<blockquote>
  <p>How precise are the observational measurements for the speed of gravity?</p>
</blockquote>

<p>Not very. See the Wikipedia article on <a href="https://en.wikipedia.org/wiki/Speed_of_gravity#Possible_experimental_measurements" rel="nofollow noreferrer">the speed of gravity</a> which refers to dissent surrounding the claims made by Sergei Kopeikin and Edward Fomalont. The dissenters include Clifford M Will and Steve Carlip who are fairly well respected. The <a href="https://arxiv.org/abs/1602.04188" rel="nofollow noreferrer">2016 paper</a> about the LIGO detection said the measured speed was less than 1.7c. The <a href="https://arxiv.org/abs/1707.06101" rel="nofollow noreferrer">more recent paper</a> by Neil Cornish and others said it was between 0.55c and 1.4c. This is not at all precise. </p>

<p>Note that in seismology <a href="https://en.wikipedia.org/wiki/Seismic_wave#Primary_waves" rel="nofollow noreferrer">p waves and s waves</a> travel at different speeds. So IMHO it wouldn't be unreasonable to expect different types of waves in space to travel at different speeds. As to whether one should expect light waves and <a href="https://en.wikipedia.org/wiki/Gravitational_wave#Effects_of_passing" rel="nofollow noreferrer">gravitational waves</a> to travel at exactly the same speed is a slightly different matter, complicated by the way a gravitational wave is thought to be a quadrupole wave.  </p>

CC BY-SA 3.0
2017-09-01T15:02:58.883Z
I don't know if referring to p and s waves in seismology is an apt comparison.
zephyr
CC BY-SA 3.0
2017-09-01T19:16:22.210Z
@zephyr It's just an analogy that highlights the idea that there are many different kinds of waves. I like it.
Florin Andrei
CC BY-SA 3.0
2017-09-02T17:44:14.983Z
@zephyr : IMHO when you read [Einstein's old material](http://einsteinpapers.press.princeton.edu/~searchResults?searchMode=quick&searchText=continuum&context=-2&sortField=Sort) there's a definite sense of continuum mechanics. Mind you, this is an interesting discussion [following a lecture](http://einsteinpapers.press.princeton.edu/vol3-trans/370?highlightText=%22faster%20than%20light%22).
John Duffield
CC BY-SA 4.0
2020-08-05T20:49:09.683Z
Quite out of date.
ProfRob
CC BY-SA 3.0
2017-09-01T12:51:54.653Z
2017-09-01T12:51:54.653Z
John Duffield
<p>The accuracy is extremely good thanks to LIGO and a binary neutron star merger.  It's accurate to about 3 parts in 1 quadrillion!</p>
<p>See the paper <a href="https://arxiv.org/abs/1710.05834" rel="nofollow noreferrer">Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A</a></p>
<p>The paper constrains &quot;the difference between the speed of gravity and the speed of light to be between <span class="math-container">$−3×10^{-15}$</span> and <span class="math-container">$+7×10^{−16}$</span> times the speed of light.&quot;</p>
<h3>Older response before the LIGO observation:</h3>
<p>One of the more recent of gravity was first measured in 2003 using Jupiter and a quasar.  The measurements were for the purpose of proving a finite speed and weren't very precise.  <a href="https://www.nrao.edu/pr/2003/gravity/" rel="nofollow noreferrer">See the paper for more</a>.</p>
<p>More recently in 2013 a Chinese group built a model using Earth's tides that helped them narrow it down.</p>
<blockquote>
<p>... [T]he speeds of gravity are from 0.93 to 1.05 times the speed of light with a relative error of about 5%. This provides first set of strong evidences to show that the speed of gravity is the same as the speed of light.</p>
</blockquote>
<p>This is so far the most accurate measurement I've seen.  <a href="https://link.springer.com/content/pdf/10.1007%2Fs11434-012-5603-3.pdf" rel="nofollow noreferrer">See the paper for more.</a></p>
<p>In the near future, <a href="https://arxiv.org/abs/1707.06101" rel="nofollow noreferrer">LIGO may be able to provide more accurate measurements</a> by comparing the distance among detectors and the delay of observation.</p>
<p>Also related, see the question &quot;<a href="https://physics.stackexchange.com/questions/146655/how-is-the-most-accurate-value-of-g-measured/">How is the most accurate value of  G  measured?</a>&quot;</p>

CC BY-SA 4.0
2019-08-13T02:02:35.190Z
fyi I've just asked [Have LIGO/VIRGO gravitational wave measurements narrowed down the speed of gravity?](https://astronomy.stackexchange.com/q/33009/7982)
uhoh
CC BY-SA 4.0
2020-08-07T02:29:27.013Z
fyi I've just asked [How error bars on recent speed of gravity determination from gravitational waves and coincident gamma ray burst? Was Hubble constant in there?](https://astronomy.stackexchange.com/q/38318/7982)
uhoh
CC BY-SA 4.0
2017-09-01T06:14:24.683Z
2020-08-07T01:35:12.833Z
2020-08-07T01:35:12.833Z
Zamicol
<p>General Relativity says that gravity moves at the speed of <em>c</em>.  How precise are the measurements?</p>

<gravity><speed>
How precise are the observational measurements for the speed of gravity?
Zamicol
# How precise are the observational measurements for the speed of gravity?

