Thursday, May 31, 2007

Blue moon, you saw me standing alone...


Image credit:Kostian Iftica, ExploreTheCosmos.com
Today, at 10:04pm EDT, the second full moon of the month of May (as seen from the U.S.) will occur. In popular astronomy, this event (the second full moon in a single month) is called a "blue moon." The moon isn't really blue tonight, it's just a name given to the moon.

But even this name is not technically correct. First, astronomers use Universal Time (Greenwich Mean Time, or the time in Greenwich, England when it is not Daylight Savings Time). And, by that measure, the full moon occurs early in the morning on June 1 (1:04am UT, to be precise). So the astronomical blue moon will be next month, when the second full moon will be June 30 at 1:34pm UT.

Second, using the term "Blue Moon" to refer to the second full moon in a month started as a mistake. This article from Sky & Telescope magazine explains how that mistake was made. In the past, the term "blue moon" referred to the third full moon in a season that had four full moons instead of the normal three. But the mistake is now ingrained in popular culture, and there is no need to try and correct it (in my humble opinion).

Scientifically, there is nothing interesting about a blue moon. It takes the moon 29.5 days to go through a set of phases, and months (except for February) are longer than this. So, it is possible, with the exception of February, to have two full moons in a month. This happens every two and a half years or so, including this (or next) month.

In this way, a blue moon is like Leap Day -- it is an occasional event because our calendar (based on the Earth going exactly once around the sun) doesn't match up exactly with cycles of the moon's phases (a "moonth," if you like) or the Earth's spinning about its axis (a "day").

So, although there is nothing special about this full moon, I am happy for the press. Anything that can get people to go and look at the sky is a bonus. If you go out looking for the blue moon this evening, look for the planet Venus (by far the brightest "star" in the western sky after sunset right now.) The Big Dipper is high in the sky in the early evening, too. Just above and to the right of the moon is the star Antares, the heart of Scorpio. To the left of the moon, the bright "star" is the planet Jupiter. Compare the colors of Jupiter to Antares, and you might be surprised to notice that Antares is definitely reddish in color. (It may be a little hard because of the glare of the moon). And Venus is definitely whiter than either Jupiter or Antares!

Tuesday, May 29, 2007

Is all the romance gone from astronomy?

In this article from CNN, astronomer and planet-hunter Geoff Marcy, nearing the end of a night on the Keck Observatory, laments:

"There are no eyepieces anywhere. In fact, we don't have an eyepiece for the Keck telescope. Some of the romance of astronomy is gone."
Is this true? Is technology removing the "romance" from astronomy?

Most people have the picture of the astronomer as a lone man on a mountain top, looking night after night through an eyepiece on the back of a giant telescope, somehow making measurements of other worlds and other galaxies. There was a time when this was true, but over the past 75 years, astronomy has been transformed by technology. Believe it or not, it was the phtographic plate, invented in the late 1800s, and not computers or digital cameras, that "doomed" the romantic view of astronomy. For, with a photographic plate, astronomers could see fainter than ever before and could take information home to study over long periods of time. By taking information home, more accurate measurements could be made, and more careful analysis performed. Suddenly, an astronomer didn't need months of time to gather all the information he wanted; he could gather a lot of information in a few nights and work on it for months to come.

With computers and digital technology, the science of astronomy has changed even more. Some astronomers don't go to the telescope at all -- some telescopes will take data for the scientist and send it over the internet. There are good points and bad points to this method of observing. I find the quality of my science data isn't as reliable when somebody else takes it, but for some telescopes, like the Hubble Space Telescope, there is no choice!

Modern technology has also opened up new fields that were impossible before. Planets around other stars, Geoff Marcy's main point of study, can only be detected with modern instruments. Yet now, as we find a wide variety of planets around all sorts of stars, our imaginations can run wild with ideas of what we may find. The Hubble Space Telescope has taken amazing pictures of everything from nearby stars and nebulae to the most distant galaxies in the Universe. Due to modern technology, we have discovered black holes a billion times more massive than the sun and watched stars exploding halfway across the Universe.

