What don’t we know?

August 26, 2015 • 11:55 am

by Matthew Cobb

Here’s a quiz you can all respond to: what are the most interesting scientific questions we don’t know the answer to?

Please comment below. Let’s skip over the obvious Big Things – why/how the Universe began, why/how Life began, what is consciousness, why the Cambrian Explosion happened – we all know those.

Think hard and and come up with simple (ish) questions that the general public would like to know the answer to, and post them in the comments. Please cover the full range of science – maths, physics, chemistry, biology, geology, anthropology, psychology etc.

My favourite? Different bird species make different-shaped nests out of different material – we have no idea how those different construction programmes are encoded in genes. I can come up with a hand-wavy explanation, but no one actually knows.

Off you go!

308 thoughts on “What don’t we know?

    1. We know why they can’t. The unsolved problem is how to bridge them.

      Quantum physics and our best explanation for gravity (general relativity) make different and irreconcilable assumptions about the granularity of the universe.

    2. I think most theoretical physicists in the relevant fields are confident, or at least hopeful, that an ultimate theory of quantum gravity will emerge. Eleven dimensions is hard!!1!

    3. They are, except at high energies/small scales. And if string theory works, they are reconciled even there.

      My gripe on the recurring gripe.

        1. They are 100 % reconciled in the sense that they agree when they are well defined, as far as I know. When GR breaks down (large energies) or QFT breaks down (small scales), they are obviously hard to do anything with.

          There is one string (M) theory, in the same way that there is one QED theory. You are asking what parameters it has, but that isn’t relevant to the fact that GR (gravitons) is predicted by all (nice) string theories. (As far as I understand it, no string theory here.)

  1. This is probably more neurological than psychological: what the heck are migraines and where so they originate: the cortex or the brain stem.

    This might be a big physics question that everyone knows but what the heck is dark energy?

    1. A current plausible guess for dark energy is that it is the so-called zero-point energy, but integrated over the surface of the universe rather than the volume. The latter gives a value tens of orders of magnitude too high.

    2. On the migraine issue, and this is strictly anecdotal, but I’ve noticed that everyone I know who’s had one or gets them is blocking or not addressing a big fat issue they’d probably better off dealing with and getting out. Everyone needs a spit valve. Some need bigger ones and to tend to them more often than others.

        1. I’ve not heard of eye drops for losing weight. But if you have a single engine, I wouldn’t recommend flying in anything but fair weather. Also, no Chinese food. 😉

    3. Ironically, your brain, Diana, is able to detect dark energy. So the extra oomph of the expanding universe is stretching your brain and it hurts.

    4. From people I know with chronic migraines, nothing seems to work. Or the disparity of what does work is so…well…dispariging; it’s needle in the haystack medicine. Perhaps migraines originate from both sources (cortex and brain stem). It is a horrible affliction, and hopefully good science will one day conquer it. I have acute asthma…without medication, my life would be utter hell…actually, I’d probably be dead. I truly hope that migraine sufferers will one day be free. Dark energy for sure…on a metaphorical stance that is.

        1. Typically, those are migraines with only aura. I don’t get aura but aura come before the pain in hose who get it. Those migraines still go through the same steps as other migraines but the pain step (the last one) doesn’t happen. I don’t know if this is because people with those kind of brains don’t interpret the jabbering neurons as pain at that point or if the neurons shut up at that point with them.

          1. True. A trip to the ED last year put migraine variant on my differential for a sudden, painless, bilateral, partial blindness that resolved.

            I’m fine per CT, but it was interesting.


            1. My aunt had the same thing. I told her I didn’t want to hear about her random, painless migraine. 🙂

              Migraine sufferers are more likely to develop epilepsy as well as migraines physically change the brain, giving you lesions.

      1. I used to have a migraine every day for 2 years. They came on in my 30s which is probably unusual. Now I get about 10 or so per month. The medication I take, Relpax, is very effective but I still get the other cognitive issues like not being able to find words and having no short term memory.

    1. That’s more a strictly mathematical than a scientific question, isn’t it?

      But I would certainly like to know whether it is the case, and understand why.

  2. I have seen a mouse flatten itself out to go under a door where a piece of paper wouldn’t even fit. Genetically why did this develop? Did mice need to get into crevices to keep away from predators? Since mice appear to be ubiquitous, why was this type of selection necessary?

      1. … And my attic and my pool shed and even chewed through wires in the electronics of my pool heater over a winter. Dryer sheets repel them and poison limits their ubiquitous spread.

              1. That last period should have been a comma. In the winter, I am in Florida. Summer in Massachusetts.

  3. cold fusion

    why people think homeopathy is real

    why people think biology has anything to do with religion, when anthropology is what shows religion is a cultural product

    we were taught elements are not transmutable, but in nuclear reactions they are

    so how does splitting an atom make a bomb

    but shifting it’s subparticles and changing it doesn’t?

    1. These are intriguing issues for us laymen, no doubt, but I don’t think they are unresolved scientific questions. I think science has pretty good explanations for the first and the fourth through sixth, and the social sciences have insights to offer on the second and third.

    2. It’s still true that elements are not transmutable by chemistry. But we know more now about nuclear physics than 19th-century chemists did.

      Splitting one atom doesn’t make a bomb; you have to split a whole bunch of them, in a chain reaction. It’s like falling dominoes: if you don’t set them up just right, the whole thing fizzles.

        1. I’m not entirely sure what you’re getting at, by my (perhaps incorrect) understanding is that fission reactions at Fukushima stopped with the meltdown of the reactor cores. There’s still a lot of radioactive debris, which produces a lot of heat through decay processes. But that’s a not a fission reaction that needs to be “shut down”; it’s just what unstable nuclei do.

          In any case, there’s no scientific mystery here; the physics of all this is well understood (or else we wouldn’t know how to build fission reactors in the first place). The puzzle is how to clean up the mess.

          1. Yes, the core melted because they lost power and for some reason had the back up generators in he basement instead of on the roof. So, there was a run away reaction that couldn’t be stopped quickly enough.

  4. The “different-shaped nests” question is a special case of how is animal behavior programmed into the brain?
    I think the general public is fascinated by some of the issues that arise. One would be, what determines sexual attraction and sexual preference in humans? For heterosexuals, they take there own feelings for granted and wonder how in the world you get a gay brain? Yet, its clear that straights can’t really take themselves for granted. What is that drive anyway? How does it actually work?

    1. Also – how about the programming of different types of spider webs? And complex parasitic behaviors? Simply mind boggling.

      1. The simplest answer to the spider web question would be that the spider has an innate symbolic map of it’s web in it’s brain. An arrangement of neurons that it tries to build a correspondence to when building the actual web. That could be fairly simple. Probably not *that* simple though.

        1. Actually I think it’s fairly unlikely that the spider has a mental image of a finished web that it tries to replicate in silk. It’s much more likely that the spider has a rote procedure that it carries out, which natural selection has fine-tuned to produce an effective web.

          This procedure might involve pattern-matching on a partial web in order to select the next step, but that’s different from having an ultimate goal in mind and formulating a plan to get there.

          1. I can see your point. It could be that the minimum map to create a complete web is not a mirror image of a web, but some abstract representation of several angles and start stop points, or something like that.
            Now, if we could just configure an MRI machine at the requisite scale.

    2. Yes, I think this a huge question. A highly sophisticated computing machine emerges from the information contained in the genome plus the information in the developmental environment. But we really have very little idea how this happens.

      We know that the genome encodes proteins and sophisticated instructions and feedback mechanisms about when and where to fabricate those proteins. Although we don’t know all the details, it’s not difficult to see how this type of information can in principle lead to the development of gross structure, even something as sophisticated as an eye. After the brain, the second most complex system is probably the immune system – and we know a whole lot about how the instructions to build the immune system are encoded in our DNA. But the brain is vastly more complex – and I don’t think we have a clue how our DNA encodes the instructions to make a brain.

      Human brain development does include cultural transmission, which adds a whole extra layer of information. But at birth, the hardware is largely in place, and even in humans, large amounts of software are clearly already “programmed”. People may argue about how much is pre-programmed, but I don’t think anyone would dispute that a baby is born with a highly sophisticated computing machine in its head. And in most non-human animals, cultural transmission is not significant, so presumably in addition to the hardware, virtually ALL of the computational software of the brain (i.e., instinctive behaviour) is encoded by the genome.

