Amazing things are out there waiting to be noticed

March 22, 2021

It is said that, some time around 1590 AD, Galileo Galilei dropped two spheres of different masses from the Leaning Tower of Pisa[1], thereby demonstrating that they fell at the same rate. This was a big deal because it contradicted Aristotle’s theory of gravity, in which objects are supposed to fall at a speed proportional to their mass.

Aristotle lived from 384–322 BC, which means his observably incorrect theory had been scientific orthodoxy for more than 1,900 years before being overturned[2].

How did this happen? For nearly two millennia, every scientist had it in his power to hold a little stone in one hand and a rock in the other, drop them both, and see with his own eyes that they fell at the same speed. Aristotle’s theory was obviously wrong, yet that obviously wrong theory remained orthodox for eighty generations.

My take is that it happened because people — even scientists — have a strong tendency to trust respected predecessors, and not even to look to see whether their observations and theories are correct. I am guessing that in that 1,900 years, plenty of scientists did indeed do the stone-and-rock experiment, but discounted their own observations because they had too much respect for Aristotle.

But even truly great scientists can be wrong.

Now, here is the same story, told on a much much smaller scale.

Well into the 2010s, it was well known that in sauropods, caudal vertebrae past the first handful are pneumatized only in diplodocines and in saltasaurine titanosaurs. As a bright young sauropod researcher, for example, I knew this from the codings in important and respected phylogenetic analysis such as those of Wilson (2002) and Upchurch et al. (2004).

Until the day I visited the Museum für Naturkunde Berlin and actually, you know, looked at the big mounted Giraffatitan skeleton in the atrium. And this is what I saw:

That’s caudal vertebrae 24–26 in left lateral view, and you could not wish to see a nicer, clearer pneumatic feature than the double foramen in caudal 25.

That observation led directly to Matt’s and my 2013 paper on caudal pneumaticity in Giraffatitan and Apatosaurus (Wedel and Taylor 2013) and clued us into how much more common pneumatic hiatuses are then we’d realised. It also birthed the notion of “cryptic diverticula” — those whose traces are not directly recorded in the fossils, but whose presence can be inferred by traces on other vertebrae. And that led to our most recent paper on pneumatic variation in sauropods (Taylor and Wedel 2021) — from which you might recognise the photo above, since a cleaned-up version of it appears there as Figure 5.

The moral

Just because “everyone knows” something is true, it doesn’t necessarily mean that it actually is true. Verify. Use your own eyes. Even Aristotle can be wrong about gravity. Even Jeff Wilson and Paul Upchurch can be wrong about caudal pneumaticity in non-diplodocines. That shouldn’t in any way undermine the rightly excellent reputations they have built. But we sometimes need to look past reputations, however well earned, to see what’s right in front of us.

Go and look at fossils. Does what you see contradict what “everyone knows”? Good! You’ve discovered something!

 

References

Notes

1. There is some skepticism about whether Galileo’s experiment really took place, or was merely a thought experiment. But since the experiment was described by Galileo’s pupil Vincenzo Viviani in a biography written in 1654, I am inclined to trust the contemporary account ahead of the unfounded scepticism of moderns. Also, Viviani’s wording, translated as “Galileo showed this by repeated experiments made from the height of the Leaning Tower of Pisa in the presence of other professors and all the students” reads like a documentary account rather than a romanticization. And a thought experiment, with no observable result, would not have demonstrated anything.

2. Earlier experiments had similarly shown that Aristotle’s gravitational theory was wrong, including in the works of John Philoponus in the sixth century — but Aristotle’s orthodoxy nevertheless survived until Galileo.

 

14 Responses to “Amazing things are out there waiting to be noticed”

  1. Matt Wedel Says:

    I am guessing that in that 1,900 years, plenty of scientists did indeed do the stone-and-rock experiment, but discounted their own observations because they had too much respect for Aristotle.

    I wonder. From what I’ve read, there was little widespread use for empiricism among the intelligentsia during that time. Still, one imagines at least a few people must have tried the experiment.

