This made me wonder how far we are from being able to create and detect gravitons. The Wikipedia page on gravitons [0] addresses this question:<p><i>Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector. The reason is the extremely low cross section for the interaction of gravitons with matter. For example, a detector with the mass of Jupiter and 100% efficiency, placed in close orbit around a neutron star, would only be expected to observe one graviton every 10 years, even under the most favorable conditions. [...]<p>However, experiments to detect gravitational waves, which may be viewed as coherent states of many gravitons, are underway (such as LIGO and VIRGO). Although these experiments cannot detect individual gravitons, they might provide information about certain properties of the graviton. For example, if gravitational waves were observed to propagate slower than c (the speed of light in a vacuum), that would imply that the graviton has mass [...].</i><p>Fascinating! I take it that the question of whether the graviton could have mass is now considered to be well answered in the negative.<p>[0] <a href="https://en.wikipedia.org/wiki/Graviton" rel="nofollow">https://en.wikipedia.org/wiki/Graviton</a>
I remember learning about the LIGO experiment back when it was being built, a decade ago, and at the time it seemed so amazing: a giant tube of vacuum, sealed underground and so sensitive that it could detect animals walking nearby, listening to the moving and twisting of space itself… I guess we're finally seeing that with immense human ingenuity and the most careful of engineering, the universe will offer its secrets up to us.<p>This also means that between LIGO and ATLAS/CMS, the last few years have screwed in the final screws on two of the big physics advances of the 20th century: quantum field theory and general relativity are now both experimentally complete, and both look nearly unassailed in their correctness. The next steps for physics look increasingly abstruse: understanding the exceptional cases, like black holes, holography, and the fundamentally computational form of the universe. It's an exciting time, and it looks more and more like we're close to the very bottom, since we have to look so far now to find anything outside our models.
A conceptual issue that some of the commenters may have missed is that part of the detection is done by matched filtering (<a href="https://en.wikipedia.org/wiki/Matched_filter" rel="nofollow">https://en.wikipedia.org/wiki/Matched_filter</a>), in which it is necessary to have a good idea of the signal you're looking for. This detection has built upon analytical and numerical advances in relativity. While people may not know about the prevalence of e.g. binary black hole collisions, they have a pretty good idea of the signal that would result if such a collision were to occur. Similarly with other potential sources like binary neutron star collisions.
> <i>And then the ringing stopped as the two holes coalesced into a single black hole, a trapdoor in space with the equivalent mass of 62 suns. All in a fifth of a second, Earth time.</i><p>Am I reading this correctly, that shortly after the detector came online we just happened to observe the exact moment a billion years ago that two black holes collided?<p>Was that extremely coincidental? Or do these events happen all the time, and so if it wasn't those two black holes it would be two others?
From the abstract of the paper, energy equivalent to three solar masses were radiated away in gravitational waves. That's a simply incredible amount!<p>Possibly stupid question: Given how far away it was, and that the inverse square law applies, would the effect of these waves be visible on the human scale if we were closer? We can see the effects of the compression of spacetime with LIGO after all, so presumably we could?
According to this paper ( <a href="https://dcc.ligo.org/LIGO-P150914/public" rel="nofollow">https://dcc.ligo.org/LIGO-P150914/public</a> ) they detected the signal first at Livingston, Louisiana and 6.9ms later in Hanford, Washington. The distance between them according to wikipedia ( <a href="https://en.wikipedia.org/wiki/LIGO" rel="nofollow">https://en.wikipedia.org/wiki/LIGO</a> ) is 3002km (Ok, the 3002 km distance is on the Earth). If the gravity wave travel at the speed of light they should detect 10ms later (300 000/3002 sec = 1/100 sec = 10ms ). From these data the gravity travels at 434 000km/sec instead of 300 000km/sec. Almost 50% faster then light... Is there any error in my calc?
