Wikipedia:Reference desk/Archives/Science/2016 June 2

= June 2 =

"oxygen glass" string?
(I don't know if I can be back)

49.135.2.215 (talk) 01:11, 2 June 2016 (UTC)(Like sushi)


 * What is the question? The Quixotic Potato (talk) 04:36, 2 June 2016 (UTC)


 * You keep saying you won't be back, and you keep coming back. How about instead of asking new questions when you come back, you actually ask a complete question with enough context so people here know what you are talking about.  It's hard to provide you with references when we don't even know what you are asking.  -- Jayron 32 02:45, 3 June 2016 (UTC)
 * Glass fiber and fibreglass. For amorphous solid oxygen see http://people.virginia.edu/~rej/papers-scan/cuietal-IntJQC89.pdf Graeme Bartlett (talk) 03:28, 5 June 2016 (UTC)

Orbital mechanics
Is it possible, from the perspective of orbital mechanics, to visit all the planets in the order in which they appear in Gustav Holst's The Planets? If so, approximately how long would such a mission take, from launch to Neptune fly-by? 2601:646:A180:C88C:F88D:DE34:7772:8E5B (talk) 05:01, 2 June 2016 (UTC)

The starting date will have a crucial effect on the time taken, as will the delta v of your spaceship, since a sufficiently fuelled ship can ignore orbital mechanics and just blast from planet to planet. You may be interested in Interplanetary Transport Network Greglocock (talk) 06:27, 2 June 2016 (UTC)


 * As far as delta-V is concerned, let's assume the largest delta-V possible with today's technology. 2601:646:A180:C88C:F88D:DE34:7772:8E5B (talk) 07:16, 2 June 2016 (UTC)


 * It's certainly possible; you just need enough thrust. It's an engineering problem. You'd probably want to use something efficient like a solar sail or ion thruster, though this means your journey will be more leisurely. Here's a video analyzing Breakthrough Starshot, something even more ambitious. --71.110.8.102 (talk) 08:06, 2 June 2016 (UTC)


 * Unfortunately, making the trip longer in a manned ship means you need more food, water, oxygen, electricity, and shielding (to protect from radiation), all of which adds weight, meaning you need more fuel or sail to propel it all, and more fuel or sail to propel the additional fuel or sail, etc. It quickly spirals out of control. StuRat (talk) 13:07, 2 June 2016 (UTC)


 * Actually, my question was for an unmanned probe, because it's not possible to perform a manned mission of this length with today's technology. 2601:646:A180:C88C:F88D:DE34:7772:8E5B (talk) 00:48, 4 June 2016 (UTC)


 * OK, time is less critical then, but more time does still require more shielding for the electronics to survive radiation and micrometeorites, and a bigger power source, to last longer. StuRat (talk) 03:04, 4 June 2016 (UTC)


 * There isn't a movement for Earth - so presumably you cannot start from here. That is really going to complicate things, as you will have to build your ship on Mercury! 86.191.126.192 (talk) 08:35, 2 June 2016 (UTC)


 * No, according to The Planets, Mars is where you'd have to build it. Hmm.  Maybe we need to study The Martian . --69.159.60.83 (talk)  —Preceding undated comment added 11:09, 2 June 2016 (UTC)
 * Here is the voyage itinerary listing each planet to visit with the planet's greatest distance from the Sun expressed in AU or multiples of the distance from the Earth to the Sun.
 * Mars, 1.666
 * Venus, 0.728
 * Mercury, 0.467
 * Jupiter, 5.455
 * Saturn, 10.086
 * Uranus, 20.11
 * Neptune, 30.33


 * As a passenger you may take photographs of each planet but don't remain Saturn Uranus for too long or you will get Asteroids.                     AllBestFaith (talk) 13:07, 2 June 2016 (UTC)

this user enquires the specific process via which, viral hepatitis performs temporary relapses when the patient performs physical movement contrary to bed rest
knowledge should be discovered quickly in universeFAMASFREENODE (talk) 14:45, 2 June 2016 (UTC)
 * See the article Hepatitis and the section Hepatitis. AllBestFaith (talk) 18:22, 2 June 2016 (UTC)

