Knocking on Heaven's Door (8 page)

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FIGURE 7
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Galileo measured how quickly a ball went down an inclined plane, using bells to register their passage.

Galileo’s science also went beyond what he could observe. He created thought experiments—abstractions based on what he did see—in order to make predictions that would apply to experiments no one at the time could actually perform. Perhaps most famous is his prediction that objects—in the absence of resistance—all fall at the same rate. Even though he couldn’t set up the idealized situation, he predicted what would occur. Galileo understood gravity’s role in objects falling toward the Earth, but he also knew that air resistance slows them down. Good science involves understanding all the factors that might enter into a measurement. Thought experiments and actual physical experiments helped him to better understand the nature of gravity.

In an interesting historical coincidence, Newton, one of the greatest physicists to continue this scientific tradition, was born the year that Galileo died. (At a talk Stephen Hawking gave, he expressed his pleasure that his own birth came precisely three centuries later.) The tradition of designing physical or thought experiments, interpreting them, and understanding their limitations is one that scientists today continue, whatever their year of birth. Current experiments are more subtle and rely on far more advanced technology, but the idea of creating an apparatus to confirm or rule out the predictions from hypotheses continues to define science and its methods in research today.

In addition to experiments—the artificial situations he created to test hypotheses—another of Galileo’s game-changing contributions to science was understanding and believing in technology’s potential for advancing our observations of the universe as it presents itself. With experiments, he moved beyond pure intellect and reason, and with new devices, he moved beyond unfiltered observations.

Much of earlier science relied on direct unmediated observations. People touched or saw objects with their own senses, not through an intervening device that in some way altered the images. Tycho Brahe, who among other things discovered a supernova and accurately measured the orbits of the planets, made the last famous astronomical observations before Galileo entered the scene. Tycho did use precise measuring instruments, such as large quadrants, sextants, and armillary spheres. He in fact designed and paid for the construction of instruments of greater precision than anyone had used before, leading to measurements that were sufficiently accurate to allow Kepler to deduce elliptical orbits. Yet Tycho made all his measurements through careful observations with his naked eye, with no intermediary lens or other device.

Notably, Galileo had an artistically trained eye and an astute musical ear—he was, after all, the son of a music theorist and lutenist—but he nonetheless recognized how observations that employed technology as a mediator to his observations could improve on his already formidable faculties. Galileo trusted that the indirect measurements he could make with observational tools at both large and small scales would go far beyond those made purely with his unassisted faculties.

Galileo’s best-known application of technology was the use of telescopes to explore the stars. His use of this instrument changed the way we do science, the way we think about the universe, and the way we see ourselves. Galileo didn’t invent the telescope. It was invented in 1608 by Hans Lippershey in the Netherlands—but the Dutch used telescopes to spy on others, hence the alternative name of spyglass. Yet Galileo was among the first to realize that the device was a potentially potent tool to make observations of the cosmos not possible with the naked eye. He updated the spyglass invented in the Netherlands by developing a telescope capable of magnifying sizes by a factor of 20. Within a year of being presented with a carnival toy, he turned it into a scientific instrument.

Galileo’s act of observing through intermediate devices was a radical departure from previous ways of measuring and represented a major advance essential to all modern science. People were initially suspicious of such indirect observations. Even today, some are skeptical about the reality of the observations made with big proton colliders or the data that computers on satellites or telescopes record. But the digital data cataloged by these devices are every bit as real as—and in many respects more accurate than—anything we can observe directly. After all, our hearing comes from oscillations of air hitting our eardrums and our vision from electromagnetic waves hitting our retinas and being processed by our brains. This means that we too are a sort of technology—and not a highly reliable one at that, as anyone who has experienced an optical illusion can attest. (See Figure 8 for an example.) The beauty of scientific measurements is that we can unambiguously deduce aspects of physical reality, including the nature of elementary particles and their properties, from experiments such as those physicists perform today with large and precise detectors.

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FIGURE 8
]
Our eyes are not always the most reliable means of ascertaining external reality. Here the two checkerboards are the same, but the dots on the one to the right make the squares appear very different.

Although our instinct might be that observations made unaided with our eyes are the most reliable and that we should be suspicious of abstraction, science teaches us to transcend this all too human inclination. The measurements we make with the instruments we design are more trustworthy than our naked eyes, and can be improved and verified through repetition.

In 1611, the church accepted the radical proposition that indirect measurements are valid. As Tom Levenson relates in his book
Measure for Measure
,
⁷
the scientific establishment of the church had to decide whether observations from a telescope were trustworthy. Cardinal Robert Bellarmine pressed the church scholars to decide this issue, and on March 24, 1611, the four leading church mathematicians concluded that Galileo’s discoveries were all valid: the telescope had indeed produced accurate and reliable observations.

