Wikipedia:Reference desk/Archives/Science/2016 May 14

= May 14 =

A method to scientifically test the existence of god
A lot of people have near death experiences, where in some cases they report seeing doctors trying to revive them and said they heard/seen things around them during the time "they died". if there was something very definite they can verify, e.g. putting a 6 digit number out of the sight of the dead body, but would be clearly visible from another angle, and if they can recall the number after they get revived, that would prove existence of afterlife and therefore of god. these tests can be run on death row inmates, kill them in a way that it's possible to revive them (e.g. anaesthetic overdose), and say if they can recall the number then they'll get life sentence instead of death (for some incentive).

This is the single most important question in human history, and we have the means to test it. So why haven't we done it? — Preceding unsigned comment added by Money is tight (talk • contribs) 00:33, 14 May 2016 (UTC)


 * Would you change your behavior if you would have proof that (a) god did or did not exist?


 * I don't think that that question is very important, it is quite irrelevant to me, and I don't think that the existence of an afterlife would be proof for the existence of a god or gods. People have scientifically tested the existence of a god, and the conclusion was that there is no reason to believe in a god or gods.


 * For example, back in 1872 Francis Galton concluded that prayer does not work, because the life expectancy of the British royals was not higher than that of the rest of the population despite weekly prayer for their health, and that churches burned down, got hit by lightning and destroyed by earthquakes at the same rate as other buildings of a comparable size. The Quixotic Potato (talk) 01:05, 14 May 2016 (UTC)


 * One of Isaac Asimov’s essays notes that when the lightening rod was invented, churches were reluctant to install them, as it would be attempting to thwart God’s vengeance. They gradually came around when they noticed the brothels and taverns being spared by the rod, while churches burned to the ground. Willondon (talk) 16:45, 15 May 2016 (UTC)


 * Or one could draw the conclusion that God wants to be worshiped in a rather different fashion than we imagined. It's not unprecedented. StuRat (talk) 16:40, 16 May 2016 (UTC)


 * (EC) Well, first, it has been done, though in a less grizzly fashion than you suggest - see the first three or so paragraphs at Near-death_experience. As to your suggestion, there are major ethical problems in experimenting with death in the way you suggest, besides the whole idea being abhorrent. And then there's the point that even did the test pan out - near dead person sees something his body could not have seen - you have not proved god, but merely got yourself an observation for which it is difficult to construct an explanatory mechanism. All ethical and practical considerations aside, those who do not believe in god are unlikely to mount this test, since the anticipated absence of evidence (of god) is not evidence of absence - in other words, nothing gets proved by the experiment. Those who do believe in god are unlikely to put her to the test in this fashion. So the potential queue to perform the experiment is very very small indeed. --Tagishsimon (talk) 01:11, 14 May 2016 (UTC)


 * Houdini had a famous test where he told his wife some keywords that she had to memorize, and said he would tell them to any psychic who truly contacted him after his death. He died, and many psychics claimed to have contacted him, but none knew the keywords.  Draw your own conclusions. StuRat (talk) 01:13, 14 May 2016 (UTC)


 * Houdini, dead ? What if the psychics could never have told her the special keywords ? ..the same result.. would occur.. --Askedonty (talk) 19:15, 15 May 2016 (UTC)


 * Some years ago a psychic was scheduled for an appearance on the local radio station. She arrived late, and said she was "caught in traffic." Apparently her psychic abilities did not include traffic reports. ←Baseball Bugs What's up, Doc? carrots→ 19:38, 15 May 2016 (UTC)


 * They usually weasel out of this by saying they can't predict everything, 100% of the time, which is of course true, if quite an understatement of what they can't predict. StuRat (talk) 16:35, 16 May 2016 (UTC)


 * Do you speak French? https://www.youtube.com/watch?v=rB33z6qFJqM
 * So, you say you are a clairvoyant, that you can foresee the future?
 * - Yes, I can see the future.
 * SLAP!!!
 * - And this? Didn't you see this coming? As you can see, it doesn't take much to expose a liar.
 * The Quixotic Potato (talk) 17:36, 17 May 2016 (UTC)


 * But again, that would only disprove a claim that they can see 100% of the future with 100% accuracy. They are smart enough not to claim that.  Also, if they could do that, they would buy a winning lottery ticket, so wouldn't need to take money from their marks clients.  A nice way around this is for them to say "You must be committed for me to see your future, and a contribution is a sign of this commitment".  StuRat (talk) 17:56, 17 May 2016 (UTC)


