<p>Earth didn't get here before GW's. GW's have been around since the early universe. We have just recently developed the technology to detect the large gravitational waves associated with very massive disruptions in the fabric of space-time. </p>

<p>We also know that our sun is not a 1st generation star, so much of the matter used to create our sun and planets came from a much earlier super-nova explosion.</p>

CC BY-SA 3.0
2017-09-27T18:10:26.380Z
2017-09-27T18:19:25.580Z
2017-09-27T18:19:25.580Z
Natsfan
<p>Let's look at <a href="https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves" rel="nofollow noreferrer">GW150914</a>, the first directly detected gravitational wave event. <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102" rel="nofollow noreferrer">The source was a binary black hole, with a calculated luminosity distance of $410^{+160}_{-180}\text{ Mpc}$</a> - roughly 1.3 billion light-years, give or take. This means that the signal was produced about 1.3 billion years ago. The system itself is much older, of course; the progenitor stars formed <a href="http://www.nature.com/nature/journal/v534/n7608/full/nature18322.html?foxtrotcallback=true" rel="nofollow noreferrer">about 10 billion years before the merger</a>.</p>

<p>Earth didn't come onto the scene until roughly 4.5 billion years ago. At that point, the binary black holes had yet to merge together; the system was producing gravitational waves, but nothing as strong as the ones detected by LIGO. The gravitational waves we detected were produced 3 billion years <em>after</em> the Earth was formed - and it took them 1.3 billion more to reach Earth!</p>

<p>The point is, the signal LIGO detected was created after Earth was formed, and created far away. They did not start out at the same time Earth did.</p>

CC BY-SA 3.0
2017-09-27T20:33:41.480Z
+1 for the cool looking formula that makes zero sense to me. But I totally understand what you are saying overall.
iMerchant
CC BY-SA 3.0
2017-09-27T21:08:28.987Z
@iMerchant: It just means that the distance could be between 230 Mpc (410–180) and 570 Mpc (410+160), but that 410 Mpc is the best estimate.
chirlu
CC BY-SA 3.0
2017-09-27T21:47:44.060Z
Non astronomer here. Lol. Mpc = miles per century? Lol. Don’t know mpc. Sorry for my ignorance. Just trying to learn new things like everyone else.
iMerchant
CC BY-SA 3.0
2017-09-27T22:20:35.287Z
@iMerchant: Mpc = megaparsecs. A parsec is roughly equal to 3.26 light-years, so a megaparsec is 3.26 million light-years. 410 Mpc is therefore 1.34 billion light-years.
Jim421616
CC BY-SA 3.0
2017-09-27T22:26:03.037Z
Jim421616 - And 13 parsecs = Kessel Run. Got it.
iMerchant
CC BY-SA 3.0
2017-09-27T19:55:27.060Z
2017-09-27T19:55:27.060Z
HDE 226868
<p>If GWs propagate at near the speed of light, how did Earth (and its constituent elements) arrive at its current location billions of years before the GW arrived here (or light from distant stars for that matter)?</p>

CC BY-SA 3.0
2017-09-27T17:59:21.943Z
The Earth follows the movement of the Sun due to its gravitation. And the Sun moves inside the galaxy according to its initial momentum, when it (the Sun) was created. But I feel, that it's not the answer you're looking for.
George
CC BY-SA 3.0
2017-09-27T18:07:24.987Z
The Earth didn't come from the place that GW are coming from.
A. C. A. C.
CC BY-SA 3.0
2017-09-27T18:17:56.813Z
@A.C.A.C. - Didn’t we all come from the same singularity (Big Bang) though?
iMerchant
CC BY-SA 3.0
2017-09-27T19:09:39.807Z
@iMerchant That would assume that both the Earth and GWs came into existence at the same time during creation of the universe with the Big Bang. The Earth is only 4.5ish billion years old.
zephyr
CC BY-SA 3.0
2017-09-27T19:46:05.820Z
@iMerchant: The far-away objects haven’t moved away from us, though; instead, the intervening space has expanded. Related: https://astronomy.stackexchange.com/questions/14336/are-there-any-galaxies-which-fell-out-of-sight-horizon-due-to-cosmic-expansion
chirlu
<gravitational-waves><speed>
How did Earth get here before gravitational waves?
iMerchant
# How did Earth get here before gravitational waves?

(Asked by: username_0 on 2017-09-27)

If GWs propagate at near the speed of light, how did Earth (and its constituent elements) arrive at its current location billions of years before the GW arrived here (or light from distant stars for that matter)?

**Tags:** gravitational-waves, speed

> **Comments:**
> **username_1**: The Earth follows the movement of the Sun due to its gravitation. And the Sun moves inside the galaxy according to its initial momentum, when it (the Sun) was created. But I feel, that it's not the answer you're looking for.  
> **username_2**: The Earth didn't come from the place that GW are coming from.  
> **username_0**: @A.C.A.C. - Didn’t we all come from the same singularity (Big Bang) though?  
> **username_3**: @username_0 That would assume that both the Earth and GWs came into existence at the same time during creation of the universe with the Big Bang. The Earth is only 4.5ish billion years old.  
> **username_4**: @username_0: The far-away objects haven’t moved away from us, though; instead, the intervening space has expanded. Related: https://astronomy.stackexchange.com/questions/14336/are-there-any-galaxies-which-fell-out-of-sight-horizon-due-to-cosmic-expansion  

---

## 2 answers

### Answer by username_6 on 2017-09-27. Score: 4 | Accepted answer

Let's look at [GW150914](https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves), the first directly detected gravitational wave event. [The source was a binary black hole, with a calculated luminosity distance of $410^{+160}\_{-180}\text{ Mpc}$](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102) - roughly 1.3 billion light-years, give or take. This means that the signal was produced about 1.3 billion years ago. The system itself is much older, of course; the progenitor stars formed [about 10 billion years before the merger](http://www.nature.com/nature/journal/v534/n7608/full/nature18322.html?foxtrotcallback=true).

Earth didn't come onto the scene until roughly 4.5 billion years ago. At that point, the binary black holes had yet to merge together; the system was producing gravitational waves, but nothing as strong as the ones detected by LIGO. The gravitational waves we detected were produced 3 billion years *after* the Earth was formed - and it took them 1.3 billion more to reach Earth!

The point is, the signal LIGO detected was created after Earth was formed, and created far away. They did not start out at the same time Earth did.

> **Comments:**
> **username_0**: +1 for the cool looking formula that makes zero sense to me. But I totally understand what you are saying overall.  
> **username_4**: @username_0: It just means that the distance could be between 230 Mpc (410–180) and 570 Mpc (410+160), but that 410 Mpc is the best estimate.  
> **username_0**: Non astronomer here. Lol. Mpc = miles per century? Lol. Don’t know mpc. Sorry for my ignorance. Just trying to learn new things like everyone else.  
> **username_7**: @username_0: Mpc = megaparsecs. A parsec is roughly equal to 3.26 light-years, so a megaparsec is 3.26 million light-years. 410 Mpc is therefore 1.34 billion light-years.  
> **username_0**: username_7 - And 13 parsecs = Kessel Run. Got it.  

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### Answer by username_5 on 2017-09-27. Score: 3

Earth didn't get here before GW's. GW's have been around since the early universe. We have just recently developed the technology to detect the large gravitational waves associated with very massive disruptions in the fabric of space-time.

We also know that our sun is not a 1st generation star, so much of the matter used to create our sun and planets came from a much earlier super-nova explosion.


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