Wikipedia:Reference desk/Archives/Science/2015 September 25

= September 25 =

Fish tank hook up
I am planning a house with my architect and we wish to have a 7 foot long nearly 300 gallon fish tank on the main floor. We will have plans for extra support beams for the three thousand pounds that it will eventually weigh, but in terms of plumbing, what should I have at my disposal? He offered to put a water spout right near the tank, so that I can do easy water fills. Can I put a suction spout in -- does such a thing exist? Someone suggested that I do water changes out of the wet/dry filter and have that assembled downstairs in the basement. Thanks!  DRosenbach  ( Talk 00:12, 25 September 2015 (UTC)


 * Ever thought of connecting a hose (maybe a typical garden hose) to a sink? My Dentist has a 100 gallon tank in the waiting room and I had the pleasure of watching a tech change the water and clean the aquarium. Void burn (talk) 00:18, 25 September 2015 (UTC)


 * Yes, they do sell tubing for this (one common brand is called a Python apparatus) but if I have a dedicated spout, it should make it easier.  DRosenbach  ( Talk 12:29, 25 September 2015 (UTC)


 * Maybe take some pictures and ask for recommendations from your local aquarium store. I would surmise that they would be much more knowledgeable/helpful/experienced than an architect in this specific situation. Void burn (talk) 00:22, 25 September 2015 (UTC)


 * I'm trying to circumvent expensive devices, etc. by having it built with the house, and figure that the store might be biased. But more importantly, then I only get to speak with one or two people, rather here where I could receive great information from knowledgeable people from all sorts of places.  DRosenbach  ( Talk 00:39, 25 September 2015 (UTC)


 * I hope an expert replies here to assist you. If not here may be some useful references: utube video forum1 forum2 forum3 i wish you the best of luck mate. Void burn (talk) 01:04, 25 September 2015 (UTC)
 * I hope an expert replies here to assist you. If not here may be some useful references: utube video forum1 forum2 forum3 i wish you the best of luck mate. Void burn (talk) 01:04, 25 September 2015 (UTC)


 * If you're having it built in, the intriguing thing to contemplate is using a basement sump filter tank, which you should either ask about or google. Here's one site: . Definitely the aquarium people are the ones to ask, rather than architects. - Nunh-huh 01:31, 25 September 2015 (UTC)


 * For the fresh water, you might consider PEX piping, which is flexible and hence easier and cheaper to install. In order to drain the tank, if it's on an outside wall you might put in a drain through the wall into the garden, driveway, etc.  It might smell a bit fishy right after you drain it, but that could save you some expensive plumbing.  It might even be good fertilizer for a garden.  BTW, where do you plan to put the fish when you drain the tank ? StuRat (talk) 04:04, 25 September 2015 (UTC)


 * @StuRat (talk) you can either leave the fish in there with enough water for them to breathe or catch them with a net and put them in plastic bags Void burn (talk) 04:19, 25 September 2015 (UTC)


 * I'm thinking a smaller backup tank would be a better option. StuRat (talk) 04:29, 25 September 2015 (UTC)


 * Have you kept fish before? If not you need to know that you don't use water straight from the water main. You need to dechlorinate first either by leaving it to stand overnight or by using a dechlorinator . Also, you shouldn't ever need to change all the water at once. Richerman    (talk) 05:43, 25 September 2015 (UTC)


 * Yes, I have kept fish before, although admittedly they were goldfish, which are about the easiest fish to keep alive. I had a large aquarium and a smaller bowl.  When it was time to clean the aquarium I used a net to transfer them to the smaller bowl (which had been filled with tap water the previous day).  I then cleaned the aquarium out completely, dumped the water, changed the sand, filled it with tap water and let it sit for a day.  Then I poured the fish from the small bowl back into the aquarium.  This worked just fine, at least for goldfish. StuRat (talk) 02:50, 26 September 2015 (UTC)


