Wikipedia:Reference desk/Archives/Science/2015 July 22

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July 22

Adult Growth of Vertebrates

Mammals grow until they are adults and then stop growing, so that humans are the same height for most of their life. Birds grow until they are adults and then stop growing. Some long-lived vertebrates, including some fish and crocodilians, continue to grow. I am assuming that the difference is that mammals and birds are warm-blooded, and that so-called cold-blooded reptiles and fish continue to grow. Is that correct, and is there a reason, such as having to do with energy use in adult warm-blooded vertebrates, why growth stops for warm-blooded vertebrates? Robert McClenon (talk) 02:55, 22 July 2015 (UTC)

The truth is Robert, there's a slight adjustment to be made in the way you are conceptualizing this issue that will greatly improve your understanding of it. Specifically, most any complex organism's growth (and especially that of metazoans) will eventually plateau - these organisms simply very greatly in the length of time it will take them to reach this point, their liklihood of dying first from predation, disease, or an environmental factor and the exact nature of the interplay between environmental constraints and innate epigenetics. In a sense though, you are correct that certain clades show a preponderance for having higher populations of individuals that have stalled out in their growth; its just that the explanation for this difference is often not entirely explained by the relative difference in any two species' physiologies with regard to just things such a growth factors, cellular differentiation, replication errors, and the like, but rather also the entire sum of their genetic qualities and their environmental context (including such things as diet, space, breeding context and other factors which influence growth through epigenetics, but then also dumb luck with regard to survival). So you will find that phylogenetics only sets you up so much to understand which of these species will have great variety in ultimate sizes of individual specimens and/or what proportion of the population have begun to slow (or even have stopped) in their growth; sometimes two very closely related species will vary drastically in this regard, simply because they have a slightly different ecological niches. All of this is not to say that there aren't clades which have genetic features that allow them to grow more tissue of certain types without stalling out or to avoid cancers and other effects of senescence; it simply means that for most organisms, the situation is a little more complex than just these factors. Of course, it is true, since you specifically cite adulthood, that certain species are more likely to stop growing roughly at sexual maturity. As you observe, this trait is particularly strong in Mammalia, but you'll also find great variation in other kinds of tetrapods. Forgive the lack of citations; super exhausted here; will try to cobble together the sourcing and more complete discussion of these issues tomorrow. Snow ^{let's rap} 07:25, 22 July 2015 (UTC)

There are some differences in the biology of bone growth (which is usually what we really mean by "growth"; otherwise we find ourselves all too capable of growing in mass throughout adulthood!). I haven't given this paper a tenth the attention it merits, but see [1] which discusses the differences between Actinopterygii and tetrapods. So in modern fish, "Perichondral bone is deposited on the surface of the cartilages and continues to grow centrifugally as periosteal bone" whereas in tetrapods a rod of cartilage is quickly covered by bone, except for growth at the epiphyseal plate, which ultimately fuses to stop any further bone growth. That said, epiphyseal fusion still does not have to happen; that is a sort of choice made by the developmental plan of the organism.

I would speculate that there may be adaptive reasons for the differences. We have all probably seen pictures of human 'giants' who can't stop growing, hobbling around on crutches. It seems like aquatic organisms are less affected by changes in scale than those on land, since they rarely need to support their own weight. But that's purely a guess. Wnt (talk) 12:50, 22 July 2015 (UTC)

Well, I am unaware of any documented case of a human being continuing to grow for the duration of their life, long after reaching sexual maturity. Even those with gigantism eventually top out or begin to slow, though yes, generally well past a point where their general health has begun to suffer as a result of their atypical biomechanics. Though, to be fair, some have continued to grow at least into their 20's and in the most extreme cases, before modern clinical analsysis and mitigating treatment, they tended to die not long after; if not for the pressure this unconstrained growth put on their systems, its hard to say whether it would have otherwise been boundless, but I suppose it is feasible a pituitary disorder would cause them to continue to grow for years more yet.

