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Asked by emmab12 to Mark, Matthew, Mike, Paul, Sabina on 7 Mar 2014. This question was also asked by ladylily123.
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Matthew Malek answered on 7 Mar 2014:
Good question! There is so much about light that is interesting!
I was first tempted to answer by saying that it is the very nature of light, being something that is partially like a particle and partially like a wave. However, that’s not unique to light — all fundamental “particles” of the universe are like this. Electrons are just as “wavelike” as light.
Instead, I’ll say that the most interesting thing about light is how much we can learn from it. Look at astronomy, for instance. How much have we learned about the universe from just looking at visible light? We can only see photons (or “particles of light”) in a very narrow frequency range… yet we have learned so much about places so far away from studing the light from space. Once we learned how to detect other parts of the light spectrum, like gamma rays and x-rays and radio waves, we gained the ability to learn even more.
For example, just look at the cosmic microwave background. This light is the “echo” of the Big Bang, a snapshot of the universe when it was only about 380,000 years old (or about 0.3% of a % of its current age). By studying this ancient light, we have learned about the age of the universe, the contents of the universe, the expansion of the universe, dark matter, dark energy, and so much more! Pretty nifty, huh?
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Mark Jackson answered on 7 Mar 2014:
It doesn’t experience time! From the photon’s point of view, absolutely no time passes; it was both created and destroyed in the same instant! So the light that we see left over from the Big Bang is completely unaware of the 13.8 billion years which have passed. This makes me think of light as the loneliest of elementary particles: it doesn’t get to look back on its life, and has nothing to look forward to.
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Sabina Hatch answered on 7 Mar 2014:
This is a tough question! In my opinion light gets really interesting when it interacts with material with similar dimensions as its wavelength (50-200nm). This is when it can create electricity and also leads to chemical reactions. It is amazing to think that something without mass, just pure energy can have such a huge effect on a material. An example of this is how UV-light can trigger the terrible effect of skin cancer.
Another thought is that without light, there would be no life. Everything needs light to survive, even those creatures in the depths of the ocean that have no light (because they feed on the creatures that fall from above).
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Mike Lee answered on 10 Mar 2014:
Light is laced with darkness.
Image there is only one colour, how about red. This is the light of a laser. If you shine a (low power) laser pointer at a wall, and look at the spot, you can see it’s speckled with dark spots. These are actually lines and loops of darkness which happens because light can twist as it moves.
If there are more colours, these dark lines occur in different places, so average each other out and become hidden.
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Paul Coxon answered on 11 Mar 2014:
One of the most interesting properties about light is the colour purple – it doesn’t exist. It’s a complete figment of our imagination. How to believe but it’s true!
There are three colours in optics, in increasing wavelength: red, green then blue.
Red and green are next to each other, so where they overlap we see yellow. Where green and blue overlap we see cyan. But because red and blue are at opposite ends of the spectrum, when red and blue light overlaps with each other, our brain tries to work out what colour it should be and comes up with purple!
Comments
lumiereclair commented on :
Light photons don’t age? Or ‘don’t experience time’ at all? That’s both amazing, and mind-boggling. Great question emmab12!
Mark commented on :
Nope! Photons really do not experience time or age, as you very poetically put it.
One of the consequences of Einstein’s Special Theory of Relativity is that not everyone will agree on how much time has passed between two events, or even on their distance of separation. What they *will* agree on is a combination of these numbers: the square root of the time separation-squared minus the distance separation-squared divided by the speed of light-squared:
Delta s = Sqrt( (Delta t)^2 – (Delta x)^2 / c^2 ).
In the case where the events happen to be you now and you in the future, just set the distance-separation to zero and as expected, the amount of time you experienced was Delta t. This doesn’t just work for you, it works for anything that is capable of sitting still.
Now try it for photons, or anything which cannot sit still: since they always move at the speed of light (that’s why it is called the speed of light!) the distance they travel is Delta x = (Delta t)*c. And you will always get that Delta s is zero – they didn’t experience any time!