      How does this happen? How is this information stored in our DNA? It’s hard to understand how even the most subtle instructions for protein expression can lead to the development of a vast number of complex synaptic connections in all different parts of the brain.

  5. 1) Metastasis.
    What are the stages of tumors spreading and what can we do about it?

    2) Can we make certain cancer cells revert to well-behaved cells?

  6. No one can predict within ± 1 cm accuracy where each of my cats will be this Sunday at noon. Likewise, no one can predict what human’s will look like in 1000 years.

    1. Assuming advances in transhumanism (bio-genetics, nanotech, etc.), I think your second sentence is correct. If left to the processes of natural selection, humans a thousand years from now will likely look as much like us as we do those who were around in 1,000 CE.

    2. Per Milford Wolpoff, Rachel Caspari (Race and Human Evolution: A Fatal Attraction), if you dressed a Neanderthal in a suit he could ride the subway without attracting attention. Over 100,000 years and they do not look that different.

      1. My understanding is that the Neanderthals are not among our direct, lineal ancestors (except to the extent a small amount of their DNA made it into the human genome through interbreeding), but more like our cousins. They went extinct around 35,000 years ago.

        I think you’re right that if you cleaned ’em up and gave ’em a shave, they could almost pass for homo sapiens. Hell, if I ran into one on the subway, I’d probably make him for one of my in-laws.

      2. But our ability to manufacture changes to both our genetics and or cybernetics will far out pace anything evolution has so far done (hypothetically).

        I look forward to Dumbledore-like pensieves, where we can play with memories, not only our own but of others. Given that we can hardly remember things after seven to ten decades, we will need help.

    3. I am afraid that humanity will look like a huge assortment of historical monuments. If, in fact, something happens to be there to see them.

      Just another failed biological offshoot.

      My new theory of ethics: That which is Good is that which extends the existence of human genes and their descendant genes the furthest into the future. Of course, we don’t know which behaviors or conditions subject to our influence will optimize that outcome.

      Personally, I think that what we usually think of as ethics is just a conditioned response based on a biological imperative or a “goal” and set under the direction of a biological “suggestion” by

      Hey, it just occurred to me that this could apply to the top level question: what don’t we know? It could be considered a scientific question under Jerry’s definition of scientific. I paraphrase: Science is true knowledge. Knowledge, reflecting the real world is the best way to get to the Good.

      1. Sorry. 😕 “…by” I got distracted by a blue-gray gnatcatcher working around the trees.

        … by a biological computer with a powerful processor tied to a field of vision limited by a short temporal span. Goals are set and we try to meet them. What is Good is redefined to provide a societal target or goal in line with what is preceived to be reality. Goals are set at a time based on our temporal span. In the main, religion seems to occupy a set of historical goals which the advancement of science has shown to be either destructive to a “genetic Good” or impossible to meet because they are not based on reality. Plus, religion distorts the culturally accepted view of what reality is.

        We probably could cope culturally but probably not fast enough. Science could have saved us but we started too late. Our temporal span again.

        Maybe intelligence just doesn’t work.

    4. Likewise, no one can predict what human’s will look like in 1000 years.

      1000 years, about 30 generations. I’ll bite.
      They’ll be bipedal mammals, between 1.5 and 3m tall at maturity. skin pigmentation will remain moderately variable. They will reain constrained height-wise by knee, ankle and heart problems which will worsen with age. Backs will continue to cause problems. Hair pigmentation and texture will remain variable (as well as being cosmetically variable amongst the female of the species, and possibly the males too). In short, no great changes.
      If (big IF), we get an isolate population under considerable selection pressure – say the first asteroid dwellers, or Lunatics) – then we might see more rapid evolution in that population, but to be honest I do not anticipate sufficient separation from the rest of the population. If a generation ship gets launched to Alpha Centauri Bb (if it exists), then there is a higher probability of significant change there, but I’m not really placing bets on that either.

      1. I’m guessing that with increased travel and intermarriage among members of diverse populations, racial categories will have broken down — though I think (and hope) you’re correct that “skin pigmentation will remain moderately variable.” Vive la standard deviation difference!

  7. I used to have a copy of Jacob Bronowski’s book The Origins of Knowledge and Imagination. The first chapter was titled Why?. Bronowsky asserted that this is the most fundamental and unanswerable question. It is usually the first question a child asks, and the last thing an adult ponders.

  8. The oldest unsolved problem in number theory going back to the ancient Greeks and predating Fermat’s Last Theorem by millenia is in two parts

    Is the set of even perfect numbers finite or infinite?

    Are there any odd perfect numbers at all?

    A perfect number is the sum of all of its divisors less then itself, the two lowest being 6 = 1+2+3 and 28 = 1+2+4+7+14

    I could say more but see the Wikipedia article.

    1. I should add that one consequence of Godel’s incompleteness theorem is that we might never know the answer.

    2. I’m working on it with a scratch pad and a No. 2 pencil; will get back to you with the answer shortly.

      1. Given Wiles’ proof (150 odd pages IIRC), do maths stationery suppliers now provide scratchpads in, say, a 200 page size called a “margin”?

    1. I like the sleep question. All animals sleep as far as I know. Do plants do something similar? Do simple single cell critters nap as well?

      1. Don’t know if all plants do, but most plants do have a cycle that includes a period analogous to sleep.

    2. Really?

      I’ve never thought about it at length, but I always just assumed that sleep was the natural state and awake was the energy-drain state necessary to find food and have sex.

    3. I like to look at what’s analogous first, and it always seemed to me sleep was part of a binary: Sleep off / wake on. Ipso fatso, a cycle, of which there are examples everywhere/anywhere in science. Like plants working at night. We simply used the cycle to improve our survival by regenerating and discarding.

  9. Morphology: walking through the woods, I marvel at all the myriad different shaped leaves, which led me to wonder at the limits to shapes of every sort. What tells an organism to grow and then stop growing in a specific shape? Genes – but that is not a complete answer. How do genes do it? How many are involved – different numbers of genes for every different shape, contour?? This is probably simple for you, Drs Cobb & Coyne – but it stirs my curiosity.

    1. Why major chords sound “happy,” minor “sad,” major/minor sevenths, sixths, ninths, etc. sound exotic, other-worldly, etc.

    2. Why music makes one happy

      There are sufficient people for whom that is not the case to make the question experimentally tractable. IF you could persuade them to waste their time in such a useless pursuit.

      1. I totally disagree – why is that a useless pursuit? I think it’s really interesting question from both a scientific and human interest perspective.

        1. It may be interesting to you. As a pretty-near amuse (is that the term for someone with no interest or appreciation of music?) I can see the intellectual interest, but I can’t say I could give a good goddamn about participating. “Cross,” as the Diddikoi says, “my palm with silver.

    1. https://en.wikipedia.org/wiki/Einstein_field_equations

      Though, why does gravity work the way it does. No idea, why is it so theoretically disparate from quantum mechanics? No idea. But if you consider NSIT clocks (order of 1/10^18) they require inputs from the curvature or our world on spate-time, so that puts a rather large practical range for which General Relativity is succsesful at predicting outcomes.

  10. How do gall formers (certain midges, wasps, etc.) induce gall formation in plants? How did the ability to induce galls evolve?

  11. When the earth goes through its irregular geomagnetic polar reversals, with a “zero point” of unknown duration, does the inflow of cosmic rays increase enough to temporarily, but significantly, boost the genetic mutation rate?

    1. I seem to recall that was pretty much ruled out during the Nemesis wars of the 1980s and ’90s, when people were trying hard to correlate extinctions with all manner of geophysical and astrophysical phenomena, and mostly failing.

      But perhaps some expert can correct me.

    2. I think the answer to that is no since there have been no mutation correlations. Most likely, such a thing would result in deleterious mutations too (as most mutations are anyway).

      1. Correct. Is has not been possible to correlate magnetic reversals with extinction rates and changes in species diversity. This applies to both terrestrial and marine environments, macro- and microorganisms.

