Having to pick out the singular most incredible concept in physics would be an interesting task (to say the least). Rarely a day goes by without me invoking the term ‘awesome’ in some context or other. I really do have a wonderful job.

Today however I came to what I think may be my favourite – the structure of the atom. You see the concept of solidity is merely an illusion. That table appears to be solid but actually it is 99.9999999% empty space.

“But it looks solid!”
Yup – but that’s (just) an optical illlusion caused by the interaction of electrons and incoming electromagnetic radiation.

“But it feels solid – when I bang my hand off the table I feel a solid surface!”
Again an illusion I’m afraid. This time caused by the interaction between electrons in your hand and electrons on the surface of the table repelling each other.

So next time you’re sitting in your car holding on to the steering wheel, just remind yourself that the steering wheel is hardly even there – neither is the car and for that matter neither are you (I’m trying not to have an exclamation mark at the end of every sentence here, but it’s not easy).

Now there is a (very, very) small amout of ‘matter’ in you. And here’s the thing; if you somehow managed to remove all the empty space in your body you would be left with a lump of solid matter which would be smaller in size than a grain of salt. How much would it weigh you ask? Why the very same as you do now, after all we have only removed the empty space (having a real tussle with the exclamation mark key here).

Okay, but this is all theoretical right?
Well maybe. It’s theoretical for humans, but there are objects out there which do not have empty space in them and which therefore are incredibly dense. They’re called neutron stars and to quote from Wikipedia:

this density is approximately equivalent to the mass of the entire human population compressed to the size of a sugar cube.

This gives them some other unusual properties. The radius of a typical neutron star is about 12 km, and just like a pirouetting ice-skater whose rate of rotation increases as they draw their arms in, so also does the rotation of a neutron star increase as its radius decreases. So how long does a full rotation last (remember that on Earth this is 24 hours)? On average there are somewhere between 100 and 1000 full rotations per second (see, if I can’t use exclamation marks at least I can use italics).

But back to the atom. To help students appreciate that it’s not just me who is bonkers, here I invoke the assistance of some more well-renowned experts.

Professon Brian Cox

Note that it took Rutherford two years to arrive at a correct interpretation of these results. It’s not like what you see in the textbooks – describe the experiment and then form an obvious conclusion.

It kinda freaked him out – Neil de Grass Tyson (audio link)

And for a bunch of other links see the related page on my website.

And finally, while you are expected to know that the atom is mostly empty (and be familiar with the experiment that ‘proved’ it), there is no sense in either the syllabus or any textbook I have come across of the wonder associated with this crazy idea. In fact it’s normally presented as just another piece of information to be learned off my heart. And I never hear anybody giving out about this, so I save my rants for unfortunate students and the odd blog post like this.

Now that’s mad!!