State of the Universe(s)

October 19, 2009

Last night I had the honor of moderating a fantastic discussion between three leading cosmologists: ASU's Lawrence Krauss (of The Physics of Star Trek fame), University of Michigan's Katie Freese, and Neil Turok, now the director of the Perimeter Institute, which organized the city-wide Quantum 2 Cosmos festival. The Q2C organizers have gone all out with the multimedia: most lectures and panels are available online, streaming live while in progress, along with a Twitter feed.

We covered a lot of ground in 55 minutes, discussing the unprecedented explosion in our scientific knowledge of the universe during the 20th century and looking to the future by exploring the mysteries currently facing cosmologists: dark matter, dark energy, gravitational waves, whether inflationary theory is correct, and what might have existed before the Big Bang? These are deep waters, Watson. Okay, I had to ask Krauss about the whole "red matter" scenario in the latest Star Trek reboot (he liked the movie, had little use for the "science"). But other than that, we stuck to the serious stuff. Mostly.

I always learn something new when I talk to scientists, and this time was no exception, thanks to Katie Freese. She told me about "dark stars": not the precursors of black holes first hypothesized back in the 1700s, but a new kind of star that may have been the first type of star to form in the early universe. Freese and a few colleagues published the seminal paper on dark stars in January 2008 in Physical Review Letters, and she's still uber-excited about the possibilities for the existence of these objects -- as well she should be.

See, if these things turn out to exist, it would significantly change current theoretical models for star formation. Right now, scientists believe the first stars formed inside clouds of dark matter, in which hydrogen and helium cooled down sufficiently to make nuclear fusion possible. The only role dark matter plays in this scenario is to supply the gravity needed for the gases to clump together in the first place.

But if Freese and her colleagues are correct, then the concentrations of dark matter particles would be so high that those particles would collide with each other and annihilate, releasing energy, and keeping the almost-star too hot to collapse down to sufficiently high density for fusion to begin. In short, it's an entirely different fuel source than that which powers "normal" stars. The next step is actually detecting them, and Freese thinks the new James Webb Telescope slated for launch in 2011 will be able to see them, although she cautions that while dark stars may shine, "they will look different than stars that operate by fusion." Emissions of gamma rays, neutrinos or antimatter could all turn out to be "signatures" of dark stars.

Like any new idea, it has its skeptics in the scientific community. Freese et al's model does rely on some necessary assumptions that may turn out to be incorrect. Most notably, their calculations are based on a type of Weakly Interacting Massive Particle (WIMP) called a neutralino -- it's the leading candidate for dark matter particles, but it may not be the right one, or the only one. But it's not an implausible scenario either. Like so much in cutting edge cosmology and astrophysics, the excitement comes from exploring what we don't know, because that inevitably leads to new discoveries.

Anyway, we ran out of time before we could really discuss dark stars in detail during the panel, but we covered lots of other great topics, and we certainly didn't ignore the "dark side of the universe." That's where all the cosmological action is these days. You can watch the whole thing below. (Note: For some reason, the "embed" feature has been giving me grief. If it's not showing up in the post, you can still watch the entire panel discussion here.)

Dark Energy Sing-a-Long

June 10, 2009

There's a whiff of dark energy in the air this week, permeating the cultural zeitgeist. First, our new fearless leader here at Discovery Space, Ian O'Neill, has a terrific IM interview up with Dr. Richard Orbousy about the latter's master plan for harnessing dark energy to build a futuristic warp drive. Because wormholes are just so 2007, ya'll. Sure, it'll take the energy equivalent of the entire mass of Jupiter -- or, according to less optimistic calculations, 1 trillion Jupiters -- but that's just a technology problem.

Second, physics blogger Andrew Jaffe over at Leaves on the Line reports on the final exam results for his latest crop of graduate students. Apparently said students grappled mightily with the problem of the cosmological constant -- a leading candidate to explain this bizarre phenomenon of dark energy that is causing our universe to accelerate at an ever-faster rate. Per Andrew:

There was one question that almost all students got wrong, however. I asked about the “Cosmological Constant Problem” and whether it could be solved by the theory of cosmic inflation. The Cosmological Constant is a number that appears in General Relativity, and, although we can’t predict it for certain, we are pretty sure that if it’s not strictly zero, in most theories we would estimate that it ought to have a value something like 10<120> (that is 1 followed by 120 zeros!) times greater than that observed in the Universe today. ... Inflation involves something very much like the cosmological constant, but occurring in the very early Universe — so inflation can’t help us with the 120 zeroes, alas.

