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David Darling's Newsletter #5


November 20, 2002


1. Meanderings
2. Dark energy
3. Bookends

1. Meanderings

One of the great things about having a web site is that you never know who's going to drop in. Last week, for instance, my visitors included the Department of Defense wanting to know about "convergent evolution" (where is the connection there, I wonder?), Boeing and Lockheed Martin ("antigravity", among others), and Microsoft ("unexplained SETI signals"). My prize for the most unusual hit, however, goes to a lady who runs an animal rescue ranch in Nebraska who e-mailed me to ask about the biomolecular makeup of feathers. She was trying to figure out how best to feed her orphan ostriches, geese, and chickens over the winter and was starting from the real nitty-gritty chemical stuff. Searching under "keratin + feathers" on Google, she'd managed to find my encyclopedia page on fibrous protein. I told her what I could (not much!) and pointed her in the direction of Nebraska's veterinary school. My most mysterious visitors are from the NIPR.mil domain, which, I understand, serves as a gateway from DOD computers to the public internet. If I were a conspiracist — which, I hasten to add, I'm not! — I could make all sorts out of their searches under "Roswell", "cetacean intelligence", and "unidentified flying objects". Probably just some young underlings idly surfing while on duty. If so, they're running quite a risk as all their Internet activity is closely monitored. (This Big Brother surveillance, I've discovered, shows up as split-second double hits.)

Even before I had a web site, though, all sorts of interesting and unexpected material arrived at my door. My filing cabinet must be a quarter-full of letters, unpublished papers, and handwritten plans on perpetual motion machines, gravity shields, faster-than-light propulsion systems, alien abduction and flying saucers, cities on Mars, and out-of-body experiences. Some of these folk want my advice, others my collaboration (usually involving some hefty financial outlay!), but most simply want someone to listen to them. A recurring theme is the idea that the Universe is pervaded by an unseen and previously unrecognized force that can be tapped by a suitable combination of electromagnets, antennae, and other gizmos. If I weren't such a sentimentalist I'd toss the whole lot in the bin. On the other hand — segue coming! — it could just be . . .

2. Dark energy

Darth Vader would have been delighted. Not only is the force with us but it seems that it is after all dark and all-powerful. Yes, the Universe runs on dark energy! Of course, we should have expected it. Black seems to be nature's favorite color. First there were black holes. Then along came the discovery, now widely accepted, that nine-tenths of the material in the Universe is "dark matter" (its composition still uncertain). Now, it seems, the fate of the whole cosmos is determined by vast amounts of dark energy.

Scientists got on to the trail of dark energy in 1998 based on observations of distant supernovae (exploding massive stars) which suggest that the Universe isn't just expanding, it's expanding faster and faster. Check out CNN's story on this startling breakthrough. Observations of the most distant supernova ever seen, in April last year, described this space.com article backed up the idea of accelerating cosmic growth.

Remember Newton's laws of motion? The second one says, basically, that to accelerate something you need a force. The trouble is that the only significant known force in the Universe that acts between galaxies (and clusters of galaxies) is gravity, which is always, so far as we know, attractive. Even if the Universe is flying apart, like shrapnel from a bomb, and even if it is doomed to carry on flying apart, its growth rate ought to be slowing because of the mutual pulling-together effect of gravity. On the other hand, if it's accelerating in its headlong outward rush, then something must be pushing against gravity. That "something" has been dubbed "dark energy."

The idea really isn't as new as it sounds. It even predates Star Wars. In fact, Einstein, the very guy whose equations foretold an expanding Universe, stuck in a factor, called the cosmological constant, to make sure the Universe stayed the same size. At the time (pre-1920), there wasn't any data to suggest that the Universe was expanding and the constant seemed necessary to square the theory of general relativity with reality. A few years later, when Hubble and others showed that we live inside a growing cosmos, Einstein called his fudge factor "my greatest blunder." If you want to dig more into the background and physics of this, read this good but dated Sky & Telescope article [link broken], this more mathematical overview at UCLA, or this really excellent but deep treatment by Peebles and Ratra.

As this last paper points out, there's a close link between Einstein's cosmological constant, which is a kind of antigravity, and the new concept of dark energy.

So what is dark energy? All we know for sure is that, if it exists (which scientists are still debating), it exerts a negative pressure on the very fabric of spacetime, causing it to stretch faster and faster as time goes on. It could be associated with the vacuum energy of empty space, in which case it would be very much like Einstein's cosmological constant (except instead of just balancing out gravity it accelerates the expansion). It could be a cosmic field associated with inflation — that weird phase transition, which, for a split-second right after the Big Bang, caused the Universe to swell up at a fantastic rate. Or, it could be a different kind of energy field dubbed "quintessence" (literally the "fifth stuff" since it's additional to the four known forces of nature). This uncertainly comes as a fresh but always-welcome embarrassment to science. Already we were in the dark about the exact nature of dark matter. Now we're scratching our heads about this new discovery. As Saul Perlmutter, leader of the Supernova Cosmology Project headquartered at Berkeley Lab put it: "The Universe is made mostly of dark matter and dark energy, and we don't know what either of them is." Hmm, maybe some those crazy ideas stored away in my filing cabinet aren't so crazy after all!

3. Bookends

"The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity" is now in print! Be sure to order dozens of copies for your family and friends this Christmas (or, at least, tell them about it so they can order their own!) Available from Amazon (which has 69 inside pages you can browse through), Barnes & Noble, and Powells Books on-line, or, as they say, from any good bookstore.

Until next time,
Best wishes,
David Darling