Javier Fernández Panadero
There are questions that are very easy to ask and not so easy to answer… but let's try it
Simple answer: Do you see this banana? Yes? Well, it is made of atoms. Conclusion: you see the atoms.
Are you sure? I don't know about you, but my eyes don't see "bananas." My retina is sensitive to light, not to fruit.
That means that, when I talk about seeing something, what I'm actually doing is detecting light that comes from what I say I see. Either because that object emits it or because it reflects or scatters it.
In the case of bananas, part of the incident light is absorbed and another part is reflected, but not in the same way for all colors. Frequencies close to "yellow" are reflected to a greater extent. In this way, the reflected light reaches my retina and thus I perceive the shape, "its" color, whether the skin is smooth or rough, and other characteristics that are capable of altering the incident radiation in some way, so that the reflected "transport "Information about them.
Well, is that, then, SEE?
SEE is a process that may begin in the eye, but certainly ends in the brain.  Answer me this question: What is this?
If you have said "A cube", you are talking about something beyond what the eyes see. A cube is a three-dimensional figure, but what you see is a FLAT drawing. They are lines on a plane that "make you think" of a three-dimensional object, it is what we call perspective. In fact, if you concentrate, you can be able to see the "cube" in two different ways, depending on whether you choose in your mind if the lower vertices are the ones "in front" or the higher ones.
Therefore, the act of SEEING is completed when the mind models the pattern of points and interprets a model of what it is perceiving.
Sometimes "seeing" things that do not exist, for example "completing" the perceived image, as in this case, where the triangle white, which we all "see", does not exist.
Look at this other.
In this case, our mind interprets that the "tracks" are parallel, and are moving away, so that yellow bar that is "a the distance ”must be greater than the one“ in front ”. But all these are interpretations of our brain to adapt the perception to the model of the world that we have been building … and this far exceeds the information that is contained in the image, in fact, it can lead us to erroneous conclusions about it, such as in this case.
Well, but let's go back to the initial question.
Assuming all these limitations on the act of SEEING, can we see the atoms, Javi?
No, they are very small, your eyes do not reach to both. If we think about the optical part of your eye: the lens, the pupil, the moods, the resolution of the retina … No, you don't get to solve something so small.
Very well – you protest, but what about this?
They are spermatozoa, too small to be seen with the naked eye, but visible through optical methods, interposing lenses of enough power to magnify them until you can perceive them using your eyes.
Therefore, using “fat magnifying glasses” we can “see with the eyes” very small things. Could we, then, put a huge lens on and see the atoms?
No. They are too small. But bear with me, I really want to answer your initial question. Look at the following image and answer me a question.
You can do an experiment on this with the camera of your mobile phone and a remote control. Look at the "light bulb" on the remote control. When you press a button you can't see anything … because the emission is infrared. Now, look at it through the camera of your mobile and press a button on the remote. Through the mobile you will see that it emits a blink, a code with the order that the remote control is sending. Depending on your phone, you will see it in a slightly different color, for example purple or white (it works on almost all phone models). But if you look directly at the command you will see … that you don't see anything. Here you can see a video with this demonstration of my book Experiments to understand the world. Science for all .
I have a question for you. That violet color that I see through the camera, is it purple? I mean: Is it the violet color of visible light that I normally see? No right? If that "light bulb" emitted violet light, the "true" one, I could see it without the need for a camera. That color is "invented" by the mobile camera, it has converted that infrared radiation into visible light with the color that it seemed. We call that false color.
Let's go back to the photo of the cat. That cat has no orange, white, or purple parts. These are color codes that the thermal imaging system chooses to represent different temperatures. In fact, you have the correspondence between color and temperature on the right of the image. As you can imagine, these scales can be modified, depending on what we want to measure.
And now I ask you, in view of this image, would you say that we are SEEING the temperature?
There are those who would answer that no, that We can only talk about SEE if we are using optical systems and the eye. For them, their journey ends here. We cannot see the atoms.
But if you are more flexible in your definition and allow yourself to call SEE to what we have done with temperature, let's say to change your retina for a sensor system and your mind for a processor that converts it In an image, I will tell you that yes, we can see the atoms.
For this we are going to need a system that is capable of measuring at a sufficiently small scale, and then compose, create, invent an image from these data, A representation. Same thing we did with the cat and the false color temperature map. It is important that you remember that this colored image of the cat does not exist, it is not "real", it is built from data.
But also with the atom we have another problem … an atom is not "solid". It looks more like a small particle (the nucleus) surrounded by a swarm of electrons that, due to their movement, give the impression of forming a small “ball”, but it is not something solid.
So again we have a problem . What are we going to try to "see" of the atom? Well, we are going to try to "perceive" that swarm of electrons, which, even if only one, moves through a region so wide and at such a speed that it gives the impression of a spherical negative charge distribution around that nucleus, of a "cloud" .
An apparatus capable of this is the tunneling microscope . And this is a diagram of how it works:
A sufficient voltage is available small so that, according to classical physics, a current is not established between the tip and the material … but due to a curious quantum property, a current will be produced. And that current has a very close relationship to the width of the gap between tip and material. In this way, by measuring the current, we can estimate that distance.
As you may have noticed, this is very different from what we usually call “seeing”.
If we move the tip over the entire surface of the material and we calculate the distances … we could DRAW a "map" of that material, put it on a screen and … see it.
Indeed, here you are:
Well, actually, they are the distance measurements, calculated from the measurements of electric current that we have obtained by walking the tip of the microscope through the gold sample.
Well, actually, it is the graphic representation of those distances, (which have been PAINTED yellow to make it look more like gold to you, what cheats ), in a photo, made pixel by pixel.
As That, finally, we have reached the end of the road and I am going to answer the question with which we started …
Atoms are so small that we cannot see them with our naked eyes.
Atoms are so small that we cannot we can see them with optical systems.
Atoms don't even have a “solid body” that we could see, so we are content to be able to “feel” their electronic cortex.
So what we do is use devices that measure with more precision than our senses and putting all that data in the form of an image.
For me, that is SEEING. Measure and organize data to be able to make myself a model of the world.
Therefore, I see the atoms.
What do you think? Do you think you just saw atoms?
About the author: Javier Fernández Panadero is a physicist and high school teacher as well as a prolific author of popular science books.