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Re: What-if 0060: "Signs of Life"

Posted: Wed Aug 28, 2013 8:43 am UTC
by wraith
Klear wrote:
willpellmn wrote:Who is this Borislav?


The guy who asked the question.


aka me :roll:

Re: What-if 0060: "Signs of Life"

Posted: Wed Aug 28, 2013 8:53 am UTC
by Copper Bezel
davidstarlingm wrote:Another iteration (great circle bisecting largest angle) produces six 45-45-90 triangles and six 45-90-60 triangles. I don't know if these all have equal surface area.

Wait what? On a sphere?

Re: What-if 0060: "Signs of Life"

Posted: Wed Aug 28, 2013 9:03 am UTC
by Istaro
Klear wrote:I believe most kinds of monoculture are a sign of human influence. This is what ruined the opening fight in the forest in Gladiator for my brother-in-law.


Poor guy! I'd guess that ruins a lot of otherwise perfectly good[citation needed] movies for him.

tsadi wrote:So what's site who's source code is in all caps? Because I looked at http://contrailscience.com and it wasn't it.


That's a chemtrail-debunking page, not a chemtrail page, yeah?

Re: What-if 0060: "Signs of Life"

Posted: Wed Aug 28, 2013 9:26 am UTC
by Flumble
wraith wrote:
Klear wrote:
willpellmn wrote:Who is this Borislav?

The guy who asked the question.

aka me :roll:

So, it has come to this.

Re: What-if 0060: "Signs of Life"

Posted: Wed Aug 28, 2013 11:51 am UTC
by solune
WIMP wrote:how many life-bearing planets have intelligent life that tested nuclear weapons a few decades ago then stopped, versus how many were near a recent supernova


How many planets are near a recent supernova: many
How many life-bearing planets are near a recent supernova: very few.

Given only these two hypothesis I'd go with intelligent life. (I'm assuming that free oxygen is incontrovertible proof of life)

Re: What-if 0060: "Signs of Life"

Posted: Wed Aug 28, 2013 7:17 pm UTC
by Raen7
I guess I interpreted his question differently than Randall did.. I would have thought he meant something like, "If I teleported to a random location on Earth, what are the chances that I'd come into contact with another human or with some form of human civilization" -- in other words, it seemed to me more like a "population density" question, like what are the odds you'll end up in a completely uninhabited area vs. an inhabited one? Or to put it another way, how much of Earth is still "wilderness" vs. "developed". Maybe it's just me...

Re: What-if 0060: "Signs of Life"

Posted: Wed Aug 28, 2013 11:07 pm UTC
by dalcde
Raen7 wrote:I guess I interpreted his question differently than Randall did.. I would have thought he meant something like, "If I teleported to a random location on Earth, what are the chances that I'd come into contact with another human or with some form of human civilization" -- in other words, it seemed to me more like a "population density" question, like what are the odds you'll end up in a completely uninhabited area vs. an inhabited one? Or to put it another way, how much of Earth is still "wilderness" vs. "developed". Maybe it's just me...


I guess the intention of the question is to ask if a alien magically landed on Earth, what's the probability that it finds signs of human civilization (assuing it didn't see all the lights and houses during landing).

Re: What-if 0060: "Signs of Life"

Posted: Thu Aug 29, 2013 8:43 am UTC
by dalcde
tsadi wrote:So what's site who's source code is in all caps? Because I looked at http://contrailscience.com and it wasn't it.

Sites that spread nonsense (that contrail = chemtrail)

Re: What-if 0060: "Signs of Life"

Posted: Thu Aug 29, 2013 10:12 am UTC
by Klear
Strangely, I have yet to find a chemtrail website written in all caps. What is Randall hiding?!?!

Re: What-if 0060: "Signs of Life"

Posted: Thu Aug 29, 2013 11:27 am UTC
by wraith
dalcde wrote:I guess the intention of the question is to ask if a alien magically landed on Earth, what's the probability that it finds signs of human civilization (assuing it didn't see all the lights and houses during landing).


What I meant by asking it was similar to this, but it was about plainly visible human impact.

Me and a couple of friends have such "what if" discussions all the time. In one of those my theory was that if you have Earth and Parallel-Earth - the same, but without humans - if you were to be teleported at a random place on one of them, it would be impossible to tell which one is it without sophisticated instruments, as you'd have less than 1% chance of stumbling upon man made artifacts in sight on Earth.

According to Randall, this chance is not 1 but 7-10% (100% at night), which still sounds a bit much to me.