Caterpillars on my gooseberry bush
I have a lot of small, green caterpillars on my gooseberry bush, and I'm trying to identify them. They are small (about 10-15mm long), green (the same shade as the leaves, with no obvious markings). At first I assumed theywould be some sort of sawfly larva (probably Small or Pale, judging by the description). However, all the sources I've found say that the sawflies pupate in the soil. These caterpillars roll up the leaves and pupate inside them. Can anyne ID them for me? Iapetus (talk) 18:29, 2 June 2016 (UTC)


 * Was it "inching" along in inchworm style? Do they look like this ? That could indicate Geometridae. But also maybe look at the cabbage loopers and kin in the Noctuidae. I think the former family pupates in leaves, and at least some of the latter do . The problem with size of caterpillars is they can go through tons of instars, and even giants were once tiny. Are you saying the pupae are also 10-15 mm? Also where in the world is this? SemanticMantis (talk) 18:48, 2 June 2016 (UTC)
 * Location is SW England. They do look similar to the first image, although I think they have more pseudopods (although I haven't checked closely, and haven't seen any for a few days - I think I've got rid of them all).  I'm not sure how they move, because I rarely see them do (they just sit right on the edge of the leaves and eat them).  If disturbed, they'll sometimes grip the leaf with their pseudopods and rear up / curl up / wave their front around.  10-15mm seems to be the maximum size they reach.  The pupae are smaller - about 7mm.  They only affect my gooseberry bush - I have broccoli growing close by and they don't touch that.


 * This forum has larvae matching your description, however it's in Canada (but maybe the fauna travels with the flora). Identified by somebody as a "current worm" from a sawfly. If you fancy something more scientific, Arthropod pests of currant and gooseberry crops in the U.K.: their biology, management and future prospects by the Scottish Crop Research Institute has a list of coloured plates in the appendix and might be a good read if you are having difficulty falling asleep tonight. Alansplodge (talk) 22:19, 4 June 2016 (UTC)

Occupying Territories
I know humans occupy a lot of territory, so much that non-human animals are losing their natural habitats and being forced to live in wildlife parks and in human neighborhoods. But what if there is a population of humanoids existing on a fertile patch of soil, and neighboring humans want the land? Will the population of humanoids be forced to assimilate into the human society and interbreed, or will the population of humanoids be eliminated by killing, or will the population of humanoids be protected like other wildlife? 198.30.87.2 (talk) 18:30, 2 June 2016 (UTC)


 * Please identify the Humanoids concerned so that someone can point out that the Ref. desk won't provide predictions or legal advice. AllBestFaith (talk) 19:00, 2 June 2016 (UTC)


 * Never mind. I just thought of the answer, even though there have been many instances in history where the three mentioned situations have all been done. 198.30.87.2 (talk) 19:08, 2 June 2016 (UTC)


 * I assume the OP is using the term humanoids to refer to groups of our species homo sapiens who are of a “different” culture. Examples may be Neanderthalians, Celtic tribes in Europe, Amerindians or the Ainu.  Arguably, all three scenarios mentioned by IP 198… have been “deployed”.  --Cookatoo.ergo.ZooM (talk) 19:44, 2 June 2016 (UTC)


 * Neanderthals (and Denisovans) were actually different sub-species. Replacement (either through extermination or by out-competing) happened, as did interbreeding (some of that may have been rape).  But if there was any attempt to "preserve" those two, it obviously didn't work, as they are long gone (except some DNA mixed into our own). StuRat (talk) 20:12, 3 June 2016 (UTC)

What's the least radiation pressure detectable with no instruments or spaceflight?
What's a good test for this?

