I’m still kind of exhausted from the effort (see yesterday’s post) of completing our survey of some of the many unexpected ways that the newly discovered Higgs particle might decay. But I would be remiss if, before heading off into the holiday break, I didn’t issue some well-deserved congratulations.
The Jade Rabbit rover on the surface of the Moon, 15 December. Credit:Xinhua
Congratulations, first, to China — to the scientists and engineers who’ve managed to put a lander and a rover on the Moon. If you think that’s easy… think again! And they succeeded on their first attempt, a real coup. Now let’s see what science they can do with it, exploring a region of the Moon that apparently may offer answers to important questions about the Moon’s history. Specifically, by accident or by design, the rover is going to be able to explore an area of considerable geological importance, involving one of the Moon’s giant lava flows, a relatively young one (1-2.5 billion years rather than 3 billion or more).
Soyuz VS06, with Gaia, lifted off from Europe’s Spaceport, French Guiana, on 19 December 2013. Copyright: ESA – S. Corvaja, 2013
Congratulations, next, to the scientists and engineers of the European Union, who’ve put a fantastic telescope into space, destined to orbit the sun. The Gaia mission is aimed at doing the extraordinary: mapping, with ultra-high precision, the locations and motions of no less than 1 billion stars within our galaxy — nearly 1% of the total number. The distance to each of these stars will be determined by parallax — looking at how the positions of stars wobble, from the perspective of the spacecraft as it orbits the sun — and the real motions of the stars will be determined by how they drift across the sky, and by the Doppler effect for light. This wealth of information will help scientists figure out the shape and history of the galaxy to a degree never previously possible. Meanwhile, Gaia will also be able to do a lot of other science, picking up distant supernovas outside our galaxy, nearby asteroids orbiting our sun, and signs of planets around other stars, as well as brown dwarfs (small failed stars) that may be floating around between the stars. Gaia can even check some aspects of Einstein’s theory of gravity! Read here about all the wonderful things this mission can do.
Congratulations also to the scientists and engineers in Iran, who’ve apparently moved their rocketry program, and its potential application to human space flight, among other things, another step forward. A second monkey has made the trip to the edge of space, a suborbital trip. (Did the first survive? it’s not clear, and admittedly Iran is known for photo-shopping reality into supporting the story it wants to tell. Not that it matters; it took the US several tries, back over 60 years ago, before a monkey survived the trip, and the survival rate continued to be poor for a while. ) Anyway, it puts Iran well on its way toward its goal of a human in space by 2018.
And finally, congratulations to my own country, the United States, for having passed a budget deal. Not out of the woods yet, but at least it was bipartisan, and we’re not yet talking about another damaging government shutdown, or worse, default. Politics isn’t rocket science. We’ll have to hope our politicians can learn something from China: that it’s good to find some common and worthy goals to work toward together, rather than to fight about absolutely everything and bring the nation’s operations to a halt.
I’m sure you’ve all read in books that Venus is a planet that orbits the Sun and is closer to the Sun than is the Earth. But why learn from books what you can check for yourself?!?
[Note: If you missed Wednesday evening’s discussion of particle physics involving me, Sean Carroll and Alan Boyle, you can listen to it here.]
As many feared, Comet ISON didn’t survive its close visit to the Sun, so there’s no reason to get up at 6 in the morning to go looking for it. [You might want to look for dim but pretty Comet Lovejoy, however, barely visible to the naked eye from dark skies.] At 6 in the evening, however, there’s good reason to be looking in the western skies — the Moon (for the next few days) and Venus (for the next few weeks) are shining brightly there. Right now Venus is about as bright as it ever gets during its cycle.
The very best way to look at them is with binoculars, or a small telescope. Easily with the telescope, and less easily with binoculars (you’ll need steady hands and sharp eyes, so be patient) you should be able to see that it’s not just the Moon that forms a crescent right now: Venus does too!
If you watch Venus in your binoculars or telescope over the next few weeks, you’ll see proof, with your own eyes, that Venus, like the Earth, orbits the Sun, and it does so at a distance smaller than the distance from the Sun to Earth.