 * +1. Keeping tropical fish is not as easy as it would seem, and poor advice from people who clearly have no experience of doing it won't help you.  I would suggest that you start by getting a small tank with a few fish and get used to what's needed in terms of partial water changes, water monitoring, filter maintenance, feeding, etc.  Once you know what you're doing, you'll be in a better position to understand how best to install the monster tank you're talking about.--Phil Holmes (talk) 08:32, 25 September 2015 (UTC)


 * + another 1. Exactly. All this talk of putting tap water straight into the tank or draining it to clean it is just horrible. A fish tank needs a suitable environment to be set up well in advance of introducing fish. Have a look at the article here on aquarium. And find someone who knows about them to help you. If you can afford an architect you can afford that. Dmcq (talk) 08:45, 25 September 2015 (UTC)


 * Agree. Unless you're a billionaire and planning to hire someone to do all the maintenance for you. You really do need to like fishkeeping as a hobby and know more about it. I have a ~65 gallon tank, and it's not easy. How much more for a 7-foot tank.


 * I don't have experience with custom-built tanks, but depending on what fish you want to keep (you need to plan that in advance!), you will need specialized equipment. You haven't mentioned, for example, whether you are making a saltwater or a freshwater tank. Coldwater or tropical. Live plants or plastic. What substrate do you plan to have (if you're having any). Then there's lighting and heating (if you live in areas with winters), in addition to plumbing. And you still need ways to manually get in there and clean it (filtration will only get you so far, you will still need to scrub that thing down every few weeks or so), etc. Noise reduction is also something you need to consider as pumps and aerators can be noisy.


 * So yeah. I think you do need to talk to aquarium professionals rather than just your architect. For your basic question though, in a tank that size, you will need a sump setup.-- O BSIDIAN  †  S OUL  09:30, 25 September 2015 (UTC)


 * Without any knowledge of how to keep fish, having a drain below the level of the tank would allow you to siphon the water out fairly easily. You could even have the siphon tube permanently attached, and place a valve below the level of the tank (so that you eliminate the need to suck water through the start the siphon process). MChesterMC (talk) 09:06, 25 September 2015 (UTC)


 * For goodness sake - please stop guessing about how to set up a fish tank if you don't know. Leaving a syphon in place can easily accidentally empty the tank or allow someone else to do it.  Result: dead fish and water damage.  I repeat my previous comment to the OP - pay no attention to comments made by random internet users - ask an expert and read some books if you really plan to do this.--Phil Holmes (talk) 09:50, 25 September 2015 (UTC)


 * Exactly, but at least MChesterMC says at the start they know nothing about keeping fish. You don't need to suck water into a syphon - you use something like this. Richerman    (talk) 10:50, 25 September 2015 (UTC)

Thanks for the comments. I have had a 29 gallon tank for about 7 years, and am planning to upgrade to the large one next spring when we move. The plan is to have freshwater only (oscars, arowanas, etc.) and the water was not meant to go directly from the plumbing into the tank or the filter -- I was merely asking the question in an abridged version. I will have heavy rugged garbage pails to hold the water for a duration of time sufficient for chlorine evaporation. I've already spoken to the fish people, but they said they are unfamiliar with what sort of plumbing I might be able to have, and since my architect didn't know, I thought I'd ask here. But thanks for the help from those who provided (or tried to).  DRosenbach  ( Talk 12:29, 25 September 2015 (UTC)

Driving a steam train
At medium speed (defined as 30 mph) or limited speed (45 mph), with a train of 50 or so empty cattle cars, what control settings use less steam -- wide-open throttle and short cutoff, or partly-closed throttle and long cutoff? (The engine is a ten-coupled freight engine, DRB Class 52 or similar.) 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 08:46, 25 September 2015 (UTC)
 * I can't think of a thermodynamic reason why maximising cut off wouldn't be more efficient, up to the point where there is enough steam to do so. But at some point with limited steam available in the cylinder you might need to add more throttle rather than just expanding what there is, as the piston force could go negative. I've never driven a steam engine, I've built a small vertical engine. And I've probably spent more time with steam charts than most. Greglocock (talk) 09:20, 25 September 2015 (UTC)


