On Mon, 1 Oct 2018 18:41:05 -0700 (PDT), Gary Harnagel
wrote:
On Saturday, September 29, 2018 at 3:55:55 AM UTC-6, Paul Schlyter
wrote:

On Fri, 28 Sep 2018 05:49:40 -0700 (PDT), Gary Harnagel
wrote:

On Friday, September 28, 2018 at 3:47:01 AM UTC-6, Paul
Schlyter
wrote:

You are hopelessly overoptimistic. The typical distance
between
galaxies is millions of light years or more.

That's true ... TODAY. What about 9 billion years ago?

Back then the galaxies were some 3 times closer to one another
than
today, so the typical intergalactic distance were perhaps about a
million instead of millions of light years.

But, more importantly, back then there were few if any population
I
stars in existence. All stars back then were population II stars,
which have very little, if any, elements heavier than H and He.
Those
heavier elements are required to form life. So back then there
was no
life in the universe, that we can say with great certainty. Back
then, our Sun and our Earth did not even exist. Life, of all
kinds,
formed later.

9 billion years ago there certainly WERE stars with heavy elements:


http://www.astronomy.com/news/2016/0...rly-galaxies-c
hallenges-star-forming-theory

Although their metallicity was only 20% of stars near us, that's
pretty
good for 11 billion years ago, wouldn't you say?

Lower metallicity means less material from which life can form.


Therefore you are saying that any civilisation would with
great
probability learn interstellar travel at or near light speed.

I believe there are other alternatives.

Such as wormholes? Or did you have something else in your mind?

Wormholes, Alcubierre=type drives, transit to other branes, and
ways not
even a glimmer in the eyes of theoretical physicists.

Now you've entered the realm of science fiction...

Are you even aware of the difficulties involved? For instance,
colliding with a grain of sand near light speed would mean
the end of
your expedition.

Indeed, I am quite aware of the difficulties. That's why I
think
there are alternatives.

WHICH alternatives? How can you travel millions of light years in
just millions of years without traveling at near light speed?
Answered above.
So that one survivor can spread its DNA over the whole
galaxy
in a few million years.

Now you are getting more modest, which is good. Earlier you
claimed
that this one survivor could spread its DNA to **other**
galaxies
within the same time span of a few million years. That would
require
travel near light speed.

Not necessarily. If this civilization developed, say, 5
billion years
after the big bang, the galaxies would have been closer
together.

Not by much. Since the big bang happened 13.5 billion years ago,
5
billion years ago the intergalactic distances already had about
60%
of their current value.

And maybe there's a way to "wink out" there and "wink in" here
vitually
instantaneously. We haven't had millions of years of scientific
development yet.

More sci-fi...

And as we seem to agree, travel near light speed has certain
high-probability risks. I think there are alternative ways to
get
from one place to another.

You are very quiet about these alternative ways... why?
"Wink out", "wink in" :-)
Your grasp of probability theory must be very weak, or else
you
would not make such claims.

I have to laugh at your assertion again :-)) Are you familiar
with
the Law of Large Numbers?

Do you consider one to be a large number? One is the number of
planets known to have life...

The law of large numbers say that if you repeat an experiment a
large
number of times, the outcome will be very close to the expected
value. But, in the case of life in the universe, we have no idea
what
the expected value is. So the law of large numbers does not help
us
here.

Sure it does. We don't have to know the expectation value. We
KNOW it
happened ONCE. Given ENOUGH chances, it will happen again.

Sure, but have there been ENOUGH chances? We don't know, we can only
guess or believe.

Given what
we know about planetary systems today, about the number of stars in
our
galaxy, about the number of galaxies in just the VISIBLE universe
and
the tininess of the visible universe, you don't believe it hasn't
happened
MANY times? If so, you are an amazing pessimist!

You see? All we can do is believe, we don't know. We are getting to
know the first few factors of the Drake equation, but several factors
remain unknown to us. And these unknown factors are the hardest to
get to know. For instance, what is the typical lifetime of a
technologically advanced civilization? Apart from beliefs and
guesswork, hov can we actually get to KNOW that value?

And how can we be certain that this lone surviving
intelligent
? civilization would devote itself to space travel over
intergalactic
distances?

Or develop some alternative means where distance isn't
important? If "a"
civilization didn't, another one would.

That's your guess, and it is a far cry from "absolutely certain"
that
it actually is so.

YOU are the only one talking about "absolute certainty." I'm
talking about
probabilities.

Even if you call it "very high probability' it's really the same
thing. One thing about extraterrestrial life is that ve cannot be
"almost certain" about anything.


You and I are working from different assumptions. Are you
familiar
with Paul Steinhardt's Ekpyrotic theory?

https://arxiv.org/abs/hep-th/0103239

https://en.wikipedia.org/wiki/Ekpyrotic_universe

It posits a cyclic universe. If it has any credence it means
that past
universes existed. If intelligent life is as rare as some here
believe,
it becomes a virtual certainty that it developed in a previous
genesis,
maybe millions of times. If some couldn't find a way to
transport itself
from one genesis to the next, one would have. Imagine, a
civilization
billions of years old appearing on the scene 13 billion years
ago!

But what if it doesn't have any credence? We don't know if it
has, so
we can only guess. And you must do much better than guesswork to
be
able to reliably claim that something is "almost certain".

Don't be such a pessimist! It's bordering on a mania :-)

Don't be such a dreamer... When you talk about extraterrestrial life,
don't you mean real life in the real universe and not just your
fantasies and wishes?

That might make a great SF story to outdo even Olaf Stapledon.
But I
don't think it's SF. Anyway, now you see why no argument about
probability has any affect on me whatsoever. So, want to
discuss the
probability of Steinhardt et al. being right? :-)

You can fantasize as much as you want, but please stop trying to
misuse probability to claim something is "almost certain" when it
actually just is a guess of yours.

Pessimist!

No, I'm a realist.

Nope! Something supernatural is something which
contradicts physics.

https://www.merriam-webster.com/dictionary/supernatural

"departing from what is usual or normal especially so as to
appear to
transcend the laws of nature"

With that definition, radio communication would have been
"supernatural"
a few centuries ago.

Exactly! Now you're getting it :-)

The scientific method requires that a phenomenon be
repeatable by any
competent researcher. It also requires the ability to
change the
inputs.

No it doesn't. Astronomers cannot experiment with the
universe by
changing the input, but despite that astronomy is regarded as
a science.

Astronomical science requires that experiments performed here
on earth be
valid elsewhere in the solar system, galaxy, universe. Now
that we have
sent missions throughout the solar system, that part is no
longer
assumption, and we have no choice but to assume it's true
throughout the
universe. It SEEMS to be, anyway, but it IS a weakness that
certain
scientific disciplines have. Cosmology is a case in point. We
have the
Big Bang model, but there are alternatives ...

There are no alternatives today that match empirical data so well.

Irrelevant since we're talking about billion-year-old civilizations.

You are then talking about something neither you nor anyone else on
Earth know anything about.


The discovery of the cosmic background radiation made the "big
bang"
win over the "steady state" cosmology. But note that this is not
final. If and when a cosmology appears that matches empirical
data
even better, then it will replace the "big bang" as the standard
cosmological model.

The standard model assumes inflation. There are scientists that
dispute that.


https://www.wired.com/2008/02/physic...ng-wasnt-the-b
eginning/

There are always people questioning, that's a natural part of the
scientific process. Time will tell who is right.