So, if you consider the "romance" of astronomy to be a lone man on a mountain top struggling to comprehend the Universe, then that romance is lost. But if you, like I, consider the romance of astronomy to be the exotic nature of the Universe around us, then modern technology only serves to open entire new worlds to the power of the human mind and imagination. (Note also that, due to positive changes in society, astronomers are no longer just males; an ever-increasing number of women are contributing to every aspect of the science.)

A News Note: This week, astronomers from around the country have congregated in Honolulu for the summer meeting of the American Astronomical Society. I am not there due to teaching commitments, but you will probably see lots of astronomy news in the coming days as new results are announced!

Thursday, May 24, 2007

An astronomer without a computer feels so lost

Computers are a central element to all modern astronomy research. All of our observations are taken digitally and written to computer. Interpreting these images requires a computer. We write computer programs to simulate the Universe, to mine our data, and to test our work. We are in constant touch with other astronomers by email. Even most of our professional journals are online, so we read them online rather than walking down to the library.

My computer is getting a tune-up this week. The operating system was quite old, and many new programs wouldn't work on the machine. So, while the machine is getting upgraded, I only have my laptop. That means I can check email, read journals, and do blog postings, but I can't do very much research.

So, here's hoping that the upgrade goes smoothly and I can be back working again later today. In the meantime, I will work on writing papers and a few other chores that need done.

Wednesday, May 23, 2007

Will Astronauts visit Hubble's replacement?

If next fall's visit by astronauts is successful, the Hubble Space Telescope will be with us for at least another five years. But plans are already in place to launch NASA's next large space telescope, the James Webb Space Telescope, in 2013 (although I'd be surprised to see it launched that year).

Although the Hubble has been well-served by four (and soon a fifth) servicing missions by astronauts, we've always assumed that JWST would not be able to be visited by astronauts. Hubble is in low Earth orbit (just a few hundred miles up), where the Space Shuttle can easily fly. But the JWST is going to be at the second Lagrange point, a spot about 1 million miles away from the Earth where the Earth and the Sun's gravity balance perfectly. The main reason for this distance is to get the telescope, which will look at infrared light, far from the heat of Earth. But none of our current rockets can carry humans to this Lagrange point, so it seems that repair of the telescope is out.

So I was surprised today when NASA announced that it was going to add a docking port to JWST in case future astronauts ever visit the spacecraft. Their reasoning is that if this expensive telescope fails to work, their new Orion rockets might be able to take astronauts to the Lagrange point to try and salvage the telescope.

If astronauts were to go to the JWST, it would mark the furthest humans had ever ventured away from the Earth -- it is nearly four times further from the Earth than the moon. It would also be a very risky and very expensive mission. Would it be worth the trouble? I don't know. Certainly astronauts would probably like to try if the chance of success seemed reasonable, and I don't doubt their ability to fix the spacecraft.

But adding a docking ring adds weight and complexity to the telescope, two things that are not always desirable. I am not a space engineer, so I really do not know how much the docking ring affects the spacecraft. But it could also mean that some science may need to be scaled back to reduce the weight of the telescope. Again, this is just my guess, I don't know.

So, I have mixed feelings about the announcement. In some ways, I am glad NASA is thinking ahead and allowing for new possibilities we hadn't previously dreamed of. But I have reservations, and until I know more about the plans, I'll remain skeptical.

Saturday, May 19, 2007

Ice Geysers

Image Credit: NASA/JPL/Space Science Institute

I received an email from Tom B. this week asking about this news story claiming that water geysers observed on Saturn's moon Enceladus may be due to friction of ice plates rubbing together:

You may have seen the new suggestion regarding how gas plumes form on Enceladus. It suggests that thick ice plates are rubbing together and creating a vapor that escapes as plumes of water vapor. Would you please provide some explanation of how a place as cold as Enceladus could produce anything so hot as water vapor simply by friction?

I can certainly try to explain it! In the outer reaches of our Solar System, water (usually in the form of ice) is very common. Most of the moons, comets, and even larger objects (like Pluto) are made mostly of water ice. Partly this is because the outer solar system is so cold -- temperatures out there are a chilly -325 degrees Fahrenheit! So if you want to make geysers out of this water, you would need to warm the water up by 350 degrees, right?

