[Roger Slater]

what makes you think that there is some kind of "ghost image" where two perpendicular mirrors meet?

This. Look at the first picture.

[Alexander Givental]

Originally Posted by Roger Slater

This. Look at the first picture.

It is an unfortunate viewing angle: move the camera, and you'll see that the middle image is not at the intersection line at all.

[Carl Copeland]

Originally Posted by Alexander Givental

when I ask 3rd graders, I draw a girl with a flower and ask how many flowers she sees.

I feel like that third-grader. You ask her how many flowers the girl sees. The third-grader answers, “One” (as some of us did), and you say, “No, eight!”

[Alexander Givental]

Originally Posted by Carl Copeland

I feel like that third-grader. You ask her how many flowers the girl sees. The third-grader answers, “One” (as some of us did), and you say, “No, eight!”

That's not how it works. Third-graders give different answers: 1,4, infinity. Then we consider the case of 2 mirrors and draw pictures. Kids argue and eventually convince each other that it is 4: by someone explicitly drawing the 4 trajectories of the light ray from the flower to the eye (and finding a universal way of drawing them all). Then it becomes clear to everyone in class that in the 3-space the answer is 8 (though it is hard to draw pictures), and in the 4-space 16, and so on.

[Matt Q]

[misunderstanding]