Cosmos: A Spacetime Odyssey, episode 5, Hiding in the Light

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Logo for the television series Cosmos: A Spacetime Odyssey. Fox Entertainment

In this fifth episode of the new Cosmos series, astronomer and physicist Neil deGrasse Tyson asks the question of how the modern world developed, how we went from bands of hunters and gatherers to living in cities and a global civilization. Conceding that there is no one single answer, he proceeds to build a narrative around humanity's growing understanding of the nature of light.

Mozi and Ancient Chinese Science

He begins by discussing Mozi (or Mo-Tzu, 470 - 391 BC), an ancient Chinese scholar who is credited by some with having invented the first camera obscura. Little is known about Mozi, except for some limited saved writings from his disciples. According to the episode one of them, called "Against Fate" (though it sort of sounds like Tyson says "Against Faith"), "a 3-pronged test for every doctrine is proposed," consisting of the following steps:

  1. Question its basis.
  2. Ask if it can be verified by the sights and senses of the common people
  3. Ask how it is to be applied and if it will benefit the greatest number.

Mozi's followers were then smacked down by Emperor Qin, the "first emperor" who unified China, and who is best known for the army of terra cotta warriors. The authoritarian nature of Qin's legalism is certainly painted as the antagonist in this story, as it led to the suppression of all dissent, including a massive book burning (or would it be scroll burning?) of ideas that did not conform to his doctrines.

As mentioned in some previous episode reviews, there have been criticisms that Cosmos and Tyson are a little too quick to take a simplistic view of the complex relationships between mysticism and scientific inquiry in history. For example, the teachings of Mozi were strong influences on the Chinese philosophy known as mohism and, it seems, the Mohists were perfectly fine in believing in ghosts and spirits, despite the Mozi teachings outlined above.

While I don't think these criticisms are baseless, I do think they largely miss the point. Tyson clearly states that Mozi's teachings are "early stirrings of the scientific method," and there's no claim that Mozi and his followers completely abandoned mysticism in favor of a fully rational worldview. The point with these stories is, in fact, to attack the authoritarian doctrines and political structures that have repeatedly stood in the way of any sort of scientific advancement. In fact, when discussing the oppression of Emperor Qin's legalism, it is clear that all dissent was oppressed, and the writings of both Confusion and Mozi were burned, so Tyson is clearly condemning the suppression of both religions and non-religious speech in that era. As Tyson says:

"Science needs the light of free expression to flourish. It depends on the fearless questioning of authority. The open exchange of ideas."

The episode then proceeds a thousand years into the future, to the next period where insights into the nature of light were developed.

Alhazen and Islamic Science

In Basra, Iraq, during the golden age of Islamic science, the scholar Ibn Alhazen (965-1040 AD) made new insights into the nature of light.

The importance of the cultural openness is again highlighted:

"His culture was open to new ideas and questioning. It was the golden age of science in the Islamic world. One that stretched from Cordoba in Spain all the way to Samarkand in central Asia. Christian and Jewish scholars were honored guests at the research institutes in Baghdad, Cairo, and other Islamic capitals. Instead of burning books, the Caliphs sent emissaries around the world in search of books.

"The Caliphs lavishly funded projects to translate, study, and preserve them for future generations. Much of the light of ancient Greek science would have been permanently extinguished without their efforts. The re-awakening to science that took place in Europe hundreds of years later was kindled by a flame that had long been tended by Islamic scholars and scientists."

Alhazen figured out that light moved in straight lines, and then also figured out how to create a small aperture in order to create a narrow, focused image of the light. He then went on to create his own camera obscura. His work on the science of optics would lay the foundation for the invention of the earliest telescopes, and would not be surpassed until the revolutionary theory of optics developed by Sir Isaac Newton.

From Tyson's perspective, though, Alhazen's greatest achievement was that "he was the first person ever to set down the rules of science. He created an error-correcting mechanism, a systematic and relentless way to sift out misconceptions in our thinking." The narrative shows the following, as if it were a direct quote from Alhazen (which appears to be from his Doubts Concerning Ptolemy):

"Finding truth is difficult and the road to it is rough. As seekers of the truth, you would be wise to withhold judgment and not simply put your trust in the writings of the ancients. You must question and critically examine those writings from every side. You must submit only to argument and experiment and not to the sayings of any person. For every human being is vulnerable to all kinds of imperfections. As seekers of the truth, we must also suspect and question our own ideas as we perform our investigations, to avoid falling into credulous or careless thinking. Take this course and truth will be revealed to you."

