<p>Luminosity distance is simply the distance that the object would have to be at in a static special-relativistic (or Newtonian) universe to have that luminosity. It's not the distance in the expanding general-relativistic universe that we actually inhabit.</p>
<p>Out to distances of roughly 1 billion light years, spacetime is roughly flat, the Hubble speed is not too large, and the luminosity distance is not too inaccurate. At substantially larger distances, it's way off.</p>

CC BY-SA 4.0
2020-09-03T21:16:53.837Z
To "expand" on this... Since the universe is expanding, the light it kind of going "uphill".  Thus it hasn't traveled as far as you would expect it to have.
IronEagle
CC BY-SA 4.0
2020-09-03T17:29:36.747Z
2020-09-03T17:29:36.747Z
benrg
<p>According to this article about the gravitational wave observation, GW190521, the estimated luminosity distance is appx 5+/-2 Gigaparsecs, which is appx 16 billion light years +/- 6:</p>
<p><a href="https://dcc.ligo.org/public/0165/P2000020/012/LS17910.pdf" rel="nofollow noreferrer">https://dcc.ligo.org/public/0165/P2000020/012/LS17910.pdf</a></p>
<p>While I understand that this is a crude measurement, is it not true that the distance cannot be greater than the appx 13.7 billion light years of the universe?  If so, should not there be another constraint on the distance? Or is it just more accurate to report the calculated luminosity distance and leave it at that in the report?</p>

<gravitational-waves>
GW190521's Luminosity Distance is greater than the age of the universe - how?
Daniel Williams
# GW190521's Luminosity Distance is greater than the age of the universe - how?

(Asked by: username_0 on 2020-09-03)

According to this article about the gravitational wave observation, GW190521, the estimated luminosity distance is appx 5+/-2 Gigaparsecs, which is appx 16 billion light years +/- 6:

<https://dcc.ligo.org/public/0165/P2000020/012/LS17910.pdf>

While I understand that this is a crude measurement, is it not true that the distance cannot be greater than the appx 13.7 billion light years of the universe? If so, should not there be another constraint on the distance? Or is it just more accurate to report the calculated luminosity distance and leave it at that in the report?

**Tags:** gravitational-waves

---

## 1 answers

### Answer by username_1 on 2020-09-03. Score: 3 | Accepted answer

Luminosity distance is simply the distance that the object would have to be at in a static special-relativistic (or Newtonian) universe to have that luminosity. It's not the distance in the expanding general-relativistic universe that we actually inhabit.

Out to distances of roughly 1 billion light years, spacetime is roughly flat, the Hubble speed is not too large, and the luminosity distance is not too inaccurate. At substantially larger distances, it's way off.

> **Comments:**
> **username_2**: To "expand" on this... Since the universe is expanding, the light it kind of going "uphill".  Thus it hasn't traveled as far as you would expect it to have.  

---

