Tag Archives: light

Happy New Year (of Light)!

150 years ago today (1 January), James Clerk Maxwell published his work on light, electricity and magnetism. Our resident physicist, Dr. Harry Cliff, reflects on how Maxwell helped transform the way we live.

Whether you were up with the lark this morning to greet the dawn of the New Year or crawled bleary-eyed from bed after an over-exuberant farewell to 2014, it’s likely that one of the first things you did was to switch on a light or throw open the curtains.

An appropriate way to start what UNESCO has proclaimed as the International Year of Light, a 365-day celebration of light science and technologies, inspired by a number of major scientific anniversaries that fall this year.

It was 150 years ago today that one of the most important scientific articles of the 19th century was published in the Philosophical Transactions of the Royal Society. Written by the Scottish physicist James Clerk Maxwell, it was titled A Dynamical Theory of the Electromagnetic Field, and its contents were to profoundly alter the way we think about light, electricity and magnetism and transform the way we live.

A facsimile of Maxwell's 'A Dynamical Theory of the Electromagnetic Field' on display in the Science Museum’s new Information Age gallery.

A facsimile of Maxwell’s ‘A Dynamical Theory of the Electromagnetic Field’ on display in the Science Museum’s Information Age gallery.

Maxwell had been grappling with the relationship between electricity and magnetism for a number of years, in particular with a very old and thorny problem: how is it that when I hold a magnet some distance away from a piece of iron, the iron is moved without actually touching the magnet?

This so called ‘action at a distance’ was troubling in a mechanical age when scientists were trying to describe all forces in terms of direct physical contact between physical entities. In Maxwell’s previous work on electromagnetism, he had made an attempt to explain action at a distance using the commonly-accepted existence of an all-pervading invisible fluid, the luminiferous aether, full of spinning vortices that transmitted electrical and magnetic forces.

Maxwell’s great breakthrough in his new paper came from his decision to try to describe electricity and magnetism without worrying very much about the details of what the aether was like. Instead he introduced the concept of the electromagnetic ‘field’, which in his words:

    “is that part of space which contains and surrounds bodies in electric or magnetic conditions.”

In other words, the electromagnetic field described the force that would be experienced by an electric charge or magnet when placed close to another charge or magnet. A common experiment at school is to visualise the magnetic field around a bar magnet by sprinkling it with iron filings.

Iron filings showing the magnetic field lines produced by a bar magnet. Source: Newton Henry Black, Harvey N. Davis (1913) Practical Physics, The MacMillan Co., USA, p. 242, fig. 200.

Iron filings showing the magnetic field lines produced by a bar magnet. Source: Newton Henry Black, Harvey N. Davis (1913) Practical Physics, The MacMillan Co., USA, p. 242, fig. 200.

However, whereas today physicists consider the electromagnetic field to have existence in its own right, Maxwell still thought of it as an effect of the arrangement of some underlying physical luminferous aether.

Armed with his electromagnetic field concept, Maxwell derived twenty equations that could be used to describe almost any electromagnetic system, and made plain the deep connections between electricity and magnetism. He then applied his equations to describe undulations or waves travelling through the electromagnetic field. His goal was nothing short of explaining the nature of light itself.

James Clerk Maxwell and his wife, Katherine in 1869.

James Clerk Maxwell and his wife, Katherine in 1869.

What Maxwell found was to change the course of science and technology forever. He derived an equation that described a wave of oscillating electric and magnetic fields; little ripples in the electromagnetic field that could even travel through empty space. Calculating the speed with which these ripples would travel, Maxwell found that it agreed precisely with the best measurement of the speed of light. Maxwell concluded:

“The agreement of the results seems to show that light and magnetism are affectations of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws.”

This was a stunning result, but it would take time for Maxwell’s theory to become widely accepted. The mathematics were so unfamiliar that most physicists were unable to understand, let alone appreciate Maxwell’s work. In 1879 a prize was offered by the Prussian Academy of Science for anyone able to provide experimental verification of Maxwell’s theory.

