Question about distant galaxies

[Heuristix]

It is often stated that observation of the most distant stars inform us about the early universe because the light we observe now was emitted from the stars when the universe was young. In fact this is a quote from space.com:

"The universe is about 13.7 billion years old. Light reaching us from the earliest known galaxies has been travelling, therefore, for more than 13 billion years."

I, as a lay person, am puzzled by this because I would have expected those stars to have been much closer to us when the universe was young (than they are now) and only moved away with the expansion of the universe. So in the example above, why did it take light 13 billion years to get to earth? Would not those stars have been much closer to us when the light was emitted?

 

[russ_watters]

The galaxies were closer then than they are now, yes. The quote doesn't say either how close they were then nor how far they are now.

Since the universe is expanding, though the light traveled 13 billion light years, the galaxies would have been closer than 13 billion light years when the light was emitted. And at the same time, they would be much further than that now.

 

[charng]

Thank you for your question. This is a common misconception about the expansion of the universe and the distance of distant galaxies. The key concept to understand is that the expansion of the universe is happening at a constant rate, meaning that the distance between objects is increasing over time. This means that even if a star was relatively close to us when it emitted its light, over the course of billions of years, the expansion of the universe would cause it to move further away from us.

To put it simply, think of the universe as a balloon being inflated. As the balloon expands, all the points on its surface move further away from each other, even though they were initially close together. Similarly, as the universe expands, all the galaxies and stars within it are moving further away from each other, even if they were initially close together.

So in the example above, the light from the distant galaxies took 13 billion years to reach us because during that time, the universe was expanding and the galaxies were moving further away from us. It is not that the light itself took 13 billion years to travel, but rather the distance between the galaxies and us increased due to the expansion of the universe.

This is why studying distant galaxies can give us valuable information about the early universe. The light we observe from these galaxies has been traveling for billions of years, giving us a glimpse into what the universe was like in its early stages. I hope this helps to clarify any confusion.