I was watching a film the other day in which one of the characters said "atoms are really really small, micrometric, so tinny we need a microscope to see them". I shaked my head in disagreement. I said, "man, this guy really has a problem of scale".
Almost everyone has heard microscopes help to see what is really really small. If you take a single hair or a poor fly and you place them under a convetional optical microscope, you will see details you could never see with your bare eyes. If you are a bit pretentious you could even go to your partner or children and say "look, augmented reality". Yeah, all right. It is indeed augmented reality. But, could you see anything you want with an optical microscope? I mean, the smallest things that are there? atoms? subatomic particles? quarks?could you? Unfortunately, the answer is no. Optical microscopy (i.e. the microscope you came across in your biology lab at high school) has its limits. You could normally see in the range of micrometers, maybe a quarter times less than a micrometer if you really have a brand new expensive model and you are looking in the visible range (we humans tend to like the visible range, because it is what our eyes see without any additional instrument). With a conventional "high school microscope" you may clearly distinguish different types of cells and even regions within a cell. You can take a drop of water and see microorganisms inside. That for sure! It is a quite good trick to get 8 year old children into nature. Let them collect a water sample from a local river/lake and they will amaze with what is inside. But, how much can we really see? And, what is equally important, what happen with smaller things? Because atoms, are smaller, right? so can we see them with an amateur microscope? and how much smaller than my "augmented fly" are them?
Let´s start with a quarter of a micrometer. That is a really small quantity if we compare it with everyday things. It is for example the size of certain viruses (which may be even smaller) or small bacteria. You can also make artificial objects "easily" of this size in the shape of beads, for example (polystyrene beads of a quarter of a micrometer, i.e. 250 nm are common in laboratories all over the world). However, these things can be seen with a really good optical microscope (the best ones, and probably not with that found under the dust in the corner of our high school lab). The visible light going through the microscope and back to us "let us" see it. However, this won´t be the case if we want to see smaller things. But what is smaller than that? for sure atoms, electrons, quarks...
Let´s for example think in 25 atoms sitting one after the other in a straight line (and not interacting with each other!). We could not see them with an optical microscope because there is something fundamentally wrong: they use visible light, which is a type of wave (electromagnetic) and therefore is a periodic sequence of maximum, minimum, maximum, minimum (of intensity, if you wonder). But light behaves different when encounters objects as small as the distance between two of its consecutive maxima (or minima). And this means one cannot really "see" objects of such small size, one cannot distinguish them one from another or resolve them if a few of them are sitting together.
But let´s get back to our 25 atoms in a straight line (and as I said before, let´s ignore any type of force which could be acting among them). How far are we from our optical microscope's limit? Are we close, I mean, could we see them if instead of 25 atoms I have 26 of them? Let´s just have a look to the following image (Figure 1):
Fig.1. Stars of proportional sizes, where the star labelled as (3) is 100 times (1), and the star labelled as (2) is 10 times greater than (1).
If we think that the optical microscope can only see things as big as the star that is not fully drawn in Figure 1 because it is too big to fit in the image, but from which one of the pointy parts of the star is shown (and labelled with a (3) ), then, the 25 non-interacting atoms laying one after the other in a straight line would be of the size of a single tinny black star such as the one labelled in Figure 1 as (1). So tiny! And we are talking about 25 atoms and not just one!
We have given a specific name to quantity that measures things as small as atoms ( I should say "they", beacuse I have nothing to do with the naming!) This unit is the
angstrom, which is a tenth of a nanometer. Therefore, 25 non-interacting atoms in a straight line would be easily measured in nanometers. Scientists tend to use units which do not require to add numbers with lots of zeros. I could say a bridge is 20 000 000 000 nm high, but it is just ridiculous, so why not to say 20 m?
But let´s get back again to our 25 atoms, which could measure all together up to a few nanometers (looking in the "right" direction). This group of atoms can´t be seen with an optical microscope, not even the best one, because they are simply too small . Actually one could see them with other type of microscopes that do not use visible light or any light at all, like atomic force microscopes or scanning tunneling microscopes, which I would like to talk about other day. Therefore, we conclude an optical microscope cannot see atoms, not single atoms, not even 25 in a row. It cannot see when things are of nanometric size and of course not if they are just a few angstroms. However, with our high-school optical microscope we can see things of the size of micrometers, which are therefore big enough. They are of thousands of nanometers! Our beloved optical microscope will still work for cells, for ants and for a drop of blood if it is thin enough.
Well, now you know why I was a bit disappointed with the film, which just confused either my little niece and my grandma. To mix an angstrom with a micrometer is like to confuse a big titan (have you watched "attack on titan"?/"shingeki no kyojin"?) with a worm. Not really a deal?
