Month: August 2007

Would You Eat Alien Pizza?

Everything was ready for the celebratory feast. Weeks earlier, the alien fleet had entered Earth’s orbit and made radio contact, and now the visitors would receive their official welcome. Dozens of heads of state would greet humanity’s guests during an official dinner at the White House.

The aliens looked remarkably similar to us—apart from their green scales, that is. Moreover, the chemistry of their bodies and of ours was also very similar, scientists from the two worlds had concluded. Sure, the alien cells produced molecules not found in human biochemistry, but the building blocks of those molecules were essentially the same carbon-based amino acids and sugars as the ones in our bodies.

But on the eve of the great meeting, the science adviser to the President burst into the Oval Office. “The dinner must be called off, or the aliens might die!” the adviser told the startled President. “We forgot to check their chirality!”

Crick and Watson
Photo Researchers, Inc.
WHAT’S WRONG WITH THIS PICTURE? (See illustrations at the end of this post for the answer)

That’s a word that few politicians—indeed, few people outside science—will know. But chirality, or handedness, is an essential characteristic of the molecules of life. Most naturally occurring organic molecules are chiral, meaning that they are distinct from their mirror images in the same way that our right and left hands differ.

In the lab, chemical reactions that synthesize amino acids and sugars create the right- and left-handed versions of the molecules in equal amounts. Life on Earth, however, uses one version almost exclusively, preferring what are conventionally called right-handed sugars and left-handed amino acids. A molecular preference for only one handedness is what chemists call homochirality.

In principle, organisms could exist that use both kinds of molecules or that exclusively adopt the opposite forms from those used in life on Earth. This is what troubled the scientists in the alien state dinner scenario: Just as our bodies can’t absorb organic matter of the wrong handedness, so too the aliens might find our food equally indigestible—and perhaps even toxic.

Most scientists believe that Earth life’s choice of chemical handedness was purely random. “The most plausible idea is that it was an accident,” says biochemist David Deamer of the University of California, Santa Cruz. It’s possible, then, that the chemistry of some alien forms of carbon-based life—assuming such things exist—may well have the opposite chirality to ours. We might find alien pizza even harder to digest than deep-dish.

On the other hand, a few scientists say that something more fundamental might be going on. They argue that throughout the universe, nature might consistently choose one handedness over the other. That intrinsic preference, these scientists suggest, might originate from the influence of the weak nuclear force, the only fundamental force of nature that can tell left from right. In recent years, a number of experiments have provided tentative—if controversial—support for this proposal.

Continue reading “Would You Eat Alien Pizza?”

Dark Matter Ineffable

Just when the universe had barely begun to get us used to a new level of weirdness — what with the pervasiveness of dark energy, the anti-gravitational push that wasn’t even on the map until ten years ago — here comes a new discovery that seems to contradict even the little we thought we knew.

Even dark matter isn’t what it used to be

The weirdness in this case is that of dark energy’s lugubrious pal, dark matter.

Last year, astrophysicists reported remarkable evidence for the existence of dark matter by observing the results of the collision of two clusters of galaxies, collectively known as the bullet cluster. (See Dark Matter Really Exists, the article I wrote about what I declared my favorite science story of 2006.)

In the bullet cluster, the collision had taken the clusters apart. While the intergalactic gas from the two clusters had bungled up together, the galaxies themselves had sped through each other, apparently unaffected. The galaxies’ halos of dark matter in that case had kept traveling along with the galaxies themselves. Dark matter is invisible, but its presence was revealed by how it curved space around itself, squeezing the images of galaxies in the background.

Dark matter has never been caught in the lab, and its nature is largely unknown. The fact that it has never been detected means that it tends to zip through ordinary matter without interacting. In the bullet cluster, scientists saw evidence that dark matter particles from one cluster also did not interact with those from the other cluster.

While the clouds of intergalactic gas from the two clusters were slowed down by mutual friction, the dark matter particles simply kept going, even though the dark matter clouds were probably denser than the gas ones. Dark matter can zip not only through ordinary matter, but also through dark matter itself.

Or not. The new mapping of dark matter, galaxies, and intergalactic gas around Abell 520, a “train wreck” of a galaxy cluster, announced today by NASA (see the NASA Web site) seems to throw everything into discussion. By imaging Abell with multiple methods, astrophysicists found a chaotic dismemberment that no theory seems to explain too well now.

In the artist’s illustration above,

the bulk of the matter (blue) is found compared to the individual galaxies (yellow) and the hot gas (red) in the aftermath of a massive galaxy cluster collision. The material shown in blue is dominated by dark matter. As with the Bullet Cluster there are large separation between the regions where the galaxies are most common (peaks 2 and 4) and where most of the hot gas lies (peak 3). However, unlike the Bullet Cluster, a concentration of dark matter is found (peak 3) near the bulk of the hot gas, where very few galaxies are located. In addition, there is an area (peak 5) where there are several galaxies but very little dark matter [courtesy of the X-ray observatory Chandra].

What this means for our understanding of dark matter, it is probably too early to say (I haven’t talked to any experts about this yet). But one thing is for sure: the universe is a bizarre place.

Oily Loch Ness

Since I’ve started working at Science News, I have been too busy writing to find time to write about my writing. But there’s no reason why I shouldn’t at least share some cool images from my stories.

Oily Loch Ness
Matthew Thrasher/Univ. of Texas

Here’s what oil looks like when you pour it in a pan. No, really.

When you pour oil from a good height, the falling stream does not merge right away with the oil already in the pan. What happens is that the falling oil carries a sheath of moving air around it, which acts like a cushion and keeps the stream isolated for a while.

Physicists tried pouring mineral oil into a round pan, while making the pan spin. The stream bounced back, looking like an oily Loch Ness monster.

The researchers published their findings in Physical Review E, and — unusually for a scientific paper — included instructions on how replicate the experiment at home.

(See Slick Serpent, in the July 28 Science News.)