Galaxy size and civilizations

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stefan r
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Main Question or Discussion Point

This is developing into yet another game of Astronomical Top Trumps. There is always some parameter that can put an astronomical object near the top or near the bottom of a list.

The milky way is what it is. Now, if someone could come up with something relevant about whether Galactic size might relate to Alien Civilisations (other than some pro-rata rule) then that could be interesting.
We do not currently have the ability to detect a Kardeshev 1.0 civilization at Alpha Centuari. Here is a paper showing Alpha Centuari has infra-red emission close to a K1.5 civilization. Emissions from a K1.0 would be completely lost in the noise.

There is some evidence that Kardeshev 2.0 civilizations are rare in a galaxy like the Milky Way at the Sun's radius. A single data point does not convey any statistical information about galaxies in general.

For a "top galaxies" category the Milky Way and the Orion Spur could still be close to the top in terms of quality. It appears that it is not yet infected with species that over-consume all potential resources. The Milky Way might still be in a fairly pristine state.


There is a survey of galaxies looking for KIII civilizations using data from WISE. Out of around 105 sources the authors recommended 95 of them for further study. 5 have been studied some. The other 90 were not studied at the time of publication. In order to make that list a civilization needs to capture more than 50% of the galaxy's starlight (or produce energy equal to starlight). Colonizing 80% of the stars in a galaxy and using on average 63% of individual star's light would still count the galaxy as uncivilized. Also galaxies where 100% of F,G,K, and M stars had colonies with 95+% energy utilization but most of the A,B,O stars did not have colonies would have been counted as uncivilized too.

There is effectively no data about the civilizations in galaxies except for the solar system containing Earth.
 

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sophiecentaur
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There is some evidence that Kardeshev 2.0 civilizations are rare in a galaxy like the Milky
What sort of evidence would that be? Would it be that someone had arranged the stars in neat rows (not really) or some other meaningful pattern? Would it be that many stars were occulted (power harvesting)? That power-based classification of K civilisations makes a huge assumption about the nature of 'advancement' of civilisations. It's like a crude version of an Azimov future and that was based on 1950s ideas about technology. And, of course, Azimov is shamelessly anachronistic which allowed him to make up very entertaining tales and situations (20th century anthropomorphic to an extreme). Great entertainment but hardly a very good basis for extrapolation from our present technology and culture.
 
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A civilization as we understand it would want to harvest low-entropy energy (like visible light), do stuff with it and dump high-entropy energy (infrared, maybe even longer wavelengths). The signature would be an excess of long-wavelength radiation compared to what we would expect based on visible light.
We do not currently have the ability to detect a Kardeshev 1.0 civilization at Alpha Centuari. Here is a paper showing Alpha Centuari has infra-red emission close to a K1.5 civilization. Emissions from a K1.0 would be completely lost in the noise.
ELT will get a direct image of planets, if there are any in the habitable zone.
 
sophiecentaur
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A civilization as we understand it
Yes. And that's the point. If we actually manage to alter our behaviour over the next few decades, there's every possibility that we could 'advance' our civilisation and, at the same time, use considerably less Energy. So the K scale may not be very relevant to the level of actual civilisation in terms of quality of life and wellbeing. It may be the best stab that we could make at the moment but receiving just one example of meaningful information would be far more useful than the thermodynamic information that K works on.

I ask myself just how much money it's worth spending on this sort of thing, compared with some other areas of research. Very much diminishing returns, I think. Good entertainment, though.
 
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Every civilization bound to the laws of thermodynamics will do this. Every civilization doing this can be measured on that scale. There are fundamental limits how much you can do with a given amount of energy.

These studies are a side-product of galaxy/star surveys. We don't know the chance that they will lead to the discovery of civilizations, although even a small chance would make it worth studying.
 
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A civilization as we understand it would want to harvest low-entropy energy (like visible light), do stuff with it and dump high-entropy energy (infrared, maybe even longer wavelengths). The signature would be an excess of long-wavelength radiation compared to what we would expect based on visible light.
Obviously Moon is far more civilized than Earth. Moon converts 88% of incident sunlight into heat, while Earth only converts 63%

Sure, you cannot have a perfectly white civilization. But there is a plenty of black stuff in nature besides civilization.
 
sophiecentaur
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There are fundamental limits how much you can do with a given amount of energy.
Could you define "how much you can do" ?

If Civilisation is synonymous with Population then you may have a point - if all civilisations use the same energy per head. At this point in our history, it seems that it's quite possible that the amount we are using per head will lead to the end of our present civilisation. That could indicate another "fundamental limit" and that we should perhaps rethink what is civilisation. Self annihilation doesn't seem a very civilised behaviour.
The Kardeshev idea seems far too vague because it seems to lack a proper definition of what is meant by Civilisation. With just one data point and a very wooly connection between the entropy distribution then I cannot see that it is worth pursuing at the moment.
 
