Wikipedia:Reference desk/Archives/Science/2015 February 23

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February 23

brightness of an inferior planet

Suppose you have in inferior planet like Venus. Assume that the planet orbits are circular and in the same plane. What is the equation of the apparent brightness of the inner planet as a function of where it is in its orbit? (When it is more than 1 AU away, more of it is lit but it is farther away, etc.) Bubba73 ^{You talkin' to me?} 02:12, 23 February 2015 (UTC)

Well, there's one formula for how brightness reduces with distance, another for what phase the body is in relative to Earth, and then the average insolation angle must also be considered. That is, is the sunlight reflected towards Earth from sun rays that hit the planet straight on, and are thus bright, or at a shallow angle, and are thus dim ? I suppose the average reflectivity of the place on the planet reflecting light towards Earth should also be considered, if it's not uniform for the planet. Mars has more reflective polar caps, but neither Mercury nor Venus do. StuRat (talk) 06:15, 23 February 2015 (UTC)

And assume that the planet is uniform. Bubba73 ^{You talkin' to me?} 08:24, 23 February 2015 (UTC)

I am really curious. What makes a planet inferior? That is a term I have never heard of when referring to a planet. 175.45.116.60 (talk) 22:29, 23 February 2015 (UTC)

I think every planet is inferior to the Earth. :-) But astronomically it means that it orbits closer to the sun/star. In our case, Venus and Mercury are inferior planets, see Inferior and superior planets. Bubba73 ^{You talkin' to me?} 00:35, 24 February 2015 (UTC)

• What will matter is the cross section of the plant visible, the planet's albedo, its distance from the sun (how much light is hitting it--which you are assuming is a constant, given a circular orbit) and how far from the earth it is (how much of that light is getting here. The lessening of the brightness will differ by the square of the distance. For an exact mathematically written formula you could pose this at the math desk. μηδείς (talk) 22:39, 23 February 2015 (UTC)

The actual albedo doesn't matter since it is assumed to be constant. Years ago I thought about working this out, but never got around to it. Maybe someone knows the answer to a simplier version - when is the inferior planet the brightest? Bubba73 ^{You talkin' to me?} 00:35, 24 February 2015 (UTC)

Well, yes, the albedo's constant, but two planets at the same distance will have different relative brightnesses as seen from earth if they have different albedos. In any case, I suggest you ask at the Math Desk, as someone will very quickly come up with an actual equation for your specified parameters.

(For example, I had an argument once over whether it made sense to run between shelters in a rainstorm. I argued that all other things being equal, the less time spent in the rain, the less wet you will get. But then we considered the effects of angle of attack. If you have a glass plate 1 meter square of negligible thickness (approximating an ideal windshield) and the plate is held horizontally and moves at a slow speed it ill get much wetter on the surface than a vertically held plate.

Paradoxically, if the plate is moving at the speed of light between shelters, it will get wetter when held vertically, because it will "scoop up" all the drops in front of it, whereas if held horizontally, it will get between shelters before many, if any drops can manage to fall on it. I posted that scenario at the Math Desk and quickly got a response that gave an answer for accumulated wetness depending on angle, speed and volume of rain per cubic meter and the angle and speed of the windshield.) μηδείς (talk) 18:27, 24 February 2015 (UTC)

Oh, an as to when the planet will appear brightest in the simplified question is a minimax equation that will be a function of the relative angle to the sun. As the planet gets closer to the earth it will shrink in appearance from a crescent to only showing the dark side when the angular difference is zero. As the angular distance increases, the amount of reflective face visibe t the earth will increase, but the brightness that reaches the earth will lessen in proportion to the square of the increasing distance. I don't know myself how to calculate the area of the visible crescent, so for the exact formula, again the Math Desk will be of help. μηδείς (talk) 18:35, 24 February 2015 (UTC)

Well, I found equations for the actual brightness of the planets in Astronomical Algorithms, by Jean Meeus, chapter 41. Bubba73 ^{You talkin' to me?} 19:15, 24 February 2015 (UTC)

OK, then let's mark this Q resolved. StuRat (talk) 19:23, 24 February 2015 (UTC)

Resolved

Did the speed of light been a constant in nature?

The speed of light is been a constant only in the inertial closed physico-mathematical systems in which the observer and the light source are moved simultaneously, is it been so? I’m thinking that the speed of light in nature had an initial speed and final speed, is I’m right?--83.237.203.228 (talk) 11:27, 23 February 2015 (UTC)

Read the article speed of light if this topic interests you. --Jayron32 12:08, 23 February 2015 (UTC)

Thanks! I’m assume that the speed of light is been a constant only in the case where the light source to constantly been in front of the observer.--83.237.244.173 (talk) 13:18, 23 February 2015 (UTC)

Someone asked a similar question a while ago. It seems to depend on whether the light spectrum is an idea of optical or magnetic. I haven't seen that guy around in a while, but if you find him, he may be able to elaborate. InedibleHulk (talk) 13:31, 23 February 2015 (UTC)

In anyway cases, problems with the speed of light is always been solving in aggregate systems.--83.237.244.173 (talk) 13:36, 23 February 2015 (UTC)

Like the gravel industry? Yes, asphalt can create some breathtakingly inferior mirages. Turns heat to water, at least as far as our optical systems are concerned. No electrical resistance, though. InedibleHulk (talk) 13:50, 23 February 2015 (UTC)

I'm talking about the fact that the study of the light is always been conducted in aggregate (totally) systems, that's why we been interested in aggregate (totally) sloving these problems.--83.237.244.154 (talk) 14:29, 23 February 2015 (UTC)