He ends with an amusing YouTube video of his colleague, Lloyd Knox, a physics professor at the University of California, Davis, who penned a little ditty about dark energy to help his own students with the cosmological conundrum. (h/t: Sean Carroll, via Twitter) Granted, I doubt Professor Knox will be wowing Simon Cowell on American Idol any time soon, but can this season's winner, Kris Allen, come up with lyrics like this?

What is causing this rush?
This late great cosmic flush, hurtling all things apart
Cosmo constant, scalar field,
No compelling theories yield
To the best of our creative and daring minds
Young and bright
Who strain, and reach, and struggle to know why

[Complete lyrics can be found here.]

Fun with Jelly Beans

January 14, 2009

One of my favorite visual analogies for the distribution of "stuff" (as my cosmologist spouse likes to call it) in the universe is a big old jar of jelly beans:

Note that most of them are black, with just a few colored jelly beans dotted about. Those scattered bits of colorful beans represent every single bit of visible matter in the universe: every star, every planet, every galaxy, every planet, every person. It adds up to about 4%. Another 26% is dark matter: we can't see it, but we know it's there because we can see the gravitational effects from all that invisible (to us) mass. The rest of the "stuff" -- a whopping 70% -- consists of dark energy, and scientists still know very little about what this mysterious energy might actually be. But again, they figure it's got to be there, because we can observe its effects in the accelerating expansion of the universe.

I like the image above because it drives home the point of just how insignificant we beings of ordinary matter are in the grand cosmic scheme of things. (As Sean likes to say, we are merely the olive in the martini.) Which in turn makes it all the more amazing that we can accomplish such feats as "weighing" the stuff in the cosmos in the first place -- or, more mundanely, a simple mathematical trick like guessing the number of jelly beans in a one-liter jar.

An episode of the popular TV series Monk showed the "defective detective," Adrian Monk, at a local carnival. In between dodging his usual phobias, he enters a contest to guess the number of jelly beans in a jar -- and naturally, he wins. Such a task is a snap for someone with OCD. That said, he figures it out in part because he observed a bunch of empty jelly bean bags near the jar, and made an educated guess.

Even without that, he could probably have come pretty close, using one possible calculation I found detailed on the back of brochure being distributed at the AAS meeting by the Chandra X-Ray Observatory:

1. First, it's useful to know that your average jelly bean is roughly 1 centimeter long and 1.5 centimeters wide (diameter). You also need to know the volume of the jar (1000 cubic centimeters).

2. Second, they are irregularly shaped, so they're not going to rightly packed in the jar; assume that about 80% of the volume will be filled.

3. Per the brochure, "The number of jelly beans is the occupied volume of the container (80% of one liter) divided by the volume of a single jelly bean." To figure out the volume of a single jelly bean, figure on the volume of a cylinder measuring 2 cm long and 1.5 cm in diameter. (Can't remember how to do this? That old geometry textbook will tell you. Go ahead, get it, we'll wait...) That's about 3.5 cubic centimeters.

So, the approximate number of jelly beans in a one-liter jar is (.80 x 1000 cubic centimeters. divided by 3.5 cubic centimeters... or around 229 beans. And if we're using the above jar as the sample case, and it accurately represents the distribution of stuff in the universe, we can then figure out how many of those jelly beans are going to be black (dark): 96% of them.

See? Was that so hard? There are supposedly other possible calculations, but most of us just need one winning strategy. Now we have one, courtesy of NASA. I just need to bide my time until I happen upon a "guess the jelly beans" contest....

Photo: Fermilab.

The Wide Angle: Dark Energy and The Big Yawn

December 16, 2008

This post is part of our in-depth look at how astronomers have caught dark energy in the act of slowing down the universe's development. For much, much more of our series The Wide Angle, click around in the box at the end of this post.

One of the advantages of living with a cosmologist is that I get to meet some of his fascinating colleagues -- like Brian Schmidt, who shared an office with Sean when both were at Harvard, and now lives and works in Australia. Shortly after I'd moved to LA, he came to town and we had a nice dinner at Ciudad, punctuated by their signature mojitos and pisco sours.

