How many atoms are you made of?
This is not a post about science per se, but about perspective.
If you take the idea of an atom as a given, the answer is easy to figure out…
Take your bodyweight in kgs and stick 26 zeroes on the end. Or, multiply it by a hundred trillion trillion.
For example, if you weigh 70kg, then you consist of approximately 7,000 trillion trillion atoms.
That’s 7,000,000,000,000,000,000,000,000,000 (7 x 1027 for short). Or, if you are among the largest humans, like Eddie Hall at his maximum weight of 197kg, that’s almost 20 octillion atoms.
To put this in perspective, that’s roughly the number of peppercorns you would need to fill the earth (if it was hollow, obviously). Or alternatively, a billion times the number of grains of sand on earth, including all the deserts.
Atoms are very small. But even smaller than atoms are protons and, smaller still, quarks.
One quark is approximately one billionth the length of an atom and one octillionth the volume. Said another way, in terms of length and volume, a quark is to an atom roughly what an atom is to a human. To an atom, a quark is very small.
We are gigantic compared to atoms, let alone quarks. But the sun is gigantic compared to us.
The sun is on the order of one billion times ‘longer’ than we are. It’s about 1.4 billion metres in diameter. In terms of volume it’s also on the scale of octillions—about ten octillion average humans (or three octillion Eddie Halls). Said another way, our star relative to a human is pretty commensurate with what a human is to an atom.
A galaxy is gigantic compared to the sun. A typical galaxy is on the order of 100 billion times wider than the sun (and some much bigger still). Said another way, a typical galaxy relative to our sun is 100 times what we are to an atom.
So where do we humans sit, in the grand scheme of things?
If you imagine everything we know of on a scale, with the ‘typical largest object’ at one end—a typical galaxy—and the smallest observed object at the other—quarks—what sits smack bang in the middle? Something about three metres long; on the order of a human or, if you prefer, a standard piece of plumbing pipe.
These aren’t the only ways to draw this scale. If you take the largest known galaxy as the upper end, the middle ground lands as something on the scale of your immediate locale, about 77m across. If you swap out the smallest object for neutrinos, and the largest for the entire observable universe, you still get a space that reaches about 50m in every direction. Either way, humans, and the immediate things and places around us, just happen to fall somewhere in the middle.
Given just how big and how small things can apparently get, the fact we find ourselves pretty close to the middle is remarkable whichever way you look at it.
Some would explain this through the anthropic principle—that we live at the only scale possible—a kind of material Goldilocks zone—large enough to be complex, but small enough for our biochemistry to work—large enough that quantum uncertainty doesn’t wreak havoc, but small enough that gravity doesn’t crush us.
But I find these explanations unsatisfactory. They call on terms that are themselves derivative of our minds and subject to the same limitations. The fundamental ‘why’ remains unanswered. What if we not only live in the only kind of universe capable of supporting us, but that the universe that appears to us is the only kind that could?
After all, what is an ‘atom?’ It’s an idea. A model that works well enough for us for what is observed. We don’t know what an atom is ‘in itself’ or to what extent it is even ‘real’ outside of our minds.
When writing this very post, I had to decide the boundaries. Should I establish them using even smaller ideas—neutrinos, strings, the Planck length? What about even larger ones, like galaxy filaments, the universe itself, the theoretical non-observable universe, or ideas around multiverses? In an attempt at fairness, I settled on the smallest and largest ‘observable objects.’ But even the sizes of these, and what constitutes ‘observable’ and ‘object,’ are questionable.
These boundaries are defined by what human consciousness, aided by technology, can observe. We are the ones setting the frame.
Asking how many atoms there are in your body is like asking how many characters there are in the collective unconscious.
Perhaps we sit in the middle because we are the ones looking.
…
For those interested in the maths: a typical galaxy measures roughly 1020 meters in diameter, while the smallest scale we can observe—through quark interactions—is around 10-19 meters. (Quarks appear to be point particles with no actual size; this figure just represents how small we can probe.) The geometric mean between these extremes is √(1020 × 10-19) ≈ 3 meters. Using the largest known galaxy (IC 1101, ~6 × 1022 m) puts the middle at about 77 meters, while using neutrinos (~10-22 m) and the observable universe (~1026 m) gives a middle of about 100 meters.
