Blogs / Cosmic Variance

I spent last week attending the “Formation and Evolution of Black Holes” conference at the Aspen Center for Physics, organized by Andrea Ghez, Vicky Kalogera, Fred Rasio, and Steinn Sigurdsson (who blogs over at the Dynamics of Cats). It was a great mix of observers and theorists, and we covered the full range, from stellar-mass black holes in our galaxy to supermassive black holes on the far side of the Universe. I was particularly interested in two topics: gravitational-wave recoil and black hole binary inspiral (I’ll blog about both soon enough). And I made another pilgrimage to the Highlands bowl, this time with 15″ of virgin powder.

The Aspen Center runs a public lecture series in conjunction with each conference. So last Wednesday Andrea Ghez gave a lecture on the black hole at the center of our galaxy. It’s our closest big black hole, roughly 25,000 light years (2×10¹⁷ kilometers) away, and four million times the mass of our Sun. Andrea has been leading a team studying the motion of stars orbiting around this black hole. These orbits are one of the best ways (short of the detection of gravitational waves from black hole mergers) of confirming that black holes exist. The orbits tell us the mass of the central object. And the innermost passage of the closest orbit gives us an upper limit on the size of the central object. Combining these numbers gives us a lower limit to the density of the “dark object” at the center of our galaxy. At this point, a black hole is the only viable model for what we see. There is no way to make sense of the orbits using a cluster of (dark) stars at the center, or a massive gas cloud, or anything else we can think of. Gravity tells us that any normal stuff we put there (including “conventional” dark matter) will evaporate or collapse to a black hole. We are not yet probing the horizon of the black hole (in some sense, its surface), but we are getting closer and closer with each passing year.

But, more importantly, Andrea is responsible for one of the coolest movies in all of science:

This shows the orbits of stars around our galactic center. This isn’t an artist’s conception. This isn’t some abstraction of other data. This is a real movie of stars circling the black hole over the last 15 years. In particular, watch S-02. It loops around the black hole, and closes its orbit; we have watched it over one full S-02 “year”. It is an incredible feat of observational astronomy to make these movies. It requires adaptive optics on the largest telescopes in the world (the Keck telescopes on Mauna Kea). We used to think of the heavens as eternal and unchanging. Now we watch movies of stars orbiting black holes.

I’ve been meaning to link to this post at the arXiv blog, which is a great source of quirky and interesting new papers. In this case they are pointing to a speculative but interesting paper by Martin Perl and Holger Mueller, which suggests an experimental search for gradients in dark energy by way of atom interferometry.

But I’m unable to get past this part of the blog post:

The notion of dark energy is peculiar, even by cosmological standards.

Cosmologists have foisted the idea upon us to explain the apparent accelerating expansion of the Universe. They say that this acceleration is caused by energy that fills space at a density of 10^-10 joules per cubic metre.

What’s strange about this idea is that as space expands, so too does the amount of energy. If you’ve spotted the flaw in this argument, you’re not alone. Forgetting the law of conservation of energy is no small oversight.

I like to think that, if I were not a professional cosmologist, I would still find it hard to believe that hundreds of cosmologists around the world have latched on to an idea that violates a bedrock principle of physics, simply because they “forgot” it. If the idea of dark energy were in conflict with some other much more fundamental principle, I suspect the theory would be a lot less popular.

But many people have just this reaction. It’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920’s: energy is not conserved in general relativity. (With caveats to be explained below.)

The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.

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Hey, nobody told me that having a blog would involve homework. But here’s Jerry Coyne, nudging me into talking about a story in this morning’s New York Times. Fortunately it’s interesting enough to be worth taking a swipe at.

