When we look up on a sunny day, we see a blue sky, as shown in the previous image of the balloon. But this is because we have evolved to see visible light. We have done so, no doubt, both because the light from the surface of our Sun peaks in the visible region, and also because many other wavelengths of light get absorbed in our atmosphere, so they cannot reach us on the Earth’s surface. (This is fortunate for us, since much of this radiation could be harmful.) In any case, if we had instead evolved to “see” microwave radiation, the image of the sky we would see, day or night, as long as we
...more
