<p>The impact of this measurement on the status of quantum gravitation is exactly zero.</p>

<p>The proper statement of the incompatibility of general relativity and quantum mechanics is that <em>the quantum field theory of general relativity is not renormalizable</em>. Renormalizability essentially means that the theory is well-defined at all energy scales, which seems like a reasonable demand on a proposed fundamental theory.</p>

<p>So what we know is that taking classical general relativity and quantizing it, we do not get a fundamental theory of quantum gravitation. This does nothing to rule out other proposed quantum theories of gravitation, for example, LQG or string theory.</p>

<p>Furthermore, the way physics works is that new theories must reduce to old ones in the domains of applicability of the old theories. Whatever the correct quantum theory of gravitation, its low-energy limit should be quantized general relativity, and the classical limit of that is classical general relativity. It's just not true that you have to choose between general relativity or quantum mechanics. </p>

<p>So this measurement of a prediction of classical general relativity does absolutely nothing to show that no quantum mechanical model of gravitation exists. It couldn't, because we already have a quantum mechanical model of gravitation: quantized general relativity. It's not as "nice" as we would like, but that really only rules it out as the <em>fundamental</em> theory.</p>

CC BY-SA 3.0
2016-02-13T21:07:54.200Z
This site attracts quite high quality answers. I upvoted the whole lot (and I do not do that .. just about ever..)
WestCoastProjects
CC BY-SA 3.0
2016-02-14T12:53:11.917Z
Indeed.. Very smart answers @javadba
Odin
CC BY-SA 3.0
2016-02-12T16:25:26.033Z
2016-02-12T16:32:29.153Z
2016-02-12T16:32:29.153Z
Robin Ekman
<blockquote>
  <p>Another question, how can we identify the ripple's origin (let's say that if it's the result from the big bang or another big event)?</p>
</blockquote>

<p>(I'm just answering this part of the question, as James has already answered the main part about GR vs QM.)</p>

<p>LIGO have produced <a href="https://www.ligo.caltech.edu/image/ligo20160211b" rel="noreferrer">an image</a> which shows their best estimate of where these two black holes were:
<a href="https://i.sstatic.net/PA21I.jpg" rel="noreferrer"><img src="https://i.sstatic.net/PA21I.jpg" alt="&quot;Where the Gravitational Waves Came From&quot; by LIGO"></a></p>

<p>All they can say is, somewhere in the southern sky. In the future a network of more detectors will allow such events to be pinpointed much more precisely.</p>

CC BY-SA 3.0
2016-02-12T13:37:24.950Z
That's truly amazing.. Thanks for sharing this
Odin
CC BY-SA 3.0
2016-02-13T23:34:48.473Z
Just one more detector coming online will make a huge difference.   The two LIGO detectors were only able to localize this event to a 600 square degree region.  During the press conference once of the scientists stated that after the Virgo detector comes online later this year they should be able to narrow it to a single digit number of square degrees.  That's a small enough area of space for fast response optical scopes to survey for the afterglow expected from the merger of [neutron stars (last paragraph of conclusion)](http://arxiv.org/pdf/1602.03868.pdf).
Dan Is Fiddling By Firelight
CC BY-SA 3.0
2016-02-16T06:17:03.823Z
If you want a little more new details about that part of the question, check the edit on 16-2-2016 @Andy :)
Odin
CC BY-SA 3.0
2016-02-18T13:03:04.667Z
The ability to locate sources should get another huge improvement in a couple of years now that LIGO India has [been approved by the Indian government](http://economictimes.indiatimes.com/news/economy/policy/government-gives-in-principle-approval-for-ligo-india-project/articleshow/51026129.cms).
Chris Mueller
CC BY-SA 3.0
2016-02-12T12:08:14.070Z
2016-02-12T14:26:23.530Z
2016-02-12T14:26:23.530Z
Andy
<p>At the announcement press conference (2/11/2016), Kip Thorne said that the detection puts an upper limit on the rest mass of the graviton. They determined this limit by looking at distortions of the detected signal waveform compared to the idealized signal produced by computer simulations. The upper limit from the publication is $m_{graviton} &lt; 1.2  × 10^{−22} \frac{eV}{c^2}$ or $1.9 × 10^{−41} kg$.</p>