        1. I’ve read that the geomagnetic field is one of the most important (perhaps THE most important) barriers to primary cosmic rays. I’ve also read that secondary cosmic rays (primary rays rarely make it to the ground) are one of the main causes of spontaneous changes in DNA.

          It would be very difficult to get evidence to support this sort of relationship. You’d need to have levels of dating accuracy significantly greater than we currently have in order to correlate them to the relatively short close-to-zero-point period of time.

          I don’t think mass extinctions need be a result. True, a higher mutation rate will result in mostly harmful mutations, not necessarily enough to wipe out a species. There would also be a slight uptick in beneficial mutations, probably unnoticeable many millennia later.

          1. I don’t think that is true.

            The heliosphere magnetic field blocks ~ 90 % of CR. Less so, when the solar wind is minimal (no spots, IIRC).

            The atmosphere blocks most of the rest of CR, as far as I know.

            The geodynamo is good at stopping the solar wind though.

            1. I meant in close proximity to earth, not out beyond Neptune. I suppose if there’s a “galectopause” it might block more cosmic rays than the heliopause.

              1. As “proximity” means (briefly) nearness or vicinity, then “close proximity” does seem redundant, as you suggest. Then again, both “nearness” and “vicinity” are relative terms. Relative to galactic center, the Oort cloud in the proximity of Earth. For this case, let’s say “close proximity or “proximity” is inside the moon’s orbital distance.

          2. So, guys, what does a geomagnetic polar reversal augur for the top of the food chain — which is where most of my friends, and some of my family, reside?

            1. So, guys, what does a geomagnetic polar reversal augur for the top of the food chain

              The geological record is replete with geomagnetic reversals. The geological record is also pretty replete with extinctions. Where the record is good enough to locate an extinction event to better than +/- 1 geomagnetic reversal (not a common event, because reversals are so closely spaced), there is no convincing case for a correlation between geomagnetic reversals and extinctions.
              People have been looking at this question for as long as I’ve been a geologist. No one has made a convincing case for there to be a positive significant correlation between reversals and extinctions, and when such correlations have been proposed, they’ve not stood up against dispute for more than a few years.
              Geomagnetic reversals do not seem to have any significant effects on high trophic levels in the food chain. There’s also no evidence of there being any significant excess deaths (without extinction) at these times.

        2. Yes, cosmic rays really mess up your DNA. Even pilots are at a higher risk being up so high so often.

          I try to blame my cancer on cosmic rays for LOLs but none of my doctors seem to enjoy my joke. My theory is my joke is hilarious (like all my jokes) but they don’t know what cosmic rays are.

            1. Yeah I considered writing “air crew” or such as I had the same thoughts but then I got lazy and just wrote “pilots”.

              1. And here I was all set to ask about the chromosome and locus where the flight attendant cosmic-ray-immunity mutation could be found…

              2. I’d have to harness some of that if that were the case! I’d get cocky, climb mountains & dare the cool rays to mess with me!

    3. From what I have read (peer reviewed, though I cannot find it now), no. Pole reversals are not as significant as one might be led to believe.

      Recall that the atmosphere above our heads at sea level is equivalent to several meters thick of concrete.

      1. More precisely, equivalent to about 10m of seawater, so (say) 4m of concrete at density of 2.5 (tonne/m^3 or S.G.), 1.3m of steel (S.G. 7.75) …
        Mass is important for absorbing radiation ; composition is also important, but less so. Hydrogen is good (elastically scatters protons and neutrons, absorbing their energy). Boron or cadmium are good for absorbing neutrons. Lead is helpful for getting a lot of mass into a small volume. so if you really wanted to go for effective radiation shielding, you might just go for an ice of borate-containing water, cementing grains of lead ore.
        But to be honest, I’d just start my planning from carving out the inside of a dirty snowball comet or asteroid for my spaceship, and have a hundred or two hundred metres of radiation shielding, which doubles up as reaction mass. Several layers of plastic bags buried in the ice and melted to seal things should keep the atmosphere where I want to put it, and I can probably spin it for gravity to offset the effects of long flights.

        1. I don’t think a dirty snowball or rubble-pile is likely to hold together under spin gravity. A solid chunk of rock might, but I’m not sure I’d want to bet my life on it. A properly engineered centrifuge spinning in a hollowed-out interior space seems like a safer choice.

          1. I don’t think a dirty snowball or rubble-pile is likely to hold together under spin gravity.

            that is why you start by wrapping your dirty snowball in Cling Film (other thin plastic sheets are available) before you start to use the heat tools to carve out your tunnels down to living space. The waste heat from carving (and living) in the ice helps it to consolidate.
            If you used a smaller dirty snowball as a source of steam for the carving jets, then adding the mass of the smaller to the interior of the larger, the whole being in a fairly tight wrap, would result in a much better managed material.
            No one builds kilometre-tall skyscrapers out of the sands of the desert – they mix the sands with cement first.

  12. One question that I have always found particularly interesting is why do some birds bob their heads when walking while others don’t? There are various explanations for why head bobbing would be advantageous (e.g. helps with depth perception, sharpens focus, etc.), but why did it evolve in only some birds? What’s more puzzling to me is that it seems to have evolved multiple times – or perhaps the adaptation was lost multiple times.

    Case in point, some small North American gulls bob their heads when they walk (e.g. ring-billed or mew gulls), but larger ones do not (e.g. glaucous-winged or western gulls). At the same time, crows often bob their heads, but ravens generally do not. Anecdotally, there appears to be a weak correlation with size (smaller birds have more of a tendency to bob their heads), but that doesn’t explain much, and their are plenty of counterexamples (like cranes).

    From the realm of mathematics, the most famous unsolved problem has to be the Riemann Hypothesis: https://goo.gl/ubGDcS

    Another big analytical problem that remains unsolved (and we are a *long* ways off from resolving it) is the classical Kakeya conjecture: https://goo.gl/99GQqu. Basically, does a set that contains a unit line segment in every direction still have to be “big” – i.e. of full dimension?

    1. Ed: In addition to head bobbing, there is also tail wagging, butt-wiggling and whole-body dipping. These “bobbers” have eyes on the sides of their heads rather than on the front (e.g. owls & other raptors), reducing their binocular vision and their depth perception (perhaps only for short distances). So my money is on bobbing as an adaptation to improve depth perception – they are superimposing one view with a 2nd view from a slightly different angle and their brain is assembling it into a single view.

      I don’t know how one would prove this conjecture, though. Cover one eye with a pirate-eyepatch, and see how they do?

      1. Interesting. My hypothesis is that they would bob their heads from side to side rather than front to back, since that would then be the only way for them to get any depth perception.

        1. I’d always assumed the head-bob in birds was analogous to arm-swing as practiced by most featherless bipeds — if they do it, it’s because they gain speed and/or efficiency in walking. Perhaps species-specific variations among birds reflect different biomechanical relationships of leg-length, neck-length, head mass, center of gravity and stride turnover. Or they may want to look urgent like a race-walker or goose-stepping soldier…

          1. The arm swing, I thought, was in large part a kind of reflexive motor pattern from our quadrupedal past. But maybe it does have an effect on adjusting our center of gravity.
            As for the head bob and adjusting center of gravity, I think that is a good idea.

        2. I think bobbing would work better than side-to-side, as when a human swivels on the neck, because 1) both eyes are getting a slightly different view from same distance (above & below) rather than each eye getting view from slightly different distance, and 2) most birds doing this have body postures closer to horizontal than vertical, making swiveling more difficult than it is for humans. Tail-bobbing works the same way by causing the head to move slightly vertically.

      2. Possible reason for back-to-front head bobbing in small birds: Dangerous predators and any number of other interesting things can first be detected because they move and the background doesn’t. However, if you’re moving, the image of the background is moving across your retina. If you keep your head still, you can pick up the movement — but then you have to jerk the head forward to catch up with the body. Then keep the head still to see movement, and repeat.

        1. That would be my thought as well. Chickens exhibit this most clearly.
          Your description sounds like the invention of a new dance sensation.

        2. In films of flying long-necked birds (storks, geese, cranes, etc.), when they flap their wings downward their torso rises, but the head stays level.

