Extreme Microscoping. Part 1.
A microscope is an essential instrument in the collective imaginary that surrounds science. But what do we scientists resort when normal techniques are not available? What do we do when we want to see into the smallest known systems, into atomic nuclei? This is where extreme microscopes are needed!
I remember the first time I saw a magnifying glass. I was absolutely fascinated by such an object. It allowed me to see so much more than I could normally (even then, when I could actually see something without glasses or contacts). It was the most amazing thing I had seen until then. Well, what was an amazing discovery for me, had been around for ages in the human history. Lenses and objects which resemble magnifying glasses date back four thousand years! But of course, our curiosity is boundless, we humans always need more. As I found myself wanting to see even deeper into this weird, amplified, creatures, and even myself, humans didn’t wait a lot to yearn for this better resolutions.
Its well known that Galileo invented the modern telescope (from greek tele,meaning far way,and skopein, to look). However, the history of the microscope-basically a magnifying glass on steroids- is a bit blurry. No one really knows who invented it, but you can find a lot of names associated to it. Zacharias Janssen, Hans Lippershey, Cornelis Drebbel and even Galileo himself are candidates for the invention. What we do know precisely, is that Giovanni Faber coined the word microscope, using the ancient greek micron,meaning small, or tiny).
And so, scientists everywhere embarked in a journey looking to understand tinier and tinier things. From tissue, they went to cells and bacteria. From there, they tried to understand the parts of the unicellular organisms, as well as digging deeper and understanding cellular nuclei, and chromosomes. The next step is to dig even deeper and look for molecules, and atoms, right? Here, they hit a wall.
You see, the optical microscope uses light produced by an object (or bounces from it), and by the means of lenses and intricate array of refracting and reflecting of light, we can make bigger pictures of tiny things. Once again, let me just say that a microscope is a very powerful magnifying glass. However, the problem is that light has its own intrinsic sizes. The first intrinsic size is called amplitudeof the wave, and it measures the intensity of the light. This translates to the brightness of the light emitted. The other size is called wavelength and it r.elatesto how many times the wave oscillates in a given distance. You may be also familiar with the frequency of the wave, which is related to the wavelength and the wave velocity. Since the speed of light is always the same -roughly 300 000 km/s-, talking about wavelength and freaquency tends out (mathematically) to me basically the same. Just remember, higher frequencies imply smaller wavelengths, and viceversa!
Everything with the classical electromagnetism picture is nice, but we are quantum people, and we want to talk about quantum stuff, right? So let’s relate this to quantum mechanics (QM), shall we? In QM, waves and particles are two faces of the same coin, and that means that even when normally we think of light as waves, they are also particles, which are called photons. The amplitude of the wave measures the number of photons that we find in a given wave, which makes sense. More photons, more intensity. On the other side, the frequency, or wavelength, gives the energy of the photon. Higher energies imply higher frequencies, which imply smaller wavelengths.
Now this is an interesting notion here. Size is the problem scientists stumbled upon. If something is smaller than the wavelength of light, you cannot see it (probe itis a better phrasing). Why is that? Well, imagine you have a very irregular wall, one of those which where very popular at some point in the twentieth century. The ones that look like you painted cereal into the wall. You know which ones, right? So you throw a huge ball, which has a radius way bigger than the size of these cereal pieces into the wall, and well, it just bounces normally, as if these little thingies were not even there. Nonetheless, if you did it with a tiny ball, comparable to the pieces, it would bounce everywhere, depending on where it hits. Throwing many many many times the ball around would help you understand the distribution of irregularities, average and variation of their sizes, amongst many other variables, or as we call them in physics, observables.
A cool example of this are microwave ovens. In a microwave oven you use wavelenghts of the order of a few centimetres to basically rotate around water molecules, this extra movement creates extra temperature. That is why things get hot in there. Clever, right? Well, we have water in our bodies, right? Why are we not getting burned by being right there, in the same kitchen? It works using exactly the same principle as before. The waves are too big to see the little holes in the door. In the perspective of the microwaves, the whole oven is surrounded by metal plates, completely sealed, and so the bounce inside without a chance to escape.
This is where our troubles start.
-But what troubles? Just make the wavelength smaller, so you can access smaller sizes. Easy peasy lemon squeezy.- you may comment, rightfully so. However, things can get a bit complicated when we make our wavelengths smaller. Remember that doing so increases the energy. The problem with doing this is that there is a point in which hitting the desired object with light actually destroys it.
Take, as our first subject for a nice thought experiment a bacterium. This little fellas tend to be sized in the order of a millionth of a meter. This length is perfect, as it is around ten times bigger the range of visible light! Also, the energies of this kind of light cause the colour transitions in molecule -which is the reason we can observe the world-. These transitions mean that electrons jump around, playing with the light, but always remain inside the molecule. You see, if an electron decides to leave a molecule, motivated by a bad boy photon, the bond between atoms may break. Anyway, everything seems safe in this environment.