Well, not necessarily. In my last post, I was talking about the strange forms of "hot ice" that could exist on a Neptune-mass planet around another star. As part of that post, I included this graph showing the phases of water as a function of temperature and atmospheric pressure.

The moons in the outer solar system (except for Titan) have extremely tenuous atmospheres; essentially they have no air pressure. So, looking at the diagram, you notice that the freezing point of water in very low atmospheric pressures goes way down -- only 200 Kelvin (-100 Fahrenheit). So, on these moons, you don't need to warm up the ice quite as much before it changes into a gas, at which point it will find its way through any cracks of the moon's frozen surface and vent into space.

But we also need to consider these big plates of ice. Enceladus orbits Saturn in a near-perfect circle. But it is not quite perfect -- some times it is slightly closer to Saturn than other times. And when it gets closer to Saturn, it gets squeezed a little more. This energy from squeezing (or gravitational tides) seems to cause plate tectonics on Enceladus, just like on Earth, except with water ice instead of rock making up the plates.

On Earth, plate tectonics is responsible for many volcanoes and for earthquakes. Until this press release, scientists thought that the geysers of Enceladus were like Earth's volcanoes -- ice is melted deep in the moon, and near the edges of these plates, the magma (in this case, water), finds it easier to escape to the surface and be erupted out.

So, finally, to the new idea about the geysers. This new concept blames the friction of the ice plates grinding together for the heating of the ice. We on Earth know of frictional heating -- it is why your hands get warm when you rub them together, and why your car's brakes overheat if you use them too much. Friction happens during earthquakes, too, and during moonquakes on Enceladus. In both cases, tremendous amounts of heat are generated. In an earthquake with a magnitude of 4.0 (enough to cause noticeable shaking, but in most of the U.S., there would be little or no damage -- Californians experience 4.0 earthquakes all the time), there is as much energy released as a ton of TNT. A major earthquake, say magnitude 7.0, releases 32 megatons of energy -- dozens of the largest nuclear weapons worth!

This energy has to go somewhere, and most of it goes into friction and heat. As you might imagine, this heat can be tremendous. But on the Earth, it isn't enough to melt rock, which has to get up to thousands of degrees to melt. So an extra couple of hundred degrees deep in the Earth makes no noticeable change. But on Enceladus, this energy would be enough to change the ice into gas, which would then vent out through the fault line that had the moonquake. Remember, these ice sheets are miles thick and acting much more like rocks on Earth than like the ice floes in our arctic oceans (which do gently rub together, and don't create geysers).

The calculations reported in the news story on Enceladus show that friction alone makes enough energy -- remember we are talking about thousands of tons of ice rubbing against each other. But this isn't proof that the geysers on Enceladus are powered by friction; it just shows that it is possible. Yet one thing we know from decades of modern physics is that when strange things are possible (think of black holes and neutron stars), these things tend to happen.

So, in short, the reason the frigid ice on Enceladus could melt due to friction is (a) you don't need to warm it up too much, and (b) remember that we are talking about tremendous amounts of ice, sheets of ice a dozen miles thick, rubbing against each other in sudden releases of energy. And more tests are needed to show if this idea is correct or not.

Thursday, May 17, 2007

A Snowball in hell?

A news story making the rounds for the past few days contains claims that astronomers have found a hot planet (called "GJ 436b") made out of ice. How can this be?

First, let me state that I am far from convinced about this claim. What do we really know about the planet? We know its mass, which we have measured by the planet's gravitational pull on its parent star. We also know its diameter, because the planet passes in front of its star as we see it from Earth, and we can measure how much light it blocks out. Because we know its diameter and its mass, we also know its average density. In these ways, the planet is very close to a twin of Neptune.

But this is really all we know for certain. We can guess how hot GJ 436b must be based on how close it is to its parent star (this works well in our solar system for Mercury and Mars, it's close for Earth, and fails miserably for Venus). But we have no direct data on what the planet is made out of. The claim that the planet must be made out of "hot water ice" is a guess. An educated guess, but just a guess. So don't start buying beachfront real estate on GJ 436b yet.