But returning the issue of variation amongst species and your guess, I'm doubtful (and have never seen any research or researcher speculation that suggests) that the difference is to any significant extent driven by differences in selective pressures with regard to the ocean vs. land-dwelling; many terrestrial species display "life-long" growth and many aquatic species do not. For that matter, I cannot recall seeing support from a researcher along the lines of Robert's notion that it is determined significantly by differing aspects of the physiology of cold-blooded vs. warm-blooded organisms. Rather it has more to do with the creature's complete ecological niche and A) the practical benefits of being large (and it's cost in resources) vs. the advantages of staying small (including smaller dietary needs) B) sexual selection, C) the nature of its genetics with regard to this sustained growth and whether it is likely to cause abnormalities as a result, and D) epigenetics; note that not all of these creatures are determined to grow large, some will only continue to grow if the conditions are just right. Snow ^{let's rap} 21:47, 22 July 2015 (UTC)

From a the perspective of evolution and ecology, this is about the trade-offs between allocation of resources to growth vs. reproduction. Lifetime fecundity is one of the main drivers of growth patterns - vertebrate organisms are generally hovering around a local maximum where growth is halted after sexual maturity, unless additional growth will increase lifetime fecundity. A key term is indeterminate growth, though that is used more often for plants. The broad topic would come under Life_history_theory, See e.g. here [2], [3], [4] for (freely accessible) research discussing why indeterminate growth occurs in animals, and how it's tied to resource allocation and impacts of life-history strategies. SemanticMantis (talk) 14:35, 22 July 2015 (UTC)

Solar system distances vs. gravity

Looking at real-scale models of our solar system, it occurred to me that if the sun was scaled down to a 1 cm wide ball, pluto would be a mere grain of dust at about 40 meters away. Yet the gravitational forces make it rotate around the sun. How can that be, especially with all other planets in between? Gil_mo (talk) 09:55, 22 July 2015 (UTC)

It goes to show you how strong gravity really is. Bear in mind that in space there is no friction, so your Earthly impressions of gravity don't apply to space. Things clump together in space. If there was no strong force of gravity, there wouldn't be planets.217.158.236.14 (talk) 10:26, 22 July 2015 (UTC)

Friction exists in outer space. I think what you intend to say is that in a vacuum, there is negligible air resistance... and even though this statement is true, gravity is not in any way reduced by friction. (Perhaps you are conflating the force due to gravity with the total net force on an object, which is computed by summing gravity with any other force that might affect some object). Other forces, including frictional resistance force, may oppose gravity in some cases, reducing the net force; but they don't actually reduce the magnitude of the force of gravity. This is a really important distinction that is usually learned in your first physics courses, and the difference between "net" and "component" forces still matters, even in advanced topics.

In fact, according to our theories that are as accurate as our best we can measurements, force due to gravity is unhindered by anything : there is no way to "shield" the effects of gravity. This means that even our outer planets feel the force of gravity: the effect is not "blocked" by inner planets. In fact, if you apply Gauss's law for gravity, the outer planets actually experience more inward pull, because they are pulled inward by the sun and all the other matter in the solar system! Nimur (talk) 16:16, 22 July 2015 (UTC)

As for "all the other planets" - the sun makes up an incredible 99.8% of the solar system's mass, and almost all of the rest is Jupiter. Uranus and Neptune do have a small impact on Pluto's orbit - over its history, they've nudged it here and there - but they don't even come close to the sun's effect. The closest Pluto comes to another planet is that it sometimes passes 11 astronomical units (AU) from Uranus, while the furthest it ever comes from the Sun is 49 AU. Even at those extremes, the Sun's pull on Pluto is a thousand times greater than that of Uranus (you can see the sums here and here). Smurrayinchester 10:52, 22 July 2015 (UTC)

Actually, gravity is the weakest of the fundamental forces, by far. It's astonishingly weak compared to the others. Just think about it: every time you lift anything, you're overcoming the gravitational force of the entire Earth, all 5,972,190,000,000,000,000,000,000 kilograms of it, on that object. The apparent weakness of gravity is a big reason why a lot of physicists like string theory, because it predicts the existence of extra dimensions. If gravity "leaks" into those extra dimensions, that would explain why it appears so weak in the three spatial dimensions that we perceive. The fact that Pluto is still captured by the Sun's gravity despite the great distance between the two is, rather, a testament to how massive the Sun is. Stars are ENORMOUS. The Sun contains over 99% of the entire Solar System's mass. Everything else is a rounding error. An even better illustration of the Sun's massiveness is the Oort Cloud, which is over a thousand times farther from the Sun than Pluto is, yet still bound by the Sun's gravity. But even the Sun is a lightweight compared to some other objects in the universe. Our Sun, along with everything else in the Milky Way, orbits the supermassive black hole at the center of our galaxy. It's 26,000 light-years away from us, yet so massive that it still pulls us along for the ride. And in turn, our galaxy is gravitationally bound up with other galaxies into mindblowingly huge groups and superclusters of galaxies. Just look at something like the Great Attractor, which has a gravitational influence that extends for hundreds of millions of light years, to truly get a sense of the scale of the universe. I'll quickly plug Crash Course Astronomy here for anyone looking for a nicely accessible introduction to space. --108.38.204.15 (talk) 11:36, 22 July 2015 (UTC)

