speed of light [2 of 4] concepts in renaissance

© ABCC Australia 2015 www.new-physics.com

LIGHT SPEED IN RENAISSANCEInfinite Speed


Infinite Speed of Light

Since the days of Greek cultural revival, the idea of an infinite speed of light was persistent and influential mainly because of the influence of Aristotle.

Even in the days of renaissance in the16th century, the great French philosopher and mathematician René Descartes (1596-1650 A.D.) was in favour of such an infinite speed idea.


Instant Transmission

Descartes believed that space is filled up with a stable fluid made of microscopic spherical particles (the Plenum), acting as a medium for the propagation of light. The light particles transmitting motions in a straight line across the medium instantly, “like a stick transmits a push on one end to the other end” In other words, light is a kind of pressure transmitted through a medium at infinite velocity. . . . .

Descartes' Principia Philosophiae(Principles of Philosophy) published in 1644.


Johannes Kepler

Johannes Kepler (1571-1630), the renowned astronomer who established the first two laws of planetary motion, also put his faith on an infinite velocity of light. He believed that the speed of light was infinite since empty space presents no obstacle to it.

In fact, most of philosophers of the time were quite happy with the ancient idea. So the idea of light with an infinite speed remained popular for a further 200 years after Descartes.


Wave theory demands finite speed.

Christiaan Huygens and Robert Hooke (1635-1703) were in favour of the wave theory of light. They held that these waves were disturbances transmitted through the plenum proposed by Descartes. Like all disturbances through a medium a finite velocity is therefore the necessary consequence.

However, not many of their contemporary philosophers were doubtful about the idea of infinite velocity. If there was any, Galileo Galilee (1564-1642), was one – the most prominent one.


Galileo Galilei

Galileo Galilei (1564-1642) was an Italian physicist, mathematician, engineer, astronomer, and philosopher who played a major role in the scientific revolution during the Renaissance.

His achievements include improvements to the telescope so much so that data could be collected to support Copernicanism. Galileo has been variously called the “father of modern observational astronomy”, the "father of modern physics”, the “father of science”, and “the father of modern science”. When Newton said that he could see further because he was on the shoulder of giants.” Galileo is no doubt the giant he referred to.


The Speed of Light by Galileo GalileeGalileo was quite convinced that light did not suddenly appear out of nowhere when a light source was unshielded. It sounded physically absurd that a ray of light could be anywhere in the universe at the same time.

His conviction was fully reflected in his book entitled “Dialogues Concerning Two New Sciences” published in 1638. In the book, there were three interlocutors named Salvanti, Sagredo and Simplicio discussing certain scientific problems. The following quotation from the book embraced all the problems Galileo knew about the speed of light.


Dialogues Concerning Two New Sciences [01]Salvanti (who represents Galileo’s opinion): “We see that fires and dissolutions are accompanied by motion, and very swift motion; behold the action of lightning and of gunpowder used in mines and bombs..... So I cannot believe that the action of light, however pure, cannot be a kind of motion which is of the swiftest kind.”Sagredo: (The inquirer) “But what kind and how great should we take the speed of light to be? Is it instantaneous or momentary? Or does it, like other movements, require time? Could we assure ourselves by experiment?”


Dialogues Concerning Two New Sciences [02]

Simplicio (An Aristotalian): “Everyday experience shows that the propagation of light is instantaneous. When we see an artillery fired far away, the brightness of the flames reaches our eyes in no time, but the sound comes to our ears only after a noticeable interval.”

Sagredo:“Well, Simplicio, from this well-known experience, I can only deduce than that sound travels slower than light. It does not assure me whether the light is instantaneous or very fast. Your observation is no more conclusive than it would be to say: “As soon as the sun reaches the horizon, its splendour reaches our eyes.” For who will assure me that the rays did not reach the horizon before they reached our vision?”


The Galileo Experiment

With this conviction, Galileo did try to set up an experiment to measure the speed of light in 1638. Galileo and his assistant each took a shuttered lantern, and positioned themselves on hilltops one mile apart. As soon as the assistant saw Galileo flashing his lantern, he would reply by opening the shutter to his own lantern. Galileo would then mark down how long it took before he saw the light from the other lantern. Dividing the return trip of two miles with the time, he would obtain the speed of light in just the same way of measuring the speed of any moving daily object.


Result of Experiment

However the velocity of light is too great for such a crude set up. In the tick of the clock, a ray of light would have travelled around the earth seven and a half times. Light from Galileo’s lantern would have only taken 11 microseconds to cover the return trip [a microsecond is a unit of time equal to one millionth (10-6) of a second]. With his naked eye, flickering lantern, mechanical shutter, and crude timing instrument, the total reaction time would have well over 0.2 second. It would have been a miracle that Galileo could have detected such an interval of time for light. He could only conclude that the speed of light must have been ten times faster than sound – that is, about 3000 metres per second, as compared to the modern figure of 299,792,458 metres per second.


Father of Modern Science

Although Galileo have failed in the attempt to produce any precision figure, he was undoubtedly the first man in history making an effort to carry out such a measurement. This, together with his other achievements in astronomy, mathematics and philosophy, he was made the pioneer genius of all time and was crowned with the honour of being the “Father of Modern Science”.

What is more, Galileo discovered three of Jupiter's four largest moons with a telescope devised by himself, paving the way for the discovery of the speed of light by celestial measurement in a later time by others.