Paper here: <a href="https://dcc.ligo.org/LIGO-P150914/public" rel="nofollow">https://dcc.ligo.org/LIGO-P150914/public</a>
How do the detectors work? In my mind they don't make physical sense. They're saying the distance between the mirrors changes, but I don't understand how that's possible in this context.<p>Let's say a gravitational wave compresses space. To someone inside that compressed space, there should be no noticeable difference. Light will still flow the same way through the compressed space at the same speed <i>relative to the compression</i>. Matter will behave identically, because both light and matter are part of the fabric of that space. As I understand it, the only way the mirror lengths could change is if space is created or destroyed.<p>If that doesn't make sense, consider the 2d analogy of drawings living on paper. Assume also that light moves only along the surface of the paper. If you bend the paper, the light will bend with it. But when you bend the paper, the creatures living on the paper can't know it's bent. The fabric of the paper is still identical. Even if some of the paper gets compressed in one direction, it will still have the same amount of particles, so any light travelling through there will hit the same amount of resistance. And stretching the paper, even if you're a drawing on the part being stretched, would have no effect. A 2d creature looking at something 1 foot away, even if the paper is stretched to 10 feet, won't see any difference, because the fabric light travels through is also stretched.<p>The only way I can see this making sense is if light travels independent of the fabric of space, but it's my understanding that light travels <i>through</i> it, not independent of it?
Weird nobody mentioned here the excellent threads on this topic here <a href="https://www.reddit.com/r/science/comments/458ppo/ligo_makes_gravitational_wave_announcement_today/" rel="nofollow">https://www.reddit.com/r/science/comments/458ppo/ligo_makes_...</a> and here <a href="https://www.reddit.com/r/askscience/comments/458vhd/gravitational_wave_megathread/" rel="nofollow">https://www.reddit.com/r/askscience/comments/458vhd/gravitat...</a>
Are there any potential competing theories this detection could also support? I'm wondering how much room there is here for confirmation bias, but I suppose that's a pretty hard thing to measure without the benefit of hindsight.
I sometimes wonder why tech people like space-related stuff so much. It is a major news indeed and a feat of science and technology, but why is space so popular? Because it's otherworldly, large-scale and kind of making you feel empowered or united? I'm probably more interested in mundane, obscure and humble stuff, so this disproportionate popularity of space-related news is always baffling to me.
The mechanical and software engineering underlying these research endeavors is breathtaking. The laser apparatus, LISA pathfinder, ELISA - how on earth do they calibrate/debug/test such complex systems?<p>... and I shudder to think that more often than not, anything I code in C/C++ will segfault on first run.
I wonder of this means the space version of these antennas, eLISA, will get more funding. Using space seems like a much better way to access long distance laser conduits in a vacuum needed to detect gravitational waves.
It was mentioned that during this event, three sun's mass equivalents were turned into gravity waves, I guess that means that matter particles were turned into gravitons.<p>But what happens to them? Is there any way to turn them back into matter? If not, then at some point, will all matter in the universe end up as gravitons?<p>Also, if an object moving through space creates gravitational waves, doesn't that violate the law that states that a non-accelerating object will not lose/gain any energy? Because if you have to emit gravitons as you move in space, and emitting them requires energy or matter expenditure, then an object moving through space will slowly lose all it's mass?
Does anyone know if G-Waves are effected by velocity, like EM-Waves are?<p>In other words, if two bodies are moving relative to one another, one emits G-Waves, and one detects them. Are the waves at the detector doppler shifted in frequency by the relative velocities?
<i>Lost in the transformation was three solar masses’ worth of energy, vaporized into gravitational waves in an unseen and barely felt apocalypse. As visible light, that energy would be equivalent to the brightness of a billion trillion suns.</i><p>Beautiful.
Note this is a stellar black hole merger of several tens of solar masses.
Imagine the disturbance of a galactic core black hole mergers of millions of stellar masses. These are probably much rarer, but do occur when galaxies merge.
I have a question: what does this mean for theoretical physics? (except for Einstein was right) Does it settle any major debates? Does it make any competing theory more or less likely?<p>Sorry I am not vary knowledgeable on the topic.