<p>Refs:
<a href="https://www.youtube.com/watch?v=vy5vDtviIz0&amp;feature=youtu.be&amp;t=1h5m23s" rel="nofollow">https://www.youtube.com/watch?v=vy5vDtviIz0&amp;feature=youtu.be&amp;t=1h5m23s</a>
<a href="https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102" rel="nofollow">https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102</a> (page 8)</p>

CC BY-SA 3.0
2016-02-14T11:46:31.153Z
A little too short maybe. Reference?
SE - stop firing the good guys
CC BY-SA 3.0
2016-02-14T11:33:34.143Z
2016-03-04T22:29:34.340Z
2016-03-04T22:29:34.340Z
randomquestionasker77
<p>Though the twin discovery of Gravitational Waves and Black Hole merger might not affect directly the status of QM it might indirectly bring new "surprises" For example, in this link:
<a href="http://news.discovery.com/space/weve-detected-gravitational-waves-so-what-160213.htm" rel="nofollow">http://news.discovery.com/space/weve-detected-gravitational-waves-so-what-160213.htm</a>
They comment that:
"For some reason, the final spin of the black hole is slower than expected, indicating that the two black holes collided at a low speed, or they were in a collision configuration that caused their combined angular momentum to counteract each other. “That is very curious; why would nature do that?” said Lehner."
And the final comment is:
"This early puzzle could be down to some basic physics that hasn’t been considered, but more excitingly it could reveal some “new” or exotic physics that is interfering with the predictions of general relativity".
Wow! "Interfering with general relativity" is a polite way of suggesting that it might be wrong. So maybe QM might come to the rescue of Gen.Relativity rather than the other way around.</p>

CC BY-SA 3.0
2016-02-17T18:37:03.437Z
2016-02-17T18:37:03.437Z
Francisco Muller
<p>No more than the observation of light waves disproves quantum mechanics.</p>

<p>Light has properties of both a particle and a wave. At low energies, the particle nature of light is hard to detect: radio waves are made of photons, but individual radio wave photons are pretty hard to detect. I'm not sure that we have directly detected individual photons with energies below the infrared band. </p>

<p>Gravitational waves (probably) also have both a wave and a particle nature. The gravitational field is probably quantised. But at the frequencies and sensitivity at which LIGO operates, individual quanta cannot be measured. So this detection does not prove the ascendency of GR over QM.</p>

<p>If anything, understanding extreme events like black hole mergers might lead to a theoretical understanding of the quantum nature of gravity.</p>

