Regardless of how substantial a rainbow looks, it’s only an optical illusion. And like other optical illusions, people don’t always see it the same way. With rainbows, however, it’s scientifically impossible for two people to see exactly the same thing.

As National Geographic reports, a rainbow occurs when light waves encounter water droplets at an angle, often when sunlight shines through raindrops. The combination of the light waves’ angled paths and the fact that they’re passing into a new substance causes them to change speed and appear bent—a process called refraction. When they encounter the other side of the droplet, they ricochet off it (reflection) and then exit the droplet, refracting again as they move back from water to air. Since the colors don’t all refract at the same angle, we see them as separate layers.

And because no two people can view that resulting rainbow from exactly the same angle, it’s going to look slightly different for each of us. As HowStuffWorks explains, there’s essentially a line running from the sun to the very center of the rainbow’s full circle (called the antisolar point), which passes straight through your vantage point along the way. If you stood on your toes, crouched down, or moved two feet to your left, that line would change—and so would the rainbow, though it might not be very noticeable.

But if you moved out of the way and had someone stand right where you’d just been, wouldn’t they then see the rainbow just as you’d seen it? Sure, it may look pretty much the same. But since a rainbow isn’t a static image, as meteorologist Joe Rao wrote for Live Science, “its appearance is always changing.” You’d need to be in the exact same place at the exact same time, which only happens in science fiction (as far as we know).