Chapter 26: Problem 17

(a) Explain why the radius of the observable universe is continually increasing. (b) Although the universe is \(13.7\) billion years old, the observable universe includes objects that are more than \(13.7\) billion light- years away from Earth. Explain why.

Short Answer

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The radius of the observable universe is continuously increasing because the universe is expanding, so as it grows, more of it comes into our observable range. Although the universe is 13.7 billion years old, we can observe objects more than 13.7 light-years away because those objects have moved farther away due to the universe's expansion, but their ancient light is just now reaching us.

Step by step solution

Explain why the radius of the observable universe is continually increasing

The universe is expanding. This was first observed by Edwin Hubble in the 20th century when he noticed that distant galaxies were moving away from us in every direction. This phenomenon, known as Hubble's Law, indicates that the universe is not static but growing. As the universe continues to expand, more of it comes into our observable range, thereby constantly increasing the radius of the observable universe.

Discuss why the observable universe includes objects more than 13.7 billion light-years away even though the universe is only 13.7 billion years old

To understand this seeming paradox, it's essential to realize that the universe has been expanding during the 13.7 billion years since the Big Bang. When looking at objects that are 13.7 billion light-years away, we're seeing them as they were 13.7 billion years ago. However, because the universe has been expanding for all of that time, those objects are much farther away now. Therefore, we can still see the light they emitted in the early universe, but they are now located much more than 13.7 billion light-years away due to the constant expansion of the universe.

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(a) Explain why the radius of the observable universe is continually increasing. (b) Although the universe is \(13.7\) billion years old, the observable universe includes objects that are more than \(13.7\) billion light- years away from Earth. Explain why.

Short Answer

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Explain why the radius of the observable universe is continually increasing

Discuss why the observable universe includes objects more than 13.7 billion light-years away even though the universe is only 13.7 billion years old

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