    2. Why do little dogs twirl in circles, bob their heads, and lick their chops (nervously? neurotically? . . . irritatingly!) and big dogs don’t? (At least in the case of poodles.) Neoteny?

    3. I was watching a crow a couple of days ago ; it would walk a few paces without bobbing, then hop several paces (on a different tack) with bobbing. It seems that birds can vary their gaits as conditions and desires dictate.

      1. Yes, I’ve noticed something similar – with some species. Ring-billed gulls for example really only bob their heads when they are searching the tides for worms, not when they are just walking from point A to point B. But then you look at a species like a rock pigeon, and they seem to bob their head all the time, regardless of the circumstance. Maybe they are just always on the lookout for food?

        1. All of the dove species I’ve seen bob when they walk or peer at the ground. I don’t think they do it when perched. Check the next group you see sitting on a wire – they’re fairly motionless, if I recall correctly. Males in courting displays do all sorts of puffing and bobbing.

  13. What if cholesterol has nothing whatsoever to do with atherosclerotic plaques, just as “type A” personality had nothing to do with stomach ulcers or “refrigerator mothers” has nothing to do with autism? Might there be a better explanation, as there was for those disorders?

  14. Might preexisting momentum, rather than dark matter, explain the unexpected surplus of rotational speed in the outer portions of galaxies?

    1. No. Galaxies aren’t rigid objects like bicycle wheels, capable of spinning at any arbitrary speed. The only thing holding them together is gravity, so if the galaxy is spinning faster than we think it should, there has to be some unseen mass to account for that; otherwise it would fly apart.

      1. Rigidity not needed. If 2 (or more) large nebulae speeding through space passed by one another close enough for mutual gravitational attraction to occur and they collided / spiraled in on one another, then the momentum one would see in the later rotating galaxy would be caused by the initial momentum of the 2 (or more) nebulae. This is an arms-in-to-center view.

        This view of course contradicts the current center-out-to-arms conjecture that rotational velocity is the result of nebula contraction initiating galactic rotation.

        If the momentum preceded the formation of the galaxy, then dark matter becomes an unnecessary explanation.

        1. Why should the history make any difference? If there’s not enough visible mass to keep the stars in the orbits we observe them to have (regardless of how they got that way), then there are only two possibilities: either there’s unseen mass making up the difference, or our understanding of orbital mechanics is wrong. Invoking pre-existing momentum doesn’t change that.

      1. The moving nebula, prior to galactic formation, would have both momentum and internal gravity. If it didn’t gravitationally encounter another moving nebula, it could coalesce, perhaps into a galaxy (but maybe not a spiral) via its own gravity, as is currently conjectured for all galaxies.

        1. The issue is not that galaxies are spinning faster than galaxy formation models predict they should be. The issue has nothing to do with how galaxies ended up rotating at the rates we currently observe.

          The issue is that the amount of mass that we can “see” in a typical galaxy is not enough, by a significant amount, to hold the galaxy together via gravity given the observed rotation rate. Given the observed values of mass and rotation rate galaxies should fly apart given what we know about orbital mechanics. And we have very good reason to suppose that our understanding of orbital mechanics is not the problem.

          An analogy would be swinging a mass at the end of a rope around in a circle. The rope is gravity, the mass at the end of it is a star and the person at the center spinning around is the center of mass of the galaxy. The faster the mass is rotated the greater its inertia. At a certain rate of rotation the rope fails and the mass hurtles off, no longer bound to its orbit about the person spinning.

          That is the issue with observed galaxy rotation rates. The gravity of the observed mass, analogous to the rope, is not strong enough to keep the galaxy together at the rate it is spinning. A hypothesis that accounts for this mystery is that there is more mass than we are currently able to observe. And it would have to be a lot more. The model of a halo of dark matter surrounding galaxies is by no means definitive, but the evidence for dark matter is mounting.

          1. Darrelle: Thanks for the explanation. I’ll have to read up on this some more.

            I had read that the problem was that the outer portions of galaxies (perhaps only spiral galaxies) were moving more swiftly than they ought to be relative to the inner cores, if assumes as correct the view that galaxies formed by contraction from whatever preceded them, presumably vast nebulae of matter.

            I hadn’t read (or I forgot) that presumably they would fly apart at current rotational speeds were it not for dark matter binding them gravitationally.

            What about when galaxies collide? I believe we now have photos of various stages of these events. Doesn’t some matter fly off, some go straight through, and sometimes they get sufficiently gravitationally entangled to form a single new galaxy?

    2. Didn’t observations regarding the displacement of stars during galaxy collisions take the momentum out of MOND and other alternatives to dark-matter theory?

  15. How does a species transition from herbivore to carnivore or vise versa? Can we tell through development, DNA or other clues how many times it has happened in a particular species?

    1. By passing gradually through a stage in which the diet is varied. There’s no switch to throw that turns an obligate carnivore into an obligate herbivore. That’s why giant pandas are bears, not cats.

      The main way we can tell about switches in such characters is by mapping them onto phylogenies. Which is telling through DNA, more or less.

  16. Why are people attracted (sexually or otherwise) to certain others, indifferent probably to most, and repulsed by some?

      1. You can’t argue pheromones when these days a large portion of those we are attracted to are only available visually. Tom Hiddleston doesn’t smell good in Avengers.

      2. So, people with no sense of smell (I think if a friend who fractured his skull and severed his olfactory nerve) do not feel attraction or repulsion?

    1. I can’t think of anything else that combines a real possibility of being answered in our lifetimes with this much cosmological significance for humans.

      This question isn’t getting enough love here.

      1. Thanks. It treads rather close to the origin-of-life questions Matthew said he didn’t want to hear about, but I figured it was different enough to be worth mentioning anyway.

  17. A deep understanding of the 2nd Law of Thermodynamics and Entropy as it manifests itself in our universe. This, to me, really defines how reality works.

    To me again, We, the royal we of humans, animals, plants, planets, stars, etc…, are just eddies in a stream that flows from a high point to a low point.

    I think if we understood that process, we pretty much understand reality and how it works… Maybe not why its here, but we understand the whole thing itself…

    1. Check out the Maximum Power Principle (MPP) and Maximum Entropy Production Principle(MEPP) As far as I know, there are no exceptions. Why that is…is my question!

      1. Interesting, I’ll read up on those. In fact, just got this from my quick perusal of the Wikipedia explanation:

        “Lotka provided the theory of natural selection as a maximum power organizer; under competitive conditions systems are selected which use their energies in various structural-developing actions so as to maximize their use of available energies. By this theory systems of cycles which drain less energy lose out in comparative development. However Leopold and Langbein have shown that streams in developing erosion profiles, meander systems, and tributary networks disperse their potential energies more slowly than if their channels were more direct. These two statements might be harmonized by an optimum efficiency maximum power principle (Odum and Pinkerton 1955), which indicates that energies which are converted too rapidly into heat are not made available to the systems own use because they are not fed back through storages into useful pumping, but instead do random stirring of the environment.”

        Good stuff!

      1. One of the biggest mysteries of the modern age is: does the light stay on or go off when you close the door?

        1. If only some fridge company would make a fridge with a glass door so that we could find the answer.

            1. In the sock dimension. Like the flying spaghetti monster, it has tentacle-like wormholes reaching out to all the washers and dryers of the universe, through which it has vacuumed up all the missing socks.

              This leaves unanswered the question: is the sock dimension sentient and what does it want with all those socks? Perhaps the socko-theologists can address that.

  18. The obvious quickie is this recent notion (Web/meme-wise) that octopuses are essentially aliens compared to all other Earth species regarding their eyes and extended DNA. My own question would be: Why is tinnitus worse after a nap or a short sleep?

    1. Octopuses have expanded some gene sets having to do with their senses, and for their larger brains. Nothing at all surprising, really.
      The real mystery is why science journalists so often do such a terrible job.

    1. I have previously mentioned in comments here the ethologist Paul Leyhausen, author of the book Cat Behavior, who was one of the world’s foremost authorities on cats domestic and wild, big and small. He noted that cats which do purr do so under disparate circumstances, such as when apparently content, when in pain, when nestling with kittens and so on. His conclusion was that the principal message conveyed by purring is simply, “I am not a threat”. He also noted that cats of all sizes are silent when stalking and hunting prey, so an audible cue such as purring says, “Trust me.” and indicates that an attack is not in the offing. Note that this does not apply to cats fighting other cats or against animals attacking them, which is frequently accompanied by vocalization. Leyhausen also noted that cats are individuals, and that idiosyncratic behavior can easily violate norms as they so with humans.

