Arguments and the Physical World


and the Physical World


To win an argument you must be able to demonstrate what you are proposing either physically or logically and in doing so show the faults of other arguments. The following story of light, color and vision illustrates this.

The Story of Light, Color and Vision

The first significant step in critical thinking is to appreciate how physical world observation and experimentation (Foundation Idea number 2) affect the argument of ideas. There have been arguments going on for thousands of years. However, only slowly through this time have people started to appreciate the significance of physical world observation and experimentation and effect that they have in the argument of ideas. One example is the story of ideas about Light, Color and Vision. 

2000 Years of Argument

The Ancient Greek ideas about light, color and vision were argued over for 2000 years. In the 5th century BC Empedocles stated that everything was made of four elements: fire, water, earth and air. He believed Aphrodite lit a fire in the eye and this shone out. Empedocles' theories combined his beliefs about the Greek Gods and his ideas of the four elements.  
This combination was common at the time and arguments developed around three key schools of thought:

  • One opinion held that the eye sends out rays to objects and that these rays give the viewer information about color and shape. Among the best known proponents of this view were the Pythagoreans, adherents to the religious and scientific philosophy developed by Pythagoras.
  • A second opinion held that sight depended upon an interaction between images that were ejected from the eye and the perceiver's own spirit, or soul. Socrates and Plato were among the best known supports of this theory.
  • Another opinion held that when people see, they actually make contact with the objects they see, or with replicas of those objects. 
Aristotle argued for ideas based on observation and logical reasoning. He rejected Plato's idea because it was not supported by observation. If your eyes produce light then why can't you see in the dark? He stated that only luminous objects such as fire produce light and that sun light was reflected from objects into the eye. However he was not consistent in checking the ideas he proposed with observations. In his book History of Animals he claimed that human males have more teeth than females. Simple observation would have shown him that this was not true. He also stated that  heavier objects fall faster than lighter objects. Galileo showed by a simple experiment that this was not true. Aristotle only partially realized the significance of observation and experiment in the argument of ideas.

No way to distinguish ideas

Euclid like many before him argued that light emanated from the eye but he added his ideas of geometry to the explanation of vision. Light travel from the eye in straight lines creating a cone focused on the eye. When the rays hit an object it becomes visible.

An alternative to the eye emitting rays was that the rays came to the eye. Lucretius wrote in On the nature of Things (55BC):- "The light and heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove." With the benefit of hindsight this idea showed remarkable insight but debate, logical reasoning and reference to authorities gave no way of deciding between the competing ideas. Consequently the arguments continued for ten centuries. From personal experience people knew there were problems with these ideas:
  • If there was a light in the eye beaming out why couldn't we see in the dark
  • Why do distant object appear smaller?
  • If you are seeing a projected replica of yourself in a mirror why is it facing you and not facing the same way you are?
Slowly progress was being made. More ideas were developed, the ideas were discussed and criticized with reference to peoples beliefs, the strength of the argument, its consistencies or inconsistencies etc.  Animals and humans had been dissected and their anatomy studied at least as early as 1600 BCE. The Ancient Greeks first used human bodies for dissection in the 4th century BCE. Amongst many other discoveries Herophilos identified the cornea, retina, iris and the choroid coat of the eye. But having more competing ideas and more information about the parts of the eye etc did not help resolve the arguments about which ideas were incorrect.

Ibn al-Haytham and physical world experiments

Ibn al-Haytham [965 to c. 1040] like Aristotle challenged ideas and rejected those that did not correspond with observations. However, he went further and combined the use of mathematics in the definition of his ideas and the extensive use of experiments as evidence to illustrate the truth of his ideas. He is recognized as the "father of optics" and he resolved the argument about the eye emitting rays of light or receiving rays of light in his Book of Optics (1021) showing that the eye received rays of light. To do this he formulated his ideas on optics using mathematics. 

The diagram above shows Ibn al-Haytham's presentation of how he thought light passed through a pin hole.

