Light occupies a central place in our understanding of the world both as a means by which we locate ourselves in nature and as a thing that inspires our imagination. Light is what enables us to see things, and thus to navigate our surroundings. It is also a primary means by which we learn about the world – light beams carry information about the constituents of the universe, from distant stars and galaxies to the cells in our bodies to individual atoms and molecules. The impact of light on the modern world is immense, and often unrealized. For this reason, 2015 has been designated by the United Nations as the International Year of Light – a celebration of light and what is made possible by it.
Light is a remarkable thing. It is able to fuse atoms together at extraordinarily high temperatures to enable new modes of energy generation and at the same time to cool atoms down to the lowest temperatures imaginable – a few tens of billionths of a degree above absolute zero. Yet it might surprise you to know that what light actually is was only really properly understood less than a hundred years ago, and even now we are ekeing out new insights from our current understanding. It’s a great story, reaching back into the ancient world, with a global cast of contributors, from Euclid in Athens and Al-Hazen in Baghdad, conceiving the idea of light rays, to Ted Maiman in Los Angeles and Shuji Nakamura in Tokushima developing lasers, by way of Thomas Young in London and Albert Einstein in Bern showing the wave/particle duality of light. In each case, new understanding (say of refraction) has led to new applications (such as eyeglasses for correcting vision). It’s amazing how short is the path from discovery to technology when light is involved.
Here’s just a few things that people are using light for today:
- The Internet is powered by light. Light has an immense capacity to carry information, and can be guided along thin strands of glass called optical fibers. In fact, fiber broadband telecommunications allows thousands of billions of bits of information per second to be streamed into your home.
- The most precise clocks in the world rely on light. Timing is central to navigation and to commerce. The most precise way we know to measure time is by looking at particularly stable electron motion in atoms. Lasers allow us to connect the specific frequencies of this motion into frequencies that are used for time standards, thus making possible better GPS systems.
- The best tools for cutting fabrication of metals and other materials are often laser beams. Things as diverse as stents for stabilizing blood vessels and surface patterning for more efficient solar cells are made by laser machining. Lasers weld together many of the structural components of modern automobiles and slice up silicon wafers into computer chips.
- The shortest controllable events made by humans are pulses of light. The current record is a pulse of less than a billion-billionth of a second in duration, which is used to look directly at electrons moving around in atoms and molecules by using it as a sort of stroboscope.
- The strangeness of the quantum world is exemplified by light. Scientists are able to generate particles of light – photons – that have properties that are very strongly correlated – such as their color and timing. In fact, these correlations are much stronger than anything we can imagine if we took separate photons with definite colors and arrival times. And even more strange is that it is possible to use these correlations between photons to build a completely secure communications system.
- The tiniest objects can be manipulated using light. Laser beams can hold onto small particles, from plastic beads down to atoms, and move them around. These “optical tweezers” enable single molecules to be studied for biophysical applications, make it possible to hold onto single cells to see how they stick together and to perform “micro surgery” on them, and to monitor the environment by analysing very small quantities of aerosols, for example.
This is just a small sample of how light is used in the laboratory and in everyday life. Despite having studied light for millennia, we are still learning new things about it, and new ways to use it. 2015 is going to be a great year for light!
Featured image credit: ‘Steel Wool Produces Light’, by 5zal Photography. Public domain via Pixabay.