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@snorkack: That's why we can't find Kardashev level 1 civilizations easily that way. Dust is the issue with level 2 civilizations.
Could you define "how much you can do" ?
Computing power, in the generalized sense. How much information you can process in some way per time. There is a temperature-dependent minimal amount of energy you need to put into every computing step that is irreversible, the lower the temperature the smaller the energy needed. Reversible computing is an interesting concept but it has some limits.
 
sophiecentaur
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@snorkack: That's why we can't find Kardashev level 1 civilizations easily that way. Dust is the issue with level 2 civilizations.Computing power, in the generalized sense. How much information you can process in some way per time. There is a temperature-dependent minimal amount of energy you need to put into every computing step that is irreversible, the lower the temperature the smaller the energy needed. Reversible computing is an interesting concept but it has some limits.
That's true but it assumes that you need a larger population to be more 'civilised. There is no logical link of that sort. A 'high level' civilisation might have an almost undetectable effect on the entropy per head but a large 'civilisation' of piratical savages with a high technology level could be swamping the Universe with evidence of its presence. Basically I am saying that population size need not be an indication of 'civilisation'. An example of that, on our planet, is the relative masses of Prokariotes (bacteria and the like) and the much smaller mass of Eukariotes (' advanced' organisms).
Just what would be a totally valid definition of the term civilisation? Like us on a good day? (I don't mean the United States btw)
 
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Basically I am saying that population size need not be an indication of 'civilisation'.
No one claimed that, so what is your point?
The topic was "there is evidence that level 2 civilizations are rare". We can check this by checking for signatures of this specific type of civilizations. "A civilization might have a lower power consumption" is both correct and irrelevant for that discussion.
 
sophiecentaur
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so what is your point?
I thought I had made my point quite clear and that is there is no point in trying to classify something with an invalid system. What is "civilisation"? Is it just numbers of individuals, or perhaps total mass?
"A civilization might have a lower power consumption" is both correct and irrelevant
Imo, it is entirely relevant if there is to be any point in the use of this particular form of classification. I guess the problem with that particular form of classification is that it is way too anthropomorphic to be worth using. Why would every other life form be enough 'like us' to justify the K level rating?
OH yes - and another thing: the size of population implies a level of 'production' as well as just using computers. Bigger population implies a higher K rating. (Certainly when applied to Earth.)
 
stefan r
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... Why would every other life form be enough 'like us' to justify the K level rating?...
The K rating is only useful when considering what sort of activity we could detect.

...ELT will get a direct image of planets, if there are any in the habitable zone.
But what would it tell you if you looked at Earth? We have continents, oceans, clouds, and snow. Earth is rotating. What else would show up?

Computing power, in the generalized sense. How much information you can process in some way per time. There is a temperature-dependent minimal amount of energy you need to put into every computing step that is irreversible, the lower the temperature the smaller the energy needed. Reversible computing is an interesting concept but it has some limits.
Edit:
My post was edited by DrClaude in a way that changed the meaning so I am deleting the rest. There was a link to the Washington Post. Apparently the Washington Post publishes articles which are deemed unfit for Physics Forums.

IMO this warning and censorship from Physics Forums makes my point much better than the argument that I made. More computing power is not an indication of better content. Having a space program and powerful servers does not make a project inherently worth doing.
 
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I thought I had made my point quite clear and that is there is no point in trying to classify something with an invalid system.
It's a definition, it can't be invalid. Whether you like this definition or not is a different question. Feel free to create your own classification system (and see if anyone will use it). Once it is published we can discuss its merits here, you know the rules.
But what would it tell you if you looked at Earth? We have continents, oceans, clouds, and snow. Earth is rotating. What else would show up?
Absorption from CF4 and CCl3F if you can view Earth in transit with a telescope a bit better than JWST. Sodium emission spectra from street lights if the telescope is sensitive enough. Note that we are far away from level 1.
 
sophiecentaur
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What else would show up?
Haha. It could, perhaps show a high proportion of greenhouse gases. What would that indicate apart from the imminent demise of any 'civilisation' on the planet.
It's a definition, it can't be invalid.
That's a logical statement but there are nuances involved for people able to see them and quality judgements come into the situation. It's just another Top Trumps situation. Many classification systems, based on 'definitions' can be irrelevant or even offensive so validity, in the wider sense, could (should) come into it. Imagine, for instance, that two 'civilisations' were spotted within a useful distance of Earth. Money is only available to contact one of them and the choice happens up to the public. I, for one, would not be happy to accept the decision of a public that had a majority of racists, xenophobes and ultra-nationalists; the K rating could (would) indicate, to them, a very skewed assessment of the desirability of contact with the two civilisations.
These points are, of course, not just Physics based but could one really say they are not relevant? Quality and quantity are not the same thing.
 
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The Kardashev scale is clearly relevant as the numerous publications using it show.
Money is only available to contact one of them and the choice happens up to the public. I, for one, would not be happy to accept the decision of a public that had a majority of racists, xenophobes and ultra-nationalists; the K rating could (would) indicate, to them, a very skewed assessment of the desirability of contact with the two civilisations.
Wait, what?
 
sophiecentaur
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The Kardashev scale is clearly relevant as the numerous publications using it show.Wait, what?
Let me explain. It depends what sort of 'civilisation' rings your bell. The other lot are just biomass.
 
russ_watters
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The Kardashev scale is clearly relevant as the numerous publications using it show.
Does it actually have significant traction in peer reviewed research? Is there a way to measure that? Are the results of this research anything above exactly zero?

It's always sounded very science fictiony to me.
 
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3800 hits in Google scholar.

As comparison: "charm cp violation" has 27600 and that is a whole field in particle physics.
 
sophiecentaur
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3800 hits in Google scholar.

As comparison: "charm cp violation" has 27600 and that is a whole field in particle physics.
A very different potential readership, though.
 
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Yes, very different topics tend to have very different readers.
 

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