
Mass Extinction and the Structure of the Milky Way (2013) - DrScump
https://arxiv.org/abs/1309.4838
======
fizixer
As a non-astronomer, I hadn't thought of that but now that I read the
abstract, it makes complete sense (assuming evidence supports the thesis)

\- Might be related to why moon's surface is so scarred and yet in many
centuries of recorded (astronomical) history (since the invention of
telescope) we haven't seen any major lunar impact events.

\- Also I was reading the other day how our solar system is going through a
local "bubble" (region of unusually low interstellar density) but is heading
towards a certain G-Cloud.

Mind blowing stuff. I guess once we have fixed the planetary mess (climate
change) and biological-aging, we'd have a serious type-I [2] problem to worry
about (and we can't even handle/track the inner solar system objects yet, NEO,
asteroids, etc).

[1]
[https://en.wikipedia.org/wiki/Solar_System#Galactic_context](https://en.wikipedia.org/wiki/Solar_System#Galactic_context)

[2]
[https://en.wikipedia.org/wiki/Kardashev_scale](https://en.wikipedia.org/wiki/Kardashev_scale)

~~~
bamboozled
What needs to be _fixed_ about biological aging exactly?

~~~
fizixer
Ehh ... it needs to be eliminated? [1]

[1]
[https://en.wikipedia.org/wiki/Life_extension](https://en.wikipedia.org/wiki/Life_extension)

~~~
semi-extrinsic
I never understood the people who argue for indefinite life extension. Imagine
a world _with essentially no children_. No generation of young adults growing
up and spurring change in the world. I think it would not just take away a
crucial part of the human experience, but our entire economic system would
collapse. There's just too much of it tied into the constant churn of people.

(Of course, you might imagine indefinite life extension springing into
existence only after we've started rapid colonisation of space; a pipe dream
if I ever saw one. Even then, Earth would still be holden to what I describe.)

In two-three generations, most everyone alive in the countries where life
extension was widely adopted would be old farts that didn't want to take up
much further debt, with few new ideas and not much drive left in them.
"Science advances one funeral at a time", as do many other fields key to human
progress.

Meanwhile, the countries too poor to see mass adoption of life extension would
out-grow and out-innovate our collective asses faster than you can say
"collapse of Western civilisation".

So you'd live forever, but in increasing poverty (due the countries that
produce most of the things you buy having much higher growth than yours) in a
stagnant, crumbling society.

If we were to invent indefinite life extension that was affordable beyond the
0.1%, I think it would be the ultimate tragedy of the commons.

~~~
Nursie
You embody my greatest fear and annoyance in this area.

I think it's perfectly possible that, within my lifetime, significant or
indefinite life extension could become possible.

But I'd bet that fears about effects on society, as well as the arrayed forces
of religious conservatism, will create so much strife on the matter that it'll
be denied to people for long enough that I'll die unnecesarily.

~~~
bamboozled
Ironically your wish to "live eternally" kind of sounds like something out of
the bible ;)

~~~
Nursie
Not really, I said indefinitely. There's not really such thing as eternal.

For instance - in under a billion years the earth is likely to become too hot
for liquid water to exist on the surface, likely seeing the end of (most) life
on earth. Beyond that, much/most of the solar system gets destroyed when the
sun goes red-giant. Unless interstellar travel is commonplace by then, it's
pretty final.

~~~
Arizhel
Oh, come on. The reason we balk at interstellar travel these days is because
it'll take thousands of years to get to the nearest star with current
propulsion technology. But thousands of years is still far less than 1B years.
If we're still around in several hundred million years and the Earth is
getting too hot, and we haven't invented warp drive yet, then of course we're
going to build a bunch of generation ships and take our chances in
interstellar space. By that point, it really shouldn't be that hard to build
such ships that are reliable enough to last indefinitely, powered by fusion
reactors.

------
legolas2412
From Wikipedia entry on milky way, "These oscillations were until recently
thought to coincide with mass lifeform extinction periods on Earth.[148]
However, a reanalysis of the effects of the Sun's transit through the spiral
structure based on CO data has failed to find a correlation.[149]".

Those papers are from 2008 and 2009. Is this paper proposing something
different?

------
Sukotto
Neat coincidence to see this on the front page today. On the train this
morning I was re-reading David Brin's "The Deadly Thing at 2.4 Kiloparsecs".
His 1984 article examining Earth's fairly regular mass extinctions and what
might be causing them.

As a new forward to the story, Brin mentions the OP-linked theory.

Imho, the article still holds up well and you can read it here:
[http://davidbrin.blogspot.jp/2015/07/the-deadly-thing-
at-24-...](http://davidbrin.blogspot.jp/2015/07/the-deadly-thing-
at-24-kiloparsecs-are.html)

------
antonmks
"significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago" \-
it seems that periods between extinctions events are so large that you can
easily fit there hundreds and even thousands of civilizations like ours. So
not much to worry about, we will have plenty of opportunities to kill
ourselves before a comet does us in.

