9 ms·
The Gravitational-Wave “Revolution” Is Underway
- SiempreViernes 7y agoSummary: ”everything is going well”
- izzydata 7y agoWell that's a relief.
- wwarner 7y agoI would recommend (as I've done before) Kip Thorn's book _Black Holes and Time Warps_ (https://www.amazon.com/dp/0393312763 https://www.amazon.com/dp/0393312763) to learn more about LIGO.
- ksangeelee 7y agoThere's a lovely Sean Carrol podcast interview with Kip Thorne where he discusses the people and the work that led to the discovery. https://www.preposterousuniverse.com/podcast/2018/11/26/episode-24-kip-thorne-on-gravitational-waves-time-travel-and-interstellar/ https://www.preposterousuniverse.com/podcast/2018/11/26/epis...
- jamiek88 7y agoI can second this. The book is still worth getting too but this podcast is an excellent discussion around the subject.
- sho 7y agoTalking about Sean Carrol, I'd also recommend his latest book, Something Deeply Hidden - a fascinating, and very readable, exploration of the theories, history and even philosophy of modern quantum mechanics.
- hinkley 7y ago> Just as light can be bent and magnified when it passes through the gravitational fields of galaxies and other massive objects, gravitational waves should be warped in the same way, too. I'm gonna need a refresher course on that.
- bpchaps 7y agoGravity propagates at the speed of light. So, imagine you have a massive celestial body floating out in space, with a large gravitational field. Its gravitational field is always propagating. Now, take that celestial body, and make it completely and instantaneously disappear. There's now a gravitational differential between the now-gone body, and its previously propagated gravity field. You should be able to detect that if you're close, say through tidal differences. Very similar happens with black holes colliding, except the gravity differential comes from the two black holes oscillating near each other, close to the speed of light. Edit: this obviously isn't exactly how this works, since it makes a lot of assumptions, such as the ability to instantaneously remove something. So, don't think of this as how "things actually work", but as a model to help build your intuition.
- Filligree 7y agoBe careful with that example. You probably know this, but stars can't disappear instantaneously, and so if you start with that assumption it's easy to get paradoxical results from relativity. That doesn't mean there's anything wrong with the model. It's just GIGO.
- Enginerrrd 7y agoExactly. As soon as you magically remove the gravitational body, you are magically removing the waves too according to GR. There is no such thing as curved spacetime without mass. (Except for the cosmological constant, but that's different.)
- raattgift 7y agoGeneral Relativity admits general curved vacuum metrics (vacuum meaning: no matter anywhere), and many of them are useful theoretical approximations to real astrophysical systems. Famous ones include the Schwarzschild and Kerr metrics (both of which have T^{\mu\nu} = 0, where T is the stress-energy tensor), de Sitter and anti-de Sitter space, and Minkowski space. Useful ones include vacuum pp-waves, used in studying gravitational radiation from the perspective of an observer at large distance from the source. There's even the Sexl ultraboost, which can approximate ultrarelativistic motion between a black hole and a low-mass observer. These are usually probed by adding test masses of some sort, letting them evolve along available trajectories. Some such test masses are pointlike, neutral, and nearly massless; others are some sort of classical or quantum field. In most cases, the goal is to keep T^{\mu\nu} negligible. One can alternatively be lead by the stress-energy tensor, and may be tempted to call T^{\mu\nu} the matter tensor in that case. One typically chooses some vacuum background -- Minkowski space, usually, but any background can be used -- and then uses perturbation theory to capture how the chosen matter alters that background curvature. This is very common in cosmology. > Except for the cosmological constant, but that's different No, it's not different; one has flexibility to move the cosmological constant into the RHS for calculational convenience without having to change its interpretation as part of the background curvature: https://en.wikipedia.org/wiki/Lambdavacuum_solution https://en.wikipedia.org/wiki/Lambdavacuum_solution
- gfodor 7y agoA revolution would imply there has been a breakthrough that would potentially lead to new theory. However, as with most modern physics experimental breakthroughs, it seems gravitational waves provide just further support for existing theories (with a few minor exceptions.) Not to say that this isn’t exciting, but it seems long overdue for us to stumble upon something major that is unaccounted for.
- ganzuul 7y agoIt's telescope 2.0. Not physics 2.0.
- Ididntdothis 7y agoSeems dark energy and matter are what you are thinking about. We knew with good certainty that they exist but nobody knows what they are. It’s a wide open field.
- Jerry2 7y agoProf. Sabine Hossenfelder has an interesting blog post on LIGO [1] and a related HN thread [2]. [1] https://backreaction.blogspot.com/2019/09/whats-up-with-ligo.html https://backreaction.blogspot.com/2019/09/whats-up-with-ligo... [2] https://news.ycombinator.com/item?id=20881986 https://news.ycombinator.com/item?id=20881986
- joeyrideout 7y ago> the distribution of the boring events is fascinating This line needs to be made into a motivational poster, or a statistics meme.
- perl4ever 7y agosomething something smallest uninteresting number...
- eukaryote31 7y ago"Boeing events are fascinating, for sufficiently large values of boring"
- typon 7y agoThis is giving me chills after reading Dark Forest. I hope this sparks a new era of SETI with gravitational waves as the medium. I believe a civilization advanced enough would use gravitational waves for communication.
- Ar-Curunir 7y agoWhy are gravitational waves better for long distance communication than EM waves?
- Florin_Andrei 7y agoIt's hard to shield them. But bandwidth would probably suck.