 * a fundamental problem too is that any experience of God still runs into the problem of Descartes radical doubt: Cogito ergo sum 68.48.241.158 (talk) 02:04, 14 May 2016 (UTC)
 * How is Descartes' belief in his own existence a fundamental problem? AllBestFaith (talk) 13:52, 14 May 2016 (UTC)


 * it's related to the notion of radical doubt..that is, even if one had the experience of God appearing before her etc, there's no way to no for sure that this is really what is occurring...one could be being fooled by an entity other than God etc etc...just as our experiences could be something other than what they appear..see "brain in a vat" etc etc...68.48.241.158 (talk) 14:13, 14 May 2016 (UTC)


 * Far from succumbing to despairing that everything is doubtful as you suggest, René Descartes who was evidently a male person who served in the army and fathered an ill-fated illegitimate daughter Francine, turned his ability to doubt into the tool of methodological skepticism with the goal of sorting out true from false claims. Since Descartes considered himself to be a devout Catholic, though his attempt to ground theological beliefs on reason encountered intense opposition, you may be doubly mistaking him for an atheist female. AllBestFaith (talk) 14:48, 14 May 2016 (UTC)


 * you seem to somehow have confused my use of the female pronoun in my example as suggesting Descartes was himself female...this would be an instance of poor reading comprehension..regardless, what I describe is accurate and has relevance..68.48.241.158 (talk) 15:00, 14 May 2016 (UTC)


 * There is no reason to assume that an afterlife requires the existence of God, or vice versa. ←Baseball Bugs What's up, Doc? carrots→ 02:33, 14 May 2016 (UTC)


 * Agreed. The OP needs to think about what the hypothesis is and what the experiment is here.  It is possible to picture a worldview in which there is an afterlife without God, or without a noticeable God.  It is also very possible to imagine an afterlife that does not involve having some kind of disembodied vision.  I mean, think about it - the colors we see are the product of red, green, blue receptors of a certain frequency.  Our vision has a certain acuity, fails to pick up far infrared or (usually) ultraviolet.  For that vision to be replicated after death by something that is invisible - i.e. which does not absorb light - seems extraordinary.  Testing this kind of remote viewing has been attempted by some very unexpected agencies - see Project Stargate; there's no reason to assume a person would have to be dead to do it, if these disembodied eyes are part of some soul that exists in a living person also. Wnt (talk) 02:47, 14 May 2016 (UTC)


 * posting of banned user removed. The Quixotic Potato (talk) 12:27, 16 May 2016 (UTC)


 * Because a car manual contains accurate and useful information, it is not a work of fiction. The Quixotic Potato (talk) 09:46, 15 May 2016 (UTC)


 * The Bible is the designer's manual for use by humans? That view clearly reflects the belief system you have been given, and adopted, but your belief system is just one that has been created to date, and it is significantly different to the belief systems adopted by many others around the world. Dolphin  ( t ) 10:58, 15 May 2016 (UTC)

Whether we could prove "scientifically" that God exists, in the end, You will either believe Him without such proof, or You won't, and I do not believe such proof can be found in this Age, since the Just shall live by Faith. Chris the Russian Christopher Lilly  09:21, 15 May 2016 (UTC)


 * The motor manufacturers set out to provide practical information in their manual.  Why would you assume that the object of the people who put together the Bible was to tell a fairy story?   As for the efficacy of prayer, if you pray that you will win the lottery you might not have much luck, but if you were to pray that a close relative be delivered from a serious illness you might be more successful.
 * posting of banned user removed. Fut.Perf. ☼ 08:15, 16 May 2016 (UTC)
 * Are you trolling? Shouldn't you be a lot more humble? Are you allowed to judge others? I noticed you haven't apologized yet. Praying for a sick relative is a waste of time. It is far better to bring them to a hospital, or call an ambulance. In the hospital they don't pray for the patient, they actually do useful stuff, like giving them medicine. There is a reason that god does not heal amputees. Your idea of god is just as made up as all the others. It is 2016, why do you still believe that nonsense? The Quran, Torah and Bible are all the same story about the same idea of a god, and the differences between them are quite small. I've read all three, maybe you should too! God loves atheists. The Quixotic Potato (talk) 12:03, 15 May 2016 (UTC)