    Your hypothesis — that people did the experiment, but discounted or modified their results to avoid contradicting a respected expert — has a well-documented example from the last century. The 1909 oil drop experiment by Robert Millikan and Harvey Fletcher to determine the charge of the electron won them the Nobel Prize, and it was so respected that later researchers were loathe to publish discordant results. Here’s Richard Feynman talking about that case, in his commencement address at CalTech in 1974 (copied from this Wikipedia page):

    “We have learned a lot from experience about how to handle some of the ways we fool ourselves. One example: Millikan measured the charge on an electron by an experiment with falling oil drops, and got an answer which we now know not to be quite right. It’s a little bit off because he had the incorrect value for the viscosity of air. It’s interesting to look at the history of measurements of the charge of an electron, after Millikan. If you plot them as a function of time, you find that one is a little bit bigger than Millikan’s, and the next one’s a little bit bigger than that, and the next one’s a little bit bigger than that, until finally they settle down to a number which is higher.

    “Why didn’t they discover the new number was higher right away? It’s a thing that scientists are ashamed of—this history—because it’s apparent that people did things like this: When they got a number that was too high above Millikan’s, they thought something must be wrong—and they would look for and find a reason why something might be wrong. When they got a number close to Millikan’s value they didn’t look so hard. And so they eliminated the numbers that were too far off, and did other things like that …”

    A third possibility: during the time that Aristotle was the Roman-Catholic-Church-approved foundation of natural knowledge, people were hesitant to broadcast contradictory results because they didn’t want to get burned at the stake. Which is a different thing from not wanting to challenge Aristotle because of his pre-eminent reputation.

    A fourth possibility: people did the experiment, got an answer which contradicted Aristotle, but without printing presses or a culture of dissemination of scientific knowledge, had no way to distribute their findings. How many famous empiricists do we know of between Aristotle and Galileo, to even have findings from? (I’m asking out of ignorance, not snark, but I struggle to come up with examples.)

  2. Matt Wedel Says:

    Also, full disclosure, I explicitly claimed in my 2003 JVP paper and my 2005 book chapter that caudal vertebrae in brachiosaurids were not pneumatic. So I am as guilty as anyone else of perpetuating that idea, and more guilty than most, since documenting pneumaticity was my particular ambit, whereas for other researchers caudal pneumaticity was just one tiny group of characters among the total sauropod set.

    I did mention caudal pneumaticity in Giraffatitan in my 2009 air sac paper, but only because Mike had shown me his photos from Berlin. Mike and I saw and photographed the tail of Giraffatitan in our Berlin visit in December, 2008, but my air sac paper was already in press at that point.

    (All these papers are freely available at https://sauroposeidon.wordpress.com/.)

  3. Brad Lichtenstein Says:

    Greeks were in many cases anti-observational. They constructed elaborate theories upon which to build a literally “pure” model of the observable universe, and observations to verify would simply not have been elegant enough to be warranted, compared to their mental edifices. They eyeballed the sun and moon, and decided it looked like 2 degrees of subtended arc. Any fool with a protractor could have measured the 1/2 degree, but it just never occurred to them to bother. The exception I’m aware of, was the guy who hired someone to pace the distance from his locality in Greece, to the well in Egypt where, on some day of the year, the sun at local noon shone straight down and reflected back up from the surface of the water. And on that day, he measured the angle of the sun to local vertical – and combined the two measurements to get within a few miles of the actual diameter of Earth. Even in the time of da Vinci, when his machines were making obvious contributions to winning real wars, and his sculpture and paintings were recognized as genius – the fact that he worked with his hands, that he measured and calculated his faces and bodies – he was NOT socially on par with the nobility, because those things were simply beneath them. Engineering as a respectable profession, probably began sometime around the mid-18th century, usually away from nobility – which is why the small business entrepreneur was basically built into the US Constitution. Notably not in the French Republic.

  4. Mike Taylor Says:

    Matt, The Millikan experiment is a great example — once an experiment has won an actual Nobel Prize, it’s terribly bad manners to question whether it’s actually correct or not.

    And I think you might be onto something with difficulties of dissemination. My guess — and I admit this is 100% unverifiable — is that hundreds of people between Aristotle and Galileo figured out that objects fall at a speed independent of their mass, but none of them had a way to get the word out before someone as prestigious as Galileo got there.