- choeger 7y agoOh come on, just collapsing some million black hole pairs to get the latest JavaScript based ad across the whole Galaxy. Let's not pretend there are still people with a 56k gravitation modem out there.
- ClumsyPilot 7y agoWe will send you thin information even if you don't want it! Otherwise, there isn't much obstacles in empty space.
- nerfhammer 7y agothey can propagate through literally anything
- semi-extrinsic 7y agoSo do neutrinos. They're a lot easier to make.
- Florin_Andrei 7y ago
- jackcosgrove 7y agoI am a complete neophyte regarding these topics. I did notice that the detected events (black holes merging, neutron stars merging) seem really exotic, while I assume gravitational waves are all around us all the time. Is our instrumentation for detecting gravitational waves simply very insensitive compared to the instrumentation used to detect electromagnetic waves? Or are they harder to detect for some more fundamental reason?
- JohnBooty 7y agoGravity is super, super weak compared to the other forces. Every time you lift an object, you are overcoming the gravitational force of an entire planet. Gravity is that weak. Meanwhile, the incredible destruction caused by a nuclear bomb is the product of the energy stored in just a handful of atoms.
- gibolt 7y agoGravitational waves are hard to detect because of their scale, speed and required precision. Some of the most precise lasers built are repeatedly bouncing light over miles in a tunnel to track changes in arrival significantly less than a trillionth of a second different. Doing this while filtering out noise from miscalibrated sensors or just small vibrations outside the chamber is HARD, but improving. It gets better as more come online around the world to confirm detections and aid in better directional targeting.
- Retric 7y agoThey are hard to detect because you can only infer their existence from a mass of data vs directly detect them.
- jackcosgrove 7y agoSo in other words these telescopes are measuring "the dog that didn't bark" rather than actually detecting gravitational waves? Much like we infer exoplanets from deviations of their stars' behaviors from what we would expect given no orbiting planets?
- jobseeker990 7y agoIf gravity waves exist, does that mean we could theoretically produce a gravity wave laser?
- pdonis 7y agoJust having "waves" is not enough for a laser. You need bosons--i.e., quantum particles with integer spin. To see the quantum aspects of gravitational waves that would correspond to this, you would need extremely strong sources--much stronger even than the black hole mergers that LIGO has observed. Nobody has any expectation of observing any quantum aspect of gravitational waves in the foreseeable future, much less being able to control such sources in order to make a laser.
- lolc 7y agoThey're listening on a really noise channel. It seems premature to talk about the frequency of the detected events matching some expected rate when they keep tuning their filters to the expectations. I recently read an article deploring the missing confirmation of the mergers through light-based astronomy. I can't find the article now, so I'm just going to list another one: https://www.newscientist.com/article/mg24032022-600-exclusive-grave-doubts-over-ligos-discovery-of-gravitational-waves/ https://www.newscientist.com/article/mg24032022-600-exclusiv... Has anything changed from what is described in the article?
- deleted 7y ago[deleted]
- kryptiskt 7y agoThere has been confirmation, I don't know why that article doesn't bother to mention it. https://en.wikipedia.org/wiki/GW170817 https://en.wikipedia.org/wiki/GW170817
- lolc 7y agoThe article does mention the 17. August 2017 event just not under the GW170817 name. From the article: > They point out that the collaboration initially registered the event as a false alarm because it coincided with what’s known as a “glitch”.
- narrator 7y agoUnlike Electromagnetism, gravitation is boring because it is only a positive quantity. If you had positive and negative you could have maxwell's equations for gravitation and gravitational circuits and conductors and stuff.
- mhh__ 7y agoMaxwell's equations for gravitation otherwise known as the Einstein Field Equation(s) .
- ollybee 7y agoI recommend watching videos by Rana Adhikari if you want to know about gravitational waves. I went down a rabbit hole about a year ago with his video's, he is increasingly engaging. Also even in a short time his predictions for the field are coming to pass.
- platz 7y agoI really enjoyed this account of the technical aspects of LIGO The Technical Challenges of Measuring Gravitational Waves – Rana Adhikari of LIGO https://blog.ycombinator.com/the-technical-challenges-of-measuring-gravitational-waves-rana-adhikari-of-ligo/ https://blog.ycombinator.com/the-technical-challenges-of-mea...
- wwarner 7y agoBtw -- everyone should see the new documentary Chasing Einstein! I just got out of the theater and was BLOWN AWAY.
- H8crilA 7y agoThe fundamental thing about gravitational waves is that those are a new form of data that the universe has always been sending towards us, and that we can read now. It's like being able to read the radio waves coming from the universe for the first time, not just the visible spectrum, or close to the visible spectrum. If future advances in this field permit we may even use those to communicate. Who knows, perhaps someone is already talking in that language.
- ravar 7y agoCommunicating with gravity waves would be very inefficient given how weak Gravity is. I don't see any reason why you would want to use gravity for communications... but who knows.
- AstralStorm 7y agoQuantum entanglement is much more feasible instead.
- fsh 7y agoQuantum entanglement does not allow communication. This is known as the "no-communication theorem".
- de_watcher 7y agoCommunicate using gravitational waves by shuffling some charged black holes with a giant electric magnet...
- z3t4 7y ago> Within those, 20 have been black hole mergers, two have been neutron star mergers And here I am on a blue planet, surfing the web.
- Khelavaster 7y agoThe high-frequency gravity wave revolution has been especially interesting. Keep an open mind.