CC BY-SA 3.0
2016-02-12T11:46:48.353Z
Thank you for your answer it really helped me understand the idea.. I'll mark it as the answer in a couple of hours to give a little more time for other answers as well
Odin
CC BY-SA 3.0
2016-02-12T15:38:23.620Z
@Odin: waiting a couple (or rather something like 5, or 7) days seems better than just a couple hours, as experts are not always behind their screen...
Olivier Dulac
CC BY-SA 3.0
2016-02-12T16:44:17.250Z
There are probably no reasonable experiments that can detect an individual graviton. Here reasonable means things like "is not large enough to collapse to a black hole", and "detects at least one graviton per age of the universe". http://arxiv.org/abs/gr-qc/0601043 And this event really isn't close to where you would expect quantum gravitation. For black holes of 30 solar masses, the Schwarzschild radius is something like $10^5$ m, but the Planck length is something like $10^{-35}$ m.
Robin Ekman
CC BY-SA 3.0
2016-02-12T16:49:18.000Z
Of course compared to something like the solar system, this is extreme: a distance of $1$ AU from the sun (i.e., here on earth), the curvature radius is on the order of $10^{12}$ m, at the surface of the sun some $5\cdot 10^8$ m. But gravitation is *seriously* weak so you are still many many orders of magnitude from quantum gravitation. (Note that large curvature *radius* = small curvature. A large sphere is less curved than a small one.)
Robin Ekman
CC BY-SA 3.0
2016-02-13T22:23:16.350Z
By the way, if anyone knows the energies of the lowest energy photons that have been directly or indirectly observed, I'd be interested.
James K
CC BY-SA 3.0
2016-02-14T07:59:45.687Z
"Probably": certainly. The uncertainty principle is contagious and once introduced must apply to everything. You will find that the object's momentum in response to a gravitational force will be an all-or-nothing lump of some minimal size. How that comes about might be more or less convoluted, but the principle must hold. After all, the time and energy (in general) are already showing quantum effects due to the existance of a smallest scale and the conjugate pairing of thise two.
JDługosz
CC BY-SA 3.0
2016-02-14T13:38:56.880Z
How does the observation of light *disprove* quantum mechanics? The existence of "particles" doesn't disprove QM any more than that GR could.
rubenvb
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2016-02-14T14:28:07.337Z
@rubenvb You have misread my answer. The observation of gravitational waves doesn't "disprove" QM. Nor does the observation of light waves.
James K
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2016-02-14T14:46:36.540Z
Right. I see it now. Never mind me then :)
rubenvb
CC BY-SA 3.0
2016-02-12T08:33:30.207Z
2016-02-12T20:33:28.477Z
2016-02-12T20:33:28.477Z
James K
<p>Of course everyone knows by now of the <a href="http://www.iflscience.com/space/gravitational-waves-observed-first-time">detection of Gravitational waves</a></p>

<p>But, since General Relativity and Quantum Mechanics <a href="http://io9.gizmodo.com/why-cant-einstein-and-quantum-mechanics-get-along-799561829">don't get along</a>, can we say now that this detection proves that Quantum Mechanics doesn't actually apply and that General Relativity did prevail?</p>

<p>Another question: how can we identify the ripple's origin (let's say whether it's a result of the big bang or another big event)?</p>

<p><strong>EDIT 16-2-2016</strong></p>

<p>I was reading an <a href="http://www.iflscience.com/space/seeking-source-those-gravitational-waves">article</a> today and I thought I'd share it here; It's basically saying that without a third detector we can't triangulate the signal. 
Some scientists tried ways to observe the light of the event directly after the observations of the wave but they couldn't detect the merger simply because it's too far away or too faint to be observed with our current technology.</p>

CC BY-SA 3.0
2016-02-12T08:34:51.527Z
It was a black hole merger, not from the big bang. Primordial gravitational waves have an even longer wavelength, probably too long for LIGO,
James K
CC BY-SA 3.0
2016-02-16T02:12:31.920Z
Quantum physics and Relativity are NOT competing theories. They are complimentary theories , with relativity about what happens at massive scales, and quantum talking about really tiny scales. The controversy is nobody really knows how to unify these two fiels. What physicists want is a theory that in one comlete swoop describes how everything works. Maybe an elegant equasion or a set of simple rules. We're not even sure such a thing actually exists, but it'd sure be nice if it did, because that theory would be the pinacle of human scientific achievement. Problem is, nobody really knows how.
Shayne
<general-relativity><astrophysics><gravitational-waves><quantum-field-theory>
Quantum Mechanics after the detection of Gravitational Waves
Odin
# Quantum Mechanics after the detection of Gravitational Waves

(Asked by: username_0 on 2016-02-12)

Of course everyone knows by now of the [detection of Gravitational waves](http://www.iflscience.com/space/gravitational-waves-observed-first-time)

But, since General Relativity and Quantum Mechanics [don't get along](http://io9.gizmodo.com/why-cant-einstein-and-quantum-mechanics-get-along-799561829), can we say now that this detection proves that Quantum Mechanics doesn't actually apply and that General Relativity did prevail?

Another question: how can we identify the ripple's origin (let's say whether it's a result of the big bang or another big event)?

**EDIT 16-2-2016**

I was reading an [article](http://www.iflscience.com/space/seeking-source-those-gravitational-waves) today and I thought I'd share it here; It's basically saying that without a third detector we can't triangulate the signal.
Some scientists tried ways to observe the light of the event directly after the observations of the wave but they couldn't detect the merger simply because it's too far away or too faint to be observed with our current technology.