~~~
dghughes
I'm not a math wizard but going by that pattern it seems the periods are
getting shorter.

I tried to find a sequence
[https://www.wolframalpha.com/input/?i=415,+322,+300,+145,+33...](https://www.wolframalpha.com/input/?i=415,+322,+300,+145,+33,+..).

~~~
mrec
The periods (intervals between events) there would be [93, 22, 155, 112] My.
That doesn't look like they're getting shorter.

~~~
swamp40
But they _are_ getting closer! :)

------
Gargoyle
Hmmm. If this hypothesis held up, you'd want to factor it into the Drake
Equation. Number of systems that didn't cross some threshold of intensity or
frequency of arm crossing events that could cause mass extinctions often
enough to make intelligent life impossible to develop.

Or something like that.

~~~
d4nt
I suppose it's possible that just the right amount of mass extinction events
are necessary for intelligent life to emerge.

Too many and evolution doesn't build up any momentum, too little and there
isn't enough change to make intelligence (i.e. adaptability) worth having. So
the Drake equation would need to be looking for that Goldilocks zone of mass
extinctions.

~~~
flukus
Isn't the reverse just as likely, that many potential paths to intelligence
were snuffed out by extinction events. The currently accepted theory is that
it the evolutionary pressure of climate change was enough for us to evolve
intelligence.

~~~
baking
I think that humans as a species are more likely to survive a mass extinction
event (even if 99% of the population is killed) through manipulation of their
environment, stored food, eating rodents, insects and fish, and the
cooperation of communities for having babies and raising children. Therefore,
mass extinctions might serve as a winnowing out of dominant species that can't
adapt to major changes. Of course the adaptability of humans has not yet been
tested in that way (unless you count the recent ice age.)

Also there is the whole "multi-planetary species" option.

------
jmeyers44
This is eerily similar to the plot of The Three-Body Problem[1], specifically
the cyclical development of intelligent life and its race to avoid mass
extinction caused by intersecting one of three suns in its stellar system.

[1][https://en.wikipedia.org/wiki/The_Three-
Body_Problem](https://en.wikipedia.org/wiki/The_Three-Body_Problem)

~~~
perseusprime11
I heard this is a great book but could not get into this book. I was listening
to an audio book. Maybe I should try a physical book next time.

~~~
jmeyers44
Highly recommend (I read the physical book). It picks up after the first 100
pages or so.

------
edem
I'm a bit puzzled here. I thought the arms themselves were moving around the
galactic core. What does the Sun pass then? Little hint?

~~~
brutuscat
_Originally, astronomers had the idea that the arms of a spiral galaxy were
material. However, if this were the case, then the arms would become more and
more tightly wound, since the matter nearer to the center of the galaxy
rotates faster than the matter at the edge of the galaxy. The arms would
become indistinguishable from the rest of the galaxy after only a few orbits.
This is called the winding problem._

 _Lin and Shu proposed in 1964 that the arms were not material in nature, but
instead made up of areas of greater density, similar to a traffic jam on a
highway.[3] The cars move through the traffic jam: the density of cars
increases in the middle of it. The traffic jam itself, however, does not move
(or not a great deal, in comparison to the cars). In the galaxy, stars, gas,
dust, and other components move through the density waves, are compressed, and
then move out of them._

------
codeulike
So how long till next arm?

~~~
blauditore
I don't know where we stand now, but there are two arms and a galactic year is
~250 million terrestrial years, so I'd say a priori on average ~250/2/2 = ~60
million years from now.

