Of Particular Significance

Category: Astronomy

A Solar System Test of String Theory?!

Baloney. Hogwash. Garbage.

That’s what’s to be found in the phys.org news article claiming that “Scientists at Towson University in Towson, Maryland, have identified a practical, yet overlooked, test of string theory based on the motions of planets, moons and asteroids, reminiscent of Galileo’s famed test of gravity by dropping balls from the Tower of Pisa.”

Sounds too good to be true, right? And it is.

What the scientists have done (or at least claim to have done, and I’ll be happy to take their claims at face value, since I can’t easily check them) is carry out a technique to test the equivalence principle, a foundation stone of Einstein’s theory of gravity, which implies that all objects, no matter what material they are made of and no matter how heavy they are, will be pulled by gravity in the same way… with the same acceleration. This principle, in Einstein’s theory, lies behind why all objects on earth fall with the same acceleration (when air resistance can be neglected), and behind why astronauts float in their space stations.

By looking at the precisely measured orbits of different objects in the solar system, which are made from different materials, the authors (James Overduin, Jack Mitcham and Zoey Warecki of little-known Towson University) claim in their July 2013 paper to have provided new tests that the equivalence principle applies to different materials. That’s very nice work. The principle works to the precision reached by their tests — which aren’t as precise as some other types of tests, but do explore some domains that haven’t previously been explored.

But what’s that got to do with string theory? If you read their paper, you will notice that the word “String Theory” appears in only one obscure sentence in the introduction, referring to a very specific form of string theory [with an extremely light spin-zero field, called the dilaton], implying that their work might be relevant for string theory if we lived in a stringy universe that had such a field. Not even the conclusion, much less the bulk of the paper, mentions strings or string theory. That’s because the paper has nothing to do with testing string theory; it is merely testing Einstein’s theory of gravity.

The reason it can’t test string theory is

String theory doesn’t make a precise prediction for how the equivalence principle will be modified, and among the many possible universes string theory can lead to, many have no measurable modification of the equivalence principle;
Even if a violation of the equivalence principle had been detected, or is detected in the future, it isn’t necessarily due to string theory. It might be due to some other modification of Einstein’s gravity — in fact, the authors consider one such modification in their paper!

So here we have a nice little paper that tests Einstein’s theory of gravity and puts constraints on various alternatives to it — though none of those alternatives is unique to string theory nor is uniquely predicted by string theory. How did this get billed as a practical test of string theory?

You’ll have to ask the author of the phys.org article, which appears to be a Towson University press release. [“Provided by Towson University”, says the last line of the phys.org article.] Or you’ll have to ask the scientists involved (unless one of them is the author) — who ought to be pretty darned embarrassed that their work was billed in this way. I hope they didn’t do this on purpose. It’s certainly great free advertising for Towson University; who cares if the article’s right if people are willing to read it? But a willingness to distort the facts to impress and mislead the public is not a worthy attribute.

POSTED BY Matt Strassler

ON January 13, 2014

Happy (Chilly) New Year

Welcome 2014! And quite a start to the year, with a cold snap that rivals anything we’ve seen in two decades. I don’t remember cold like this since the horrid winter of 1994, when the Northeastern U.S. saw snowstorms and extreme cold that alternated back and forth for weeks. Of course, when I was a child in the 1970s, such chills happened a lot more often; I remember a number of New England mornings where I awoke to a thermometer reading of -20ºFahrenheit (-29ºCelsius) [244 Kelvin].

The scariest negative temperature numbers that one hears about from the media are associated with the “wind chill”, which is a number that is supposed to measure how cold the air “feels” to your skin. But “wind chill” is a rather subjective and controversial measure — there’s no unique way to define it, since you’ll feel differently depending on how much exposed skin you have, on your body weight, on your age and conditioning, etc. By contrast, the temperature measured by a thermometer is defined independent of how humans feel, and experts agree on what it is and means. Oh sure, people use different scales to measure it: Fahrenheit (F), Centigrade or Celsius (C), and Kelvin (K). But the differences are no more than the distinction between meters and feet, or between kilograms and pounds; it’s straightforward, if a bit annoying, to convert from one to the other.

So everyone agrees the temperature is and feels extremely cold, But is it, from the point of nature, really that much colder than usual? To say it another way: it was 84ºF (29ºC) in southern Florida yesterday. How much warmer is that than the -40ºF (-40ºC) that was registered in the cold Minnesota morning?

Well, you might first think: wow, it’s a difference of 124ºF (69ºC), which sounds like a huge difference. But is it really so huge? (more…)

POSTED BY Matt Strassler

ON January 7, 2014

Some Pre-Holiday International Congratulations

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.

POSTED BY Matt Strassler

ON December 20, 2013

No Comet, But Two Crescents

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 but grows and shrinks 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. — 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.

