Listener Dex Wood sends us the following question:
I am kind of concerned about proving our ability to extrapolate with past evidence. This concern came from a discussion I was having with someone about evolution. I claimed that the large body of evidence allows us to determine the course that evolution took in the past. They returned with, “You weren’t there, and there was no direct observation.” It is true that I was not there to directly observe it, and showing someone that evidence being used as observation is valid, seems difficult. How do you deal with someone arguing that things could have been different a long time ago? This can apply with radioactive dating or physics in general.Thank you for your reply,
This is a classic strategy of denial, used most prominently in evolution denial (i.e. creationism/intelligent design). It is simply an attempt to deny one form of legitimate scientific evidence and reasoning.
First, I want to point out that “extrapolation” is not the best word to use for what Dex is asking. Extrapolation specifically means to find a pattern within existing data and then to project that pattern beyond the data. The specific example he gives, figuring out the path of prior evolution, is mainly interpolating – filling in data between existing data points. The fossil evidence represents snap-shots of the evolutionary past and we infer what happened between those snap-shots.
But the actual key to the process is inference – using observations of the present to infer what happened in the past. All historical sciences rely upon intelligence inference to reconstruct the past – including cosmology, archaeology, paleontology, and history itself.
Obvious examples are often helpful to illustrate a principle. For example – how does anyone know that the world existed before they were conceived? They were not there to see or experience any of it. (This is slightly different than the question of how do we know that God did not create the universe 5 second ago, complete with our fake memories of the past, in that it is singling out direct observation as the only form of “legitimate” evidence.)
There are fundamental assumptions in science – there has to be otherwise science has no framework in which to operate. We try to make these assumptions as fundamental as possible, so as not to constrain the scientific endeavor unecessarily. One of these fundamentals is the principle of cause and effect – every effect has a preceding cause. Causes must come before effects – there is an arrow of time. This principle is born out by all reliable direct observation.
Therefore, if every effect has a cause, then you (an effect) must have been caused by something (your parents). That cause must in turn have a cause (your grandparents), etc. We can therefore work backwards, infering prior causes as best we can with the remnants they have left in the present, all the way to the beginning of time – the big bang.
To deny cause and effect is to deny all of science.
Another basic principle of science is that of universality – the laws of the universe are the same everywhere and always. We do say that the laws of physics “break down” in certain situations, like within the event horizons of black holes and in the moments after the big bang, but what we really mean is that our current description of those physical laws is incomplete and cannot account for those situations. Our mathematical equations break down – we need better more complete ones, even though they work well in most situattions. Newtons laws of motion work well as long as relativistic effects are not important – for that we need Einstein’s better equations.
But even when searching for an equation of quantum gravity to describe black holes we are assuming that the physical laws inside black holes are the same as those inside your living room. We are searching for one equation to describe it all.
This assumption of universality is actually an example of inductive reasoning, which is another cornerstone of science – the formation of a general rule based upon a limited set of observations. We observe that when we measure constants they do not seem to change over time and place. We therefore induce (a more precise term than extrapolation in this situation, but extrapolation is not bad) that the constants are constant always and everywhere.
When we measure the speed of light today we get the same figure as we did 20 years ago (within the precision of our instruments) and so we induce that it was the same 20 million years ago.
Scientists can say with a high degree of confidence that the totality of existing evidence points to the conclusion that the laws of physics and the universe are constant and universal. This has been sufficiently established that it is treated as a rule – a law of its own. As with all of science, we build on such reliable conclusions to form further conclusions. We can therefore infer what happened in the past with the same degree of confidence by which we infer the laws of the universe do not change willy-nilly.
The law of constancy has been sufficiently established that anyone claiming it is not true now has the burden of proof – they have to convincingly demonstrate that radioactive decay half-lives were different in the past, or that they change over time. No one has met this burden of proof.
What evolution-deniers are actually doing is called ad-hoc reasoning – they make up an explanation as needed in order to arrive at a pre-determined and desired conclusion. Ad-hoc reasoning is worthless because you can use it to defend any hypothesis. There are always an infinite number of possible hypotheses that are compatible with all existing evidence – if you use ad-hoc reasoning to fix any problems that occur.
Current dating methods roughly agree on an ancient earth about 4 billion years old. If you don’t like that conclusion, however, you can pull an ad-hoc argument out of your nether regions and say that the laws of physics were different in the past, all in precisely the way necessary for the age of the earth to be what I want it do be. This strategy is sometimes called a “fudge factor”, which is a euphamism for cheating.
What evolution deniers often don’t realize is that by denying the principles of cause and effect and the constancy of physical laws they are denying all of science – not just historical sciences, and not just evolution.