There is relatively little doubt (but it still requires confirmation by another experiment!) that BICEP2 has observed interesting polarization of the cosmic microwave background(specifically: B-mode polarization that is not from gravitational lensing of E-mode polarization; see here for more about what BICEP2 measured)
But no one, including BICEP2, can say for sure whether it is due to ancient gravitational waves from cosmic inflation, or to polarized dust in the galaxy, or to a mix of the two; and the BICEP2 folks are explicitly less certain about this, in the current version of their paper, than in their original implicit and explicit statements.
And we won’t know whether it’s all just dust until there’s more data, which should start to show up in coming months, from BICEP2 itself, from Planck, and from other sources. However, be warned: the measurements of the very faint dust that might be present in BICEP2’s region of the sky are extremely difficult, and the new data might not be immediately convincing. To come to a consensus might take a few years rather than a few months. Be patient; the process of science, being self-correcting, will eventually get it straight, but not if you rush it.
I’m not going to drag my readers into the mud of the current discussion, both because it’s very technical and because it’s rather vague and highly speculative. Even the authors of the two papers admit they leave the situation completely unsettled. But to summarize, the main purpose and effect of these papers seems to be this:
Comparable in size to the Milky Way, our host galaxy, the Andromeda galaxy is the most distant object easily visible (in dark skies) to the naked eye; it lies 2.5 million light-years away. About 2.5 million years ago, something in this distant star city went “boom”. And in doing so it flashed, brightly, in high-energy photons — particles of light (or, more precisely, particles of electromagnetic radiation, of which visible light is just an example) — photons that carry many thousands of times more energy than do the photons that our eyes are designed to see.
The Andromeda Galaxy (photo from Creative Commons), which contains perhaps 100 billion stars or more. Something in here exploded a while back, and we just found out about it.
Some of these photons, after traveling for millions of years across space, arrived at Earth this afternoon. They showed up in the Swift satellite’s telescopes, which are designed precisely to notice these things. And Swift’s telescopes identified these photons as arriving from a location somewhere within Andromeda… within a globular cluster of stars, a tightly-knit neighborhood within the city that is Andromeda. NOTE ADDED: Actually, a combination of low-probability events caused
a false alarm, of a sort that’s rare but not unexpected: a known object in Andromeda that emits X-rays appeared to brighten, as a result of electronic noise in Swift’s instruments (such noise is always present, in all scientific instruments, and it is normal to occasionally get a strong burst of it)
followed (due perhaps to a poorly-timed computer problem at Swift’s data center, which slowed the arrival of more complete information the Swift people know why but haven’t explained it in detail) by a delay in identifying this apparent brightening as a false alarm;
all of which is explained here. The apparent brightening, which was rather mild, would in fact have been completely disregarded if it hadn’t occurred in Andromeda; for relatively nearby objects like Andromeda, the Swift team sets a low threshold for false alarms, because something real would be so amazingly important and exciting that we can’t afford to miss it.
What caused this colossal explosion, perhaps the nearest of its type ever observed by modern astronomers? That is the burning question that astronomers, and their friends in gravitational physics and particle physics, are aching to know. It is likely that by tomorrow morning, and certainly within the next couple of days, we’ll know much more… perhaps we’ll even learn something of great importance. NOTE ADDED: And indeed, we know.
For the moment, though, there’s lots of guessing, mostall of which will turned out to be wrong. (Maybe, some are speculating, this is a gamma-ray burst, perhaps caused by a merger of two neutron stars, with consequent bursts of neutrinos and gravitational waves that we might detect; but right now there’s no evidence for this, so don’t get your hopes up.) You can read many breathless articles by following the Twitter hashtag #GRBm31. Admittedly you might be better off without it. NOTE ADDED:Yep.
But do stay tuned as the facts emerge. The opportunity to observe such a nearby explosion is rare. So this is certainly going to be interesting… and maybe, if we’re very lucky, it will be more than merely interesting…
NOTE ADDED: Actually, we were very unlucky, and it was completely uninteresting —except as an illustration that it can be very difficult, in the heat of a moment when data is sparse, to distinguish between something scientifically fascinating and a weird fluke. Scientists do expect these things to happen sometimes. Fortunately, science is self-correcting. Even if Swift’s team hadn’t identified this signal as a fluke in their data, other telescopes would have been unable to find the object they’d identified, and doubts would quickly have emerged as a result. If something’s real, everyone will see it.
The lesson, in my view, is that when new scientific results are announced, be patient. Give the experts a little time to check things, and don’t do science the way Twitter does.
And finally: if you are inclined to criticize the Swift team, you’re making a big mistake. On the contrary, they did exactly what they were supposed to do, as quickly as they could. Gamma-ray bursts [GRBs] are extremely rare and extremely valuable and extremely brief; Swift’s job is to let the scientific community know, as quickly as possible, that one may have been seen, so that others may look at it. Inevitably, someone with such a job will occasionally give a false alarm. Swift has discovered so many GRB’s, and made so many direct and indirect contributions to our knowledge about them and about other objects in the sky, that scientists, while disappointed that this was a false alarm, will certainly not view Swift as irresponsible.
From the very beginning of the BICEP2 story, I’ve been reminding you (here and here) that it is very common for claims of great scientific discoveries to disappear after further scrutiny, and that a declaration of victory by the scientific community comes much more slowly and deliberately than it often does in the press. Every scientist knows that while science, as a collective process viewed over time, very rarely makes mistakes, individual experiments and experimenters are often wrong. (To its credit, the New York Times article contained some cautionary statements in its prose, and also quoted scientists making cautionary statements. Other media outlets forgot.)
Doing forefront science is extremely difficult, because it requires near-perfection. A single unfortunate mistake in a very complex experiment can create an effect that appears similar to what the experimenters were looking for, but is a fake. Scientists are all well-aware of this; we’ve all seen examples, some of which took years to diagnose. And so, as with any claim of a big discovery, you should view the BICEP2 result as provisional, until checked thoroughly by outside experts, and until confirmed by other experiments.
What could go wrong with BICEP2? On purely logical grounds, the BICEP2 result, interpreted as evidence for cosmic inflation, could be problematic if any one of the following four things is true:
1) The experiment itself has a technical problem, and the polarized microwaves they observe actually don’t exist.
2) The polarized microwaves are real, but they aren’t coming from ancient gravitational waves; they are instead coming from dust (very small grains of material) that is distributed around the galaxy between the stars, and that can radiate polarized microwaves.
3) The polarization really is coming from the cosmic microwave background (the leftover glow from the Big Bang), but it is not coming from gravitational waves; instead it comes from some other unknown source.
4) The polarization is really coming from gravitational waves, but these waves are not due to cosmic inflation but to some other source in the early universe.