 * "Maximising cut-off" can be interpreted in two ways, from the rest of your answer, I take it you mean cut off early in the stroke?
 * Anyway, for the OP: the basic principle is that throttling means loss of efficiency, because it reduces pressure without doing useful work. Throttle has an explanation. Google books gives plenty of results that explain in detail the advantages of using cut-off instead of throttling when you search for steam train throttle cut-off.
 * So in theory, open throttle and short cut-off would use less steam. Whether medium speed is even possible with wide-open throttle, I don't know. Perhaps you need to reduce throttle to keep the speed down, in that case the most efficient way would be shortest cut-off and using throttle to control the speed.
 * Real trains may have all kinds of inefficiencies, and throttling may have a few advantages, like preventing initial condensation in the cylinder. Didn't find details about that specific model, whether it will behave as expected, I can't say.
 * This video (71000 Duke of Gloucester) gives a good demonstration of driving a steam train (it uses a British Caprotti valve gear, not very typical I presume), starts with cut-off at 65%, opens the throttle, reducing the cut-off (gear) gradually to 15% while accelerating.  Ssscienccce  (talk) 05:07, 26 September 2015 (UTC)

is this airsoft weapon so strong that it destroys the magazine?
pic I was interested in buying this weapon via amazon and I found this picture, does someone has experience with this revolver?--Hijodetenerife (talk) 12:21, 25 September 2015 (UTC)
 * This is not a weapon but a replika, a model. Its made of plastic (Material: Hauptsächlich Kunststoff) and thus not suited to shoot projectiles or worth mentioning projectile like air effects. --Kharon (talk) 15:26, 25 September 2015 (UTC)
 * Very weak compared to other airsoft guns. In a normal spring-powered gun it's the weapon that contains the spring, here the spring is in the cartridge: much smaller, your pellets won't reach very far. Compare for example the little spring in that picture with the one shown here. Reloading is time-consuming, removing the cartridges from the gun and reloading them individually by placing the cartridge in a holder, pushing down and cocking the spring with the supplied tool, then inserting the pellet. This video shows the loading and firing of such a revolver: https://www.youtube.com/watch?v=ze4krZ3ioEo . Ssscienccce  (talk) 16:09, 25 September 2015 (UTC)

Icelandic rifting period
I ran across a few instances of one story that says that Iceland enters a "rifting period" every 140 years, which will be at its peak for the next 20 or so. I see no other hits online for the "Icelandic rifting period". I probably should have done more digging, but it seems like an interesting topic to raise here anyway: what is this ... is there a better name for it ... and above all, does it have a noticeable average overall effect on global climate that can be tracked back over many cycles? On a related point, that story says Bardarbunga released more sulfur dioxide than Europe's industry - is that presently having an effect on global climate like Pinatubo, or are other aspects of the eruption too different for that to happen? Wnt (talk) 12:56, 25 September 2015 (UTC)


 * This paper goes into some detail about what goes on in one of these rifting episodes. Mikenorton (talk) 13:34, 25 September 2015 (UTC)


 * That paper sounds pretty tentative, and certainly doesn't highlight the 140-year cycle. I see 100-1000 and 200-250 years as ranges, unless I missed something.  But apparently it is well recognized that there was a "major rifting episode at Askja" in 1874-1875, but also minor episodes in 1920s and 1961-1962.   Still, that latter source says "Episodes of rifting have occurred in the  Northern Volcanic  Zone about  every  100 - 150  years", citing Björnsson  et  al.  1977; clearly I don't understand everything! Wnt (talk) 18:50, 25 September 2015 (UTC)


 * I can only see the abstract of that 1977 paper, which states "Historical records show that similar episodic rifting occurs in this region every 100–150 yr", so presumably there are good records going back many centuries, perhaps to soon after Iceland was settled in 870 (CE/AD as you prefer) to allow that statement to be made. Mikenorton (talk) 19:45, 25 September 2015 (UTC)

Saving lives and time paradoxes
Hi. It is often claimed that you can't go back in time and save your friend from dying, because if he doesn't die, you won't have the motivation to go back in time to save him, so he'll die... and so you generate a paradox.

