Groupthink in science isn’t a problem; it’s a myth

It’s often said that the great arc of science always bends towards the truth, but sometimes it takes an awfully long time to get there. Around 500 years ago, there was really only one scientific phenomenon that was, without controversy, extremely well-understood: the motion of the celestial objects in the sky. The Sun rose in the east and set in the west with a regular, 24 hour period. Its path in the sky rose higher and the days grew longer until the summer solstice, while its path was the lowest and shortest on the winter solstice: part of the annual cycle. The motions of the stars also exhibited a similar 24 hour period, as though the heavenly canopy rotated throughout the night. The Moon migrated night-to-night relative to the other objects by about 12° as it changed its phases, while the planets wandered according to the geocentric rules put forth by Ptolemy and others.

Many who study science often ask themselves, “How was this possible?” How did this geocentric picture of the Universe go largely unchallenged for so long: for over 1000 years? There’s a common narrative but untrue narrative that certain sets of scientific dogmas, like the Earth being stationary and the center of the Universe, could not be challenged. But the truth of why a theory like geocentrism could hold sway for so long is far more complex. The reason the geocentric model beat back all challengers for so long wasn’t because of the problem of groupthink, but rather because the evidence fit it so well: even better than any of the alternatives, such as heliocentrism.

The biggest enemy of scientific progress isn’t groupthink at all, despite the commonness of this accusation. Instead, the culprit is how successful the leading, established theory already is at explaining what we can observe. Here’s the story behind it.

This chart, from around 1660, shows the signs of the zodiac and a model of the solar system with Earth at the center. For decades or even centuries after Kepler clearly demonstrated that not only is the heliocentric model valid, but that planets move in ellipses around the Sun, many refused to accept it, instead hearkening back to the ancient idea of Ptolemy and geocentrism.

Although it isn’t well known, the idea of a heliocentric Universe goes back at least 2300 years, and perhaps even longer. The first recorded writing about it comes from Archimedes, who himself was writing in the 3rd century BCE, when he published a book called The Sand Reckoner. Inside, Archimedes begins contemplating the Universe beyond the Earth, and starts recounting various ideas about what its nature could be. Although he isn’t quite convinced by one of the arguments he’s encountered, he summarizes the (now lost) work of his contemporary, Aristarchus of Samos, who argued the following:

“His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun on the circumference of a circle, the sun lying in the middle of the orbit, and that the sphere of the fixed stars, situated about the same center as the Sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface.”

The work of Aristarchus was recognized as having great importance for two reasons that have little to do with heliocentrism, but nonetheless represented huge advances in the early science of astronomy.

The observed path that the Sun takes through the sky can be tracked, from solstice to solstice, using a pinhole camera. That lowest path is the winter solstice, where the Sun reverses course from dropping lower to rising higher with respect to the horizon, while the highest path corresponds to the summer solstice.

First: why do the heavens appear to rotate?

This was an enormous question that mystified the ancient world. When you look at the Sun, it appears to move through the sky in an arc each day, where that arc is a fraction of a 360° circle: about 15° each hour. This is true regardless of the time of year that you look: whether it’s the long, drawn out days of the summer months or the short days, where the Sun only makes a low arc in the sky, of the winter months. Each night, again irrespective of the seasons, the stars also move in the same fashion: with the entire night sky appearing to rotate about the Earth’s north or south pole (depending on your hemisphere) at that exact same rate of 15° (about each pole) per hour. The planets and Moon do nearly the same thing, just with the tiny, extra addition of their nightly motion relative to the background of stars superimposed atop that rate.

The issue that puzzled the ancient world was that there are two ways to account for this phenomenon, and they both appear to be equally successful explanations:

1. The Earth is stationary, and the heavens (and everything in them) rotate about the Earth with a rotational period of 360° every 24 hours. In addition, the Moon and planets have a slight, extra motion.
2. The stars and other heavenly bodies are all stationary, while the Earth rotates about its axis, with a rotational period of 360° every 24 hours.

If all we saw were the objects in the sky, either one of these explanations could fit the data perfectly well.

Above the central array of the Atacama Large Millimetre/Submillimetre Array (ALMA), the southern celestial pole can be pinpointed as the point about which the other stars all appear to rotate. The length of the streaks in the sky can be used to infer the duration of this long-exposure photograph, as a 360 degree arc would correspond to a full 24 hours of rotation. This observed phenomenon could, in principle, be due either to the rotation of the heavens or to the rotation of the Earth.