The aggregate (totality) of tasks is always been determines the solution of the problem.--85.141.236.167 (talk) 15:55, 23 February 2015 (UTC)

I have a bit of trouble parsing all of the question, but the speed of light in a vacuum (the thing we usually mean by "speed of light" and the thing thing that is constant for each observer) is constant for all observers, at least according to special relativity, which has been, to a very high degree, verified in nature. This includes unintuitive results such that two observers, one at rest with respect to a light source, and one approaching it at 1/2c in the frame of reference of the first observer will both measure the speed of a photon from that light source as the same constant c. --Stephan Schulz (talk) 16:21, 23 February 2015 (UTC)

If you watching the speed of light in different inertial systems, it will never been a constant, that's what I'm talking about.--83.237.242.202 (talk) 16:41, 23 February 2015 (UTC)

No, if you are watching the speed of light in different inertial systems, it will ALWAYS be a constant. That's the basis for the various Einsteinian theories of relativity. --Jayron32 17:56, 23 February 2015 (UTC)

As I know, Albert Einstein solved the problem of relativistic quantum mechanics in the form of the closed inertial system which represents an aggregate (totality) of inertial systems. That’s why I think that Albert Einstein is been right in his particular case of physics which was been occupy whole physics.--83.237.215.99 (talk) 18:51, 23 February 2015 (UTC)

There is been optics which based on the Laws of mechanics of the Isaac Newton, so why could exist the relativistic quantum mechanics which been based on the Laws of mechanics of the Isaac Newton?--85.141.236.229 (talk) 21:07, 23 February 2015 (UTC)

By definition, optics involves light traveling through matter. That is, something not a vacuum. The speed of light in a vacuum is the universal constant. Light slows down when it travels through matter. --Jayron32 21:12, 23 February 2015 (UTC)

I’m thinking so, the optical medium is been a closed inertial system in which there is been an observer, and also to the same state of vacuums including the state of inert sparse vacuums are been unstable, so that the vacuum state is not been the ideal physical environment.--85.141.239.130 (talk) 21:35, 23 February 2015 (UTC)

Everyone of those words is an English word, and yet that is completely nonsensical. Perhaps you'd have more success finding an "ask a question" website in your native language. It is hard for us to help correct your misconceptions when we can't tell your misconceptions from your impenetrably bad syntax. --Jayron32 00:53, 24 February 2015 (UTC)

Thank you! It is pity, but I was banned in the Russian version of Wiki. What from your point of view are being an optical mediums, it is a mediums which containing a light in self, or mediums which refract a light?--85.141.239.139 (talk) 01:18, 24 February 2015 (UTC)

What be if we assumed that in nature the optical mediums are always been conductive environments, but not been dielectric environments?--85.141.239.5 (talk) 02:41, 24 February 2015 (UTC)

As far as I know even Albert Einstein told that the cases of quantum mechanics been fully applied to the cases of conventional mechanics (mechanical movements of Isaac Newton), but I argue that this situation is been vice versa, that’s is been, the cases of conventional mechanics (mechanical movements of Isaac Newton) been generalized and complemented the cases of quantum mechanics.--83.237.242.202 (talk) 17:03, 23 February 2015 (UTC)

From my point of vision, it is been natural, that quantum mechanics is been a part of conventional mechanics (mechanical movements of Isaac Newton)!--83.237.242.202 (talk) 17:29, 23 February 2015 (UTC)

Can I recommend (again) that you seek the advice of the Language Desk on the proper use of the various parts of the verb 'to be'? It would make your posts here a lot more comprehensible. AlexTiefling (talk) 22:11, 23 February 2015 (UTC)

A Really Tall Ship, or how to "fly" a planet.

This is a question about flying an Earth-sized planet like a spacecraft.

The rules would be,

• A roughly Earth-sized planet, not a gas giant. The latter would have lots of hydrogen and helium, which would make nuclear fusion more feasible than on Earth. However, if that's easier, an existing planet like Mars could be chosen, or even a plausible planet that doesn't exist (say, one halfway between Earth and Mars).
• There should be mainly today's technologies, including everything we know but don't have in that quantity. Far future technology is forbidden; for example, with Honorverse technology and its near-magical gravity projection, flying a planet would be much easier, not to mention with Treknology.
• Large-scale application is allowed and even encouraged. The planet might have an enormous number of fission plants for propulsion; however, the fuel needed must be plausible.
• Efficiency figures can be estimated with some optimism; I'm not trying to fly away with Mars or anything based on replies on the internet. :)

The thoughts I came up with:

• A "free" planet (not in the Lensman sense, just a planet that doesn't orbit a star) doesn't need a lot of acceleration; whenever it approaches a star, its inhabitants would see that for millions of years in advance, even with today's telescopes. That would, even if they were on a collision course with a star, open a very long time window to avoid that star. One millimeter per second is about 31km per year, or 1AU in 5000,000 years, so that tiny course correction would add up to a successful evasive maneuver. The disadvantage of the free planet is that it doesn't have access to cheap fusion, i.e. a star.
• A free planet would also be much colder than Earth, and thus still have more hydrogen / helium in its atmosphere.
• A "bound" planet like Earth could possibly use the solar wind to its advantage and slowly spiral in or out. Out being the way to go to counter solar expansion, but would it be fast enough? What I'm thinking of is a magnetic "sail" , a shaped magnetic field which deflects more particles to the direction from where the planet came than where the planet is going, and thus providing net momentum change. That would add to orbital velocity and cause the planet to spiral away from the star.

My question is if there are estimates, or maybe even scenarios on these cases, and if there are acceleration and/or delta v figures for bodies which fit my criteria. Or maybe some fatal flaws which would make my ideas fall flat.

