Posts Tagged ‘Sir Isaac Newton’

At number 1 in The Guardian’s list of the ten best physicists is Isaac Newton.

At no. 1 in The Guardian's list of the 10 best physicists is Isaac Newton.

At no. 1 in The Guardian’s list of the 10 best physicists is Isaac Newton.

It shouldn’t come as any surprise to find Newton at number 1 in this list. He practically invented modern physics, one can think of him as the father of physics (with Galileo maybe being the grand-father 🙂 ). His major accomplishments include developing his law of universal gravitation, his three laws of motion which underpin the whole subject of mechanics, and his co-invention of calculus. Of course he did a lot more than this, these are just the highlights.

Newton’s brief biography

Isaac Newton was born on Christmas day in 1642, the same year that Galileo died. He was born in a small village in Lincolnshire, in the East of England, growing up on a farm. He was born three months after the death of his father. His mother remarried, and Newton was brought up by his maternal grandmother. At the age of 12 he was sent to a boarding school in Grantham (The King’s School). In 1661, age of 18, he was admitted to Trinity College, Cambridge. He obtained his degree in 1665, and soon after the University temporarily closed due to the Great Plague. Newton returned to his home in Woolsthorpe and continued his private studies. He returned to Cambridge in 1667 as a fellow of Trinity College, and then in 1669 he was appointed the Lucasian Professor of Mathematics at the University.

Newton published his masterpiece, “Pilosophiae Naturalis Principia Mathematica” (“Mathematical Principles of Natural Philosopy”, usually just referred to as Principia) in 1687. It catapulted Newton to National fame, and established him as the greatest scientist of his age. Newton was one of the founding members of the Royal Society, he served as a member of Parliament for Cambridge on two occasions (1689-1690 and 1701-02), and was appointed as warden of the Royal Mint in 1696. In 1699 he became Master of the Royal Mint. He was made a Sir in 1705, and died in his sleep in 1727. In the latter 30 years of his life he became increasingly preoccupied with alchemy and religion, spending far more time on both than he did on physics and mathematics. But, the work he did from 1666 to 1704 ensured his status in the pantheon of great scientists.

Newton’s main accomplishments

It is difficult to imagine where physics would be today if it were not for the genius of Newton. Although Galileo had laid the groundwork of much of mechanics, it was Newton who set out the mathematical framework upon which calculations could be made. In addition to his universal law of gravitation, and his three laws of motion which underpin the subject of mechanics, Newton co-developed calculus, an essential tool for analysing systems which do not change smoothly, and he did important work on optics too, showing that white light was a combination of the colours of the rainbow, and developing a reflecting telescope which were, in some ways, easier to manufacture than the refracting (lens) telescopes in use at the time.

Little is known of Newton’s private life, but he was certainly a prickly character. He had a long-standing feud with Gottfried Leibniz, the co-developer of calculus, and he despised his fellow Royal Society founder member Robert Hooke with a passion. His famous quote

If I have seen further than others
It is by standing on the shoulders of giants

is thought to have been a dig at Hooke, who was a hunchback. It seems to be generally accepted today that Newton probably suffered from Asperger’s syndrome, he had few friends, and would often go for weeks without seeing anyone but his servant. He would sit motionless on the edge of his bed, having got up and then become lost in thought, only to find 8 or 10 hours later that he had not moved, so he would just get back into bed.

But, whatever his personality quirks, there is no doubting his seminal contribution to physics. I think there is little doubt that, along with Albert Einstein, the two stand head and shoulders above the other physicists in this (or any) list of the best physicists.

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You can read more about Paul Dirac and the other physicists in this “10 best” list in our book 10 Physicists Who Transformed Our Understanding of the UniverseClick here for more details and to read some reviews.


Ten Physicists Who Transformed Our Understanding of Reality is available now. Follow this link to order


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When we look at objects giving off light (or reflecting light) we find three types of spectra. They are produced in different ways, and can actually tell us about the physical properties of the materials producing the spectra. In many ways it was the development of studying and understanding the spectra of astronomical objects that led to the development of astrophysics as opposed to the more traditional astronomy. This happened from the mid 1800s.

