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?
- MikeLv 74 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".
- davidLv 44 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.
- Adullah MLv 74 weeks ago
It is logic, rational, and full of reason to think it that way.
- HoarsemanLv 44 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 .
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- nebLv 74 weeks ago
No. The CMBR we see today was emitted 13 billion years ago, 380,000 after the Big Bang.
So, go back 13 billion years ago and pick an observation point. Pick another point that will be at the limit of your observational horizon. The observational horizon point emits electromagnetic radiation toward your observation point at the temperature it was at 13 billion years ago. The observational horizon point expands away from you. The emitted radiation is stretched out and takes 13 billion years to get to you because of expanding space. When you receive it it will be at the CMBR temperature. Meanwhile the observational horizon point has expanded away to about 43 billion light years - and also has aged 13 billion years.
That’s how we define the observable universe - we see the radiation that was emitted 13 billion years ago. The region of space that emitted the radiation has expanded away to 43 billion light years and has aged 13 billion years also.