We can't turn actual objects into computer files, but we can make models on the computer, and we can digitize shapes and images. For example of modeling, we can predict the flow of air around an airplane wing by simulating what would happen if we treat the air like a bunch of very soft, tiny Nerf balls packed in a box with a wing moving through it. The computer keeps track of each squishy ball and how much force it exerts on its neighbors and on the wing. The programming looks like this:For each Nerf ball, consider how close it is to its neighbors:
1. If the nearest Nerf ball below is closer than the Nerf ball above, then it's pushing upward, so move up a little bit. If the ball above is closer, move down a little bit. The closer the balls are to each other, the harder they push, just like squeezing two Nerf balls together.
2. Same thing with the Nerf balls front and back of me.
3. Same thing with the Nerf balls left and right of me.
4. If there's a wing above me, push up on it. If there's a wing below me, push down on it. (If the wing is balanced between equal forces, it won't move.)
5. Repeat steps 1-4 for all the Nerf balls.
6. Then move the wing a little bit forward and repeat the whole thing again. By tracing the motion of the Nerf balls for each step in the wing motion, you can see how the wing shape would affect the air around it. Then you can see how much lift the wing has, or how much turbulence it generates.

Digitizing is much simpler. You just assign numbers to each position in space. A photograph (image) is a kind of digitizing. You can think of a digital photograph as a huge paint-by-number kit: for each pixel or dot on the screen, there's a number assigned to it, and that number represents a color. Put enough dots together, and it looks like a real object or scene.

A computer is a machine that takes bits of information and performs calculations using this information. The information is stored on a magnetic disk in the form of energy states on that disk, but there are certain devices that can read information from other sources, such as light input from a camera, and these devices can feed their information to a computer. The computer then writes an equivalent set of energy states onto its disk, which it can then read again later to get the information back.

Suppose we continue with our camera example: you have a camera that takes a photograph. If this is an old-fashioned film camera, then light is focused by the camera lenses onto a chemical film that reacts to the light and forms a picture of the image created. In a more modern digital camera, the light is instead focused into an image on an array of light sensors in the back of the camera. Each of these sensors detects the color of the light that is focused upon it, and then sends this information, along with the coordinates of the sensor, back to the computer. All of this information is just numbers at this point, usually measured in the intensities of the three primary optical colors (red, green, blue), and in the x and y coordinates of the sensor. The computer then stores these on its disk, or in its memory.

Now, you tell the computer to show you the image on the screen of the photograph you took a month ago. What your simple command actually does is it tells the computer to run a program that sends these information bits to the screen in the appropriate order as they are in the image, as well as the color of each of these pixels, each of which corresponds to one of the original light sensors in the camera. This allows your screen to light up its own pixels in the appropriate order, forming a replica of the original image you took with the camera.

In short, the depiction of something real that you see on a computer screen is like a rainbow: it is an illusion, not something real, but it can represent something that is real and recreate something that appears real.