~~~
vorg
There are two thick arms, and two thin ones in the picture, as well as a spur
(the Orion Spur in which our Sun presently dwells). The article postulates the
existence of a second spur on the far side of the galaxy where we can't see,
based on the history of extinction events in the past 250 million years and
the observed symmetry of many other spiral galaxies.

------
steinystein
Full text:
[https://arxiv.org/pdf/1309.4838.pdf](https://arxiv.org/pdf/1309.4838.pdf)

With what reasoning or evidence do they propose their new model of the galaxy?

Is it:

\- extinction events, therefore new model

or

\- astronomical data, therefor new model, and look how nicely it correlates
with known extinction events

~~~
T-A
A bit of both.

They say that with the model depicted in Fig 1, based on Spitzer/GLIMPSE
surveys [1], nine of eleven extinction events which they identify (the six
"canonical" ones plus five other significant drops in marine biodiversity,
Section 2.2) occurred while the solar system was passing through a spiral arm
(Section 3).

They then point out that it's easy enough to modify the model to fit all
eleven events: we can't see what's on the other side of the galaxy, so we can
hypothesize a "spur" there, similar to the Orion spur on our side, with some
support for that idea coming from the symmetry of other galaxies.

But even without such modifications, nine out of eleven is not bad. Spiral
arms need not necessarily explain every single one of them.

[1]
[http://inspirehep.net/record/817646?ln=en](http://inspirehep.net/record/817646?ln=en)

~~~
steinystein
Great summary. Thank you.

------
DrScump
Here's an excellent interview of Jonti Horner by John Batchelor on this topic
(free podcast):

[https://audioboom.com/posts/4827661-mass-extinction-and-
the-...](https://audioboom.com/posts/4827661-mass-extinction-and-the-
structure-of-the-milky-way-joint-horner?t=0)

------
llccbb
Interested parties should also look at the work of Dr. Adrian Melott[0].

[0]
[https://scholar.google.com/citations?user=GWB114EAAAAJ&hl=en...](https://scholar.google.com/citations?user=GWB114EAAAAJ&hl=en&oi=ao)

------
ryan-allen
I wonder when we're due for another crossing?

~~~
rusanu
We're in the middle of the (minor) Orion Arm right now:
[https://en.wikipedia.org/wiki/Orion_Arm](https://en.wikipedia.org/wiki/Orion_Arm)

------
cheez
This isn't new. I remember reading about this years ago. I suppose the new
contribution is offering an actual model to do this.

------
perseusprime11
One of the reasons why we need to find a way to get to Mars and other places
where humans can thrive. If we were the only wonder in the world, imagine the
travesty of getting wiped out.

~~~
avz
How would Mars help? Mars, like Earth, is on a tight (1.6 AU) gravitational
leash of the Sun. When the Sun dives into one of the galactic arms, so do Mars
and Earth.

