How Galileo got the Diurnal Tides Wrong

Galileo was famously prosecuted for his 1632 book onheliocentrism. He had agreed not to advocate heliocentrism, but invited to write a book presenting alternate views. So he wrote the book as a dialog, with the Pope being a foolish character named Simplicio.

One thing I have never understand is how such a brilliant scientist could write this book making his main argument based on a completely bogus theory of tides.

Apparently he was fully aware that the Mediterranean Sea had tides contradicting his theory. But he claimed that the Lisbon tides supported his theory.

That is also wrong, and he was told that it was wrong.

A new paper takes a deep dive into the issue.

Galileo’s argument that the tides of the sea are a product of the motions of the Earth in a heliocentric universe needed diurnal tides to bolster it, because the driving action resulting from those motions would be diurnal. If diurnal tides existed, he could explain away other tidal periods as being a result of the local characteristics of sea basins. Given that when writing the Dialogue Galileo had on hand (thanks to Giovanfrancesco Buonamici) information from Andrés García de Céspedes on diurnal tides occurring in the East Indies, and given the reduced length of the Dialogue’s discussion of tidal periods and its content compared to Galileo’s 1616 discourse on tides to Cardinal Orsini — which included (in error) mention of diurnal tides occurring in the Atlantic at Lisbon — it seems reasonable to suppose that Galileo somehow overlooked adding the Céspedes information to the Dialogue. It seems as reasonable to make this supposition as it is to suppose (as has been done in the absence of awareness of Buonamici’s work) that Galileo clung to an idea in the teeth of adverse evidence, evidence that he even suppressed, leaving himself open to criticisms of his tidal theory in his time, and to the criticisms of modern scholars today.

A diurnal would be one high tide and one low tide per day. That's what Galileo thought, and needed to explain the motion of the Earth. Actually, the tides are caused by gravity, with two high tides and two low tides per day.

You are probably going to say that the Church should not have prosecuted him anyway, because the Church scholars were probably not smart enough to understand the errors in the tide theory. Maybe not, but they were smart enough to recognize that Galileo did not have a compelling argument for the motion of the Earth. It is fine to praise Galileo for his good ideas, but we should also recognize his errors.

It is important to get the Galileo story correct, as it is used as an example so much. India-American activist Sunil Mehta writes:

History offers a chilling precedent. In the 17thcentury, humanity teetered on the brink of intellectual darkness when the church, then the world’s most powerful institution, sought to suppress scientific progress and perpetuate the myth of a geocentric universe. Galileo Galilei, a pioneer of physics, dared to challenge this dogma with evidence showing that the Earth revolved around the sun. Threatened with death, he was forced to recant publicly. But legend has it that despite being compelled to disavow his theories aloud, he muttered under his breath: “And yet it moves!”

Whether or not this story is true, it metaphorically represents the intellectual fight that Galileo and many other brave individuals waged on behalf of science. Thankfully, in the end, darkness was averted and truth prevailed.

What? "Whether or not the story is true ... truth prevailed." And thanks to "brave individuals waged on behalf of science."

No, he is an embarrassment to science. Truth does not prevail by telling falsehoods.

It gets worse.

Today, we stand at a similar crossroads. The world’s most powerful nation, a beacon of intellectual freedom for centuries, is now in danger of coming under the control of a demagogue who wants to build an authoritarian regime on the foundation of misinformation and lies. A plague of intellectual darkness has infected half our nation. Hollow nationalism and misguided xenophobia have taken hold. It is hard to fathom this is happening in the 21st century, but the harsh reality is that a divided country and the quirks of the Electoral College could easily pave the way for an authoritarian future.

What can we do to avert this catastrophe? We must follow the example of Galileo and his followers and fight hard on behalf of truth and facts. The candidates in the upcoming election who are weaponizing misinformation (by making outlandish claims that immigrants are eating pets, for example) need to be soundly defeated.

He has this backwards. I wonder how long he has even been in the USA. The Biden-Harris administration has been much more authoritarian than Trump's, by any measure. The Democrats are the ones trying to restrict the free flow of information. California Democrats just passed a law against political parodies.

The Haitians in Ohio are not even immigrants. They have been allowed to stay temporarily for a couple of years. They are supposed to go back. There is some dispute about what animals they eat.

Whatever your political views, how does this relate to Galileo? The Catholic Church did not seek to suppress scientific truth, and neither does Trump. The whole thing is idiotic.

The Galileo story is told as a story of an authoritarian Church suppressing Galileo's truths. It is all a lie. No truths were supressed. It was not a truth that the Earth moved, because motion is relative, and Galileo had compelling argument for it. There were legitimate scientific arguments for and against. Galileo had a mixture of good and bad arguments.

It is a historical fact that science did best in Europe, under Christian domination. If the Christian authorities were so anti-science, then you might expect science to advance more rapidly away from the Christian authorities. Nope. Science advanced best under Christianity.