However, an alternate viewpoint says that you can do it as long as you leave behind an exact copy of your friend's corpse so that your past self will still be motivated to travel back in time to save your friend.

What is the name of the latter theory, so I can Google more information about it? Thanks a lot. Leptictidium (mt) 21:16, 25 September 2015 (UTC)


 * Sounds like the Hitler paradox which a version of the Grandfather paradox. It is all explained here -sort of. Only I don't feel motivated to go back and read it because the butler did it (and he left the body under the stairs).--Aspro (talk) 21:33, 25 September 2015 (UTC)


 * The point is that time travel isn't possible. There are no viable theories for how it might be possible.  So "what happens if..." isn't a question that science can answer - the answer is "it can't happen".   Now, if you're going to raise a hypothetical - then any conclusions you might arrive at are just as hypothetical.  We had a time travel question about a week or so ago - and I was able to list 21 possible outcomes of going back into the past and changing something - no one of those is any more "correct" or more "likely" than any of the others - and I'm pretty sure there aren't names for those possibilities. SteveBaker (talk) 22:21, 25 September 2015 (UTC)
 * In general, the lack of an understood mechanism for how something could happen does not make it meaningless to ask what would happen if it did. We can reason about black boxes without being able to look inside and see how they work.  In this case, though, I agree that the question is underspecified. --Trovatore (talk) 22:25, 25 September 2015 (UTC)
 * We can take a black box, examine the outputs produced by various inputs and make reasonable statements about what might be happening inside - and perhaps that allows us to make good predictions about what the outputs will be for some hypothetical input that has not yet been tested. But with speculation on the consequences of time travel, we have no clue what the outputs might be for any input whatever.  So we can't possibly say anything whatever about the inner workings of the process - which means that we can't even remotely guess what the outputs would be for our OP's specific set of input conditions.  SteveBaker (talk) 14:57, 26 September 2015 (UTC)
 * You're missing the point. We don't (in general) need to know anything at all about the "inner workings", to make it meaningful to talk about what would happen "if".
 * Say your fairy godmother waves her magic wand and gives you three apples, and mine waves hers and gives me two. How many apples would we have together?  Five.  That's meaningful and true and does not require us to have even the slightest hypothesis about how the wand works. --Trovatore (talk) 18:41, 26 September 2015 (UTC)
 * (For a less trivial and more relevant example, let's revisit the tachyonic antitelephone. It doesn't have to be based on tachyons.  We don't have to know anything about the mechanics of how one event causes another one too far away to be reached by light.  All we have to know is that it works and is Lorentz invariant, and all the paradoxical conclusions must necessarily obtain.) --Trovatore (talk) 18:44, 26 September 2015 (UTC)
 * What could happen might be answerable. What would happen is not. ←Baseball Bugs What's up, Doc? carrots→ 14:26, 26 September 2015 (UTC)
 * I disagree. On the basis of about 10 minutes of thinking about it, I came up with 20 different and wildly contradictory "What could happen" results - most of which are explored at length in science fiction books and movies.  There are likely to be hundreds of other could happen consequences that neither I, nor the minds of sci-fi authors have yet considered ("You go back in time, tread on a butterfly and every object in the universe becomes the exact same shade of pink").  In an unknown situation there are a literal infinity of possible "What could happen" answers - and picking any one of them to discuss is pointless - because the probability that your speculation is useful is just about zero.  With such a gigantic spread of what "could happen" - we can't even begin to speculate about what "would happen" and have any reasonable chance of being correct - and that puts us into the realms of complete speculation - which isn't allowed here on the ref desks. SteveBaker (talk) 14:57, 26 September 2015 (UTC)
 * I'm trying to figure out what part you're disagreeing with. ←Baseball Bugs What's up, Doc? carrots→ 19:41, 26 September 2015 (UTC)
 * I'm disagreeing with your statement that "What could happen might be answerable." - I don't think it is answerable. In the total absence of any actual information on the subject, there are no limits to what might result - and an infinity of outcomes could conceivably result.  So you can't possibly enumerate what could happen. SteveBaker (talk) 19:54, 29 September 2015 (UTC)