The news is an interesting result from RHIC, the Relativistic Heavy Ion Collider at Brookhaven Lab on Long Island. RHIC has been quite the source of surprising new results since it turned on in 2000. It’s not the highest-energy collider in the world, nor did it ever aim to be; instead, it creates novel conditions by smashing together the nuclei of gold atoms. Gold nuclei have lots of particles — 79 protons and 118 neutrons — so the collisions make a soup known as the quark-gluon plasma. (We ordinarily think of a proton or neutron as consisting of three quarks, but those are just the “valence” quarks that are always there. There are also large numbers of quark-antiquark pairs popping in and out of existence, not to mention scads of force-carrying gluons that hold the quarks together. So you are actually create a huge number of quarks and gluons in each collision.)

We think we understand the basic rules of quarks and gluons very well — they’re described by the theory of quantum chromodynamics (QCD), and Nobel prizes have already been handed out. But knowing the basic rules is one thing, and knowing how they play out in reality is something very different. We understand the basic rules of electrons and electromagnetism very well, but chemistry and biology (not to mention atomic physics) are still surprising us. Likewise with quarks and gluons: the results at RHIC have yielded quite a few surprises. Most interestingly, in the aftermath of the collisions the hot plasma of quarks and gluons seems to behave more like a dense fluid than a bunch of freely-moving individual particles. Still much to be learned.

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If we celebrate provocative new experimental findings, we should also celebrate the careful null results (experiments that agree with existing theories) on which much of science is based. Back in October we pointed to a new analysis that used observations of gravitational lensing by large-scale structure to test Einstein’s general relativity on cosmological scales, with the intriguing result that it didn’t seem to fit. And the caveat that it probably would end up fitting once we understood things better, but it’s always important to follow up on these kinds of clues.

So now we understand things a bit better, and a number of people have been working to dig into this apparent anomaly. Here is a new paper from this week, that presents their own way of using these kinds of data to test GR against large-scale structure.

Testing General Relativity with Current Cosmological Data
Authors: Scott F. Daniel, Eric V. Linder, Tristan L. Smith, Robert R. Caldwell, Asantha Cooray, Alexie Leauthaud, Lucas Lombriser

Abstract: Deviations from general relativity, such as could be responsible for the cosmic acceleration, would influence the growth of large scale structure and the deflection of light by that structure. We clarify the relations between several different model independent approaches to deviations from general relativity appearing in the literature, devising a translation table. We examine current constraints on such deviations, using weak gravitational lensing data of the CFHTLS and COSMOS surveys, cosmic microwave background radiation data of WMAP5, and supernova distance data of Union2. Markov Chain Monte Carlo likelihood analysis of the parameters over various redshift ranges yields consistency with general relativity at the 95% confidence level.

One issue, as we noted way back when, is that it’s very hard to “test GR” without committing yourself to a model of the mass and energy sources that are causing the curvature of spacetime. So the game is to make some plausible assumptions and see where you go from there. This group seems to have assembled a sensible framework for testing deviations from Einstein, and come back with the answer that everything is on the right track.

We keep getting new and better data, of course, so we’ll keep testing. I suspect Einstein will continue to be right, but probably a lot of people thought Newton would continue to be right a century ago.

This is an idea that has been bouncing around for a while, but is now apparently seen in experiments: real-world photosynthesis taking advantage of quantum mechanics. (Story in Wired, via @symmetrymag. Here’s the Nature paper on which it’s all based.)

The idea is both simple and awesome: you want to transport energy through an “antenna protein” in a plant cell to the “reaction-center proteins” where it is chemically converted into something useful for the rest of the plant. Obviously you’d like to transport that energy in the most efficient way possible, but you’re in a warm and wet environment where losses are to be expected. But the plants somehow manage the nearly impossible, of sending the energy with nearly perfect efficiency through the judicious use of quantum mechanics.

We can think about this in terms of Feynman’s way of talking about quantum mechanics: rather than a particle taking a unique path between two points, as in classical mechanics, a quantum particle takes every possible path, with simple paths getting a bit more weight than complicated ones. In the case of the protein, different paths for the energy might be more or less efficient at any particular moment, but this bit of quantum trickery allows the energy to find the best possible route at any one time. Imagine at rush hour, if your car could take every possible route from your home to the office, and the time it officially took would be whatever turned out to be the shortest path. How awesome would that be?