Why would astronomers guess that the planet is made of "hot ice?" First, in our solar system, the planets Uranus and Neptune, the planets closest in size and average density to GJ 436b, are thought to be made of ices (including water ice) covered by an extraordinarily thick atmosphere of methane. So, it is not unreasonable to guess that all planets the size and density of Neptune and Uranus look like Neptune and Uranus. But, again, this is just an educated guess.

How can ice exist if the planet is hot? Look at the phase diagram for water below, which shows what form water will take as a function of its temperature and its pressure. For temperatures and pressures on the Earth (about 250-310 degrees Kelvin and a pressure of about 100,000 Pascals), water is near the point where all three phases of water -- gas (tan), liquid (green), and ice/solid (blue) can exist. On the diagram, notice that even at extremely hot temperatures, like 600 Kelvin (by chance, about 600 degrees Fahrenheit), water can be in the form of ice if it is at high pressures -- at least 10 million times the pressure on Earth's surface.

Image credit: Martin Chaplin / London South Bank University

So, if GJ 436b has a very thick atmosphere, like Uranus and Neptune, the pressure inside the planet can be high enough to make water turn into ice, even though it would be very hot! This ice is not quite like ice on Earth -- the structure of ice crystals on Earth is not the same structure of ice crystals at high pressure. And, if this hypothesis is right, most likely the atmosphere of the planet would go through a gradual transition from air to liquid to solid. This is quite unlike the Earth, where there is an abrupt transition from the atmosphere to the sea and again from the sea to the sea floor. On GJ 436b, there is probably no real "surface" to the planet.

So, as I've said before, take this new press announcement with a grain of salt. Until we have observations showing us what a planet around another star is made out of, we can only make educated guesses. And the makeup of this "snowball in hell," GJ 436b, remains just that -- an educated guess.

Tuesday, May 15, 2007

The Dark Ring

The title to this post sounds like the title of a bad cross between Star Wars, The Lord of the Rings, and maybe a little of Wagner's Ring Cycle to boot. But, actually, this is the topic of a press conference NASA will be holding later today to announce some new findings about dark matter.

I'm a little interested in what the press conference has to say, although I expect a lot of the announcement to be overblown (like NASA often does with scientific results). But what is the big deal?

Most of you have probably heard about dark matter -- matter that has gravity but doesn't interact with light, the way normal matter does. There are many different lines of evidence for dark matter. So why would it be big news?

One of the problems with dark matter is that we don't know what it is. Some physics theories predict particles with properties similar to dark matter, but until we actually detect dark matter in the laboratory, dark matter remains just a hypothesis.

There is a competing explanation for the observations of "missing matter" called MOND (for "Modified Newtonian Dynamics"). The MOND hypothesis is that there is not missing matter, just that our theory of gravity is wrong. One of the main problems with MOND has been that it has proven very good at "postdiction," or explaining observations once they have been made, but it hasn't made any predictions that can be tested and, if proven wrong, falsify the theory.

This is a crucial point. Any scientific theory must be able to make predictions that, if proven wrong, falsify the theory. Einstein's General Relativity made several predictions, such as the existence of gravity waves and the changing of time itself in gravity, that were crucial to the whole theory but were not tested until decades later. And relativity passed those tests. Until MOND can make a prediction that both differs from dark matter and, if shown to be wrong, falsifies the theory, MOND remains an interesting concept.

MOND adherents claim the same is true of dark matter, but the best dark matter theories do make a prediction that can falsify dark matter -- the existence of dark matter particles with certain properties. In the coming few decades, particle accelerators on earth should be able to detect signatures of these particles. If we don't detect them, dark matter is wrong.

Today's NASA press conference is going to be about the discovery of a "ring" of dark matter in a cluster of galaxies. We see the evidence for this ring because the gravity from the dark matter distorts light from more distant galaxies, bending them into funny shapes. And, when we look with a variety of instruments, we don't see regular matter shaped in the needed ring. So, the ring must be dark matter. Probably.

About a year ago, NASA made a similar press release from another galaxy cluster where the center of the gravitational pull of the galaxy cluster didn't match up with the visible, ordinary matter. There are probably dozens more galaxy clusters where similar observations can be made, so you will probably see many more press releases in the future. The fact remains, though, that until we detect dark matter in the laboratory, some reasonable scientists will doubt the existence of dark matter.