And yet, practically everyone in the ancient, classical, and medieval world went with the first explanation and not the second.

Why? Was this a case of dogmatic groupthink?

Hardly. There were two major objections that were raised to the scenario of a rotating Earth, and neither one was successfully addressed until the Renaissance.

The first objection is that if you dropped a ball on a rotating Earth, you wouldn’t expect it to fall straight down from the perspective of someone standing on the Earth. Instead, what you’d expect would be that the ball would fall straight down, in a straight line, while the person on the surface of the rotating Earth would be moving relative to that falling ball. This was an objection that was raised in the ancient world, and that persisted through the time of Galileo. In fact, that objection was only resolved in the 1600s: once we gained an understanding of relative motion and the independent evolution of horizontal and vertical components for projectile motion. Today, many of these properties are known to be a consequence of what we now call Galilean relativity.

The second objection was even more severe, though. If the Earth rotated about its axis every 24 hours, then your position in space would differ by the diameter of Earth — about 12,700 km (7,900 miles) — from the start of the night to the end of the night. That difference in position should result in what we know astronomically as parallax: the shifting of closer objects relative to the more distant ones.

The stars that are closest to Earth will appear to shift periodically with respect to the more distant stars as the Earth moves through space in orbit around the Sun. Before the heliocentric model was established, we weren’t looking for “shifts” with a ~300,000,000 kilometer baseline over the span of ~6 months, but rather a ~12,000 kilometer baseline over the span of one night: Earth’s diameter as it rotated on its axis. The distances to the stars are so great that it wasn’t until the 1830s that the first parallax, with a 300 million km baseline, was detected. Today, we’ve measured the parallax of over 1 billion stars with ESA’s Gaia mission.

Second: why could we not observe any stellar parallaxes for the stars?

And yet, no matter how acute your vision was, nobody had ever observed a parallax for any of the stars in the sky. If the stars were allowed to be positioned at a multitude of different distances from us and, at the same time, the Earth was rotating, we’d expect to see that the closest stars to Earth would appear to shift in their positions, relative to the other stars, from the beginning of the night to the end of the night. And still, despite that prediction, no parallax was ever observed among the stars. This even persisted through the age of the telescope: no parallax was ever detected throughout the 1600s or 1700s; it was not until the mid-1800s that the first stellar parallax would finally be observed.

With these two “null results” combined:

• the fact that there was no evidence for the rotating Earth here at Earth’s surface,
• and the fact that astronomers saw no evidence for parallax (and hence, a rotating Earth) among the stars in the heavens,

the explanation of the rotating Earth was disfavored. This left the explanation of a stationary Earth and a rotating sky — or a “celestial sphere” beyond Earth’s sky — to choose from as the preferred explanation. You can clearly see, based on the evidence, how easy it would be to draw the incorrect conclusion.

And so it makes sense to ask, in hindsight, “were we wrong?” And the answer is yes: we absolutely were.

This Foucault pendulum, on display in action at the Ciudad de las Artes y de las Ciencias de Valencia in Spain, rotates substantially over the course of a day, knocking down various pegs (shown on the floor) as it swings and the Earth rotates. This demonstration, which makes the rotation of the Earth very clear, was only concocted in the 19th century: more than 200 years after the death of Galileo.

The Earth really does rotate, but we didn’t have the tools, the technology, or the necessary precision to make quantitative predictions for what we’d expect to see. We didn’t know how to translate the assumed physical phenomenon (the rotation of the Earth) into an experiment or observation that would quantitatively show its effects in a measurable fashion. It turns out that the Earth does rotate, but the key experiment that allowed us to see it on Earth, the Foucault pendulum, wasn’t developed until the 19th century.

Similarly, the first parallax wasn’t seen until the 19th century either, owing to the fact that the distance to the stars is enormous, and it takes the Earth migrating by millions of kilometers over the course of weeks and months, not thousands of kilometers over a few hours, for our telescopes to detect it. (Even today, modern telescopes can’t detect stellar parallax over the course of merely a single night!)

