: : To answer the question, though; yes, those are atoms; or the nearest we can get to actual physical proof of them. : : We can't ultimately prove that they exist in much the same way that you can't ultimately prove your neighbour's car exists; there is evidence to support the theory; and we can do experiments that would show us if they didn't exist.
: : Such experiments have not shown us that they don't exist, so we go with the theory until a better one comes along.
: So, the question is, are atoms real? Or are atoms inventions of men which fit the model predicted by using particular instruments?
Is anything 'real'? When it comes down to it, you can ultimately prove nothing; for all we know, everything could be an illusion.
However, sitting around saying that nothing else exists is a) boring and b) ultimately unrewarding. Most lifeforms like to work out patterns in nature that can help them; and humanity is no exception.
This is the foundation of science; the looking at what appears to be 'the real world' and the deduction of underlying principles from the way the world behaves.
How does a chimp tell the difference between edible and inedible? - by the evidence relayed to it by its senses. How do you tell the difference between J.S. Bach (Baroque) and C.P.E. Bach (Rococo)? - by your senses.
The senses are not infallible, but they are our sole information inputs; and cataloguing phenomena is an important survival skill (e.g. knowing what a poisonous mushroom looks like). Inquiry into the natural sciences is nothing more than an extension of that habit.
Sitting in a cave and declaring that everything is your imagination is all very well; but it doesn't get you food. To get food, you need an empirical set of rules to work out what 'food' is.
To do this, you have to work on the assumption that the physical world does exist and that it resembles the sensory inputs you receive (not infallible; the senses can be fooled, but a good working guideline).
From this process come induction and causality; induction says 'today will follow the same basic physical laws as yesterday' and causality says 'a cause results in an effect'; both of these are well within the mental capabilities of most mammals; witness the ways squirrels learn to break into nut holders in a garden.
All science is ultimately nothing more than an extension and abstraction of these fundamental principles; see what works, see waht doesn't work and try to figure out the difference.
To do this, you need a critical approach; you must apply every sort of test you can think of to your theory; do your best to destroy it; and if it survives, it's probably a pretty good theory.
Because of this, science in general is something that people stake their lives on without a second's thought; the axioms that govern the way your car works have been tested exhaustively.
You can't prove your car exists; you can't ultimately prove the existence of anything physical or non-physical. However, to stay alive, you need to assume that the observed physical world is real.
When you drive your car, or eat food, or breathe, you are making that assumption automatically without even thinking about it.
And as far as the experimental data in the observed physical world goes, yes, those are small bundles of what we have called protons and neutrons and electrons; they are what we call atoms. We place our day-to-day survival on the atomic theory; and we haven't died yet.
(And computers also rely on the atomic theory; you wouldn't be seeing this if the natural world didn't appear to be composed of atoms.)
: Obviously, something appears to be there which we call atoms, but how do we know that we are really seeing atoms?
When you pick up an apple, how do you know that you are really seeing or holding an apple?
Your senses, obviously. Our senses are limited; but we can make tools that help us see beyond our natural capabilities.
Does a person born blind have a concept of the colour 'red'? - unlikely; but does that mean that there is no such thing as 'red'? Of course not. The fact that humans cannot see atoms does not mean that they do not exist; we build a tool to help us see them, just as we build a tool to help the blind see.
As far as we can tell using our limited senses and equipment, atoms exist; we are confident in this to make our day-to-day lives dependent on this science; computing, plastics, nuclear power, genetics, chemistry - all are dependent on the atomic theory.
Of course, we can never be sure that anything exists; but I'm going continue breathing in oxygen atoms; I trust the atomic theory enough to risk my life on it.
(As do you, although you may not realise it.)
Gideon.
