
Space and Time - rndn
http://thegreatatuin.blogspot.com/2015/07/space-and-time.html
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evanb
Let's not forget about the habitable epoch of the early universe [1]. There's
a good 7 million years near the beginning of the universe that in principle
was inhabitable to Earth-like life. None can say if the physicists of that
epoch (if there were any) had enough observational evidence to foresee their
quickly approaching end.

[1] [http://arxiv.org/abs/1312.0613](http://arxiv.org/abs/1312.0613)

* do actually I believe there was early-epoch life sophisticated enough to think up physical theories? No, but what does that matter?

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jakeogh
"It should be noted that a full 90% of the non-dark-matter mass of the
universe appears to be in the form of very thin X-ray-hot plasma clouds
surrounding large galaxy clusters, unlikely to condense to the point of star
formation via understood processes."

Wow. Non-dark matter is ~5%, so non-xray-hot-halo matter is 0.5% of the matter
universe? That's all the rocks, all the stars, all the exotic objects we can
count. Half a percent?

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planck01
The article shows that the Fermi paradox is even more mysterious than some
thought, because we will probably not be the civilization in this universe or
galaxy that is 'in front' as we are not early but average.

However, something always bothers me about the Fermi paradox. I've never seen
the most obvious resolution mentioned (at least to me). I think that we are
just not (yet) able to detect any civilization given the maximum technological
state a civilization may reach. Many people assume that because technological
progress has been exponential last century for humans, that this can be
projected indefinitely into the future. Similarly like some thought about
indefinite economic growth. But this is nonsense, it is much more likely we
will plateau at some point. The Seti-project listens for radio signals with
star strength, assuming that a proper developing civilization is able to
manipulate stars as radio beacons. I find this highly unlikely that any
civilization will ever reach such technology or that it is even physically
possible. I think it isn't.

The only thing one can say is that apparently in this galaxy, no civilization
seems far enough 'progressed' yet to have colonized the entire galaxy, as I
also think that crossing galaxy boundary will be a no go for any civilization.
But will humans ever undertake such a quest? It will mean building
generational ships, enough DNA diversity to make a new civilization feasible
(minimum 5000 people?), finding a good habitable planet from here or be doomed
as traveling will take thousands of years and will be tremendously costly in
terms of effort, energy, materials and personal costs. How likely is that we
will ever do that for every planet in the galaxy? Technology to turn one
selves inward (e.g. VR) seems a much more likely turning point at which
outward exploration might not seem that interesting anymore.

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Gravityloss
This is something that's hard to get in general science journalism.

The logic of why things happen (why elliptical galaxies or small galaxies are
not good for life) is only easy to explain if you master the subjects very
well.

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zem
fun to read this alongside landis's "the melancholy of infinite space":
[http://www.geoffreylandis.com/infinite.htp](http://www.geoffreylandis.com/infinite.htp)

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tvawnz
Hmmm, great article that summarizes some of the more advanced explanations for
the Fermi paradox.

Some say that the Sun is young and so if there's other intelligent life, some
would naturally have a 7 or 8 gyr lead on us. But the contra is that the young
sun evolved just when the metallicity of the gas was high enough to actually
form rocky planets and the solar system.

The article notes that the universal star formation rate has been decreasing
for a while, since about redshift 2. So everything that's going to get a start
has already gotten it. The vast majority of possible planet host environments
are hostile because of SNe, AGN feedback, stellar winds etc. etc. etc. in the
article.

Short of the long, sure we could say that we are approximately at the time
when one would expect to see the emergence of advanced life give or take a
couple billion years.

HOWEVER, this article neglects the fact that there are still billions of stars
similar in aspect to the sun, that have cosmically long lifetimes, high
metallicities and relatively quiescent environments.

From Kepler we know that planet formation is not the exception, it is the
norm; at this juncture, it is impossible for us to say if rocky planet
formation is an exception or a norm. You have to understand that the Kepler
mission was not designed to figure that out, it was designed just to figure
out if planets were common. The next major ESA planet mission, PLATO (and I
think NASA may have a similar project in the works), will answer that
question, and until that time, it's entirely plausible that the galaxy is
filled with goldilocks planets.