Sean's a theorist, Brian's an experimentalist, but both have worked on dark energy: Sean on theoretical models (natch) and Brian -- well, he headed one of two teams that discovered our universe is actually accelerating in its expansion in 1998, by studying supernovae. The dual observation rocked the physics world and completely changed the face of astrophysics. Specifically, there had to be dark energy, a kind of repulsive force to counter the effects of gravity.

How quickly we become jaded. It's been 10 years, and scientists still don't know what the dark energy is, although evidence seems to be piling up in favor of the cosmological constant (lambda): Albert Einstein's mathematical "fudge factor" first introduced in the theory of general relativity to essentially offset his calculations indicating that the universe should be expanding. At the time, prevailing scientific opinion held that the cosmos was static and unchanging. Einstein needed lambda to balance out the "push" and "pull" in order to produce a model consistent with a static universe.

Twelve years later, when Edwin Hubble produced evidence that the universe was, in fact, still expanding, Einstein dismissed the cosmological constant as his "greatest blunder." It's a testament to Einstein's genius that even his blunders are significant.

Lambda implies the existence of a repulsive form of gravity. And the simplest example of this can be found in quantum mechanics, where even the vacuum of space is teeming with energy in the form of "virtual" particles winking into existence and annihilating just as rapidly.

This roiling sea of virtual particles could conceivably give rise to dark energy, giving the universe that little extra "push" so it can continue accelerating. In fact, as the various stars, galaxies and other obects in the universe get further and further apart, the universe should accelerate even faster, because the pull of gravity is less, while dark energy (as far as we know) is constant.

It's certainly not the only possibility. There are a handful of modified theories of gravity floating about, for example, offering alternative models, as well as a theory of something called quintessence, in which the dark energy is not constant, but fluctuating -- and let's not even get into the possible influence of string theory's unseen extra dimensions. But consensus seems to be emerging that there is some form of dark energy, with the cosmological constant as the favored candidate, despite one big sticking point: the quantum vacuum contains too much energy. The universe should be accelerating much more quickly than it is.

And now comes news that the Chandra X-Ray Observatory has studied the development of galactic clusters and found evidence of arrested development in their formation that could very well be due to the effects of dark energy. "Whatever is forcing the expansion of the universe to speed up is also forcing its development to slow down," said Alexy Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, MA. The cosmic growth spurt is coming to an end, at least when it comes to the formation of new structures.

It's taken years to compile this data, which further buttresses evidence that the dark energy is, indeed, the cosmological constant, especially when taken in conjunction with other methods of dark energy research -- such as Brian's work with supernovae. If you look at a phenomenon from different angles, and still get results that are in agreement, you've got the foundation for a pretty solid case.

Yet when I mentioned this exciting new piece of evidence to my beloved spouse, who has worked extensively in this area (among others), his response was more of a shrug than a shout of glee. Interesting, yes, but hardly earth-shaking. That seems to be the response of several folks, in fact. Dark energy? That's just so 1998! And yet it remains one of the greatest unresolved questions of the cosmos.

More of the Wide Angle

News: Dark Energy Revealed

Top 10: Things You Didn't Know About Dark Energy

Video: Study Sheds Light On Dark Energy

IM Interview: How To Hunt For Dark Energy

My Take: Exciting Times Ahead for Dark Energy Search

Blog: The Dark Energy Doubters

Blog: Far Future Forecast: Deep Darkness

Blog: The Big Yawn

HowStuffWorks: How The Fate Of The Universe Works

What's one more incremental advance, you may ask? Well, sure, it's not s exciting as the original discovery, but incremental advances add up over time, collectively providing conclusive evidence. It's actually quite rare in science to get the kind of result that the original observation of dark energy provided -- something revolutionary that sets science on its ear and forces us to re-examine our most cherished assumptions about our universe. Every now and then, I like to remind folks that there's a lot of painstaking, thankless hard work behind the scenes that lays the groundwork for the occasional earth-shattering discovery. After all, Brian Schmidt's team (and the other, led by Saul Perlmutter) surveyed an awful lot of supernovae over the years before they made their momentous announcement.

Photo: A "map" detailing what scientists now believe constitutes the makeup of our universe. Source: NASA (public domain).