The problem was that we hadn’t yet gathered sufficient evidence, with specific experiments and/or observations to point to, to tell these two predictions apart. Moreover, the flaw in our reasoning was that we conflated “absence of evidence” (I see no evidence of the rotating Earth or of Earth revolving around the Sun) with “evidence of absence.” We couldn’t detect a parallax among the stars, which we expected for a rotating Earth, so we concluded that the Earth wasn’t rotating. We couldn’t detect an aberration in the motion of falling objects, so we concluded that the Earth wasn’t rotating. We must always keep in mind, in science, that the effect we’re looking for might actually be present, it just might be present at a level that’s below the current threshold of where we’re currently capable of making measurements.

61 Cygni was the first star to have its parallax measured and published (back in 1838), but also is a difficult case due to its large proper motion. These two images, stacked in red and blue and taken almost exactly one year apart, show this binary star system’s fantastic speed. If you want to measure the parallax of an object to extreme accuracy, you’ll make your two ‘binocular’ measurements simultaneously, to avoid the effect of the star’s motion through the galaxy. Gaia is exceptionally good at characterizing the orbits of nearby stars with small separations from their companion, but faces more challenges with more distant, wider binary systems.

Still, Aristarchus was indeed able to make important advances. Despite having an interest in heliocentrism, he was also able to set his preference for a heliocentric Solar System aside, and was then able to use light (from the Sun) and geometry (between the Sun, Moon, and Earth) within the prevailing geocentric framework to concoct the first method for measuring the distances to the Sun and the Moon, and to concurrently also estimate their sizes. Although his values were way off — mostly due to his claims that he could “observe” a dubious effect now known to be beyond the limits of human vision — his methods were sound. Using modern (technology-assisted) data, Aristarchus’s methods can indeed be leveraged to calculate the distances to and sizes of the Sun and Moon to remarkable precision.

It was only in the 16th century that there was a revived interest in Aristarchus’s heliocentric ideas, notably from Nicolaus Copernicus. Copernicus’s big revelation was to show how the most puzzling aspect of planetary motion, the periodic “retrograde” motion of the planets, could be equally well-explained from two perspectives that led to equivalent observables.

1. Planets could orbit according to the geocentric model: where planets moved in a small circle that orbited along a large circle around the Earth, causing them to physically move “backward” at occasional points in their orbit.
2. Or planets could orbit according to the heliocentric model: where every planet orbited the Sun in a circle, and when an inner (faster-moving) planet overtook an outer (slower-moving) one, the observed planet appeared to change direction temporarily.

One of the great puzzles of the 1500s was how planets moved in an apparently retrograde fashion. This could either be explained through Ptolemy’s geocentric model (left), or Copernicus’ heliocentric one (right). However, getting the details right to arbitrary precision was something neither one could do. It would not be until Kepler’s notion of heliocentric, elliptical orbits, and the subsequent mechanism of gravitation proposed by Newton, that heliocentrism would triumph by scientific standards.

Beyond Aristarchus and a third consideration: why do the planets appear to make retrograde paths?

This was the final key question that would raise its head when it came to comparing heliocentrism versus geocentrism. Right here, we have two potential explanations for an observed phenomenon that approach the problem from vastly different perspectives, yet both were capable of producing the phenomenon that was observed. On the one hand, we had the old, prevailing, geocentric model, which accurately and precisely explained what we saw with the introduction of equants, deferents, and epicycles. But on the other hand, we had the new, upstart (or resurrected, depending on your perspective), heliocentric model, which could also explain what we saw by leveraging the relative motions of inner and outer planets orbiting the Sun.

Unfortunately for Copernicus, the geocentric predictions were more accurate — with fewer and smaller observational discrepancies — than the heliocentric model. Copernicus could not sufficiently reproduce the motions of the planets as well as the geocentric model, no matter how he chose his circular orbits. In fact, Copernicus even started adding in epicycles of his own to the heliocentric model to try and improve the orbital fits, in hopes that it would approach the accuracy of the geocentric model. And yet, even with this ad hoc fix, his heliocentric model, although it generated a renewed interest in the problem, did not perform as well as the geocentric model in practice.

This animation shows the apparent motion of Mars during one of its recurrent retrograde motion periods: in this case, during August and September of 2003. During most years, there will be a period where Mars will appear to slow down in its migration across the sky, stop, reverse directions, speed up and slow down, and then stop again, resuming its original motion. This retrograde period stands in contrast to the normal prograde motion.