The reason you can’t do that is that your car is a giant macroscopic object that can’t really be in two places at once, even though the world is governed by quantum mechanics at a deep level. And the reason for that is decoherence — even if you tried to put your car into a superposition of “take the freeway” and “take the local roads,” it is constantly interacting with the outside world, which “collapses the wave function” and keeps your car looking extremely classical.

Proteins in plants aren’t as big as cars, but they’re still made of a very large number of atoms, and they’re constantly bumping into other molecules around them. That’s why it’s amazing that they can actually maintain quantum coherence long enough to pull off this energy-transport trick. Previous studies had hinted at the possibility, but only by cooling the proteins down and shielding them from external jiggling. This new work happens at room temperature in the context of marine algae, so it seems to indicate that it can happen in real environments.

One step closer to building my teleportation machine. Get to work, quantum engineers!

Every year, not long after the state of the union address, the administration unveils its budget request to Congress. Then comes the long authorization and appropriations process; in an election year I’d bet that they try hard to have it done before November. The Obama administration’s request came out yesterday, and so it’s time to take a look at how science may fare next year.

Jeffrey Mervis at ScienceInsider over at the AAAS has a nice article summarizing the general picture for science in the budget, including an 8% increase for the National Science Foundation and a smaller 3% boost to the National Institutes of Health. The Office of Science and Technology Policy (headed by the president’s science advisor) has a set of fact sheets on science policy. Check out the one on doubling the science budget – the administration is on track for doing just that by 2017. Will Congress support that?

But, being funded by it, I always start first with the DOE Office of Science. The DOE has a summary document with budget highlights; for the Office of Science the most succinct table shows the breakdown by program and year (click on it for a bigger version):

Overall, the OS is looking at a 4.4% increase over FY2009, not including the stimulus bump in 2009, listed in the column called “recovery”. In a year when the administration wants to freeze discretionary spending, that is not bad for science. It’s clearly coming from savings elsewhere, meaning someone’s program got cut, and those people (and their congressional representatives) will be fighting like crazy to restore it.

Within the OS there are winners and losers as well. Basic Energy Sciences, which covers a host of research in condensed matter including nanotechnology, materials, and multipurpose facilities such as the large light sources, gets the lion’s share of the OS budget, and are slated for a 12% increase. I think this reflects the administration’s desire to foster research in areas that could lead in the near to medium term to new sources of energy. That increase, though, along with increases for advanced computing and bio/environment research, has to come from the other programs in OS, and it appears that fusion energy (-10%) and a line titled “Congressionally Directed Projects” . Now what on earth is that?

Now, I am not a Washington insider by any means, but I don’t recall seeing that designation explicitly in the tables before. I believe, though, that it means projects funded through Congressional earmarks. Are all earmark-funded projects being killed? It certainly appears so…

Within my own field the tea leaves say that the administration is requesting that the Tevatron remain in operation through 2011, support participation in the LHC and work on future upgrades to the experiments, and begin to develop the next big project at Fermilab, so-called “Project X” (which deserves a post all by itself some day). Project X will deliver an ultra-intense beam of protons for neutrino and rare decay experiments, including the Long Baseline Neutrino Experiment proposed for the Deep Underground Science and Engineering Laboratory (DUSEL) in the Homestake Mine in Lead, South Dakota. There is also a substantial appropriation for the Dark Energy Survey; Fermilab is building the camera.

So begins the 2011 budget cycle.

