunderstanding of what “science” is – one that I have talked about before. Science is not merely a list of facts in a dusty book on a shelf – it is a process that involves taking a bird’s eye view at a group of facts and organizing them into a central concept that can be tested for validity. Any change in scientific understanding must, at the very least, continue to explain those things which have already been observed to be true. It has to be able to explain all of those things that have observed to be true, not simply cherry-picking those facts that agree and neglecting all of the contradictory evidence.
This is why I am confident making statements like “God isn’t real” or “homeopathy doesn’t work” or “vaccines don’t cause autism.” Woo-woo supporters are quick to pipe up “you can’t know that for sure”, demanding the impossible proof of the negative. Claims about an intervening supernatural being, or the (selective) memory of water, or the supposed link between vaccination and developmental disability would require a completely new understanding of physics, physiology, biology, and a handful of other ‘-ologies’ that are based on a wealth of evidence. “Science is changing all the time,” they whine “so we just may not know how it works yet.” Once again, I say unto them “bullshit.” Not only is there insufficient evidence that reiki, or intercessory prayer, or cell phones causing brain cancer, are in any way factual, in order for them to be even plausible, we’d have to invalidate everything we have learned about reality so far.
So while developments can, have been, and will continue to be made in scientific fields, they work in a linear fashion as long as we continue to follow the evidence. It is because of this that I am satisfied to put my trust in this method, rather than one based on faith or magic.
TL/DR: New discoveries don’t “replace” older ones, they add to an always-growing body of evidence that help us to understand the world. Woo-woo theories require us to throw out the evidence, or at least pretend it isn’t there.