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Reference desk Archives Science 2019 September 22

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= September 22 =

Old models of galaxy formation

I was reading Galaxy formation and evolution. Decades ago they were trying to get models of the formation of galaxies. I went to a lecture at Florida State University about 1977, and the presenter had a model that produced the features of a particular spiral galaxy. But this was long before supermassive black holes and dark matter were known, and we are now pretty sure that they are important in galaxy formation. It seems to me that old models of galaxy formation could not have been very good at all. Is that right? Bubba73 You talkin' to me? 02:11, 22 September 2019 (UTC)
Dark matter is really just a fudge factor to explain the missing mass of the universe. So, just giving something we don't understand a name doesn't really solve the mystery, it just coins a term for it. Imagine if scientists came up with a theory that predicted the number of bacteria species there should be, but then a careful count showed us that this only predicted 15% of the true amount. Would adding an "extant bacterial enumeration adjustment quotient" to account for the discrepancy mean our model was now accurate ? SinisterLefty (talk) 02:47, 22 September 2019 (UTC)

But dark matter does affect things gravitationally. And it has been mapped, so it is "out there". Quoting the article "Current models also predict that the majority of mass in galaxies is made up of dark matter, ...". Bubba73 You talkin' to me? 02:50, 22 September 2019 (UTC)

:But this "mapping" is just figuring out where missing mass would have to be to make our old model work. See Dark_matter#In_philosophy_of_science. SinisterLefty (talk) 02:57, 22 September 2019 (UTC)

::You're oversimplifying the case for dark matter. It's not like cosmologists just draw the missing matter in with a sharpie and call it a day. They create models for the behavior of dark matter assuming specific particle properties, and simulate those models over the evolution of the universe. It's true of course that these models were tailor-made to match the data that has been gathered, but that's just science, generally. Dark matter theorists also made new hypotheses based on those models and simulations for things that had not yet been measured. If you look over the observational evidence section of the dark matter article and its sources, you will notice that many of these phenomena were predicted in advance of their observation. Even if cold dark matter does not actually exist, the model built from the assumption makes accurate predictions. Someguy1221 (talk) 05:32, 22 September 2019 (UTC)

:::Dark matter is the very opposite of a "fudge factor". The choice is really simple: either we rework our theory of gravity (that is, include some fudge factor, in something that works really well except on this very specific matter), or there must be some elusive mass out there. The first option is not ruled out. Could even be partially both (although we usually have rather a single explanation) Gem fr (talk) 11:50, 22 September 2019 (UTC)

::::Some of this "dark matter" and "dark energy" stuff reminds me of the spheres-within-spheres to explain retrograde motion, or the "aether" to explain wave propagation. ←Baseball Bugs What's up, Doc? carrots→ 11:58, 22 September 2019 (UTC)

:::::One of the reliable features of aether models of light and Ptolemaic epicycles is that they only made accurate predictions of things already observed. The moment new phenomena were available for measurement, whether through the invention of increasingly precise methods, or simply the passage of time. Basically, "we will continue to see what we have seen, until you look for something new, at which point we will have to change the model again." The Standard Models of Quantum Mechanics and Cosmology have a lot of open questions, gaping holes, and possible inconsistencies. But unlike those earlier theories, they are not utterly useless, and instead manage to accuratly predict some things in advance. Someguy1221 (talk) 12:12, 22 September 2019 (UTC)

:::::I understand this feeling, and even somewhat feel it myself about dark energy, but, then again, dark matter is NOT something you use to turn a broken model into a working one. Aether was not, either: experiences could be (and were) designed to actually measure how the Earth fared in the hypothetical aether, and after these it was concluded it couldn't exist. The same work is currently done on dark matter, bearing results. That is the opposite of tricks used to save a broken model. Gem fr (talk) 00:33, 25 September 2019 (UTC)