One thing I don't quite understand - how can the "chirp" from LIGO be unambiguously categorized as extraterrestrial in origin? The waveform shown onscreen in the NYtimes video looks like an extremely noisy signal - not sure if that's the actual sampled data or just an artistic rendition. Couldn't there be a variety of physical disturbances that explain a sine-tone sweep like that, given how sensitive the instrument is to physical vibrations?
This is live now: <a href="https://www.theguardian.com/science/across-the-universe/live/2016/feb/11/gravitational-wave-announcement-latest-physics-einstein-ligo-black-holes-live" rel="nofollow">https://www.theguardian.com/science/across-the-universe/live...</a>
Wow, the list of authors to the paper is three pages long:<p><a href="https://dcc.ligo.org/public/0122/P150914/014/LIGO-P150914_Detection_of_GW150914.pdf" rel="nofollow">https://dcc.ligo.org/public/0122/P150914/014/LIGO-P150914_De...</a>
On November 25, 1915 (at the time of WWI) Einstein presented the actual Einstein field equations to the Prussian Academy of Sciences.
Almost exactly 100 years later on September 14, 2015 LIGO observed the first gravitational-wave signal.
Is that a coincidence?
The original science paper is here [0]<p>[0] <a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102" rel="nofollow">http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116...</a>
ok, so some of the best minds on Earth can build a machine to detect gravitational waves from an event 1.3B light years away. This is an incredible motivation for those of us on what is possible with technology in simple terrestrial projects.
Honest question: there is any example of Einstein being proved <i>wrong</i>?<p>Was he indeed always right on his theories for phenomenons before they could be proved by experiments; or is that the case that we only hear about when he is proved right?
No they haven't proven Einstein right, they've failed to prove him wrong; that distinction is the essence of science. Theories are never proven right, they can only be proven wrong.
Is the speed of light affected by the gravitational fluctuations mentioned in the article?<p>Or, put another way, is the speed of light only a constant because we measure it in constant gravity?
I am not sure why but I am really hung up on the quote “Finally, astronomy grew ears. We never had ears before.” They are detecting gravitational waves not sound waves.
But there is no "fabric of space-time". Time is a mental concept, it cannot be detected.<p>Whatever they have detected or calculated is something else.
Better video directly from LIGO/Caltech: <a href="https://www.youtube.com/watch?v=wrqbfT8qcBc" rel="nofollow">https://www.youtube.com/watch?v=wrqbfT8qcBc</a><p>And here's more detailed from PBS Space:
<a href="https://www.youtube.com/watch?v=gw-i_VKd6Wo" rel="nofollow">https://www.youtube.com/watch?v=gw-i_VKd6Wo</a>
A hole that is less than the sum of its parts. Three suns’ worth of mass has been turned into energy, in the form of gravitational waves;<p>The coalescing holes pumped 50 times more energy into space this way than the whole of the rest of the universe emitted in light, radio waves, X-rays and gamma rays combined.
Einstein wasn't sure at first. It was Feynman who introduced the thought experiment that settled the debate in the physics community:<p><a href="https://en.wikipedia.org/wiki/Sticky_bead_argument" rel="nofollow">https://en.wikipedia.org/wiki/Sticky_bead_argument</a>
Tangential question. With blackholes merging, can more and more merge some time in future, creating a net gravitational pull to slow down the expansion of the universe and then may be eventually cause the universe to collapse into that continually merging mega black hole.
I'm interested to know how they can be so sure that the change in distance between the two arms of LIGO is attributed to gravitational waves? I would of thought that miniscule movements in the Earth's crust would be a more likely culprit.
<i>once shot up the outside of one of the antenna arms in Louisiana, and a truck crashed into one of the arms in Hanford</i><p>Does this mean an actual truck, a vehicle? Did they accidentally hurt someone?<p>I liked this quote: <i>The future for the dark side looks bright.</i>
I understood how LIGO works but one question I have is, how did scientists conclude the gravitational waves they detected are from a collision of 2 black holes that happened before 1.3 Billion/Million years ago.<p>Could someone explain ?