Experimental support for the theory would not arrive until after Maxwell’s death in 1879 at the age of just 48. In a series of experiments conducted between 1886 and 1888, Heinrich Hertz demonstrated the transmission of electromagnetic waves, proving Maxwell right and opening up a new technological age, one in which electromagnetic signals could be beamed across the planet, radically shrinking the size of the world and allowing communication at a distance never before imagined.

Replica of a set of Knochenhauer spirals used in what proved to be the starting point of Hertz's work on electromagnetic waves. See the spirals on display in the Science Museum’s Information Age gallery. Image: Science Museum

Replica of a set of Knochenhauer spirals used in what proved to be the starting point of Hertz’s work on electromagnetic waves. See the spirals on display in the Science Museum’s Information Age gallery. Image: Science Museum

Although Maxwell never lived to see the full impact of his work, those who followed in his footsteps transformed the scientific landscape. It was Maxwell’s wave equation that inspired Einstein’s theory of special relativity, which did away with the lumineferous aether and recast the very notions of space and time. Einstein himself kept a framed photograph of Maxwell on the wall of his office, and Maxwell is now widely regarded as one of the greatest physicists to have ever lived, second perhaps only to Isaac Newton and Einstein himself.

I will leave the final word to the 20th century quantum physicist Richard Feynman:

“From a long view of the history of the world—seen from, say, ten thousand years from now—there can be little doubt that the most significant event of the 19th century will be judged as Maxwell’s discovery of the laws of electromagnetism. The American Civil War will pale into provincial insignificance in comparison with this important scientific event of the same decade.”

Find out more about how Maxwell’s work opened up a new age of telecommunication in the Science Museum’s new Information Age Gallery.

Shedding light on the matter of rubbish

In the latest of our blog series linked to The Rubbish Collection, the Science Museum’s Inventor in Residence Mark Champkins finds an ingenious use for our discarded materials.

The second phase of The Rubbish Collection exhibition is open at the Museum until 14 September. Having documented every piece of waste that passed through the Museum for a month, this second phase is a chance to see what would have been thrown away.

Of the material that hasn’t been selected for display, I collected a small box of bits that I hoped to turn into a product that we might sell in the shop. I like the idea that with a little bit of effort and imagination, items that would otherwise be chucked, can be turned into something desirable. Unfortunately the collection of items in the box that I had gathered didn’t look at all desirable. A couple of umbrellas, some bits from a light fitting, an old copper funnel, an ash tray, some plastic cutlery, some glass cups and a selection of ball bearings didn’t look very promising.

A box of bits © Mark Champkins

A box of bits © Mark Champkins

The germ of my idea came from digging out the copper funnel and investigating it further. It was heavily corroded and covered in green verdigris, but underneath was structurally solid, and a beautiful shape.

I read somewhere that vinegar could be used to clean copper, so I popped down to the café, to get a couple of sachets to try out. It turns out it does a reasonable job on lightly tarnished areas, but can’t handle the extent of corrosion on the funnel. However, it did encourage me that the funnel could be saved.

An old copper funnel © Mark Champkins

An old copper funnel © Mark Champkins

Next I pulled apart the umbrellas, lined up everything from the box and had a think what I might make. A happy coincidence was that the handle from the umbrella fitted exactly into the top of the funnel.

 

An umbrella handle © Mark Champkins

An umbrella handle © Mark Champkins

My first thought was to make some sort of loudspeaker people could shout through. Next, I thought the umbrella handle might plug the funnel to make a water-tight vase or container of some sort. Finally, looking at the shining clean patch of copper I thought, coupled with a 1950s-style squirrel cage bulb, it might make a really nice light fitting.

The next step was to recondition the copper funnel. In the basement, the Museum has metal and wood workshops responsible for building, installing and maintaining the structures for new exhibitions. Amongst their equipment is a sandblasting machine, which I used to blast the corrosion from the funnel.

Sandblasting the copper funnel © Mark Champkins

Sandblasting the copper funnel © Mark Champkins

I decided to leave the matt finish left from the sand blasting on the inside surface, and polish up the outside. Using Brasso and eventually a buffing wheel I polished up the outer surface.

Polishing © Mark Champkins

Polishing © Mark Champkins

Using a buffing wheel © Mark Champkins

Using a buffing wheel © Mark Champkins

To ensure the lamp remains pristine, I decided to use a polymer based lacquer, applied in the workshop’s spray booth.

