Tag Archives: Aliens

Monster Pumps

Yesterday’s Science has a long paper on an exciting new scaling law. For a century we’ve known that larger organisms have lower metabolisms, and thus lower growth rates. Metabolism goes as size to the power of 3/4 over at least twenty orders of magnitude:


So our largest organisms have a per-mass metabolism one hundred thousand times lower than our smallest organisms.

The new finding is that local metabolism also goes as local biomass density to the power of roughly 3/4, over at least three orders of magnitude. This implies that life in dense areas like jungles is just slower and lazier on average than is life in sparse areas like deserts. And this implies that the ratio of predator to prey biomass is smaller in jungles compared to deserts.

When I researched how to cool large em cities I found that our best cooling techs scale quite nicely, and so very big cities need only pay a small premium for cooling compared to small cities. However, I’d been puzzled about why biological organisms seem to pay much higher premiums to be large. This new paper inspired me to dig into the issue.

What I found is that human engineers have figured ways to scale large fluid distribution systems that biology has just never figured out. For example, the hearts that pump blood through animals are periodic pumps, and such pumps have the problem that the pulses they send through the blood stream can reflect back from joints where blood vessels split into smaller vessels. There are ways to design joints to eliminate this, but those solutions create a total volume of blood vessels that doesn’t scale well. Another problem is that blood vessels taking blood to and from the heart are often near enough to each other to leak heat, which can also create a bad scaling problem.

The net result is that big organisms on Earth are just noticeably sluggish compared to small ones. But big organisms don’t have to be sluggish, that is just an accident of the engineering failures of Earth biology. If there is a planet out there where biology has figured out how to efficiently scale its blood vessels, such as by using continuous pumps, the organisms on that planet will have fewer barriers to growing large and active. Efficiently designed large animals on Earth could easily have metabolisms that are thousands of times faster than in existing animals. So, if you don’t already have enough reasons to be scared of alien monsters, consider that they might have far faster metabolisms, and also very large.

This seems yet another reason to think that biology will soon be over. Human culture is inventing so many powerful advances that biology never found, innovations that are far easier to integrate into the human economy than into biological designs. Descendants that integrate well into the human economy will just outcompete biology.

I also spend a little time thinking about how one might explain the dependence of metabolism on biomass density. I found I could explain it by assuming that the more biomass there is in some area, the less energy each biomass gets from the sun. Specifically, I assume that the energy collected from the sun by the biomass in some area has a power law dependence on the biomass in that area. If biomass were very efficiently arranged into thin solar collectors then that power would be one. But since we expect some biomass to block the view of other biomass, a problem that gets worse with more biomass, the power is plausibly less than one. Let’s call a this power that relates biomass density B to energy collected per area E. As in E = cBa.

There are two plausible scenarios for converting energy into new biomass. When the main resource need to make new biomass via metabolism is just energy to create molecules that embody more energy in their arrangement, then M = cBa-1, where M is the rate of production of new biomass relative to old biomass. When new biomass doesn’t need much energy, but it does need thermodynamically reversible machinery to rearrange molecules, then M = cB(a-1)/2. These two scenarios reproduce the observed 3/4 power scaling law when a = 3/4 and 1/2 respectively. When making new biomass requires both simple energy and reversible machinery, the required power a is somewhere between 1/2 and 3/4.

Added 14Sep: On reflection and further study, it seems that biologists just do not have a good theory for the observed 3/4 power. In addition, the power deviates substantially from 3/4 within smaller datasets.

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If Post Filter, We Are Alone

Me four years ago:

Imagine that over the entire past and future history of our galaxy, human-level life would be expected to arise spontaneously on about one hundred planets. At least it would if those planets were not disturbed by outsiders. Imagine also that, once life on a planet reaches a human level, it is likely to quickly (e.g., within a million years) expand to permanently colonize the galaxy. And imagine life rarely crosses between galaxies. In this case we should expect Earth to be one of the first few habitable planets created, since otherwise Earth would likely have already been colonized by outsiders. In fact, we should expect Earth to sit near the one percentile rank in the galactic time distribution of habitable planets – only ~1% of such planets would form earlier. …

If we can calculate the actual time distribution of habitable planets in our galaxy, we can then use Earth’s percentile rank in that time distribution to estimate the number of would-produce-human-level-life planets in our galaxy! Or at least the number of such planets times the chance that such a planet quickly expands to colonize the galaxy. (more)

New results:

