**â€œExpansion of the Universeâ€**

By **Najma and Najla**

Asalamu alaikum today we are going to talk about The Expanding Universe. So for thousands of years, astronomers wrestled with basic questions about the size and age of the universe .You might be thinking that if the universe goes on forever or not or probably your thinking that does it have an edge somewhere or even more questions like has it always existed or did it come to being sometime in the past? In the 1900â€™s, Edwin Hubble, an astronomer made a serious discovery. He discovered that the universe was expanding.

The old Greeks recognized that it was difficult to imagine what an infinite universe might look like. But they also wondered that if the universe was finite, and you stuck out your hand at the edge, where would your hand go? The Greeksâ€™ two problems with the universe represented a paradox â€“ the universe had to be either finite or infinite, and both alternatives presented problems.

After the rise modern astronomy, another paradox began to puzzle astronomers. In the early 1800â€™s German astronomer Heinrich olbers argued that the universe must be finite. He said if the universe was infinite and contained stars throughout, Olbers said, then if you looked in any particular direction, your line-of- sight would eventually fall on the surface of a star. Although the apparent size of a star in the sky becomes smaller as distance to the star increases, the brightness of this smaller surface remains a constant. Therefore, there are dark areas in the sky, so the universe must be finite.

But, when Isaac Newton discovered the law of gravity, he realized that gravity is always attractive. Every object in the universe attracts every other object. If the universe truly was finite, the attractive forces of all the objects in the universe should have caused the entire universe to collapse on itself. This clearly had not happened, and so astronomers were presented with a paradox.

When Einstein developed his theory of gravity in the general theory of relativity, he thought he ran into the same problem that Dr.Newton did: his equations said that the universe should be either expanding or collapsing, yet he assumed that the universe was static. His original solution contained a constant term, called the cosmological constant, which cancelled the effects of gravity on very large scales, and led to a static universe. After Hubble discovered that the universe was expanding, Einstein called the cosmological constant his â€œgreatest blunder.â€

So basically I told you half of the story but didnâ€™t tell you if the universe was finite or in finite letâ€™s find out moreâ€¦ The expanding universe is finite in both time and space.