What stays the same when science changes?

"Science always changes so there's really no way know what is correct. Years from now everything we think we know could be wrong." -- Anonymous Internet Philosopher

That statement is so generic and I have seen so many countless permutations of it that I have no practical way of counting them. Every single time I have seen statements like that it is a subtle way for the person to say, "I don't want to talk about this anymore and no matter what you say I won't listen to you." This post is not for people like the anonymous commenter, but for people who have sincerely asked the question, "If everything in science can change, then what can we trust?"

So in the midst of the constant change of science what stays the same? Or does anything stay the same?

Let me give an example (I may have shared this story a few years ago). One day I was talking to an acquaintance and he asked me "What if it turns out that gravity isn't real?"

My response was simple, "Rocks still fall down. The Earth continues going around the sun. Gravity doesn't change."

What he was really trying to ask was, "What if gravity doesn't turn out to work the way we think it does?"

There is a difference between the two questions. One deals with what we observe, the other deals with our explanation of why it happened, and how we can predict future events. The former never changes, the latter can change.

One of the earliest explanations of gravity (that we know of) came from Aristotle. His explanation was standard explanation for almost 2,000 years. When Galileo first measured how objects accelerate due to gravity, and Riccioli confirmed his theory and made refinements to his measurement, the universe did not suddenly snap to conform to the new understanding. Things fell towards the Earth as they always had. Their motion remained the same. If you dropped a stone one day and then dropped another the next day the same thing would happen.

These basic observations are the things that do not change when science changes. Over 2,000 years ago Eratosthenes measured the circumference of the earth and also proved that it was a sphere. Since then our understanding of the shape of the Earth has not changed drastically. We still call it a sphere or a globe, but we have also found that it is not perfectly spherical. It bulges slightly at the equator. Our understanding of the shape of the Earth will change and grow as we make more observations, but our new observations will not change our previous observations. We will still view the Earth as roughly spherical.

What will NOT happen is we will wake up one morning and find that the Earth has been a flat disk all along. It won't suddenly become a doughnut shaped object. So when we say that science will change it means that our previous observations will only become more refined.

This brings us to the age of the Earth, which is almost always the topic that prompts the comments like the one I started with. In the years to come there will be changes and refinements to our understanding of the age and formation of the Earth, but just like the globe, we won't suddenly wake up one morning and find that scientists have figured out that they were wrong all along and that the Earth is actually 6,000 years old.

When changes in science come the changes must explain and agree with our previous observations. If we change the way we view the formation of the Earth, or how life evolved, what won't change is the rocks and fossils we analyzed previously. There are plenty of ways that our understanding of evolution may change in radical ways, but what won't change is the fact that it took millions of years, and that we have a part in it. Any new explanations we have must explain the evidence we have and what we currently observe.

Our explanations will become more refined and there may even be major shifts in our understanding, but the evidence will stay the same. Too often we fall into the trap of wanting the evidence to fit our worldview, but we must first make sure our worldview can accommodate the evidence.

The sentiment expressed by the quote at the beginning is a wish that in the future evidence will be found that makes everyone else conform to the worldview of anonymous, rather than a desire to find a worldview that accommodates all the evidence.