  19. Probably boring to all but a couple dozen people in the world, but:

    What is a hoatzin? And why haven’t we been able to figure it out yet, even with complete genomes?

    1. Is it uncertain that it belongs within Cuculiformes (Cuckoos & allies)? I know its classification has bounced around quite a bit in the past. It certainly looks Cuckoo-like, and most new world cuckoos build their own nests (unlike old world cuckoos), as does the Hoatzin, for whatever that’s worth.

      1. It’s almost certain that it isn’t a cuckoo. Nor is it a galliform, another popular destination of the past. We know quite a bit about what it isn’t. But what it is, ah that’s the problem.

        Best attempt so far:

        Suh et al. 2015

        But their conclusion is “we have no idea, and the question itself may be meaningless”. (That is, there may have been such a quick radiation at the base of Neoaves that there are multiple, simultaneous branches with no further structure.) Still, I have hopes.

    1. I know someone who just served me some baked bacon…yum.

      And first thing this weekend, I will put some cookies on the frying pan….double yum.

        1. Yeah, but I already knew which one was not a frying pan. 🙂 Clearly the one that was a tea pot in disguise.

  20. How is behaviour carried in genes? Collie dogs insinctively round things up and Jack Russell’s kill rats without being taught. So different and the same species.

    1. The mimiviruses are a group of giant viruses. They have genomes that are comparable in size to some bacteria, and they have genes for synthesizing amino acids and nucleotides. This is mainly why they have been considered (by some) to represent an early stage of life, or a bridge between cells and viruses. That viruses may bridge between these things has been an idea kicking around for a long time.
      But like all viruses mimiviruses are totally dependant on their host cells to do any form of biosynthesis. They are completely inert on their own (as far as I have heard), and so are not considered alive. That they have these additional genes could simply be b/c they picked up DNA from host cells at some time in the past.

    1. Which raises the important question: why do people keep those factory-installed advertisements in their email sigs?

  21. I’m shocked that the placebo effect has not been mentioned as of yet . . . biologically, how psychological thoughts/beliefs drive physical manifestations.

    1. Scrolling down I thought “wow, I’m going to get to ask my question about the placebo effect, but then, third from the end….

      Anyway, technically you haven’t asked it, so how does the placebo effect work?

  22. Why do almost all human cultures have some form of dancing/group dancing?

    Group dancing is known to increase oxytocin and thus makes the participants like/trust each other more. But… why?

    1. We are social animals and cannot thrive alone. If we don’t like and trust other members of our group, at least to some extent, group living doesn’t work well either. Natural selection should see to it, one way or another, that we tend to like and trust our companions.

  23. Why is there only one “Tree of Life”? On earth, all single-celled and multi-celled creatures share DNA. This is why we can study fruit flies and the results are applicable to all life. According to one source, we share 60% of our genes with a banana.

    Why? Why aren’t there 2 or 3 patterns rather than just one? Why isn’t there a branch of living things that humans, insects, plants and the rest are not related to?

    Presumably, if there is complex life elsewhere, it will have DNA or coding different from earth DNA. So why isn’t there another pattern on earth either with different DNA codes or a completely different genetic coding system?

    (Forgive the non sciency knowledge of the subject.) (And if there is some weird bizarre exception with non-DNA, why isn’t it common)?

    1. I suspect that another tree of life evolving separately the DNA/RNA tree of life would be out competed or gobbled up by ours, as ours was more prevalent. In fact abiogenesis may have happened a few times on earth in different epochs or locations. It has not been discovered as it was wiped out by our tree long before it got chance to leave its mark.

    2. David Raup asked this question a long time ago. Here’s a link.

      Here’s the take-home message: “Using simple stochastic models for diversification and
      extinction, we conclude: i) the probability of survival of life is low unless there are multiple origins, and ii) given survival of life and given as many as 10 independent origins of life, the odds are that all but one would have gone extinct, yielding the monophyletic biota we have now.”

  24. Could we ever develop practical methods of time travel and human space travel to other solar systems and galaxies.

    Will Pluto ever be a planet again?

    Will the US elect Donald Trump president? What will his excuse be if they don’t?

    1. – Time travel has a lot of obstacles in physics. I especially like the computer science obstacle: since computers are physical systems, analog systems mimic them well. E.g. you can show that when computers have difficulties (takes long time) to calculate minimal energy surfaces, a toy model with soap bubbles will also have difficulties and end up with many wrong solutions.

      Okay, so a computer that utilizes time travel can solve all problems yesterday. So no problems are difficult. Yet physics _have_ difficult problems. So no time travel can exist. (It is a little bit like “if time travel existed we would already have met the travelers”.)

      – Will Ceres ever be a planet again?

      – I don’t _want_ to know.

    2. Depends on what you mean by “ever” and “practical” and maybe “human” as well.

      Centuries from now it may become possible to launch a lightweight interstellar probe containing a digital map of the human genome plus sufficient self-replicating technology to bootstrap a space habitat, an artificial womb, and a robot nanny. Does that count as “practical human space travel”?

    3. Could we ever develop practical methods of time travel

      We already have cheap effective time travel. It’s one-directional (form past into future) and the rate can be varied somewhat s=around one second per second.

      and human space travel to other solar systems and galaxies.

      See above : generation ships. Already they’re more of a will power and sociology issue rather than a technical issue. We are probably about half way between the origin of our species and our first interstellar colony sending off it’s first interstellar probe.

  25. Oh wow what an amazing question! I may have many more but these are my first musings:

    Why are prime numbers distributed as they are? I know cracking the Riemann hypothesis will be a huge step in the right direction but we are not really any closer to proving it than we were 100 years ago?

    Why are human brains so attuned to tackling massively abstract mathematical concepts when, on the face of it, they bear no relation to the problems we encountered during our evolution?

    How has depression, which has a significant genetic component, persisted in humans when it appears to be so maladaptive?

    Why do we dream? Any why are dreams so damn weird? How can genes and the proteins they encode produce a susceptibility to dream about specific things like crumbling teeth (one of my regulars) or running through treacle?

    1. In addition, I’d like to know if there could be other systems of understanding the universe besides mathematics — ie: if there were an alien species that sucked at math but had some other way of essentially doing the same thing math does.

      The real question here is what would alien-to-earth minds work like.

    2. Are you sure curling up in a pile of skins and not wanting to getting up until spring (except when it’s really really necessary) is maladaptive?

      I have seasonal effective disorder — I’m depressed in winter. In our current culture I take medication for it, but it seems like it might have been useful more often than not at times in the past.

      1. I don’t have seasonal effective disorder, but hibernation doesn’t sound so bad to me, either. Wouldn’t mind fattening up and socking into some place cozy for a season.

      2. Seasonal affective disorder is one thing – and I can see that there may be some sort of biological basis for this, especially for our remote mammalian ancestors. Severe depression is a whole different kettle of fish though. I have suffered from it a couple of times and it’s a horrendous thing to go through. It robs you of nearly everything including confidence, energy, interests, hobbies, resourcefulness, forward planning and frequently results in almost complete social isolation. It most often happens to people of prime reproductive age, effectively removing them from the mating pool and / or making them far less able to look after their offspring. It also often occurs in response to traumatic or difficult life events – exactly when a robust and energetic response would be most required. I know there is a theory that depression enables an individual to remove themselves from a difficult situation in order to think it through but I don’t buy that at all. To my mind, and from experience, it’s about as maladaptive as it gets – how has it persisted? The best idea I have is that it was far less common in ancestral days when we had very different lifestyles and social environments so the pressure was not there for it to be selected against.

  26. Why is our solar system arranged so, with the gas giants further out from the rocky inner planets? In the majority of the extrasolar systems that we have observed the gas giants have seemingly spiral in towards their sun, mopping up the smaller planets on the way.

    Additionally, how does this knowledge affect the Drake equation?