 * posting of banned user removed. Fut.Perf. ☼ 08:15, 16 May 2016 (UTC)


 * Translated into English????? What are you talking about? You have not answered my questions. Are you trolling? Shouldn't you be a lot more humble? Are you allowed to judge others? And you haven't apologized yet. Don't worry, I'll forgive you, and I will ask your god to forgive you because you obviously don't know what you are doing. The Quixotic Potato (talk) 12:56, 15 May 2016 (UTC)


 * posting of banned user removed. Fut.Perf. ☼ 08:15, 16 May 2016 (UTC)


 * I wrote: "Translated into English?????"... You seem to know very little about the Bible (you wrote: Part of the Bible is the Torah (translated into English).), and religion in general (you wrote: How can a religion not have "a god or gods"?) . Have you read the bible? How old are you? People do continue to visit Lourdes even though they don't derive benefit from it (or, you know, no miraculous cures). You have not answered my questions. Are you trolling? Shouldn't you be a lot more humble? Are you allowed to judge others? Have you read my userpage? What is your accountname? You should read this and watch this and that and this too. Have you read , & ? The Quixotic Potato (talk) 13:45, 15 May 2016 (UTC)

Can someone close this thread and collapse the against policy behavior of "Quixotic Potato" and whoever else he's been engaging with??68.48.241.158 (talk) 14:14, 15 May 2016 (UTC)
 * Hahahaha. Welcome to the Science reference desk mate. Your most recent block ended 2 weeks ago, maybe it is a good idea to improve some articles? The Quixotic Potato (talk) 14:15, 15 May 2016 (UTC)
 * Some of the comments above go beyond the scope of the original proposed method, but they have some of the same issues regarding their hypotheses. Testing the existence of God by praying for healing assumes, for example, that, despite creating it, God doesn't see any beneficial use for disease; it also assumes that the purpose of prayer is to make magic happen rather than, for example, to provide insight or inspiration.  Reifying "the Bible" minimizes the fact that it is made up of different books by different people that were independently circulated.  So there is much needless conflict produced because people are taking a very specific notion of religion and then saying either it is all true or it is all false, when maybe the most important bits are independent of the most testable bits.  After all, the most significant form of healing is resurrection into a new and better universe, yet it is clearly not possible to tell whether such a thing could occur by ordinary scientific means of investigation. Wnt (talk) 18:59, 15 May 2016 (UTC)

FYI, an IP is yelping at WP:ANI about this section, if anyone wants to comment there. ←Baseball Bugs What's up, Doc? carrots→ 19:04, 15 May 2016 (UTC)

Actually, praying for the sick or for anything else does work. For sure, one must use the Medical Knowledge God has also allowed us, but the effectual fervent prayer of a righteous man availeth much, and thus Prayer is indeed useful, and may even accomplish what even Modern Medicine cannot. The Bible would not say such things if they were not true - and by the way, all of the Bible is true, does not matter what one can, or what one thinks one can prove "scientifically". What I see in some of these attempts to prove the Bible by Science ends up being reducing God's real Miracles to natural acts that can be explained away. As for judging, one can only do so if they are not doing the same things wrong. If one has genuinely turned to God, it should only be because they have first judged themselves in the Light of God's Word, as Judgment must begin at the House of God. But judging others should only be according to God's Righteous Judgment. Whether or not is 2016, and even that Number we use for this year is based on timing with respect to the Bible, that is to say, it is said to be about 2016 years since the Birth of Christ ( when I understand He might actually have been born around September, 4 BC ), whether or not indeed it is 2016, or whatever year it happens to be in any given moment, as people have said such things up to now, should have no bearing on our Belief in God, or any lack of it, since Jesus Christ is the Same, yesterday, today and forever, and whatever people think about Belief in Him being out of Date, it never is. His Word, which endureth forever, is just as valid now as it ever was or will be. It is also interesting that when things go wrong, People blame God, and yes, nothing happens that He does not ultimately allow, since if He wished, He could stop it, but the same People might not thank and praise Him for all that He has done and created that is Good - He gets a lot of the blame, but hardly any of the Credit, and think of it, if we live in a World which in general does not honour Him, does not run things in the Way He in His Wisdom knows and commands they should be run, we ought not be surprised if He allows unfortunate events to occur. But the thing is, if we all did turn to Him, He would hear us, and forgive us ( 2 Chronicles 7:14 ), because He does not bear a grudge against those of us here on Earth who still have a Chance to turn to Him. May God forgive us all for each and all of our own sins, for there is none that sinneth not, and I would not presume to speak of God if I had not acknowledged my own sins to Him. To finish - He knows and hears all, and whatever we say or write, we will give account, and I can only pray that if we have offended Him, we can admit that, and turn to Him. One way or other, in the end, when all is said and done, whether or not we think God exists, we will find out for sure. Chris the Russian Christopher Lilly  00:39, 16 May 2016 (UTC)


