Lots of photons

If a person is inclined to think about the very small or the very large, huge numbers arise. One billion trillion stars in the observable universe. (10 to the 21st power). As for atoms in the human body? 10 to the 27th power. But exponents in the 20s are just symbols for us -- we have no intuitive sense of them.

One way of making large numbers real has had me going "wow!" lately. Photons. Lots of photons. Consider a fixed cubic millimeter of space, say in your front yard. A millimeter is about one 25th of an inch. A cubic millimeter is the size of a sesame seed, roughly? A sunflower seed is too big. If you stand three feet away and look through it, you see something on the other side, and let's assume that it's three feet away, and it might be something different from what you see through the cubic millimeter right next to it. (Let's say you've got one eye closed to keep it simpler). It also might change rapidly in brightness or color. Think of a strong wind blowing the leaves on a bush. The light reaches your eye from each point on that bush as it changes. But back to a single point, this happens because a steady stream of photons is traveling from that point on the bush through your chosen cubic millimeter of space to your eye. If you move your eye one millimeter to the left, there is a different steady stream of photons going through that central millimeter at a very slightly different angle. This continues as you move around in a circle, one millimeter at a time. It continues as you lower your head a bit or stand on tiptoes. And of course it continues if you could move your eye further up or down to each square millimeter on the surface of a 6-foot sphere. From each of those locations, you receive a different steady stream of photons from the point directly opposite you that travels through the original cubic millimeter in the middle. My quick calculation is that there are 10 million separate square millimeters on your 6-foot sphere, but you probably get a more intuitive understanding of the size if you think of it one millimeter at a time than 10 million (1 to the 7th power).

There's also a steady stream at every different wavelength of light in the point you see. Say there are 20 relevant wavelengths/colors of visible light your eye can distinguish.

Doesn't it seem like it would get awfully crowded in that cubic millimeter, with all those photons whizzing through? But they hardly ever bump into each other. Each travels in a straight line, unaffected by all the others.

I chose a millimeter to keep it at a size we can understand, though in fact light likely travels reliably in a certain direction at angles much more precise than that. If the Hubble Telescope turns its very sensitive eye in a particular direction, it counts on a stream of photons traveling through light years at exactly the right angle to fill in an accurate image, distinguishing tiny angles, while an equally accurate image would be formed pointing the telescope in each direction, or positioning the telescope at a slightly different location and then going through all the directions. That's a lot of photons! Though the Hubble takes a long exposure because it is not such a steady stream at such tiny gradations and it's adding them up.

Different things make different people go, "Wow!" But that's my candidate for the day. I wonder if anyone who's gone further than me in physics (which was one high school course) could tell me if I've got this right or not.