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Introduction to the Elements

Entry 1891, on 2017-12-30 at 09:55:36 (Rating 1, Science)

The Greek philosophers were incredibly smart people, but they didn't necessarily know much. By this I mean that they were thinking about the right things in very intelligent and perceptive ways, but some of the conclusions they reached weren't necessarily true, simply because they didn't have the best tools to investigate reality.

Today we know a lot more, and even the most basic school science course will impart far more real knowledge to the average school student than what even the greatest philosophers, like Aristotle, could have known.

I have often thought about what it would be like to talk to one of the ancient Greeks about what they thought about the universe and what we have found out since, including how we know what we know. Coincidentally, this might also serve as a good overview of our current knowledge to any interested non-experts today.

Of course, modern technology would be like total magic to any ancient civilisation. In fact, it would seem that way to a person from just 100 years ago. But in this post I want to get to more fundamental concepts than just technology, mostly the ancient and modern ideas about the elements, so let's go...

The Greeks, as well as several other ancient cultures, had arrived at the concept of there being elements, which were fundamental substances which everything else was made from. The classic 4 elements were fire, air, water, and earth. In addition, a fifth element, aether, was added to account for the non-material and heavenly realm.

This sort of made sense because you might imagine that those components resulted when something changed form. So burning wood releases fire and air (smoke) and some earth (ash) which seemed to indicate that they were original parts of the wood. And sure, smoke isn't really like air but maybe that's because it was made mainly from air, with a little bit of earth in it too, or something similar.

So I would say to a philosopher visiting from over 2000 years ago that they were on the right track - especially the atomists - but things aren't quite the way they thought.

Sure, there are elements, but none of the original 4 are elements by the modern definition. In fact, those elements aren't even the same type of thing. Fire is a chemical reaction, air is a mixture of gases, water is a molecule, and earth is a mixture of fine solids. The ancient elements correspond more to modern states of matter, maybe matching quite well with plasma, gas, liquid and solid.

The modern concept of elements is a bit more complicated. There are 92 of them occurring naturally, and they are the basic components of all of the common materials we see, although not everything in the universe as a whole is made of elements. The elements can occur by themselves or, much more commonly, combine with other elements to make molecules.

The elements are all atoms, but despite the name, these are not the smallest indivisible particles, because atoms are in turn made from electrons, protons, and neutrons, and then the protons and neutrons are made of quarks. As far as we know, these cannot be divided any further. But to complicate matters a bit more there are many other indivisible particles. The most well known of these from every day life is the photon, which makes up light.

Different atoms all have the same structure: classically thought of as a nucleus containing a certain number of protons and neutrons surrounded by a cloud of electrons. There are the same number of protons (which have a positive charge) and electrons (which have a negative charge) in all neutral atoms. It is the number of protons which determines which atom (or element) is which. So one proton means hydrogen, 2 helium, etc, up to uranium with 92. That number is called the "atomic number".

The number of neutrons (which have no charge) varies, and the same element can have different forms because they have a different number of neutrons. When this happens the different forms are called isotopes.

Protons and neutrons are big and heavy and electrons are light, so the mass of an atom is made up almost entirely of the protons and neutrons in the nucleus. The electrons are low mass and "orbit" the nucleus at a great distance compared with the size of the nucleus itself, so a hydrogen atom (for example, but this applies to all atoms and therefore everything made of atoms, which is basically everything) is 99.9999999999996% empty space!

When I say protons are big and heavy I mean this only relatively, because there are 50 million trillion atoms in a single grain of sand (which means a lot more protons because silicon and oxygen, the two main elements in sand, both have multiple protons per atom).

When atoms combine we describe it using chemistry. This involves the electrons near the edge of an atom (the electrons form distinct "shells" around the nucleus) combining with another atom's outer electrons. How atoms react is determined by the number of electrons in the outer shell. Atoms "try" to fill this shell and when they do they are most stable. The easiest way to fill a shell is to borrow and share electrons with other atoms.

