# What did Carl Sagan get wrong? **URL:** \ **Category:** Great Debates\ **Created:** [April 10, 2023, 11:27pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476 "2023-04-10T23:27:07Z")\ **Posts on this page:** 11\ **Page:** 5
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [April 15, 2023, 7:38pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/81 "2023-04-15T19:38:11Z")
But all this is a kind of side-track, rather than a hijack; not really a discussion of what Sagan got wrong, although I’m sure he would have joined in this discussion with enthusiasm. Another group of Sagan H8ters is the diminishing band of supporters of Immanuel Velkovsky. These people accuse Sagan of falsifying his arguments against the arguments put forward in Worlds in Collision. In fact, Sagan did a very good job of demolishing the Velikovskian argument, but apparently made a few minor errors in his calculations that WinC proponents have seized upon. These minor errors do not detract significantly from Sagan’s arguments - but you would never know that if you only read the accounts of Velkovsky’s supporters. I am somewhat dismayed that a number of Sagan’s other detractors have also taken issue with his dismissal of the WinC thesis, saying he was acting unscientifically and submitting Velikovsky’s ideas to ridicule. Well, some ideas really do merit ridicule; on the other hand even Sagan came to the conclusion later in his life that these ideas were subjected to almost universal disdain, making it very difficult to consider ideas of catastrophism fairly. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [April 15, 2023, 7:48pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/82 "2023-04-15T19:48:40Z")
> [@FlikTheBlue](#): > > The first question is where will these settlers / explorers / voyagers, whatever you want to call them get their resources from? The best source of energy we can hope for in the Oort Cloud is fusion. Plenty of fusible elements out there - but this would require advances in technology we currently do not have. The reason I don’t think Oort-cloud hopping is a very good strategy is that it requires too many velocity changes. Every time you travel from one asteroid to another you have to accelerate and decelerate - by the time you get to the edge of the Cloud, the objects are so far apart you’d have to travel hundreds of AU to find the next one. After thousands of such velocity changes you would have used more power than by accelerating directly towards Proxima and coasting the rest of the way. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [April 15, 2023, 9:48pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/83 "2023-04-15T21:48:28Z")
> [@Stranger\_On\_A\_Train](#): > > It is difficult for people who have grown up on a diet of space opera to really grasp, but the scale of interstellar space is enormous (literally astronomical), and the resources and energy required to transit these scales using the momentum transfer mechanics that are offered by our current understanding of physics is just prohibitive even before you get into the details of how to make an automated probe reliable enough to function after many thousands of years of exposure or the thermodynamics of rejecting all of the waste heat developed from a high performance propulsion system. Even if we had an endless amount of resources ability to achieve any speed necessary to transit to even stars in our local neighborhood is daunting. Except that I pointed out, a few times, that I’m not talking about space opera. I’m not talking about ships crossing the void. I’m talking about slowly settling rocks further and further out from the sun, until you are so far from the sun that you are actually closer to another star. Sure, that’ll take tens of thousands of years or more, but what’s the rush? > [@Stranger\_On\_A\_Train](#): > > Without some fundamental advances in basic physics of propulsion or some other method of going around spacetime instead of through it, sending even hypothetical automated, self-replicating probes would not just take a few million years but tens or hundreds of millions. And that assumes that some alien civilization would be motivated to do so for…reasons? It can’t be commerce, and not conquest in any conventional sense. Exploration? By the time such probes would reach systems that are beyond the range of advanced telescopes and other passive methods of observation, such a civilization would likely advanced to a new phase or collapsed completely. I said nothing about self replicating probes. But, since you asked why you would do it… First, you wouldn’t be sending a probe to another solar system and have it replicate there and then send out to others. There is plenty of material in this solar system and maybe close by to make all you need. And you wouldn’t be sending them to the closest stars, you’d be sending them out to the furthest reaches of the universe, as far out as you can calculate you can make it before things fall over the cosmic horizon. There they would replicate and start turning the stars into Shkadov thrusters to start bringing the material back. This will extend the amount of time until you have to give in to the heat death of the universe by potentially quadrillions of years. That’s obviously much longer term planning, but it’s the kind of galaxy engineering that we will need to be doing within the next few billion years, though sooner is better than later, every second we wait to do so loses trillions of years of resources. > [@Stranger\_On\_A\_Train](#): > > This