Last week in Aspen we learned that this week would be when a major decision was reached by CERN at the annual Chamonix meeting as to how to operate the LHC at high energy. Following the magnet quench incident in September 2008, a year-long shutdown ensued for repairs to the magnets, and retrofitting of the rest of the machine for better quench protection circuitry and helium pressure release valves. Not all sectors were warmed up to room temperature for the retrofit last year, but all magnets were trained to go as high as beam energies of 5 TeV (design energy is 7 TeV per beam).

In November and December the LHC commissioning resumed, and it became the world’s highest energy collider on December 8, eventually delivering about 50,000 collisions at 2.36 TeV to CMS and ATLAS before shutting down for Christmas.

But the question facing the LHC managers this week was whether attempting to operate the LHC at 5 TeV on 5 TeV in 2010 was worth the risk to the machine itself. Clearly another disaster of the scale of the one in 2008 would cripple the program for a long time. In the end the decision is to operate the LHC at 3.5 TeV on 3.5 TeV (7 TeV collision energy, 3.5 times that of the Tevatron) and accumulate a substantial amount of physics-quality data: 1 inverse femtobarn, or stop by the end f 2011, whichever comes first. This corresponds to something like ten trillion proton-proton collisions, of which only a small fraction will yield events interesting enough to record for later analysis by the experiments, and of these, only a tiny fraction yielding data relevant for physics.

After a one to one-and-a-half year shutdown in 2012 to retrofit the rest of the machine and make other preparations, the LHC will attempt to double the energy, to 14 TeV in the center of mass, in 2013 and accumulate substantial physics data. My best guess is that if the Higgs boson is to be discovered, it will be at high energy with this large sample of 14 TeV data. We might be able to rule it out at 95% confidence in certain mass ranges if it’s not there, but we ought not be able to do that if it is, right? Patience, patience!

Nevertheless, there is no question that in a few weeks, when operated at 7 TeV collision energy, the LHC will become an awesome discovery machine. There are many new physics scenarios in which we will be able to see new phenomena with just a fraction of the full 1 fb^-1 sample. Will nature give up her secrets so readily though? She may not – we may spend this year and the next rediscovering the Standard Model, building up understanding of the detector, and sharpening our analysis tools in order to discover quite subtle effects. No matter what happens, this is the most exciting time in particle physics in decades.

I happen to be visiting UCSD this week, and woke to the news that Geoffrey Burbidge passed away yesterday afternoon. He was a giant in the field of astronomy and cosmology, and (despite himself) was one of the main contributors to the establishment of the standard Big Bang model of cosmology. He was perhaps best known for his work in stellar nucleosynthesis (encapsulated in the B2FH paper: Burbidge, Burbidge, Fowler, and Hoyle 1957, Rev. Mod. Phys. 29, 547), which in some sense established that we are all made of “star stuff”. There are few research papers that are widely known simply by their author’s initials (especially over 50 years later); the paper even has its own wikipedia page. (Off hand, the only other one I can think of is EPR.)

However, for the past years Burbidge was primarily associated with advocating a steady-state model for the Universe. For many decades this model was incredibly important, as it provided a foil with which to challenge the big bang theory. It pushed us to get as much data as possible, and helped usher in the era of precision cosmology. In some sense, it is because of the steady-state model that we are as confident as we are in the big bang model. [Famously, the very name "big bang" was coined derisively by Hoyle, one of the originators of the steady state model, and the "H" in B2FH.] Burbidge was a proponent of his alternative cosmology, long after the vast majority of people in the field abandoned it. The data became overwhelming (in particular, the incredibly perfect black body spectrum from COBE, and then the completely incontrovertible “acoustic” peaks from WMAP, among other things). Burbidge was adamant that we should always question, and carefully distinguish between data and models. He did not like the “bandwagon” aspect of science, and remained leery of the broad consensus behind the big bang.

There’s an article in our very own Discover Magazine which nicely sums up Burbidge’s personality and science. He did vital and important work in the field, and should be remembered for this.

