The concept of The Aether, the invisible and omnipresent substance that permeates every corner, nook, and cranny of the universe is almost as old as humanity itself. Blame it on our natural fear of the void, yet on this feeling we’re not alone: hurricanes, tornadoes, maritime vortexes, perfect storms, you name it. Many physical phenomena are living proof of nature’s abhorrence of vacuum and the emptiness it brings. They are nature’s violent response to the ephemeral absence of matter.

So it comes to no surprise that as late as the late 19th century some scientists were still speaking of the aether as a fish will speak (or not) of water. For them (the scientists, not the fish) it was the only possible way to explain the transmission of light and electromagnetic waves through those places of the cosmos where no substantial presence could be detected, neither macro nor microscopically. Space, they claimed, is filled everywhere by a medium, substance, or field through which waves (electromagnetic, gravitational, etc) are propagated.

A famous dispute on the subject is recorded between Leibniz and Huygens in the later half of the 17th century. To the bold suggestion of Huygens of discrete atoms and a vacuum between them as a way to explain gravity, Leibniz invoked the principle of continuity in metaphysical and theological terms. God has chosen perfection and vacuum is imperfect, therefore, he claimed, everywhere is full. Period.

Later, in the turn of the 20th century, Max Planck almost fell into an existential crisis because, despite the overwhelming experimental scientific evidence he had accumulated for it, he could not bring himself to accept that in a subatomic scale matter manifests its presence unevenly in jumps and leaps, and that, necessarily, in between those jumps there is absolutely nothing. But in 1900 he took the irrevocable plunge to acknowledge what he called the “quantum discontinuity” of energy and proclaim to the world that electromagnetic energy can only exist in steps (quanta) and that no matter or phenomena can possibly exist nor occur in the space or time between them. It took 18 years for the Nobel Prize academy to finally accept how right Planck was to once and for all embrace the idea we float in a world where 99.9999% is void.

Almost at the same time as Planck’s discovery, the Michelson-Morley experiment compared the speed of light in perpendicular directions in an attempt to detect the relative motion of matter through the assumed drag of the “aether wind”. Their conclusions were definitive: there is no such thing as aether and we’d better get used to float like virtual fishes in a vacuum tank where we drift along other minor, tastier-looking impurities. Not that he really needed it, but the experiment’s confirmation provided Einstein’s confidence with plenty of ammunition to proceed with the development of his special relativity theory, for which stationary aether was simply a non entity.

But why could a theory that we now think of as far-fetched and unfounded (praise be to the great advantages of hindsight), could have had such a tremendous hold on the highest minds of our past? I for one would like to think of that famous parable once posed by David Foster Wallace to a college graduating class, about the two young fish swimming happily in the sea when greeted by an older fish swimming the other way: “morning boys, how’s the water today?”, he asks. To which address the young fishes look at each other in wonder: “and what the hell is water?”

In other words, consider yourself lucky if you’re ever approached by an old chap wanting to know how’s the void today because you could have been approached by an even older chap wanted to know how’s the aether today.

To wrap up I would like to mention a recent conversation I had with my dear wife while drinking a huge 50cl bucket of Hoegaarden white beer in a guinguette by the river Seine. It was perhaps the vision of so much of the amber nectar under the summer sun that brought us to the topic of, oh surprise, the aether. And for some strange reason, the more I drank of the beer the more passionate I became to explain to her what had led scientists of the 19th century to imagine such a thing. Searching for arguments to explain the concept, I resorted to the timeless ontological question we all learn first in high school.

“Think about how can you be sure I am really here speaking to you and I’m not simply a product of your own mind” I suggested.
“…” She was nonplussed.
“If we were both floating in aether, you would have no need to reach across to make sure I’m here because you could rightly assume that, like yourself, I am one with the aether. All substance, all matter. Right?”
“…” She was more nonplussed than before.
“Whereas in the void, you wouldn’t even know if I am perhaps a projection of some virtual reality.” I insisted.
“I get it now. Aether is a substance, but vacuum is not. In a world of aether, we can only exist as matter, but in the void, we can exist as virtual too.”
“There you go.”
“Then how can you tell your bucket of beer is not virtual?”
“I guess if we are talking about aether, it must be very real.”
“And how’s the beer today?”
“What beer?”

I then realized with horror that, just like the void, my beer was no more.