[Hypothetical] Feb 11: We found gravitational waves!

  1. As physics history, would would/does this rank next to other milestones in physics, eg light-bending? The Mercury deflection was evidence of the entire enchilada of general relativity, I think, so nothing “matches” that.

But gravitation waves are a “missing link” for an enormous theoretical network of force carrier theory, right?

[1b: will this be the equivalent of the wild Mission Control moon/Mars landing I-remember-where-was whoop-dee-doos? ]

  1. This article from Nature, http://www.nature.com/news/gravitational-waves-6-cosmic-questions-they-can-tackle-1.19337, lists “six cosmic questions” in which this evidence should play a major part.

Based on the kind of data (I presume their outline is known), which branches of physics are off-and-running “the most,” to start plugging them in?

Are there any relatively long-standing physical theories of depth and utility (eg aether, of course) that have bet the farm on there not being gravitational waves, and which now can be shut down, presumable available for even more fruitful scavenging?
FTR, this OP is posted February 10. The hed is not particularly prolepsis, hypophora, or occupatio, which are the ones I checked. Fictional historical present. A rhetorical maneuver of some sort, a lie.

The gravitational wave is predicted by Special Relativity, and it has already been indirectly detected by measuring the orbital decay of binary pulsars (the orbit decays because orbital energy is carried away by gravitational waves). So, direct detection of gravitational waves only confirms our understanding of the universe.

Of course it’s enormously exciting, but I think it’s more interesting as an astrophysics tool (direct detection of coalescing neutron stars, etc) than as a work of pure physics. (Then again, that may be my bias as an astrophysicist.)

It’s important, but in some ways the discovery of gravitational waves doesn’t tell us anything we didn’t already know.

Gravitational waves are usually seen as predictions of general relativity, which has a respectable evidence for it, but perhaps nowhere near the amount of evidence for say quantum mechanics or special relativity. A lot of the most direct evidence such as gravitational time dilation and the precession of the perhelion of Mercury, which may seem like slam-dunk proofs of general relativity, have been demonstrated in regimes,where general relativity behaves like a generic relativistic theory of gravity. Though of course there is other evidence for GR, most importantly cosmological evidence.

Gravity waves exist in the weak field (only in weak fields can gravitational waves be rigorously defined) and simply demonstrating their existence doesn’t by itself add more evidence for GR than the demonstration of gravitational time dilation by GPS. Indeed it is almost inconceivable that gravitational waves don’t exist in some form or other as otherwise that would suggest gravity has an infinite propagation speed, at odds with special relativity.

Of course what is going to be more interesting is the details of the detection and what it tells us about their source, etc.

I’m with scr4. While hardly of any basic theoretical significance in and of itself - is there a physicist on the planet who doesn’t believe in gravitational waves? - if this plays out then it’s important.
Just on PR terms, if it plays out, then it’s a certain Noble.

Going by the rumours, it may be a bit more than that. If they’ve got such a clear signal, then that’s a whole new window into astronomy. Which was always part of the rationale in the first place. We’ll never know until we look. Just looking is always worth the punt.

This detection in itself doesn’t do much for us. Our by-far-best-accepted models all agreed that gravitational waves should exist, so learning that isn’t particularly big news. And the source of the waves detected here is presumably something of an unremarkable sort, most likely a merger of two neutron stars or black holes (objects that we already knew exist, and which must merge occasionally).

Now, as time goes on, we’ll be able to detect more and more of these anticipated sorts of events, and hence learn more about things like the abundance of neutron stars in the Galaxy. Which will be useful information, but unless they’re a heck of a lot more or less abundant than we expect, still won’t be revolutionary.

What’s really big here is that, now that we’re able to detect gravitational waves, sooner or later we’ll detect them from some sort of source which we didn’t know existed, or possibly even didn’t suspect existed. Once that happens, we’ll have a huge advancement in our understanding of physics.

The catch is, the hardest part of detecting gravitational waves is in picking out the signal from the noise. In fact, with current instruments, it’s so hard that the only way we can do it at all is via template matching: You take a bunch of expected possible events, calculate what a gravitational wave would look like from each of them, and then compare your data stream to each of them to see if it matches. This is sort of like how, at a crowded party, you can’t follow a conversation at the other end of the room (it’s too noisy to figure out what the words are), but you can still recognize when someone says your name across the room (because you have a template of what your name sounds like, and you’re always listening for it). This method works, but it has the drawback that you can’t find anything that you don’t already have a template for.