Technical details and hints on future results: <a href="https://news.ycombinator.com/item?id=11092982" rel="nofollow">https://news.ycombinator.com/item?id=11092982</a>
Live stream from the NSF: <a href="https://www.youtube.com/user/VideosatNSF/live" rel="nofollow">https://www.youtube.com/user/VideosatNSF/live</a>
For those who missed the live announcement by the team <a href="https://youtu.be/aEPIwEJmZyE?t=27m13s" rel="nofollow">https://youtu.be/aEPIwEJmZyE?t=27m13s</a>
Where can I find out more about how thermal effects in the LIGO optics are controlled for?<p>Basically, I want to understand how it's possible to measure a distance change on the femtometer scale.
Are gravitational waves supposed to be that weak or is it because of the distance between us and those black holes? Do they lose power as they travel through space?
So does this verification of gravitational waves help with Physics theory-building? Have people really doubted Einstein : the existence of gravitational waves?
As with most physics experiments for the last 40 years, nothing new was discovered that we didn’t already predict. Confirming something widely believed to be true isn't nearly as valuable as finding out we don't understand something. This is actually one of the reasons I dropped out of my physics phd program.
1.1. billion and 40 years vs. pencil and paper and a few years. That should tell us something about education, mode of thinking and research. And a few other things.
The "proving Einstein right" part would be more fitting if there was some independent evidence of the collision. As it is it seems to go in circles.<p>But that's the NYT I guess.
I swear a big bang theory rerun about this was on last night. Sheldon detected waves at the north pole, but they were actually a blender turned on by the rest of the gang. He's embarrassed and goes home. Leonard beds Penny. Decent episode.
I am a bit skeptical of the conclusion given the methods. Here, there's no observable phenomena independent of the test apparatus that corresponds to the proposed cause. The conclusion is circular.<p>1. Theory predicts gravitational waves when massive objects collide and that the gravitational waves would have an effect that could be measured by the experimental instruments.<p>2. The experimental instruments measure something.<p>3. This is considered proof that massive objects collided.<p>4. Therefore gravitational waves exist.<p>To reframe my skepticism, the experiment measures something. The conclusion as to what it measures, however, is unsupported by statistical inference or direct experience of a causal phenomenon. That's not to say that what the phenomena measured -- the earth resonating -- is uninteresting or unimportant or even inconsistent with the theory of gravitational waves.<p>Yet, I don't find the possibility of a geophysical cause -- i.e. that the earth maintains consistent dimensions at a sub-atomic scale -- the many orders of magnitude less likely than gravitational waves necessary to reach a conclusion. In particular, I find natural fluctuation to be more likely because the experiment acknowledges its existence.<p>For a point of comparison, consider the Perihelion precession of Mercury that provides evidence in support of general relativity. The theory was used to predict the results of an observable event. The experimenters trained their telescopes at a particular location and particular time and observed phenomena consistent with a prediction based on the theory. The same is true of the Higgs. In both cases the experiment is of the form "when X, I will observe Y."<p>The reasoning here is:<p><pre><code> If X, then Y.
Y, therefore X.
</code></pre>
It treats an ordinary implication as mutual implication.
Everyday we're getting sun rays <a href="https://en.wikipedia.org/wiki/Crepuscular_rays" rel="nofollow">https://en.wikipedia.org/wiki/Crepuscular_rays</a><p>Why are we surprised at gravitational waves when 2 black holes collided?
A detector of this sensitivity seems like a boon for spying. Rather difficult to relocate, fortunately, but it makes me wonder about the future of the technology. No one would have looked at the first computer and envisioned an iPhone.
I'm wondering no-one mentioned Electric Universe which is the greatest opponent of this gravitational hocus-pocus religion. It would be much more beneficial to the humanity to focus smart peoples' attention to Birkeland currents or plasma or to the recent experiments of the SAFIRE project. They have several series on their youtube channel:<p><a href="https://www.youtube.com/user/ThunderboltsProject/videos" rel="nofollow">https://www.youtube.com/user/ThunderboltsProject/videos</a>