That said, interplanetary travel is probably something we need to get good at
before we try the interstellar kind, so in a way, Mars settlement brings us a
tiny bit closer to galactic safety.

~~~
yourapostasy
If I'm reading that paper correctly, then we need more than interstellar
capability, we need near-intergalactic capabilities. We would have to be
solidly past a Kardashev Type II and almost attaining a Type III
classification, to either move our own solar system, or establish habitats in
safer galactic zones outside the arms (like outside the galactic poles or
positioned above the arms). Perhaps these transitions is the Fermi Paradox's
Great Filter: might it be exceedingly difficult for a civilization to hit the
Kardashev Type II-III level and implement the necessary avoidance/mitigation
sufficiently fast enough?

------
vanderZwan
Wasn't this theory part of the inspiration of the story arc for the Mass
Effect games?

------
nthcolumn
Not so goldilocksie after all

------
DrScump
Abstract: "We use the most up to date Milky Way model and solar orbit data in
order to test the hypothesis that the Sun's galactic spiral arm crossings
cause mass extinction events on Earth. To do this, we created a new model of
the Milky Way's spiral arms by combining a large quantity of data from several
surveys. We then combined this model with a recently derived solution for the
solar orbit to determine the timing of the Sun's historical passages through
the Galaxy's spiral arms. Our new model was designed with a symmetrical
appearance, with the major alteration being the addition of a spur at the far
side of the Galaxy. A correlation was found between the times at which the Sun
crosses the spiral arms and six known mass extinction events. Furthermore, we
identify five additional historical mass extinction events that might be
explained by the motion of the Sun around our Galaxy. These five additional
significant drops in marine genera that we find include significant reductions
in diversity at 415, 322, 300, 145 and 33 Myr ago. Our simulations indicate
that the Sun has spent ~60% of its time passing through our Galaxy's various
spiral arms. Also, we briefly discuss and combine previous work on the
Galactic Habitable Zone with the new Milky Way model."

TL;DR: our Sun's bumpy orbit through the spiral arms of out galaxy means
periodic increases of comets and other bodies being jarred loose and later
hitting Earth, resulting in mass extinctions.

The full paper is a free download from this page.

~~~
PhasmaFelis
...Huh. I always assumed that most stars kept approximately the same position
relative to the rest of the galaxy. (Barring "up/down" oscillation if the
orbital plane isn't perfectly aligned with the galaxy's.) There must be some
kind of overall structure to maintain distinct spiral arms, right?

Does the Solar System actually make a complete circuit of the bulk of the
Milky Way? Is that unusual?

~~~
jamestnz
The spiral arms are not fixed masses. If they were, they would quickly wind
themselves up tighter and tighter, as the inner areas are orbiting faster than
the outer parts. Within a short time the spiral arms would be dispersed.

Instead, you can think of the spiral arms as being like the highest-density
part of a traffic jam. In a traffic jam, cars are slowing down and bunching
onto the back of the queue, while other cars are finally trickling off the
front of the queue and speeding back up. In this way the traffic jam itself
stays in a stable position, while individual cars constantly move through it.

In other words, it isn't the same stars that make up the spiral arms over
time. As stars orbit the galactic center, they move in and out of the spiral
arms.

~~~
colechristensen
Put a different way, a galaxy's spiral arms are like waves.

------
spenrose
Maybe update the title to say (2013)?

------
Cozumel
There's interesting parallels with the Hindu Yugas here.
[https://www.thoughtco.com/the-four-yugas-or-
epochs-1770051](https://www.thoughtco.com/the-four-yugas-or-epochs-1770051)

~~~
averagewall
It might be interesting if the people who invented the Yugas could have had
any awareness of mass extinctions and the structure and behavior of the
galaxy. Since they surely didn't, there's obviously no connection at all and
it's not interesting - just made up myths.

------
ucontrol
Oh shut up.

The number of people that keep living in denial and rationalization of their
sub-optimal circumstance astounds me.

Just face it and be honest. There is nothing noble in being a 50 year old for
an infinity given the option to be youthful and mentally/physically fit
instead.

Vanity, superficiality, shallowness... All these buzzwords that criticize
something that is perfectly natural to desire, in an effort to signal some
higher moral ground.

Come on.

~~~
milquetoastaf
Yea I am signalling the moral high ground because HN is full of fucking
sociopaths who want to live forever so they can execute their dumb ass startup
until the heat death of the universe or learn new languages - at the expense
of completely fucking up the world and our place in it. It helps to take a
look in the mirror sometime.

Life extension technology is going to ruin humanity and the earth. Look up
this comment in fifty years and tell me I'm wrong.

~~~
dredmorbius
Make that 500 years, and you might get some takers to seal the deal ....

~~~
milquetoastaf
Fair point. I will extend my offer even up to a thousand years.

------
ptr_void
Is this supposed to be some sort of academic joke? Reminds me of
[http://tylervigen.com/old-version.html](http://tylervigen.com/old-
version.html) Maybe this isn't, sometimes science do work in strange ways.

