Today is International Day of Light, a worldwide initiative sponsored by UNESCO to celebrate the role of light in scientific innovation, culture, and art. Why today? Because it marks the first successful operation of the laser by Theodore Maiman in 1960. 10 things you might not know about light:
- The speed of light is 186,282.4 miles/299792km per second – in a vacuum. When light has to pass through stuff of any kind it interacts with the atoms making up that stuff which slows it down. For example, the speed of light is 77,500 miles/124724km per second inside a Diamond, because diamonds are so dense that photons have to ping about a lot in order to find their way out. That is why diamonds sparkle. Lenses can magnify things and correct vision due to the same process as light bends as it slows.
- There is a special kind of stuff that scientists have made called Bose-Einstein Condensates, which consist of supercool atoms. This stuff really slows light down, to 25 km/15 miles an hour. Scientists have found it is possible to store light in this medium.
- It took half a million years for the universe to expand enough for light to travel freely after the big bang.
- Visible light, also known as white light, makes up less than one ten-billionth of the electromagnetic spectrum, which stretches from radio waves to gamma rays.
- A "jiffy" is more than just a figure of speech. It's an actual measurement relating to the speed of light. It's defined as the time it would take light to move one centimetre in a vacuum. 33.3564 picoseconds, to be exact. A picosecond is a trillionth of a second. So if you tell someone you'll "be there in a jiffy" you'll have to move pretty damn fast.
- All living things emit light to varying degrees. This is called bio-luminescence. 90% of the creatures living more than 1,500 feet below the surface of the sea are bio-luminescent enough for the human eye to see them glowing. World War II aviators used to spot ships by the bio-luminescence in their wakes. Scientists are working on extracting bio-luminescence from Jellyfish and fireflies with the aim of using it to make trees which glow in the dark.
- I said all living creatures – that includes human beings, although we don't emit enough light for the human eye to detect. However, scientists have worked out that we are brightest during the afternoon, around our lips and cheeks.
- There a law in England called the ‘Right to Light’. This law dictates that if someone has received natural light in their building for more than 20 years, they can forbid the construction of buildings that would block their light. That's assuming the UK government didn't do away with it along with a whole raft of other rights in 2020. I wouldn't put it past them.
- How do scientists know how much a star weighs? It's not like you can bung it on the scales. To calculate the mass of a star, astronomers use light. Massive objects such as a star can curve spacetime, so it's possible to work out the mass of a star by measuring the difference between the actual position of the star and the position it appears to be in.
- Scientists have found all kinds of interesting uses for lasers. Optical tweezers work by using a laser beam to trap and isolate microscopic objects such as strands of DNA. There is even a laser device which is less than a millimetre thick and can be made into a contact lens, so people will effectively be able to emit lasers from their eyes, at least when another laser shines on it. This doesn't mean people will be able to shoot people with their eyes like Superman or Cyclops, but it may have some use as a wearable security tag.
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