https://arstechnica.com/science/2023/06/nanograv-picks-up-si...
Astrobites articles are usually written by post-grad students working in the relevant area, with the writing level targeted at undergrad astrophysics students. This one was written by NANOGrav collab members, all (or at least most) of whom directly worked on the results that will be all over the press today and tomorrow, and maybe hits a level for an advanced undergrad student or so.
The journal these papers are published in is open access: no paywall.
The Ars article focused on the NANOGrav raft of papers; NANOGrav is just one of the several pulsar timing array collaborations that are in this synchronized un-embargoing of papers. There is substantial overlap between, say, the NANOGrav papers in the Ars Technica article and the joint InPTA/EPTA set which includes https://arxiv.org/abs/2306.16225 https://arxiv.org/abs/2306.16214 and https://arxiv.org/abs/2306.16226 but also enough non-overlap to encourage reading all of them (and to refresh one's foundational knowledge by consulting e.g. Burke-Spolaor et al 2019 "The astrophysics of nanohertz gravitational waves", <https://link.springer.com/article/10.1007/s00159-019-0115-7>).
Unfortunately I find myself griping about a focus on -- to be rude -- only the USA-based-institutions-dominated collaboration (<https://nanograv.org/collaboration/partner-institutions>, although of course there are non-USA and non-North American institutions and researchers in that collab too). Relatively USA-institution-light collabs will chase press attention in different markets and in different ways, of course, but there is scant sign of them in the Ars article (which at least names and links to IPTA) or in the WaPo one (which only lists "Europe, India, Australia and China", not naming the actual collabs).
The inter-collab two year plan on synchronization of paper releases (the "3P+ agreement") itself is something of a story; I wonder if it's going to get much attention in anyone's press.
That said, I don't mind either Ouellette's or Achenbach & Jaggard's reporting. I think they serve amateur enthusiasts well enough that their summaries of the results and science don't need to be nitpicked. Other than that both articles use the unhelpful cliché "fabric of space[-]time" (the latter also has "fabric of the cosmos", "fabric of space and time", because variety is important right?), grrrrrrrr.
They can and do replace submitted URLs under numerous conditions, including not only clickbait but superior articles.
I'll do so here, though being ~15 h after initial submission, it's largely a moot point.
Ranting over poor link quality in the thread itself is not useful in this regard.
Why arent we using midjourney for obligatory space article pictures?
World’s most replaceable job award goes to Astronomy editorial artists
You? I have absolutely no idea why you did not do this and I wish you would! It'd be even better if you could make some kind of "Astronomy.com's RSS feed -> yieldcrv's midjourney prompt" but one step at a time.
To me it’s especially clear that using AI to make art is immoral when you use it for a purpose that you would have previously hired a human artist for. Harvesting work from artists without permission and then using that to replace them is pretty scummy.
"The gravitational wave background, as described by the astrophysicists, does not put any torque on everyday human existence. There is not a weight-loss discovery in here somewhere. A burble of gravitational waves cannot explain why some days you feel out of sorts. But it does offer potential insight into the physical reality we all inhabit."
This is just embarrassing for the Washington Post; the scientists who worked so long for this result deserve better science journalism.
The odds of this being a good article were pretty low.
WashPo is many things... but good journalism and scientific journalism is not two.
I might be huge comparatively but still too small to measure it's effects maybe?
Gravitational radiation can form caustics, so in one way, yes. This was an area of theory that Bondi and Pirani were interested in during the 60s to 80s. Caustics are meant in the sense of the bright spots in https://en.wikipedia.org/wiki/Caustic_(optics) but rather than some "rogue wave" you might get a black hole.
More recently mathematical-relativity studies of the stability of Kerr black holes included a 900+ page paper https://arxiv.org/abs/2205.14808 which among other things considers something like a rogue wave passing through a spinning black hole, and asking: does the black hole swallow up some of the wave? or does part of the wave get entrained into a sort of accretion disc? in that disc do caustics appear, and if so do they lead to black holes? if so, do those black holes fall in, fly away, or coalesce into long-term orbiting bodies around the original black hole? These questions were asked because "stability" means "if perturbed (e.g. by a powerful gravitational wave), does an initially Kerr-like black hole relax back into a Kerr-like black hole, or does it become something very much not like Kerr?".
Caustics may also form by a powerful gravitational wave gravitationally-lensing around some massive object like a heavy galaxy cluster. And if that massive object has enough angular momentum, it's possible the caustic will evolve into a significant gravitational wave enhanced somewhat analogously to a slingshot manoeuvre by a spacecraft.
Conversely, we can start with a rogue wave existing, and see what it does.
Bondi and Pirani were also interested in spacetimes with enormous gravitational wave impulses. One family of those is the "sandwich wave", https://royalsocietypublishing.org/doi/10.1098/rspa.1959.012... (1959) (put "https://sci-hub.se/ in front of that URL if you need to).
Loosely, it's called "sandwich" because the spacetime is pretty bland (like white bread?) or even flat on either side of the wave, which divides the spacetime into three parts (including the wave itself).
Thirty years later they showed that the sandwiches are pretty unhealthy as they tend to destroy everything in the universe they pass through (any set of finitely-but-widely-separated galaxy clusters in such a spacetime will end up colliding with each other in finite time). https://royalsocietypublishing.org/doi/10.1098/rspa.1989.001... (also on sci-hub, and with nice late-1980s diagrams).
Fortunately, I don't think anyone has any idea how to generate a sandwich wave - it's just a feature of the spacetime put in by hand.