Thanks in advance. 217.255.147.211 (talk) 15:47, 23 February 2015 (UTC)

For a planet without an atmosphere (including where the would-be atmosphere is frozen or liquid), I like the idea of coilguns, pointing up from the surface. You could mine the planet for iron, accelerate it to the speed of light, and fire it in whichever direction you want to flee from. You'd have one main (fixed) coilgun, and smaller ones, which could be tilted, for maneuvering. Nuclear fusion would be a good power source. StuRat (talk) 16:05, 23 February 2015 (UTC)

(deleted - OP)

I didn't want any treknology or "accelerate it to the speed of light" magitech. See item #2 217.255.137.5 (talk) 08:08, 24 February 2015 (UTC) (OP)

That's not the way to comment on a reply even if it's off. StuRat probably meant "relativistic velocity". And he was talking about accelerating the iron to that kind of velocity, not the planet itself. Still a bit energy-intensive, though. - ¡Ouch! (^{hurt me} / _{more pain}) 09:27, 24 February 2015 (UTC)

Correct on all counts. OP, if you continue to behave like that, we may delete your Q and ban you from asking any more. StuRat (talk) 19:27, 24 February 2015 (UTC)

With enough guns, they need not even swivel. Most of the time, I imagine, "fire whenever the target acceleration vector is below your horizon" is enough control. —Tamfang (talk) 20:24, 24 February 2015 (UTC)

If none of the guns were tilted, then each would push the planet along a different vector, but none would rotate it so that the main gun could be used. You could have multiple guns with different tilt angles, as opposed to a smaller number (even just one) that swivel, but that would mean the vectors wouldn't be perfect, so you would waste some energy and matter that way. However, if making guns that can swivel is problematic, that might be the preferable solution. StuRat (talk) 20:31, 24 February 2015 (UTC)

You might find some fun stuff at this TV tropes page [1]. Lots of refs to sci-fi media, many of which at least wave their hands at the physics. SemanticMantis (talk) 17:45, 23 February 2015 (UTC)

I was thinking myself about Unicron. --Jayron32 17:54, 23 February 2015 (UTC)

These are fun. However, most depictions are just "bigger is cooler" stuff. In one old Japanese movie (1950s or early 1960s, and it's not listed at Planet Spaceship#Film), they used some huge chem-thrusters to move Earth, within months. 217.255.137.5 (talk) 08:08, 24 February 2015 (UTC) (OP)

• Alright, Earth gives you the problem figure: 5.97219×10²⁴ kg = 3.0×10-6 solar mass (The latter is actually pretty amazingly high, when I think about it). To move that course, say, a km in a million years means an average transverse velocity of 1 mm/year (plate tectonics manages speeds this high, but only for thin little bits of crust, not the whole planet). That's an acceleration of ( 2 mm/year )/10^6 years (the 2 comes in because it only has top speed at the end...) So we need a force F = m a of 6 x 10²⁴ kg * 2 x 10^-6 mm/yr² = 1.2 x 10¹⁹ kg mm/yr². Now substitute 1 mm = 10^-3 m and 1 yr = (365.25)(24)(60)(60) s and we get ... 12 kg m / s^2 ?!. Hmmm, that's pretty remarkable. We're talking about, like, 1.2 kg of weight tugging on the planet continuously for a million years. Either I fouled up or this is more doable than I thought. Still, we have to bear in mind that to avoid a star you can't just move the planet by one km, but by some significant proportion of an astronomical unit, i.e. millions of kilometers. I think I'll pause and wait to be found out for an idiot before going on. Wnt (talk) 18:00, 23 February 2015 (UTC)

No it is quite practical, see [2] for instance. It won't turn the earth into a nippy Star Trek type spaceship but it could be used to for instance move the earth out to a safe distance as the sun gets hotter near the end of its life. Dmcq (talk) 21:08, 23 February 2015 (UTC)

IIRC, Master of Orion was the first computer game to feature a planet-sized starship. It was called "The Guardian". Coincidence? - ¡Ouch! (^{hurt me} / _{more pain}) 09:27, 24 February 2015 (UTC)

I was looking at a different approach: install some fission plants, power some big, probably city-sized ion thrusters and fire them when they are pointing the right way. This only assumes that the planet rotates at all, and doesn't have an atmosphere. For north/south maneuverability, one would need half a dozen thrusters and good timing. At the exhaust velocity of ion thrusters, vaporising the iron, or whatever, is only a minor power/efficiency issue before accelerating.

However, that "let a comet pull Earth forward a bit, and recharge it by letting Jupiter pull it" idea sketched in The Guardian looks really elegant. 217.255.137.5 (talk) 08:08, 24 February 2015 (UTC) (OP)

(H:EC)Earth is about 6*10²⁴kg, so we need about 6*10²¹kg m/s of momentum to get that 1mm/s velocity change.

It's well known that you need less reaction mass if you throw it out faster; OTOH, we're on a limited energy budget (again), and throwing it faster will use much more energy (4 times for doubled velocity).

OTOH^2, if we don't achieve escape velocity, which is about 11km/s, we won't change Earth's momentum, because the ejecta will return. It'd be a closed system.

The details are complicated, but an exhaust v which slightly exceeds escape v will result in a momentum change which depends strongly on how slightly we exceed escape v. I'll use 16.8km/s (1.5 times Earth's escape v ) from now on, which will result in about 12.6km/s "final" velocity.

So, we need to eject about 4.8*10¹⁷kg to get the desired delta v of 1mm/s.

Putting these together, we get m/2 v² = (2.4*10¹⁷) (2.8*10⁸)kg (m/s)² = 6.7*10²⁵ J.

