# Because space is expanding, light takes a longer time to travel distances than if space weren't expanding, right?

In a non expanding universe, light from a galaxy three billion light years away should take three billion years to reach earth. But in an expanding universe, it should take longer, right? So in a non expanding universe, when light from a galaxy three billion light years away reaches earth, since we know the universe isn’t expanding, and that the light should take three billion years to reach us, we can conclude that the galaxy was three billion light years away three billion years ago. However, in an expanding universe, it should take light from a galaxy three billion light years away longer than three billion years to reach us. So when we measure the light from a distant galaxy to be three billion light years using A=L/πr², that light must be older than three billion years old since the distance it traveled became longer than three billion light years with expansion after it left its host galaxy. Thus, why do scientists measure the cosmic microwave background radiation to be around 13 billion light years away at a point in time about 13 billion years ago? In other words, shouldn’t the age of the universe be older than what they say it is? And since the cosmic microwave background is about 13 billion light years away, and the Hubble’s constant is about 70 km/s/megaparsec, ignoring accelerated expansion, this puts the cmbr recession speed at about 280,000 km/s which is just about the speed of light. Didn’t the light take a much longer time than 13 billion years to reach us?

Relevance
• Mike
Lv 7
4 weeks ago

Think of it this way.

If you are walking towards a car that is moving away, even if you are moving faster than the car it still will take longer to get to it than if the car was standing still.

The CMBR is not "around 13 billion light years away".

• david
Lv 4
4 weeks ago

No. Light goes the same distance over time. The light receptor is no longer present. This is my problem with Einsteinian time dilation. Just because you didn't see it doesn't mean it didn't happen.

• 4 weeks ago

It is logic, rational, and full of reason to think it that way.

• 4 weeks ago

Are you getting confused between light years -- a distance -- and time ,in years ?

The "universe" is 13 billion years old ,but the CMBR ,reaching us today ,came from a point that is now over 40 billion light years away from us -- but when it started out , it was more like only 40 million light years away .