How long will the sun be able to sustain life on earth?

Is there life on Mars?

How hot can a star get?

What are imaginary numbers?

What would happen if an irresistible force met an immovable body?

What is cosmic dust and where does and where does it come from?

What is meant by curved space?

What is, briefly and simply, Einstein’s theory of relativity?

How dangerous are cosmic rays to men in space?

How did life begin?

Why did the dinosaurs die off?

What is the difference between a brain and a computer?

What is the greenhouse effect?

How will the earth end?

I tend to think of this book as an honorary essay collection, since, as with the series of books which started way back with Fact and Fancy, it contains articles from a column written by Asimov. The column in this case was “Isaac Asimov explains” in Science Digest. Readers would send in science questions, and the magazine would provide 500-word answers to them. At first, Asimov was only one of the authors involved, but he did so well that before long he was the only one and the column was renamed to reflect the fact.

You can’t get into an awful lot of depth in 500 words, of course, but Asimov manages very nicely. There is, for example, his famous explanation of what happens when an irresistible force meets an immovable body, as recited to his fiancé before they were married (and found in Opus 200). He also does a good job explaining things like relativity in relatively few words. The book is indexed, furthermore, which is a help at getting to specific information.

The shortness of the items in the column and the fact that the column died in the mid-1970’s before a second “Please Explain” book could come out have relegated this volume to a relative and undeserved obscurity. It’s really rather pleasant and worth getting one’s hands on.

It would also be nice if some kind soul could make the remaining columns Asimov wrote in this series generally available.