In the Voidpunk universe, there’s a fifth fundamental interaction of nature that I named ether for convenience, whereby—in classical description—a fundamental interaction provides a way for objects to exchange energy or transform energy from one state to another.

Now in some posts, I called the ether also the fifth fundamental “force” of nature. And while that is perfectly equally legit, some readers objected to this because it implies that gravity is a force. Another objection was, why is it the “fifth” and not the fourth? What about the unification of electromagnetism and the weak nuclear force into the electroweak interaction? Let’s dive into all this for a bit.

To state it upfront: yes, Virginia, gravity is a force of nature in classical Newtonian description. Then, in terms of general relativity, gravity is a field that reflects the curvature of spacetime. Then again, in terms of quantum gravity, all these descriptions break down and it’s something different altogether that we don’t yet have a handle on. It can be explored mathematically within loop quantum gravity or M-theory, but even there it can’t be made to rhyme with the other interactions/forces so far even theoretically. And collecting experimental data is impossible, as it would mean making measurements at the Planck scale. (To give you an impression, particle energies at the Planck scale are above 10²⁸ electronvolt, while the LHC’s current maximum collision energy is a paltry 10¹³ eV. That’s a difference of fifteen orders of magnitude!)

So, which is it? Well, it’s all three! As Matt Strassler put it in a podcast earlier this year, it’s a matter of linguistic choice. One language says it’s a force of nature; one language says it’s a curvature of spacetime; one language says it’s, perhaps, a condensate from spin 2 particles. According to Strasser, all of these languages are correct—but they’re mutually incompatible and you have to choose one at one time. Yet, they all describe the same underlying phenomenon.

Then, there’s the question of why the electromagnetic and weak nuclear interactions/forces are counted separately instead of being unified into electroweak, just like electric charge and electromagnetic fields have been unified into electromagnetism. The answer to that is that electromagnetism is right here, right now at work in our universe, whereas electromagnetism and the weak nuclear force are only unified at energies of 100 GeV, equivalent to temperatures of 10¹⁵ K—which is a condition that existed only for a short time after the Big Bang.

As a final remark, the etherfield does a lot of heavy lifting in the Voidpunk universe—from the field itself for interplanetary travel and etherpoint locations for star system entry and exit choke points to etherspace and etherstrands for interstellar travel and several types of thaumaturgy. But the four fundamental interactions of nature that we know and love—electromagnetism, strong nuclear force, weak nuclear force, and gravity—do at least as much heavy lifting to keep our universe running along in interesting ways!