Physics

Physics: space, time and philosophy

Physics is the science of matter and motion, of space and time. The word comes from the Greek fusis, meaning natural things, and the aim of physics is to understand the natural world. (The earlier word 'physic' meant medicine, as in physician.) Its origins lie thousands of years ago in ancient astronomy, but for most of the intervening centuries physics was allied with chemistry, mathematics and sometimes philosophy, into a discipline called 'natural philosophy', separating into distinct subjects about 1800. (Although, a physics professorship at TCD is still called the 'Erasmus Smith Chair of Natural and Experimental Philosophy'.) Image: The deepest visible-light image of the universe,the Hubble Ultra Deep Field

Courtesy of ESA/NASA/STScI

Physics: space, time and philosophy
Courtesy of ESA/NASA/STScI

Physics: space, time and philosophy

Courtesy of ESA/NASA/STScI

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Sir William Rowan Hamilton

Hamilton (1805-65) was arguably the greatest Irish scientist. He made many contributions to physics, especially in mechanics and optics, as well as inventing quaternion algebra. His greatest work is his general theory of dynamics. His Hamiltonian operator (H) was crucial to the development of quantum mechanics, and today it is used by physicists, engineers and even economists. Hamilton spent all his working life as Astronomer Royal at Dunsink Observatory.

Image: Sir William Rowan Hamilton, MRIA, 1805-1865 (© RIA)

Sir William Rowan Hamilton
Image: Sir William Rowan Hamilton, MRIA, 1805-1865 (© RIA)

Sir William Rowan Hamilton

Image: Sir William Rowan Hamilton, MRIA, 1805-1865 (© RIA)

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The 19th century belonged to the physicists. They built new instruments such as spectroscopes to study the structure of chemicals and even distant stars. They discovered the mysterious phenomena of x-rays and radioactivity. They investigated electricity and magnetism and radio waves, and their work gave rise to whole new industries.

Physics had emerged as a distinct subject about 1800, but still had strong links with chemistry, mathematics and astronomy, medicine and biology.

Many of the towering figures of this time were from Ireland, among them William Rowan Hamilton, William Thompson (Baron Kelvin), John Tyndall and George Gabriel Stokes.

These great scientists introduced powerful new mathematical techniques, conducted key experiments and explained fundamental phenomena. Their legacy survives in the many techniques, discoveries and institutes named after them.

They were part of the growing world of professional science then: they studied and worked abroad, their circle included the other great scientists of the day, and they were honoured internationally.

Sir William Rowan Hamilton's lasting legacy is in dynamics, optics and mathematics and his work was fundamental in the development of quantum mechanics. John Tyndall explained why the sky is blue and how glaciers move and, in an unusual contribution to biology, did the crucial experiments that proved Pasteur's germ theory of disease.

Kelvin made important contributions to thermodynamics: he was the first to see that heat, movement, light and electromagnetism were all forms of energy, and the absolute temperature scale is named after him. He also had numerous inventions, and helped make possible the first successful transatlantic telegraph cable in 1866.

Stokes was important in the fields of light, viscosity, friction and fluid mechanics, and was the first to explain fluorescence, and how the blood pigment haemoglobin works.

One of the great ideas people of the late 19th century was TCD scientist George Francis FitzGerald. A visionary physicist, he predicted a key element of Einstein's theory of relativity (the contraction of rapidly moving bodies), and a way to produce radio waves.

Later he helped Irish-Italian radio pioneer Guglielmo Marconi: the pair collaborated on the first ever sports radio transmission - a Morse code ship-to-shore transmission of the Dun Laoghaire regatta results in 1898!

An Irish scientist important in the development of the modern subject of geo-physics was John Joly. This inventive man used radioactivity to date rocks, helped calculate the age of the Earth, invented an early technique for colour photography in 1894, and developed the first effective radiation therapy for cancer in 1910.

Chemistry and Electricity

In the 1830s, the modern induction coil and a powerful and cheap new battery were invented by an unusual Catholic priest from Co Louth. Rev Nicholas Callan (1799-1864) was professor of natural philosophy at the Catholic training college, St Patrick's College Maynooth. His work spanned physics and chemistry: as well as his battery and the induction coil, he invented a way of protecting metals from corrosion and made it into the Encyclopaedia Britannica when he built what was then the world's most powerful electromagnet. Images: (right) Callan's induction coil incorporated miles of wiring and could generate an estimated 600,000 volts (left) An original Maynooth battery (© National Science Museum, Maynooth)

© National Science Museum, Maynooth

Chemistry and Electricity - © National Science Museum, Maynooth

George Gabriel Stokes

Stokes (1819 1903) was born in Co Sligo and came from a noted Irish scientific family. He went on to become one of the towering figures of 19th-century science and held the same job at Cambridge University as Isaac Newton before him, and Stephen Hawking today: Lucasian Professor of Mathematics. A measure of Stokes's importance is the many things named after him: Stokes's conjecture, Stokes's phenomenon, Stokes's layer, Stokes's line, Stokes's law of hydrodynamics and his law of fluorescence, the Navier-Stokes equations... there is even a unit named after him: the stokes, the standard unit of kinematic viscosity, is equal to 1cm^2/second. And if you prove the Navier Stokes equations describing how a viscous fluid flows, you can claim a $1 million prize from the Clay Mathematics Institute. Image: Portrait, widely used and not credited, but may have originated with the Royal Society

George Gabriel Stokes -

The Age of the Earth

Dublin-born James Ussher counted the generations in the Old Testament, consulted ancient Egyptian and Hebrew texts and calendars and concluded that the world began on October 23rd 4004 BC. Other scholars calculated similar dates, but Ussher's was the one that was widely accepted. In the 19th century, scientists tried other ways of calculating an age: based on the amount of salt that had accumulated in the oceans, for instance, or the time it had taken the Earth to cool from a molten ball to a solid planet. Some techniques were useful, others were flawed. The discovery of radioactivity in the early 20th century provided new ways of dating rocks accurately. We now know our planet is 4.6 billion years old. Irish scientists who made important contributions to this work in the 19th century were geologists Samuel Haughton and John Joly and physicist William Thompson (Lord Kelvin).

Image: James Ussher (1581-1656)

The Age of the Earth - Image: James Ussher (1581-1656)

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