This may be the best legacy of MOND. I have lots of problems with MOND, too many to type out. But it is forcing astronomers to stay on their toes and look for new ways to test gravity and our theories about the makeup of the Universe. And that is a good thing.

Friday, May 11, 2007

How old is it?

Just like stars in Hollywood, stars in the heavens don't like you to know how old they really are. There are a few clues -- we know that the biggest stars don't live more than a few billion years, and when a star is getting ready to die, we know because it begins to swell up into a red giant star. But for most stars, we can only make educated guesses.

But sometimes we get lucky. Anna Frebel, a postdoc here at the University of Texas, announced yesterday that she has discovered a star nearly as old as the Universe itself. Frebel's luck was in finding a star where she could detect radioactive elements she could use as clocks to measure the age of the star. Her skill comes in recognizing the utility of those elements and being able to make precise measurements, which is very difficult to do.

The heaviest elements in the Universe, elements like uranium, lead, gold, and mercury, are made in the death throes of dying stars. Some are made by slow processes in the atmospheres of red giants, while others are made quickly during supernova explosions. Some elements can be made both ways, while others are only made by one process or the other. But the amazing thing is that the relative amounts of each element produced one way or another doesn't change from one star to the next. For example, for every three atoms of the element europium in a star, you will find one atom of barium.

So, if you can find and measure radioactive elements in a star and can predict how much of that material the star must have started with, you can determine how old the star is. This is just like radioisotope dating on the planet Earth. It's not used that much in stars because the radioactive elements are hard to find -- their "fingerprints" in the light from the star are usually buried by fingerprints of other metals, especially iron. But in some of the first stars, not much iron had been created in the lifetime of the Universe, so those radioactive lines are buried.

What Frebel did was measure the amount of uranium and thorium in her star. These are both radioactive elements, and they decay at different rates. She then compared the amount of those two elements with three elements that are not radioactive: europium, osmium, and iridium. She then calculated how much time had to pass for the "missing" amounts of uranium and thorium to have decayed. And the answer, which gives the age of the star, is: 13.2 billion years.

How accurate is this measurement? There are ways to make mistakes in measuring how much of each element, and there are some uncertainties in the exact ratios of each element that the star would have started with. For any single element, the error is pretty large. But, because Frebel had six measurements (two radioactive elements to compare to each of three stable elements), those errors get reduced in size. So, the age of the star is very likely within a billion years of being correct.

This measurement is an important one. Since this star is in the Universe, we know that it has to be younger than the age of the entire Universe. But because the star has so little iron and other metals, we think it must have been made early in the Universe. Once our galaxy started producing iron, it produced it at a very fast rate.

From studying the echoes of the Big Bang, astronomers have estimated the age of the Universe to be 13.7 billion years. This agrees well with Frebel's age for her star of 13.2 billion years. This is comforting to us as astronomers. Two completely different lines of reasoning give roughly the same answer for the age of the Universe. This makes astronomers more confident that our understanding of the physics behind the formation and early history of the Universe is correct. And there are other even more different observations that give a similar age to the Universe, giving us yet more confidence in this age.

Thursday, May 10, 2007

Government oversight

I'm always a little surprised when I hear tales about mishandling of government money. Not because it is unusual (alas, it isn't), but because of all the hoops, red tape, and rules surrounding research money I get from the government. You would only have to read the several webpages dealing with proper travel planning procedures that I have been sent to wonder how anything ever gets done in government. It reminds me of a quote attributed to Eugene McCarthy:

"The only thing that saves us from the bureaucracy is inefficiency. An efficient bureaucracy is the greatest threat to liberty."

Whatever the truth may actually be, I am enmeshed in writing a slew of end-of-the-year reports for various research grants through which I receive funding. I have to make a list of all of the papers I've written, talks I've given, and places I've gone. I also have to summarize progress and results of research projects, educational and outreach progress, and any other relevant information.

So, as I'm gathering statistics, I thought I'd just mention a few random stats that I've uncovered about this site. Since September (when my current research grant that supports this site started), the monthly number of visitors to the blog has climbed from 660 to 3140. This number supposedly excludes robots (who don't like astronomy anyway) and other automated web indexing programs. So, there are roughly five times more of you now than in September. Welcome! During that same 9 month period, the web site served up over 1.1 gigabytes of data -- not bad for a website where most of the content is text!

