What Will It Mean If LIGO Detects Gravitational Waves?
theguardian.com
theguardian.com
If the rumors are true that LIGO has detected the merger of two black holes, the observed waveform will be the first test of the predictions of general relativity in the strong gravity limit. This is the most interesting limit because this is where physics diverges the most from Newtonian gravity. Moreover, it's much easier to detect deviations from general relativity in this limit.
LIGO's detection won't be the only test of GR in the strong gravity limit for too long, however. The Event Horizon Telescope has been trying to directly observe the event horizon of the supermassive black hole at the center of the Milky Way (or its shadow, anyway) and should have its first images within a few years.
Better PR team?
Now his ideas are being put to the test with the same apparatus.
So cool.
GEO600 is operational, but it is much less sensitive that the Ligo detectors.
Also, how effing cool is it that we are able to detect changes in spacetime itself!
The announcement itself, of course, will be on topic when it happens, but we can be patient.
I don't believe that's been proven yet. I was under the impression that this was an experiment to provide evidence of the speed of gravity propagation.
That being said, of course, anything could happen. Nature is not bound to follow our assumptions.
Given however that c is considered and so far demonstrably the maximum velocity of information propagation in this spacetime, instantaneous propagation seems unlikely, particularly given the Mercury orbital confirmation.
That all said, we may be looking at things naively.
Black holes for example dilate time, and may either not exist (since they take infinite time to form), or may produce gravity waves that are too time dilated (i.e. slow) to detect.
This is wrong, and based on not taking into account that in GR, simultaneity is not only a relative thing, but also a local thing. There is much more detail in several great answers to this Stack Exchange question:
http://physics.stackexchange.com/questions/5031/can-black-ho...
But since we are here on Earth we care about how it looks to a distant observer, and from our point of view black holes never form. And what the infalling matter sees is irrelevant to us.
NOTE: You do not need black holes to make gravity waves, neutron stars will also make them. But time is still enormously dilated by neutron stars, and I'm wondering how that affects the gravity waves they make.
Saying that something objectively "doesn't happen" because an observer infinitely far away can't see it is ridiculous.
No. You are misunderstanding things.
> because an observer infinitely far away can't see it
No, it's not that the observer can't see it (too hard to see or something like that). It never occurs in the timeline of the observer.
From the point of view of the observer it never actually exists. That it exists from the point of view of someone else is irrelevant. It's not a semantic game about I can see it you can't.
It literally and actually simply does not exist.
(Not to mention the context is gravity waves, so if it never exists from the point of view of the observer it also can't make gravity waves.)
The event horizon is within the future null infinity of your observer; i.e. the observer may choose to travel towards to black hole, and will asymptotically fall into it and thus undeniably observe it. Hence it does actually exist even for this observer. Moreover, the observer can observe the shadow, effect on nearby masses and the gravitational lensing produced by the black hole, thus indirectly observing the black hole, even though he cannot see the actual event horizon.
Eventually, though, a conclusion that gravity waves don't exist would be enormous. It would completely upend mainstream theories of gravity, which all posit gravity waves (of some sort.)
In fact, I'd say the only reason we're looking for gravity waves is to tick a box -- we don't even consider the possibility that they don't occur, we just think it would be cool to have seen one.
Although I do wonder if an array of detectors might be able to use time differences in the arrival of the waves to differently located detectors, and some math to get some directional hints.
There's little reason, almost none at all, to think they don't exist. The standard model clearly predicts they should exist, and non-direct evidence has been seen already.
While I can turn off my add blocker, I won't, my mother can't because she's not aware I have installed one for her and has no idea what it is and what it does.
I can also 100% guarantee they split tested this, before rolling it out, to make sure it was the right cost/benefit choice.
http://www.nature.com/news/gravitational-waves-5-cosmic-ques...
> a way to ensure those people avoid Forbes altogether in the future
I have an ad blocker and never ended up doing this. I either forget which websites are "blocking ad blockers", or I just click without checking the source, especially if the link is in the home of a site I trust like HN.
What if they also start blocking access to users with subtract blockers, or even multiply or divide blockers?