Fire a laser at gold foil hung in a vacuum and see if moves? Fire pulses at the sky at various hertz and see if you hear (or feel?) anything? Is there a way to distinguish the sounds of air/ionized air expanding from the momentum of light pushing the air? How damaging is a beam that shows the momentum of light? Sagittarian Milky Way (talk) 23:27, 2 June 2016 (UTC)
 * See the Nichols radiometer, which was a sort of torsion balance which, over 100 years ago was used to measure relatively small radiation pressures. -- Jayron 32 02:43, 3 June 2016 (UTC)

Laser guns
I've always wondered how powerful traditional space opera laser guns could get before they reached genre-breaking wattages. The smallness, efficiency, and storage capacity may be near-magic but I want a real life physics laser beam after the muzzle. First of all I assume a laser beam that causes damage as fast as even the weakest guns we still fight with would burn friendly retinas if it bounced back, am I right? Even if you could afford them I don't know if perfect aim and not having to reload would make it worth it. Then again if the media is real 20th century rate of fire is already high enough that a lot of modern gunfighting is peeking around a wall and shooting a million times before you finally hit someone. And you could train fighters "close eyes, 1 second burst, open eyes" or something, have reduced power wargames till they have reflection geometry instincts, give them reflective eyepatchs, let them run from battle to a life pension if unpatched eye's destroyed. So maybe replacing a large portion of projectile guns with lasers might still be worth it.

What's the limiting factor? Is it the beam becoming so bright that it's hard to see what you're cutting or shooting pulses at? Is it heating the air so powerfully that the sound and/or heat reduces combat effectiveness more than the stronger beam helps it? (if beams this powerful would make space opera tactics suicidal let's say that either 1. Both sides wear armor that requires them 2. It's only used against lower tech planets without guns this strong)

Could you notice light's momentum with those beams and what would they sound and look and heat like? How good are they (cuts through x inches steel/concrete/humans per second, how long to boil x liters of y, many common things explode when hit or no (containers, rocks etc.), beam temperature, vaporizes so fast it's impossible to see blood or red or not quite that good at cauterizing, things like that (do non-gaseous substances who's bond breaking is exothermic explode on contact because the molecules decompose to gas like gunpowder exploding?)). How long will the best mirror shield survive and how much damage could the reflected beam cause? How many watts is it? What does the beam do to the air? Sagittarian Milky Way (talk) 23:51, 2 June 2016 (UTC)


 * Why not look at the website of the Air Force Research Laboratory's Directed Energy Directorate? They study military applications of laser light sources; as part of their mission, the Directorate "develops and transitions technologies in four core technical competencies: lasers systems, high power electromagnetics, weapons modeling and simulation, and directed energy and electro-optics for space superiority."
 * In reality, the biggest limiting factors are that lasers are less effective than conventional weaponry for most purposes; very powerful lasers are surprisingly inconvenient; and there are all sorts of legal, ethical, and treaty-obligation- reasons that forbid the use of laser energy during many types of combat.
 * The most convincing tests I've ever seen out of DED are the Boeing Airborne Laser and the Raytheon LaWS laser product. Neither one was convincing enough to continue warranting a large amount of additional funding.  Some obvious problems with both systems pertained to targeting accuracy; the incredible engineering challenges of sustainably delivering such quantities of optical energy and power; and the general assessment of their utility - especially in competition with more conventional weapon systems.
 * In the United States, our military and our government also have an obligation to uphold the 1980 Protocol on Blinding Laser Weapons - part of the Convention on Certain Conventional Weapons as well as many other international agreements. These agreements forbid our military from using unnecessary cruel and unusual weapons during warfare.  For the most part, this means that our military will not field laser weaponry in combat.
 * Nimur (talk) 03:41, 3 June 2016 (UTC)
 * Defense Secretary Robert Gates, who reined in a lot of ... ridiculous military expenditures that were encouraged by his predecessors..., had this to say about the Airborne Laser:
 * "There's nobody in uniform that I know who believes that this is a workable concept," as quoted in Nature, (2012), "Secret Weapons."
 * One may presume that some percentage of those 87 billion dollars - ostensibly approved as an emergency-measure to win the war in Iraq, including $65 billion to fund undisclosed classified military activities - probably helped pay for fuel on the laser airplane. Either way, those 87 billion dollars surely didn't end the war in 2004.  Nor have any of our major operational successes depended on infantrymen armed with laser rifles.
 * I have always suggested that our best and most cost-effective military technology strategy would have been to air-drop 87 million iPods. In the statistical aggregate, the average enemy combatant, faced with the choice between the horrors of war, and chilling out with two free iPods, would opt to remove himself from the fight... and we could use the left-over laser budget to airdrop some disco lights... win without fighting!  But hey, what do I know about military strategy?
 * Nimur (talk) 03:50, 3 June 2016 (UTC)


