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Chapter 26: Problem 18

Imagine an astronomer living in a galaxy a billion light-years away. Is the observable universe for that astronomer the same as for an astronomer on Earth? Why or why not?

Short Answer

Expert verified
No, the observable universe for an astronomer living a billion light-years away would not be the same as for an astronomer on Earth. This is because the observable universe for any observer is limited to the parts of the universe from which light has had time to reach them. Therefore, since the observer is a billion light-years away, their observable universe would be shifted by a billion light-years compared to ours.

Step by step solution

01

Understanding the concept of a light-year

A light-year is a unit of distance. It is the distance that light can travel in one year. Considering that light travels at a speed of approximately \(299,792\) kilometers per second, in one year, it can cover about \(9.46\) trillion kilometers.
02

Considering the observable universe

The observable universe is the part of the universe that we can technically observe from Earth. The observable universe is not the entire universe, but only the part of it from which light has had time to reach us. As we know, the universe is about \(13.8\) billion years old, so light from objects further away than about \(13.8\) billion light-years has not had time to reach us yet, limiting the extent of our observations.
03

Applying the concept to the astronomer a billion light-years away

If the astronomer is a billion light years away from Earth, then their observable universe would not be identical to ours. This is because the farthest objects they would be able to see would be different from the farthest objects an astronomer on Earth could see. They would also be able to see certain objects that for an Earth astronomer might be beyond the observable universe. Therefore, their observable universe would be shifted by a billion light-years compared to ours.

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Most popular questions from this chapter

What is meant by "the observable universe"?

Do you think there can be "other universes," regions of space and time that are not connected to our universe? Should astronomers be concerned with such possibilities? Why or why not?

How did the abundance of helium in the universe suggest the existence of the cosmic background radiation?

Temperatures in the Early Universe. Access the Active Integrated Media Module "Blackbody Curves" in Chapter 26 of the Universe Web site or eBook. (a) Use the module to determine by trial and error the temperature at which a blackbody spectrum has its peak at a wavelength of \(1 \mu \mathrm{m}\). (b) At the time when the temperature of the cosmic background radiation was equal to the value you found in (a), was the universe matter-dominated or radiation- dominated? Explain your answer.

Before the discovery of the cosmic microwave background, it seemed possible that we might be living in a "steady-state universe" with overall properties that do not change with time. The steady-state model, like the Big Bang model, assumes an expanding universe, but does not assume a "creation event." Instead, matter is assumed to be created continuously everywhere in space to ensure that the average density of the universe remains constant. Search the World Wide Web for information about the steady-state theory. Explain why the existence of the cosmic microwave background was a fatal blow to the steady- state theory.
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