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David Darling's Newsletter #3


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August 11, 2002



Contents

1. Meanderings
2. Wormholes
3. Bookends



1. Meanderings

Oops! A bit later than I'd intended, but finishing up the latest book and preparing to head off to the UK for my daughter's wedding has caused a few delays with other projects — including the Newsletter. I've also been putting a little time into the Astrobiology Central website, which is in the throes of expanding into the fields of astronomy, physics, and spaceflight as well. As a precursor to this I've inserted a visitor tracker that, if you occasionally visit the site, you may have noticed as an enigmatic little symbol at the bottom of each page. If you click on this, it will give you all sorts of interesting stats about the site usage. My goal in putting this in was to get a profile of the type of visitors that come on to the site and which parts of it they tend to make a bee-line for, so that these areas can be developed more. To my surprise, Astrobiology Central is visited about three times more often than I'd previously thought, averaging more than 100 visits a day and more than double this number of page clicks — not bad for a very specialist site. If previous years are a guide this should more than double when the new academic year starts in Sep-Oct. Which, all in all, is quite encouraging. Astrobiology Central has more than 2,000 pages to it and is what they call "high maintenance, " so it's nice to see it being put to some use. Over the coming months, you'll see new areas of it spring up devoted to such snazzy fields as cosmology, quantum mechanics, and SETI. I've just joined a discussion group, which has a JPL engineer onboard, that is looking to promote the scientific search for extraterrestrial probes in the Solar System?Bracewell probes and the like?so news from this front will also begin to percolate through. For more on this topic, check out this web site (www.interstellar-probes.org).

I'll also be adding material on advanced concepts in space propulsion and possible faster-than-light travel. And with that little link, lets take a trip down . . .



2. Wormholes

What an incredibly unromantic name for a wonderfully evocative and exotic concept! Arthur C. Clarke's "star gate" is much more mouth-watering. As indeed is the formal name for these short-cuts through space and time: Einstein-Rosen bridges. Of course, wormholes are a science fiction writer's dream. Just hop in at one end, have a snatch of conversation or a cup of coffee, and, hey presto, minutes later, you're on the other side of the Galaxy. Unfortunately, but pretty obviously, it isn't going to be quite that simple in practice.

To start with, there's the question of whether wormholes exist, or can be made to exist in reality. We're 99.99% sure that black holes are real, which is a start. Also, the mathematical equivalent of wormholes crop up as solution to the equations of Einstein's general theory of relativity amazingly often. That doesn't prove they exist. But general relativity has shown itself to be so successful in coming up with other predictions that were borne out (bending of light rays, gravity lenses, slowing down of pulsars, etc) that it's an encouraging that it seems to "like" the idea of wormholes.

Assuming they do exist, could you ever travel along them? The first inkling of these things, as far as I'm aware, came to an obscure Viennese physicist, by the name of Ludwig Flamm, in 1916. He was looking, mathematically, at the simplest kind of what would later be called black holes — so called Schwarzschild black holes. And he found that by adjusting the solution, you could effectively make the surface of spacetime (kind of like a rubber sheet) drop down through hyperspace and connect to another universe. You could go through a black hole here, zip along the wormhole, and emerge from a "white hole" in this parallel cosmos. Only you couldn't, in fact, as it turns out. The trouble with wormholes of this type is there're inherently unstable. Any scrap of matter going into them, even a subatomic particle, would cause them immediately to collapse.

Which seems like bad news for Deep Space Nine and all the other would-be users of wormholes. Yet, not all is lost. Theorists have gone back to the drawing board in recent years and looked at several types of wormhole, both artificial and natural, that don't involve black hole mouths and that might possibly act as faster-than-light conduits. This new wave of interest, I think, was sparked by Carl Sagan who wanted to know if his plot line in "Contact" — whisking his heroine to the star Vega in a few shakes of a lamb's tail — made scientific sense. So he got in touch with his Caltech buddy Kip Thorne who, like any Ph.D. supervisor worth his salt, immediately handed the problem to a couple of his students Michael Morris and Uri Yertsever, and (in 1987) they put out a paper on the subject. What Morris-Thorne-Yertsever (MTY) found was that such a journey might be possible if a wormhole could be held open long enough for a spacecraft (or any other object) to pass through. They concluded that to keep a wormhole open you'd need matter with a negative energy density and a large negative pressure. This kind of weird stuff is called exotic matter.

As a source for their wormhole, MTY turned to the quantum vacuum. ?Empty space? at the smallest scale, it turns out, isn't empty at all but seething with violent fluctuations in the very geometry of space-time. At this level of nature, ultra-small wormholes are thought to continuously wink into and out of existence. MTY suggested that a sufficiently advanced civilization could expand one of these tiny wormholes to macroscopic size by pumping in energy. Then the wormhole could be stabilized using by placing two charged superconducting spheres in the wormhole mouths. Finally, the mouths could be transported to widely-separated regions of space to provide a means of faster-than-light communication and travel. For example, a mouth placed aboard a spaceship might be carried somewhere many light-years away. Because this initial trip would be through normal space-time, it would have to take place at sub-light speeds. But during the trip and afterwards instantaneous communication and transport through the wormhole would be possible. The ship could even be supplied with fuel and provisions through the mouth it was carrying. Also, thanks to relativistic time-dilation, the journey needn't take long — even as measured by folk back on Earth. For example, if a fast starship carrying a wormhole mouth were to travel to Vega, 25 light-years away, at 99.995% of the speed of light (giving a time-dilation factor of 100), shipboard clocks would measure the journey as taking just three months. But the wormhole stretching from the ship to Earth directly links the space and time between both mouths — the one on the ship and the one left behind on (or near) Earth. Therefore, as measured by Earthbound clocks too, the trip would have taken only three months — three months to establish a more-or-less instantaneous transport and communications link between here and Vega.

There are few technical issues with the MTY scheme, as you might expect! One of which is that the incredibly powerful forces needed to hold the wormhole mouths open might tear apart anything or anyone that tried to pass through. In an effort to design a more user-friendly environment for travelers hopping down a wormhole, Matt Visser of Washington University in St. Louis dreamed up an arrangement in which the space-time region of a wormhole mouth is flat (read "force-free") but framed by "struts" of exotic matter that contain a region of very sharp curvature. Visser envisages a cubic design, with flat-space wormhole connections on the square sides and cosmic strings as the edges. Each cube-face may connect to the face of another wormhole-mouth cube, or the six cube faces may connect to six different cube faces in six separated locations. Sounds great! But I don't expect Icelandair will have one in place in time for me to get from Minneapolis to Glasgow next weekend. Oh well, there's always the movie and free drinks service to look forward to!

If you want more, here's a really nifty and accurate site on wormholes with graphics. For something a bit more speculative, you might try this site.


3. Bookends

The Complete Book of Spaceflight (John Wiley & Sons) moves ever closer to publication in November. Amazon and Barnes & Noble now having pages and ordering information. And the next opus, The Universal Book of Astronomy, is now also in the works, with the manuscript on its way to the publisher for a release date in 2003.

That's it for this time.
All the best,
David Darling