One Joule is one watt-second, so 3.1*10⁷Ws are a watt-year, and 3.1*10²²Ws are a million gigawatt-years. If we could run 2200 gigawatt plants for one million years, we could eject all the matter necessary for 1mm/s.

With a bit of luck, we would invent a fusion plant before our fission fuel runs out. (With today's technology, we only have two sources of power: fusion and fission. Everything except fission fuel is ultimately solar fusion energy if you go all the way back. And solar fusion wouldn't be available on a rogue planet (that's what you called a "free" planet). I assume you don't want me to invent things as exotic as a p-brane tap, which would provide essentially unlimited energy.)

For a rogue planet, any encounter with a star is an opportunity; the closer you get, the more it will deflect your course. If you get close enough, you can use an early course adjustment in the range of mm/s to get a deflection in the km/s range.

"All I ask is a tall ship, and a star to swing her by." - ¡Ouch! (^{hurt me} / _{more pain}) 09:27, 24 February 2015 (UTC) BTW, I like that word. "Treknology".

Fun though this is, the Reference Desk isn't really here to engage in speculation. This question would be better asked of Randall Munroe in the "What If" section of his xkcd comic strip. RomanSpa (talk) 09:05, 24 February 2015 (UTC)

I suppose this is a valid RD question. For one, the IP didn't ask for speculation, nor "But what if we tried more power?" - ¡Ouch! (^{hurt me} / _{more pain}) 09:33, 24 February 2015 (UTC)

I think it's possible to defeat the OP's suggestion of using a thruster that is timed to fire only when the planet rotates into the right position, but alas, my physics-fu feels weak today. I'm thinking that there's no obvious drawback to realigning the rotation of a rogue planet however is convenient; and of course what's convenient is to have one pole facing in the direction you intend to thrust so that you can fire your thruster 24/7. (If you're using thrusters that is) Problem: how much energy does it take to realign a planet's axis? Well... I'm thinking it's not energy, but angular momentum... in theory, you ought to need very little energy I think, provided you're able to throw off enough sheer mass of propellant (because KE = 1/2 mv^2, but momentum is just mv, in this case multiplied by the torque arm) But what the practical minimum is, assuming some grand space elevator, balancing KE vs. lifting energy vs. escape velocity... that I don't know. It's also worth noting that angular momentum changes can sometimes be put on a planet from a fairly long range, as with the precession of the Earth's axis, and I don't know how clever and creative you can be with that. I'm thinking a better answerer could come up with a calculation to put those timed rocket firings right out of your mind, but that's just a guess. Wnt (talk) 23:01, 24 February 2015 (UTC)

The problems with using a thruster only when the planet rotates into the right position:

1) The thruster will only move in a circular pattern (well, precession of the equinoxes may eventually move it in a broader band, but that would take thousands of years). There's no guarantee that the direction they want will lie on that circle.

2) Obviously, you'd only be able to use the thruster a small portion of the time. This means either you would accelerate much slower, or you would need a far bigger thruster.

3) Turning the thruster on and off might create annoying tremors around the site, and eventually cause structures to crack and fail. (Presumably any thruster would need to be turned on and off periodically for maintenance, but hopefully not once a day.) StuRat (talk) 23:11, 24 February 2015 (UTC)

1) That's why I had a dozen or so in mind, not just a single thruster; that way, I could use a combination of the thrusters that come closest.

2)Yes, that would definitely be an issue, but I could use it for 6 hours a 24-hour day, if I could live with the partial cancellation of "diagonal" thrust near the beginning and the end of each burn. (Tamfang & StuRat suggested a similar approach, but with ~12 hour burns.)

3)I had a gradual ramp-up, maybe during one or two hours, and a corresponding power-off at the end in mind. I don't know if that would complicate or simplify thruster design and maintenance; maybe the thrusters don't work properly if they don't run at or near design specs? The worse angles near the beginning and end of each thrust cycle would exacerbate the diagonal thrust cancellation, too.

4)Sorry StuRat, for my rude reply yesterday. I got the "accelerate to light speed" part of your reply wrong, and overreacted. Thanks Wnt & Ouch! for the numbers. Fuel availability looks like the bigger issue; power demands look high but not prohibitive (at least if we assume high efficiency). And thanks for recognizing the "tall ship" reference.

With a captured planet like Earth, would the solar wind provide enough force to push Earth? The magnetic field idea looks quite good to me; deflecting the particles should be easier than coating Earth with solar cells. 217.255.131.112 (talk) 11:21, 25 February 2015 (UTC)

Awww hell, this isn't what you meant but you gave me an idea... Iapetus orbits about 9.5 AU from the Sun, so it gets 1/90 * 1366 W/m2 (which is what the Earth gets) * [the 2D area] pi * 735 km^2 of light on it. That's roughly 2.6 x 10¹³ watts of power. When it is going away from the Sun, it bounces half of that power back out in a roughly hemispherical pattern I won't pretend to calculate accurately; I'll pretend roughly half of that is bounced straight back at the Sun. When it is approaching the Sun almost all is absorbed. (That's because it's the famous black-and-white moon) Adding another fudge factor I'll divide by, oh, 6, because it only really gets that extra push at one edge of the orbit. So that's, oh, maybe 2 x 10¹² watts of power bounced off in such a way as to propel it faster in its orbit by light pressure. Energy = momentum x c, so 2 x 10¹² W [kg m^2 / s^3] / (299792458 m/s) = roughly 7000 kg m / s^2. Divide by the mass of Iapetus = 1.8 x 10²¹ kg and you get a steady acceleration of ... 4 x 10^-18 m / s ^ 2. To increase the moon's orbital velocity by 1 m/s it therefore should take 2.5 ¹⁷ seconds / 31557600 = 8 x 10 ⁹ (8 billion) years, which is indeed a slow, but not utterly insignificant effect. But to simply move it a meter forward in its orbit means you get to square the time, so inverting 2 x 10^-9 /s means you need, oh, roughly 16 years. But since that just moves it in a circle it's not very noticeable. :) Wnt (talk) 18:15, 25 February 2015 (UTC)

So, a Pioneer anomaly writ large? - ¡Ouch! (^{hurt me} / _{more pain}) 09:55, 27 February 2015 (UTC)

Another link that could be useful: [3]. The grav assist is the highest on their list, too. But it doesn't work on rogue planets.

