Have you heard of parallel universes? Some scientists believe that there might be other universes right alongside ours. Our universe may be just a part of a tree of universes that are all there at the same time—only in different states of time with different pasts and different futures.

What does this mean? It means there is a different “you” in these parallel universes. You might be a Hollywood star in one of them!

In parallel universes, there may be completely different physical laws (物理法则). World wars might have different results. Really, humans themselves might have become extinct (灭绝的) in certain parallel universes!

The idea of parallel universes dates back to 1954. Hugh Everett Ⅲ, a Princeton University student in the United States, developed the idea that parallel universes—exactly like and related to our universe—are there. However, many physicists and astronomers say that this theory can’t be tested, so it’s not really a theory at all.

But since then, the idea has shown up in comic books, television and movies. Shows like Star Trek and Doctor Who use the idea to develop their stories.

Parallel universes might not only be there in the movies. If their stories are true, some people might have already experienced other realities.

First covered by newspapers in 1952, Cornelio Closa, a schoolboy from the Philippines, kept disappearing right in front of his friends and family. Sometimes disappearing for days, he would somehow disappear from his locked family home and crowded school classroom.

While such stories may sound crazy, even the known universe is far older and larger than we are. So, who’s to say that one day we won’t learn to cross dimensions (维)?

It can be hard to believe that it is just an illusion (错觉) when the moon has a “changing” size, but it is true. You can actually test it yourself and even catch it with a camera.

People mainly notice the moon looking bigger when it is full and near the horizon (地平线). 【小题1】 Imagine you are standing outside close to your house. Your house will look big, and if the moon rises next to it, the moon will look normal. If you look at a house from far away, though, the house looks very small.

【小题2】 However, the things—a house, a mountain or anything else—that are compared with the moon have “changing” sizes. They look bigger or smaller depending on how far away from them you are. 【小题3】

There are several explanations that sounds reasonable but wrong for the moon illusion. 【小题4】 The moon’s orbit is not perfectly round, so the moon does get nearer and farther away over the course of a month.

It’s easy to test the moon, illusion, and you can do it yourself. Next time you see the moon looking bigger than usual, bold out your hand with a straight arm. 【小题5】 Wait a little while until the moon moves higher into the sky and try the experiment again. The moon may look smaller, but your same finger will over it just the same.

We have always been interested in the moon. 2, 000 years ago, people already knew it moves around the earth and where it would be in the sky at different times of the year. At that time, everything about the moon was learned by watching it carefully in the sky.

When scientists could use telescopes to study the moon more closely, their ideas began to change. They could see the moon was made of rocks. Most scientists thought moon rocks would be different from those on the earth. This was because they believed the moon had once been a planet that had been caught in the earth’s gravity (重力) millions of years earlier.

In 1969, moon rocks were finally brought to the earth and studied. Much to their surprise, scientists found that, except for water, the moon and the earth were made of the same things. Once again new ideas were needed for this new information.

After years of study, most scientists now think that the moon was once part of the earth. They believe very early in its history, maybe 4 billion years ago, something about the size of Mars hit the earth. This sent billions of rocks into space around our planet. These rocks slowly joined together and after many years became the moon.

In the future, though our ideas about the moon may change again, we will still be interested in it.