**Tags:** general-relativity, astrophysics, gravitational-waves, quantum-field-theory

> **Comments:**
> **username_1**: It was a black hole merger, not from the big bang. Primordial gravitational waves have an even longer wavelength, probably too long for LIGO,  
> **username_2**: Quantum physics and Relativity are NOT competing theories. They are complimentary theories , with relativity about what happens at massive scales, and quantum talking about really tiny scales. The controversy is nobody really knows how to unify these two fiels. What physicists want is a theory that in one comlete swoop describes how everything works. Maybe an elegant equasion or a set of simple rules. We're not even sure such a thing actually exists, but it'd sure be nice if it did, because that theory would be the pinacle of human scientific achievement. Problem is, nobody really knows how.  

---

## 5 answers

### Answer by username_1 on 2016-02-12. Score: 29 | Accepted answer

No more than the observation of light waves disproves quantum mechanics.

Light has properties of both a particle and a wave. At low energies, the particle nature of light is hard to detect: radio waves are made of photons, but individual radio wave photons are pretty hard to detect. I'm not sure that we have directly detected individual photons with energies below the infrared band.

Gravitational waves (probably) also have both a wave and a particle nature. The gravitational field is probably quantised. But at the frequencies and sensitivity at which LIGO operates, individual quanta cannot be measured. So this detection does not prove the ascendency of GR over QM.

If anything, understanding extreme events like black hole mergers might lead to a theoretical understanding of the quantum nature of gravity.

> **Comments:**
> **username_0**: Thank you for your answer it really helped me understand the idea.. I'll mark it as the answer in a couple of hours to give a little more time for other answers as well  
> **username_11**: @username_0: waiting a couple (or rather something like 5, or 7) days seems better than just a couple hours, as experts are not always behind their screen...  
> **username_3**: There are probably no reasonable experiments that can detect an individual graviton. Here reasonable means things like "is not large enough to collapse to a black hole", and "detects at least one graviton per age of the universe". http://arxiv.org/abs/gr-qc/0601043 And this event really isn't close to where you would expect quantum gravitation. For black holes of 30 solar masses, the Schwarzschild radius is something like $10^5$ m, but the Planck length is something like $10^{-35}$ m.  
> **username_3**: Of course compared to something like the solar system, this is extreme: a distance of $1$ AU from the sun (i.e., here on earth), the curvature radius is on the order of $10^{12}$ m, at the surface of the sun some $5\cdot 10^8$ m. But gravitation is *seriously* weak so you are still many many orders of magnitude from quantum gravitation. (Note that large curvature *radius* = small curvature. A large sphere is less curved than a small one.)  
> **username_1**: By the way, if anyone knows the energies of the lowest energy photons that have been directly or indirectly observed, I'd be interested.  
> **username_12**: "Probably": certainly. The uncertainty principle is contagious and once introduced must apply to everything. You will find that the object's momentum in response to a gravitational force will be an all-or-nothing lump of some minimal size. How that comes about might be more or less convoluted, but the principle must hold. After all, the time and energy (in general) are already showing quantum effects due to the existance of a smallest scale and the conjugate pairing of thise two.  
> **username_13**: How does the observation of light *disprove* quantum mechanics? The existence of "particles" doesn't disprove QM any more than that GR could.  
> **username_1**: @username_13 You have misread my answer. The observation of gravitational waves doesn't "disprove" QM. Nor does the observation of light waves.  
> **username_13**: Right. I see it now. Never mind me then :)  

---

### Answer by username_3 on 2016-02-12. Score: 21

The impact of this measurement on the status of quantum gravitation is exactly zero.

The proper statement of the incompatibility of general relativity and quantum mechanics is that *the quantum field theory of general relativity is not renormalizable*. Renormalizability essentially means that the theory is well-defined at all energy scales, which seems like a reasonable demand on a proposed fundamental theory.

