Our experience of reality is fairly continuous. We see surfaces everywhere, and underneath those surfaces are solid or fluid volumes. It all seems like pretty connected stuff.
But this all breaks down when things get either much bigger than us or much smaller than us. In a neat bit of symmetry, “bigger” and “smaller” in this case both mean about a factor of a billion.
Once you get to the size of a typical star (like our sun), which is about a billion times bigger than we are, the Universe starts to look like a bunch of little specks with a whole lot of empty space between them. This pattern continues up to the largest “things” we know about, galactic superclusters, which are about 224 times bigger than we are.
If you look in the other direction, pretty much the same thing happens. Everything seems fairly continuous until you get down to the level of small molecules, which are about a billion times smaller than we are.
Any smaller than that, and everything is little specks inside vast empty spaces, first at the level of atoms within molecules, then nucleii within atoms, and all the way on down to neutrinos, the smallest “things” we can measure, which are about 224 times smaller than we are.**
So in a sense we are in the middle of a kind of island. When you look at the entire span of scales in the known Universe, it’s mostly dust to dust, with just a little patch of land right in the middle. That little patch is where we are.
** Strings in string theory can get about 100 billion times smaller than neutrinos, but we have no direct evidence that they exist, let alone any way to measure them.
Hmmm… We sort of see that because we expect to see it.
When I look at my hand, it seems solid because the light bouncing off my keyboard doesn’t make it through my hand. Also when I move my hand toward another macroscoping thing, it doesn’t move through the other thing. So I think my hand is solid.
But consider the neutrinos streaming through my hand; if I had neutrino-detecting eyes instead of photon-detecting eyes, my hands would seem pretty transparent. Or if I attempt to fire an electron through even a sparse plasma, it will rapidly get deflected and absorbed.
What appears solid to us is just what construction is stable under the influence of perturbing forces that we experience. At small scales, there are still stable structures and phenomena, and in fact the atom is not ’empty space’ – most of the atom is ‘full’ of the electron wavefunctions. If you fire another particle through the atom, it may well get through, but that’s because you fired it at higher energy; if you used a slow electron you would have a chemistry lesson rather than a particle collider.
At large length scales, we find that the electrical charges on things like planets is approximately zero, and the other forces are short-range, which leaves just gravity. Since gravity only attracts, it cannot form structures that would repel an incoming object, so the same interaction my hand has with the desk cannot be had between gravitational objects; they can only attract each other. Galaxies collide, however, they do not pass through each other; the interaction is different, but in the same way that my hand seems smooth despite the lumpiness of its mass density, the galaxies only seem lumpy because we ignore the field of force between the planets; if you plotted it and ignored the high peaks, you would see a disc of one galaxy intersecting the disc of the other. And if you used light with a frequency of several light-years, or perhaps gravity waves, you wouldn’t be able to see through the galaxy either.
We do seem to be at an interesting point on the scale spectrum, though; we experience both gravity and electromagnetic effects, and sometimes the latter is stronger than the former. At a much smaller scale, if we could somehow use smaller structures for our intelligence, we could experience a world where the electromagnetic effect dominates, and gravity is but a correction. At the atomic scale, the electromagnetic effect is like gravity; all-pervasive but predictable, and the strong and weak forces are the interaction of the small and complex.
Remember that as a human, you suffer an enormous sampling bias. An alien would likely see us staring at a box emitting a narrow band of EM and vibrations for hour after hour and wonder what was so interesting. For us, the television emits most of the colours we can see and most of the sounds we can hear. I expect us to start expanding those ranges over the next century.
Thanks for the explanation. I now see my post for what it was: A few small points, scattered here and there, but mostly just empty and devoid of substance.
Yet your comment has illuminated my seemingly vacuous post, revealing an energy between these scattered points. When seen in the light of that energy, the words and ideas become more solid.
😉