Europe's Light Discoveries

Proceeding several hundred years, Tyson discusses how Newton - using this method - discovered that white light contained all of the colors of the rainbow, when he discovered the visible spectrum of light. What Newton didn't discover, however, was a secret that would instead be discovered by the German scientist Joseph Fraunhoffer

But first, Tyson returns to William Herschel (remember him from an earlier episode), working in 1800, to discover that different colors of light carried different temperatures. Instead, by a fortunate unexpected experimental result, Herschel ends up discovering infrared light.

Fraunhoffer's narrative is intriguing. He was a young indentured servant to a glassmaker, but then a building fell on him. When Fraunhoffer was pulled free, he caught the notice and sympathy of the prince, who helped sponsor his interest in science. Fraunhoffer became meticulous lensmaker and began studying optics with a royal patron to support his activities.

To understand what Fraunhoffer is about to discover, Tyson takes a brief interlude to discuss the nature of waves. For sound waves, he demonstrates (using an organ) how the wavelength of sound determines the pitch of the sound. Similarly, for light, the wavelength of the light wave indicates the color of light that is seen.

Light is split apart by a prism because when the light collides with the glass at an angle, the light with different wavelengths change speed at slightly different levels. The result is that the light bends, spreading out to show a rainbow of colors.

Birth of Astrophysics

What Frauhoffer discovered was that if you look at light from a star through a prism, you see some vertical black lines ... light that is missing! This discovery was, in Tyson's words, "the marriage of physics and astronomy, the birth of my own field of science: astrophysics." It was also the discovery of the method known as spectroscopy ... and results that would take "100 years of thinking, questioning, and searching to decipher" this hidden message from distant stars.

One of the key insights is, again, that different colors represent different energy levels of light waves. The light we see from an object is all based on which energies are absorbed by an object and which are reflected from that object.

"Color is the way our eyes perceive how energetic light waves are."

The black lines that Fraunhoffer saw came about because those specific wavelengths of light were absorbed instead of transmitted by the star in question. What could be absorbing this light?

The explanation for this requires looking at quantum physics and the structure of atoms, which tell us that electrons within the atoms absorb light in order to jump between different quantum orbits.

"If you look at sunlight through a prism, you'll see its spectrum. When you magnify the spectrum with a telescope, like Joseph Fraunhoffer did, you raise the curtain on the electron dance within the atom. When the energy of the electron flags and it drops to a lower orbital, the light wave it emits scatters. Most of it doesn't reach us. That leaves a dark gap, a black vertical line in the spectrum. These dark lines are the shadows cast by hydrogen atoms in the atmosphere of the sun."

"Sodium atoms cast different shadows. Their electrons dance to a different tune. A grain of table salt is composed of sodium and chlorine atoms. Ten million billion of them, doing the crazy dances in a single grain of salt.

"And a single iron atom, with 26 electrons, is like a great big production number in a Broadway musical.

"When you look at a star with a spectroscope, you see the dark lines from all the elements. Show me the spectrum from anything, whether here on Earth or from a distant star, and I'll tell you what it's made of. Fraunhoffer's lines are the atomic signatures of the elements, writ large across the cosmos."

Unfortunately, Fraunhoffer's time as a scientist was short, possibly because of his exposure to toxic chemicals during his youth. There's a little subtle advocacy incorporated at this point in the documentary, pointing out that we don't know where genius will come from. Bavaria became a center of technology due to the opportunities offered to a young peasant boy without any prospects.

Though Bavaria kept his industrial techniques for creation of optical glass as a state secret for nearly a century, Fraunhoffer openly published all of his scientific discoveries. 

"As soon as Fraunhoffer discovered the spectral lines, he published everything he knew about them. The reverberations of his momentous discovery echoes still. His spectral lines revealed that the visible cosmos was all made of the same elements. The planets. The stars. The galaxies. We ourselves and all of life. The same starstuff."

Tyson concludes this praise by pointing out that this same spectroscopy method has helped to reveal the presence of massive amounts of unseen dark matter, which emits no observable light of any type and appears to interact with other matter only through the force of gravity.

In fact, we have only begun to open our eyes to the types of light that can be seen within our cosmos.

Watch Cosmos

Cosmos: A Spacetime Odyssey is available (at the time of this writing) for online streaming through the Cosmos website and through Hulu.  The entire series is also available on blu-ray and DVD.