Discoveries and Opinions of Galileo

“The earth, in fair and grateful exchange, pays back to the moon an illumination similar to that which it receives from her throughout nearly all the darkest gloom of night.”

Galileo seeks to explain why the moon emits a “secondary light,” a question that gave rise to varying theories. He concludes that this light does not come directly from the sun or from a star, but from the earth reflecting the sun’s rays. This was a significant advance on previous understandings.

“We shall prove the earth to be a wandering body surpassing the moon in splendor, and not the sink of all dull refuse of the universe.”

Galileo believes that his new discoveries prove the Copernican system, which states that the earth revolves around the sun instead of remaining fixed in place. Galileo hopes to treat this topic in full in a planned work, “System of the World,” but he believes that his ideas in “The Starry Messenger” already hint at this conclusion.

“The galaxy is, in fact, nothing but a congeries of innumerable stars grouped together in clusters.”

Using the telescope has allowed Galileo to see more clearly than ever before the “nature and material” of the Milky Way. Galileo’s discoveries led to an expanded understanding of the vastness of the universe and the immense number of stars.

“For names and attributes must be accommodated to the essence of things, and not the essence to the names, since things come first and names afterwards.”

A basic philosophical principle is that our conclusions must conform to the truth that we see, instead of our bending our conclusions to our preconceived ideas. Galileo insists throughout his writings on the necessity for unclouded judgment in science and philosophy.

“Therefore I see nothing discreditable to any philosopher in confessing that he does not know, and cannot know, what the material of the solar spots may be.”

Galileo states his belief in the necessity of intellectual humility in those who seek knowledge. One must have the humility to admit that one does not know something, instead of pretending to have knowledge. Galileo thus declares his conviction that science has limited objectives and can never grasp complete knowledge of all things.

“Indeed, I hope that this new thing will turn out to be of admirable service in tuning for me some reed in this great discordant organ of our philosophy—an instrument on which I think I see many organists wearing themselves out trying vainly to get the whole thing into perfect harmony.”

Galileo hopes that his discoveries about sunspots will aid in advancing astronomy. He uses a musical metaphor, comparing astronomy to an organ that must be well tuned to sound harmoniously. In the same way, ideas in astronomy must work together to produce a coherent system. Galileo was himself a talented musician and enjoyed playing the lute and organ.

“For I seem to have observed that physical bodies have physical inclination to some motion (as heavy bodies downward), which motion is exercised by them through an intrinsic property and without need of a particular external mover, whenever they are not impeded by some obstacle.”

Galileo states the principle of inertia: the idea that physical bodies have within themselves an intrinsic tendency to some motion. He derives this idea from observing the rotation of sunspots around the sun. The principle of inertia became fundamental to modern physics.

“And finally by elevating us to the ultimate end of our labors, which is the love of the divine Artificer, this will keep us steadfast in the hope that we shall learn every other truth in Him, the source of all light and verity.”

This passage reflects the religious dimension that, for Galileo, lies at the heart of astronomy. Scientific inquiry, which examines the works of God’s creation, leads us to a knowledge and love of God Himself. Galileo acknowledges that we cannot attain perfect knowledge in this life, but we will learn all things when we meet God in Heaven.

“So far as I can see, their education consisted in being nourished from infancy on the opinion that philosophizing is and can be nothing but to make a comprehensive survey of the texts of Aristotle, that from divers passages they may quickly collect and throw together a great number of solutions to any proposed problem.”

Galileo criticizes his contemporaries for being too beholden to the authority of past thinkers, particularly Aristotle and Ptolemy. Instead of observing the world around them and forming conclusions, they merely rearrange Aristotle’s conclusions and think that this suffices for education and knowledge. This is one of the main themes of Galileo’s writings.

“But whatever the course of our lives we should receive them as the highest gift from the hand of God, in which equally reposed the power to do nothing whatever for us. Indeed, we should accept misfortune not only in thanks, but in infinite gratitude to Providence, which by such means detaches us from an excessive love for earthly things and elevates our minds to the celestial and divine.”

In another quote reflecting Galileo’s theological beliefs, he affirms the need to have gratitude for God’s blessings, including even misfortunes, which are for the strengthening of our soul and character. Galileo is specifically referring to the sickness and inconveniences that both he and Mark Welser are experiencing, which impede their normal activities.

“Kepler, who is cited by Apelles here, is a man of free and brilliant mind and more a friend to truth than to his own opinions.”

Galileo refers to Johannes Kepler (1571-1630), the German astronomer whose research into planetary movement paralleled Galileo’s own work. Galileo praises Kepler for his intellectual integrity and honesty, qualities that Galileo greatly values as a scientist.

“[…] in the sciences the authority of thousands of opinions is not worth as much as one tiny spark of reason in an individual man.”