    Also, so funny that you asserted apneumatic brachiosaur tails twice in the published literature! Did we make that point in our 2013 paper? I don’t remember that we did. (And it’s hard to check by searching the published version because of PLOS’s stupid numbered-references system.)

    Brad, the idea of actively anti-observational scientists is so alien to me that I’m struggling to wrap my mind around it. Thanks for raising it, though!


  5. In Europe, Aristotle’s tutor Plato was the last word in philosophy until the Renaissance, and he actually claimed that observation was so inherently flawed as to be useless (the famous “shadows on the cave wall” metaphor). The church accepted Plato’s idealism in the form propagated by later followers such as Plotinus. Aristotle was treated more as a good source for various facts than as a proper source of philosophy, so even his limited embrace of empiricism was rejected for centuries in favor of pure cogitation. The idea was that the human mind, being of spiritual origin, had access to realms of divine truth that could not be gained by anything so gross and physical as the eyes.

    Very similar and much deadlier trends occurred in medicine. Educated doctors unquestioningly followed the classical physician Galens, and their patients suffered accordingly. Barber-surgeons and herb-peddlers, unburdened by education, at least occasionally hit on an effective remedy, but their ideas were of course beneath the notice of the elite.

  6. Allen Hazen Says:

    Aristotle gets a lot of bad press, and I’m not sure he always deserves it. Favourite example: he claimed that women had fewer teeth than men, and Bertrand Russell made fun of this as an example of a priori dogmatism: “Why didn’t he look in his wife’s mouth?” Well, some people never get their “wisdom teeth) (third molars)– my wife for example. And apparently, at least in European populations, “third molar agenesis” is more common in women: so it’s at least possible that the problem was that he DID look in his wife’s mouth!
    And in lots of ways he was an empiricist, looking to observation. In Raphael’s painting of the “School of Athens,” Plato and Aristotle are shown side-by-side, Plato pointing up to heaven and Aristotle pointing out into the world! Which is how he was able to make real contributions to biology. (He was Alexander the Great’s former teacher, and made use of his connections to have biological specimens shipped back to Athens to examine.)
    As to the experiment… it’s not as easy to do as it sounds. You need something like the Tower of Pisa: drop things from arm’s length and they will hit the ground too quickly for a reliable judgment of which one hit first. (Galileo, therefore, when working out the principles of gravitational acceleration, did it, not by dropping things, but by rolling balls down ramps, so the speed would be enough lower that he could make useful comparisons.) And it probably helps to have heavy things to drop (some versions of the story abut the Leaning Tower of Pisa specify cannonballs!)– drop lightweight things and there are likely to be confounding air resistance effects: a dropped stone really does hit the ground faster than a dropped feather!

    (Sorry, I’ve been participating in a seminar on the history of formal logic, and Aristotle’s contributions to THAT science are so impressive that I tend not to think he was likely to be an utter fool elsewhere.)

  7. Tony Zbaraschuk Says:

    “Nullius in verba.”

  8. Marja Erwin Says:

    Galileo also used the thought experiment of 2 balls connected by a chain or by a bar. If heavier objects fall faster, would these fall at the speed of the separate weights or the combined weight?

    The combination of easier-to-time experiments with inclined planes, harder-to-time ones with free fall, and thought experiments may have been more persuasive than any one alone.

    Aristotle was trying to save the appearances– i.e. observed reality– when earlier philosophers such as Parmenides and Zeno had rejected it as an illusion. That may have made him reluctant to trust results which went against intuition, and since Zeno’s thought experiments were supposed to disprove observed reality, especially reluctant to trust more thought experiments.

  9. Michael Traynor Says:

    Trouble with the “…they didn’t want to get burned at the stake.” bit is that nobody was ever burned at the stake over their scientific claims. And to anticipate the Bruno trope, his claims were not scientific ones but purely philosophical. And, at the time Galileo got in trouble with the Church, the Church was the one with science on its side. For some reason, Galileo was pure Copernican, ignoring Kepler’s work so when he wrote his Dialogue on the two chief world systems, he was whiffing on both of the two then chief world systems. One part was his preferring Copernicus’ mystical spheres and the other pretending the Church preferred the Ptolemaic system when it supported the Tychonian system (Sun and Moon orbit Earth and planets orbit the Sun).

