Of Particular Significance

Category: Astronomy

Arguably the two greatest problems facing particle physicists, cosmologists, string theorists, and the like are both associated with an apparent failure of a notion called “naturalness”.  Until now, I’ve mostly avoided this term on this site, because to utter the word demands an extended explanation.  After all, how could nature be unnatural, by definition?

Well, the answer is that the word “natural” has multiple meanings.  The one that scientists are using in this context isn’t “having to do with nature” but rather “typical” or “as expected” or “generic”, as in, “naturally the baby started screaming when she bumped her head”, or “naturally it costs more to live near the city center”, or “I hadn’t worn those glasses in months, so naturally they were dusty.”  And unnatural is when the baby doesn’t scream, when the city center is cheap, and when the glasses are pristine. Usually, when something unnatural happens, there’s a good reason.

I’ve started writing an article about naturalness and unnaturalness, and how there are two great mysteries about how unnatural our universe is, one of which lies at the heart of the Large Hadron Collider‘s [LHC’s] research program.  What I’ve written so far explains what naturalness means and (in part) how it applies to the Standard Model (the equations we use to describe the known elementary particles and forces).  I’ll be extending the article to explain this in more detail, and to explain the scientific argument as to why it is so unnatural to have a Higgs particle that is “lonely” — with no other associated particles (beyond the ones we already know) of roughly similar mass.  This in turn is why so many particle physicists have long expected the LHC to discover more than just a single Higgs particle and nothing else… more than just the Standard Model’s one and only missing piece… and why it will be a profound discovery with far-reaching implications if, during the next five years or so, the LHC experts sweep the floor clean and find nothing more in the LHC’s data than the Higgs particle that was found in 2012.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON August 27, 2013

Have you perhaps wanted to go into space someday, so you could float around and do somersaults like the astronauts you see on TV? You know, out in space, where everything floats, because … because …

…

because there’s no gravity in outer space???

  • Hmm… If there were no gravity in space, what would keep the Earth orbiting the Sun? Or the Moon orbiting the Earth?

umm… because…

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 8, 2013

I’ve finished (more or less) a version of the promised article on IceCube — the giant neutrino experiment that may have made a major discovery, as announced last week, and that had an opportunity to make another a few weeks ago (though apparently nature didn’t provide).  The article is admittedly a bit rushed (darn computer trouble) and therefore a bit rough, and it also leaves out some more subtle points that may become important in the future — but I think it’s complete enough to help explain how IceCube made their most recent measurements.  As usual, please send comments and questions, and I’ll work on it further.

Here’s the link to the article.  You may also find it interesting to read more generally about how neutrinos are detected, and about the weird story of neutrino types, and how they can oscillate from one type to another as they travel.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON May 23, 2013

I was sent or came across a few interesting links that relate to things covered on this blog and/or of general scientific interest.

It was announced yesterday that the European Physical Society 2013 High Energy Physics Prize was awarded to the collaboration of experimental physicists that operate the ATLAS and CMS experiments that discovered a type of Higgs particle, with special mention to Michel Della Negra, Peter Jenni, and Tejinder Virdee, for their pioneering role in the development of ATLAS and CMS.  Jenni and Virdee are both at the LHCP conference in Barcelona, which I’m also attending, and it has been a great pleasure for all of us here to be able to congratulate them in person .

One thing that came up a couple of times regarding weather forecasting (for instance, in forecasting the path of Hurricane Sandy) is that the European weather forecasters are doing a much better job of predicting storms a week in advance than U.S. forecasters are.  And I was surprised to learn that one of the the main reasons is simple: U.S. forecasters have less computing power than their European counterparts, which sounds (and is) ridiculous.  The new director of the U.S. National Weather Service, Louis Uccellini, has been successful in his goal of improving this situation, as reported here.  [Thanks to two readers for pointing me to this article.]