(Asked by: username_0 on 2017-09-01)

General Relativity says that gravity moves at the speed of *c*. How precise are the measurements?

**Tags:** gravity, speed


---

## 2 answers

### Answer by username_0 on 2017-09-01. Score: 17 | Accepted answer

The accuracy is extremely good thanks to LIGO and a binary neutron star merger. It's accurate to about 3 parts in 1 quadrillion!

See the paper [Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A](https://arxiv.org/abs/1710.05834)

The paper constrains "the difference between the speed of gravity and the speed of light to be between $−3×10^{-15}$ and $+7×10^{−16}$ times the speed of light."

### Older response before the LIGO observation:

One of the more recent of gravity was first measured in 2003 using Jupiter and a quasar. The measurements were for the purpose of proving a finite speed and weren't very precise. [See the paper for more](https://www.nrao.edu/pr/2003/gravity/).

More recently in 2013 a Chinese group built a model using Earth's tides that helped them narrow it down.

> ... [T]he speeds of gravity are from 0.93 to 1.05 times the speed of light with a relative error of about 5%. This provides first set of strong evidences to show that the speed of gravity is the same as the speed of light.

This is so far the most accurate measurement I've seen. [See the paper for more.](https://link.springer.com/content/pdf/10.1007%2Fs11434-012-5603-3.pdf)

In the near future, [LIGO may be able to provide more accurate measurements](https://arxiv.org/abs/1707.06101) by comparing the distance among detectors and the delay of observation.

Also related, see the question "[How is the most accurate value of G measured?](https://physics.stackexchange.com/questions/146655/how-is-the-most-accurate-value-of-g-measured/)"

> **Comments:**
> **username_5**: fyi I've just asked [Have LIGO/VIRGO gravitational wave measurements narrowed down the speed of gravity?](https://astronomy.stackexchange.com/q/33009/7982)  
> **username_5**: fyi I've just asked [How error bars on recent speed of gravity determination from gravitational waves and coincident gamma ray burst? Was Hubble constant in there?](https://astronomy.stackexchange.com/q/38318/7982)  

---

### Answer by username_1 on 2017-09-01. Score: 3

> How precise are the observational measurements for the speed of gravity?

Not very. See the Wikipedia article on [the speed of gravity](https://en.wikipedia.org/wiki/Speed_of_gravity#Possible_experimental_measurements) which refers to dissent surrounding the claims made by Sergei Kopeikin and Edward Fomalont. The dissenters include Clifford M Will and Steve Carlip who are fairly well respected. The [2016 paper](https://arxiv.org/abs/1602.04188) about the LIGO detection said the measured speed was less than 1.7c. The [more recent paper](https://arxiv.org/abs/1707.06101) by Neil Cornish and others said it was between 0.55c and 1.4c. This is not at all precise.

Note that in seismology [p waves and s waves](https://en.wikipedia.org/wiki/Seismic_wave#Primary_waves) travel at different speeds. So IMHO it wouldn't be unreasonable to expect different types of waves in space to travel at different speeds. As to whether one should expect light waves and [gravitational waves](https://en.wikipedia.org/wiki/Gravitational_wave#Effects_of_passing) to travel at exactly the same speed is a slightly different matter, complicated by the way a gravitational wave is thought to be a quadrupole wave.

> **Comments:**
> **username_2**: I don't know if referring to p and s waves in seismology is an apt comparison.  
> **username_3**: @username_2 It's just an analogy that highlights the idea that there are many different kinds of waves. I like it.  
> **username_1**: @username_2 : IMHO when you read [Einstein's old material](http://einsteinpapers.press.princeton.edu/~searchResults?searchMode=quick&searchText=continuum&context=-2&sortField=Sort) there's a definite sense of continuum mechanics. Mind you, this is an interesting discussion [following a lecture](http://einsteinpapers.press.princeton.edu/vol3-trans/370?highlightText=%22faster%20than%20light%22).  
> **username_4**: Quite out of date.  

---

