Horror movie ‘Blob’ impossible in geometric world

“The Blob” was a 1958 horror movie starring Steve McQueen and a theme song written by Burt Bacharach before either of them was famous.

It was the story of a monstrously sized amoeba that terrorized a town in Pennsylvania. You probably aren’t surprised to know that not only was it not true, but it alsowas impossible.

But you might not know why it was impossible.

The Blob grew to the size of a human, let’s say 6 feet tall (it really wouldn’t matter if it was only 4 feet tall: still impossible).  To explain why this is impossible, let us examine a hypothetical box.

Imagine a box that is exactly a 10-inch cube.  The surface area of one face of that cube would be the length times the height (10 times 10), or 100 square inches. But because a cube has six sides, the surface area of the entire cube is 600 square inches.

This is more interesting than it sounds if you simply apply this concept to your favorite beverage on a hot summer day after mowing the lawn.

The speed with which you can get anything out of a bottle depends on the surface area of the opening.

Obviously, one can drain a wide-mouth quart canning jar faster than a quart container with a narrow, wine-bottle type of opening. Of course the reverse is true.

One can fill a wide-mouth bottle more quickly than they can fill a narrow-mouth bottle.

Blobs (at least according to the movie) apparently ingest their prey in the same manner as an amoeba, a process called phagocytosis, meaning they literally engulf their prey whole through the membrane by just wrapping their cell membrane around it.

But what that means is the surface area of a Blob determines how fast it can ingest prey.

So you see, surface area is not as boring as it seems. It is tremendously important if you are Bacharach or McQueen being pursued by the Blob.

But a Blob, or a box, also has a volume. Our 10-inch box would have a volume of 1,000 cubic inches (10x10x10). It stands to reason that our 6-foot tall movie Blob couldn’t ingest anything with a bigger volume than itself, but it could ingest something only slightly smaller than itself (say Aneta Corsaut, who later also had a role in “The Andy Griffith show”).

But what happens when the Blob grows larger?

Imagine a second box exactly twice as large as the first, or 20 inches on a side.

This box would have a surface area of six sides, each with areas of 20x20 (or 400) square inches, for a total surface area of 2,400 square inches.

So even though this box is only twice as long on a side, the surface area is four times greater than our 600-square-inch box.

But the volume of the enlarged box would be 20x20x20, or 8,000 cubic inches, eight times the volume of the original box.

Thus we can see, as size increases, volume increases faster than surface area.

At some size, the volume of the Blob needing nutrients will outgrow the ability of the surface area’s ability to transport those nutrients. That limiting factor, entirely because of the geometry we have just seen, is surprisingly small.

The vast majority of living cells, and amoeba, are less than 100 micrometers in size (a micrometer is a thousandth of a millimeter).

So you can see, it would probably be impossible for a man-eating Blob to exist.

As it increased in size, its volume would increase so much it could no longer take in nutrients through the surface area fast enough to survive.

The Blob, I fear, is just an imaginary monster created to launch the career of a major movie star and composer.


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