From: "Keith F. Lynch" <kfl at KeithLynch.net>
To: WSFA members <WSFAlist at KeithLynch.net>
Subject: [WSFA] Re: Voyager 1 anniversary
Date: Wed,  6 Sep 2017 22:29:28 -0400 (EDT)

"Mike B." <omni at omniphile.com> wrote:
> Thanks, Keith!=C2=A0  Those figures really re-inforce what Douglas
> Adams w= rote: ...

You're welcome.  I used that quote just a few weeks ago on another
list, in response to someone suggesting that starships would collide
with planets that aren't in any solar systems:

  From: "Keith F. Lynch" <kfl at KeithLynch.net>
  Subject: [WSFA] Re: Lots of smaller 'Ronin' (sun-less/ejecta) planets
  Date: Wed, 26 Jul 2017 23:10:24 -0400 (EDT)

  > FYI -- And we thought that Earth's orbits were getting full of
  > space junk...

  > I can envision 'Star Trek'-like starships ending up like
  > windshield-splatted bugs in picoseconds...

  "Space is big.  Really big.  You just won't believe how vastly,
  hugely, mind-bogglingly big it is.  I mean, you may think it's a
  long way down the road to the chemist, but that's just peanuts to
  space."  -- Douglas Adams

  A collision in interplanetary space is extremely unlikely.  James
  White wrote a novel titled _Deadly Litter_, in which littering in
  space is a serious crime, since a collision at interplanetary speeds
  with a single discard coffee ground would wreck a spaceship.

  I did the math.  Collisions in low Earth orbit are an issue,
  Collisions in interplanetary space are not.  If I recall correctly,
  I determined that if every person who ever lived had a spaceship
  and traveled at random in the solar system, spending all their time
  tossing coffee grounds overboard, and kept doing so until the sun
  turned into a red giant in a few billion years, there would probably
  not be a single collision.  This was partly because the speeds
  all exceeded solar system escape velocity, so the litter wouldn't
  accumulate.  Debris in the asteroid belt would be a much bigger
  concern, since there's more of it and since it doesn't dissipate.
  But even though there are trillions of unmapped objects there big
  enough to destroy any space probe, not one of the probes that's been
  sent through the belt has been damaged, and probably none ever will.

  And the "ronin" planets aren't in interplanetary space, but in
  interstellar space, which is a couple dozen orders of magnitude
  larger.  A chance collision in interstellar space, even with a grain
  of sand, is absurdly unlikely.  If there was much stuff there, we
  couldn't see very far, but in most directions we can see all the way
  to the cosmic horizon.

  Mankind has sent five probes into interstellar space.  (Whether any of
  them have reached it yet depends on your definition, but they'll all
  get there eventually.)  It's interesting to think about how any of
  them could be someday detected by aliens, or, conversely, how our own
  remote descendants could ever detect similar probes from other solar
  systems.  Suppose every one of the ~10^11 stars launched, over its
  lifetime, a thousand Voyager-like probes into random interstellar
  trajectories, all of which will forever remain within the galaxy.
  How would an advanced civilization go about finding any of them?
  (Not counting ones that had been launched in the past thousand
  years or so, hence were still close to their parent star.)

  Unless there's some completely unknown science, the best way seems to
  be radar.  To have a reasonable chance of success, most of the mass of
  the galaxy would have to be turned into search ships, and every one
  of them would have to have a radar so powerful that not only would we
  have already picked it up if it was operating anywhere in the universe
  in our past light cone, Marconi would have picked it up too.

  > A handful of free-floating planetary-mass objects have been
  > discovered by infrared surveys of young stellar clusters and
  > star-forming regions as well as wide-field surveys, but these
  > studies are incomplete for objects below five Jupiter masses.

  I'd bet that those studies are incomplete for objects above five
  Jupiter masses, too.  ....

Any novel, movie, or short story that depicts a chance meeting in
interstellar space, unless it has some kind of explanation such as
an infinite improbability drive, I will not waste my time finishing.
Life is too short to waste reading authors who think space is just
like the Atlantic Ocean only dryer.

> Traveling for 40 years, currently moving away at 17 km/sec, and it's
> STILL not even 1 light-day away!=C2=A0  Wow.

And for most of those 40 years it was going faster than that.

It's fun to do math, if only just to get a feel for the sizes of
things.  I've discovered lots of unexpected things.  For instance:

The average person generates more heat than the sun, per unit mass
per unit time, by a factor of about ten thousand.  Similarly per
unit volume per unit time, since people have about the same density
as the sun.

Our galaxy is about 100,000 light years in diameter, and about 1000
light years thick, and masses hundreds of billions of times more than
our solar system.  What is its average *area* density?  In other
words, what if you flattened those 1000 light years into a thin
uniform sheet?  I calculated that it would have about the same area
density as a potato chip.  If it *was*, in fact, a potato chip, it
would have about 10^48 dietary calories.  To burn them off you'd have
to walk about 10^27 light years, i.e. walk to the furthest known
galaxy and back about 10^17 (100 quadrillion) times (ignoring the
expansion of the universe).

The sun radiates about 4*10^26 watts, mostly as visible light.  If it
was in the form of gravitational waves instead, all those watts of
power could go through you without hurting you.

The most powerful event ever detected was gravitational wave radiation
from two black holes merging 1.3 billion light years away.  It was
3.6E+49 watts, i.e. 200 solar masses per second annihilated.  If it
had been visible light, it would have not just been bright enough to
see from here, it would have been bright enough to read by.  (In Planck
units, however, that power is only about 0.001.)

Although it lasted less than a tenth of a second, if we'd been
able to catch and store all that energy, it would have powered our
civilization for about 10^28 years, i.e. about a million trillion
times longer than the lifetime of the universe so far.  Or if it all
went to me, I could use it to heat my room for 10^38 years, or to run
my laptop computer for 10^39 years.

Interstellar distances are long, but not incomprehensibly so.  The
total distance cars have driven is in the hundreds of light years.
But don't get too proud of our technology; the total distance ants
have crawled is certainly in the billions of light years at least.

About half a century ago ago, I found some fossils that I recognized
as dating to the Ordovician period.  The time since the Ordovician is
to half a century what half a century is to how much time?

How long would it take to send everything on the Internet in Morse
code with a hand key?

How fast would standard punched paper tape have to move for it to be
possible to play high definition video from it?

Ignoring, once again, the expansion of the observable universe,
suppose you were to travel to the far end of it, not at walking speed,
but at the speed at which a stalactite grows.  And then move over by a
centimeter and head back at the same speed, past your starting point,
until you've reached the opposite end of the observable universe.  And
then repeat the process, again and again, until you've visited every
cubic centimeter.  Consider that it's absurdly easy to accidentally
write a computer program that would take much longer than that to finish.

Also see https://what-if.xkcd.com

And please turn off the MIME.  Thanks.

Does anyone have a current email address for Eric Jablow?  Thanks.