Who is Alhazen?
Alhazen, whose real name was Hasan lbn al-Haytham was a scientist, mathematician and astronomer who lived back in 965 AD. Alhazen was born in Basra, in Iraq and made revolutionary advancements in the world of science. Optics was one of Alhazen’s main areas of study and it is his discoveries in this field that laid the foundation for cameras and photography as we know it today.
Despite science being his passion, Alhazen actually worked first as a civil servant, before being appointed minister in Basra and the regions surrounding it. During this time, Alhazen spent a lot of time working on mathematics and writing about the impossible problem of squaring the circle.
After some time working for the government, Alhazen quit his job and moved to Cairo, Egypt, to devote his life to his scientific studies.
Alhazen and The Nile River
During the life of Alhazen, Egypt was ruled by Caliph Al-Hakim, who was the sixth ruler in the Fatimid dynasty. Al-Hakim was renowned for his eccentricities and cruelty, but also had great respect for the sciences. This led him to take an interest in Alhazen, who had become well-known for his scientific work.
At the time, all of the agriculture in Cairo and Egypt was heavily dependent on the Nile River. This was becoming a problem, however, as its annual flooding was destroying the crops in all of the lands downstream. Alhazen, overly confident in his mathematical and scientific abilities, felt that he was capable of controlling the Nile’s flow by implementing a dam. Caliph Al-Hakim was delighted at this and placed him in charge of building the dam.
Unfortunately, while travelling along the Nile, Alhazen soon realised he had overestimated his abilities. He concluded that building a dam with the technology available to him was impossible. This realisation struck great fear into Alhazen as he was well aware of the cruel ways that the Caliph dealt with those that failed him. So, in order to escape the Caliph’s wrath, Alhazen decided to pretend that he had gone mad and was confined to house arrest until Al-Hakim died in 1021 AD.
It was during this period of house arrest that Alhazen did his greatest work, including writing his famous Book of Optics.
What is Optics?
Optics is a branch of physics that studies the science of light and how it interacts with the world. It is through the study of Optics that scientists have been able to provide explanations for many questions to do with light, such as how rainbows exist, how light reflects off mirrors and how light refracts through water etc.
Light is actually a type of electromagnetic radiation in the form of a wavelength that is visible to the human eye. Each wavelength is perceived by the eye as a different colour, all of which, when put together, make a rainbow. Rainbows show the entire spectrum of visible light. Other colours can only be seen by using specialised equipment. Optics studies, not only visible light but also the invisible parts.
For more information on how light travels, check out this amazing KS2 How Light Travels PowerPoint.
Optics has been used to create many things that we use today, such as, spectacles, cameras and microscopes. Scientists have also discovered how to make light travel through a thin wire, made out of glass or plastic, called optical fibre. These optical fibres are what is used to carry phone calls and allow internet to travel between cities. Therefore, we have the science of optics to thank for a lot of our modern technology.
The Book of Optics
One of, if not the most famous of Alhazen’s works is his Book of Optics. This extensive book was made up of seven volumes, all centred around Alhazen’s work on optics. Before Alhazen published the Book of Optics, the scientific discussion around vision was pretty contentious. There were two pre-existing theories of vision at the time and they conflicted heavily with one another. The first was ‘The Emission Theory’, which stated that the eyes emit light rays, which results in the perception of vision. This theory was supported by great philosophers like Euclid and Ptolemy. The second theory was ‘The Intromission Theory’, which stated that visualisation was made possible by light bouncing off different subjects and objects and entering the eye. This theory was famously supported by Aristotle. Alhazen’s Book of Optics supported the second theory, backing it with Galen’s work on anatomy. In his Book of Optics, Alhazen stated that it is in fact not our eyes that emit light, but instead, light is reflected from the object of vision into the eye. He proved this by conducting a number of experiments.
Around the beginning of the 13th century, Alhazen’s works were translated into Latin which allowed them to be circulated more widely. This led to Roger Bacon, an English philosopher, using Alhazen’s work as the basis to make spectacles to help elderly people who had issues with their eyesight.
The Scientific Method
In addition to his advancements in the science of optics, Alhazen also pioneered the use of the scientific method. The scientific method is an approach to seeking knowledge used by scientists when they have a question they need answers to. This approach starts with making observations that form a hypothesis. This hypothesis is then tested through a series of rigorous experiments to ultimately provide a conclusion.
The scientific method used by Alhazen was remarkably similar to the method used in modern science. Both these methods complete a cycle of observation, hypothesis, experimentation and independent verification in order to find the answer to their original question. This method was revolutionary in the world of science as it required each conclusion or answer that was found throughout the process to be supported by substantial evidence. This removed any subjectivity from the scientific method and meant that the conclusions reached could be trusted.
The scientific method varies slightly depending on who is carrying out the process, but the steps taken usually go as follows:
Make an observation
Ask a question
Put together background information
Form a hypothesis
Test this hypothesis through an experiment