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How small is light?
Understanding how light can be fused with matter is the key to a major new technology — but researchers in Southampton have found a limit to how small you can go, write ROX MIDDLETON, LIAM SHAW and JOEL HELLEWELL
light
Trump’s economic adviser has exposed the actual strategy: forcing other countries to provide financial support for US world hegemony
Activist Angie Zelter has been arrested more than a hundred times. She’s not stopping now, writes LINDA PENTZ GUNTER
Natalia Marques looks at last week's ruling that Khalil can be deported and its implications
We are not here to advocate for the arms industry or its CEOs, writes STEVE HANDFORD, and that means we must take a stand against the government’s spending on war
Educators must fight for an inclusive, creative system that values all children
Although our sector is hearing better things from the current government, the recognition that what we do is education in its own right, rather than just childcare, is still not reflected in policy, writes LUCY COLEMAN
LIGHT is a wave. But what is doing the waving? The abstract idea of a disembodied wave is extremely hard to conceive of. Just as you can’t imagine a wave in the ocean without the ocean, or a wave of a hand without a hand, it’s confusing that we would ever try to imagine a light wave without thinking about what the wave is travelling through.
In order to answer “what is waving,” the physicists who invented our modern description of light constructed the idea of the electromagnetic field. The field permeates every point of space in the universe, whether there is any matter or light at that point or not. The field at any point describes the amount and direction of electrical and magnetic force that is present at that place.
The wave that is light is a pulse of energy that passes in a straight line, carried as fluctuations in the electromagnetic field. Any point on the line undergoes a very quick change back and forth in the electric and magnetic forces as the light passes through. In fact the changing back and forth of the field is itself the light moving. Just like the way that water at the surface of a lake moves up and down as a ripple passes through the surface, and the movement up and down of the water is actually the ripple itself.
Why is it helpful to think about the wave-like nature of light? There are many effects that are easier to explain once you have the idea that light acts like a wave passing through a field.
One particularly striking feature is that when you imagine the light wave that passes through the field, it necessarily means that the wave takes up a certain amount of physical space.
The light wave has a length over which the light at any time is spread. To think about the water waves again, if you are on a boat bobbing up and down as waves pass underneath the boat, then the length of the wave is the distance between the peak of the wave you have reached the top of, and the next wave that you can see coming.
More from this author
A small Japanese trial has reported some positive results for stem cell therapy to treat spinal-cord injuries
Man-made canals like Panama and Suez face unprecedented challenges from extreme weather patterns and geopolitical tensions that reveal the fragility of our global trade networks, write ROX MIDDLETON, LIAM SHAW and MIRIAM GAUNTLETT
It’s sunny times for the solar industry which is expected to continue to grow rapidly — but there are still major environmental issues with how solar cells are made, explain ROX MIDDLETON, LIAM SHAW and MIRIAM GAUNTLETT
Fraud in Alzheimer’s research raises difficult questions about the current state of science, write ROX MIDDLETON, LIAM SHAW and MIRIAM GAUNTLETT