The proof is simple enough, and Galileo himself provided it, by pointing his rudimentary telescope at the Sun 400 years ago, and watching Venus carefully, week by week. What he saw was this: that when Venus was in the evening sky (every few months it moves from the evening sky to the morning sky, and then back again; it’s never in both),
it was first rather dim, low in the sky at sunset, and nearly a disk, though a rather small one;
then it would grow bright, larger, high in the sky at sunset, and develop a half-moon and then a crescent shape;
and finally it would drop lower in the sky again at sunset, still rather bright, but now a thin crescent that was even larger from tip to tip than before.
The reason for this is illustrated in the figure below, taken from this post[which, although specific in some ways to the sky in February 2012, still has a number of general observations about the skies that apply at any time.]
A planet (such as Mercury or Venus) with an orbit that is smaller than Earth’s has phases like the Moon. The portion of Venus that is lit is a half-sphere (shown in light color); the portion of Venus we can see is a different half-sphere (dashed red lines); the overlap is shaped like the wedge of an orange and looks like a crescent in the sky. But unlike the Moon, which is at a nearly fixed distance from Earth, such a planet appears to grow and shrink during its orbit round the Sun, due to its changing distance from Earth. It is always largest when a crescent and smallest when full, and is brightest somewhere in between.
So go dig out those binoculars and telescopes, or use Venus as an excuse to buy new ones! Watch Venus, week by week, as it grows larger in the sky and becomes a thinner crescent, moving ever closer to the sunset horizon. And a month from now the Moon, having made its orbit round the Earth, will return as a new crescent for you to admire.
Today, Wednesday December 4th, at 8 pm Eastern/5 pm Pacific time, Sean Carroll and I will be interviewed again by Alan Boyle on “Virtually Speaking Science”. The link where you can listen in (in real time or at your leisure) is
What is “Virtually Speaking Science“? It is an online radio program that presents, according to its website:
Informal conversations hosted by science writers Alan Boyle, Tom Levenson and Jennifer Ouellette, who explore the explore the often-volatile landscape of science, politics and policy, the history and economics of science, science deniers and its relationship to democracy, and the role of women in the sciences.
Take a ball of loosely aggregated rock and ice, the nucleus of a comet, fresh from the distant reaches of the solar system. Throw it past the sun, really fast, but so close that the sun takes up a large fraction of the sky. What’s going to happen? The answer: nobody knows for sure. Yesterday we actually got to see this experiment carried out by nature. And what happened? After all the photographs and other data, nobody knows for sure. Comet ISON dimmed sharply and virtually disappeared, then, in part, reappeared [see the SOHO satellite’s latest photo below, showing a medium-bright comet-like smudge receding from the sun, which is blacked out to protect the camera.] What is its future, and how bright will it be in the sky when it starts to be potentially visible at dawn in a day or two? Nobody knows for sure.
[Note Added — Now we know: the comet did not survive, and the bright spot that appeared shortly after closest approach to the sun appears to have been all debris, without a cometary “core”, or nucleus, to produce the additional dust and gas to maintain the comet’s appearance. Farewell, ISON! Click here to see the video of the comet’s pass by the sun, its brief flare after passage, and the ensuing fade-out.]
I could not possibly express this better than was done last night in a terrific post by Karl Battams, who has been blogging for NASA’s Comet ISON Observing Campaign. He playfully calls ISON “Schroedinger’s Comet”, in honor of Schroedinger’s Cat, referring to a famous and conceptually puzzling thought-experiment of Erwin Schroedinger, in which a cat is (in a sense) put in a quantum state in which it is neither/both alive nor/and dead. Linking the comet and the cat is a matter of poetic metaphor, not scientific analogy, but the metaphor is a pretty one.
Battams’ post beautifully captures the slightly giddy mindset of a scientist in the midst of intellectual chaos, one whose ideas, expectations and understanding are currently strewn about the solar system. He brings to you the experience of being flooded with data and being humbled by it… a moment simultaneously exciting and frustrating, when scientists know they’re about to learn something important, but right now they haven’t the faintest idea what going on.
Comet ISON, a pristine chunk of rock and ice from the extreme edges of the solar system, is making its first visit to the vicinity of the Earth and the Sun. And what a trip!
