From: David Rudiak <DRudiak@aol.com>
Date: Sat, 20 Nov 1999 15:06:53 EST
Fwd Date: Sun, 21 Nov 1999 09:38:06 -0500
Subject: Re: The Drake Equation


 >From: Dennis Stacy <dstacy@texas.net>
 >Date: Tue, 16 Nov 1999 17:35:46 -0600
 >Fwd Date: Wed, 17 Nov 1999 17:01:09 -0500
 >Subject: Re: The Drake Equation


 >>From: David Rudiak <DRudiak@aol.com>
 >>Date: Tue, 16 Nov 1999 10:07:01 EST
 >>Subject: Re: The Drake Equation
 >>To: updates@globalserve.net

<snip>

 >>Incidentally, relativity theory never has said that
 >>slower-than-light interstellar travel was impossible, as some
 >>debunker's claim.

 >Talk about your truisms!

Obviously you don't understand what I'm talking about.  Many
SETI people, e.g., argue that aliens would never come here
because the distances are too vast. To reduce the travel times
requires speeds some significant fraction that of light (say 10
to 30%), which requires vast expenditures of energy.  Thus the
argument, I have frequently heard, that UFOs couldn't exist,
because interstellar travel is impossible -- not extremely
difficult -- simply impossible.  E.g., physics profressor
Lawrence Krauss, in his debate with Stanton Friedman, took that
position.  Kent Jeffrey, in his Roswell debunking debate with
Kevin Randle on Nightline 2 years ago, also took that position.

 >Relativity has always insinuated that
 >any form of interstellar travel would necessarily be subluminal
 >by definition, unless you wanted to become a photon in the process.

No, that's not the point.  The claim is that relativity theory
makes interstellar travel impossible, not because it is
subluminal (sheesh!), but because of the distances and energies
involved.

However, NASA doesn't necessarily agree.  E.g., NASA director
Dan Goldin has proposed a small interstellar probe to Alpha
Centauri, perhaps 40 years from now, powered by large space
lasers aimed at a large sail attached to the probe, and which
could possibly slowly accelerate the probe to 10% light speed.

An article on several proposed interstellar propulsion schemes
appeared recently in Popular Science

(http://www.popularscience.com/context/features/startravel/).

 >But let's talk about interstellar travel at 99% the speed of light.

Why does it have to be 99% of the speed of light?  Most schemes
call for 10 - 30%.  At 10%, a trip to Alpha Centauri takes 50
years.  Journeys between nearby stars on the orders of decades
are certainly managable.

 >How you gonna turn?

Why do you need to turn when going between Star A and Star B --
to visit the next McDonalds?

As you approach your destination, you slow down to more
conventional speeds so that you can explore.

 >And what happens when you run headon into a grain of dust
 >at such speeds, never mind a rock the size of your fist?

Certainly a legitimate practical question, also faced BTW by
other space vehicles.  Near earth orbit, e.g., is far, far
dirtier than interstellar space, which is about as perfect a
vacuum as you are going to get (only about 1 hydrogen atom on
average per cubic centimeter).  How many disastrous dust
collisions have happened so far in tens of thousands of hours of
operation of Mir and space shuttles in dirty near earth orbit?
How many rocks have they run into?  I'm not saying that this
can't happen, just that it isn't that common to run into
anything sizable out in space, particularly in the interstellar
void.

As I remember, one of the Voyager spacecraft was deliberately
sent through the rings of Saturn and emerged unscathed at 70,000
mph.  Interstellar space is far, far cleaner than that.  Odds
are you could fly from here to Alpha Centauri without ever
encountering a dust particle, much less a rock.

Running into a microgram dust particle at 10% light speed would
be like running into a stick of dynamite.  One possible solution
would be to use passive shielding, like that being proposed for
the international space station to protect it from orbiting
space debris.  It would be several perimeters of material like
Kevlar to catch and diffuse any collisions, sort of like a giant
bulletproof vest around the space station.  Something like that
might possibly work for very small material for a starship.

Another possible way to deal with the problem would be active
shielding of some kind, say powerful forward lasers or
microwaves which either directly sweep small material out of the
way, or break it up and ionize it so that it can be steered
around the sides with electromagnetic fields.  This, however,
would require a continuous small propulsion to counter the
braking effect of the active shielding.

 >And how you gonna apply the brakes, anyway?

You decelerate the same way you accelerated to begin with.  Am I
going to fast for you?

 >A pretty picture not, I think.

That's because you're doing your usual mostly pointless stirring
of the pot.

<snip>

  >In any case, interstellar travel and galactic colonization by
  >older, more advanced space races, would indeed seriously change
  >any estimates made by the Drake equation of the number of
  >civilizations out there. With colonization, they could
  >conceivably number in the millions or billions.

  >David Rudiak


 >Just as the odds against their chances of having ever
 >materialized could equally well number in the millions and
 >billions. Very Large Numbers work both ways.

What gobblydegook!  The law of large numbers says that even very
improbable events can happen given sufficient trials, such as
someone winning the lottery even if the odds are 10 million to 1
against.  What the hell are you arguing anyway -- that because
there are ten million times more losers there can never be any
winners?

Probability theory also says that the probability of something
happening depends on the number of ways it can happen.  Even
extremely rare events usually have more than one way they can
happen.  Different lottery winners, e.g., don't need to scratch
off the same numbers or buy tickets at the same liquor store.

Even though it is very improbable for intelligent life to evolve
in any given star system, the bet among most scientists is that
the odds are not so small that it won't happen elsewhere in our
galaxy, given the hundreds of billions of stars out there.

David Rudiak