 * Sounds like a Causal loop (ontological paradox, bootstrap paradox or predestination paradox). Ssscienccce  (talk) 22:37, 25 September 2015 (UTC)


 * You may be referring to the Novikov self-consistency principle, which basically states that you can only travel back in time if by doing so you can't/don't actually change anything for yourself (or the time travel machine) up until the point you left. Or in other words, with the Novikov self-consistency principle no time-travel paradoxes can ever be generated because in any situation where the generation of a paradox would be possible, it is impossible to travel back in time in the first place. Note that this does have certain implications about the free will of time travelers. -- 160.129.138.186 (talk) 22:43, 25 September 2015 (UTC)


 * But this is the science reference desk. We're supposed to discuss what is known on the topic.  What we know is:


 * Science knows of no possible, or even remotely plausible, way to travel backwards in time.
 * The consequences of time travel are utterly unknown because there is no means to reason about it. Doubly-so when paradoxes are involved.
 * The Butterfly effect means that creating a paradox is almost a certainty (eg the plot of A Sound of Thunder). Merely appearing in the past is sufficient to move more air mass than a butterfly's wing - to change weather patterns in the future (but in your past) - to change who lives and who dies - to utterly change the world as you know it...so forget shooting your grandfather or saving the live of a friend - or even stepping on a butterfly.  Taking one breath of air is sufficient to cause uncountable numbers of paradoxes.
 * Free will is a huge issue in some anti-paradox solutions to the problem - but physics doesn't really admit the existence of free will anyway.


 * What we know for 100% sure is that the only answer to questions about the consequences of time travel is at best: "We Don't Know" and most likely "This is a meaningless question". SteveBaker (talk) 14:57, 26 September 2015 (UTC)


 * Certain solutions of general relativity contain closed timelike curves in spacetime, as Kurt Gödel showed in 1949. But they don't imply that the past can be changed, rather, they "place restrictions on the physically allowable states of matter-energy fields in the universe": only those configurations where going back in time results in the identical state are possible. Which is basically the Novikov self-consistency principle. So we can give an answer within the context of general relativity, without having to decide about the actual or possible existence of such loops in time. These are no just science fiction concepts, physicists study such problems all the time. Take the Cosmic censorship hypothesis, over which Hawking made a bet against John Preskill and Kip Thorne; that question about the existence of naked singularities is not so different from the question whether closed timelike curves can exist, they both imply a "failure" of determinism.  Ssscienccce  (talk) 18:30, 26 September 2015 (UTC)
 * It's not a question of whether closed timelike curves can exist - it's a question of whether they do actually exist - and whether they could be created. That's the problem here...at which point, all we hear from pop-sci TV show presenters is...mumble,mumble,WORMHOLES!,&lt;handwave&gt;...and the "How to create a wormhole" explanation is typically "if we could do XXX  (which we can't)  then we could do YYY and then we have our wormhole! "...or better still "if we could find a stable wormhole just handily lying around someplace, then...".  The 'XXX' step typically requiring things like 'more energy than there is in the visible universe' and such and the 'just find one lying around' approach suffering from the issue that science has never recorded even the smallest hint of such things being 'out there', no mechanism for their natural creation.
 * It's just like unicorns - there is no physical, chemical or biological reason why a white horse with a spirally horn on its nose should not exist. But yet, there are no unicorns.  Even if there were unicorns, it's not likely that they'd go around granting people wishes.
 * The principle that everything has to be self-consistent is a reasonable concept - but it doesn't in any way help to explain what actually prevents a time-traveller from killing his grandfather - it just says that he doesn't ever do that for completely unspecified reasons. SteveBaker (talk) 15:27, 27 September 2015 (UTC)
 * Models with a billiard ball returning back to the past and colliding with itself found an infinite number of self-consistent solutions (for a ball with fixed initial and final positions that traverses the wormhole once). However, they considered a two-dimensional case. In three dimensions, it turns out that only those trajectories that comply with the principle of least action are self-consistent. So the self-consistency principle is no more than a consequence of the principle of least action. It was originally believed that in some cases a self-consistent solution couldn't exist, but so far no such example has been demonstrated. Perhaps it is a property of the universe and its physical laws that every initial condition has exactly one self-consistent solution. A time-traveller who wants to kill his grandfather will not exist, because the only possible time-traveller is the one who's actions lead to him becoming the time-traveller. If one takes the eternalist view of a block universe, then the question of what came first (what caused it the "first time"), is meaningless, time-space simply exists, unchanging, and consistent.  Ssscienccce  (talk) 00:21, 28 September 2015 (UTC)
 * Note that the same issues are encountered with precognition, and unlike time travel, that actually can be encountered, though it is not to be recommended. There is only one past, one present, one future; but I would suggest the presence of causal loops, which are neither random nor preordained, is the basis of free will. Wnt (talk) 18:34, 26 September 2015 (UTC)