One of the possible interpretations of the new class of high-energy neutrinos reported by IceCube (see yesterday’s post) is that they come from the slow decay of a small fraction of the universe’s dark matter particles, assuming those particles have a mass of a couple of million GeV/c². [That’s much heavier than the types of dark matter particles that most people are currently looking for, in searches that I discussed in a recent article.]  I didn’t immediately mention this possibility (which is rather obvious to an expert) because I wanted a couple of days to think about it before generating a stampede or press articles.  But, not surprisingly, people who were paying more attention to what IceCube has been up to had recently written a paper on this subject.  [Here’s an older, related paper, but at much lower energy; maybe there are other similar papers that I don’t know about?]  At the time these authors wrote this paper, only the two highest energy neutrinos — which have energies that, within the uncertainties of the measurements, might be equal (see Figure 2 of yesterday’s post) — were publicly known.  In their paper, they predicted that (just as any expert would guess) in addition to a spike of neutrinos, all at about 1.1 million GeV, one would also find a population of lower-energy neutrinos, similar to those new neutrinos that IceCube has just announced. So yes, among many possibilities, it appears that it is possible that the new neutrinos are from decaying dark matter.  If more data reveals that there really is a spike of neutrinos with energy around 1.1 million GeV, and the currently-observed gap between the million-GeV neutrinos and the lower-energy ones barely fills in at all, then this will be extremely strong evidence in favor of this idea… though it will be another few years before the evidence could become convincing.  Conversely, if IceCube observes any neutrinos near but significantly above 1.1 million GeV, that would show there isn’t really a spike, disfavoring this particular version of the idea.

Regarding yesterday’s post, it was pointed out to me that when I wrote “The only previous example of neutrinos being used in astrophysics occurred with the discovery of neutrinos from the relatively nearby supernova, visible with the naked eye, that occurred in 1987,” I should also have noted that neutrinos were and are used to understand the interior of the sun (and vice versa).  And you could even perhaps say that atmospheric neutrinos have been used to understand cosmic rays (and vice versa.)

In sad news, in the “all-good-things-must-come-to-an-end” category, the Kepler spacecraft, which has brought us an unprecedented slew of discoveries of planets orbiting other stars, may have reached the end of the line (see for example here), at least as far as its main goals.  It’s been known for some time that its ability to orient itself precisely was in increasing peril, and it appears that it has now been lost.  Though this has occurred earlier than hoped, Kepler survived longer than its core mission was scheduled to do, and its pioneering achievements, in convincing scientists that small rocky planets not unlike our own are very common, will remain in the history books forever.  Simultaneous congratulations and condolences to the Kepler team, and good luck in getting as much as possible out of a more limited Kepler.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON May 17, 2013

IceCube [here’s my own description of the experiment], the big high-energy neutrino experiment cleverly embedded into the ice at the South Pole, announced a very interesting result yesterday, following on an already interesting result from a few weeks ago, one that I failed to cover properly. They have seen the highest-energy neutrinos ever observed, ones that, unlike previously observed high-energy neutrinos, appear not to be generated by cosmic rays hitting the top of the atmosphere. Instead, they apparently come from new sources far out in space. And as such, it tentatively appears that they’ve opened up, as long anticipated, a new era in neutrino astronomy, in which high-energy neutrinos will be used to understand astrophysical phenomena!

[The only previous example of neutrinos being used in astrophysics occurred with the discovery of neutrinos from the relatively nearby supernova, visible with the naked eye, that occurred in 1987. But those neutrinos had energies millions of times smaller than the ones discussed here.  And there was hope that IceCube might see neutrinos specifically from gamma-ray bursts, including the one that occurred just two weeks ago; but that appears not to have happened.]