Today, in a few hours, at 1:45 in the afternoon on the U.S. east coast, the comet will pass exceptionally close to the Sun — much, much closer to the Sun than the Earth or even the planet Mercury. At its closest, the distance from the comet to the Sun’s center will be only 2.5 times larger than the distance from the surface of the Sun to its center. To say it another way, the radius of the Sun is about 700,000 kilometers (430,000 miles) and the comet’s closest approach will be 1,200,000 kilometers (730,000 miles) above the Sun’s surface, or 1,900,000 kilometers (1,160,000 miles) from its center.
This will be a very fiery place for an icy object to find itself!! A comet may or may not survive such a close approach; its central core (or “nucleus”, an agglomeration of rock and ice, about the size of a big mountain on Earth) may fragment if the heat radiating from the sun sufficiently vaporizes and weakens the core. If it does survive, and perhaps even if it fragments, we may begin to see it in the sky in a couple of days, just before sunrise. And if we’re very lucky, it will be spectacular. [Note Added (updated): It appears we are unlucky this time. Indications are now strong that Comet ISON’s nucleus (mostly) did not survive its close approach to the sun, and began falling apart just before or shortly after this post went on-line. You can see evidence of this in a video from SOHO’s close-up camera.Whether the remnants of its dust tail might be visible for a few days isn’t clear to me (or probably to anyone) yet.We can now see that some fragment of the nucleus appears to remain, but the comet is a shadow of its former self. We’ll know soon how visible it will be. [Unfortunately it appears that was visible was all dust, and the comet is just debris now; it will not be visible at all.]]
Over the first few days of December, the comet will dim, but it will also move away from the sun and from the brightest light of dawn, and so it will also become easier to see. Try to look for it in the coming week! My current amateur’s guess (to be updated when I know) is that its remnant dust trail will spread out and dim very rapidly; you should not wait too long if you want to try to see it.
For the moment, you can’t see the comet by eye; it is way too close to the incredibly bright light of the sun. The only way to observe the comet right now is via satellites. The close approach is best watched through the camera of SOHO (the Solar and Heliospheric Observatory satellite). There’s a recent movie here from SOHO that shows the comet has brightened very rapidly in the last 24 hours. [The sun lies at the center of the image, drawn as a white circle, and is shaded from SOHO’s camera by a shield that forms a larger black dot in the center of the image.] The bright star Arcturus sits at the lower left of the image, and the comet is [was, this morning,] much brighter than that! Its maximum brightness may eventually approach that of the brighter planets, Jupiter and even perhaps Venus.Click here for the latest SOHO image, and here for the latest closeup image (which as of writing doesn’t show the comet yet.) A recent image is below.
Comet C/2012 S1 ISON from the NASA SOHO spacecraft on November 28th as it approached the sun. [Image credit: NRL/NASA]
For those who don’t know of him, Sean is a very fine scientist, an expert on the early and current universe, among other things, as well as a very skilled and engaging writer and speaker… and very importantly, he maintains very high standards for accuracy and clarity. I recommend him highly!
Sean and I were interviewed on a Virtually Speaking Science on-line radio show in February (you can listen to it here) and will be appearing again in early December. (By the way, I also appeared on this show when the hunt for the Higgs was still on…)
Some readers may remember that back in May, as I discussed in some detail, the IceCube experiment reported a new and exciting observation — possibly the first discovery of high-energy astrophysical neutrinos: neutrinos, with energies 5 – 50 times higher than those of the protons at the Large Hadron Collider, created in outer space and arriving on earth. This is to be contrasted with most neutrinos measured at IceCube and other previous similar experiments, which have lower energy and are created in the earth’s atmosphere by other types of particles hitting atoms in the air (see Figure 4 of this article.) Specifically, where the IceCube folks expected to measure 10 candidate events from non-neutrino backgrounds, they instead measured 28. Well, these results were reported at a conference in May, but only now is the paper appearing in published form, in the journal Science.
Here’s the IceCube press release about the publication of their paper, http://icecube.wisc.edu/news/view/171 . All indications are that there are few changes since May, except for greater confidence in the result; the numbers quoted all match the ones that I wrote about back in the spring. If there is anything strikingly different from May, I haven’t yet noticed it; please let me know if you’re aware of something.
For those of you who missed this back in May, I wrote a few relevant posts back then that you may find useful.
