When it is hot and sunny, the expressway becomes a mirror, which can reflect the reflection?

The principle of this phenomenon is that light has different refractive indexes in air with different densities.

Because of the dark color of asphalt pavement and its strong absorption ability in the hot sunshine in summer, the air near the pavement will be heated rapidly, and the temperature of the lower air will rise very high, while the temperature of the upper air is still very low, thus forming an abnormal distribution of air temperature. Due to thermal expansion and contraction, the density of hot air in the lower layer near the road surface is small, and the density of cold air in the upper layer is large, so that the refractive index of air is small and the air in the upper layer is large. When the light reflected by a higher object in the distance enters the sparse air in the lower layer from the dense air in the upper layer, it continuously refracts, and its incident angle gradually increases until it is equal to the critical angle. At this time, if people look against the reflected light, they will see the reflection of other objects.