Gravity is the weakest of the four known fundamental forces as usually measured, but it has two characteristics that compensate for that "weakness". First, unlike the strong and weak forces, and like electromagnetism, it operates at an infinite distance, with an inverse-square law. (The differences between general relativity and the original equations of Newton are not that important.) Second, it has no negatives, so that it is cumulative and pulls everything together. As previous editors have noted, the Sun is enormous compared to the rest of the solar system, which extends out to the Oort cloud. Robert McClenon (talk) 22:12, 22 July 2015 (UTC)

Ha ha, I know it's a weak force in comparison to the others, but it is capable of being massively strong nonetheless. It's strong enough to form planets and keep the solar system together.217.158.236.14 (talk) 14:10, 22 July 2015 (UTC)

It is "weak" compared to the nuclear forces, but, unlike the nuclear forces, gravity operates at unlimited distance. It is "weak" compared to electromagnetism, but, because electromagnetism has positive and negative, and like signs repel, there aren't large charges pulling across astronomical distances. Robert McClenon (talk) 22:15, 22 July 2015 (UTC)

You've scaled the distances down by about 1.4E11, but in doing so you've scaled the masses down by around 2.7E33, since the dependence of mass on length is cubic. Therefore the gravitational force (which depends linearly on mass) has been disproportionally scaled in your thought experiment.--Phil Holmes (talk) 11:09, 22 July 2015 (UTC)

If you scale down all distances in the solar system and scale down masses in proportion to the cube of distances (i.e. keep the average density of each body the same) *and* scale down velocities too then the orbital periods will be unchanged. So your model Earth will still orbit your model Sun with a period of one year - but it will be moving very slowly. Gandalf61 (talk) 11:46, 22 July 2015 (UTC)

If you are impressed by Pluto orbiting the Sun, don't forget that our entire solar system is orbiting the Galactic Center which is over 25000 light years away! Vespine (talk) 01:33, 23 July 2015 (UTC)

This is sort of a fun exercise to get your ducks in a row. Gravitational force is proportional to m1m2/r^2. So if you multiply mass by a factor of K^3, and the radius by a factor of K, the force is now multiplied by K^4 (i.e. K^3*K^3/(K)^2). But F=ma, where a is acceleration, and so that is multiplied by a net K (the preceding K^4, divided by a K^3 mass increase). So the acceleration is slowed to scale with the rest of the scale model, and the orbit continues unabated.

While detecting gravity in the mundane world is difficult, the Cavendish experiment was done in 1797 with a wooden beam and a wire! It measured a force about the weight of a grain of sand from the attraction of lead balls. A true scale solar system model, held in perfect frictionless vacuum, with two hundred years to measure an effect, is going to be much more sensitive than something you rig up in a barn. Wnt (talk) 13:50, 23 July 2015 (UTC)

What would the mass of the 1 cm sun be in Gandalf's model? Edison (talk) 19:33, 24 July 2015 (UTC)

Thanks all for the enlightening replies!Gil_mo (talk) 06:46, 23 July 2015 (UTC)

How does pregabalin work

Hi. I'm trying to find out exactly how pregabalin works for neuropathic pain and need some help. What I don't understand is how it could "know" to deal with the pain in the painful part of the body and not elsewhere - unless it sort of numbs all sensations everywhere? Thank you for pointers. 184.147.131.217 (talk) 14:09, 22 July 2015 (UTC)

The keyword you may want is "mechanism." which leads to many publications available at no cost on PubMed, a service of the National Institutes of Health. Here's one such paper, Pharmacology and mechanism of action of pregabalin, (2007), which rapidly drives into the technical details of the biochemistry. Nimur (talk) 16:37, 22 July 2015 (UTC)

Thank you very much! Can you help a little with the translation? It says subtly reduces the synaptic release of several neurotransmitters and a mechanism that may entail reduction of abnormal neuronal excitability through reduced neurotransmitter release. Is this saying that it does indeed reduce all feeling across all nerves equally, especially those that are reacting to something (eg biting tongue same as the neuropathy)? 184.147.131.217 (talk) 16:50, 22 July 2015 (UTC)

1) "subtly reduces the synaptic release of several neurotransmitters" sounds like it applies to all nerves.

