Wikipedia:Reference desk/Archives/Science/2010 November 21

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November 21

Full name for invertebrate zoologist named Grube or Grübe, mid C19

Hi all,
Pet peeve is authorities without biographies. "Grube" is the binomial authority for Chirocephalus josephinae, Peripatopsis capensis, as "Grübe" -- and with one "Oersted" -- Themiste alutacea, and so on. From the last mentioned, I'm guessing he or she may well be Danish.
Thank you! --Shirt58 (talk) 09:23, 21 November 2010 (UTC)

This is where the internet fails! I eventually found it by searching for " Grube nineteenth century taxomony" and found his initials are AE Grube, then google scholared that and found this which says he is Adolph Eduard Grube. The Oersted is Anders Sandøe Ørsted based on the third hit for a search of "A S Ørsted Themiste" (tried posting a link but the syntax gets screwed up as it has square brackets in the URL). SmartSE (talk) 12:28, 21 November 2010 (UTC)

If you replace the [ and ] with %91 and %93, which are the ASCII escaped equivalents, then it should work. CS Miller (talk) 09:08, 22 November 2010 (UTC)

Uuh, mmm, yeah, I'll try that the noo the morn --Shirt58 (talk) 13:19, 23 November 2010 (UTC)

Thanks all! Turns out he's Polish. fr.wikipedia has an article about him. The redlink above might turn blue... perhaps. Thanks again.--Shirt58 (talk) 09:09, 26 November 2010 (UTC)

Actually it should be %5b and %5d which are the hexadecimal values, not decimal. CS Miller (talk) 16:01, 26 November 2010 (UTC)

Is autism a human polyphenism similar to those of social insects?

This isn't a topic I know much about, but I was thinking... It is well recognized that locusts switch between a solitary existence and one in which they form vast gregarious migratory swarms. This is dependent on a very simple mechanism involving the foraging gene (a cGMP-dependent protein kinase or PKGI) and increased serotonin levels in the nervous system. This mechanism has a similar function in Drosophila melanogaster, and also controls foraging vs. defender behavior in worker ants.[1]

Now the same sort of PKGI protein controls serotonin uptake by SERT in mammals also.[2] Variants of SERT have been associated with certain autistic traits,[3] Autism can be associated with increased serotonin levels, and various SSRIs have been suggested as treatments.[4] (At first glance the elevated serotonin seems the wrong way, but one could argue that it is in some way compensatory... I'll leave this hanging for now)

Now putting together these things, and if I credit the common ancestor of bilateral animals with some sophistication, I am tempted to suppose that there was some primordial mechanism to use PGKI and serotonin to dictate a different "phase" or behavioral phenotype which was more social in nature. This leads to the idea that at least some forms of autism are a pre-existing, adaptive model of human behavior, rather than a disease. Perhaps it was maintained if as a variation in populations of all preceding ancestors, or at least as a working genetic regulatory system that could be called upon at need; or else it might be that the way the nervous system works allows the same genetic changes to recreate similar changes of behavior even hundreds of millions of years apart from the first instance. (Autism could also result from non-adaptive genetic mutations, just as white skin can arise from albinism rather than an ancient variant of MC1r)

But now to the question. Is it possible for an autistic person to live in a traditional hunter-gatherer society, either Paleolithic or Neolithic (or as best an approximation as can be found) without suffering any selective disadvantage? Apparently autism is still relatively uncharacterized in developing countries, but does exist.[5] Most of the discussion I find about autism and hunter-gatherer lifestyles focuses more on hunter-gatherer diet, said by some to help with the disease, but that's not what I'm looking for. In order for autism to be a true human polyphenism, there has to be some environment in which it is not maladaptive. Actually, that last sentence was quite a stupid thing to say, especially in reference to insect polyphenism! What I mean is that the potential to become autistic would have had to have been preserved by some means, even if the mechanism is prone to be phrased in terms of the ever-controversial group or kin selection. Wnt (talk) 10:06, 21 November 2010 (UTC)

I don't accept your implicit assumption that autism would automatically be maladaptive in hunter-gatherer societies, at least not in relatively mild forms. You could argue, for example, that mild autism could be a benefit for someone who is engaging in solitary trapping of small animals. Modern hunter-gatherer societies show a high level of individual specialization, and hence can accomodate a range of personality types. Physchim62 (talk) 12:02, 21 November 2010 (UTC)

Sorry if I was confusing: that's not my assumption but the question. While I would speculate that it is possible that autistic people could do well in such societies (otherwise the answer to the title question is probably "no"), I'd really like to see if there's evidence. Certainly it is believed in conventional circles that autism is a disease and a disability, and I'd like to actually have a concrete example to point to to show otherwise.