 * Precognition isn't hard to understand.  I place an egg on the ground and drop a 50lb weight onto it...at the instant the weight is released, my sense of precognition says that the egg is going to get splatted!  I foresaw the future!  Wow!  The issue is that the degree to which this is possible is sharply limited by chaos theory, quantum weirdness, heisenberg's uncertainty principle and a few other 'hard physics' rules.  So we may remain skeptical of many such claims to accurately predict the future with high reliability and precision for more than a very short time into the future.  We know, for example, that it's physically quite impossible to predict whether it'll rain in my back yard on January 1st 2016.  It's not just difficult, it's impossible - by any means.  SteveBaker (talk) 15:38, 27 September 2015 (UTC)
 * The Heisenberg uncertainty principle is a limitation on how well we observe the present, not the future. It hinders the ability to extrapolate from momentum where a particle was as much as where it will be.  And yet... the particle was somewhere, and you may even know where it was. Wnt (talk) 17:33, 27 September 2015 (UTC)
 * There's a difference between predicting the future and remembering it. Precognition is stuff like knowing in 2000 that the third plane crashed somewhere in Pennsylvania.  And I think it's more common than people generally believe. Wnt (talk) 19:12, 29 September 2015 (UTC)
 * The dictionary definition of the word "remember" is "have in or be able to bring to one's mind an awareness of someone or something that one has seen, known, or experienced in the past" - so "remembering the future" is a meaningless phrase. "predict" means "say or estimate that (a specified thing) will happen in the future or will be a consequence of something".  So your cute use of metaphor and poetry here doesn't mean a darned thing.  When you make a statement about the future - no matter how you came about the information - it is a "prediction" - and cannot possibly be a "remembering" - it's not a matter of physics, meta-physics, clairvoyance, precognition, pseudo-science or anything else...it's what those words mean in the English language.  You may remember that you made (learned about) a prior prediction - but I don't think that's what you mean. SteveBaker (talk) 19:48, 29 September 2015 (UTC)
 * By "remember", I'm referring to a specific model, the only one that seems to make any physical sense: the memory is formed at a specific time and place, and accessed at another specific time and place; in this case it merely happens the former is later than the latter. The conduit of transmission is presumably the hippocampus, with the same 4D distribution in spacetime that carries memories from past to future.  Since physics is generally time-reversible, that is not so big a stretch, really; the arrow of time is a philosophical mystery, not something proved to be absolute.  Now there is a gradient of entropy that would seem statistically to make information flow one way and not the other, perhaps...  However, it is not clear to me that "information" as experienced in the mind is mapped in any simple way to "information" in the physics sense, and so memory as people experience it might not be subject to the same rules. Wnt (talk) 21:39, 29 September 2015 (UTC)