Re: What-if 0060: "Signs of Life"

Posted: Thu Aug 29, 2013 11:29 am UTC
by dalcde
Klear wrote:Strangely, I have yet to find a chemtrail website written in all caps. What is Randall hiding?!?!

Yeah but look at this: http://www.chemtrailcentral.com/
It's not in all caps, but half-cap half-regular with no apparent pattern!
(and it has a black background)

EDIT: And this: http://www.chemtrails911.com/
~90% of the source (tags) is in caps. Then a small portion is lowercase.

Re: What-if 0060: "Signs of Life"

Posted: Thu Aug 29, 2013 2:46 pm UTC
by endolith
wraith wrote:Me and a couple of friends have such "what if" discussions all the time. In one of those my theory was that if you have Earth and Parallel-Earth - the same, but without humans - if you were to be teleported at a random place on one of them, it would be impossible to tell which one is it without sophisticated instruments, as you'd have less than 1% chance of stumbling upon man made artifacts in sight on Earth.


The non-human Earth would be obvious because it would still be populated by large predators?

Re: What-if 0060: "Signs of Life"

Posted: Thu Aug 29, 2013 7:08 pm UTC
by mathmannix
endolith wrote:
wraith wrote:Me and a couple of friends have such "what if" discussions all the time. In one of those my theory was that if you have Earth and Parallel-Earth - the same, but without humans - if you were to be teleported at a random place on one of them, it would be impossible to tell which one is it without sophisticated instruments, as you'd have less than 1% chance of stumbling upon man made artifacts in sight on Earth.


The non-human Earth would be obvious because it would still be populated by large predators?


I assume you're not talking about T. rex here. It would certainly be obvious if you happened upon a Smilodon or one of the other large, exctinct felids native to North America (especially if you could somehow determine that you were in North America!) but chances are greater you would (even if you landed on, well, land) end up in a jungle or desert, and I don't think those really support predators larger than about 100 lbs., like a leopard or jaguar. Also, the larger extinct carnivorous mammals tend to look like, well, larger versions of extant species, like lions and bears, so although Smilodon would probably be instantly recognizable as something different, others might not be.

Large herds/flocks of extinct herbivores would be a better tipoff - in addition to the extinct ones like mammoths, giant sloths, your various "rhino-like" ungulates, and passenger pigeons, you also might find enormous flocks of bison or other hooved animals that no longer flock in groups that large outside of the Serengeti.

Re: What-if 0060: "Signs of Life"

Posted: Fri Aug 30, 2013 4:20 pm UTC
by mfb
endolith wrote:I wonder what uncontacted tribes or even contacted hunter-gatherer tribes think of satellites. Surely they've noticed them, and that they didn't exist in the relatively recent past. Do missionaries explain it to them? Do they understand through the language barrier?

Airplanes are much more mysterious in that respect. Sure, they look a bit like birds, but they can leave strange trails... (no, not chemtrails :p).

endolith wrote:The non-human Earth would be obvious because it would still be populated by large predators?
The density of large predators would be significantly lower than the density of humans is, as large predators (except humans) don't use agriculture to increase the population.

Re: What-if 0060: "Signs of Life"

Posted: Fri Aug 30, 2013 8:34 pm UTC
by rmsgrey
mfb wrote:
endolith wrote:The non-human Earth would be obvious because it would still be populated by large predators?
The density of large predators would be significantly lower than the density of humans is, as large predators (except humans) don't use agriculture to increase the population.

Also, large predators tend to be fairly conservative in their choice of prey - go after something that can fight back enough to injure you, and you're probably dead - by the time you heal up (if you do) you've probably starved. Of course, if it acts like it thinks you can take it, you can figure it probably knows better than you do - but until you figure it out, or get desperate enough, you should probably ignore it and concentrate on something you know you can take.

Re: What-if 0060: "Signs of Life"

Posted: Fri Aug 30, 2013 9:19 pm UTC
by MartianInvader
Shouldn't it be super easy to generate random coordinates on a sphere just by using the fact that all horizontal slices (edit: OF EQUAL HEIGHT :P) have the same area? So just choose a height uniformly from -1 to 1, then choose a longitude uniformly at random?

Re: What-if 0060: "Signs of Life"

Posted: Fri Aug 30, 2013 9:24 pm UTC
by endolith
MartianInvader wrote:the fact that all horizontal slices have the same area?

o_O

Re: What-if 0060: "Signs of Life"

Posted: Fri Aug 30, 2013 10:19 pm UTC
by rmsgrey
endolith wrote:
MartianInvader wrote:the fact that all horizontal slices have the same area?

o_O


Zero is constant, yes. I think what he's meaning is something more like that if you take two parallel planes a distance epsilon apart and slice through a sphere with both of them, then the area of the surface between the planes is constant. I've not proved this, but it seems plausible when you consider that the height from -1 to +1 is the sine of the latitude, so all he's suggesting is picking latitude as arcsine of a uniform random variable on the interval (-1,1)...

