If you've ever happened to look out of your plane's window during a flight to see another plane alongside it, it's almost always a slightly amazing sight.
Seeing another metal tube full of humans whizzing along at crazy speed is a really inspiring reminder of how incredible our technology is - but sometimes, it can be just a bit confusing.
A Reddit post from a few months ago shows quite perfectly that seeing another plane out of your window can instead be an absolute mind-blower, if the perspective is just right.
The post shows a plane that appears for all the world to be completely static in the air, floating above a long bridge and seemingly not moving at all.
With over 38,000 upvotes sending the post viral, thousands of people were clearly amazed by it, and it's not hard to see why - it looks like something has gone wrong with the fundamental laws of physics here.
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In reality, though, the explanation is actually very logical - and as the post's title says, it's all about the parallax effect.
This refers to the difference in how an object appears to be moving compared to how it actually is, based on seeing it from different points of view.
What's happening in this case is that the plane the poster is filming from is moving at just the right speed compared to the one outside, and its perspective remains almost exactly the same, despite both being in motion.
The reason you don't see clips like this all the time is because it requires quite a significant coincidence of flight paths, speeds and timing for it all to come together as perfectly as this video.
One very level-headed comment in the thread under the post explained this a different way: "The change in observer's angle coupled with different speeds of both planes is deceiving depth perception. This is the same reason when trees further away don’t move as far as those closer to the train when looking out the window."
Of course, this being social media, most people commenting on the post aren't entirely serious - the top comment in the thread said: "The pilot had to pause his game."
Another joked: "Air Canada is delayed again. Smh."
This has also drawn comparisons to the famous scene in The Matrix when Neo sees the same cat twice - a glitch in the simulation that has no rational explanation, which you could be tempted to conclude about this floating plane if you didn't know any better.