Understanding the Age of the Universe

[Zeno Ether]

TL;DR Summary

Considerations about the currently accepted Cosmology

I'm quoting from Wikipedia the article about GN-z11 (the oldest and most distant known galaxy):
"At first glance, the distance of 32 billion light-years (9.8 billion parsecs) might seem impossibly far away in a Universe that is only 13.8 billion (short scale) years old, where a light-year is the distance light travels in a year, and where nothing can travel faster than the speed of light. However, because of the expansion of the universe, the distance of 2.66 billion light-years between GN-z11 and the Milky Way at the time when the light was emitted increased by a factor of (z+1)=12.1 to a distance of 32.2 billion light-years during the 13.4 billion years it has taken the light to reach us."

This means that space (3D) has expanded at 2.2 times the speed of light (on average), since light has left GN-z11. Correct?

 

[Orodruin]

Summary:: Considerations about the currently accepted Cosmology

This means that space (3D) has expanded at 2.2 times the speed of light (on average), since light has left GN-z11. Correct?

This is really not a good way of describing things. Expansion is a rate, not a speed.

 

[Zeno Ether]

Ok, it's a rate. But is this reasoning correct?

 

[Orodruin]

No. A rate is not a speed so you cannot measure a rate in multiples of c.

 

[Ibix]

Ok, it's a rate. But is this reasoning correct?

Not really. The difference between distances between us and the galaxy through the "then" and "now" spatial slices in FLRW coordinates divided by the proper time along either of our worldlines is about 2.2c, yes. But that isn't anything you could meaningfully describe as a speed.

You've tagged this thread A, meaning you have postgraduate knowledge of this field. I'm guessing this is not correct. Perhaps you could tell us what level of study you've actually completed, and then we can pitch answers at that level.

 

[phinds]

@Zeno Ether it might be instructive for you to consider that the objects that are "now" at the outer edge of our Observable Universe are receding from us at about 3c. This is not proper motion, however, which is why no speeding tickets are issued. Specific objects can be thought of as having a specific recession velocity at a given point in time, but as has been pointed out, expansion is a rate, not a velocity or even a speed.

 

[Zeno Ether]

Hi Ibix, I'm a mechanical engineer and I'm trying to understand the currently accepted theories about the Universe.

 

[Bandersnatch]

What you could say, is that that particular galaxy has receded with that average recession velocity. It doesn't make sense to say that the expansion of space has any velocity, since the recession velocity depends on distance. The rate of expansion is a global property; the recession velocity is a property of a particular object (or an abstracted point in space that is comoving with the expansion).

This is like with a savings account - you can say that your savings grew on average by X dollars per month over some interval of time, or you can say that your account has an interest rate of Y percent per month. It does not make sense to say that the interest rate in your bank is X dollars per month, since the actual value accrued depends on the amount deposited. The interest rate is a global property of all deposits on all accounts; the dollars/month increase is a property of a particular amount deposited.

 

[Zeno Ether]

Ok, thanks, perfectly clear.