 * I'm late to the party, but no one has yet mentioned at least one serious attempt to approach this exact question God: The Failed Hypothesis by Victor_J._Stenger. If you are at all interested in this subject, I can recommend this book, I found it quite interesting and informative. Vespine (talk) 06:18, 16 May 2016 (UTC)
 * 1) Any experiment involving killing human subjects is unlikely to pass ethical standards.
 * 2) The experiment proposed wouldn't answer the question.  At most it could prove that, at the point of death, your soul/spirit/consciousness leaves the body and can see things that you couldn't while still in your body.  It wouldn't prove that the soul was immortal (maybe it evaporates a few minutes after body death), nor that it can "pass on" to some sort of after life, not that there is a God or gods.  And it certainly won't prove which of the many proposed gods and after-lives is the correct one.
 * 3) Also, the idea that your "soul" can see things after it leaves the body would raise some other problems.  Like, why do you need eyes to see while your soul is still inside its body?  If the soul can see without eyes, what is the point of them?  And if the soul's movement is trapped by its body, and its vision is blocked by flesh, what else blocks it?  How does it get out of the room to wherever it is supposed to go? Iapetus (talk) 10:45, 16 May 2016 (UTC)
 * 1) Also, the idea that your "soul" can see things after it leaves the body would raise some other problems.  Like, why do you need eyes to see while your soul is still inside its body?  If the soul can see without eyes, what is the point of them?  And if the soul's movement is trapped by its body, and its vision is blocked by flesh, what else blocks it?  How does it get out of the room to wherever it is supposed to go? Iapetus (talk) 10:45, 16 May 2016 (UTC)


 * There is no evidence that "praying for the sick or for anything else does work." At best, it can make the patient feel better psychologically, provided he knows about it. There is only one kind of prayer that works - praying for one's own spiritual strength. That works, if the patient is open to it. But praying for an event or any other kind of "thing" doesn't "work". If it appears to work, it's superstition - it's really just randomness that happened to turn out well. ←Baseball Bugs What's up, Doc? carrots→ 15:12, 17 May 2016 (UTC)

Could an asteroid be ring-shaped ?
I picture a spherical asteroid, struck dead-on by a small, fast moving object, that punches a hole through it. Somehow I doubt if that would work, though, either breaking the asteroid into many fragments or melting it, in either case allowing it to coalesce back into a sphere. Maybe if the asteroid was flattened out from a high spin rate and the object struck it right on the axis ? StuRat (talk) 01:41, 14 May 2016 (UTC)
 * If the spin rate an dcollision speed were fast enough for the material to not coalesce in a sphere, it would be dispersed entirely. Fgf10 (talk) 12:27, 14 May 2016 (UTC)


 * Toroidal planets are possible, but they are not highly stable. A large impactor will cause them to collapse. So such a body is possible, but it has to coalesce from a primordial cloud with a high spin, and can't be created by the specific method StuRat proposes. (I only just found this out recently, but couldn't recall my source.) μηδείς (talk) 16:45, 14 May 2016 (UTC)
 * For future reference (since the search results will likely change) the leading search results include, , . I remain less than confident this is possible from what I've read so far, but they think so and I can't rule it out. Wnt (talk) 19:13, 15 May 2016 (UTC)


 * Couldn't an exceedingly improbable string of tiny impacts "sculpt" an asteroid a few meters wide into a ring? Sagittarian Milky Way (talk) 19:45, 14 May 2016 (UTC)

larva on Mentha
Hey everyone, I found this larva on my Mentha. I try to identify this creature. I would glad to some help. I think it is a Chrysodeixis eriosoma but I'm not sure. thanks alot, --Tomsky2015 (talk) 09:22, 14 May 2016 (UTC)