isn’t to say that there isn’t some loophole that provides some non-momentum exchange propulsion or ‘wormholes’ around the plenum of normal spacetime, but even if such possibilities theoretically exist they make require more energy than is practicable. While I think that we have plenty left to learn about the universe and the rules that govern it, I don’t think we will find gaping loopholes that allow FTL or perpetual motion, but we don’t need it. > [@Stranger\_On\_A\_Train](#): > > with that assumption and a 1,000 year lifespan for an industrial civilization before it (collapses or advances to something unrecognizable) What is that based on? If we settle asteroids and start moving out, what causes the collapse? What causes the entire species, spread out among millions of rocks and trillions of miles to _all_ die off? > [@Stranger\_On\_A\_Train](#): > > And I know someone is going to put forth the argument that an industrial civilization would advance up the “Kardashev scale” and at least leave residual megastructures that would be observable from their interference with normal spectral emissions of a star, but that is purely an assumption that is not only unvalidated but unlikely once you delve into the details of what it would take to build a megastructure, and what motivation a civilization would have if they had the resources to do so. What is the motivation that we have to be building a Dyson Sphere? We are building one right now. Every satellite we put up is one more piece of it. You don’t set out to build a Dyson Sphere, a Dyson Sphere is what you end up with as people put up more and more objects orbiting the sun, blocking out more and more of the light. > [@Stranger\_On\_A\_Train](#): > > However an advanced civilization will develop is likely as unimaginable to us today as our current technology would be to a Saxon or Viking Except they knew _nothing_ about science or the world around them, much less the universe above their heads. While there is still a lot to learn, comparing our ignorance to that of the Vikings isn’t reasonable. > [@Stranger\_On\_A\_Train](#): > > assuming that technology must develop as a linear extension of current methods is essentially the only prediction that we can say is certain to be wrong One of the things that science communicators like to point out when the question is asked as to how we know we aren’t just as wrong as the ancients that thought that the Earth was the center of the universe and everything revolved around it is that as we learn things, we aren’t just throwing out the old. Newtonian mechanics aren’t _wrong_, they are an extremely good approximation in almost all cases. Relativity isn’t right, we know that there is _something_ missing in order to make it compatible with QM, but it still works for everything that we’ve ever tested, and will continue to be close enough for all but the most extreme edge cases. Short of discovering new laws of physics that throw everything out the window, then technology _will_ develop as a linear extension of current methods, and any objection to that needs some pretty extraordinary evidence. > [@Stranger\_On\_A\_Train](#): > > as is any narrow restriction on how alien civilizations or technology must develop, or how they might think and communicate. Right, like restricting them to not ever having _any_ human like characteristics. While it seems hard for some to believe that we are alone in the observable universe, it seems even harder for me to believe that we are not alone, and yet we are absolutely unique. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [April 15, 2023, 10:00pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/84 "2023-04-15T22:00:07Z")
> [@FlikTheBlue](#): > > Maybe my picture if interstellar space is completely incorrect. From what I understand, however, once we get past Pluto there’s a few smaller things out there in the Oort Cloud, and some hypothetical Planet X around the size of Uranus and Neptune. Even that will taper out well before getting halfway to Alpha Centauri, where we could maybe start using the Alpha Centauri Oort Cloud. Overall it just seems like there isn’t anywhere close to enough stuff in usable form to be able to survive, let alone thrive long enough to build a new civilization. Stuff gets further apart, but there’s still a lot of it. [Oort Cloud: Facts - NASA Science](https://solarsystem.nasa.gov/solar-system/oort-cloud/in-depth/#:~:text=There%20may%20be%20hundreds%20of,long%20fall%20toward%20our%20Sun). > [@](#): > > There may be hundreds of billions, even trillions, of icy bodies in the Oort Cloud. And it doesn’t take much. A rock a few miles across will provide the resources for millions of people for millions of years. > [@FlikTheBlue](#): > > The first question is where will these settlers / explorers / voyagers, whatever you want to call them get their resources from? That far out they can’t rely on energy from the sun, and by the time they get close enough to Alpha Centauri to use solar energy again they would have already completed the hard part of the journey. Nuclear. Plenty of Thorium in asteroids. > [@FlikTheBlue](#): > > Nuclear is probably going to be equally difficult, because even if they can find some uranium or thorium out there (and that far out I’m betting that stuff is a lot more rare and difficult to get at than it is here on Earth), how are they going to get the energy to concentrate it into a usable form? I’m not sure I understand your concern here. They would use nuclear power for the energy to build more