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Catastrophe

The devil is in the detail
"The saddest prospect - we are completely alone in this universe.
A happier prospect - there are type 2 and 3 civilizations, but they are hiding from us until we reach certain technological capabilities
An interesting prospect - there is some great filter that inhibits the development of nearly all life. . . . . . . . . . . . . . . . "

This does not compare closely with the estimates of Avi Loeb (I guess you have heard of him - his qualifications are too many for me to type out): (I only just started reading this)

"Given so many worlds - fifty billion in our own galaxy! - with similar life-friendly conditions, it's very likely that intelligent organisms have evolved elsewhere."
"And that's counting only habitable planets in the Milky Way. Adding all other galaxies in the observable volume of the Universe increases the number of habitable planets to a zetta, or 10^21 - a figure greater than the number of grains of sand on all the beaches on Earth."

Avi Loeb, "Extraterrestrial" John Murray Publishers, 2021.

Just to confirm those numbers:
50 billion in our own galaxy
A zettta (10^21) in the observable universe.

May we please ask the source of your suggestions?

Cat :)
 
Jun 1, 2020
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"The saddest prospect - we are completely alone in this universe.
A happier prospect - there are type 2 and 3 civilizations, but they are hiding from us until we reach certain technological capabilities
An interesting prospect - there is some great filter that inhibits the development of nearly all life. . . . . . . . . . . . . . . . "

This does not compare closely with the estimates of Avi Loeb (I guess you have heard of him - his qualifications are too many for me to type out): (I only just started reading this)

"Given so many worlds - fifty billion in our own galaxy! - with similar life-friendly conditions, it's very likely that intelligent organisms have evolved elsewhere."
"And that's counting only habitable planets in the Milky Way. Adding all other galaxies in the observable volume of the Universe increases the number of habitable planets to a zetta, or 10^21 - a figure greater than the number of grains of sand on all the beaches on Earth."

Avi Loeb, "Extraterrestrial" John Murray Publishers, 2021.

Just to confirm those numbers:
50 billion in our own galaxy
A zettta (10^21) in the observable universe.

May we please ask the source of your suggestions?

Cat :)
I’m curious how they got 50 billion?

We only have a handful of habitable planets out of ~ 5000 discovered. But even 50 million is an exciting and hopeful number for the MW.

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Catastrophe

The devil is in the detail
Helio, I have been expecting that question. My guess is that maybe the number of intelligent species in the observable universe is between 1 and 1 zetta.

Avi Loeb is a very clever man - Chair of Harvard's Astronomy Department, and all the rest - but he may be a little optimistic. Better, anyway, than 1 in the observable universe (yet to be found). Perhaps the species who sent, or used, Oumuamua?

I have been looking for your answer, which I remember seeing. I promise I will reveal it when I find it.

Meanwhile, I would like to revisit the Drake Equation, which is clearly on topic. Quotes from Loeb ibid.
"Drake's equation focuses solely on the transmission of communication signals; he limited his aspirations to finding N and from it the number of interstellar communications that would establish the existence of extraterrestrial intelligence. This exclusive interest in communication predicts the equation's second limitation, epitomised by its variable L,, which represents the length of time an intelligent species would be able to produce such signals. . . . . . . our species has been producing radio signals for mere decades."

Next, remember the length of time built into c. Also think of the direction(s) chosen to look for such signals (as may have existed) - do we need to point our telescopes at very limited areas?

Off to look for your answer.

Cat :)
 

Catastrophe

The devil is in the detail
Helio, yet to find specific, but have Googled and found this for starter:

About Half of Sun-Like Stars Could Host Rocky, Habitable-Zone Planets | NASA


A New Search for Evidence of Technological Civilizations
https://www.universetoday.com › a-new-search-for-evi...


22 Jun 2020 — With this many planets available for study, researchers have been able to apply new constraints on how likely habitable planets are.


How Many Habitable Planets are Out There? | SETI Institute
https://www.seti.org › press-release › how-many-habita...