There are three ways past this problem: You can construct general-purpose templates that would match a wide variety of sources (but which give you less signal-to-noise benefit than a specific one), you can try to decrease the amount of noise you have, or you can try to find some other way of picking out signals from the noise. Personally, I favor the last approach, specifically by building more detectors: A real gravitational wave will show up in all detectors at the same time (or rather, delayed by an amount corresponding to the separation between them), but the noise sources at different detectors will be mostly unrelated to each other, so something that shows up in many detectors at once is more likely to be a real signal. The big advantage of this is that it doesn’t require development of any new technology: It just requires us to build more of what we already have.

Moderator Note

Leo Bloom, please do not post misleading thread titles in GQ. Since this is hypothetical, I have moved it to IMHO and clarified the title.

General Questions Moderator

I’m wondering about the bit in the linked article that said that gravitational astronomy will be able to resolve matter to the level of the mass of the proton.


Right now, we need monstrous big detectors, filling chambers in salt mines, to try to detect waves from binary pulsars, exploding supernovae, and the like. How could we conceivably build a detector that would even resolve, say, Jupiter’s Moons as they accelerate (orbit) let alone the gravel of Saturn’s rings, and finally something like proton-scale resolution?

Was that hyperbole times 10^17?

ETA: Thank you, Colibri, for clarifying that this was a hypothetical. (Yeah, I don’t even know what today’s date is!) For just a minute, I was bouncing off the ceiling, thinking this had actually been announced.

(Can’t wait till tomorrow! Currently armoring my celing!)

Will you move it back tomorrow?

Leo, this obviously should have been placed in IMHO in the first place. Please take more care where you place your threads, and as I said, please don’t give them confusing titles just to be cute.

Colibri, you should chill out. This is no more IMHO than any single other thread on gravitational waves, or any random handful of physics threads. No difference.

Im sorry I made you reach for your keyboard with a sigh.

I posted the date in the hed. Yup, ol’ Leo, he’s cute.

Confusing titles are not really new are they?

This OBVIOUSLY is GQ topic and thread. You put it here on strict obedience of the law, which says you can.

We’re all proud of you.

Either bounce this to ATMB or not, I take damn care where I place my OP.

Plus, I intended that as a joke, not as something that the honor of the mods and of the Colibri must respond to. I put a fucking smiley on it, as may be noted. As I said before, and in a similar situation in the past, you start fights when none was necessary.

(Now you’ll say if I didn’t do x and y to begin with… Maybe.)

Leo, I would just like you to comply with what I’ve repeatedly asked you to do in GQ, that is, consider whether a thread belongs there, and give it a clear title. I just gave you a polite reminder here. This would be a courtesy both to me and other posters. I got reports about the confusing title of your thread. It would be helpful if you would just give straightforward titles to your threads, at least if you post them in GQ.

Nitpick: LIGO is not in a salt mine or even underground. You’re thinking of things like the Sudbury Neutrino Observatory and the like.

There’ve been rumors of this going around since August or September. Somewhere I heard that LIGO had a small team that could test the system by modifying the data that researchers got. The modifications would make it look likeit detected gravitational waves. The idea was that the data analysis would find these mods and report discovery. At some point before papers were submitted to journals (and I assume before any press conferences were scheduled), this team would reveal that the data was bogus and they’d have to do the analysis over again. (Personally, I find this a somewhat bizarre way of doing science, but I’m not in charge.) Anyway, I was wondering if these rumors would turn out to be due to this rather than an authentic discovery. However, they’ve scheduled a press conference, so apparently not.

This, more than anything else. I’ve been wondering why the hyperbole in the press. If somebody proved (somehow) that there were NO gravity waves, that would upend physics.

It is fun to imagine, though, that there is a nice solid detection or three, perhaps a very close orbiting black hole pair or some such, which we can keep looking at. And that as the next few decades roll by, gravity wave detectors give way to real gravity wave imaging and gravity wave telescopes. I’d love to see a gravity wave map of the sky!

[We found them!


So, this happened…

Are you a wizard, Leo Bloom?

Why would he be a wizard? This has been in the news.

Typical. Experimentalists spend decades designing and building instruments, and finally succeed in making a measurement, theorists say “meh, we knew that already.”


And they rake in the money doing horoscopes on the side :slight_smile:

This is what I was posting over in the MPSIMS thread that was started on this. Trying to understand value and uses. I look forward to attempting to read this.