2) "reduction of abnormal neuronal excitability" sounds like it only applies to nerves which are malfunctioning, such as in neuropathy. StuRat (talk) 16:54, 22 July 2015 (UTC)

Thanks, but I would like to know what it actually means not just what it sounds like. What I really want to understand is how (or if it actually does) the drug would distinguish between all nerves and malfunctioning nerves. 184.147.131.217 (talk) 17:07, 22 July 2015 (UTC)

In other words, you would like to know whether there is a method of targeted drug delivery, or if there is some binding affinity or functional selectivity for this drug. I don't know the answers, but these keywords may help your literature survey. Nimur (talk) 17:40, 22 July 2015 (UTC)

Thank you again Nimur. I'm far from unwilling to do such searches, but all the results I have found are unintelligible to me, being written in scientific shorthand. I mean look at [5]! No clue what any of it means. I think I need to request help finding sources written for the general public, please. 184.147.131.217 (talk) 02:04, 23 July 2015 (UTC)

There are two factors I would emphasize with regard to explaining how the drug can act selectively to reduce neuropathic pain without numbing parts of the body unassociated with the pain. First, as with many substances that regulate neurotransmitters and general neuronal excitability, the chemical will adjust transmission rates within a certain threshold. Neurotransmitters employ various forms of biofeedback (the details of which are best left vague here if you wish to avoid clinical language - suffice it to say, they self regulate when they have already been firing at abnormally high rate). In neuropathic pain, these nerves are often firing excitably either because of damage the cells themselves or other related physiological causes. Regardless of which, if you manipulate the regulatory mechanism so that these cells will only fire so often in a certain context, you can alleviate the pain, while the functions governed by other similar neurons are not affected if they were already not firing at a particularly excited threshold.

The second factor to consider is that nociception is handled by its own neural pathways that, while somewhat intertwined with those govern tactile sensation and other somatic sensation, it is to some extent separate, and thus there are many analgesics alleviate pain in one manner or another but which do not cause a sensation of numbness (localized or general) with regard to other somatosensory modalities. I hope that helps some; feel free to ping me if I've still not hit the right balance between technical and plain language and I will clarify further. Snow ^{let's rap} 07:14, 23 July 2015 (UTC)

• "The precise mechanisms by which gabapentin produces its analgesic and antiepileptic actions are unknown." RxList. μηδείς (talk) 18:59, 22 July 2015 (UTC)

Thank you, however I am looking for a drug called pregabalin. 184.147.131.217 (talk) 02:04, 23 July 2015 (UTC)

I suppose I should have clarified, but they are both similar-acting GABA-analogs prescribed for the same reasons. If you're in the US you can even just call a local pharmacy, ask for the pharmacist, and they will tell you. μηδείς (talk) 21:20, 23 July 2015 (UTC)

Generic plastic solvent

I have a bunch of rare earth magnets imbedded in plastic in a toy. I would like to dissolve away the plastic to get all the magnets for a different project. Any suggestions on what sort of solvent to start with? The toy in specific is "Geomag" a magnetic stick and ball construction set. Tdjewell (talk) 14:57, 22 July 2015 (UTC)

Can you get your hands on some dichloromethane? That works on most plastics. 209.149.113.45 (talk) 15:16, 22 July 2015 (UTC)

There are lots of types of plastic, and at least two very different broad categories - Plastic#Thermoplastics_and_thermosetting_polymers. I looked at the company web page [6], and cannot easily determine what kind of plastic they use. I think knowing the type of plastic will be pretty important. SemanticMantis (talk) 15:19, 22 July 2015 (UTC)

You might try peppermint oil. It can dissolve some plastics and isn't nearly as toxic as most other solvents (it is toxic in high enough doses, though). Plus it makes everything smell nice. StuRat (talk) 16:49, 22 July 2015 (UTC)

