Alpha and Omega
Interview with Charles Seife : Part II
Astrobiology magazine had the opportunity to discuss 'how the universe began and how it will end' with Science magazine writer, Charles Seife. Seife is the author of a new book, Alpha and Omega, which describes how cosmologists today are trying to answer these age-old questions. Seife previously has written on the mathematical and cultural genesis of the number 'zero'. His latest adventures in cosmology bring a characteristic enthusiasm for a remarkable field undergoing a revolution.
Alpha and Omega asks the questions: how did the universe begin and how will it end? And how do we know?
|Click here for larger image. Cepheid variable stars (like this one in Galaxy M100) vary in brightness over time.
Image Credit: Weber State University/Bradley W. Carro
Astrobiology Magazine (AM): How much of Alpha and Omega is about fitting the universe to human sensory data, given that proposals are put forward for exotic dark matter, and invisible parts of light spectra to explain why the universe 'looks' the way it does? For instance, there is a long debate by Da Vinci to prove that the Sun itself is not the actual size you see, as written from the vantage point of a painter's lifelong study of perspective. But that would seem obvious to a child today, or anyone who watches a horse get bigger apparently as it approaches from the horizon. But not in his time. Are modern astronomers comparable to a version of perspective painters, confronted with creating new dimensions out of what our telescopes see as a flat canvas?
Charles Seife (CS): Very much so. It doesn't take much imagination to think of the night sky as a sphere enclosing the Earth. It took a lot of work to show that the heavens had depth -- vast depth. Astronomers have to use subtle clues to flesh out that extra dimension: parallax,Cepheid variables, the Tully-Fisher relation, and supernovae are all tools which gave scientists more and more understanding of how deep the universe really is.
AM: Are the following notes roughly consistent with the synopsis? The universe is most likely:
· flat (in a curvature sense, from measuring the clumpiness of the cosmic microwave background)
· expanding (from redshift of starlight in all directions)
· accelerating in this expansion (from supernova Ia data, where a red giant feeds a white dwarf to just the right density for a calibrated brightness measurement)
· clumped energetically like an acoustic wave, and like Swiss Cheese spatially under the influence of gravity and radiation
· driven by the balance between gravity (mass density) and radiation pressure (initial energy) from the big bang
CS: That's pretty much correct, though there are interrelationships between the observations that make you more confident in each of these conclusions.
|The oldest 1a supernovae known, lying near an elliptical galaxy at a distance of ~11.5 billion l.y., is shown as a bright incandescent cloudlike object in the above image.
The acoustic waves and were important until the universe was 400,000 years old and set the pattern for the clumping of matter in the cosmos; until then, the important forces were gravity and the radiation pressure of photons bouncing off of matter, set against the backdrop of an expanding universe. And don't forget dark energy in addition to gravity and the initial energy of the big bang as a driver!
AM: Our observations are limited to about 400,000 years after the big bang (the most 'ancient light'), when matter recombined and left us a faint hissing signature of microwaves. Would you consider it correct to say therefore, that we are surrounded all the time by the 'stuff' that began it all, the microwave background?
CS: Absolutely. It's as if we're surrounded by walls of fire. No matter where you look in the sky, the most distant, most ancient object visible to any sort of telescope is an image of the last scattering surface, the plasma that filled the universe when it was only 400,000 years old.
However, there is a hope of peering beyond those walls, at least indirectly. The cosmic microwave background is polarized -- the photons have preferred "orientations" at different parts of the sky -- and that polarization contains information about gravity waves that rattled around the universe since a tiny fraction of a second after the big bang. The Planck satellite or its successors should be able to extract that information from the CMB.
AM: To paraphrase what Richard Feynman said about particle physics, it can be compared to playing chess while seeing only four squares, watching chess pieces appear and disappear inside those four squares, and then guessing at the rest of the board and even the rules for the 60 unknown squares. Is there an added cosmological complication in the quest from Alpha to Omega, that the rules may change dramatically in the middle of the game?
|The Planck Satellite.
Credit: European Space Agency
CS: There's always a chance that something dramatic will happen, but the longer you observe, the more confident you are in your models and the less "important" such a rule change will tend to be. I put "important" in quotation marks because I need to clarify what I mean -- after all, quantum mechanics and relativity were incredibly important and dramatic changes of the rules that occurred after several centuries of scientific observation and theory.