Meanwhile, you may also remember that there was a big Gamma Ray Burst [GRB] observed in April — the most energetic ever measured. [We were hoping that IceCube would observe neutrinos from that GRB, but it did not.] Science is also publishing papers about that event, and how measurements of it are making people rethink their understanding of how GRBs occur. Once I’ve learned more about this, I’ll post something more detailed.
Curiously, both of these stories are appearing in the press with big headlines, as though they are new news… but if they sound familiar, it’s because they are indeed six months old.
[Apologies: due to a computer glitch, the figure in the original version of this post was not the most up-to-date, and had typos, now fixed.]
On Tuesday, the New York Times Editorial page ran an Op-Ed about dark matter… and although it could have been worse, it could certainly have been better. I do wonder why these folks don’t just call up an expert and confirm that they’ve actually got it right, before they mislead the public and give scientists a combination of a few giggles and a headache.
Here is the last paragraph from the Times:
“This experiment is probing a major hole in the way we understand the cosmos. Roughly speaking, the force of gravity in the universe can be explained only by a corresponding amount of mass, or matter. Some undiscovered mass — dark matter — must exist in order to explain gravity, but no one has seen any traces of it. Those traces, when they are finally found, will be exotic particles left over from the Big Bang. In the tale we tell about everything we know, scientists have now brought us to the edge of the deep, dark woods. They, and we, are waiting eagerly to see how the rest of the story goes.”
Ok, out comes the professorial red pen.
First, a relatively minor point of order. “…the force of gravity in the universe can be explained only by a corresponding amount of mass, or matter…” This isn’t great writing, because mass and matter are not the same thing. Matter is a type of substance. Mass is a property that substance (including ordinary matter, such as tables and planets) can have. Mass and matter are as different as apples and applets. You can read about these distinctions here, if you like. The author is trying to evade this distinction to keep things simple: the more correct statement is that gravity (in simple circumstances) is a force exerted by things (including ordinary matter) that have mass.
But here’s the real offending remark: “Some undiscovered mass — dark matter — must exist in order to explain gravity, but no one has seen any traces of it.” Dark matter is most certainly not needed to “explain gravity” in some general way; there’s not one bit of truth in that remark. For instance, the gravitational pull of the sun on the earth (and vice versa), and the pull of the earth on you and me (and vice versa), has absolutely nothing whatsoever to do with dark matter, nor is dark matter needed to explain it.
What the author should have said is: since the 1960s we have known that gravitational forces on large astronomical scales seem to be stronger than we can account for, and so either our equations for gravity are wrong or there is matter out there, pulling on things gravitationally, that we cannot see with any type of telescope. The reason the latter possibility is taken more seriously than the former by most experts is that attempts to modify gravity have not led to a convincing case, while the evidence for additional “dark” matter has grown very strong over recent decades.
Here’s one of the several arguments that suggest the possibility of dark matter… the simplest to explain. Experts study the motions of the stars in our own galaxy — the star city known as the Milky Way — and also study the motions of stars in other galaxies. [The overall motions of galaxies themselves, inside giant clusters of galaxies which can be found in deep space, are also studied.] Now what we ask is this; see Figure 1. Supposing all of the matter that is out there in the universe is of a type that we can see in one way or another: stars, gas, dust of various types. Then we can figure out, just by looking with a telescope and doing simple calculations, roughly how much measurable matter is in each galaxy, how much mass that matter has, and where it is distributed inside the galaxy. We can next use that information to figure out how hard that matter pulls on other matter, via the force of gravity. And finally — crucially! — we can calculate how fast that pull will make the matter move, on average. And what do we find when we measure how fast the stars are moving? Our calculations based on the matter that we can see are wrong. We find that the stars in the outer edges of a galaxy, and the galaxies inside clusters, are moving much, much faster than our calculation predicts. (This was discovered in the 1960s by Vera Rubin and Kent Ford.) It’s as though they’re being pulled on by something unseen — as though the gravity on the stars due to the rest of the galaxy is stronger than we’ve guessed. Why is this happening?
Fig. 1: One of several lines of evidence in favor of the hypothesis of dark matter is that stars in the outer regions of galaxies move much faster than would be the case if the galaxy was made only from what we can see.