29 Oct 2020 — ... from the Kepler space telescope, it's estimated that there could be as many as 300 million potentially habitable planets in our galaxy.
Missing: loeb ‎| Must include: loeb


habitability of large elliptical galaxies
https://academic.oup.com › mnras › article


by DP Whitmire · 2020 · Cited by 4 — (2015) modelled the number of habitable terrestrial planets in local (⁠z ≈ 0) ... galaxies and their antecedents can be obtained from Forbes & Loeb (2018), ...


Planetary habitability - Wikipedia
https://en.wikipedia.org › wiki › Planetary_habitability


This spectral range probably accounts for between 5% and 10% of stars in the local Milky Way galaxy. "Middle-class" stars of this sort have a number of ...


On the Habitability of Our Universe - arXiv
https://arxiv.org › pdf

PDF
by A Loeb · 2016 · Cited by 6 — of the Milky Way galaxy, and may have planetary systems in the habitable zone ... appears to fall away for stars with [Fe/H] < –3.0 since many of these ...



Cat :)
 

Catastrophe

The devil is in the detail
Helio, found, for what it's worth:

"Based on Kepler satellite data, I argued, we knew that about a quarter of all stars hosted habitable Earth-scale planets"

I will try to follow up on Google results to see whether I can find elaboration, but it won't be quick in getting back.

Cat :)
 

Catastrophe

The devil is in the detail
Astronomer Avi Loeb Says Aliens Have Visited, and He's Not
https://www.scientificamerican.com › article › astronom...


1 Feb 2021 — Astrophysicist Avi Loeb at the unveiling of the Breakthrough Starshot ... which is that based on the data from NASA's Kepler mission, ...

Avi Loeb and the Great Unknown - Futurism
https://futurism.com › avi-loeb-and-the-great-unknown


4 Feb 2021 — Avi Loeb's controversial argument is that 'Oumuamua may have been a ... “We now know from the Kepler satellite data that about half of the ...

About Half of Sun-Like Stars Could Host Rocky, Habitable ...
https://www.nasa.gov › ames › kepler-occurrence-rate

TRY THIS FIRST
29 Oct 2020 — According to new research using data from NASA's retired planet-hunting mission, the Kepler space telescope, about half the stars similar in ...
Missing: Loeb ‎| Must include: Loeb
You've visited this page 2 times. Last visit: 13/10/21

Kepler Mission Data Resources in the Exoplanet Archive
https://exoplanetarchive.ipac.caltech.edu › docs › Keple...


10 Feb 2021 — The Kepler Mission, a NASA Discovery mission launched on March 6, 2009, was the first space mission dedicated to the search for Earth-sized ...
Missing: Loeb ‎| Must include: Loeb

In a new frontier called space archaeology, as
http://www.cfa.harvard.edu › ~loeb › Atmos

PDF

Abraham Loeb, the man who coined the ... Second, recent data from the Kepler satellite ... technological civilizations by digging in space. I label this.
6 pages

Have We Already Been Visited by Aliens? | The New Yorker
https://www.newyorker.com › Magazine › Astronomy


READ THIS

"18 Jan 2021 — As astronomers pored over the data, they excluded one theory after another. ... In 2009, NASA launched the Kepler space telescope, ...

Since there are at least four billion sunlike stars in the Milky Way, this means that somewhere between 1.5 billion and 2.4 billion planets in our galaxy could, in theory, harbor life. No one knows what fraction of potentially habitable planets are, in fact, inhabited, but, even if the proportion is trivial, we’re still talking about millions—perhaps tens of millions—of planets in the galaxy that might be teeming!

Extraterrestrial | 159 Pioneer Street, Red Hook, Brooklyn
https://pioneerworks.org › broadcast › extraterrestrial-ar...


27 Jan 2021 — Loeb is the bestselling author of Extraterrestrial: The First Sign of ... Thanks to data collected by the Kepler space telescope, ...

"Thanks to data collected by the Kepler space telescope, we now know that about half of all Sun-like stars, of which there are tens of billions in the Milky Way, host a rocky, Earth-size planet in their habitable zone. Within this zone, the planet’s surface temperature can support liquid water and the chemistry of life. The huge number of sites where life may exist begs the question: which fraction of these planets host technological civilizations like ours, capable of communication?"

Didn't take as long as I anticipated.