    “… without printing presses or a culture of dissemination of scientific knowledge …” Turns out there was a culture of dissemination of scientific knowledge based on exchanges of letters among scholars. There were a number of folk who served in the early Renaissance (perhaps going back into the late Middle Ages) who served as informal scientific publishers, receiving letters from scholars, copying them and distributing them to other scholars.

    I’m almost certain I recall (too late tonight to check, maybe tomorrow) that someone before Galileo showed Aristotle was wrong about falling objects but lacked Galileo’s shameless self-promotion and didn’t make a big splash.

    Anyone with an interest in the history of science and math in that period is well rewarded by reading Thony Christie’s blog ‘The Renaissance Mathematicus’ [ https://thonyc.wordpress.com/ ]. A big part of the fun there is Thony’s take-downs of scientists who think being a scientist means they know the history of science.

    Oh, and fun point about the falling problem is that in Aristotle’s view, heavy things fell to the lowest level in the universe because they were corrupt while the pure, perfect heavens were at the highest levels. So the Copernican revolution didn’t dethrone man from an exalted place at the centre of the cosmos but exalted him into the heavens or brought the heavens down to the corrupt level of man. If that seems off, remember where Hell traditionally is – at the very centre of a geocentric cosmos.

  10. Matt Wedel Says:

    Thank you for setting me straight on some things. If you do find a pre-Galileo example of someone disproving Aristotle on the falling objects, I’d love to hear an update. Especially if we know why that disproof didn’t have more legs.

  11. Mike Taylor Says:

    Posted on behalf of Nathan Myers:

    As I understand it, the Pisa experiment was described but not actually conducted. Galileo’s logical argument, of the two bodies connected by a string, was considered sufficient. If there is any evidence of Galileo performing it, I would welcome having it pointed out.

    Similarly, BTW, I gather nobody has found anyplace where Franklin writes that he actually did fly a kite in a storm. He wrote of the idea, and everybody seems to have simply assumed he had done it. After it had been repeated so often by so many, he must have been embarrassed to contradict them, so allowed them to hold onto their misapprehension.

    On a slightly more sauropod-vertebral note, it appears that the notion of cervical secondary hearts enabling plausible blood pressure even with erect necks has been dismissed solely on the assumption that cervical arterial valves would have no value on their own, so that the secondary hearts’ valves and musculature would have needed to evolve simultaneously. It Seems to Me that arterial valves would have been valuable on their own.

    If obliged to choose between sauropods unable to raise their heads without suffering a fatal embolism, or cervical secondary hearts, I know which I would choose.

  12. Mike Taylor Says:

    As I understand it, the Pisa experiment was described but not actually conducted. […] If there is any evidence of Galileo performing it, I would welcome having it pointed out.

    Like I said in the footnote to the original article, the experiment was described by Galileo’s pupil Vincenzo Viviani in a biography written in 1654, I am inclined to trust the contemporary account ahead of the unfounded scepticism of moderns. Also, Viviani’s wording, translated as “Galileo showed this by repeated experiments made from the height of the Leaning Tower of Pisa in the presence of other professors and all the students” reads like a documentary account rather than a romanticization. And a thought experiment, with no observable result, would not have demonstrated anything.

  13. llewelly Says:

    over 200 millions of years before Galileo or the church existed, Ingentia prima simultaneously dropped a large rock and a smoll rock from their mouth, and observed that they struck the ground at the same time.

    Ingentia thought this was a neat observation and showed it to all their friends.

    Eventually one of their friends said: “this is cool, you should write it up and publish it in nature”

    Ingentia agreed, and after many months of work the manuscript was ready and they tried nature.

    But nature said: “first of all you broke the embargo rule, and second, rocks are boring and this is not novel”

    On that sad day, sauropodomorphs and their descendants decided that scientific publishing was not for them, and they would focus on evolving huge sizes and long necks.

    And for about 150 million years, they were extremely successful.

    The End


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