 * Well, there aren't many characters I'm really using here: I see it has three pairs of prolegs, and it's green, and it moves like an inchworm or looper. Without looking at your suggestion (which also fell in this category), I noted that some loopers in Noctuidae have three pairs of prolegs, such as the cabbage looper.  (That, like yours, seems too fat to my eyes)  There are various Noctuidae that come up on Mentha, but so far I didn't see a green one - it's not really easy for me to search.  Pending some insight on how to find a better key, I think I'll leave this for now.  Based on the lettering, is this from Israel, or somewhere else? Wnt (talk) 11:17, 14 May 2016 (UTC)
 * Wnt, Yes, Israel. Thank you very much. I looked on internet to see if I will find it by myself. My best result was Chrysodeixis eriosoma but your suggestion look right. Thank you and good day. --Tomsky2015 (talk) 12:45, 14 May 2016 (UTC)

Formulaic relation between two units
Suppose we don't know the simple formula to convert Centigrade into Fahrenheit or vice-versa. But, some how , we do know two or three instances of relationship between the two units. For example we know for sure that 5°C equals 41.0 °F, 17°C equals 62.6 °F, whereas 45°C is equal to 113.0 °F. My question is that, using these few instances how can we come up with a simple formula that can be used to turn any value of C or F to it's corresponding equivalent. 124.253.250.54 (talk) 12:16, 14 May 2016 (UTC)


 * Yes, provided we know that there is just a multiplication factor and a constant offset. It then becomes a simultaneous equation problem:


 * We only need two equations:

45m + c = 113 5m + c = 41
 * Now multiply the 2nd equation by 9 and subtract the 1st equation from it:

(5m + c = 41)×9 45m + 9c = 369 -(45m + c = 113) 8c = 256
 * Solve for c then plug that back into the 2nd equation to solve for m:

c = 32

5m + 32 = 41 5m     =  9 m     =  1.8
 * Note that temperature conversions are a bit unusual in that they have a constant offset (except the conversion between Rankine and Kelvin). Without that you only need one conversion to find the multiplication factor, m.  Similarly, you only need one conversion to find the constant offset, if there is no multiplicative factor (in other words, if it is 1, as in a Celsius to Kelvin conversion or Rankine to Fahrenheit).    StuRat (talk) 12:44, 14 May 2016 (UTC)


 * All correct, we only need use two equations IF we already suspect the relationship is linear with an offset. The OPs third equivalence serves to confirm that. AllBestFaith (talk) 15:41, 14 May 2016 (UTC)


 * Yes, it's always a good idea to check your work by plugging the results into all equations provided. StuRat (talk) 16:50, 14 May 2016 (UTC)


 * Side note is that the mathematical definition of "linear" is there is no offset. --DHeyward (talk) 08:22, 15 May 2016 (UTC)


 * Darn, I guess most of the linear equations I've been using aren't. —Tamfang (talk) 08:22, 17 May 2016 (UTC)
 * A Linear transformation or linear operator, often represented by a matrix, has no "offset"; it sends zero to zero, as defining property. A Line, expressed as an equation in slope-intercept form (Y=mX+b), does not represent a linear map when b is not zero. Rather, it constitutes an Affine transformation. "Linear equations", confusingly, are almost surely not linear maps. SemanticMantis (talk) 03:31, 18 May 2016 (UTC)


 * The only reason why you know there is a linear relationship is because Celsius (since 1948 the preferred term, even though the guy had the scale backwards) and Fahrenheit are defined the same way, just with different numbers. Wnt (talk) 10:58, 15 May 2016 (UTC)


 * Some people, especially less technical or elderly ones, need a Mnemonic to help them remember the conversions between °C and °F. They may remember the constants 5, 9 and 32 which appear in both formulæ but not how to apply them. That incomplete memory leaves one in this quandary about converting:


 * Subtract 32 or not ?
 * Multiply by 5/9 or by 9/5 ?
 * Add 32 or not ?