Once again, Galileo declares the superiority of personal observation over received authority in science. He exalts the thinking individual over the institutional tradition that has ossified the teachings of Aristotle and Ptolemy.

“We must take care that no passion—either toward others or ourselves—bends us away from our aim of pure truth.”

Galileo reaffirms the need for an objective and unbiased pursuit of truth. Specifically, he acknowledges that the compulsion to find answers to difficult questions can lead scientists to make unwarranted claims. Scientists must therefore proceed with caution and prudence.

“I agree with Apelles in regarding as false and damnable the view of those who would put inhabitants on Jupiter, Venus, Saturn and the moon, meaning by ‘inhabitants’ animals like ours, and men in particular.”

Galileo denies the possibility of human life on other planets. The quote shows that speculations about life on the moon and other planets were already being made in Galileo’s time.

“Besides, it seems to me that we abase our own status too much and do this not without some offense to Nature (and I might add to divine Providence), when we attempt to learn from Aristotle that which he neither knew nor could find out, rather than consult our own senses and reason. For she, in order to aid our understanding of her great works, has given us two thousand more years of observations, and sight twenty times as acute as that which she gave Aristotle.”

Here again, Galileo disdains reliance on authority and exalts personal observation as the touchstone of scientific inquiry. He adds that we have the advantage over the ancients of our greater experience. We are, in a sense, more knowledgeable than they. Thus, we should not treat them as final authorities. These ideas of Galileo helped form modern experimental science and the understanding that scientific knowledge develops over time.

“They seemed to forget that the increase of known truths stimulates the investigation, establishment, and growth of the arts; not their diminution or destruction.”

Galileo responds to his critics, implying that they are opponents of intellectual progress. By “the arts” Galileo means the search for knowledge in general, whether in science or art. Using one’s intellect to search for scientific truth can only benefit knowledge, not destroy it as Galileo’s enemies claim.

“[Copernicus] did not ignore the Bible, but he knew very well that if his doctrine were proved, then it could not contradict the Scriptures when they were rightly understood.”

This quote encapsulates the main thesis of the “Letter to the Grand Duchess Christina”: Understood correctly, science and scripture are complementary. Galileo sites his predecessor Copernicus, who was a member of the Catholic clergy as well as a scientist, as someone who understood this principle and put it into practice.

“Therefore I declare (and my sincerity will make itself manifest) not only that I mean to submit myself freely and renounce any errors into which I may fall in this discourse through ignorance of matters pertaining to religion, but that I do not desire in these matters to engage in disputes with anyone, even on points that are disputable.”

In this disclaimer, Galileo declares his adherence to the Catholic faith and clarifies that he does not want to make any statement as a scientist that will contradict or damage his faith. Galileo makes clear his stance toward religion and defines the limits of his own field of science. Remaining on good terms with the religious authorities was necessary for Galileo to pursue his scientific work.

“But I do not feel obligated to believe that that same God who has endowed us with senses, reason, and intellect has intended to forgo their use and by some other means to give us knowledge which we can attain by them.”

Galileo grounds the exercise of the scientific method in a religious understanding of human anthropology. God is the source of all reason, intellect, and sense knowledge. He endowed man with these faculties and therefore desires man to use them to discover the truth of the universe that He made.

“Nor should it be considered rash not to be satisfied with those opinions which have become common.”

An individualist, Galileo exalts the truth gained through personal observation over the common notions that many in his day simply assumed to be true without being put to the test. This reflects his position as he was persecuted by conventional academic philosophers for challenging received wisdom in science.

“If in order to banish the opinion in question from the world it were sufficient to stop the mouth of a single man […] then that would be very easily done.”

Alluding to his own situation, Galileo says that enemies of the truth cannot stop scientific progress simply by silencing one person. The truth will naturally find other adherents, and its force will become unstoppable. The truth will triumph in the end.

“Within its pages are couched mysteries so profound and concepts so sublime that the vigils, labors, and studies of hundreds upon hundreds of the most acute minds have still not pierced them, even after continual investigations for thousands of years.”

Galileo refers to the Bible and the frequent difficulty of interpreting it because of its use of symbolism, metaphor, and different layers of meaning. Contrary to his opponents, he holds that the meaning of a biblical passage is not always on the literal surface. Here, he implies a criticism of his opponents for using a superficial interpretation of the Bible to silence him.

“But the mobility or stability of the earth or sun is neither a matter of faith nor one contrary to ethics.”

Distinguishing between matters of religious faith and those of physical science is essential. Matters pertaining to science should not be treated as matters of faith or morals, as science is morally neutral and unassociated with salvation. Galileo was persecuted by some theologians for stating, like Copernicus, that the earth revolves around the sun.