    1. In the majority of the extrasolar systems that we have observed the gas giants have seemingly spiral in towards their sun, …

      Although that is mostly a selection effect in that the systems with the giant planets near the star are by far the easiest ones to find. A solar system like ours is very hard to detect with current methods.

      … mopping up the smaller planets on the way.

      Although the smaller planets are not necessarily mopped up, even if the giant planets spiral inwards, as WASP-47 has now shown.

    2. – Gas and ice giants form preferentially outside the ice lines (one for each volatile), rocky worlds form preferentially in drier conditions. ALMA’s image of a forming system confirms that.

      – Reconciling that with the resulting distribution is an open question. So…

      – The effect on Drake’s equation is an open question.

    1. Because stuff is funny.

      There are some theories of humour, however.
      As someone who seems to enjoy the peculiarities of the absurd, I tend to subscribe to the theory that laughter is our brain’s way of recognizing that something doesn’t quite fit.

      It would be cool to find out if other animals do the same thing – recognize & “laugh” at the absurd.

  27. What are dark matter and dark energy? Just think – most of what is around us is a complete mystery! I surely hope I live long enough to learn the answer to this one.

  28. Two easy to state but fiendishly hard (and unsolved) problems in Number Theory:

    1. The Twin Primes problem: Are there an infinite number of twin primes, i.e., prime numbers that differ by two? Examples: 3 and 5, 5 and 7, 11 and 13…

    2. Goldbach’s conjecture: every even number greater than 2 can be written as the sum of two primes. For example, 4 = 2 + 2, 6 = 3 + 3, 8 = 3 + 5, 10 = 5 + 5, 12 = 5 + 7, etc.

    1. I think that #1 is being rapidly whittled down. A couple of years ago it was shown that there were an infinite number of primes separated by [several million] ; by last year it had dropped to a few thousand and continues downward.

  29. Does intelligent life – say that which is able to discover evolution or general relativity – have a realistic possibility of evolving given enough time and the right conditions? Or are we and our amazing brains a complete one off?

    Why did consciousness evolve? Wouldn’t a suitably wired brain, capable of complex computation, do just as well as a conscious brain? Was it because consciousness was the only way humans and other animals were able to develop the cognitive abilities that allowed us to thrive? Given that we were limited to proteins, fats, water etc rather than semiconductors and electricity?

    1. Well, we did evolve, so there must have been a realistic possibility of it.

      Your question about consciousness seems to presuppose that it’s something other than “complex computation”. What other way could there be to develop “cognitive abilities that allowed us to thrive” without mental modeling of oneself as an intentional agent in the world? And how could such modeling happen without self-awareness?

      1. That fact that we evolved doesn’t mean that there is always a realistic chance of intelligent life arising. It means it happened for us, that’s all. We might be a complete statistical freak – a one in 10^1000 chance. In one of his books Steven J Gould said something along the lines of: ‘if you rewound the evolutionary process on earth and started again the chance of human intelligence arising again would be vanishingly small’. I’m not sure I agree with him but it’s a fascinating question.

        With regard to consciousness I don’t presuppose that it involves anything other than computation. I suspect that it results purely from computation but I don’t know that; no one does. Indeed Roger Penrose has written a couple of books espousing the thesis that consciousness is not algorithmic or computable. I am not persuaded by the idea but I remain open to it – just.

        My point is that complex computational tasks do not require consciousness or self-awareness. Many machines now have the ability to perform very difficult computational tasks – such as invariant representations in visual processing systems. Yet very few people would argue that such machines are conscious. Also it is perfectly possible for animals to thrive and possess complex cognitive abilities “without mental modelling of oneself as an intentional agent in the world”. Many species of birds and mammals demonstrate incredibly complex and evolutionarily successful behaviours. They do this without being self-aware in the sense that we would recognise and especially without ‘modelling themselves as intentional agents’.

        1. I think Dennett would disagree with you that animals don’t model themselves and others as intentional agents. “That predator wants to eat me” and “I don’t want to be eaten” are among the most important things an animal can know.

          I grant that some complex computational tasks do not entail consciousness. But it doesn’t follow that the kinds of computation underlying complex animal behavior are necessarily in that category. When watching birds and squirrels solve complex feeding puzzles, the most parsimonious explanation is that they are indeed engaging in mental modeling and planning of the sort that we associate with our own conscious experience.

        2. Maybe we’re freaks, but the universe is a big place in space and time and that allows for a lot of freak things to happen.

          1. Exactly. I read a while ago a book (name escapes me) on estimating the chances of intelligent life arising on an Earth-like planet. There analysis shows it is very rare. So, if you expect to see smarts on every likely solar system in the galaxy, think again.

    1. 1. Seems we don’t really know anything about economics.

      Is there anything to know of economics?

  30. I’d like to know more about the world under my feet, i.e., when I’m on real soil (forest, prairie, wetland) particularly the soil microbial community: who, what, when, where, why and how. Their relationships, mutual dependencies and effects Ditto for the below ground mycorrhizal network.

    1. It’s called pedology, or “soil science”. Few universities have a department for it, but it is important to agronomy and agriculture departments. I’ve found it useful all career long.

  31. ” . . . simple (ish) questions that the general public would like to know the answer to . . . .”

    Question: Why is the general public no more intellectually curious than it (they?) are?

    Due to being approx. a half-chromosome away from a chimpanzee?

    I’ve lately heard that brain research has shown that the human brain, the cerebrum in particular, does not fully grow/mature until as late as age 25.

    I gather that this later maturing prevents the adolescent teen from being sufficiently intellectually curious to prompt him to determine why he is insufficiently intellectually curious. Were he otherwise curious, he would have at his disposal a scientifically-based rationalization/justification for not being intellectually curious, which he could proffer to his parents and teachers, eh? 😉

  32. The Cambrian Explosion happened due to the evolution of free will. Deterministic responding neural knots were ok for controlling a heart or gut, but a far more agile decision/control architecture was advantageous to achieve locomotion, sensor (especially eye) integration and with that navigation. A free will architecture of the brain allowed individual prey animals to incorporate novel (if only limited individual uniqueness) flight strategies, making them more difficult to catch. Similarly for a predator, variation in hunting techniques make them harder to avoid. This agile brain similarly accelerated the process of adapting to changes in terrain and environment. This agile brain is a learning brain, rather than a deterministic or knowing brain, and also allowed nominally one brain architecture to control a range of body types or sizes. This basic agile brain allowed for the rapid evolution of body types and the rapid expansion of animals into new habitats. This agile architecture is also scalable – the animal itself can learn how to use any extra neurons without going through a long evolutionary process of tailoring each new neuron to some determined function.

  33. Why does homophobia exist in so many (all?) cultures that it almost looks like a human universal? From an evolutionary perspective it does not make sense. On the contrary: Homosexuality means fewer sexual competitors and should therefore be welcomed.

    1. It may be that heterosexuality is so tightly tied to human culture that the homosexual is simply seen as not fitting into the expected pattern. This would be enough to drive quite strong rejection. The idea of competition occurs at a pre-cultural level and so is unimportant. A little like atheism within a religious culture.

    2. Why does homophobia exist in so many (all?) cultures … ?

      Haven’t spent much time in The Castro or on Fire Island, in P-town or Key West, have you? 🙂

          1. I always sensed that flick had a heavy gay subtext.

            I once overheard a lesbian wag describe Grease as the movie you’d get if you spent three hours explaining the concept of camp, and 30 seconds explaining the concept of heterosexuality, to a newly arrived space-alien screenwriter.

    3. Here’s my guess (not supported by any data that I’m aware of, but plausible, IMO): being seen as homosexual is bad for your reproductive success, at least as a man. (What hot woman would be willing to marry you if she thinks you’re gay and therefore not really attracted to her?)

      The best way to avoid this misconception is to be conspicuously hostile to gays. This leads to a feedback loop: if many men are homophobic, being considered gay is not only bad for your success with women, it also leads to being shunned by other men, increasing the pressure to avoid any suspicion of being gay.

  34. How (not why, that is ‘cus evolution) do we age? Not telomeres, not oxidative stress, not this, and not that – but what?