Cat :) :) :)
 
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We must look at the real evidence, which shows few Earth-like planets around Sun-like stars.

In this case, I would favor Rod’s assessment over Loebs. But I’m on the road with just an iPhone.
 
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Catastrophe

The devil is in the detail
Helio, I have no doubt that the answer is somewhere in the middle. Between 1 and 1 zetta leaves plenty of room for compromise.

To return to the Drake Equation, and to what I regard as an unfortunate omission. Please correct me if I am in error. but I see no term there to accommodate the chance of humans pointing their radio or tv receivers at the source of any such transmission. Presumably this is directional. By that, I understand that transmission can be multi- or all- directional, but I refer to our pointing our relevant instruments towards the source. This is not like CMB which is supposedly from every direction. There should be a factor in the Drake Equation (imho) to take into account the chance of our looking in the right direction, nicht war?

Now, such a factor would greatly decrease N and therefore take into account why we do not find more (any) signals. This is, of course, assuming that we are looking in the right wavelengths.

In favour of my suggestion, Loeb also states:
"Drake's Equation focuses solely on the transmission of communication signals; he limited his aspirations to finding N and from it the number of interstellar communications that would establish the existence of extraterrestrial intelligence."

There is no factor covering our chance of looking in the right direction.

Cat :)

P.S. From Wiki Search for extraterrestrial intelligence I see:
"ATA also supports observations in multiple synthesized pencil beams at once, through a technique known as "multibeaming". Multibeaming provides an effective filter for identifying false positives in SETI, since a very distant transmitter must appear at only one point on the sky.[28][29][30]"
My emphasis.
Presumably the wider the receiver, the more the noise, and the greater the difficulty in evaluation?

P.P.S. Just Googled targets SETI - result:
Target Selection for SETI. I. A Catalog of Nearby Habitable ...
https://iopscience.iop.org › article


by MC Turnbull · 2003 · Cited by 142 — Target Selection for SETI. I. A Catalog of Nearby Habitable Stellar Systems. Margaret C. Turnbull1 and Jill C. Tarter2.
SETI target selection - PubMed
https://pubmed.ncbi.nlm.nih.gov › ...


by DW Latham · 1995 — ... and a Targeted Search of nearby stars, one at a time, to a much deeper level of sensitivity. In this paper we propose strategies for target selection. …
Targeted Star Search | SETI Institute
https://www.seti.org › seti-institute › project › details › t...


"Since we need about one million target stars to fully utilize the capability of the ATA, a second catalog of stars was derived from the Tycho-2 Catalogue of 2.5 million stars. Unlike the Hipparcos stars, the Tycho stars did not have distance measurements. The approximately 250,000 stars of HabCat2 were selected primarily by their colors (brightness in blue and “visual” filters) and proper motion (motion across the sky)." My emphasis.

Selecting Target Stars Life as we know it developed on a planet orbiting a G2 V star, the Sun. The cryptic “G2 V” designation is the Sun's “spectral type.
Strategies for SETI target selection - SPIE Digital Library
https://www.spiedigitallibrary.org › 12.150125.full


by DW Latham · 1993 · Cited by 2 — In this paper we present a strategy for target selection and observing. The strategy has two goals: to improve the chances of successful detection of signals ...
Target Selection for SETI. II. Tycho-2 Dwarfs, Old ... - NASA/ADS
https://ui.adsabs.harvard.edu › abs › abstract


by MC Turnbull · 2003 · Cited by 54 — We present the full target list and prioritization algorithm developed for use by the microwave search for technological signals at the SETI Institute.
 
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Here is a site favoring the 300 million hab planets you mentioned above.

The program I wrote will count all the planets in the hab zone — perhaps this should be called the “wet zone” instead — of a given size for each star class. It also lets one choose planet size limits. This database is up to date so it should be more accurate than last year’s guesses. Of course, in the near future, we’ll have thousands more exoplanets discovered we can work with to get a more accurate estimate.

The program, however, ignores stars without class designation. It also can’t assume which systems are single stars. Multiple star systems reduce the chances for habitability and these systems are more numerous than single star systems, thus diminishing the hab no. But we can make a reasonable guess as to the % hab planets might be in multi stellar systems.

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