You can try acetone. It's not very toxic, but quite flammable. Test it (and any solvent you try) first - put some on a napkin and rub the plastic with it, see if it makes it "mushy". The biggest issue you will have is it will evaporate very fast, leaving the plastic behind, in a melted mass. Maybe try a glass canning jar, fill it halfway with acetone, and drop the toy inside. Then use a metal rod to stick to the magnets and pull them out. (Which is why I suggested glass, and not a metal paint can.) All that said, you will probably find it easier to remove the magnet using mechanical means. Ariel. (talk) 00:34, 23 July 2015 (UTC)

Extra note: You will probably spend more money in supplies for doing this, than the magnets would cost to simply purchase. Sell the geomags, and buy magnets, they are not as expensive as you might imagine. Ariel. (talk) 00:36, 23 July 2015 (UTC)

If you use acetone, either use it outside or in a well ventilated area, because it can quickly stink up the whole house. StuRat (talk) 02:55, 23 July 2015 (UTC)

• Why do you have to dissolve all the plastic? Have you thought of maybe a hack saw or something like that? --Jayron32 01:34, 23 July 2015 (UTC)

I think some of these guesses sound a bit dodgy. I mean, acetone? that's a solvent that is hydrophilic enough to mix with water. Really, there's no guarantee that a plastic will dissolve at all, and it matters a lot what it is, but I'd expect better odds with something pretty nonpolar (dichloromethane falls in that category, though it might be easier to use some gasoline, paint thinner etc.) It's also possible that you might weaken the plastic with solvents, making it easier to peel, by soaking out the plasticizer, which again I'd guess is more likely to be hydrophobic. Wnt (talk) 13:32, 23 July 2015 (UTC)

We have an article about Geomag (product and its company). DMacks (talk) 20:19, 25 July 2015 (UTC)

Transporters

Is it true that the transporters in Star Trek actually kill the person and then build an exact copy at the destination out of different atoms? 117.168.207.243 (talk) 16:53, 22 July 2015 (UTC)

Since it's a fictional device, there is no "truth" except for how the authors claimed it would work. That device supposedly dissembled them into atoms, physically sent those same atoms to the remote location, then reassembled them there. I would call that killing them and bringing them back to life, although whether the result is a "new person" or not is debatable. Now, as for reality, that bit about sending the actual atoms to the target is plain silly. The way a transporter would really work would be to just send the information (pattern), but reassemble the person from different atoms there. However, according to physics, one atom with the same proton, neutron and electron configuration is identical to another, so it would make no difference. This does mean the same technology could possibly be used to clone an individual as many times as wanted, so perhaps that's why they made it use the same atoms in the Star Trek universe, to avoid people from asking why the various parties don't just clone themselves an army using the transporters. StuRat (talk) 17:01, 22 July 2015 (UTC)

Ship of Theseus paradox is relevant here. shoy (reactions) 18:23, 22 July 2015 (UTC)

I think I get what you mean, but it could use an explanation. That is, the atoms in a human body are normally replaced over a period of time, so replacing them all instantly isn't much different. In any case, it can be thought of as the same person before and after. StuRat (talk) 18:28, 22 July 2015 (UTC)

Given Bones describes it as disassembling and reassembling the body's molecules, I'd say yes. Other fictional teleportation devices have the entire body converted to a single large wave-particle, which seems less destructive and more continuous. Also there is the fact that you are maintained as data in the "buffer" and can be lost or replicated due to computer problems. I recommend the short story "Think Like a Dinosaur". μηδείς (talk) 18:55, 22 July 2015 (UTC)

Yes, that is an excellent (newer) Outer Limits episode which discusses the moral implications in a way Star Trek never did. StuRat (talk) 20:06, 22 July 2015 (UTC)

Supposedly Roddenberry invented the transporter to avoid the cost of building and filming a shuttlecraft - which they eventually had anyway. Perhaps he was inspired by other sci-fi. Such as, well, let's just hope there were no flies on board the Enterprise. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:19, 22 July 2015 (UTC)

There's not much supposedly about it - there's a couple of interviews where you get it straight from the horse's mouth, but as I recall it he put the issue in a slightly different way, something to the effect of "we couldn't afford to show the ship landing each week." I find that very interesting, because he didn't (at least at the time) realize that interstellar ships that land are less feasible than those that are constructed in space and spend their entire operational existence there. Or if he did, he still would have shown it if he could, because it would have made for entertaining television and up until that point, every space explorer on TV simply set down their one and only vessel on whatever planet they were visiting. Roddenberry, as a result of television logistics, was forced to create a paradigm that actually more accurately reflected the logistics of genuine spaceflight. And that trend continued for a long time; it's rare than any ship above a certain scale lands in Star Trek or similar shows. Snow ^{let's rap} 23:01, 22 July 2015 (UTC)