Over the last few months I have had the pleasure of discussing science and science journalism with Faye Flam, who covers science for The Philadelphia Inquirer. Faye reports on all kinds of science, and a number of other topics, as you can read about on her web site. But most recently she has put a great deal of work into covering climate change; even interviewing Michael Mann, who will be visiting us at Penn for a physics colloquium in just a couple of weeks. And she has found it enough of a challenge that she has chosen to write about it as a (first of several, I hope) guest post.

This is a hot topic, as we all know, and I’m hoping we get a thoughtful and respectful discussion in the comments. Nevertheless, this might be a good place to remind people that we’ll generally delete comments that are off topic or offensive.

Now, here’s Faye.

There must be some redeeming lesson to come from covering the so-called climate gate scandal that’s dragged on over the last two months. Member of the public actually care about science. They’re even passionate about it. But when that happens it’s not always pretty.

Never in my 14 years as a newspaper science writer have I found myself on the receiving end of such a powerful stream of hate mail – searing bombs of name-calling that get fired into my personal and work inboxes, as well as screaming, profanity-laced screeds landing in my voice mail. There’s much gloating about the downfall of newspapers and speculation that soon I’ll perish on the streets, begging for pennies.

I even got my first death threat following this story. It was the first of three stories I wrote on this topic for the Philadelphia Inquirer after a cache of e-mail messages were stolen from some prominent climate scientists and picked over by their worst enemies for signs of malfeasance.

Many member of the public are raging at me for failing to point out what they see as an inexcusable case of scientific fraud. For them, there’s no distinction between committing fraud and being wrong. That might worry some members of the scientific community.

I wasn’t ordered to write anything on this issue. During the same period I also wrote a nice story about the Hubble Telescope, and one about heroic cancer researchers. I could easily have skipped this whole mess and written other nice stories – on Kepler, or maybe LHC. People always like stories about planets and particles.

But instead, I returned from Thanksgiving vacation to write this quick overview, followed by the more offbeat Q and A story linked above.

Then, in a fit of masochism, I decided to profile one of the scientists involved – Michael Mann – because he works nearby at Penn State University. That gave the whole thing a local angle.

Mann’s work has been scrutinized for years, after a researcher in Canada pointed out a possible statistical flaw in some climate reconstructions done in the 1990s. That eventually led to an investigation by a National Academy panel. They concluded that Mann’s initial papers weren’t perfect but the general conclusions held up, and there was no evidence of fraud.

In other areas of science, the public can be more tolerant. Back in the 1990s, people were in some disagreement about the age of the universe. When new information came in, some were shown to be off be a few billions years, give or take, but they didn’t get carted off to Siberia.

Others had wrong ideas about the shape and fate of the universe, since nobody back then thought it was accelerating. That’s the beauty of science. It’s self-correcting – though sometimes the corrections can take a while.

The other lesson here is that many people don’t understand the role of uncertainty in science. There is uncertainty over the way water vapor changes the situation, for example, with most experts saying it will create a positive feedback but a few arguing for a negative one.

And still, some people write to inform me that the science is “settled.” These critics are not sure what’s settled but they’ve heard this and seem to think it’s important to repeat.

Others recognize the uncertainty in climate science and find it appalling. That’s particularly true of engineers, who seem pretty well-represented among self-proclaimed global warming skeptics. It’s a level of uncertainty that would never fly in modeling systems for chemical refineries, or so they tell me.

One MIT-trained engineer said his own calculations prove that the climate models can’t work because, in short: “junk in equals junk out”. It would make for a great story if a local guy who worked for a chemical refinery took down the whole climate science establishment on the back of an envelope. Unfortunately, I have to consider the possibility that he hasn’t.

The global warming skeptics also love to use the term “AGW theory”. This proved a great strategy for debating because the scientists don’t really refer to anthropogenic global warming as a theory, and many aren’t sure what AGW theory means. That gives the critics the freedom to say it means that only humans can influence the climate – and that the climate never changed at all before humans hit the scene. Then they can point to this untenable position and say, “ha ha – aren’t these scientists dumb!”