This, right here, further helps us understand the reason it took humanity so long to reach a superior model of the Universe than the geocentric one. The reason it took close to 2000 years is because of how successful the geocentric model, and not alternative models, could describe all that we observed. The positions of the heavenly bodies could be modeled exquisitely using the geocentric model, in a way that the heliocentric model could not reproduce. It was only when the 17th century arrived, and the work of Johannes Kepler  came along— work that tossed out the Copernican assumption that planetary orbits must be reliant on circles  and replaced it with more accurate elliptical orbits— that led to the heliocentric model finally overtaking the geocentric one.

What was most remarkable about Kepler’s achievement wasn’t:

• that he used ellipses instead of circles,
• that he overcame the dogma or groupthink of his day,
• or that he actually put forth laws of planetary motion, instead of just a model.

Instead, Kepler’s heliocentrism, with elliptical orbits, was so remarkable because, for the first time, an idea had come along that described the Universe, including the motion of the planets, better, more accurately, and more comprehensively than the previous (geocentric) model could.

Tycho Brahe conducted some of the best observations of Mars prior to the invention of the telescope, and Kepler’s work largely leveraged that data. Here, Brahe’s observations of Mars’s orbit, particularly during retrograde episodes, provided an exquisite confirmation of Kepler’s elliptical orbit theory. Kepler put forth his 1st and 2nd laws of planetary motion in 1609, with his 3rd law coming 10 years later: in 1619. Copernicus, Kepler, and Galileo were among the most important figures in launching our modern scientific revolution.

In particular, the (highly eccentric) orbit of Mars, which was previously the biggest point of trouble for Ptolemy’s model, was an unequivocal success when modeled with Kepler’s ellipses. Under even the most stringent of conditions, where the geocentric model exhibited its greatest departures from what was predicted, Kepler’s heliocentric model would display its greatest success. That’s often the test case for making a scientific advance: look where the prevailing theory has the greatest difficulty, and try to find a new theory that not only succeeds where the prior one fails, but succeeds in every instance where the prior one also succeeds. Once you can do both of those things, then you truly have a chance to instigate a scientific revolution.

Kepler’s laws of planetary motion would pave the way for Newton’s law of universal gravitation, where those universal rules apply equally well to the moons of the Solar System’s planets and to the exoplanetary systems we have in the 21st century. One can complain about the fact that it took some ~1800 years, from the time of Aristarchus until the time that heliocentrism finally superseded our geocentric past, but the truth is that until Kepler, there was no heliocentric model that matched the data and observations as well as Ptolemy’s model did.

It wasn’t groupthink that was the problem, nor dogma that prevented anyone from considering the alternatives. The key problem was the unequaled success of the Ptolemaic model. It was only when a new model proved more successful that a scientific revolution would become possible. In fact, as soon as there was a new model that was more successful, the old one was swiftly replaced by scientists worldwide, with the only “dogmatic thought” coming from ideological opponents of the new theory.

The best fit cosmological model to the latest BAO data, using DESI’s DR2 data with their fit for evolving dark energy, with the black curve (at left) and the solid yellow curve (at right) indicating the predictions of the standard cosmological model. These are not the best fits to the data points (dashed yellow line at right), which instead indicate that the sum of the masses of the three species of neutrino should be negative (black line at right), which is an unphysical solution. Although the current data displays hints of evolving dark energy, it also leads to pathological predictions.

It’s vital to remember the true reason that this scientific revolution occurred at all, and that heliocentrism could become the favored theory over geocentrism. It is because there were “cracks” in the already existing theory: where observations and predictions failed to align (such as with the orbit of Mars). Whenever this occurs, that’s where the opportunity for a new revolution may arise, but even then, a revolution is not guaranteed.

• Are dark matter and dark energy real, or is this an opportunity for a revolution?
• Do the different measurements for the expansion rate of the Universe signal a problem with our techniques, or are they an early indication of potential new physics?
• What about non-zero neutrino masses?
• Or the muon g-2 experiment?

It’s always important to explore the possibilities, even the most wild ones we can imagine. But then, the key point is to always return to, and to ground ourselves in, the observations and measurements we can actually acquire. If we ever want to go beyond our current understanding, any alternative theory has to not only reproduce all of our present-day successes, but to succeed where our current theories cannot. That’s why scientists are often so resistant to new ideas: not because of groupthink, dogma, or inertia, but because most new ideas never clear those epic hurdles. Whenever the data clearly indicates that one alternative is superior to all the others — but never before that point — a scientific revolution is likely to follow.

This article was first published in August of 2023. It was updated in October of 2025.