Re: What-if 0060: "Signs of Life"

Posted: Fri Aug 30, 2013 11:22 pm UTC
by Flumble
rmsgrey wrote:Zero is constant, yes. I think what he's meaning is something more like that if you take two parallel planes a distance epsilon apart and slice through a sphere with both of them, then the area of the surface between the planes is constant. I've not proved this, but it seems plausible when you consider that the height from -1 to +1 is the sine of the latitude, so all he's suggesting is picking latitude as arcsine of a uniform random variable on the interval (-1,1)...

Indeed it does. As I can't be bothered to devise a formula, I just took a million samples using a proven formula and placed the z value in a couple of buckets: [0.1003,0.1003,0.1002,0.1004,0.1004,0.0996,0.0999,0.0999,0.0995,0.0997]

Moreover it's the same method as explained here (up to equation 8) but worded differently. :roll: (why didn't that one immediately come to mind)

Re: What-if 0060: "Signs of Life"

Posted: Sat Aug 31, 2013 2:57 pm UTC
by mfb
The linked random point generator gives an error:
509 Bandwidth Limit Exceeded
The server is temporarily unable to service your request due to the site owner reaching his/her bandwidth limit. Please try again later.
I wonder which effect could have increased the traffic... :D.

Re: What-if 0060: "Signs of Life"

Posted: Sun Sep 01, 2013 5:12 am UTC
by PM 2Ring
solune wrote:
WIMP wrote:how many life-bearing planets have intelligent life that tested nuclear weapons a few decades ago then stopped, versus how many were near a recent supernova


How many planets are near a recent supernova: many
How many life-bearing planets are near a recent supernova: very few.

Given only these two hypothesis I'd go with intelligent life. (I'm assuming that free oxygen is incontrovertible proof of life)


Large amounts of free oxygen in a planet's atmosphere does make life seem likely, but it's not incontrovertible proof: there could be weird non-life chemistry going on that permits the build-up of atmospheric oxygen. Small amounts of free oxygen could be produced by ultraviolet light splitting atmospheric water, although you'd expect that the process would slow down substantially once an ozone layer forms. Of course, you'd also expect such oxygen to react with iron & other elements on the planet's surface, but the weird chemistry may reduce or prevent that some how.

Still, if we detect free oxygen in an exoplanet's atmosphere we should consider it a promising candidate for life.

Re: What-if 0060: "Signs of Life"

Posted: Sun Sep 01, 2013 4:11 pm UTC
by rmsgrey
PM 2Ring wrote:
solune wrote:
WIMP wrote:how many life-bearing planets have intelligent life that tested nuclear weapons a few decades ago then stopped, versus how many were near a recent supernova


How many planets are near a recent supernova: many
How many life-bearing planets are near a recent supernova: very few.

Given only these two hypothesis I'd go with intelligent life. (I'm assuming that free oxygen is incontrovertible proof of life)


Large amounts of free oxygen in a planet's atmosphere does make life seem likely, but it's not incontrovertible proof: there could be weird non-life chemistry going on that permits the build-up of atmospheric oxygen. Small amounts of free oxygen could be produced by ultraviolet light splitting atmospheric water, although you'd expect that the process would slow down substantially once an ozone layer forms. Of course, you'd also expect such oxygen to react with iron & other elements on the planet's surface, but the weird chemistry may reduce or prevent that some how.

Still, if we detect free oxygen in an exoplanet's atmosphere we should consider it a promising candidate for life.


The abundance of free oxygen means that Earth's atmosphere is oxidising rather than reducing. You need something fairly energetically unlikely to be going on in order to make that transition, so, while I'm not prepared to rule out the possibility of non-life processes getting there, I'd regard it as proof of life "beyond reasonable doubt" in the absence of further reason to doubt.

Re: What-if 0060: "Signs of Life"

Posted: Mon Sep 02, 2013 2:02 am UTC
by Lenoxus
Flumble wrote:It's a casio on a plastic beach,
It's a casio on a plastic beach,
It's styrofoam deep-sea landfill,
It's styrofoam deep-sea landfill,
It's a casio on a plastic beach,
It's a casio on a plastic beach,
It's styrofoam deep-sea landfill,
It's styrofoam deep-sea landfill


I've never heard this song in my life and now it's somehow stuck in my head.