The earliest successful models of spiral galaxy formation, though they did not literally assume the existence of a supermassive black hole, actually contain one in the mathematical model Basically, there happened to be a hypothetical mass distribution close to observed distributions that permitted analytical solutions and happened to have a singularity of finite mass at the center. Those models also did not attempt to explain the formation of the galaxy itself, only the formation of spiral arms within an existing galaxy, and the assumed mass distribution was made to match observation as well. So the answer to your question is that the models worked quite well, in fact, but could not explain the assumed initial conditions. Someguy1221 (User talk:Someguy1221talk) 06:22, 22 September 2019 (UTC)
  • It may be best to think of the place we are with Dark Matter is akin to where we were with regular matter in the pre-20th century days. That is, we know it exists, we know its effect, we even know where it is. We're just not all that sure what it is made of. Just as we knew that matter existed prior to modern atomic theories, and we knew how matter behaved, we just didn't know what it was made of (protons and electrons and quarks and stuff like that). Similarly, we're at that same state with "dark matter". We're pretty sure it exists, we know what effect it has on the universe, we know how it is distributed. What we don't know is what it is made of. Is it normal baryonic matter? Is it some new, exotic type of matter? We're not entirely sure on that part, though we're working on it. --
    08:26, 26 September 2019 (UTC)

    Restoring contacts corroded by Alkaline battery leakage

    Potassium hydroxide leak from alkaline AA-cells corrodes the nickel-plated spring contacts in a battery holder. How should they be cleaned? DroneB (talk) 18:25, 22 September 2019 (UTC)
    One caution, that dried acid base becomes active again once it contacts moisture, as in your eyes or on your skin, so safety glasses and gloves are advised, and wear old clothes you don't mind having damaged. You might try using an old toothbrush on it outside (tossing it out after), so all the dried acid base goes in the grass. But if you have pets or children who might play there, you would also need to lay down rags to collect it. If the toothbrush doesn't work, try a metal brush. They actually make one for cleaning car battery contacts, but that won't have the right shape to work here. Note that I am assuming the contacts are still usable, just coated in dried acid base. If they've actually dissolved, then you would need to replace the device. Also, if the device was stored with the battery above the electronics, the acid base may have drained into the electronics and ruined them. SinisterLefty (talk) 18:46, 22 September 2019 (UTC)

    Potassium hydroxide is an acid (incredulous) ? DroneB (talk) 21:00, 22 September 2019 (UTC)

    ::Oops, I was thinking of cleaning lead-acid car battery terminals when I wrote that. Fixed now. SinisterLefty (talk) 04:04, 23 September 2019 (UTC)

    :But seriously, with an alkaline battery, try cleaning with a mild acid, eg: vinegar (and an old toothbrush that you'll throw away when done). 2606:A000:1126:28D:B0BD:7B01:D644:98D4 (talk) 03:29, 23 September 2019 (UTC) ... Here's a "How To" video: https: // ←remove blanks

    ::The video may not be what you intend. DroneB (talk) 10:21, 23 September 2019 (UTC)

    and , based on your previous answers on these topics, you two seem to have a level of expertise in this stuff; what are your suggestions? Eliyohub (talk) 13:05, 23 September 2019 (UTC)

    :Damaged batteries should not be "cleaned"; they should be safely disposed. Consult local regulations for safe disposal. Even a small number of consumer batteries are a hazardous material - and if they are leaking or corroding, this is especially important.
    :If the battery cell or pack is corroding, it is a symptom of some other damage - either internal or external to the battery. Perhaps there is an electrical fault, short-circuit, over-current condition, thermal or environmental problem, puncture or mechanical damage inside the cell, whatever it is ... simply removing the existing corroded material is not going to repair that problem. The cell is now delivering an unknown and uncontrolled electrical voltage and current, and could cause further electrical or chemical damage.

    :Here is the California Recycles! website about safe battery disposal. Your local area may have different rules.

    :Quoting the CalRecycle Public Service Announcement:


    :Nimur (talk) 16:19, 25 September 2019 (UTC)

    ::He isn't trying to fix a corroded battery. He is trying to fix the corroded contacts that a leaking battery ruined. Thus the section title "Restoring CONTACTS corroded by Alkaline battery leakage". --Guy Macon (talk) 16:47, 25 September 2019 (UTC)