Unfortunately, we could be in a sandwich spacetime and not know it yet. A sci-fi writer might speculate about a preferred orbital plane for a large number of (very-early-universe-born) supermassive black hole binaries building up an approximate sandwich wave over the course of billions of years. Or perhaps speculate that the apparent stochastic background that's the topic of the fine link at the top where I guess you get "churning" from is not caused principally by supermassive black hole binaries but by some tensor-mode reheating during cosmic inflation (or a false-vacuum-to-real-vacuum first-order (not as in recent Star Wars, or is it?) phase change), and that this effect happened to generate a sandwich wave which has already destroyed galaxies far far away. A hard-working hard science fiction writer might even be able to force a cosmologist to concede that such a picture might be consistent with observation, including the pulsar timing array results in today's news.
A sandwich wave would zip through our galaxy at the speed of light, but the sandwich-wave-induced collapse of the galaxy into a caustic might take enough time that you could really what's-the-opposite-of-enjoy the experience. Pleasant dreams.
I'm struggling to understand how a sandwich wave causes "everything in an infinite spatial volume becomes known in a finite time". Armchair physicist here.
Crazy that this stuff has already been studied 40 to 60 years ago.
I get that on Earth we don't seem to have any crazy gravitational effects from the "churning" of spacetime. However, the universe is vast. There might be some parts of spacetime that churn more than it does on Earth.
Can someone with more of a physics based background explain:
Does this mean with the appropriate detection tools, we might actually start finding hyperspace lanes?
i.e. Rather than creating spacetime bubbles with warp engines[0], we could instead "sail" / "surf" certain parts of spacetime for FTL?
Watching some 68 stable millisecond pulsars for pulse-delays over a long time let the NANOGrav collaboration spot quite a lot of gravitational radiation from heavy bodies (heavy as in billions of solar masses each) in mutual orbits lasting months to years.
LIGO, Virgo, and Kagra are sensitive to much quicker mutual orbits, where a single orbit is a fraction of a second. This also implies a much lower maximum mass for the bodies, somewhere between about 2 and 30 solar masses. A pair of bodies of lower mass can have a quicker orbit; heavier bodies will collide and merge instead.
> sail or surf
The sources of the type of gravitational radiation NANOGrav (and other pulsar timing array collaborations like CPTA, EPTA and PPTA) is sensitive to are scattered randomly across the sky at random distances and with orbits in random orientations. There is unlikely to be a directional bias in our part of the universe.
The results are close to what everyone expected, although there may be support for a greater than expected count of supermassive black hole (SMBH) binaries. Binarization channels -- the ways in which a pair of initially-separated SMBHs go into ~months-long orbits with one another will get more study. This is of particular use in understanding the formation and merger of galaxies.
Ultimately this is a mostly confirmation of 3-spacelike+1-timelike dimension General Relativity as a good theory for our universe at the largest scales. "Hyperspace lanes" have more dimensions right in the name, so I guess the NANOGrav 15-year study results seem to leave them in the land of fantasy.
At best, one can imagine a variety of non-prosaic explanations for the unexpectedly high count of gravitational waves could mean sources other than SMBHs (some early universe phase transitions, that our spacetime has topological defects, unexpected action during cosmic inflation). None of that really invites realistic thinking about "sailing" or "surfing" any more than a random scattering of SMBH binaries. The prosaic explanation for the unexpectedly large number of SMBH-like signals is simply that black holes tended grow large in dustier regions than expected.
Finally, for the most part (i.e., in not-very-dusty regions of space) light waves and gravitational waves move at the same speed, so at first glance it doesn't seem likely that gravitational waves would help one with FTL travel.
That is far short of the usual 5-sigma (1-in-3,500,000) threshold. So I guess interesting results but not really a major discovery?
That is, "General Relativity's right about gravitation yet again". Interesting, because it's yet another way of confirming the theory (at the linear level and a flavour of the equivalence principle), but not at all startling.
What's intriguing is that pulsar timing arrays ("PTA") like NANOGrav, CPTA, EPTA, InPTA, PPTA etc may be seeing more gravitational waves than expected. Assuming the sources are all SMBH binaries in ~month-long mutual orbits, then maybe there are more SMBHs than expected, or they binarize more commonly than expected or earlier in the universe than expected, or through some unexpectedly popular channel other than galaxy mergers. Pulsar timing arrays appear likely to produce increasingly useful data about galaxy formation, mergers, and evolution.
I think that having both LIGO (Hz-kHz, so ~stellar mass) and PTAs (~nHz, and much larger mass) giving views into different parts of the spectrum in gravtiational wave astronomy is pretty major. That LIGO appeared to work at all was awfully cool; and now we have these large international PTA collabs appearing to work too. I am tempted to compare high-end early 20th century optical telescopes at the dawn of radio telescopes: same electromagnetic spectrum, but sensitivity to different wavelengths, with different wavelengths associated with different phenomena and different objects.
PS: I like InPTA's set of cartoons at https://twitter.com/InPTA_GW/status/1674208503395934208 (thread).
I wonder how many science experiments were done on earth yesterday. It was probably more than a thousand. This is why if you are doing science, you should always do the sciences that will give amazing headlines if you are right. Maybe you will be one of that day's lucky one in a thousand!
There has been 1 pulsar-timing experiment looking for gravitational waves and it produced this positive, 1-in-1000 result. Seems extremely promising.
Though in that event, I suspect you might be having other priorities.
sounds very much like the Warp.
Of course the movement is so small and subtle that these movements are more like vibrations. Also known as the sound of the universe aka OM in Hindu scripture.
