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In an article titled "Gravitational Waves Could Solve Hubble Constant Conundrum" Data from the cosmic microwave background suggests the universe is currently expanding at a rate of about 41.6 miles (67 kilometers) per second per 3.26 million light-years, while data from supernovas and Cepheids in the nearby universe suggests a rate of about 45.3 miles (73 km) per second per 3.26 million light-years.

My question is independent on which of these (if either is correct)...

Let's say the universe is expanding at 41.6 mps (67 km) per 3.26MLY Does this mean that every 3.26 M LY the universe is expanding at an additional 41.6 miles per second?

Is my assumption correct or am I misreading this? - Which ok as I am not a student or scientist... just want to make sure I fully understand the article.

*edited: I ran a Excel sheet based on my understanding of this and the total expansion of the universe (if my understanding holds) is less than the speed of light if you use the 41.6 m/s. It came out to 176,092.8 mp/s - which cannot be right and there be parts of the universe expanding faster the C? can it? Wouldn't this be proof the Microwave Background Radiation is the wrong standard to use?

Using 45.3 m/s gives me an answer of 191,754.9 m/s which would allow some (but not much) of the universe to expand faster than C

Thanks

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    $\begingroup$ The distant parts of the universe are expanding away from us at faster than the speed of light. $\endgroup$
    – G. Smith
    Feb 26, 2019 at 17:30
  • $\begingroup$ Please use metric units or at least consistent symbols $\endgroup$
    – Alchimista
    Feb 27, 2019 at 10:26
  • $\begingroup$ See physics.stackexchange.com/q/60519/25301 for some explanation about the expansion faster than $c$. $\endgroup$
    – Kyle Kanos
    Feb 27, 2019 at 11:10

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Let's say the universe is expanding at 41.6 mps (67 km) per 3.26MLY Does this mean that every 3.26 M LY the universe is expanding at an additional 41.6 miles per second?

The linear relationship between distance and speed is a good approximation out to a few hundred million light-years. For example, with that value for the Hubble constant, something 32.6 million light-years away would be moving away from us at 416 miles per second. (Galaxies ten times farther away move away ten times faster.)

At further distances, it’s no longer linear, but the speed at which galaxies are moving away from us continues to increase with distance. Beyond a certain distance, they are moving away from us faster than the speed of light. But this is not because they are moving through space faster than the speed of light. It is because space is expanding so fast between us and them. There is no limit on how fast space can expand.

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  • $\begingroup$ I certainly understand about the space increasing. I guess my next question is why is the Hubble Constant that critical if it is only good for such a short distance away? $\endgroup$
    – Rick
    Feb 26, 2019 at 18:27
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    $\begingroup$ In any cosmological model, the large-distance expansion will be mathematically related to the small-distance expansion. So it’s an observable parameter that can actually determine the expansion everywhere. You just have to use more complicated formulas than linear extrapolation. $\endgroup$
    – G. Smith
    Feb 26, 2019 at 18:32

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