Why Do Mirrors Reverse Left and Right—but Not Up and Down?

课文

1. When you face a mirror, your reflection appears flipped horizontally, not vertically.

   照镜子时，你的影像左右颠倒，而非上下颠倒。

2. This happens because mirrors reflect light straight back—not sideways or upside down.

   这是因为镜子将光线原路反射回去，既不向左/右偏，也不上下翻转。

3. If you raise your right hand, the image raises the hand on its left side.

   你举起右手时，镜中影像举起的是它左侧的手。

4. But that’s only because you mentally rotate yourself to face the same direction as the image.

   但这只是因为你下意识地把自己‘转过来’，以便与影像朝向一致。

5. A mirror actually reverses front and back: it sends light back along the same path it came from.

   镜子实际反转的是前后方向：它让光线沿入射路径原路返回。

6. Try labeling your shirt with 'L' and 'R'—the mirror shows both letters backward, not swapped.

   试试在衣服上标上‘L’和‘R’——镜中两个字母都呈镜像，而非互换位置。

7. You’d get true left-right swap only if you turned around like a page in a book.

   只有像书页那样绕纵轴转身，才会产生真正的左右互换。

8. That mental rotation creates the illusion of sideways reversal, even though no horizontal flip occurs.

   正是这种心理旋转制造了‘左右颠倒’的错觉，而实际上并未发生水平翻转。

9. So the real answer lies in how we interpret depth, not in the mirror’s optical behavior.

   问题的关键在于我们如何理解深度，而非镜子本身的光学特性。

10. Understanding this helps clarify many common misconceptions about reflection and symmetry.

    理解这一点有助于澄清许多关于反射与对称性的常见误解。