Wednesday, 27 July 2016

Finding the faintest light

We can’t see as well in the dark as, for example, cats can. But what’s the smallest amount of light we can still see? Jonathan Tinsley and his team found the answer.

The faintest light bulb
Tinsley and his team found out that we can actually register the tiniest amount of light possible; single photons. But what are photons? To answer this, we first have to take a look at light itself. Light is, quite simply, a form of energy. But there’s something strange about it; light cannot just have any amount of energy. The reason for this is that a light source, like a light bulb, can only emit whole photons (a photon is like a little packet with a specific amount of energy in it). In other words, if you had a light bulb connected to an extremely precise dimmer, you would only to able to add whole photons when you turn the light up and you would only be able to take away whole photons when you turn the light down. Because of this, if you were turn the dimmer all the way down, the light would either be off or emit just one photon at a time, there’s nothing in between. And now, it turns out we can actually see light with the lowest energy possible; just single photons.

Did you see it?
In the 1940s, scientists already found out that our eyes can detect very low amounts of photons; between five and seven. This is extremely little if you keep in mind that the average light bulb emits two hundred duodecillion photons (that’s a two with 41 zeros) per second. And now, seventy years later, Jonathan Tinsley and his team have discovered that we can register individual photons. The scientists discovered this with an experiment where they asked some test subjects to take part in a sort of game. When the people that participated in the experiment pressed a button, the machine either shot a photon or did not shoot one. The test subjects then had to say if they saw the photon and also how confident they were about whether they saw it or not. After a lot of button pushing, Jonathan Tinsley and his team found that the human guinea pigs were right fifty-two percent of the time. This means that did a little better than if they were just randomly guessing, which would result in getting it right fifty percent of the time. This two percent is, of course, not a significant difference. And that’s where the confidence comes in. The times when the test subjects were really confident about whether or not they saw a photon, they got it right sixty percent of the time. The reason for this is that the photons don’t always create a signal that your brain can actually register. So sometimes there were some photons that the test subjects couldn’t see, but sometimes they could. But what can we learn about our eyes from this?

It’s not perfect
Between light entering your eyes and your brain registering the signal created by that light, there are quite a lot of steps. With every step, a bit of the signal gets lost and a little bit of noise is added. This means that everything you see gets a bit blurred and muddied. Fortunately, it has such little influence on what you actually see that you rarely notice. And now, the photon experiment gives us some new knowledge about this blurring and mudding. We now know that this blurring effect is so small that even photons don’t get affected by this. The results of this experiment aren’t, however, completely watertight yet. The tests were only done on three people, which were all men in their twenties. Future experiments can tell us if women and people of other age groups can also see photons. These experiments will tell us even more about our eyes.

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