Working in science, and more recently in science communication, I frequently find myself working in the nano-world – wavelengths measured in nanometres, nanostructures, forces that act over unimaginably short length scales. I never used to question these distances – they were all just numbers followed by ‘nm’. Recently, however, after thinking about various topics to write about on this blog, I’ve come to a realisation – I have no picture in my mind of a nanometre. None. Of course, I know exactly what a nanometre is:
A nanometre is one billionth of a metre, i.e. 1 nm = 10-9 m.
Of course, this definition is scientifically accurate, but I simply can’t visualise a billion of anything, or dividing anything into a billion pieces. I’ve never seen a billion people in one place, I’ve certainly never counted to a billion (I’ve only been alive for just over 1 billion seconds, but even if I had counted one number per second for my whole life to get to a billion, I’m still not sure that would help me visualise it!). If I had a billion pounds in my bank account (which I don’t!) I’d have to divide that number into chunks of a million to make any sense of what I could buy with it. In fact, I’m not sure whether it would be better to make a thousand piles of £ 1 million, or a million piles of £1000.
Maybe a better approach towards visualising a nanometre is to make a comparison with ‘everyday’ objects? A human hair might be a good starting point – they’re typically about 100 micrometres thick, but that’s still 100000 nanometres! Let’s go smaller, a red blood cell is apparently 6-8 micrometres (6000-8000 nanometres) in diameter, which seems more manageable to my limited imagination. Going down further in size, haemoglobin, which I generally consider to be a pretty large molecule, is typically in the range of 5-10 nm in size, and suddenly we have landed in the right ball park.
If you search the internet for ‘how big is a nanometre’ you’ll find quite a few websites and videos that take this comparative approach, often using the examples we’ve looked at above (human hair, red blood cell, protein, etc.), but I have at least two problems here when trying to visualise 1 nanometre. The first is that we quickly get involved in objects that are really not part of my ‘everyday’. A red blood cell doesn’t help my imagination leap from a human hair to a bacterium, because I can’t visualise a red blood cell very well. I’ve seen them in a microscope, but when I look through a microscope there is no point of comparison – I might know that the magnification is ‘x100’ but my brain still needs to scale these objects in relation to my ‘everyday’ objects.
And the other problem is that this chain of objects casually drops in size three orders of magnitude between the bacterium and the protein molecule. If we try to plug the gap with other objects (cell, gene etc) then we are describing objects I can’t visualise, in terms of their constituent parts, which presumably I also can’t visualise… I’ve seen some of these things through an electron microscope, but again there is no point of comparison. In fact, this time things are much worse, as the magnification is ‘x 1 000 000’, or more.
So, if it’s too hard to think of a nanometre as a distance (which is a shame because that’s what it is!), then maybe we can introduce a new quantity to help us. You might have heard of the quantity ‘1 beard-second’, which is the distance that a beard grows in one second (Google’s unit converter tells us that 1 beard second is 5 nm) .
After all, this is what they do in astronomy, with the ‘light-year’, which is the distance light travels in a year. So all I have to do is think about how fast a beard grows, and I’ll be visualising a nanometre in no time!
Except this doesn’t help! I can visualise the ‘second’ part of the beard-second, but I can’t visualise the ‘beard’ part, which is the speed that the beard is growing. And come to think of it, although I can visualise the ‘year’ part of the light-year, I struggle to visualise the ‘light’ part, which is the speed at which the light is travelling! On the bright side, however hard it is to build a picture in your head of what a nanometre is, at least Google can tell you when to shave…