nuclear power. We aren’t just going out with a space suit and a pitchfork. > [@FlikTheBlue](#): > > And that’s not even taking into account or nutritional needs. Photosynthesis is probably viable on Mars, but past that it’is out of the question. Once again, nuclear power. Then you build some hydroponics systems, and you are good to go. > [@FlikTheBlue](#): > > Is there aluminum, silicon, titanium, iron, nickel, copper, etc. out there in the Oort clouds? Yes, all of those elements are present in these rocks, and in much higher concentration than in Earth’s crust. > [@FlikTheBlue](#): > > But how are we going to build factories to process all that stuff into the spaceship parts that are needed for the next leg of the journey? The same way that we build factories for anything else. > [@FlikTheBlue](#): > > How will we know that the next stop along the way will have everything we need to continue the journey? Well, you aren’t really _stopping_, as you aren’t really on a journey. You are expanding. There will be people who stay where they are, and others who go somewhere else. Most of the rocks out there are fairly similar in composition, so we would know what they have, and it’s not that hard to use a telescope or even small probe if you want a more precises assay. > [@FlikTheBlue](#): > > It all seems way to difficult to make the journey by using such a stepping stone approach. I see nothing difficult at all about it. All of your questions have easy answers. > [@eburacum45](#): > > The best source of energy we can hope for in the Oort Cloud is fusion. Plenty of fusible elements out there - but this would require advances in technology we currently do not have. Right, and I don’t’ think that we _need_ fusion to expand, but it would be nice. > [@eburacum45](#): > > The reason I don’t think Oort-cloud hopping is a very good strategy is that it requires too many velocity changes. Every time you travel from one asteroid to another you have to accelerate and decelerate - by the time you get to the edge of the Cloud, the objects are so far apart you’d have to travel hundreds of AU to find the next one. Once again, you aren’t hopping, you are expanding. You sit on your rock and watch as your great grandchildren hop on a shuttle or small cycler that takes them to another rock that is passing nearby. They build it up and develop it, then their great grandchildren hop off and settle a bunch more. ---
**Author:** ![FlikTheBlue](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fliktheblue/32/10972_2.png) [@FlikTheBlue](https://boards.straightdope.com/u/FlikTheBlue)\ **Post date:** [April 15, 2023, 10:25pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/85 "2023-04-15T22:25:46Z")
> [@k9bfriender](#): > > I see nothing difficult at all about it. All of your questions have easy answers. Maybe. But another interesting thought occurs, although it wouldn’t be a technical obstacle. I wonder if a large number of those people would start to think of Earth as the exotic unknown and turn around, having decided that “exploring” Earth so that they can see it in person might be a lot more interesting than moving on to the next asteroid over. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [April 15, 2023, 10:46pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/86 "2023-04-15T22:46:34Z")
> [@k9bfriender](#): > > Except that I pointed out, a few times, that I’m not talking about space opera. I’m not talking about ships crossing the void. I’m talking about slowly settling rocks further and further out from the sun, until you are so far from the sun that you are actually closer to another star. > > Sure, that’ll take tens of thousands of years or more, but what’s the rush? > [@k9bfriender](#): > > Once again, you aren’t hopping, you are expanding. You sit on your rock and watch as your great grandchildren hop on a shuttle or small cycler that takes them to another rock that is passing nearby. They build it up and develop it, then their great grandchildren hop off and settle a bunch more. This isn’t the way the Oort cloud is constituted. First of all, the main body of the Oort cloud (sometimes called the Hills cloud) is thought to go out to ~0.5 light years; less than a tenth of the distance to Alpha Centauri, and of course not anywhere near to stars that might vaguely resemble our own. Oort cloud objects are mostly thought to be volatiles (water, ammonia, methane) with few heavier elements and virtually no concentrations of elements heavier than neon, and certainly not significant concentrations of uranium, thorium, or other fissile materials. They are also incredibly diffuse; the odds of a large object swinging near enough to chase after it are remote, even on the scales of hundreds of years, and you certainly wouldn’t use a cycler trajectory because it would be tens or hundreds of thousands of years before the objects come back into conjunction. Of course, all of these objects aren’t static; they are are in orbit of the Sun, and will only be even remotely in the direction of Alpha Centauri for a small fraction of that time, so the notion of incrementing a way toward the next system isn’t even remotely plausible. The outer Oort cloud, while theoretically extending several light years, is extremely diffuse and approaches the average density of the interstellar medium. @FlikTheBlue has already made the point of the lack of energy resources, and even if you posit the development of nuclear fusion you are left with the issue of expelling the waste heat which itself is a complex but rarely