By "important," I don't mean philosophically important. Relativity and quantum mechanics each changed our understanding of space, time, and the limits of human understanding. But the magnitude of the correction to classical equations are pretty small for both quantum mechanics and relativity in most cases. Newton and Maxwell still hold until you start dealing with very small objects or very fast objects or things in large gravitational fields or in solid state electronics or in other areas where the extensions of quantum mechanics or relativity are needed instead of classical laws. So even though quantum mechanics and relativity supplant classical laws, in a sense, they are extensions that are needed only under certain circumstances. In Feynman's analogy, they are like a rule for castling or a rule for en passant -- they force you to change the seemingly ironclad dicta about the way pieces can move, but these new rules have fairly limited applicability compared to the grosser rules of the game.
Yes, there are rules we don't know, and probably some of them will dramatically change the way we look at the universe. But the game of chess probably won't become a game of checkers all of a sudden; the rules we have learned will still apply most of the time, even if we have to modify them slightly to give them extended reach.
AM: When Arno Penzias and Robert Wilson first mistook the microwave static in their antennae at Bell Labs as pigeons, how long was it before this anomaly became accepted as the signature hissing left over from the Big Bang? 1965, or much later?
CS: I think it was pretty quick. The theory was there from the get-go -- the Princeton group had postulated the existence of the CMB and were setting up an experiment to detect it when they realized that they had been scooped by the Bell Labs group. By 1971, physicists were already making detailed predictions the nature of anisotropies in the CMB, and the Nobel was awarded in 1978.
|Wilson and Penzias with their historic horned antenna at Crawford Hill, N.J.
Credit: Bell Labs
AM: The need for two-thirds of the universe to be invisible (dark matter), doesn't that remain a most uncomfortable proposition for modern science to find itself in? It seems even traditional views of gravity are safe with current theory. Is it considered the strongest current indirect observation of dark matter that the rotation of galaxies doesn't decay as gravity predicts for outlying stars that should orbit slower, but instead spiral at the same speed as inner stars?
CS: It is uncomfortable, but scientists thrive on discomfort; after all, if your experiments always agree with expectations, you won't learn very much. And I think that the discomfort with dark energy is tempered by the fact that modern big bang theory already required a dark-energy-like phenomenon in the early universe; there had to be some energy driving the super-rapid period of inflation shortly after the initial singularity. Thus, the current model of the universe isn't really more complex than the one we already had. It's weirder, but it's not more byzantine.
There's a number of other indicators of dark matter besides the rotation rates of galaxies (which, of course, are what led Zwicky and Rubin to the idea of dark matter in the first place.) I'd argue that there's a stronger method nowadays: gravitational lensing on different scales. Groups like the MACHO project and OGLE have been studying dark matter with "microlensing," brief flickers in background stars that occur when a dark stellar-sized chunk of matter passes in front of it. Others have been looking at dark matter with "strong" and "weak" gravitational lensing, where the enormous mass of a galaxy or galaxy cluster distorts the image of distant light sources.
AM: One remarkable story you tell which has rarely been translated out of the scientific literature involves the quest to associate star brightness with distance. This first try used variable stars (Cepheids), which were a primary target for the Hubble Space Telescope, and give a way to use parallelax to estimate the relative separation between far distant objects. The other is the supernovae Type Ia, which are a calibration for the stellar distribution and age--a measure of how fast the universe may be expanding. Both are tied to fleshing out a third (and fourth) dimension to the sky, so like the ancients, aren't we still grappling with the basics of we only can observe directly the brightness and position in the sky, not the depth nor age, without knowing initial conditions? Were you surprised at how much of the 14 billion year timeline hinges on this observational association between brightness and distance? And the key role played by what most people have heard little about: Cepheids and Type Ia supernova?
|The Hubble Telescope.
CS: Measuring distance is a fundamental problem in astronomy, and it's why the supernova data are so important. Unless you have something to give you a direct clue, such as an object of known brightness such as a Cepheid or a Type-Ia, you've got to rely upon the Hubble relationship: if you know how fast something is receding from you, you know roughly how far away it is. Roughly.
