After a very busy few months, in which a move to a new city forced me to curtail all work on this website, I’m looking to bring the blog gradually out of hibernation. [Wordsmiths and Latinists: what is the summer equivalent?] Even so, a host of responsibilities, requirements, grant applications, etc. will force me to ramp up the frequency of posts rather slowly. In the meantime I will be continuing for a second year as a Visiting Scholar at the Harvard physics department, where I am doing high-energy physics research, most of it related to the Large Hadron Collider [LHC].
Although the LHC won’t start again until sometime next year (at 60% more energy per proton-proton collision than in 2012), the LHC experimenters have not been sleeping through the summer of 2014… far from it. The rich 2011-2012 LHC data set is still being used for new particle physics measurements by ATLAS, CMS, and LHCb. These new and impressive results are mostly aimed at answering a fundamental question that faces high-energy physics today: Is the Standard Model* the full description of particle physics at the energies accessible to the LHC? Our understanding of nature at the smallest distances, and the future direction of high-energy physics, depend crucially on the answer. But an answer can only be obtained by searching for every imaginable chink in the Standard Model’s armor, and thus requires a great diversity of measurements. Many more years of hard and clever work lie ahead, and — at least for the time being — this blog will help you follow the story.
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*The “Standard Model” is the theory — i.e., the set of mathematical equations — used to describe and predict the behavior of all the known elementary particles and forces of nature, excepting gravity. We know the Standard Model doesn’t describe everything, not only because of gravity’s absence, but because dark matter and neutrino masses aren’t included; and also the Standard Model fails to explain lots of other things, such as the overall strengths of the elementary forces, and the pattern of elementary particle types and particle masses. But its equations might be sufficient, with those caveats, to describe everything the LHC experiments can measure. There are profound reasons that many physicists will be surprised if it does… but so far the Standard Model is working just fine, thank you.
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.