One possibility is that there is matter out there that we can’t see, a lot of it, and that matter is inside galaxies and inside clusters of galaxies, exerting a pull that we haven’t accounted for properly. A huge “halo” of dark matter, in this view, surrounds every galaxy (Figure 2).
Clearly, this isn’t the only logical possibility. Another option is that there could be something wrong with our understanding of gravity. Or there could be some other new force that we don’t know about yet that has nothing to do with gravity. Or maybe there’s something wrong with the very laws of motion that we use. But all attempts to make sensible suggestions along these lines have gradually run into conflicts with astronomical observations over the recent decades.
Fig. 2: The visible part of every galaxy is believed to lie roughly at the center of a much larger halo of dark matter.
Meanwhile, during those last few decades, a simple version of the “dark matter” hypothesis has passed test after test, some of these tests being very complex and subtle. For example, in Einstein’s theory of gravity, gravity pulls on light, and can bend it much the same way that the lenses in eyeglasses bend light. A galaxy or galaxy cluster can serve to magnify objects behind it, and by studying these lensing effects, we again conclude there’s far more matter in galaxies and in clusters than we can see. And there are other arguments too, which I won’t cover now.
So while an explanation for the fast motion of stars inside galaxies, and galaxies inside clusters, isn’t 100% sure to be dark matter, it’s now, after many years of study, in the high 90%s. Don’t let anyone tell you that scientists rushed to judgment about this; it has been studied for decades, and I can tell you from experience that there’s a lot more consensus now than there was when I was an beginning undergraduate 30 years ago.
“Those traces, when they are finally found, will be exotic particles left over from the Big Bang.” Will they? Will the dark matter turn out to be particles from the Big Bang? Not necessarily. We know that’s one possibility, but it’s not the only one. Since I explained this point last week, I’ll just refer you to that post.
Now here come the big meta-questions: should the New York Times be more careful about what it puts on its editorial page? Should its editors, who are not scientists, talk broadly about a subtle scientific topic without fact-checking with an expert? What are the costs and benefits when they put out oversimplified, and in some ways actually false, information about science on their editorial page?
Last week, the LUX experiment reported its results in its search for the dark matter that (speaking roughly) makes up 25% of the stuff in the universe (see here for the first report and here for some Q&A). [See this article, specifically the “Dark Matter Underfoot” section, for some nontechnical discussion about how experiments like LUX work.] Shortly thereafter, a number of articles in the media made a big deal out of the fact that, simultaneously,
the LUX experiment did not find evidence of dark matter
yet scientists at the LUX experiment appeared to be quite happy
as though this was contradictory and mystifying. Actually, if you think about it carefully, this is perfectly normal and typical, and not the slightest bit surprising. But to make sense of it, you do also have to understand the levels of “happiness” that the LUX scientists are expressing.
The point is that whenever scientists do an experiment whose goal is to look for something whose precise details aren’t known, there are two stories running simultaneously:
The scientists are trying to do the best experiment that they can, in order that their search be as thorough and as expansive as it could possibly be with the equipment that they have available.
The scientists are hoping that the thing that they are looking for (or perhaps something else equally or more interesting) will be within reach of their search.
Notice that humans have control over the first story. The wiser they are at designing their experiment, and the more skillful they are in carrying it out, the more effective their search will be. But they have no control over the second story. Whether their prey lies within their reach, or whether it lies far beyond, requiring the technology of the distant future, is up to nature, not humans. In short, story #1 is about skill and talent, but story #2 is about luck. Even a great experiment can’t do the impossible, and even one that doesn’t work quite as well as it was supposed to can be fortunate.
Of course, there is some interplay between the stories. A disaster in story #1 precludes a happy ending in story #2; if the experiment doesn’t work, there won’t be any discoveries! And the better is the outcome in story #1, the more probable is a success in story #2; a more thorough search is more likely to get lucky.
The LUX researchers, in order to make a discovery, have to be lucky in several ways, as I described on Thursday.
Dark matter (at least some of it) has to be made from particles which are heavier than protons and have uniform properties;
These particles have to be rather smoothly distributed through the Milky Way galaxy, rather than bound up in clumps the way ordinary matter is, so that some of them are likely, just by chance, to be passing through the earth;
And they have to interact with ordinary matter at a rate that is not insanely small — no less than a millionth of the interaction rate of high-energy neutrinos with ordinary matter.