 * The rule that works is: Make the 3 choices above that each ensure numerical °F is "warmer" than numerical °C. "Warmer" here means more positive number, which is true for all temperatures except minus 40 degrees and below, which is colder than you want to think about. AllBestFaith (talk) 23:33, 15 May 2016 (UTC)


 * The choice is easy between 9/5 and 5/9.  Celsius degrees are larger than Fahrenheit ones, so when changing from Celsius multiply by 9/5 and when changing from Fahrenheit multiply by 5/9.   For those who have problems with adding or subtracting 32 there is a formula which makes use of the fact that -40 is the same in both scales.   Using the fact that 10 degrees C = 50 degrees F and looking for easy divisions I reconstructed it as follows:


 * Fahrenheit to Celsius

Add 40. Multiply by 5/9. Subtract 40.


 * Celsius to Fahrenheit

Add 40. Multiply by 9/5. Subtract 40. — Preceding unsigned comment added by 5.150.93.133 (talk) 09:13, 16 May 2016 (UTC)


 * I think it's easier to remember that freezing is 0 C and 32 F. If you can remember that 212 F = 100 C and understand 212 = 180 + 32, you're golden. Wnt (talk) 17:00, 16 May 2016 (UTC)


 * It was shown that a linear equation derived from two data points also fit the third data point. But does that really prove that there is no higher order relationship between the two variables (in cases where it is two variables of unknown relationship)? Might there be higher order relationships which also fit the three data points? Edison (talk) 14:37, 18 May 2016 (UTC)


 * Possible, but unlikely, in the general case, and it would require some slightly more complex equations. Since we know these units are each linear, and don't follow such complex equations, it shouldn't be possible here.  Perhaps where non-linear units are used, like star's absolute and apparent magnitudes, then that conversion issue might come up. StuRat (talk) 14:53, 18 May 2016 (UTC)
 * There are an infinite number of higher-order relationships, including an infinite number of different degree polynomials. A great example of students using Excel to "prove" something silly is when they curve-fit a scatter-plot of n data-points using a polynomial with degrees≥n. "It's a perfect fit, so that must be the physical relationship or equation I was trying to prove." Um, no. An infinite number of lines can pass through one point, an infinite number of parabolas can go through two given points, etc. It goes back to the number of variables (here, coefficients of each term) vs number of equations (points). DMacks (talk) 16:16, 18 May 2016 (UTC)

Would dynamic tension work in space?
Dynamic tension is about contracting your muscles and moving them against each other Dynamic_Tension Would astronauts be able to use it to stave off bone loss and keep healthy? Bastardsoap (talk) 16:20, 14 May 2016 (UTC)


 * Yes, but it might be difficult to keep tabs on them. You would need to put a strain gauge between their hands to tell how much force they are really exerting, while a stationary bike is easier to monitor.  Also, dynamic tension exercises don't do as much cardio, and that's important, too.  StuRat (talk) 16:47, 14 May 2016 (UTC)


 * It's not that hard to add cardio with dynamic tension, you just have to contract less and do more reps Bastardsoap (talk) 17:31, 14 May 2016 (UTC)


 * I'm skeptical that you can get your heart rate up and keep it up as long as on a stationary bike. StuRat (talk) 17:41, 14 May 2016 (UTC)


 * Try a ddp yoga workout and see for yourselfBastardsoap (talk) 17:59, 14 May 2016 (UTC)
 * Its not a substitute for gravity and therefor this is still a well known health issue for long missions. Besides that gravity also completely affects cords and tissue and you can not substitute all that just with "some gymnastics". For that you find extensive artificial gravity constructions in Spacevessels in better Sci-fi movies like 2001: A Space Odyssey (film). --Kharon (talk) 12:14, 15 May 2016 (UTC)


 * A better solution would be a rotation that creates a 1G force. Exercise may help certain muscle tone and bone density but balance seems more important.  To wit, a 150lb, 6 foot man can walk.  So can a 300lb, 6ft man.  I wouldn't expect that giving a 150lb backpack to the 150lb man would make him equivalent to the 300lb man in their ability to function.  Both have adapted to their condition.  --DHeyward (talk) 09:15, 16 May 2016 (UTC)


 * There are several disadvantages to a ship rotating fast enough for 1g:


 * 1) Unless it's a large radius, the difference in g force when you stand up will induce nausea.


 * 2) You lose the advantage of astronauts being able to move large pieces of equipment on their own.


 * 3) Docking can only happen at 2 points, along the axis, and then you still need to match the rotation.


 * 4) EVA's on the outside of the ship to do maintenance while it's rotating are impractical, so then you need to be able to stop the rotation and restart it, using up fuel.