The magnetic field approach doesn't sound that bad. It's very low on the qntm page, but if you made a length of wire in orbit around the Earth, it could both create a magnetic field to "grab" onto the solar wind and grav-tractor us along. Solar cells could provide the power needed.

WAIT. If we're not trying to use an electromagnet to move the planet directly, but to grab onto the solar wind and to drag the planet along by gravity, it is not really method #1 (the least plausible), it becomes method #5, which is as plausible as it gets without resulting to blunt force (#6) or the already mentioned grav assist(#7). - ¡Ouch! (^{hurt me} / _{more pain}) 09:55, 27 February 2015 (UTC)

And another relevant article: Magnetic sail. It mentions a pressure of about 0.01mPa, so you need about one km² per kg-force of thrust. A large hoop around Earth would result in billions of kg-forces, or tens of giganewtons. The article confirms that although the solar wind is weaker than sunlight, it can be "harvested" using a lighter device because it doesn't have to hit solid matter to be deflected; this could well be the way to move Earth. Oops, I'm speculating... - ¡Ouch! (^{hurt me} / _{more pain}) 10:23, 27 February 2015 (UTC)

Referencing

Am I right in thinking that when writing reports its not necessarily to reference anything that's common knowledge in that industry. So for example saying that using a clean room for any scientific experiment would reduce contamination is generally common knowledge as is using a certain type of microscope to look for certain things etc. 194.66.246.16 (talk) 19:33, 23 February 2015 (UTC)

They could still be specific. For a clean room, they could specify exactly how clean, like "removes 99.999% of all particulates above a size of ...". StuRat (talk) 19:48, 23 February 2015 (UTC)

If the report was concerning clean rooms, they would probably be aware that cleanliness is categorised using standard methods.--Phil Holmes (talk) 14:06, 24 February 2015 (UTC)

Unless the experimenters directly checked this, they would probably just name the equipment, e.g. laminar flow hood. But I don't think that's often specified in tissue culture papers. Someone might use a lab manual reference for the kaboodle, i.e. "routine cell passaging and harvest was done per [1]" where 1 is Maniatis or something, whatever your lab prefers, and that book might have a section on recommended sterile procedure. Wnt (talk) 20:51, 23 February 2015 (UTC)

In a somewhat different context, cleanliness might be implied when specific guidelines are quoted, e.g. Association for Assessment and Accreditation of Laboratory Animal Care International. Wnt (talk) 21:01, 23 February 2015 (UTC)

Over citing rarely hurts anything, while under citing because of supposed "common knowledge" can lead to misunderstandings, possibly even accidents. You may wish to read Wikipedia:You_do_need_to_cite_that_the_sky_is_blue. SemanticMantis (talk) 20:13, 23 February 2015 (UTC)

The issue, as always, is common knowledge to whom? Wikipedia should be written for people who know nothing about the subject they are reading about. It should not consider common knowledge those things which are commonly known only among experts in the field. There's a difference between citing something like "the sky is blue" which depends only on basic human experience, and citing something which requires at least some background in the field of study. One may not always need to cite the former; the latter should ALWAYS be cited. --Jayron32 21:09, 23 February 2015 (UTC)

See also WP:POPE - do you really know what everyone who reads your report already knows and doesn't know? SemanticMantis (talk) 20:19, 23 February 2015 (UTC)

The PhD dissertations I've looked at have run to dozens or hundreds of pages to cover the same material that a couple page journal article would because of the need to reference and explain every little detail. Rmhermen (talk) 20:57, 23 February 2015 (UTC)

Sure, in a dissertation, 10 or 15 papers might be cited each covering a small point. In a journal article, the material might get one cite: (reviewed by Xu et al., 2013). But that's all the domain of academics. Context is important but "reports" for an "industry" doesn't give us much to go on. I'd hope that reports in the nuclear engineering industry are more heavily cited than reports in the fashion industry... SemanticMantis (talk) 21:16, 23 February 2015 (UTC)

Title lineage of University Physics

For the textbook University Physics by Sears, Zemansky, and Young, which the referenced article says is in its 13th edition, is the title "College Physics, 7th Edition" (of which I have a copy with those authors listed) with ISBN 0-201-17285-2, one of the editions, or was/is there a separate title line in which all editions are entitled "College Physics"? 20.137.2.50 (talk) 20:08, 23 February 2015 (UTC)

I think it must be the same - Bookfinder doesn't seem to list an edition of University Physics earlier than the 10th edition. Bubba73 ^{You talkin' to me?} 01:13, 24 February 2015 (UTC)

They're different series. (Confusing, though.) See for example the 3rd editions of College Physics [4] and University Physics [5]. I believe, although I don't have them handy to check, that the secret code is "college"=algebra and "university"=calculus. --Amble (talk) 01:32, 24 February 2015 (UTC)

Oh yes, should have looked at reference #3. Bubba73 ^{You talkin' to me?} 01:52, 24 February 2015 (UTC)

And Hugh D. Young: "Young also wrote an algebra-based version named Sears and Zemansky's College Physics, which is currently in its 9th edition." Bubba73 ^{You talkin' to me?} 01:56, 24 February 2015 (UTC)

If beer and wine are acidic, then why do they taste bitter?