Also during that time, I started a page on MySpace. While it still needs sprucing up to look a bit more exciting, the number of friends there continues to climb. Right now it's at a not-so-astronomical 100 people (and about a dozen of those are personal friends, groups I'm interested in, and a few famous dead scientists). But hopefully that continues to grow and bring in new readers.

So, with a little work and a little luck, this site will continue to grow in the coming year. Thanks to all of you who read it! And, if you want to support your local scientist, feel free to write or email your Representative in Congress (or Parliament or Assembly or href="http://palaceoffice.gov.to/"Monarch, or whatever your national government may be) and request increased support for scientific research.

Tuesday, May 08, 2007

The brightest supernova ever?


Photo credit: Lick/UC Berkeley/J.Bloom & C.Hansen

This morning, there are dozens of news stories on the internet about what is being called the brightest supernova ever seen. To be honest, I was a bit surprised about the hubbub, as the details of this supernova were published in December. Although the basic idea behind this explosion is relatively unchanged, new evidence has come in that supports the hypothesis, and, as always, NASA is hungry for press releases.

So, what's the big deal? The explosion we are seeing is the death of a very massive star. Typically, when a massive star dies, it has run out of fuel in its core, having burned all of its hydrogen gas through successive stages into iron. The iron tries to burn in a nuclear reaction, but that absorbs energy instead of releasing it, and the center of the star collapses into a neutron star or a black hole. The rebound from this explosion rips the star apart.

But that doesn't seem to be the case for Supernova 2006gy (the name astronomers use for this supernova). The supernova has stayed very bright far longer than expected for this type of supernova. The only explanation we can think of is a strange physics phenomenon called "pair instability." Pretty much, that means that the center of the star gets so amazingly hot that the light radiation in the core of the star (in the form of gamma rays) becomes so energetic that the gamma rays are converted into matter and antimatter. This is a direct result of Einstein's equation E=mc2, which means that energy can turn into matter and vice versa. It takes some special circumstances (very high temperatures and densities), but in these extreme stars, those conditions are met. And, as you may know, when the antimatter hits normal matter, it annihilates and releases energy, which then is turned back into matter and antimatter again because of the extreme conditions. This circumstance is unstable, and the entire stare is ripped apart in a huge explosion. We don't know if a black hole might be left behind or not, but most of the star (which is 120 times the mass of the sun or more!) is blasted into space.

This supernova mechanism has been proposed before, but astronomers didn't expect to see it. In most galaxies these days, the giant stars are polluted by lots of metals made in previous generations of stars. Before the star finishes its life cycle, these metals act almost like a sail, and light from the star pushes the metals away from the star. When the metals leave, they take a lot of hydrogen and helium with them. In this way, a star that started life with a mass 100 times that of the sun is whittled down to fewer than 10 times the mass of the sun in just a few million years. The resulting star still explodes, but in the "normal" way.

So, if supernova 2006gy is a pair instability supernova, astronomers will need to ask how such a thing could happen in the modern Universe. Can some monster stars somehow manage to hold on to their envelopes? Or did this star form in a galaxy or a part of a galaxy where there were far fewer metals than normal? Or have we mis-interpreted the data so far? These questions will keep supernova astronomers occupied for years to come!

Monday, May 07, 2007

Back in the desert

On Friday I hopped on a plane (OK, I actually walked on the plane; if I had hopped on, I suspect they would have called security). After hopping/walking on the plane, I traveled to Tucson, Arizona, for a visit. A good friend had a wedding on Saturday, and I thought I would take a few days to visit colleagues at Steward Observatory today before returning home. I probably have several weeks worth of science I could accomplish here, but I'll settle for a day.

The wedding and reception was a lot of fun, though some may question my definition of "fun" if you consider that at least half of the crowd consisted of astronomers from across the nation. Talk would vary from how people/families are doing to evaluations of various astronomy departments to discussion of new science to how we could get various people out on the dance floor, all within a few sentences. But, if we were being geeky, we were all being geeky together. So, congratulations to Jason and Haiyin! And I'll be back to more exciting news from astronomy in a few days.