So, it looks like one could call Roddenberry a paradigm-shifter? μηδείς (talk) 01:33, 23 July 2015 (UTC)

Well, it wouldn't be the first time for him, I dare say. But with regard to this particular facet of representing future technologies, I suspect this change was inevitable. Note that while this was a development for television sci-fi, most literature of the time already represented interstellar craft as constructed in space and mostly used exclusively therein. Snow ^{let's rap} 02:17, 23 July 2015 (UTC)

Having read most of the ref desk today, I think that Medeis is attempting a bit of cleverness here with respect to an unrelated thread on the Language desk - [7]. Clever, but perhaps a bit WP:POINTY :) SemanticMantis (talk) 03:45, 23 July 2015 (UTC)

Well, at the risk of validating said off-topic digression into banter by participating in it (something I usually try to avoid here), "clever, but perhaps a bit WP:POINTY" is my basic impression of Medeis. :) Snow ^{let's rap} 06:47, 23 July 2015 (UTC)

We have an article on that: Transporter (Star Trek). The article quotes Lawrence Krauss, author of the book The Physics of Star Trek: "The Star Trek writers seem never to have got it exactly clear what they want the transporter to do. Does the transporter send the atoms and the bits, or just the bits?" So the transporter definitely disassembles the old you, but they haven't made up their minds whether the new you is put together out of the same atoms, or different ones. If it's the same atoms, you could also ask whether they are put back in the same places. One hydrogen atom is as good as another. --Amble (talk) 20:37, 22 July 2015 (UTC)

This was going to be my observation even before I saw that you had sourced it. Like most fictional technology that has been utilized over long narrative runs (and most Star Trek technology in particular), consistency of the exact mechanics for the transporter has not been great. It's been many years since I saw the relevant material, but I'm fairly certain that there were precise references to the fact that the transporter beam utilizes the same matter at both ends of the process. On the other hand, there was an episode of Star Trek: The Next Generation in which it was discovered that a transporter accident many years in the past had created a duplicate Commander Riker (or Lt. Riker rather). The accident was explained as such: the transporter beam had gotten a lock on Riker and successfully beamed him aboard ship, but interference from the atmosphere reflected a copy back down to the surface, where another Lt. Riker re-materialized (and was then abandoned on the surface of the planet for years by his oblivious crewmates). This obviously suggests that the transporter technology does (or in a pinch, can) utilize other stores of atoms to re-assemble a person, since there would otherwise be only enough atoms in the process to construct one Riker.

Certainly there are other examples of Star Trek technology that suggests this would be no more complicated than using the original material, including their "replicators" which can use stores of material to create most any object or substance for which they have molecular understanding. And there are numerous examples of an individual not materializing immediately, but their "pattern" is retained in the "transporter buffer", though they never explain if that is mere data or the actual mass plus the information on how to reconstruct it. It does raise the question of why you would ever use a technology that is dependent on the exact same atoms, when this represents an extra element of risk in being able to re-create the person that would not be there if you could use an infinite store of (really exactly identical) atoms. Perhaps the idea is that knowing it was the atoms that they started with at the beginning of the process reduces the existential heebi-jeebies of wondering whether the person who materializes at the other end is you or just a copy. There are examples of notable characters in the Star Trek run that I can recall who disliked or even refused to use transporter technology for just this very reason, or of general fear that the process wouldn't put them back together quite right. They are generally treated as similar to people today who fear airline travel and persist in this fear even when shown that statistically it is quite safe, but I never felt the situations were really analogous, given the philosophical questions involved. Of course, even in mundane pre-23rd century life, we change the mass of our bodies at a rate most people don't appreciate, and are basically a brand new person (in terms of matter) every seven years -- it's the organization of those elements which is most important.