In the spray booth © Mark Champkins

Finally I added the umbrella handle, and a lighting flex and fitting. I think the finished light looks rather good. It’ll be available for purchase in the Museum shop from mid August.

The finished light © Mark Champkins

The finished light © Mark Champkins

The lamp made from Museum rubbish © Mark Champkins

The lamp made from Museum rubbish © Mark Champkins

The finished lamp at work © Mark Champkins

The finished lamp at work © Mark Champkins

The light will be on sale in the Museum shop in mid-August © Mark Champkins

The light will be on sale in the Museum shop in mid-August © Mark Champkins

Phase 2 of Joshua Sofaer’s The Rubbish Collection runs at the Science Museum until 14 September 2014.

A hundred years of the quantum atom

Alice Lighton, content developer for our Collider exhibition, writes about the history of quantum physics. Colider: step inside the world’s greatest experiment opens in November 2013 with a behind-the-scenes look at the famous CERN particle physics laboratory. 

A few years ago, a friend asked a question that took me somewhat by surprise. “Alice,” he said, “is quantum physics right, or is it just a theory?”

At the time I was in the midst of a physics degree, so my initial response was “I hope so!” Quantum physics matches up to experiment extraordinarily well – it is often called the most accurate theory ever. But the question, and subsequent conversation, made me realise how little many people know about the subject, despite its profound impact on modern life and the way we think about the universe.

This year is the centenary of the publication of one of the theories that laid the foundation for our understanding of matter in terms of quanta – packets of energy. According to quantum mechanics, light is not a wave, but lump of energy called photons. Max Planck came up with the idea at the end of the 19th Century, though he considered his light ‘quanta’ a useful model, rather than reality.

Niels Bohr

Niels Bohr, one of the founders of modern physics.

One hundred years ago, in 1913, the young Danish researcher Niels Bohr sent a paper to the Philosophical Magazine in London that used these quanta to solve a serious problem with theories about the atom. At the time, scientists thought the atom was like a solar systems; electrons orbit a nucleus of protons and neutrons. But anything that moves in a circle gradually slowly radiates energy, and so moves closer to the centre of orbit. Eventually, electrons should fall into the nucleus of the atom.

But they blatantly don’t, otherwise everything in the Universe would collapse, and we wouldn’t exist. Bohr proposed that electrons could only sit in discrete orbits or distances from the nucleus – and therefore when electrons change orbit transitions between orbits emit only emit energy in discrete packets (quanta), not gradually. The electrons therefore stay put in their orbits, and don’t fall into the nucleus of the atom.

A hydrogen atom is made from one electron orbiting a proton. Photo credit: flickr/Ludie Cochrane

Bohr was the first to show that packets of energy could successfully explain and predict the behaviour of atoms, the stuff that makes up you and me. His results were only approximately correct, but a big improvement of previous theories.

Generations of scientists have built on Bohr’s insight to understand and create the modern world. When my friend asked whether quantum physics worked, I pointed at his laptop. Computers, nanotechnology, and the Large Hadron Collider owe their existence to the physics that began with Bohr’s generation.

The CMS experiment at the Large Hadron Collider tries to work out the rules governing the sub-atomic world. Photo credit: CERN

Bohr’s original papers are clear and comprehensible, a beautiful read for physicists. The mathematics involves nothing more difficult than multiplication and division, yet the philosophical implications are immense. Max Planck never fully accepted quantum physics; neither did Albert Einstein, despite winning a Nobel Prize for his work on the subject.

Bohr also won a Nobel Prize for his quantum theory, but his work did not stop. He founded the Niels Bohr Institute, a centre of theoretical physics in Copenhagen, worked on the Manhattan Project developing the atomic bomb, and continued to make contributions to quantum mechanics.

And he has a lovely link to the exhibition I’m currently working on, about the Large Hadron Collider. Bohr was influential in the founding of CERN, the Geneva laboratory that is home to the LHC. If he had his way, the LHC would be in Denmark, but other scientists objected – Northern Europe was too cloudy, and had too few ski resorts, for Italian tastes.