  35. Ok, I just read through these comments, and I don’t think I have overlooked this question (feel free to castigate me if I have): what is the origin of language? Ya know, what we’ve all been ‘using’ in these comments? What I think is arguably the most important of all things?

      1. Origin of Language: Necessity is the mother of invention. Communication among individuals increases likelihood of group survival and procreation. Refine those grunts, folks!

    1. I’m no expert, but my guess on the origin of language is that it’s something of a spandrel. Tool use and bipedalism created selection pressure for increased dexterity, and the developmentally expedient way to satisfy that pressure was to inflate the entire sensorimotor cortex like a balloon. Vocal dexterity got carried along for the ride, and then became fair game for exaptation and/or sexual selection (men with greater “chatting up” skills had more offspring).

  36. You (I) were born sometime between the first and last person who ever existed. It is said that 5% of all humans who ever existed are alive today. Assuming that you (I) were born in the middle 95% of the distribution of all people who will ever exist (after the first 2.5% and before the last 2.5% of all people), can this information be used to estimate when the human race will come to an end?

    1. Won’t that bell-shaped curve keep cresting out to sea for the foreseeable future, making such an estimate impossible?

      1. Ken, you could have been born any time in human history (that is a necessary premise for my argument), but there is a 95% probability that you and I will not be among the first 2.5% or the last 2.5%. If we are at the cutoff of the first 2.5%, and about 130 billion humans have already lived before the 2015 cutoff, roughly 40 times this number of people might live before it becomes unacceptably unlikely that you and I came into existence so early in human history. This is the upper limit. On the other hand, if you and I in 2015 are living at the upper cutoff, and 130 billion humans have preceded us, the End could be, using statistical criteria, as near as (2.5% of 130) 7 billion births away.

        I have, I believe, calculated statistical limits for the expected survival of the human species. There is at least one glaring flaw in my argument. Find it.

        1. I haven’t studied statistics since I was an undergraduate nearly four decades ago (but, hey, I got an A- then, which I suppose makes me something of an expert, so what the heck).

          The longer the current 5% (or greater) bulge in the population continues (as a percentage of all people who have ever lived), the more populous the potential 2.5% wake it drags along behind it becomes, making projection of the size of the final 2.5% impossible.

          (Also, given that 5% of all people who have ever lived are alive today, if half of us died today and the other half tomorrow, if you & I expired with the half that met their maker before midnight we would manage to still slip in within your 95% parameter.)

          Shorter response: damned if I know. 🙂

          1. Let me take another crack at it:

            Your hypothetical lets us make accurate calculations if we assume we are at the boundary of the left-hand 2.5% tail or the boundary of the right-hand 2.5% tail, but doesn’t furnish us with the necessary information to calculate the duration of the 95% bulk of the bell curve, if we happen to find ourselves within it.

            Getting warmer?

        2. It seems to me that there are two problems with this approach. First, it assumes a normal distribution of human population across time, when something approximating a logistic model is a much better fit to the data (at least until we hit the “stationary phase”).

          Second, we have no data and no real way to predict the equation(s) governing the right-hand side of the distribution. If resources like food and water become limiting to the population, we can expect exponential decay, with a period of low population extending into the future indefinitely (in theory). If the population is reduced catastrophically, then we’d simply have a step function… again, with no way of determining the structure of the population dynamics after the “cliff”.

          We’re in the classic scenario of “riding blind”: we can guess at the route we’re taking by the feel of the bumps and curves, but we have no information about possible stop signs or jackknife turns that lie ahead.

    2. “It is said…”.

      I found this “semi-scientific” estimate (with crappy paleontology, but it won’t affect the result): http://www.prb.org/Publications/Articles/2002/HowManyPeopleHaveEverLivedonEarth.aspx

      “Can this information be used [to predict the future population]?”:

      No. It will give the rough potential for maximal growth, but not the outcome depending on environmental constraints. Since a mammal species can become 1-2 million year on average, and we are just 0.2 million years old as a species, we may say, I think, that extrapolating the historical population growth would be very inaccurate…

      1. The actual numbers are mere hair-splitting details. The question is whether in theory it is possible to derive a statistically valid estimate of the survival of the human species based on the principle that yourself (or myself) has been born randomly into human history. If humans were to go on to conquer space and expand to a population size of many millions of gadzillions, it is very improbable that you or I would have been born (as humans) so early as 2015 on this backward little world.

        As for the numbers, the “Population Reference Bureau” website gives 108 billion as the estimate of the number of individuals of our species who have ever lived. Let’s not argue if this takes into account stillbirths. I use 7 billion as the actual size of the world population. This gives 6.4% (round to 5%) of all people who have ever lived being alive today. Using the value of 108 billion for the number of humans have ever existed, it is improbable that more than 108/0.025 (= 4.3 trillion) more humans will come to exist in the future (I have done a “two-tailed” calculation with 2.5% in each “tail”).

        If Earth’s population in the future averages 7 billion (and humans do not significantly expand offworld), time will run out (95% chance of human extinction) in about 640 generations. (If the average population size is greater, the number of generations is reduced; if smaller, the time is extended. This is just a detail.) One generation would be the duration of an average lifetime, which I will here take to be 70 years. Now let’s see: 640 generations at 70 years per generation, gives us roughly 45,000 years for a 95% certainty that humans will no longer exist. The expected value is half or less. The minimum is within our lifetime.

        Where has my logic gone bad?

        1. it is very improbable that you or I would have been born (as humans) so early

          This is the part I find problematic. However improbable you think it might be, it’s a fact that we live now and not in some other era. Moreover, our era is unique in being on the steep part of the technological growth curve. Like it or not, we stand at an inflection point in the history of our species where we can either break out to populate the cosmos with gazillions of people, or crash and burn within a century or two.

          So to me it seem pointless to try to predict anything about the expected lifespan of our species based on the assumption that there’s nothing special about the time of our birth, because that assumption is clearly false.

        2. Why do you calculate the length of a generation at 70 years rather than the average age at which an adult human reproduces? Generations are overlapping rather than contiguous. This would seem to throw your calculations off by at least a factor of three.

          1. IIRC, the medical world considered a generation as 20 years, back in the 1980s. It might be considered 25 or more, now, as a rule of thumb rounded out of some average age of childbearing.

  37. What’s beyond the observable universe? Like someone at a party, I’m stupidly concerned there’s something a lot more exciting going on out of eye and earshot.

    1. The beyonduverse is everything outside the observuverse. But that’s just speculation.
      But, in truth, I think there are two questions here. 1) Our universe has an unobserved portion and it most likely is driven by the same physical laws as the observable portion. So, we would expect it to look similar to the local neighborhood. 2) We may be a small part of a multiverse, which suggests they have differing physical laws. Thus, they would represent many configurations, some of which would contain no matter to cause much excitement.

    2. We now know that you can go out ~ 100+ radii, and the universe will look on average the same. To expand our horizons, so to say, much over that we need to wait for the next CMB mission I think.

      1. Oops. Either ~ 1000 radii or 100 +, not that mix up I produced. Quick estimate says ~ 1000 radii is the better figure.

  38. I love this idea! But first I must have a wee betch and moan.

    Ugh! I HATE the WP “reader” iteration I’m currently stuck with. There must be some algorithm trying to predict my interests because it won’t display all the comments. If there’s a setting to fix it, clearly I’m too stupid to find it.

    OK. So my question is more simple than complex, and more in the nature of asking for predictions, than answers, but here goes:
    How long will it take Josh Duggar to reject an axiom that conflicts with his beliefs resulting in an unsuccessful therapy?

    Is this a clear demonstration of a flaw in the biological cognitive process, confirming the theory that free will doesn’t exist?

  39. One question I think will never be answered is why educated and rational speaker’s of English cannot master the proper use’s of apostrophe’s.

  40. a) What – in the human genome – leads to people saying things like “I’d be only too happy to [sign your petition; wash your socks; feed your cat].”

    b) What evolutionary purpose does D. Trump’s hair have?

    1. I’ve heard scientists explain that one of their most satisfying experiences is being able to unify two seemingly unrelated phenomena under a single overarching theory.

      You might be on to something here.

  41. From my perspective, the fundamental physics questions (QM and gravitation, dark energy etc) are fascinating, but solving them won’t do one bit of tangible good for humanity.