There was another brilliant short sci-fi story (which I am delighted to find we have a stub for) called Think Like a Dinosaur that explored these themes very well. In it, an advanced extraterrestrial race has made contact with a human species on the brink of extinction after ecological devastation of Earth has come to a head. Amongst the technologies they bring with them is a transporter-like technology which unambiguously does send the information only, to construct a duplicate at the other end of the transmission. The "original person" is encased in a stasis-like substance and then disintegrated once transmission/copying is confirmed; the aliens (a pacifist reptilian species to whom the "dinosaur" part of the title refers) call this "balancing the equation". However, because the stasis process quickly kills the original, it has to be aborted if the transmission cannot be confirmed. This happens to a human traveling via this technology, only for the transmission to be later confirmed. The aliens, who know the social chaos that can be unleashed if multiple people with the same identity begin running around, have a strict ethical code about the technology's usage and insist that the original must be destroyed (though they are not willing to resort to violence to seeing it done, instead threatening to refuse further access to their knowledge and technological aid (which is essential to the survival of countless people still stuck on a near-cataclysmic Earth) should the "redundancy" be allowed to live). This creates a deep morale quandary for the humans involved, interlaced with notions of identity, materialism and consciousness. It's the kind of story I wish I had thought of first! Snow ^{let's rap} 22:27, 22 July 2015 (UTC)

Yes, both Medeis and I referred to that plot above, although we mentioned the Outer Limits episode, which seems to have accurately portrayed the story. You might want to watch that, if you haven't already, and see if you agree. StuRat (talk) 03:05, 23 July 2015 (UTC)

Oh, I missed those references entirely! Yes, actually I came to be familiar with that story through the Outer Limits episode first and read the story as a result. The episode, which in my opinion is one of the few from the late 90's Outer Limits revival that really holds up in quality today, very faithfully replicates (pun intended!) the sci-fi aspects of the narrative, though the character dynamics are a little different, as you might imagine. Snow ^{let's rap} 05:19, 23 July 2015 (UTC)

Yes, it was one of my favorites. There were some other good ones, though, like The Human Operators. StuRat (talk) 15:50, 23 July 2015 (UTC)

The implications of transportation-by-replication are also part of the plot of The Prestige, an excellent film with more cunning twists than a cunning twisty thing. Gandalf61 (talk) 08:24, 23 July 2015 (UTC)

I'd forgotten that one, and Nolan is one of my all-time favourite filmmakers; worth noting that The Prestige is also based a book of the same name. Snow ^{let's rap} 08:48, 23 July 2015 (UTC)

That's a fantastic (and also sort of horrifying) movie. Please see the move/read the book before you spoil yourself reading the wiki article, you'll thank me later. shoy (reactions) 13:41, 23 July 2015 (UTC)

The way I would answer this is a bit different. I'd start off by saying that really, all people are the same atman, and so the teleported people are 'the same person', provided the copying is accurate enough to produce another sentient human being at all. I won't even get into ka/ba distinctions and parallel universes in the chain of creation this time. :) But as you can tell, this isn't actually science. Wnt (talk) 23:21, 22 July 2015 (UTC)

Good link. I think it's also worth mentioning that our articles on person, personhood and personal identity together are fairly comprehensive and detailed. SemanticMantis (talk) 00:17, 23 July 2015 (UTC)

This all reminds me of Thomas M Disch's novel Echo Round His Bones (from about the same time as the original Star Trek series), in which the teleportation machine (unknown to the operators) leaves behind a ghostly, but living, "echo" of the person being transported. AndrewWTaylor (talk) 09:01, 23 July 2015 (UTC)

Duplication by teleporter is also the subject of Algis Budrys' Rogue Moon (1960) written before Star Trek debuted. Rmhermen (talk) 14:43, 23 July 2015 (UTC)

Outside of Star Trek, the usual name in SF for a device that reduces people or objects to their consituent atoms is "disintegrator ray". Iapetus (talk) 10:17, 23 July 2015 (UTC)

I think that's a fairly distinct topic from what is being inquired about here, given the missing and rather crucial step of re-assembling those atoms. Snow ^{let's rap} 13:46, 23 July 2015 (UTC)

Partially distinct. If you used a disintegrator ray to reduce someone to atoms, I think everyone would accept that you had killed the person. If you then used some other gizmo (or magic) to reassemble those atoms into the original person, I suppose its just a matter of philosophy (or faith) whether you have "built a copy" of the original or "resurected" the original. By analogy, I would say the answer to first part of the original question ("is it true that the transporters actually kill the person?") is "yes", and for the second part ("and then build an exact copy?") is "possibly". Iapetus (talk) 09:08, 24 July 2015 (UTC)

The Farnsworth novelty disintegrator ray was, in fact, nothing more than a harmless teleporter ray. Hardly a distinct technology! I am Nimur, seer of the tapes, knower of the episodes! Tremble before my encyclopedic knowledge of Star Trek!