Why might have caused the bitter taste? Could it be a chemical compound, or could it be the taster's genes? 66.213.29.17 (talk) 22:14, 23 February 2015 (UTC)

• Alcohol itself is considered to be one of the tastes. Beer can be bitter because it has a quantity of roasted malt byproducts, and wine picks up some of its quality from the barrels it is aged in. μηδείς (talk) 22:32, 23 February 2015 (UTC)

Hops are used to give a bitter taste to beer - the details are explained here. Apparently the hops contribute a variety of acids that taste bitter. Mikenorton (talk) 22:40, 23 February 2015 (UTC)

I am not at all sure that is correct. Hops are the closest relative there is to the cognate hemp (Cannabis). I suspect the original reason was for effect, not a biter taste. μηδείς (talk) 05:34, 24 February 2015 (UTC)

Even the most casual reading of our own hops article shows your idea is nothing but nonsense. 131.251.254.154 (talk) 17:35, 24 February 2015 (UTC)

The acidity gives rise to the sourness of beer and wine. As Mike says, the bitterness of beer comes mainly from hops, a bitter-tasting herb. The bitterness of wine comes mainly from tannins in the grape skins, and, for wine that is aged in barrels, from tannins in the oak. Looie496 (talk) 22:53, 23 February 2015 (UTC)

Simple, inexpensive white wines fermented in stainless steel will lack tannins, and will be about as sour and about as acidic as diluted lemon juice. Cullen³²⁸ Let's discuss it 22:58, 23 February 2015 (UTC)

The link claims that the bitter-tasting chemicals in hops are acids, specifically alpha acids, and our article seems to agree. I don't understand, though, how are these molecules acids? Where do the protons come from? If it's from the hydroxyl groups, why aren't they just as likely to split off an OH- as an H+ ?

Take a look at Vinylogy, which may help a bit. Mikenorton (talk) 23:17, 23 February 2015 (UTC)

Enol might be the better article, it's a bit easier to understand and the concept is the same. In any case, it's the alpha-carbon that loses the proton. shoy (reactions) 16:38, 24 February 2015 (UTC)

Also, I had the notion that bitterness was a marker of either alkalinity or reduced nitrogen (of course, they often go together), and these substances (assuming they're really acids) don't seem to supply either. So I'm missing something.... --Trovatore (talk) 23:03, 23 February 2015 (UTC)

Bitterness is not a simple chemical property. It is a measure of the ability of a substance to bind to a subset of taste receptors -- there are over 20 distinct types of receptor that contribute to the sensation of bitterness. Their biological function is to be activated by substances that have a high probability of being poisonous. Looie496 (talk) 23:14, 23 February 2015 (UTC)

Yep, we have an article on bitter taste evolution. SemanticMantis (talk) 20:41, 24 February 2015 (UTC)

To answer the point above, hops were originally used in beer as a preservative and to balance the sweetness of the malt. Now the type or blend of hops used is an integral part of the taste of bitter beer - see Hops. Richerman (talk) 10:28, 24 February 2015 (UTC)

Our article says that, with a cn tag added. I still think the reasoning is post hoc, propter hoc. I strongly doubt anyone ever said randomly, this beer is too sweet, I know, lets add some roasted hops to make it bitter. That's kind of like saying the reason you put gas in a car is to get rid of the new car smell. I suspect there was originally some other reason for adding the hops, and the bitter taste just became standard. Also, if one has had beer made with cannabis in place of the hops, it is no less bitter, but a little bit better. μηδείς (talk) 18:08, 24 February 2015 (UTC)

So 'twas better Betty Barter bought a bit of better bud? --Trovatore (talk) 18:52, 24 February 2015 (UTC)

You want to call citation needed on hops preserving beer!? Or that someone might want a more bitter brew?! I think you're just bitter because your first response was totally wrong ;) Malt is sweet, and has many sugars, including Maltodextrin, Hops are bitter, and they act as a preservative in beer. If you want a citation for the claim that hops preserve beer, check out [6]. If you think hops have have an "effect" that is not preservation or bittering (are you implying psychoactive?), then for that. Hops are in the same family as Cannabis, but so are hackberry spp, so on the claim that hops is the closest relative to Cannabis. Next, many people dislike sweet beers. Is it that hard to conceive of? Just google /beer to sweet/ for plenty of examples. Finally, taste does not say that alcohol is "considered one of the tastes", it says that ethanol tastes bitter. SemanticMantis (talk) 20:41, 24 February 2015 (UTC)

You seem to be freaking out on multiple fronts, SM, and I would appreciate some more focus on the issues, and less on me. For example, I did not add the cn tag to the hops article. You can take that up with the article's edit history.

If by Hackberry, you mean the town in Arizona, you are wrong. If you mean Celtis, you are still wrong. Hemp and hops are each other's closest relatives.