(For reference, the Kepler spacecraft's sensitivity to earthlike planets in
the habitable zone is minimal-- it's a function of size of the planet vs
distance from the star, every time the planet goes in front of the star
(function of distance) a small signal (function of size) is added to a time
series that can be coadded over and over to remove noise (so maybe it takes 7
or 8 orbits to verify a planet). This is why Kepler mostly finds molten rock
planets and gas giants. The distribution of planets we know about today _is a
function of the instrument, not the actual planet distribution_.

The more interesting projects are the ones attempting to take planetary
spectra. A spectra of a planet's atmosphere will tell you the chemical
components of that atmosphere and is performed by taking a spectra of the star
and then subtracting the spectra of the planet in front of the star (the
difference between the two being the planet. There are certain chemicals in
atmospheres, called biomarkers, that are indicative of life (ozone, for
example, only exists in meaningful quantities because of photosynthetic life).
This is an incredibly difficult and ambitious project: you need high res
spectra at large signal to noise to even see these biomarkers which means
probably multiple nights of 8-10 hour observations on modern 8m class
telescopes, in the 30m telescope era, maybe it's more plausible; you need the
right type of rocky planet, of which we know few; you need that planet to be
in the exact right spot in its orbit in front of the star; and of course god
needs to make it not rain after your 20 hour flight to Hawaii.

For all we know, not only are planets the norm, not only are rocky planets the
norm, but life is also the norm.

Thus, not seeing advanced life is a function of _our instruments_ not
indicative of the fact that advanced life is somehow new, or rare. Even with
all the notes in the article, there could be advanced life with several
billion years head start on us.

A thought I haven't devoted much time to is that perhaps interstellar travel
is just downright impossible on a meaningful scale at a reasonable speed.

... Unless of course life arose from a panspermia situation, and we are the
actual results of the most sophisticated form of interstellar travel in the
universe. Perhaps we are a colony of some monolithic species, packing their
genetic blocks into chunks of ice and tossing them willy-nilly about the
galaxy...

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imglorp
> make it not rain after your 20 hour flight to Hawaii

Why is this not a global armchair sort of affair? Staff the site with a tech
as needed, but otherwise automate the whole deal and observers can queue their
requests which will get filled as god/weather/orbits permit?

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tvawnz
First, some telescopes do do portions or all of their observations in queue or
staff mode, where you just give them the required objects and weather
conditions. Just not all of them. I think most 8m class ones will have a
mixture-- if your proposal wins just 1 night, then maybe it goes to staff, but
if you got 10 nights you get to do it yourself.

There are a few reasons. First, lots of astronomers do not trust anyone but
themselves to deal with the data (and this is a reasonable distrust as every
single telescope has a unique 'feel' and quirks)-- so they want to be there to
do reshoots if necessary.

Another is that it's not entirely schedulable, like, if you queued up the
whole year's worth of observations (this is what you do, twice per year you
can apply for time, some telescopes once per year), and then everyone's sent
you their absolute best case requirements and you end up not being able to
fulfill them on time (because maybe there's a big volcano in Iceland that
changes the atmospheric transparency for 4 months), then its inconvenient and
the astronomers feel gypped that they won the time but didn't get the
observations.

Astronomers prefer being told: okay, you get 8 dark nights, but if there's a
storm, your SOL. But this is ok because you frequently have all your buddies
on Skype at the dome, so when you say "shit well the seeing is too bad to get
these spectra" your buddy says "well I have a bright night project we can
probably do through the clouds." This is how a lot of observations and
projects that can't win time on their own get their data.

A staffer will know how to take your observation requirements, wait until the
conditions are right and get exposures of x object at y wavelength for z time.

An astronomer will be able to, on the fly say: well our original plan isn't
going to work, but I know that at this time in winter we can see Draco from
this latitude and my friend was doing a project in Draco that isn't too hard
so I'll just snap that while I'm here.

That and most people like going to observatories, best business trip ever.

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paulpauper
this is interesting, but also I'm curious how a week-old blog on a old school
blogger template with only two posts got noticed so fast?

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beaner
Somebody wrote an article and shared it. Somebody who read it linked us to it.

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redwood
Great read, thanks. Title is a bit off though

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joehilton
I agree - great article, although I was expecting something on relativity or
maybe the recent attempts to remodel physics with only events and not rates
(e.g. exploring the possible non-existence of time).

But I did love the blog title - always nice to find a fellow Terry Pratchett
fan, RIP.