 * As for the issue of protecting eye from reflections, there's a simple solution to that. Lasers only produce light at one particular wavelength/frequency, so you can wear eye protection that blocks that frequency only, and still see fine using all the other frequencies.  Of course, if the laser were pointed directly at your eyes, it would burn a hole through the eye protection, and then through your head. StuRat (talk) 19:20, 3 June 2016 (UTC)


 * Also, just to point this out, real lasers don't look like the "blasters" common in science fiction/fantasy. You can't see a laser beam unless it's either aimed right at you, or there's stuff like dust in the way of the beam that scatters some of the laser light into your eyes. One of the things that makes a laser a laser is that the light it produces is collimated; all the photons are traveling in the same direction. For you to see something, light from that thing has to enter your eye. You may have noticed that you can't see the beam of a laser pointer (again, unless there's stuff in the way that scatters some of the light). See the picture for another example. The glowing thing is the fluorescent light source for the laser, not the laser itself. Note that the laser beam isn't visible, only the spot where it hits the target. On the broader topic, you might find this TV Tropes page interesting. --71.110.8.102 (talk) 19:54, 3 June 2016 (UTC)


 * I've heard there's a power level above which the air in the beam is ionized, thus showing the beam's location (which makes sense, that has to happen eventually). Sagittarian Milky Way (talk) 23:43, 3 June 2016 (UTC)


 * Let's look at practical technology.


 * The 100 watt CO2 infrared laser in my laser cutter would cause really nasty burns at distances of tens of meters - at 5' long by six inch diameter, it's on the upper limits of what you could fit it into a large rifle-like gun. The laser's 30,000 volt power supply is pretty inefficient though - you'd need to supply about 600 watts to power it.  A standard laptop battery (15 watt/hours), would power it for about 90 seconds - maybe enough to pull off a couple of dozen decent shots.
 * I don't think you could kill someone with this - the range is pretty terrible. I don't think it would be better than a regular rifle, or even a handgun.
 * To drill holes through people with an efficiency comparable to a bullet, you'd need a more powerful laser - but not too much more. A 3000 watt laser can cut steel - so maybe a 1000 watt laser would be lethal - and a backpack with a couple of dozen laptop batteries would give you a reasonable number of shots.
 * The IR laser would be completely invisible and wouldn't harm the shooter at all.
 * In the end, the question is more about the power source than the type of weapon. Explosive charges are a pretty dense energy source (3 to 5 MJ/kg) but a lithium/air battery is more like 8 to 9 MJ/kg - so propelling bullets using an electrical system seems like a better bet for futuristic weapons - hence "rail guns" and similar tricks. SteveBaker (talk) 02:50, 4 June 2016 (UTC)
 * Fascinating figure! I looked up TNT and it is 4.1 MJ/kg; gunpowder is only 3!  Dynamite it adds is 7.5, but gasoline - not counting air - is 47.2.  So a potato cannon is, by rights, one of the most futuristic weapons available; we just need to respect it more and hone it into deadly form.  Still amazed at those lithium batteries - and just think that someday, when the right computer virus is deployed, most of them will be going off all at once. Wnt (talk) 13:07, 4 June 2016 (UTC)


 * In space, at long distances, speed may be critical, though. By the time your projectiles hit the target it may have already fried you with a laser, so you'd best use a laser, too, or something else that travels at the speed of light, if you hope to disable the enemy ship and survive the encounter.  Also, firing projectiles in space would cause the ship to move, unless countered by an opposing force. StuRat (talk) 03:00, 4 June 2016 (UTC)