Coming from the more liberal side of things, a reader suggested that even if some fatal flaw crops up in both the climate models and the climate reconstructions, and the world does plunge into a protracted global cold spell, the scientists who had done the original work shouldn’t necessarily be thrown in prison or burned at the stake.

It might seem strange, even insane, for the public to base views of the carbon cycle and water vapor feedbacks on politics. Is it a problem of science illiteracy? I don’t think so. We could all be better educated about basic physics and chemistry and this debate would still play out the same way.

It all makes more sense, though, in light of the way differing political philosophies tolerate uncertainty – whether they’re considering government-funded scientists delivering uncertainty or the prospect of policy changes based on uncertain science. How much should we know before we start conserving energy? Classify CO2 as a pollutant? Submitting to international regulations? The best we can do as scientists and science writers is respect those political differences, state what’s known as clearly as possible, and be honest about what’s not known. People will still hate us, of course. There’s no way to escape that.

We are here in Aspen for what is always the first particle physics conference of each year, the Aspen Winter Particle Physics Conference. This is the 25th anniversary of this series, hosted by the Aspen Center for Physics. I have attended myself twice in the past (1998 and 2007) and this year I am an organizer, along with Robin Erbacher, Tim Tait, and Graham Kribs.

The format of the conference is much like the other winter particle physics conferences such as Lake Louise in Canada, and La Thuile in Italy. We have a morning session of talks ending a bit after 11:00 am, a long mid-day break to allow for a bit of skiing, and an afternoon session from 4:30 pm to after 7:00 pm. It runs Monday – Friday this week, so we are half way through. Tonight the conference is hosting a public lecture from David Kaplan from Johns Hopkins at the Wheeler Opera House, with a “Physics Cafe” before hand at which we organizers will field questions from the public.

We chose as a theme for the conference “The Revolution in Particle Physics is Here” and there is definitely a palpable sense that the revolution is indeed upon us. Neal Weiner gave a great opening talk recounting the many curious anomalies that we already have observed in experiments, and speculated on what may lie in store at the LHC and in astrophysical observations. Eric Prebys, a leader of the US effort on the LHC commissioning, gave a very interesting and detailed talk about the recent successes in commissioning the LHC machine and the very bright prospects for this year. The machine will turn on again in February, and soon raise the beam energy to 3.5 TeV (a collision energy of 7 TeV). Big decisions face the CERN management: should we stay safe at 7 TeV or attempt a higher energy like 10 TeV this year? Should the LHC shut down for many months at the end of 2010 or press on in 2011 to collect as much physics data as possible?

There is truly crackling excitement for the prospects of discovery this year at the LHC, and maybe even the Tevatron. The big LHC experiments are all working extremely well out of the box and eager for physics data: we heard talks from ATLAS, CMS, and LHCb. In fact the first three days of the program are devoted to the LHC and Tevatron, including some very nice theory talks from Tilman Plehn, Paddy Fox, Martin Schmaltz, and Jay Wacker. And for every theory talk there are about three or four talks about the latest results and projections from the Tevatron and the LHC. Heady stuff!

As for Aspen itself, it’s a place of almost surreal beauty, nestled in the Rockies, with fantastic skiing at four mountain areas. It is truly the playground of the super-rich: on the mountain slope above us are arrayed dozens of trophy mansion estates running in the seven figure range. (One colleague quipped “your health care dollars at work!” Heh, heh.) The only reason we (relatively) poor physicists can enjoy such a place is due to the existence of the Aspen Center for Physics. The Center is an offshoot of the Aspen Institute, the postwar brainchild of Chicago businessman Walter Paepcke, dedicated to becoming “an ideal gathering place for thinkers, leaders, artists, and musicians from all over the world to step away from their daily routines and reflect on the underlying values of society and culture”. And so it has become – it’s a really unique place.