Wednesday, May 02, 2007

Is Dark Energy Bad For Astronomy?

Yesterday I became aware of this article by a cosmologist named Simon White (warning: the article is technical). Simon White is a well-known and well-resepcted astronomer, so many of us are mulling over his assertation that the study of "Dark Energy" could be bad to astronomy science. I have not yet read White's monograph carefully the entire way through, but I can sum up a few points.

"Dark Energy" is a name that has stuck to a phenomenon we observe in the universe -- that, as time goes on, the expansion of the universe seems to be speeding up. This is odd, because all the forces we know about in the Universe (light and gravity, mainly), work to slow down the expanding Universe. Gravity tries to act as a brake, but there seems to be a mysterious force still pushing on the accelerator.

The idea of dark energy has captured the imagination of the public, as well as many astronomers and physicists. But understanding dark energy is going to be hard and likely take decades to make much progress. And any such progress will require large investments of money and giant research collaborations.

White's main concerns are that if astronomers focus too much on exploring dark energy, we will be putting all of our eggs in one basket by requiring most of our monetary and scientific resources to go to one project that, while very interesting, may not have that much of an impact on understanding how stars and galaxies work.

The concensus of people that I've talked to is that while White makes some good points, he misses the mark a bit. First, although many large experiments are being developed to study dark energy, we are also finding new sources of money for these experiments (the Department Of Energy is supporting some research, and private individuals are donating money out of interest in dark energy), so large research projects are not eating into the budget as badly as they might.

Another concern of White's is that large collaborations will devour graduate students and postdocs, who will not get recognition for their work. This has been a concern in other large astronomy projects, such as the Sloan Digital Sky Survey, but these young researchers are generally recognized for the science they are doing.

White raises many valid points in his monograph, however. Astronomy has been different from other fields (like particle physics) in many ways, and this cultural difference is, we feel, a positive. It is good for senior and knowledgeable people to point out their concerns so that we remain on our toes and avoid making decisions that might harm the varied and vibrant research of astronomy. But I do not think that the study of Dark Energy is dangerous to the science. The danger would come if the study of Dark Energy were to begin to consume all of our resources. And I just don't see us allowing this to happen in the forseeable future. If anything, studies of Dark Energy allow astronomers to continue to wax poetic on how exotic the universe is, and how much there remains for us humans to understand.

Tuesday, May 01, 2007

Our future?

In this story from Apace.com, the author presents a new study of the far-future fate of the Universe, given what we know today. The basic gist of the article is that, if Dark Energy is real and behaves like Einstein's cosmological constant, in the distant future, all other galaxies and light from outside our galaxy will be accelerated away from us at beyond the speed of light, meaning that we will never be able to see anything outside our galaxy again. (We're talking 100 billion years from now, or 10 times the current age of the Universe.) In that sense, we are lucky to live when we do, as astronomers in that future time will not be able to figure out the history of their universe.

Many scientific predictions exist about the end of the Universe. Some are fairly mundane, in that they take the Universe as we know it and let it evolve into the future (the story above is one of these). Others hypothesize new physics (such as the "Big Rip," where the Universe expands so fast that it rips itself and everything within it asunder, or the ekpyrotic brane model, where a set of hyperdimensional membranes collide, destroying our Universe while spawning a new Universe).

One thing we learn as students is that extrapolating (or predicting future results based on what we know now) is very risky. You might stay close to the right answer for a long time, but eventually you can be quite wrong. One example is the prediction of asteroid orbits in our Solar System. We can predict very precisely where an asteroid will be a hundred years from now, and reasonably well a thousand or more years from now. But using almost exactly the same models of the Solar System with tiny differences (perhaps due to the uncertainty in where a planet is by as small as a mile or two) and looking forward millions of years, the positions of asteroids will be completely different, such that you'd never guess the original models were almost identical.

When astronomers predict the ultimate fate of the universe, we are making wild guesses. Guesses based in science and physics, yes, but still guesses. Tiny forces that we don't yet know about may eventually determine the ultimate fate of everything in our Universe. So whenever you read about the ultimate fate of the Universe, remember that these are more like descriptions of possibilities rather than hard predictions.