    Indeed I am am somewhat of an expert on this. Do a Google search on GMCFESIL.
    For your specific problem:
    Step one: unless you are dealing with a dollar store calculator, $2 flashlight, etc., throw away all of your existing batteries and replace them with Energizer Max. If it takes a long time to drain the battery (clock, calculator, TV remote) use the lithium. If it goes though batteries fairly quickly (LED flashlight), use the leak-resistant alkaline. If it really eats up the batteries, use the rechargeable. Duracell used to be the best, but the quality has dropped considerably in recent years.
    Step two: To really do a proper job cleaning something that already has damage from a leak, you really need to disassemble it and possibly desolder some wires to isolate the damaged part so that you can get it really wet. After that, soap, water, a toothbrush, and lots of rinsing under a flowing faucet followed by a flush with 91% isopropyl alcohol is the way to remove the acid/alkaline.
    It is possible to electroplate corroded contacts. If you are dealing with a valuable bit of vintage electronics, look into having someone do this for you. --Guy Macon (talk) 14:03, 23 September 2019 (UTC)

    IMO for AA and AAA batteries most purposes it's better to simply use low self discharge NiMH. You may have to change your remote etc batteries a little more often, but you should expect at least 2 years and probably longer. An exception is any devices which really can't cope with the the voltage of NiMH and either don't work or have very short life spans been recharges. And maybe emergency torches you rarely use although frankly you probably should check them every 2 years or so whatever you use so even those are a bit iffy IMO. For some high drain devices you may want the 'high capacity' LSD instead.
    Price wise, the NiMH could even end up cheaper (discounting the charger) considering the price of Energizer batteries in many countries, especially the lithium. As for spares, if you use NiMH for everything you're likely to have a few that are at most a few months since recharged and should be fine for nearly all purpose. Speaking of chargers, do make sure you have a proper smart charger. Preferably something that isn't excessively fast, but note what I said earlier; a dumb trickle charger is no good either.
    Eneloop made in Japan are generally recognised as the best NiMH, helped by the fact that they were the first real LSD. The AmazonBasics 8 pack AA or AAA which say they are "Pre-Charged using Solar Energy" and are generally black appear were once considered likely rebrands possibly of older versions made in Japan Eneloops although of course there was never official confirmation and this is even more unclear as some of these are marked made in China now. (The cheaper 16 AA or 12 AAA AmazonBasics which generally have a white label nowadays and AFAIK have always been marked as made in China.)
    But in any case, IMO people tend to overplay the difference, for many purposes any real LSD will do. (See e.g. // but note as with many such tests it seems to suffer from a lack of repetition and replication. Testing one or two sets of batteries purchased at around the same time may not give you a good idea how that brand actually performs.) E.g. Maha Imedion, the Hobby King Turnigy LSD. Just stay away from some eBay crap where you aren't sure if it's really LSD or just some manufacturer in China heard that marking their batteries as LSD would be a good idea.
    Nil Einne (talk) 07:09, 24 September 2019 (UTC)

    I think that white stuff can be dissolved and cleaned up with household ammonia. At least that works for similar looking crap leaked by old fashioned zinc-carbon cells. (talk) 07:49, 24 September 2019 (UTC)
    Please tell me that you removed the vinegar afterwards with a distilled water or alcohol flush. Vinegar is an acid, and the unseen residue will eat away the circuitry and any metal parts. --Guy Macon (talk) 07:47, 25 September 2019 (UTC)

    Yes I did. DroneB (talk) 13:46, 25 September 2019 (UTC)

    :Friends, household "kitchen chemistry" might "work", but it's not recommended by reputable sources.

    :You do not know what metals or chemicals are in the consumer-grade batteries that you buy in retail stores. You do not have an MSDS; you do not know what is inside, under the plastic-sticker they slapped on at the mass-production line that you know nothing about. You are "off-chart," and you are doing something unsafe when you are trying to repair a damaged battery.

    :Safely dispose of the damaged cell(s) and replace them with functioning units.

    :A little bit of "mildly corrosive water-based solution", plus a little bit out-of-spec battery on an only-slightly-unreliable domestic electrical supply can easily cause a fire that can very quickly kill some very smart engineers - people who could probably have out-analyzed your kitchen-chemistry if they were still around today. Just don't do it. Consumer-toy batteries pack a lot of thermal/chemical/electrical energy, and frankly, if you're soaking batteries in vinegar, you just aren't damned smart enough to handle this power.

    :Nimur (talk) 16:32, 25 September 2019 (UTC)

    ::WHOOOOSH! Read it again. He isn't trying to fix a corroded battery. He is trying to fix the corroded contacts that a leaking battery ruined. And why the totally irrelevant links? --Guy Macon (talk) 16:47, 25 September 2019 (UTC)


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