But what troubles? Just make the wavelength smaller, so you can access smaller sizes. Easy peasy lemon squeezy.
-You, puzzled by my statement.
But we want to go smaller, and that means we would like to see molecules. So, as our second subject for the thought experiment we take our favourite molecule ever, caffeine. It has a lot of different bonds between the atoms that compose it, and so it will be very nice to take it for a mental trip around the corner. Caffeine is roughly 700 pico metres. That means that the energy of a photon which has a wavelength of that size is around 1000 times bigger than the strongest bond in the molecule. You shine that light into the molecule and you can say “hasta la vista, baby” to the it. If we put light into it, we destroy it. So… difficult, difficult, lemon difficult?
The answer to this problem is easy, and probably you have already thought it: DON’T USE LIGHT! We have developed a lot of techniques to avoid this particular one. For example, we can use electrons, instead of light. When these particles interact with samples, they loose energy by many different ways (in physics we call them channels), as emission of light, lower energy electrons and heat. These channels can be then used to understand the shapes and structures of the object. For example, here you can see a terrifying close portrait of an ant, or here, where you can see a bizarre yet interesting picture of pollen.
Another fascinating method is the Atomic Force Microscope (AFM), which uses the fact that atoms hate each other! Actually, atoms have very complicated a nuanced relationships, in which they are codependent, or bonded when close, but really dislike each other when separated a bit. This results in them pushing each other as soon as they become in contact. The microscope, uses this aggression to feel extremely tiny changes in surfaces with its tiny tip. The AFM can actuallysee and make maps of material surfaces! Here you can see a nice example.
All of these ways are nice, but you may be wondering why “extreme” is in the title, right? Well, what if I tell you we want to measure things smaller than the atomic nucleus, that is one 1000000000000000th of a meter. You’re probably now wondering how much light energy we need for that. Well, a lot. It is really, a lot. You know X-rays, even more energetic than that. Actually we are talking about some very hardcore Gamma rays (you know, the ones from The Hulk). In fact it is really too much energy to use photons. So probably it is impossible, right? Nah, we can do it, and the how seems to come out of an episode of Mythbusters…
Smash them. Smash them all…
To probe a proton, we smash an electron against it at the speed of light. Yeap. That is what we do it. Shouldn’t it like, explode? Sure it does! The proton is instantly destroyed, and that is why the experiment was called Deep Inelastic Scattering (DIS). A lot of particles are produced instead, and reading the debris, we can understand the proton. Good thing is, there are quite a lot of protons in the Universe, so we can play around, blowing up many of them in our explosive path to knowledge.
But let’s go back a bit to understand the big picture. Why are we doing this?The question can be easily summarised in one phrase: we wanted to see if the proton was fundamental (hard and bouncy) or had an internal structure (soft, complicated, like a bag of potatoes), and basically the only way is to shove an electron very fast, very hard into it, and make it go bang. Ok, said like that it sounds very dumb, I give you that, but this experiment settled a lot of questions, like if quarksand gluons existed, and helped us expand a lot our understanding of deep nuclear matters.
But then… where does the highly energetic light come into this? You see, thanks to quantum mechanics and particle physics, we now know that fundamental matterparticles don’t really like each other too much. If they must interact, they do so using an intermediary particle. This would be the light particle, the photon, in case they are electrically charged. This photon will go full pinball into the photon -if the pinball could kick out very hard parts of the arcade machine — or it can split into a quark and antiquark and wreak havoc inside the proton, by making them be beaten by the gluethat binds the proton. In this chaos, a lot of particles which carry information of the structures are created and fly away, to safely crash into our detectors.
This process is therefore, a very intense and explosive microscope. Ironically, microscoping the tiniest thing requires a very big machine. The original one was a circle of 6km of circumference in Hamburg, Germany. And although it doesn’t perform the same kind of microscopy, the best machine we have right now is a circle of 27km (!) of circumference which lies under the border of France and Switzerland. So this technique is extreme in every aspect that you can imagine!
Before I finish, I will lay out a question. What happens if we use such a violent technique like this one, but with many, many particles bundled together, say in a nucleus? Do we see many copies of the same phenomena? Or do we see something more interesting, something social? Our next post will also bring some other extremeness into this mix while answering these questions.
This post originally appeared on http://www.manybodyphysics.com, our blog revolving around everything involving the science of many (quantum) things interacting with each other.
Oscar Garcia Montero is a PhD student at Heidelberg University, Germany. His work is related to nuclear forces and quantum mechanics. In his free time, he likes to illustrate, paint and drink loads of good coffee.