The Solar System formed after 80% of existing Earth-like planets (in both the Universe and the Milky Way), after 50% of existing giant planets in the Milky Way, and after 70% of existing giant planets in the Universe. Assuming that gas cooling and star formation continues, the Earth formed before 92% of similar planets that the Universe will form. This implies a < 8% chance that we are the only civilisation the Universe will ever have. (more; HT Brian Wang)

Bottom line: these new results offer little support for the scenario where we have a good chance of growing out into the universe and meeting other aliens before a billion of years have passed. Either we are very likely to die and not grow, or we are the only ones who could grow. While it is possible that adding more filters like gamma ray bursts could greatly change this analysis, that seems to require a remarkable coincidence of contrary effects to bring Earth back to being near the middle of the filtered distribution of planets. The simplest story seems right: if we have a chance to fill the universe, we are the only ones for a billion light years with that chance.

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The Evolution-Is-Over Fallacy

David Brin and Jerome Barkow both responded to my last Cato Unbound comment by assuming that the evolution of aliens would end at somewhere around our human level of development. While aliens would acquire new tech, there would be little further change in their preferences or basic psychology over the following millions or billions of years. In my latest comment, I mainly just repeat what I’d said before:

Even when each creature has [powerful tech and] far broader control [over its local environment], this won’t prevent selection from favoring creatures who better use their controls to survive and reproduce. No, what is required to stop selection is very broad and strong coordination. As I wrote:

Yes it is possible that a particular group of aliens will somehow take collective and complete control over all local evolution early in their history, and thereby forever retain their early styles. … Such collective control requires quite advanced coordination abilities. … Anything less than complete control of evolution would not end evolution; it would instead create a new environment for adaptation.

My guess is that even when this happens, it will only be after a great degree of adaptation to post-biological possibilities. So even then adaptation to advanced technology should be useful in predicting their behaviors.

I’ll call this mistake the “evolution is over” fallacy, and I nominate it as the most important fallacy about aliens, and our future. Evolutionary selection of preferences and psychology is not tied to DNA-based replication, or to making beings out of squishy proteins, or to a lack of intelligence. Selection is instead a robust long-run feature of decentralized competition. The universe is influenced more by whatever wins competitions for influence; where competition continues, selection also continues.

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What Are Aliens Like?

Over at Cato Unbound, I respond to Jerome Barkow’s survey of possible influences on the evolution of alien culture and intelligence, as clues to the kinds of aliens we might meet. Alas, Barkow assumes that alien styles are largely determined by the specific biological environments in which particular alien species originally evolved. However:

This might make sense for aliens who are a thousand years more advanced than humans are today. But it makes far less sense for aliens who are a million or a billion years more advanced – far more likely timescales. Given how much adaptation could have taken place over such times, we should expect to see older aliens selected far more by their final environment than their initial environment.

I then offer five predictions about older aliens:

First, … [they] should be very well adapted to their final physical environment. … Advanced aliens are physically similar across the universe, unless significantly different social equilibria are possible and have substantially different physical implications.

Second, … sexual reproduction is quite unlikely to last. … This doesn’t mean signaling will end. …

Third, very old aliens should be accustomed to very low levels of growth and innovation. …  We’d [not] have much general information of use to such aliens. …

Fourth, … very advanced aliens should not be either generically friendly or generically hostile to outsiders. Instead they should be very good at making their friendship or hostility appropriately context-dependent. … Such aliens would ask themselves in great and careful detail, what exactly could humans eventually do to help or hurt them?

Fifth, advanced aliens should be well adapted in both means and ends. … Advanced aliens will be very patient, but also very selfish regarding their key units of reproduction, and quite risk averse about key correlated threats to their existence. (more)

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“Slow” Growth Is Cosmo-Fast

In my first response to Brin at Cato Unbound (and in one followup),  I agreed with him that we shouldn’t let each group decide if to yell to aliens. In my second response, I criticize Brin’s theory that the universe is silent because most alien civilizations fall into slowly-innovating “feudal” societies like those during the farmer era:

We have so far had three eras of growth: forager, farmer, and industry. … In all three eras, growth was primarily caused by innovation. …

A thousand doublings of the economy seems plenty to create a very advanced civilization. After all, that would give a factor of ten to the power of three hundred increase in economic capacity, and there are only roughly ten to the eighty atoms in the visible universe. Yes, at our current industry rates of growth, we’d produce that much growth in only fifteen thousand years, while at farmer rates of growth it would take a million years.