I don’t understand certain details well enough yet to give you a careful explanation — that will probably come next week — but here’s an early description (and expert readers are strongly encouraged to correct any errors.) (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON May 16, 2013

[NOTE ADDED: A reader forwarded a message that IceCube did not see any neutrinos with energies above 1 TeV = 1000 GeV from this GRB. Maybe this is not quite the final word (there would still be sensitivity, with some effort, to neutrinos in the 100 GeV – 1000 GeV range) but clearly the neutrino signal isn’t striking, and it is probably not there at all.  But as I’ve suggested below, even a non-observation might have significant implications for the science; the question is, how many neutrinos would the standard speculations about how GRB’s work have led you to expect at IceCube?  If a reader can provide that info, I’d appreciate that.]

The very recent report of a powerful and long-lived gamma-ray burst (GRB), and questions and remarks by my readers (thank you!), have motivated me, both as a scientist and a blogger, to try to understand whether we should have observed neutrinos from this GRB. This is forcing me to catch up on the related subjects of GRB’s, searches for high-energy neutrinos, and the highest-energy cosmic rays. I’m certainly not caught up yet; there are decades of research out there, and I’m quite far behind on developments over the past three or four years. But here are some of the basics that I believe I understand. Still, be cautious with the content of this post, both because I’m not an expert and because this is a very active area of research in which some fraction of the more speculative stuff will surely turn out to be wrong.   I will try to refine this post with a more detailed and corrected article sometime later, perhaps once we know whether neutrinos from this GRB were or were not observed.

GRBs that last more than a few seconds are widely believed to be associated with an exceptional form of Type II (or “core-collapse”) supernova, though this is not known for certain. In these types of GRBs, there are (at least) two sources of photons (everything from gamma-rays to visible light to radio waves) and two sources of neutrinos. It is important not to confuse the different sources! (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON May 9, 2013

This is hot off the stellar press: as NASA announced today (with cool pictures), a brilliant, long, and rather nearby GRB, or “gamma-ray burster”, was observed on April 27th, initially by the Fermi and Swift satellites.  Gamma-rays are just an old name for photons (i.e. particles of light) which have lots more energy (per photon) than the photons of visible light.   And a GRB is a distant astronomical explosion that produces an enormously bright flare of these high-energy photons, typically for a short time (seconds or minutes), though this one lasted for hours.   It is believed that a narrow jet of high-energy particles produced in a supernova (a powerful explosion of a star) is behind these flares, but they are still poorly understood and are under active study.

Everything about last week’s GRB is on the exceptional side.  The most energetic photon detected had somewhat more energy than the photons produced in the decays of Higgs particles, a bit less than the energy of the photons that Fermi might be seeing from dark matter, and more than three times more energy than any GRB photon previously detected by Fermi. Its gamma rays were produced for many hours, setting another record.  It lasted so long that several other types of telescopes were able to observe it, including those that look at visible light (it was even seen by an amateur astronomer), and those that look at radio waves (which are made from photons with vastly lower energy).  And it was relatively close… well, relatively compared to most GRB’s.  It occured in a galaxy 3.6 billion light years away.  Now that is still a good fraction of the distance across the visible part of our universe, but still, it puts this GRB in the top 5% as far as proximity to Earth.

With such a vast amount of data to work with, it seems very likely that astronomers will learn qualitatively new things about GRBs by studying this blast.  In astronomy, it sometimes takes just one spectacular event to change the scientific landscape!  The next phase of the process will involve directly detecting the lesser (but still intense) glow from the (presumed) supernova that produced the GRB flare.  Stay tuned!  It should be a matter of a week or so…

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON May 7, 2013

Dark Matter, Dark Matter, Everywhere! It’s in your shoes, it’s in your coffee, it’s in the stars and even in your favorite cheese… at least, it’s widely believed to be wandering all about, mostly unnoticed.  Still it’s not quite as inscrutable as its reputation would lead you to believe.  It’s responsible for a galactic glow, an abundance of anti-matter, and now — three quiet little taps in an underground mine.

Or is it?

