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Ravi Kopparapu's Personal Meeting Room - Shared screen with speaker view
Graham Lau
Can all of you who have your microphones on mute yourselves? It will help with the audio a lot.
Ravi Kopparapu
can people mute their microphones?
Jason Wright
Doesn’t this mean that all of the US population growth shown in the previous slide is due to immigration, not fertility?
Evan Sneed
Does this approach assume that all food grown is perfectly distributed? As far as I know, today's hunger problem is based largely on a supply chain issue and not because we don't grow enough food.
David Grinspoon
Aren’t there other constraints more stringent than land area? Those post-green revolution agricultural capacities use a lot of fixed nitrogen (and pollute a lot of coastal waters), deplete water tables, poison areas with pesticides, etc….
David Grinspoon
(today in India they are hitting these limits - depleting water tables, increasing pesticide use to try to compensate for reduced yields, poisoning water tables with pesticide, etc…
David Grinspoon
It may well be that *most* energy intensive civilizations have short lifetimes, but that the galaxy is still full of very long lived civilizations. If the transition to very long lifetimes is low but finite, then this is the most likely situation…
David Grinspoon
(the probability of the transition, that is…)
David Grinspoon
So in this case (the most likely case IMHO) then our own likely longevity is not correlated with the likely existence of long-lived civilizations…
Jim Cleaves
This makes sense to me, I think we are already in the middle of this transition (as some of the earlier slides showed)
David Grinspoon
We are *trying*
Jason Wright
Indeed, there is a whole genre of sci-fi where the Earth is an overpopulated environmental dystopia or even uninhabitable, while a small fraction of humanity has sets up settlements spreading across the galaxy. The two scenarios are not mutually incompatible, even within a species.
Jim Cleaves
I mean the population curve is bending over, and I think the watts per person are as well (though not the total watts), perhaps that is a little more complicated.
Jessie Christiansen
Given the proximity of the tidally-locked planets in compact systems like TRAPPIST-1, I’ve always enjoyed the idea that a civilization might observe technosignatures like city lights on a nearby planet before they had explored the entire surface of their own.
Ravi Kopparapu
^ Good point Jessie! May be there will be different timescales for civilizations to develop within a system.
David Grinspoon
Would NO2 be a long lived signature? I tend to think of anything that is “pollution” as inherently short-lived, not the hallmark of a sustainable civilization, and therefore not really observable. But perhaps this is not true about NO2?
Seth Redfield
@Jessie, I’ve been look at the solar gravity lens focus (ours is out beyond 500 au), and have similarly wondered if there were inhabited planets around stars that naturally resided in an orbit that would be in their star’s gravity lens focus.
Ravi Kopparapu
NO2 is short-lived, unless a civilization colonizes a nearby planet or lives sub-surface. We never know what is the frequency of mediocre technological civilizations !
Ravi Kopparapu
*not never....we do not know I should say
Jessie Christiansen
@Seth - are there any star/planet mass ratio combinations that put the planet in the HZ?
Mark Claire
David - probably would be short lived - unless it was intentional, like in a terraforming project.
Jessie Christiansen
(I guess it’s just the mass of the star, not the planet)
Jason Wright
@Seth I don’t think so: 500 au is very far away, so there is very little free energy out there for an inhabited planet to use. I think the distance to the lens is also rather insensitive to the mass of the star (I think the distance to the lens scales as R/M, which is roughly constant for stars on the MS).
Seth Redfield
I’d have to dig out my plots (I can email them to you), but if I remember correctly, it only occurred naturally for fairly high mass star.
David Grinspoon
@Mark - so not a good technosignature?
David Grinspoon
What if you took a useless planet in your own system (ethically suspect concept I realize - but one where you couldn’t live and didn’t want to do anything and there was no indigenous life) and put some really bizarre and highly observable molecules in its atmosphere, as a beacon of anomaly?
Mark Claire
@David - Might be a semantic thing, but I would think a terraformed planet would be a perfect techno signature. Mars with 100 ppm SF6 would be far more “observable” than a few ppt of CFC or NO2 on Earth
Ravi Kopparapu
@David: we discuss these things in our paper.
Jason Wright
@David: Yes, I think of this as the “Praxis scenario”: an “industrial” planet that has no biosphere but a thick technosphere, like if we covered Mercury with solar panels and supercomputers.
David Grinspoon
Good! Can’t wait to read it.
Seth Redfield
@Jason - it does have a mass dependence. I think the HZ and the SGL cross at 80 stellar masses! It is more interesting if we consider planets orbiting white dwarfs.
David Grinspoon
@Jason - I was wondering if this might be done on a planet for no other reason than to stand out in techno signature searches. Kind of absurd. Stanislaw Lem type scenario...
The idea of using “dead” planets as industrial centers seems like a really useful idea.
Jason Wright
@Seth I’m not sure if we expect *any* rocky planets to be orbiting 80 solar mass stars?
the length of time the earth has had a detectable biosphere is roughly 2 billion years, the amount of time with a detectable technosphere (AFAWK) is ~10K years. That is a 5x10^-6 ratio from the only case we have....
Ravi Kopparapu
@Gavin, unless there are statistically more technospheres....but they have to be really large in number.
Jason Wright
@Gavin: Doesn’t that assume only one technological species every arises per planet? I would think that if one arose, another is more likely to follow.
Jim Cleaves
That is r selection, but point taken
@jason. well yes. no need to assume that, but no actual evidence to the contrary so far... ;-)
Ravi Kopparapu
Gavin has a upcoming seminar about this topic.
George Profitiliotis
technospheres without a biospheres sound fascinating, they could even be the industrial sites that are utilized in the beginning of building a Dyson swarm
Jim Cleaves
Thank you for the talk!
Jessie Christiansen
I have to run, thanks so much Jacob!
Chris Bennett
Nice talk, thank you!
Pauli Laine
Have to leave, thank you for the talk!
David Grinspoon
@Gavin it’s long been in the literature (at least since the 1960s) the idea that technosignatures will be completely undetectable unless they are much more long lived then ours is currently - because of that ratio...
Vladimir Airapetian
Thanks for your interesting talk, Jacob! This raises many interesting questions to think about. One os them is the factor of cosmic catastrophes that need further study.
David Grinspoon
George Profitiliotis
Are there any non-astronomical ways to empirically test the great filter?
David Grinspoon
Thanks for a great talk Jacob!
David Grinspoon
And thanks to the organizers for starting this series!
Vishal Gajjar
Thanks for interesting talk!
Svetlana Berdyugina
Thank you!
Evan Sneed
Thank you Ravi & Jacob!
George Profitiliotis
thanks for organizing this!!!!