This happens to be my favorite Twilight Zone episode and I would argue that the entire point of the story is that there are things in the universe that are beyond our understanding and defy simple explanations. The writers make no effort to “explain” what’s going on because doing so would defeat the purpose of the episode and diffuse the terror it creates. Ultimately, this episode is about fear of the unknown distilled to its purest form. It’s cosmic horror without the big scary aliens.
One thing that is very important in understanding this episode is the fact that it was written before the first manned space-flight launched in 1961. By leaving Earth, we were at the cusp of setting foot in a strange new world of experiences. Yes we had studied the stars and had an understanding of physics but we were still trying to touch something which had been out of our reach for the vast majority of mankind’s existence (an existence which is far, far shorter than that of the universe).
The episode tells us that this is an experimental aircraft, probably the first of its kind. While in space, these men disappear for a moment and then manage to come back and crash in the desert. Over time, each man realizes that something is wrong, their return was some kind of mistake, and something is now correcting this mistake. What really happened up there is beyond their understanding. How this mistake is being correct is also too much for simple humans to comprehend. Think of how single-celled organisms might feel when we put them in a petri dish and study them. It probably doesn’t make a whole lot of sense to them either because they aren’t anywhere near the point where they could understand what’s really going on.
If you read up on serious studies of extraterrestrial intelligence, you’ll find a prevailing opinion that your average movie or TV show gets it all wrong by showing aliens who look, think, and act far too much like human beings. They usually have two arms and two legs. They usually use machines made of metal just like we do. They tend to have the physical properties of your average carbon-based life-form rather than something that might have evolved in far different circumstances in another galaxy. So this episode goes in the other direction. These astronauts encounter a phenomenon and they come to believe that there is some kind of intelligence behind what’s happening to them (perhaps rightly, perhaps wrongly). Maybe they slipped through an anomaly of time and space that would completely change our understanding of the universe the properties that comprise it. Maybe they made contact with an intelligence that we can’t see or measure in the traditional sense. Maybe they encountered some of the dark matter or dark energy that scientists still have virtually no understanding of but that makes up the majority of our universe.
I think all those who dismiss this episode as a failure are not giving Serling enough credit. I think he knows the emotions he was trying to evoke and the point he was making even if he never said, “this episode is about the fear of the unknown.” I think you can see that simply in the context of his other scripts, particularly Mirror Image. That episode is similarly terrifying. A woman briefly catches sight of someone who appears to be her exact double. As she waits for a train, other people seem to have seen this other person who looks just like her doing things she has no memory of. They all assume that she’s crazy. This episode gives a bit of “explanation” but only in the form of speculation. The woman vaguely remembers hearing something years ago about different planes of existence; parallel worlds that can intersect with our own, sometimes leading to a person from the other places cross over to our world and forcing them to replace their counterpart to survive. But the episode doesn’t really give us anything beyond these strange ramblings making reference to a phenomenon that doesn’t exist outside of the Twilight Zone. It’s really not much different from the astronauts saying, “I don’t think we were supposed to make it back; something made a mistake and now it has to fix that mistake.”
The point of this episode is that you don’t get an explanation. The cosmos is bigger and probably stranger than we can imagine. Sometimes setting sail in uncharted waters means you get lost.