The speculation that soma, which was brewed by the early Indo-Europeans, used cannabis is of long standing (a not necessarily RS that at least mentions references). Given that cannabis was not native to Europe, but Humulus lupulus which resembles it is, it is quite possible the Europeans substituted the latter for the former. It's simply absurd Ockham's Razor to assume people started cultivating an uncommon plant to make their beer taste bitter. As for taste, the article mentions alcohol as bitter, but other studies on the net say its taste varies according to genetics, and I have indeed read where it has been proposed as a "basic" taste like fat and umami, although a quick google search was unhelpful. μηδείς (talk) 21:56, 24 February 2015 (UTC)

Hmmm, this conversation needs to be grounded in some technical discussions of gruit that are beyond my competence. While I suppose only the most die-hard aficionados of beer would say that restricting brewers to hops was Germany's worst purity law, it should be clear that beer was once a much more diverse and interesting set of multi-ingredient herbal preparations, complete with some rather alarming "narcotics" like henbane. Damn, I forgot all about one of my past daydreams to do Michurinist graft hybridization of hops onto cannabis rootstocks (now legal in some places and highly selected to produce certain chemicals) in order to see if the transferred small RNAs would create desirable changes (but not THC production!) on the hops. Wnt (talk) 23:31, 24 February 2015 (UTC)

My main point was the issue of the question, though thank you for your concern. I wanted to make sure readers knew not to trust your original response about bitterness in beer, because it is wrong. I think I have enough links now to support my case, so I'm done here. SemanticMantis (talk) 17:25, 25 February 2015 (UTC)

The relationship between acidity and taste is not straightforward. Coca Cola is very acidic. I even used it once to remove some rusty boults to replace a flat tire. But the taste of Coke is mostly sweet. And you can make a sour orange taste sweeter by adding a little salt. --Judithcomm (talk) 08:49, 26 February 2015 (UTC)

Comparing human and machine energy efficiency

Can humans or machines extract more energy from a gallon of fuel (food for the human, gas or diesel for the machine)? It's clear that maybe humans can walk, cycle or run a shorter distance due to all the heat being generated and lost. After all, maintaining life is more important than moving. But I'd like to know how the two compare, if we count all the energy humans are obtaining from food and all work done, not just locomotion.--Senteni (talk) 22:35, 23 February 2015 (UTC)

They both extract comparable amounts of energy, but what matters is the fraction of that energy that can be converted to kinetic energy, as opposed to the fraction lost to heat. The human body is generally thought to have an efficiency of energy conversion of around 20-25%. For machines the numbers vary so widely that it is impossible to generalize. Most gasoline-powered automobiles achieve efficiency comparable to the huma body, but diesel engines usually reach efficiencies in the 30-40% range.Looie496 (talk) 23:08, 23 February 2015 (UTC)

Poincare thought experiment

Martin Gardner in Relativity Simple Explained mentioned Poincare thought experiment, which says there would be no means to detect any change if the universe and everything in it tomorrow becomes proportionately larger (or possibly smaller). I had a quick thought: wouldn't we notice that it would take more (or less) time for the light to reach the Earth, for instance? That said, assuming the speed of light and time itself wouldn't change (a second would remain a second, a minute would still consist of 60 sec, etc), it should take more time (if the universe becomes larger) for the light to cover any distance, meaning we would notice the changed size of the universe, being accustomed to the previous size. Am I missing something? Brandmeister^talk 22:50, 23 February 2015 (UTC)

They were likely assuming the speed of light would change proportionately. StuRat (talk) 23:59, 23 February 2015 (UTC)

They explicitly tells you that everything would change, including wavelengths. The thought experiment is meant for you to realize a basic concept. In this case, you should ask yourself whether distance can be absolutely be measured or it is relative to other stuff.--Senteni (talk) 00:53, 24 February 2015 (UTC)

If I understand it correctly, a change in wavelength wouldn't imply change in the speed of light, but even if it also changes, we would certainly notice that it's not the same as previously. Brandmeister^talk 08:24, 24 February 2015 (UTC)

And how would you measure anything, if everything is half of what it was yesterday, including your ruler? If in a half-so-big universe the constants like speed of light are half of what they were, you'll have no chance of noticing a difference. — Preceding unsigned comment added by Senteni (talk • contribs) 15:13, 24 February 2015 (UTC)

I now suspect that something would definitely go wrong due to possible violations of baryon number and other fundamental constants, but that steps into the concept of fine-tuned Universe. Brandmeister^talk 17:22, 24 February 2015 (UTC)

can massless elementary subatomic particles within a single atomic structure be infinitely close to each other?66.87.83.122 (talk) 19:57, 24 February 2015 (UTC)

I assume you mean gluons which are the only known massless particles that that remain within the atomic structure (the others, photons and neutrinos are best regarded as waves for most purposes). I think they can be arbitrarily close, especially in a quark–gluon plasma. Dbfirs 21:10, 24 February 2015 (UTC)

But of course.66.87.83.122 (talk) 21:37, 24 February 2015 (UTC)

The point is that if you uniformly scale all the numbers that refer to distance, it's just like changing your base unit of distance, and has no physical consequence. If you can come up with an experiment that detects the change then you forgot to scale something. If you think the speed of light will be detectably different then you probably forgot to scale c. If you think the Compton wavelength of the electron will be detectably different then you probably forgot to scale h and/or c. Every quantity is scaled by the power of distance that appears in its units. For example c has units of distance/time so it should be scaled by k, the overall scale factor; h has units of mass·distance²/time so it should be scaled by k²; the diameter of the earth has units of distance so it should be scaled by k; and so on. -- BenRG (talk) 22:18, 24 February 2015 (UTC)

Thanx, those were the aspects that buffled me. Brandmeister^talk 09:24, 25 February 2015 (UTC)

you should be able to detect the change proportionally with respect to time in the the twin experiment. 2601:C:3600:46B:A926:7032:DCEE:D302 (talk) 09:32, 25 February 2015 (UTC)