The details of the Star Trek transporter technology, and all the other bits of fictional science and engineering, have severe inconsistencies across any one of the series, and it gets worse when you compare different series in the franchise at large. The posting above has already linked to Lawrence Krauss' Physics of Star Trek book; and that's probably the best place to go for information; it's pretty clear that the exact mechanism of the transporter technology varies based on plot need. I'll throw in one more resource that every fan should read: the Writers Guide, in which Gene Roddenberry (creator of Star Trek) specifically told the episode writers not to worry about technical details and to focus on making the story exciting. I linked to that document, and a whole lot of other critical literary reviews of it, the last time this came up on the Science desk, in March of this year.

Nimur (talk) 14:55, 23 July 2015 (UTC)

I think if you really want to look into it there should be a more interesting quantum mechanics question, which I wouldn't pretend to be able to answer: is it possible to "transport" a person this way and be accurate? I'm not asking whether you can manage the disintegration or reintegration or transport, but whether Heisenberg uncertainty principle limits get in the way. After all, when you do an X-ray crystallography structure, it is often hard to tell where every last hydrogen is located, and you may end up making a few assumptions about who is bound to who to get the model finished. But there are other limits besides the quantum there. Also, if the measurements are too imprecise... what if you put your transporter computer in that neat little box they shipped Schroedinger's Cat in, and destroy the computer after you finish? Will that prevent any "measurement" from taking place, so it's just like moving the object, even if you know it had higher-accuracy measurements inside it for some time while it was in the box...? Wnt (talk) 18:15, 23 July 2015 (UTC)

You can teleport the complete state, as long as you have previously exchanged enough entangled particles between the two endpoints. However, you can't make multiple copies because of the no-cloning theorem. If the transporter beam is itself a quantum channel, you can directly send the full state through it without making a "measurement". Either way, what you definitely don't want to do is measure the state, i.e. collapse it down to classical information. It's not clear whether the Star Trek implementation conforms to any of these ideas, since they use Heisenberg compensators. Nobody knows exactly how those work, but they stop the scriptwriters from having to worry too much about the uncertainty principle. --Amble (talk) 19:13, 23 July 2015 (UTC)

I don't think there is any kind of teleportation involved, in the senses that you imply here. That is, my impression from personal observation and the sourcing we have above with regard to how the writers treated this subject was that the beam somehow moves the matter through the intervening space, but does so piecemeal. I've never seen any suggestion of entanglement or quantum effects of any sort. Also, perhaps I'm mistaking your meaning here, but you seem to confusing the semantics of teleportation in the sense being discussed here and what quantum teleportation refers to, which is strictly information. Entanglement can be used to generate sympathetic states in linked particles, but no exchange of mass over distance occurs. If you are suggesting that this could be used to transmit the information over distances instantaneously, that's true, but you'd still need to either transmit the matter somehow, or have an identical store of atoms on the other end which could be used in synthesis, in which case, you would in fact end up with a copy. But these are two separate issue -- the original one discussed here, about whether the transported person is constructed of the same mass, and what you are talking about (transmitting information without an intervening medium). The transporter's exact nature (and the OP's question with regard to it) remain an uncertain factor regardless of whether or not it has an additional mechanism like the one you describe. Snow ^{let's rap} 10:23, 25 July 2015 (UTC)

I was responding to Wnt's question about what's actually allowed by quantum mechanics, which is of course not the same as what's allowed by Star Trek scriptwriters. --Amble (talk) 18:25, 25 July 2015 (UTC)

@Amble: Yes, ok, I see; in reviewing the context of your post as an answer to Wnt's specific inquiry, it makes a lot more sense. I should have re-read his post in detail before replying to yours - apologies! Snow ^{let's rap} 22:16, 25 July 2015 (UTC)

@Snow Rise: No problem. I try to follow Wikipedia:Indentation, but given the variety of styles it's often hard to tell who is responding to what. I guess I should learn to use the Ping template. --Amble (talk) 22:38, 25 July 2015 (UTC)