Atoms

Atoms don't really look like this

Atoms. Just about everyone who has any form of education knows that the universe is made of atoms. Many also know that there are three sub-atomic particles that actually make up an atom. These are the proton, the neutron and the electron. A few will also know that the current best bet is that protons and neutrons are in turn made out of something called quarks.

Quarks I am not to sure about, despite the fact that they have been "seen". Some think that the quarks may in turn be made out of strings, this is were I draw the line. String theory for me is currently nonsense. The mathematicians have taken over the asylum.

Back to the atom. Before 1905 we didn't know for sure that atoms actually existed. So why didn't we know? We knew about gravity, electricity, light, radioactivity and loads of other things such as chemistry! Why was it that some people thought that the idea of atoms was little more than a mathematical abstraction, rather than something real? Well, for one thing they are remarkable difficult to see. They are really small. So small in fact that I don't believe it is possible for the human brain to comprehend just how small they are. You can talk about how many atoms make up a millimeter, but this number, about 6-10 million, is so large that you can't appreciate it.

So how did we finally crack this one. Well bring on Einstein, he had read about a paper written 80 years earlier by a bloke named Brown, a biologist (I think).

Now Brown had watched pollen particles in water and had noticed how they had bounced around in a random way. He hadn't been able to explain it and his idea and it could not be explained using classical thermodynamics.

Einstein was able to take this observation to determine the size of atoms. This was a brilliant paper (and that of the photoelectric effect) and won him a Nobel Prize. He did not win it for Special Relativity or General Relativity as many appear to think.

The paper also proved that classical thermodynamics was not valid on atomic scales. In fact Einstein opens the paper stating this.

What I think is great is that he actually comes up with an experiment (which he does not do himself, he leaves that to others) that will be able to calculate certain values that can then be used to determine the size of atoms.

The paper also derived an equation which showed that it would be possible to calculate the site of molecules and atoms.  The equation he derived was this

N = Avogadro's number = 6.0221415 x 10²³
R = Gas constant = 8.3144  (Aside: The Boltzmann Constant is just R divided by N)
T = temperature in Kelvin, so room temperature ~ 293 K
k = viscosity of the liquid  ~ 0.001 for water
λ_x = average distance moved in a given time during Brownian motion.

P = the size of the particle or molecule.


In 1908 Perrin began to study Brownian motion using the newly developed ultra-microscope. He carefully observed the Brownian motion of particles and provided experimental confirmation of  λ_x and P in  Einstein's equation. His experiments enabled him to estimate the size of water molecules and atoms as well as their quantity.

1908 was the first year that the size of atoms and molecules were reliably calculated from actual visual experiments. Perrin's work moved atoms from being hypothetical objects to observable entities. He was awarded the Nobel Prize in 1926 for his work.

It seems strange to me that just over 100 years ago atoms were still considered by many to be hypothetical and not really based on real objects. These days children are taught about atoms in primary school. 100 years from now will children accept "facts" from physics that we still consider just theoretical today?

Of course they will, I just wish that I was there to see what those facts will be.