I have seen a number of comments lately that “consensus” has no place in science, and that claims that there is a “scientific consensus” are just thinly veiled political double-speak. I have to take issue with such criticisms. In fact, consensus is one of the cornerstones of science.

This is not quite the same consensus used in politics or everyday life. Consensus means “general agreement” and is usually achieved through some form of discussion and negotiation. Consensus is therefore agreement over opinions, and is often agreement over a course of action despite differing opinions.

In science, consensus is derived from data and independent replication of experiments. It is the consensus that an idea—specifically, a testable hypothesis—is correct. It is the expression of scientists that a hypothesis is (a) scientifically testable and falsifiable, (b) that it has not been falsified and (c) that it explains the universe better than competing hypotheses. It is a consensus derived from the replication of observations or tests by other researchers.

Part of the problem, here, is that science has a habit of taking everyday words and developing very specific meanings around them. This happens because scientists need to communicate clearly and exactly at times, and language is messy and full of fuzzy concepts. The same thing happens in a lot of occupations. For example, accountants also develop specific meanings for everyday words.

Scientists no longer argue over the validity of Newton’s hypothesis on the gravitational force because there is broad consensus that the hypothesis is correct (as far as it goes). Objects attract each other according to their mass and the distance between them, and there have been plenty of independent experiments confirming the specific relationship, F = -G M₁m₂ / r². The consensus is so strong that it’s referred to as Newton’s law of gravity. Likewise, scientists no longer argue over the geocentric model of the universe because there is broad consensus—derived from data collected over centuries by many independent researchers—that the Earth is not at the center of the solar system, let alone the universe.

Conversely, there is very little consensus when it comes to the accelerating expansion of the universe. Cosmologists agree that the universe is expanding faster than can be explained by our current understanding of the universe, but there are many, conflicting hypotheses about the causes. There is consensus over the fact of the accelerating expansion but the data does not yet support consensus on the underlying physical processes or mechanism causing it, and so there is no consensus about the physical process.

In one sense, scientific consensus is stronger, or more robust, than we are used to thinking about in politics and everyday life, precisely because it is based on observation and careful analysis by independent groups. It’s not just consensus based on what we think might be true, or what we want to be true, but based on what careful observation tells us must be true. Scientific consensus is not subject to whim.

From another perspective, though, scientific consensus is much weaker than we are used to. In science, there is no downside to abandoning or overturning a consensus when the data points in a different direction. In fact, there is significant benefit to being the person who can overturn a previous consensus; we remember Galileo, Newton, Darwin, Einstein and others precisely because their work, collecting and analyzing data, was so pivotal in altering the scientific consensus. In everyday life, if you back out of a consensus agreement, it’s likely that others party to the agreement will feel betrayed. There can be a significant social cost to pay for backing out of a consensus, even when you are convinced that you are right. Scientists may sometimes feel this same social pressure, but the scientific method provides clear guidance for adopting or abandoning consensus, and it doesn’t focus on the people involved but rather on external, objective observations of how the universe works. Scientific consensus is, perhaps, more readily changed than conventional consensus.

So consensus does exist is science and it plays an important role in science. We should be careful to distinguish, though, between consensus based on independent replication of results and consensus based on preconceptions and social negotiation.