Atoms with one electron in the outer shell or with just one missing are very close to being stable and are very reactive (examples: sodium, potassium, fluorine, chlorine). Atoms with that shell full don't react much at all (examples: helium, neon).

There are far more energetic reactions which atoms can also participate in, when the nucleus splits or combines instead of the electrons. We call these nuclear reactions and they are much harder to start or maintain but generate huge amounts of energy. There are to types: fusion where small atoms combine to make bigger ones, and fission where big atoms break apart. The Sun is powered by fusion, and current nuclear power plants by fission.

After the splitting or combining the resulting atom(s) has less mass/energy (they are the same thing, but that's another story) than the original atom(s) and that extra energy is released according to a formula E=mc^2 discovered by Einstein. This means you can calculate how much energy (E) comes from a certain amount of mass (m) by multiplying by the speed of light squared (90 thousand trillion). This number is very high which means that a small amount of mass creates a huge amount of energy.

Most reactions involve a bit of initial energy to start it, then they will release energy as the reaction proceeds. That's why lighting a match next to some fuel starts a reaction which makes a lot more energy.

So water is a molecule made from one oxygen atom and two hydrogen atoms. But gold is an element all by itself and doesn't bond well with others. And when two elements bind and form a molecule they are totally different from a simple mixture of the two elements. Take some hydrogen and oxygen and mix them and you don't get water. But light a match and you get a spectacular result, because the hydrogen burns in the oxygen forming water in the process. The energy content of water is lower than the two constituent gases which explains all that extra energy escaping as fire. But the fire wasn't an elementary part of the original gases and neither was the water. You can see how the Greeks might have reached that conclusion though.

Basic classical physics and chemistry like this make a certain amount of intuitive sense, and the visting philosopher would probably understand how it works fairly quickly. But then I would need to reveal that it is all really just an approximation to what reality is really like.

There would be a couple of experiments I could mention which would be very puzzling and almost impossible to explain based on the classical models. One would be the Michelson–Morley experiment, and the other would be the infamous double-slit experiment. These lead to the inevitable conclusion that the universe is far stranger than we imagined, and new theories - in this case relativity and quantum theory - must be used.

Whether our philosopher friend could ever gain the maths skills necessary to fully understand these would be difficult to know. Consider that the Greeks didn't really accept the idea of zero and you can see that they would have a long way to go before they could use algebra and calculus with any competence.

But maybe ideas like time and space being dynamic, gravity being a phenomenon caused by warped space-time, particles behaving like waves and waves behaving like particles depending on the experiment being performed on them, single particles being in multiple places at the same time, and particles becoming entangled, might be comprehensible without the math. After all, I have a basic understanding of all these things and I only use maths like algebra and calculus at a simple level.

It would be fun to list some of the great results of the last couple of hundred years of experimental science and ask for an explanation. For example, the observations made by Edwin Hubble showing the red-shifts of galaxies would be interesting to interpret. Knowing what galaxies actually are, what spectra represent, and how galactic distances can be estimated, would seem to lead to only one reasonable conclusion, but it would be interesting to see what an intelligent person with no pre-conceived ideas might think.

As I wrote this post I realised just how much background knowledge is necessary as a prerequisite to understanding our current knowledge of the universe. I think it would be cool to discuss it all with a Greek philosopher, like Aristotle, or my favourite Eratosthenes. And it would be nice to point out where they were almost right, like Eratosthenes' remarkable attempt at calculating the size of the Earth, but it would also be interesting to see their reaction to where they got things badly wrong!

Comment 1 (4878) by Anonymous on 2018-01-09 at 21:53:19:

Just a small question... did you fact-check this information?

Comment 2 (4879) by OJB on 2018-01-09 at 21:56:05:

Actually, no, I didn't. I did it all from my own remembered knowledge (apart from a check on a couple of numbers). Is there any specific error you have found? If anyone finds errors in my posts I am very happy to correct them.

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