Of course there’s another proof that Venus is closer to the Sun than Earth is: on very rare occasions Venus passes directly between the Earth and the Sun. No more of those “transits” for a long time I’m afraid, but you can see pictures of last June’s transit here, and read about the great scientific value of such transits here.

POSTED BY Matt Strassler

ON December 6, 2013

Wednesday: Sean Carroll & I Interviewed Again by Alan Boyle

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

http://www.blogtalkradio.com/virtually-speaking-science/2013/12/05/alan-boyle-matt-strassler-sean-carroll

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.

Sean Carroll is a Caltech physicist, astrophysicist, writer and speaker, blogger at Preposterous Universe, who recently completed an excellent and now prize-winning popular book (which I highly recommend) on the Higgs particle, entitled “The Particle at the End of the Universe“. Our interviewer Alan Boyle is a noted science writer, author of the book “The Case for Pluto“, winner of many awards, and currently NBC News Digital’s science editor [at the blog “Cosmic Log“].

Sean and I were interviewed in February by Alan on this program; here’s the link. I was interviewed on Virtually Speaking Science once before, by Tom Levenson, about the Large Hadron Collider (here’s the link). Also, my public talk “The Quest for the Higgs Particle” is posted in their website (here’s the link to the audio and to the slides).

POSTED BY Matt Strassler

ON December 4, 2013

Comet ISON Befuddles the Experts

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.

POSTED BY Matt Strassler

ON November 29, 2013

Icy Comet ISON’s Trial By Fire

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.

ISON1430 — Comet C/2012 S1 ISON from the NASA SOHO spacecraft on November 28th as it approached the sun.
[Image credit: NRL/NASA]

POSTED BY Matt Strassler

ON November 28, 2013

Sean Carroll’s Higgs Book Wins a Big Prize

Congratulations to my friend and colleague Sean Carroll, blogger at Preposterous Universe! For his book, The Particle at the End of the Universe, about the theoretical idea and experimental discovery of the Higgs field and its particle (the Higgs `boson‘), he has won the 2013 Royal Society Winton Prize! Not the 3 million that you get for being a famous string or field theorist, or the few hundred thousand that you get for inventing the [Anderson]-(Brout-Englert)-Higgs-(Guralnik-Kibble-Hagen) mechanism, but 25,000 pounds sterling will cover expenses for a few months. And more importantly, the recognition is well-deserved. Well done, Sean!

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…)

POSTED BY Matt Strassler

ON November 25, 2013

A Couple of Questions for Readers

Today I’m looking for insights from readers on two issues that were nagging me over the weekend.

The first issue has to do with the Fukushima nuclear accident and subsequent radiation fears, which I first brought up on this blog last week. I’ve been thinking about how to write articles that explain radioactivity and radiation in rather plain language, and about what we know is dangerous and what we know is not. One of the challenges is to confront the extreme irrationality of people’s fear of radioactivity. I’d like to hear my readers’ opinions of where this fear really comes from. One explanation of this fear that you’ll commonly read is that “radioactivity is scary because you can’t see or smell or feel it”. But that makes no sense; you can’t see, smell, or feel viruses either, or low levels of chemicals, so why aren’t people equally afraid of those things? Especially since the average person is far more at risk of getting cancer or other potentially deadly diseases from viruses (such as papilloma) or from chemicals (asbestos, benzene, etc.) then from radioactivity, despite all the atmospheric nuclear tests in the 1950s and 1960s and the Chernobyl and Fukushima nuclear plant accidents. So I don’t think this explanation is correct; there are plenty of invisible scary things in the world, and people’s fears are totally out of proportion to the true risks. I have my own suspicions as to the real causes, but I am wondering what my readers think.

The second issue is more technical. Comet ISON, dubbed, as is typical of our sensationalist age, “comet of the century” before it has even become easily visible [and it might still be a dud, or it might be the best of the year or even the last twenty years; but of the century? check back in 2099!]) is approaching the sun. There is indeed the tentative possibility, if it survives its very close encounter with the sun on November 28th, that it will give us a spectacular early morning display in December. In preparation, I’m wanting to read more details about the properties of cometary tails, which are generated by the physics of particles and fields (photons, ions, magnetic fields, momentum conservation, etc.). [Here’s a nice video of ISON’s tail and its interaction with the solar wind, the stream of charged particles emanating from the sun; also visible to its upper right is Comet Encke, which by chance is also near the sun. By the way you can also see, watching Encke, that its tail is not a trail; it does not point along its direction of motion but instead points away from the sun.] But I’ve been unable to find anything online other than vague descriptions with no technical information, or references to books or review articles from several decades ago. Do any of my readers know of a roughly up-to-date technical introduction to the physics of comets’ tails?

Thanks!

POSTED BY Matt Strassler

ON November 25, 2013

Ice Cube’s Neutrino Paper Appears

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.

POSTED BY Matt Strassler

ON November 22, 2013

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