Measuring distance by Hubble is difficult. For one thing, dust tends to redden light, making the source look like it's receding faster than it actually is. For another, bodies have their own "peculiar" motion in addition to the relative motion caused by the expansion of space -- motion toward or away from Earth distorts the apparent distance. (This sort of effect can make a spherical galaxy cluster can wind up looking like a long finger pointing at the Earth, something known as the "finger of God effect.") And worst of all, your distance estimate is dependent on your model of the expansion and on the Hubble constant, which, until very recently, wasn't known terribly well.
It was somewhat surprising to realize how important such a basic thing as measuring distance was to all three cosmological revolutions. Tycho Brahe showed that a comet was very distant and so, along with his supernova, showed that the heavens weren't immutable. Hubble measured the distance to galaxies and showed that the universe was larger than just our own Milky Way and that it probably had to have a beginning. And the present revolution began when the measurements of supernova distances changed the way astronomers thought about the forces that drive the universe's expansion.
AM: Is there any need for 'antigravity' in reconciling the size of the universe with Einstein's cosmological constant, if alternatively there is dark matter? In other words does this force go away if the critical density itself is adjusted?
|Harlow Shapley (left) and Heber Curtis (right).
CS: The force would only go away if the critical density were reduced by two thirds or if there were indications that the universe was strongly negatively curved. Dark energy is such an overwhelming component of the universe (according to measurements of the CMB, supernovae, galaxy clusters, primordial gas clouds, and other astronomical objects) it's hard to get around it by slight adjustments.
AM: You mention also the great debate between Harlow Shapley and Heber Curtis in April 1920 about the size of the universe. Shapley believed in one galaxy, and Curtis envisioned millions of them, of which our Milky Way is just one. Anything else from your research into that debate that didn't make into final print? No one won, or could have won, until Hubble and some telescopic proof either way. In what ways are our current theories of the universe similarly hindered by a lack of good observational data today?
|The first detailed, all-sky picture of the infant universe. The microwave-tuned image reveals 13 billion+ year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies. Encoded in the patterns are the answers to many age-old questions, such as the age and geometry of the Universe. Credit: NASA/WMAP
CS: There are lots of things that cosmologists would love to see that are just barely out of reach. I already mentioned polarization of the cosmic microwave background. Just last year, scientists got their first, blurry, glimpse of that polarization, but it will be a few years before anyone can get a precise enough picture to see a crucial component of that polarization that will reveal the nature of gravity waves in the early universe. Once they see it, though, they'll have a signal that comes directly from the inflationary era -- something that might well tell them about what caused the dramatic expansion of the infant universe.
Cosmologists would like to know a lot more about dark energy, too, and they're awaiting data from a number of fronts before they can really figure out what its properties are. They'd like to see many, many more supernovae as well as lots more "Lyman-alpha" objects -- filaments of gas in deep space that will give a better handle on the behavior of dark energy.
On Earth, particle physicists are eagerly awaiting the startup of the Large Hadron Collider in Geneva toward the end of the decade. This massive accelerator will finally reveal whether the theory known as "supersymmetry" is correct. If it is, then particle physicists will probably find the particle that is responsible for the majority of dark matter. Until then, or until somebody in a neutrino observatory gets lucky and detects this "exotic" dark matter directly, cosmologists won't be able to figure out what most of the mass in the universe is made of.
AM: So our readers will have to know, when will the universe end?
CS: I'm not sure -- but it'll almost certainly be on a Monday.
Seriously, though, the death-by-ice scenario doesn't come with a specific date attached; unlike the big crunch, which has a finite termination point, an ever-expanding universe (with a couple of theoretical exceptions) will die only when the usable hydrogen in the cosmos is consumed and (perhaps) protons themselves decay. It will be many, many billions of years hence -- longer than the current age of the universe. In comparison, we've got about a billion years of life on Earth before the sun's increasing temperature evaporates the oceans.
Part I of the interview with Charles Seife extended his conversations with Astrobiology Magazine.
Related Web Pages
A Universe Before Stars: Unraveling the Mysteries of the Earliest Moments in Time
Hunting for the Big Bang's Fossils in the Sky
Supernova Prompts New Look at How Universe Works
Galaxy Evolution Explorer
Hubble Space Telescope
Space Infrared Telescope Facility
Great Observatories Origins Deep Survey
Compton Observatory Gamma Rays
Deep Field South:
SIM (NASA's Space Interferometry Mission
GAIA - The Galactic Census Project
FAME: Full-sky Astrometric Mapping Explorer