    Here are two questions that feel like they might have a simple, but non-obvious answer, and have a large impact on humanity:

    – what causes the dramatic increase of allergies in industrialized nations in the last half century?

    – what causes the obesity epidemic? (Yes, people eat too much. But why? And why is this so hard to fix by eating less?)

    1. Without accelerators, no superconducting magnets, and no modern medicine tools of body scans. Without GR, no GPS. Without QM, no laptop.

      Without the discovery of dark matter and dark matter, no consistent cosmology, and much less understanding of astrobiological constraints, which ultimately may feed back into biology and so medicine. But mostly we know that science works in mysterious ways, we can’t tell why it is beneficial to do mass science instead of targeted such but we can see that it benefits society most.

      1. I’m all for theoretical work. It has always taken us in interesting places that have consistently paid off in real, tangible benefits.

        1. I couldn’t agree more! Abstract theoretical science leads to completely unforeseen benefits in later years. Great mathematicians like Gauss, Riemann, Hardy etc would never have dreamed that their musings on number theory would ultimately lead to the public key encryption protocols that enable secure commerce on the internet. Another example is Paul Dirac’s theoretical prediction of an anti-particle to the electron. This led to the discovery of the positron and ultimately the development of PET scanners which are used in hospitals all over the world.

    2. Why humans eat too much is because we nearly starved into extinction so many times. We, and likely Neanderthals and similarly unsuccessful apes, seem to be the only ones (with the exception of similarly barely-hanging-on orangs) the only apes that can, and will, become fat.

      Seems biologists recently observed that chimps have ~ 0.1 % or so adipose tissue, against our 10 – 30 %. (Chimps have tough skin, so I gather it wasn’t easy to recognize.) _If- you can fatten up a chimp, it will likely die very fast…

      My take is that because humans is such an unsuccessful animal (historically), we drag around a lot of unnecessary baggage – diseases or traits prone to make us sick (small mouths, bad eyesight, fat, lots of lacking metabolic enzymes) – that hamper us today.

    3. …the fundamental physics questions (QM and gravitation, dark energy etc) are fascinating, but solving them won’t do one bit of tangible good for humanity…

      Spoken like a magnetic compass maker on the eve of the invention of GPS…

    4. – what causes the dramatic increase of allergies in industrialized nations in the last half century?

      There’s a fascinating explanation for this question called the Hygiene Hypothesis. In a nutshell: humans in “First World” nations are extraordinarily clean… we just don’t get sick or parasitized very often. As a result, the immune system of First Worlders is all dressed up with nowhere to go. And so, with nothing else to do, the system mounts immune responses against innocuous things that would normally simply slip under the radar.

      A result of this hypothesis is the rise of experimental “helminthic therapy”: deliberately infecting patients with autoimmune disorders with small numbers of parasitic worms, in order to give the immune system something to do.

      So far, results have been promising!

  42. I’m sure they’ve been noted several times already; but here goes:

    1. How life on earth got started

    2. How consciousness works in the brain

  43. What are the ecological determinants of which species survive and which species don’t during a mass extinction (clearly there’s already been some great work done here, but there’s still a lot we don’t know, particularly when it comes to marine species), and how can we actually apply that knowledge to rescuing Earth’s biodiversity?

  44. Why have so many things (specifically technology advances) happened in the last 500 years or so, when hominids have been around for approximately 4 million years? I have a basic anthropology/archaeology background from undergrad courses, but my boyfriend and I have had this discussion a few times recently and I don’t know enough to be specific for him.

    1. Short answer: science.

      That is to say, systematic investigation of how the world works pretty much began (in the West at least) with Galileo. The knowledge gained lets us manipulate the world with more precision and confidence — the more we know, the more things we can do — which in turn enables us to expand the scope of our investigations. Science and technology support each other in a positive feedback loop.

  45. Hardly any ones in chemistry, so here’s a few:

    (a) What *is* a molecule? How much stability is necessary? I was reading about what some call “per-peroxides”, where there is an -O-O-O- chain, e.g., in the (perhaps) hypothetical FOOOF. What then, about (per)n-peroxides? How many oxygens are “possible”?
    (b) Is there really an atomic number after which there is no chemistry at all, because all heavier atoms react the same due to some quantum foo I don’t claim to understand.
    (c) Is neon really the only inert element? See also (a). (Helium perhaps.)

    A few others:
    (a) How exactly does shape emerge? Small things tend to (due to quantum effects) spread out and fill their container; larger things (e.g., a cyclohexane ring) have a well defined shape, even if it is (under standard conditions) in flux.
    (b) Is spacetime (i.e., spatiotemporal relations) discrete or continuous?
    (c) The entire field of what might be called “neurosemantics”.
    (d) What (if anything) does the Church-Turing thesis tell us about reality generally?
    (e) It appears that there is a split in humans on ethics – deontological vs. consequentialist, at least. How does this arise?
    (f) Which logic is the “best one” to use? Is it utopian to change our mathematics (and hence everything else) if this is not classical logic?
    (g) What determines people’s views and reactions to various sorts of risk? (It appears there is qualitative variation.)
    (h) When and how did human language arise?

  46. A few earnest questions, boys and girls, if anyone is still out there in radio land. “Most interesting questions we don’t know the answer to?” Evolution! 1. When they say life started once on earth, do they mean literally once? And same thing for the origin of multicellular animal life. Did all of this, at least at some point, hinge on a single individual? I think “yes.” Otherwise we wouldn’t have a common ancestor. We’d might have similar ancestor(s). 2. Why isn’t life originating all the time on Earth? Once in 4.6 billion years! You have got to be kidding. Yeah, go look for life on Mara and spend a hundred king’s ransoms. BTW, if your answer is “it just isn’t,” you can’t use as an explanation that we wouldn’t be here if there were more than one form of life on earth. I have other questions of the same genre, but if I bomb on these I will likely do likewise on the others.

    1. You wrote: “Evolution! 1. When they say life started once on earth, do they mean literally once? And same thing for the origin of multicellular animal life. Did all of this, at least at some point, hinge on a single individual? I think “yes.” Otherwise we wouldn’t have a common ancestor. We’d might have similar ancestor(s).”

      That looks like a circular argument: Life started once because we all have a common ancestor. Because we have a common ancestor, life started only once.

      Another reader commented that it might have started many times, but all others died out, leaving a sole surviving line. There may be other scenarios as well. This branch of science is, what?, 150 years old. We’ve barely begun.

  47. nobody’s going to read this far, but why are there no viviparous birds. I mean … the Emperor penguin?

    1. Good question. With almost 10,500 bird species, no live-bearing ones, with your Emperor Penguin and it’s almost marsupial pouch coming perhaps closest.

      Mammals feed their young (auto-feed?) with milk. The only birds I know of like that are pigeons/doves who feed their young with a regurgitant called “dove’s milk”, made from the lining of the crop. Inability to directly feed the young has to be part of the answer. Correlative, not necessarily causal.

    1. But dogs and cats are subject to artificial selection, so I guess that question can be answered by their breeders.

    1. I think studies have shown that it doesn’t. The victims will say anything to stop the torture, so much misinformation comes out.
      As the saying goes, “You can catch more flies with honey…” Treating those same captives with a modicum of respect and consideration seems to access their human nature to open up and talk. Note: I’ve not read the studies, personally.

      1. Read “The Interrogator: The Story of Hanns Joachim Scharff, Master Interrogator of the Luftwaffe.” The Germans considered him to be their best interrogator. A great read and an eye-opener relative to interrogation & torture.

        Main point: He used no torture, no threats, was always polite & friendly. Many of those he interrogated considered him a friend, even inviting him to their homes after WW2. His only “threat” was: In Germany, during this war, spies are immediately shot. I cannot do anything about this. We both know that you are a pilot, shot down and found by our troops. I do not want to see you shot, I want to see you return to your home and family, but unless you give me some proof that you are a pilot, we must assume you are a spy. Simply giving me the name of your squadron, or commanding officer, or type of aircraft will suffice.”

        The really useful information was gained after the interrogation was officially finished, when they were just sitting around talking and smoking, or walking through the countryside.

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