None of these things is necessarily true, given what we know about dark matter from our measurements of the heavens. And if any one of them is false, no detector similar to LUX will ever find dark matter; we’ll need other methods, some of which are already under way.
Now, in this context, what’s the worst thing that could happen to a group of scientists who’ve built an experiment? The worst thing that could happen is that after spending several years preparing the experiment, they find it simply doesn’t work. This can happen! These are very difficult experiments requiring very special and remarkable techniques, and every now and then, in the history of such experiments, an unexpected problem arises that can’t be solved without a complete redesign, which is usually too expensive and in any case means years of delay. Or something just explodes and ruins the experiment. Something like this is extremely depressing and often deeply embarrassing.
So if instead the experiment works, the scientists who designed, built and ran it are of course very relieved and reasonably happy. And if, because of a combination of hard work and cleverness, it works better than they expected and as well as they could have hoped, they’re of course enormously pleased, and proud of their work!
Now what could make them happier still — even ecstatic, to the point of staying up late drinking entire bottles of champagne? A discovery, of course. Discovering what they’re looking for, or perhaps something they weren’t even looking for, if it is truly novel and of fundamental importance. If that happens, then they won’t care as much if their experiment worked better than expected… because, if you’re an experimental scientist, there’s nothing, nothing at all, better than discovering something new about nature.
So with this perspective, I think the LUX scientists’ emotions (as conveyed during his talk by Richard Gaitskell of Brown University, the project’s leader) are actually very easy to understand. They are very happy because their experiment works better than they expected and as well as they hoped… maybe even better than that. For this, they get the high respect and admiration of their colleagues. But make no mistake: they’d certainly be a lot happier — overjoyed and humbled — if they’d discovered dark matter. For that, they’d get a place in the history books, major prizes (perhaps a Nobel, if the Nobel Committee could figure out who to give it to), lasting fame, and the almost unimaginable feeling of having uncovered something about nature that no human previously knew, and that (barring a complete collapse of civilization) will never be forgotten. So yes, they’re happy. But not nearly as happy as can be. They’re frustrated, too, just like the rest of us, that nothing’s shown up yet.
However, they’re also hopeful. Since they’ve built such a good experiment, and since they’ve only run it for such a short time so far, they’ll have another very reasonable shot at finding dark matter when they run it for about a full year, in 2014. Not only will they run it longer, they’ll surely also learn, from their experience so far, to be smarter about how they run it. So expect, at the very least, powerful new limits on dark matter from them in eighteen months or so. And maybe, just maybe, something more.
Tomorrow there will be a solar eclipse (i.e., the moon will pass between the earth and the sun, blocking the sun’s light.) Those of us on the east coast of the United States who wake up to a clear sky at dawn will see the rising sun partially eclipsed, as much as half blocked in many places. [Don’t forget that in the US the clocks are changing tonight, so dawn is one hour earlier, as the clock tells it, than it was today; in New York City sunrise is at 6:30 am tomorrow.] Meanwhile, a substantial partial eclipse will be visible across most of Africa, and a less substantial one in parts of southern Europe. And a little sliver of central Africa will be fortunate enough to see one of nature’s most extraordinary spectacles: a total eclipse of the sun, where for a couple of minutes the sky suddenly goes almost dark, the stars come into view, and the pink prominences and silvery corona of the sun glow and shimmer in the darkness of the moon’s shadow.
Really, this ought to have been scheduled for Halloween. Because if you didn’t know to expect a total solar eclipse, and you didn’t know what was going on, there’d be nothing more terrifying.
Remember: Except in the truly dark heart of a total eclipse, looking at the sun for even a few moments can destroy your eyes; either use specially designed “eclipse glasses” (ordinary sunglasses are completely unsafe) or use a pinhole in a piece of cardboard to project the sun’s image onto a piece of paper or a wall. [As I described here, carefully placed binoculars pointed at a piece of paper or wall will work too — but do not look through them!!! just let the sun’s image go through.] For those watching at sunrise, if there is cloud or haze in the east that dims the sunlight, you can look for a few moments — but make it very quick!