Regarding satellites, I'm now curious: some satellites are geostationary. Does this mean there are places on Earth where you can see them as stationary blinking lights?

As for the Earth-without-humans question, I would guess that the millions of years between the initial evolution of humans and today is enough time for significant evolutionary changes to happen elsewhere too, just like they did for us. So perhaps another sign of being in that alternate world would be to encounter a distinct, entirely new species. Of course, that happens frequently enough in our universe that it's far from an ironclad proof.

Re: What-if 0060: "Signs of Life"

Posted: Mon Sep 02, 2013 1:14 pm UTC
by Red Hal
keithl wrote:To see satellites, look within a couple of hours of dawn or dusk. ISS is big enough to easily see at 415 km altitude, but passes into eclipse 20 degrees after passing the terminator...
Which came as a surprise to the eponymous human-killing robot the first time, but now it's quite used to it.

Re: What-if 0060: "Signs of Life"

Posted: Wed Sep 04, 2013 5:42 pm UTC
by davidstarlingm
Lenoxus wrote:Regarding satellites, I'm now curious: some satellites are geostationary. Does this mean there are places on Earth where you can see them as stationary blinking lights?

Why would they blink?

Re: What-if 0060: "Signs of Life"

Posted: Thu Sep 05, 2013 10:17 pm UTC
by speising
Lenoxus wrote:Regarding satellites, I'm now curious: some satellites are geostationary. Does this mean there are places on Earth where you can see them as stationary blinking lights?

they are 36000km away, though. so not much chance to see them with the naked eye. and no need for navigation lights.

Re: What-if 0060: "Signs of Life"

Posted: Fri Sep 06, 2013 2:48 pm UTC
by davidstarlingm
speising wrote:
Lenoxus wrote:Regarding satellites, I'm now curious: some satellites are geostationary. Does this mean there are places on Earth where you can see them as stationary blinking lights?

they are 36000km away, though. so not much chance to see them with the naked eye. and no need for navigation lights.

I'm not sure how large most geostat sats are, but I don't think they can reflect enough sunlight to be seen with the naked eye at that distance.

Re: What-if 0060: "Signs of Life"

Posted: Mon Sep 09, 2013 12:39 pm UTC
by RogerB
rhomboidal wrote:The Great Wall of China is too skinny and snaky to see from space. Though, I've heard that Tiananmen Square around June of 1989 is even harder to catch sight of in China.


This is true, or at least it was when I was there in 2007. The English language bookshop in Beijing had shelves and shelves of Lonely Planet guide books for every country you could think of; except China.

The China one has a page about Tiananmen Square in it, and it mentions Falun Gong.

Re: What-if 0060: "Signs of Life"

Posted: Wed Sep 11, 2013 4:45 pm UTC
by bmonk
davidstarlingm wrote:Another iteration (great circle bisecting largest angle) produces six 45-45-90 triangles and six 45-90-60 triangles. I don't know if these all have equal surface area.


I recall that in studying spherical geometry, the area of a triangle is equal to the excess of the sum of the angles over 180. So you'd need to get the sum of the angles to be equal in each sub-triangle.
The error here is assuming that the bisector of the 90 degree angle on the 45-90-60 triangle would meet the opposite side perpendicularly.

Re: What-if 0060: "Signs of Life"

Posted: Wed Oct 12, 2016 4:20 am UTC
by aptriangle
A 3D artist showed me a simple way to create points randomly distributed on a sphere, to create a star field. (Simple as in, it could be done in a few steps, using only the tools already in Lightwave 3D)

Fill a box that contains your sphere with random x,y,z points.
Remove any points outside the sphere. (So you don't get more points toward the corners of the box)
Project the remaining points onto the surface of the sphere.

Re: What-if 0060: "Signs of Life"

Posted: Wed Oct 12, 2016 10:46 pm UTC
by Soupspoon
I've done something similar to that already mentioned (scale latitude positioning to cylindrical (equirectangular) projection, thus artifically shortening a latitude range even as the longitude artificially widens, prior to scattergunning on it), where I don't want to throw randomised points away all the time... I've had more difficulty ensuring the similar compensative effect in higher dimensions of hyperspherical surface-scattering, but it looks Ok, the way I've done it.

Re: What-if 0060: "Signs of Life"

Posted: Mon Dec 26, 2016 8:33 am UTC
by Thanosaekk21
I went in the first page for random coordinates and it said something about Randall M. What is happening?