So what we know is that taking classical general relativity and quantizing it, we do not get a fundamental theory of quantum gravitation. This does nothing to rule out other proposed quantum theories of gravitation, for example, LQG or string theory.

Furthermore, the way physics works is that new theories must reduce to old ones in the domains of applicability of the old theories. Whatever the correct quantum theory of gravitation, its low-energy limit should be quantized general relativity, and the classical limit of that is classical general relativity. It's just not true that you have to choose between general relativity or quantum mechanics.

So this measurement of a prediction of classical general relativity does absolutely nothing to show that no quantum mechanical model of gravitation exists. It couldn't, because we already have a quantum mechanical model of gravitation: quantized general relativity. It's not as "nice" as we would like, but that really only rules it out as the *fundamental* theory.

> **Comments:**
> **username_4**: This site attracts quite high quality answers. I upvoted the whole lot (and I do not do that .. just about ever..)  
> **username_0**: Indeed.. Very smart answers @javadba  

---

### Answer by username_5 on 2016-02-12. Score: 19

> Another question, how can we identify the ripple's origin (let's say that if it's the result from the big bang or another big event)?

(I'm just answering this part of the question, as username_1 has already answered the main part about GR vs QM.)

LIGO have produced [an image](https://www.ligo.caltech.edu/image/ligo20160211b) which shows their best estimate of where these two black holes were:
[!["Where the Gravitational Waves Came From" by LIGO](https://i.sstatic.net/PA21I.jpg)](https://i.sstatic.net/PA21I.jpg)

All they can say is, somewhere in the southern sky. In the future a network of more detectors will allow such events to be pinpointed much more precisely.

> **Comments:**
> **username_0**: That's truly amazing.. Thanks for sharing this  
> **username_6**: Just one more detector coming online will make a huge difference.   The two LIGO detectors were only able to localize this event to a 600 square degree region.  During the press conference once of the scientists stated that after the Virgo detector comes online later this year they should be able to narrow it to a single digit number of square degrees.  That's a small enough area of space for fast response optical scopes to survey for the afterglow expected from the merger of [neutron stars (last paragraph of conclusion)](http://arxiv.org/pdf/1602.03868.pdf).  
> **username_0**: If you want a little more new details about that part of the question, check the edit on 16-2-2016 @username_5 :)  
> **username_7**: The ability to locate sources should get another huge improvement in a couple of years now that LIGO India has [been approved by the Indian government](http://economictimes.indiatimes.com/news/economy/policy/government-gives-in-principle-approval-for-ligo-india-project/articleshow/51026129.cms).  

---

### Answer by username_8 on 2016-02-14. Score: 6

At the announcement press conference (2/11/2016), Kip Thorne said that the detection puts an upper limit on the rest mass of the graviton. They determined this limit by looking at distortions of the detected signal waveform compared to the idealized signal produced by computer simulations. The upper limit from the publication is $m\_{graviton} < 1.2 × 10^{−22} \frac{eV}{c^2}$ or $1.9 × 10^{−41} kg$.

Refs:
<https://www.youtube.com/watch?v=vy5vDtviIz0&feature=youtu.be&t=1h5m23s>
<https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102> (page 8)

> **Comments:**
> **username_9**: A little too short maybe. Reference?  

---

### Answer by username_10 on 2016-02-17. Score: 2

Though the twin discovery of Gravitational Waves and Black Hole merger might not affect directly the status of QM it might indirectly bring new "surprises" For example, in this link:
<http://news.discovery.com/space/weve-detected-gravitational-waves-so-what-160213.htm>
They comment that:
"For some reason, the final spin of the black hole is slower than expected, indicating that the two black holes collided at a low speed, or they were in a collision configuration that caused their combined angular momentum to counteract each other. “That is very curious; why would nature do that?” said Lehner."
And the final comment is:
"This early puzzle could be down to some basic physics that hasn’t been considered, but more excitingly it could reveal some “new” or exotic physics that is interfering with the predictions of general relativity".
Wow! "Interfering with general relativity" is a polite way of suggesting that it might be wrong. So maybe QM might come to the rescue of Gen.Relativity rather than the other way around.


---