Incidentally, I don't think you should try to learn special relativity from Martin Gardner, since I don't get the impression that he understood the theory himself. He was primarily a journalist, not a scientist, and certainly not a physicist. I'm a fan of Einstein's own Relativity: The Special and the General Theory. There are cheap printed editions available and you can download it free online since it's in the public domain. Einstein was an engaging writer and he understood the theory better than, frankly, the vast majority of later popularizers. I can't recommend his section on general relativity, though, since it's based on the "general principle of relativity" which is now a historical curiosity. -- BenRG (talk) 22:33, 24 February 2015 (UTC)

The flip side of this question is whether we "really" live in an expanding universe, or whether some of the underlying physics is changing so that atoms and various other things are getting smaller. I think I asked something along this line a while before here and basically the answer is that either you're in possession of a model by which your new paradigm makes it easier to work the math, or else you have some groovy bong-hit philosophy and your dick in your hand. :) For the original question, if we suppose that every aspect of the data (and therefore the math that underlies it, is unaltered, then the change in "actual" size, that we can't measure, has to be dismissed as unobservable. Otherwise, we start doing math on whatever observations change. Wnt (talk) 23:23, 24 February 2015 (UTC)

wnt, could you clarify what you mean by underlying physics is changing? Because I would say the physics does not have to change for that to be true. It is actually a perfect fit to help explain time. Delta t is delta shrink. That is how the universe differentiates now from now. 73.160.39.193 (talk) 03:09, 25 February 2015 (UTC)

What does it take to set up a personal laboratory in the 21st century?

I have heard and read that in history, people just funded their own research, and if they were broke, then they're out of luck, unless they asked a wealthy person to finance their research project or invention. Now, in the 21st century, what does it take to set up a personal laboratory in the 21st century in order to conduct research? Is the person allowed to publish research papers even without any academic degrees? Does the researcher have to take into account of ethical/safety standards, or will he/she have to put his/her own life at risk? 66.213.29.17 (talk) 23:40, 23 February 2015 (UTC)

It will depend greatly on what you want to research. If you want to compare the liver size in various frogs, that could be done pretty cheaply. If you want create a sustainable fusion reaction, that might cost a tad bit more. :-) StuRat (talk) 23:57, 23 February 2015 (UTC)

(ec)It depends on what sort of research you want to do. Amateur astronomy is easy to get in on with a small amount of investment. I'm guessing you're talking chemistry/biology/physics, though. There's a growing movement of DIY biology, including a growing number of hackerspaces with a science twist. Reagents and equipment can be obtained by private individuals from internet sites like eBay, or even from standard scientific suppliers. Keep in mind, though, that certain materials are illegal to purchase or possess without a license or some sort of official affiliation. This is particularly true for chemistry items, where the sale of things like Erlenmeyer flasks are restricted in some jurisdictions as "drug paraphernalia" (due to their use in meth labs). Regarding publishing, an institutional affiliation is not strictly required for publishing, but submissions from independent researchers are likely to be scrutinized more heavily than those from recognized institutions. Having a previous track record of scientific publishing would help in this regards - it's not that independent researchers can't do good science, it's just that the balance of probabilities are such that submissions from a non-affiliated researcher are likely to be from a crackpot, and no one wants to waste their time on improperly performed drivel. Independent researchers should take in to account ethical and safety standards - many journals will require ethical oversight of research, especially that involving humans or other vertebrates, and will refuse to consider research which doesn't have ethical oversight. Safety standards are less rigorously enforced by journals, but should be accounted for anyway - particularly as performing experiments without the proper safety precautions may be illegal in your jurisdiction. In *all* research, whether independent or institution-affiliated, a researcher should never perform experiments where their own health or welfare are put at risk - or where the health and welfare of others or the environment is put at risk. If an experiment can't be completed safely (or if it's unknown if the experiment is safe), it shouldn't be attempted in the first place. -- 160.129.138.186 (talk) 00:19, 24 February 2015 (UTC)

Partly false. Researchers can perform experiments where their own health and welfare are put at risk; indeed, this is sometimes the only person they are allowed to perform the experiment on. The most famous example is probably this, which won the experimenter a Nobel prize. RomanSpa (talk) 12:35, 24 February 2015 (UTC)

30 years ago yes. Today may be a bit different. --Jayron32 13:34, 24 February 2015 (UTC)

• It might help if you told us where you heard and read where such people existed. Was it natural historian? Were they sharecroppers, or clergy, heirs, and minor nobility? Have you read peer review? Have you read Einstein? He was published well before he earned a PhD. Give us some context so we can better assist you. μηδείς (talk) 05:28, 24 February 2015 (UTC)

• In some subjects it is possible to do research with very few resources, and, yes, you can (though it is rare) publish without being affiliated to an institution, as your paper will be subject to the same peer review process. My mother maintained a small research effort into the reproduction and behaviour of various weevils on a kitchen worktop. Total area used was about 1 sq metre, and academic output was principally in the form of correspondence with the Royal Entomological Society. Amusingly, her interest was piqued by finding an infestation in a bag of flour.

My niece is currently breeding Drosophila melanogaster in her bedroom. Academic output so far seems to be a couple of essays for her school biology class. Cost is negligible, as she is now using her grandmother's microscope. RomanSpa (talk) 09:28, 24 February 2015 (UTC)

Perhaps it is instructive to point out that much research and development takes place in the private sector. If a private company wishes to hire and fund your research, they may choose to do so, irrespective of your credentials. Generally, well-credentialed people have an easier time getting other people to take them seriously, so it's very common to find that an academic degree is an "implicit" prerequisite. There are exceptions: one Peter Thiel will aggressively fund ideas and individuals of his choosing, provided that the youngster signs a contract obligating them not to take any academic training. This is a notorious exception: Mr. Thiel, however wealthy or successful he may be, is a crackpot. Nimur (talk) 15:09, 24 February 2015 (UTC)