What is the largest component of the human body? Most people, remembering their high school biology, will say it is water. About 60 percent water. We don’t fall apart in a sloshy mess because of our internal skeleton and a rather tough hide called skin. To say we are mostly water is correct as far as it goes. But what about the basic atoms. Water molecules are made of oxygen and hydrogen, two atoms of hydrogen married to one atom of oxygen. So in terms of numbers, we are mostly made of hydrogen, the simplest element. But because oxygen is much ‘heavier’ than hydrogen, it contributes more to our ‘mass’. Earth life is often called carbon-based because the carbon atom is capable of combining with other atoms in multiple ways, many of which are a prerequisite for life. So we have hydrogen, carbon, and oxygen at the top of the list. To build a strong skeleton we need calcium and phosphorus. We need iron in the blood. About a dozen elements are considered essential to build a human body.
Lets go even deeper. What are the individual atoms composed of? First of all atoms are tiny, mind bogglingly tiny. About five million-million hydrogen atoms could fit on the head of a pin. There are more atoms in the human body than stars in the observable Universe.
There is a curious twist to this story. We have all the various different elements composing not only us, but also everything we can see from the farthest galaxies to the tiniest grain of sand, and yet, nearly everything is really just primordial hydrogen. That is because the Universe began with mainly hydrogen. All other elements were ‘forged’ out of hydrogen in element building factories called stars. Since the ‘beginning’, whatever that means, no new material has been added. So it comes as somewhat startling that the stuff we are made of, and everything else, is as old as the Universe, some 14 billion years. The basic bits of matter and energy are continually being recycled. Without the past, there cannot be a place called ‘now’, and without now there cannot be a future.
But we have not yet answered the original question. What is the largest component of the human body? Lets look again at the hydrogen atom. Suppose we could expand it to the size of a typical football stadium. A typical hydrogen atom has a nucleus composed of one positively charged proton and one negatively charged electron in ‘orbit’ around it. The two opposite ‘forces’ balance each other and so the atom remains stable. Getting back to our football stadium analogy, if we expand the size of the proton to the size of a marble and place it in the center of the stadium, the electron orbiting it would be way up in the nosebleed section. What about the rest of the space? What is there?
The answer is ‘nothing’. So most of the volume of an atom is nothing. Most of matter of any kind is nothing. To answer our original question: Most of us is nothing. But these bits of matter are so small that in combination and at the macro-level, our level, it all comes together as a tangible substance.
So what if we expand this idea to the cosmic level, the entire Universe. From our point of view as we gaze into the night sky or even peer into the deepest recesses of space using the most powerful technology, it all looks pretty thin. Yes there are billions of galaxies each composed of billions of stars, but taken as a whole and just like the atom, the Universe is mostly nothing. Just a vast vacuum with bits of mass scattered about. But interestingly, these bits of matter do not appear to be scattered about randomly. At the largest scales, galaxies form long ‘strings’ and clusters with a web-like structure. Are these structures part of some other much larger creation that is beyond our ability to ever perceive? What is the large-scale structure of the Universe?
Email Terry Mejdrich at firstname.lastname@example.org.