Another commemorative brass medallion that the Paduans shared with me beautifully summed up the pivotal nature of Galileo’s achievement. On one side is a picture of the 1609 presentation of the telescope to the Signoria of the Republic of Venice and to the Doge, Leonardo Dona. The other side has an inscription noting that the act “marks the true birth of the modern astronomical telescope” and begins the “revolution in man’s perception of the world beyond planet Earth,” “a historic moment that crosses the boundaries of Astronomy, making [it] one of the starting points of modern Science.”

Galileo’s observational advantages led to an explosion of further discoveries. Repeatedly, as he stared up into the cosmos, he found new objects that were beyond the range of the naked eye. He found stars in the Pleiades and throughout the sky that no one had seen before, sprinkled among the brighter ones that were already known. He publicized his discoveries in his famous 1610 book,
Sidereus Nuncius (Starry Messenger)
, that he raced to complete in about six weeks. He hastily performed his research while the printer worked on the manuscript, eager to impress and gain the support of Cosimo II de’ Medici, the Grand Duke of Tuscany—and a member of one of Italy’s richest families—before someone else with a telescope might manage to publish first.

Because of Galileo’s insightful observations, an explosion of understanding occurred. He asked a different type of question:
how
rather than
why.
The detailed discoveries that were possible only with his telescope naturally led him to the conclusions that were to anger the Vatican. Specific observations convinced Galileo that Copernicus had been correct. For him, the only worldview that could consistently explain all of his observations relied on a cosmology in which the Sun, and not the Earth, was the center of the galaxy around which all planets orbited.

The moons of Jupiter were among the most critical of these observations. Galileo could see the moons as they appeared and disappeared and moved in accordance with their orbit around the giant planet. Before this discovery, a stationary Earth seemed the obvious and only way to explain the Moon’s fixed orbit. The discovery of Jupiter’s moons meant that it too had satellites in tow despite its motion. This lent credence to the possibility that the Earth could also be moving and even orbiting about a separate central body—a phenomenon that was explained only later when Newton developed his theory of gravity and its prediction of the mutual attraction of celestial objects.

Galileo named Jupiter’s moons Medicean stars, in honor of Cosimo II de’ Medici—further demonstrating his understanding of funding—another key aspect of modern science. The Medicis indeed decided to support Galileo’s research. Later on however, after Galileo had been granted funding for life from the city of Florence, the moons were to be renamed Galilean satellites in honor of their discoverer.

Galileo also used his telescope to observe the hills and valleys of the Moon. Before his discoveries, the heavens were thought to be perfectly unchanging, ruled by absolute regularity and constancy. The prevailing Aristotelian view maintained that while everything between the Moon and the Earth was imperfect and inconstant, celestial objects beyond our planet were supposed to be spherical and invariant—of divine essence. Comets and meteors were considered weather phenomena like clouds and winds, and our term
meteorology
harks back to this classification. Galileo’s detailed observations implied that imperfection extended beyond the human and sublunar domain. The Moon was not a perfectly smooth sphere and was in fact more similar to the Earth than anyone had dared to suppose. With the discovery of the textured topography of the Moon, the dichotomy between terrestrial and celestial objects was called into question. The Earth was no longer unique, but seemed to be a celestial object like any other.

The art historian Joseph Koerner explained to me that Galileo could use light and shadows to identify craters in part because of his artistic background. Galileo’s perspectival training helped him understand the projections he saw. He immediately recognized the implications of these images, even though they weren’t fully three-dimensional. He wasn’t interested in mapping the Moon, but in understanding its texture. And he understood right away what he saw.

The third significant set of observations that validated the Copernican point of view related to the phases of Venus—illustrated in Figure 9. These observations were particularly significant in establishing that celestial bodies orbited around the Sun. The Earth clearly was not unique in any obvious way, and Venus clearly didn’t rotate around it.

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FIGURE 9
]
Galileo’s observation of the phases of Venus demonstrated that it too must orbit the Sun, invalidating the Ptolemaic system.

From an astronomical perspective, the Earth was not so special. The other planets behaved like ours, orbiting the Sun with satellites orbiting them. Furthermore, even beyond the Earth—evidently sullied by human beings—not everything was unblemished perfection. Even the Sun was besmirched by sunspots that Galileo had also identified.

Armed with these observations, Galileo famously concluded that we are not the center of the universe and that the Earth revolves around the Sun. The Earth is not the focal point. Galileo wrote up these radical conclusions. In doing so, he defied the church—although he later professed to reject Copernicanism in order to reduce his punishment to house arrest.

As if his observations and theorizing about the large scales of the cosmos were not enough, Galileo also radically altered our ability to perceive small scales. He recognized that intermediate devices could reveal phenomena at small scales, just as they did at large ones, and he advanced scientific knowledge at both frontiers. In addition to his (in)famous astronomical investigations, he turned technology inward—to investigate the microscopic world.