discussed problem with any crewed space habitat or system with an internal power source. As for “that’ll take tens of thousands of years or more, but what’s the rush?”, you realize that this is longer than human civilization as a whole has been in existence, and many orders of magnitude longer than any individual society has maintained itself without collapse, right? If anything, this extended deployment of humanity wouldn’t not result in a continuity but likely a fracturing of societies, potentially even differentiating into distinct cultures and species. Reality is not _The Expanse_ with its inexplicably efficient high thrust “Epstein Drive”; in reality it would take decades and enormous amounts of reaction mass to travel between Oort cloud objects or between the ‘inner’ solar system (including even the outer planets) and the Oort cloud even if you had some pixie magic power source. Nor is there really any incentive for doing so; the mass of material available from asteroids even inside of the orbit of Mars is sufficient to support a vast human presence in space without the problems of trying to chase down small balls of ice at the remote fringes of the solar system, and the Sun to provide essentially endless power from an external source that only needs to be shielded instead radiating heat produced internally. The “All of your questions have easy answer,” are not so easy once you actually do some research and start working through the mechanics of propulsion, power, et cetera to travel to and between the Oort cloud, much less to another star. What is ‘easy’ is throwing out conceptual notions without details; once you do a reaction mass calculation using even a vaguely plausible specific impulse, or looking at the radiator area necessary to reject the excess heat and its associated requirements, those ‘easy’ things start looking a lot closer to ‘really impractical’ and in some cases ‘essentially impossible’. Stranger ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [April 17, 2023, 5:50am UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/87 "2023-04-17T05:50:19Z")
The black Turtleneck and the Camel coat wasn’t the best look. Neil de G is gonna hear the same thing about those Fruity vests in another 10 years. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [April 18, 2023, 4:07pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/88 "2023-04-18T16:07:55Z")
I think when most people think about space fairing aliens they tend to default to the crew of the Enterprise and JLP. But any intelligent civilizations out there will almost assuredly have gone through the same evolutionary processes to get to intelligence as we did. They will have started out as goo and evolved up to locomoting forms with dexterity. That will have led to tool making. Then to Neanderthal aliens. To make rockets you’re probably going to need fire, metal, mastery of electricity and finally brains for technology. That fight for resources and dominance that allows higher forms of life should be built into the “DNA” (as it were) of any advanced civilization. The ETs of science fiction can’t jump into being without going through those steps. There is a lot of hard filters to be passed before all of any civilization reaches higher enlightenment. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [April 18, 2023, 4:28pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/89 "2023-04-18T16:28:09Z")
> [@Lucas\_Jackson](#): > > I think when most people think about space fairing aliens they tend to default to the crew of the Enterprise and JLP. But any intelligent civilizations out there will almost assuredly have gone through the same evolutionary processes to get to intelligence as we did. > > They will have started out as goo and evolved up to locomoting forms with dexterity. That will have led to tool making. Then to Neanderthal aliens. To make rockets you’re probably going to need fire, metal, mastery of electricity and finally brains for technology. That is not at all a given. It is, in fact, an assumption, and one that can be readily invalided just by positing a viable alternative, e.g. an ‘industrial’ society based upon using their equivalent of enzymes to extract and construct complex technology. Stranger ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [April 18, 2023, 4:50pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/90 "2023-04-18T16:50:08Z")
Of course it’s an assumption, so are most all the opinions in this thread. Until we actually meet an alien we won’t have answers to how they arrived at being space fairing. The point wasn’t necessarily that they need the same resources as us to build rockets, but that they will probably have an equivalent background in regards to evolving. Without competition, I don’t see a mechanism for evolving superior intelligence. Not that it can’t happen, I suppose, but it doesn’t seem logical to assume. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [April 18, 2023, 4:59pm UTC](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476/91 "2023-04-18T16:59:07Z")
Realistically, it is actually difficult to imagine a durable starship of the kind of construction we are familiar with. An actual interstellar vessel would itself have to be like a sort of living thing, capable of healing the wounds that it receives from random shit wandering the galaxy and to deal somehow with the heavy load of cosmic radiation with becoming a chunk of ementhaler. [Previous page](https://boards.straightdope.com/t/what-did-carl-sagan-get-wrong/982476.md?page=4)