Apparent effects of dark matter have been “discovered” so many times in the last decade that you may by now feel a bit jaded, or at least dispassionate.  Certainly I do.  Some day, some year, one of these many hints may turn out to be the real thing. But of the current hints? We’ve got at least six, and they can’t all be real, because they’re not consistent with one other. It’s certain that several of them are false alarms; and once you open that door a crack, you have to consider flinging it wide open, asking: why can’t “several” be “all six”?  All of the dark-matter search experiments are difficult, as they involve pushing the technological envelope. And as anyone with experience in science knows, most of the exciting-sounding results emerging from forefront experiments don’t survive the test of time. Never underestimate the challenge of science at the frontier of knowledge!

Still, as of two weeks ago, we have a new dark matter hint to talk about. So here’s a summary of the various hints, including the new one, exploring their implications and their consistency.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON April 29, 2013

[UPDATE, midnight New York time: the cloud of particles from the solar flare arrived a few hours ago, but it didn’t impact the earth’s magnetic field quite as hard as the best-guess forecast. (Remember the probability of a geomagnetic storm was only 60%; i.e. the probability of no storm was 40%.) Right now, the auroras are likely visible in Canada but probably not in the US. This could change, but don’t get your hopes up too high; we may have to wait for the next solar flare.]

I’ve been sidelined with computer troubles and non-science activities, so first, a belated thanks to everyone who left a thoughtful comment after Monday’s post and question about communicating science to the public.  I appreciate hearing your views, especially from readers with a diversity of backgrounds!

Now, many of you may have heard that there is a forecast of northern (and southern) lights, also known as auroras, tonight.  What you’ve heard is correct: today’s NOAA space-weather forecast, from  http://www.swpc.noaa.gov/forecast.html,  says

VI.  Geomagnetic Activity Probabilities 13 Apr-15 Apr
A.  Middle Latitudes
Active                30/30/15
Minor Storm           35/45/05
Major-severe storm    10/15/01
B.  High Latitudes
Active                10/15/15
Minor Storm           20/25/20
Major-severe storm    60/35/20

i.e. it shows that even in mid-latitudes (meaning northern US and southern Canada, and northern Europe, along perhaps with parts of Australia and New Zealand [?]) they are estimating a 35%-45% probability of a minor `geomagnetic storm’ tonight, with a 10-15% probability of a major storm… and a geomagnetic storm, which literally means a lot of activity in the earth’s magnetic field, generally leads to auroras further away from the north and south pole than usual. (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON April 13, 2013

The Alpha Magnetic Spectrometer [AMS] finally reported its first scientific results today. AMS, a rather large particle physics detector attached to the International Space Station, is designed to study the very high-energy particles found flying around in outer space. These “cosmic rays” (as they are called, for historical reasons) have been under continuous study since their discovery a century ago, but they are still rather mysterious, and we continue to learn new things about them. They are known to be of various different types — commonly found objects such as photons, electrons, neutrinos, protons, and atomic nuclei, and less common ones like positrons (antiparticles of electrons) and anti-protons.  They are known to be produced by a variety of different processes. It is quite possible that some of these high-energy particles come from physical or astronomical processes, perhaps very exciting ones, that we have yet to discover. And AMS is one of a number of experiments designed to help us seek signs of these new phenomena.

The plan to build AMS was hatched in 1995, and the detector was finally launched, after various delays, in 2011, on a specially-ordered Space Shuttle mission. Today, Sam Ting, winner of the Nobel Prize for a co-discovery of the charm quark back in 1974, presented AMS’s first results — a first opportunity to justify all the time, effort and money that went into this project. And? The results look very nice, indicating the AMS experiment is working very well.  Yet the conclusions from the results so far are not very dramatic, and, in my opinion, have been significantly over-sold in the press. Despite what you may read, we are no closer to finding dark matter than we were last week. Any claims to the contrary are due to scientists spinning their results (and to reporters who are being spun).
(more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON April 3, 2013

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