But a million years is still only a small blip of cosmological time. It is even plausible for a civilization to reach very advanced levels while growing at the much slower forager rate. While a civilization growing at forager rates would take a quarter billion years to grow a thousand factors of two, the universe is thirteen billion years old, and our planet is four billion. So there has been plenty of time for very slow growing aliens to become very advanced. (more)

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Guess Alien Value, Chance Ratios

Continuing the discussion about yelling to aliens at Cato Unbound, I ask:

Regarding a choice to yell on purpose, there are two key relevant parameters: a value ratio, and a chance ratio.

The value ratio divides the loss we would suffer if exterminated by aliens by the gain we would achieve if friendly aliens were to send us helpful info. I’d guess this ratio is at least one thousand. The probability ratio divides the chance that yelling induces an alien to send helpful info by the chance that yelling induces an alien to destroy us. I’d guess this ratio is less than one hundred.

If we can neglect our cost or value regarding the yelling process, then we need only compare these ratios. If the value ratio is larger than the chance ratio, yelling is a bad idea. If the value ratio is smaller than the chance ratio, yelling is a good idea. Since I estimate the value ratio to be larger than the chance ratio, I estimate yelling to be a bad idea. If you disagree with me, I want to hear your best estimates for these ratios. (more)

What are your estimates?

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One In A Billion?

At CATO Unbound this month, David Brin’s lead essay makes two points:

  1. We probably shouldn’t send messages out to aliens now on purpose, and more surely we shouldn’t let each group decide for themselves if to send.
  2. The lack of visible aliens may be explained in part via a strong tendency of all societies to become “feudal”, with elites “suppressing merit competition and mobility, ensuring that status would be inherited” and resulting in “scientific stagnation.”

In my official response at CATO Unbound, I focus on the first issue, agreeing with Brin, and responding to a common counter-argument, namely that we now yell to aliens far more by accident than on purpose. I ask if we should cut back on accidental yelling, which we now do most loudly via the Arecibo planetary radar. Using the amount we spend on Arecibo yelling to estimate the value we get there, I conclude:

We should cut way back on accidental yelling to aliens, such as via Arecibo radar sending, if continuing at current rates would over the long run bring even a one in a billion chance of alerting aliens to come destroy us. And even if this chance is now below one in a billion, it will rise with time and eventually force us to cut back. So let’s start now to estimate such risks, and adapt our behavior accordingly. (more)

As an aside, I also note:

I’m disturbed to see that a consensus apparently arose among many in this area that aliens must be overwhelmingly friendly. Most conventional social scientists I know would find this view quite implausible; they see most conflict as deeply intractable. Why is this kind-aliens view then so common?

My guess: non-social-scientists have believed modern cultural propaganda claims that our dominant cultures today have a vast moral superiority over most other cultures through history. Our media have long suggested that conflictual behaviors like greed, theft, aggression, revenge, violence, war, destruction of nature, and population growth pressures all result from “backward” mindsets from “backward” cultures.

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Good Job Templeton

Whatever else the Templeton Foundation may have done wrong, they have done very right by funding the research behind two new papers, to appear in the Astrophysical Journal. The first paper reviews what evidence of aliens we should expect to see:

We motivate the \^G infrared search for extraterrestrial civilizations with large energy supplies. We discuss some philosophical difficulties of SETI, and how communication SETI circumvents them. We review “Dysonian SETI”, the search for artifacts of alien civilizations, and find that it is highly complementary to traditional communication SETI; the two together might succeed where either one, alone, has not. We discuss the argument of Hart (1975) that spacefaring life in the Milky Way should be either galaxy-spanning or non-existent, and examine a portion of his argument that we dub the “monocultural fallacy”. We discuss some rebuttals to Hart that invoke sustainability and predict long Galaxy colonization timescales. We find that the maximum Galaxy colonization timescale is actually much shorter than previous work has found (<109 yr), and that many “sustainability” counter-arguments to Hart’s thesis suffer from the monocultural fallacy. We extend Hart’s argument to alien energy supplies, and argue that detectably large energy supplies can plausibly be expected to exist because life has potential for exponential growth until checked by resource or other limitations, and intelligence implies the ability to overcome such limitations. As such, if Hart’s thesis is correct then searches for large alien civilizations in other galaxies may be fruitful; if it is incorrect, then searches for civilizations within the Milky Way are more likely to succeed than Hart argued. We review some past Dysonian SETI efforts, and discuss the promise of new mid-infrared surveys, such as that of WISE. (more)

The second paper describes a plan to look for some key evidence:

We describe the framework and strategy of the \^G infrared search for extraterrestrial civilizations with large energy supplies, which will use the wide-field infrared surveys of WISE and Spitzer to search for these civilizations’ waste heat. We develop a formalism for translating mid-infrared photometry into quantitative upper limits on extraterrestrial energy supplies. We discuss the likely sources of false positives, how dust can and will contaminate our search, and prospects for distinguishing dust from alien waste heat. We argue that galaxy-spanning civilizations may be easier to distinguish from natural sources than circumstellar civilizations (i.e., Dyson spheres), although Gaia will significantly improve our capability to identify the latter. We present a “zeroth order” null result of our search based on the WISE all-sky catalog: we show, for the first time, that Kardashev Type III civilizations (as Kardashev originally defined them) are very rare in the local universe. More sophisticated searches can extend our methodology to smaller waste heat luminosities, and potentially entirely rule out (or detect) both Kardashev Type III civilizations and new physics that allows for unlimited “free” energy generation. (more)

I’ll be quite surprised if they see anything, as I find hard to believe that, if they have existed nearby for a billion years, aliens wouldn’t already be plenty visible in their first result. But the issue is plenty important enough to look carefully anyway.

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Silence Suggests Sim?

In 2010 I explained why I guess I’m not in a sim. In 2011 I explained why sims should be small, and focus on “interesting” folks. In 2001 I explained why it matters if you live in a sim.

Here is Tyler today:

If we are living in a simulation, does that resolve the Fermi paradox? I would think so. The “aliens” would be here, we just would not “see” them as such. … Should we expect to find alien civilizations in a simulation? The priors are not so clear. … For the time being, we are still in a “no aliens” do loop. … The Fermi paradox raises the likelihood that we are living in a simulation.

I don’t buy it. Let’s try two extreme cases. First, assume that the creatures who make your sim copy their own universe in the sim – if it has aliens, then you get aliens; if not, not. Here not seeing aliens says nothing about if you are in a sim.

Now assume the opposite, that whether the creatures running your sim give you aliens has no relation to whether or not they have aliens in their world. They decide whether to give you aliens based on the “story” (= useful sim) value of aliens, regardless of how realistic that seems to them. In this case if the scenario of your world seems to have especially high story value (relative to a real scenario), you should increase your suspicion that you are in a sim. And if your scenario seems to have an especially low story value, you should reduce your suspicion that you are in a sim.

It seems to me that if anything aliens would add to a story value. So not seeing aliens should lower your suspicion you are in a sim. And if you can’t tell if aliens help or hinder a sim story, then not seeing aliens gives no info about if you are in a sim.

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Why Silence Puzzles

Bryan Caplan:

[Recent planet] discoveries seriously undermine the Fermi Paradox. If we’ve only recently confirmed the existence of extrasolar planets, why on earth should we be surprised by the fact that we’ve failed to confirm the existence of extrasolar intelligent life? … Shouldn’t they already be here? Not if space travel (including the value of time) permanently remains extremely costly relative to the value of raw materials. It’s a lot easier to believe that space travel will forever remain a rare luxury for intelligent life than that intelligent life exists on Earth alone. ..

[Some] say, “Whatever intelligent life usually does, surely one species of intelligent life would be the exception that proves the rule.” Facile. When you multiply independent, rare events together, you quickly reach situations with zero examples. … Even if there are seven billion species of intelligent life in the galaxy, there could easily be zero species that entered our solar system during the last century, approached the earth, and stayed long enough for the scientific community to detect and confirm.

When a tree burns, what fraction of its leaves float to another tree still burning enough to ignite it? What fraction of the coconuts on an island float away to a barren island to grow a new tree there? What fraction of the virus copies in someone who is infected fly out in a sneeze to infect a new person? Why should we ever expect such fractions to be large enough to create forest fires, or coconuts on new islands, or viruses that spread to many people?

If we knew that one tree in our dense dry forrest was burned a few days ago, we should be surprised to see untouched trees near where we stand, even if we could not see that burned tree far away. We should also be surprised to see unburned coal near us if we knew a fire had started days ago far away, beyond our sight, in the same rich ventilated coal mine. And if we knew that one drop of spoiled milk was added days ago to a large room temperature vat of milk, we should be surprised to see unspoiled milk in any part of the vat we could see.

We should be surprised to think billions of technologically-advanced intelligent civilizations have existed in our galaxy for billions of years. This is because for a civ only a millennia more advanced than us, it should only take a tiny (i.e., a part in a billion or less) fraction of its resources to send out a self-reproducing seed that could colonize an empty galaxy densely (so that we’d see it everywhere we looked) within a billion years. It doesn’t matter if this venture is expensive and time-consuming relative to the typical hobby budget or time of a human today, or a bacterium on any day. What matters is that civs can be diverse, and contain great internal diversity. And it just takes one spark to start a fire.

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