He also tested and illustrated his ideas with a wide range of experiments. One experiment was based on the Camera Obscura. Ibn al-Haytham arranged a series of lamps in front of the Camera Obscura with the light of the lamps being seen on the Camera Obscura screen. If one of the lamps was extinguished then the corresponding light on the screen went out also. He reasoned that if the eye worked the same way then it was the light from the lamp that was seen in the eye. This matched physical world observation and explained why we cannot see in the dark. If it was the other way round and the light came from the eye then why did a lamp in a dark room disappear from sight when it was extinguished? 

Another of his experiments tested and illustrated his idea that "light and colors do not blend in air." He observed what happened when rays of light intersected at a pin hole aperture. For example he found that if you use a series of lamps set apart from each other one side of a Camera Obscura. The lamps could be seen on the screen. Therefore the rays of light from those lamps had  to pass simultaneously through the pin hole without blending. The use of experiments to support and illustrate an idea  fundamentally changed the argument between competing ideas.   

The rise of experimentation in arguments

The approach of using experimentation became significant in its own right. As more people started to use experimentation and observation as a core part of their investigation it also became a part of how they argued and presented their ideas. Great attention was focused on observation, measurement, devising new experiments and creating equipment to support further observation, measurement and experimentation.

Leonardo da Vinci showed that light passing through a pin hole in a dark room onto a wall formed a complete inverted image. Once the design of the Camera Obscura had improved to the point that people could see clear images it became a compelling illustration. This was a simple test everyone could see that supported the idea that light traveled in a straight line. 


It also explained why distant objects were seen as smaller than their actual size.  

Testing Ideas in the Physical World

Testing ideas in the physical world was a revolutionary idea. Even people who fundamentally did not a agree about an idea could agree to test the idea in the physical world. Testing ideas via experiments gave an impartial judge and it was a very effective way of making new discoveries. In England people who had been divided in the civil war were able to agree on the use of experiments and testing to measure the truth of  ideas. In the mid-1640s a group formed known as the "invisible college" to discuss the ideas of Francis Bacon. This lead to the official foundation of the Royal Society on November 28th, 1660,  when 12 of the "invisible college" decided to found 'a Colledge for the Promotion of Physico-Mathematicall Experimetall Learning'.  
The motto of the Royal Society is "Nullius in Verba" (Latin: "On the words of no one"). It signifies the Society's commitment to establishing the truth through experiment and they had weekly meetings to witness experiments and hold discussions.  

The society was not only influential in using and promoting experimentation, it also sponsored the creation of equipment needed for experiments (Robert Hooke's microscope etc: see picture above)  and it fostered the free flow of information which allowed others to review ideas and  reproduce the experiments. 

The significance of the ideas behind the Royal Society were recognized by many people and many countries and other similar societies were formed. Interestingly these societies have stood the test of time and are still as effective and relevant today as they were when they were founded. 

Issac Newton

Issac Newton was an early member of the Royal Society. Again he used physical world experimentation and observation to test and illustrate his ideas.  He did this in many areas of investigation including optics. One argument maintained that white light was pure. People had seen that when it passed through glass a spectrum of colors were created. However, the explanation was that the glass had corrupted the white light. 

Newton created an prism experiment to test this. He placed a prism in front of a beam of white light. A rainbow of colored beams of light was produced. He then placed a second prism in the path of these beams and they were combined again to form a beam of white light.

If the glass had corrupted the white light then the second prism should have corrupted the light further not created white light. At this point it became much more difficult to argue that white light was pure and glass corrupted it.

Newton's Prism Experiment


The importance of this story is to show that the only significant advance in the argument of ideas about light, color and vision came with physical world testing and experimentation. When a physical world test contradicted an idea it became much more difficult to continue to argue for the idea. This was true also in many other areas of investigation and argument. Ideas could now be compared, their usefulness measured and useless ideas set aside. 

Experiments caught the popular imagination and were performed for the public as seen in the picture above. It shows the creation of a vacuum. The absence of air is proved by the death of the bird
. People could see with their own eyes what was being talked about. They could if they wanted do the experiments themselves. People recognized that not only were these experiments dramatic they were fundamentally useful and the technology they delivered gave nations an advantage in trade, war etc.

Testing ideas in the physical world ushered in the Industrial Revolution and is the foundation for our technological progress.