 * 5) Solar panels and communications antenna need to be moved constantly, to keep them aimed at their targets, causing them to break down sooner. The communications problem could be solved by having a sister ship which doesn't rotate, to do all the long distance communications, but that would require station keeping to keep them apart, and maintenance wouldn't be easy there.  StuRat (talk) 15:53, 16 May 2016 (UTC)


 * Well, a lot of sci-fi designs suppose a limited centrifuge space for exercise with large nonrotating sectors at either end, to which ships dock. The centrifuge has limited uses that don't require much heavy equipment or stuff on its outer hull.  Of course, given the stress involved I'd think you'd still have to check that hull for cracks and fatigue, which involves EVAs; but in theory the angular momentum can be transferred to a flywheel or to one of the end pieces or a second centrifuge section (rotating the other way) without the need for propellant usage, just electricity. Wnt (talk) 17:04, 16 May 2016 (UTC)


 * There the joints between rotating and non-rotating parts become risky, and an astronaut entering or leaving the rotating part needs to spin up or spin down their body. StuRat (talk) 17:11, 16 May 2016 (UTC)


 * Risky, sure. But what part of getting into a rocket and being blasted into space and trying to live in a tin can surrounded by vacuum isn't risky?  I'm sure they would think of ways to protect the joints and make them safely separable under various contingencies. Wnt (talk) 10:14, 18 May 2016 (UTC)


 * Sure spaceflight is risky, but this is why they need to minimize the risk at every step. And if a stationary bike is less risky, that's what they will choose.  However, for long term space travel, like to Mars, they may need to rotate the ship because getting exercise alone just isn't enough over such long terms.  But for low-Earth orbit, why rotate the ship when you can just rotate the crew ? :-) StuRat (talk) 14:59, 18 May 2016 (UTC)

It's not that simple. According to NASA "the risks of these problems occurring [bone loss and kidney stones] cannot be completely eliminated through physical exercise alone." Richerman   (talk) 22:45, 16 May 2016 (UTC)

Measuring calories
I heard somewhere that scientists determined the number of calories in carbohydrates, fats, and proteins by measuring how much heat the body produced after eating. I know scientists have burned carbohydrates, fats, and proteins in a calorimeter and found a discrepancy between how much heat is released when protein is burned in a calorimeter and how much energy is produced when protein is metabolized in the body. The body gets 4 calories per gram from proteins, but burning a gram of protein in a calorimeter yields considerably more energy. How do scientists know how many calories the body gets from a nutrient like protein?174.131.47.80 (talk) 18:37, 14 May 2016 (UTC)


 * Yes, there is a problem using a bomb calorimeter (or any other type), in that not everything that's flammable is digestible, with an obvious example being wood. I wouldn't think measuring heat produced by a person following a meal would work, either, though, as then you have confounding factors like the amount of food energy stored as fat to be burnt later, or retrieved from fat stored from previous meals.  I would think using mice for this test would be better, since presumably they can digest about the same things we can, and you could feed them an all-protein, all-carb, or all-fat diet for their entire (short) life without violating medical ethics (although PETA might not like it). StuRat (talk) 20:34, 14 May 2016 (UTC)


 * The gross energy (GE) of a food, as measured by bomb calorimetry is equal to the sum of the heats of combustion of the components – protein (GEp), fat (GEf) and carbohydrate (GEcho).
 * $${GE} = {{GE}_p + {GE}_f + {GE}_{cho}} \,$$
 * Wilbur Olin Atwater 1844 - 1907 considered the energy value of faeces in the same way.
 * $${GE}^F = {{GE}_p^F + {GE}_f^F + {GE}_{cho}^F} \,$$
 * to develop the Atwater system for calculating the available energy of foods:
 * $${\text{Metabolisable Energy}} = \left(\text{Gross Energy in Food}\right) - \left(\text{Energy lost in Faeces, Urine, Secretions and Gases}\right).$$
 * AllBestFaith (talk) 23:56, 14 May 2016 (UTC)
 * Amino acids are not completely cataboilized by animals. Therefore the bomb calorimeter significantly overestimates their biologically relevant energy content due to the energy remaining in urea. Ruslik_ Zero 08:06, 15 May 2016 (UTC)
 * There are also whole room calorimeters that you can stick a person in, and control the gases and other materials coming in and out while also taking measurements. --OuroborosCobra (talk) 00:13, 17 May 2016 (UTC)