The three types of spectra are called “a continuous spectrum” (or continuum emission), “an emission line spectrum” and “an absorption line spectrum”. They look like the following



You can read about these three types of spectra in more detail in my new book – see http://www.springer.com/astronomy/popular+astronomy/book/978-3-319-09927-9

A continuous spectrum

When Newton did his famous experiment with a prism and sunlight, he noted that the Sun produced a “rainbow” of colours. This is a continuous spectrum. (However, as I will discuss in a future blog, if he had been able to produce a more detailed spectrum he would have noticed some subtleties on this continuous spectrum). So, light from the Sun, and any star, produces a continuous spectrum.

We also get a continuum spectrum from a hot solid, so for example the light produced by incandescent light bulbs is a continuum spectrum. These kinds of bulbs give off light by a very thin coil of metal, the filament, (usually tungsten) getting extremely hot from having an electric current passed through it. When the filament gets to thousands of degrees, it gives off light.


An emission line spectrum

If, instead of looking at the spectrum of the Sun we were to look at the spectrum of an object like Messier 42 (the Orion nebula), we would notice a very different kind of spectrum. Rather than being a continuous spectrum, we would see a series of bright lines with a dark background. We would also see an emission line spectrum if we were to look at the spectrum from one of the fluorescent light sources which are now replacing the incandescent lights in houses.



You can read about these three types of spectra in more detail in my new book – see http://www.springer.com/astronomy/popular+astronomy/book/978-3-319-09927-9

An absorption line spectrum

An absorption line spectrum is in some ways the converse of an emission line spectrum. Rather than seeing a series of bright lines on a dark background, one sees dark lines on a continuous spectrum.


Putting it all together

The diagram below shows how the three types of spectra can be produced. If we observe a continuum source (such as a star of an incandescent light) with nothing between us and that source then we will see a continuous spectrum.


If, instead, we look at a gas cloud then we will see an emission line spectrum. This is why the Orion nebula has an emission line spectrum, because we are seeing the emission from the gas cloud from which the stars have formed and still are forming. The lines are in particular places on the spectrum which depends on the composition, pressure and temperature of the gas, as well as whether it is moving towards us or away from us.

If we look at the same gas cloud but with a continuum source behind the cloud then we will see an absorption line spectrum. The dark lines are in exactly the same places (at the same wavelengths) as for the emission line spectrum, but are dark rather than bright.

This was observed by physicists as early as the 1850s. In fact the diagram above is known as Kirchhoff’s radiation laws, after Gustav Kirchhoff (1824-1887), a German physicist of the time. He and Robert Bunsen (he of the eponymous burner) did important spectroscopy work in the 1850s and 1860s. But it was actually not until the 1920s that physicists properly understood the physics of these three different kinds of spectra. I will explain this physics in a series of future blogs.


You can read about these three types of spectra in more detail in my new book – see http://www.springer.com/astronomy/popular+astronomy/book/978-3-319-09927-9

My book, "The Cosmic Microwave Background" includes a sketch of the first ever absorption spectrum seen of the Sun, and of why stars have different colours.

My book, “The Cosmic Microwave Background” includes Fraunhofer’s sketch of the first ever absorption spectrum seen of the Sun, and an explanation of why stars have different colours.

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In February I was visiting Cambridge with my son so that he could see if he wants to apply there for university next year. On the last day of our visit, we managed to go into Trinity College’s historical library, which is known as the Wren library (as it was designed by Sir Christopher Wren).

The highlight of this library for me was a copy of Newton’s personal first edition copy of his Principia Mathematica book, which introduced such important topics as calculus and his three laws of motion. For clarity, I should give the book its full title, Philosophiae Naturalis Principia Mathematica, as Bertrand Russell co-authored a book called “Principia Mathematica” in the early 20th Century.

Unfortunately, as the sign below shows, one is not allowed to take photographs in the library, so I only have a mental image of this wonderful sight. As it was Newton’s own copy, one can see his corrections in the margins to the book’s errors. It is well worth the visit.

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