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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).
3. Bookends
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.
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