Another reason to look for concrete examples is that the rate of autism in society is apparently highly variable (and currently increasing), and only in a society where autism and non-autism are of equal fitness can one see what the "natural" rate of autism among humans might be. (At least, assuming that the developmental decision process is adaptive) I should point out that if it is a polyphenism rather than a disease - in other words, if people are already "pre-loaded" with autistic developmental software and rely only on environmental cues to determine whether to activate it or not) there may be no upper limit on how common it could become - if there is some lifestyle habit, food, chemical, ultrasonic noise, etc. that affects which behavioral phenotype is expressed, you could find yourself in a situation in a few years where 50% or more of children are autistic. It is possible that some unknown trigger (for example, the concentration of carbon dioxide in the atmosphere) could cross a tipping point to cause this, but still be virtually impossible to identify. It is even possible that such stimuli could have a cumulative epigenetic effect in the parents, so that once the change occurs, it is irreversible for a large portion of society. These are of course very remote possibilities, but it's almost an apocalyptic scenario. It would help to rule out very widespread autism in the future if you can identify a society where autistic people do well and show that even there the rate is very low. Wnt (talk) 13:08, 21 November 2010 (UTC)

This is a very interesting question, but I don't think you're going to get a concrete answer and you're probably asking for opinions, as you've evidently researched this in some depth without finding anything yourself. For starters, I think it's important to question whether autism is maladaptive in today's society, although in severe cases it obviously is, at the less severe end of the spectrum though you'll find many scientists and mathmaticians - [6] by Simon Baron-Cohen who has worked on this e.g [7]. That makes me wonder whether an argument could be made that as today's world is more technical and abstract than in the past, maybe autism is adaptive. This is obviously guesswork, but maybe the industrial revolution selected for genes linked with autism and severe cases of autism are a result of individuals having two recessive alleles or something (sorry, I'm not a geneticist!). This discusses how similar points have been raised regarding schizophrenia and creativity, and reminding us of the thin line between genius and insanity (maybe they are the same). These ideas are linked to neurodiversity - it's pretty obivous that there is no such thing as "normal" when it comes to the way people think and this is a good thing because we are all good at different things. Combined, this has allowed us to go further than if we all thought in the same way and as a society we are stronger as a result. I don't think that anyone has written about this, but in the same way that a more genetically diverse animal population is more likely to survive changes in the environment, the same may well apply to the way our brains work, but in a slightly different way. For example if we need to solve a problem, you may need somebody creative (more schizophrenic) to come up with the idea in the first place, but then someone who pays attention to details (more autistic) to actually design and implement the solution. This links pretty nicely with insect polymorphism, for example in leaf cutter ants where the many different castes perform the jobs they do best and the colony as a whole benefits from that. So, I haven't really answered your question, but I've hopefully provided an alternative viewpoint. SmartSE (talk) 14:36, 21 November 2010 (UTC)

I'm starting to believe that being Neurotypical is a real live example of the Green-beard effect --Digrpat (talk) 23:46, 21 November 2010 (UTC)

I believe in neurodiversity, and more generally, that both genetic diversity and other forms of phenotypic plasticity and diversity are maintained within many species. I suspect that there are many of us here on Wikipedia who are some small distance into the autism spectrum; even so, it's been my impression that the average family returning from the pediatrician with a diagnosis of autism is not expecting a great mathematician or even an average student. When autism is accompanied by retardation, I don't know whether that is because it is one symptom of a more widespread problem, or whether autism interferes with learning as it occurs in our society. I suppose I've been assuming the latter when asking about ancient or primitive cultures; if it were the former, I suppose that Aspberger's Syndrome or some otherwise defined subset of the autism spectrum might count as the polyphenism in question above, with more severe autism being something of a red herring. But looking at locusts from an anthropomorphic perspective, I tend to doubt that: a locust who won't follow and eat with the swarm surely must seem profoundly developmentally disabled to its peers.

The "extreme male brain" model of autism seems somewhat offensive, since it's based on the idea (I would be prone to say myth) that women can't do math, science, or technical work. I think that there are (wrong) racist arguments that seem more plausible. To me it would seem more likely that men, lacking a second X chromosome, are somehow more prone to autism on a genetic basis, and a greater than expected number of subtle autistic phenotypes have tinged the studies about differences between male and female. There is also an argument regarding the idea that autism and schizophrenia are opposite ends of a spectrum, and schizophrenics aren't "more female".[8]

vortex launcher : pressure amount area

Hi guys,

recently i have been puzzling over vortex launchers because of the military non lethal one that has been proposed. It is designed to produce a vortex with enough strength to knock someone down. At first i thought that this was folly since the law of equal and opposite reactions meant that if it produced enough force going one way to knock over a person, sureley the person holding it would be knocked down as well. then I began to think, the vortex is caused firstly by an explosion in a 3inch diametre blast chamber (read the report). then the flow is expanded via the nozzle as it travels up it and out and arrives at the target as a 2ft diamtre vortex. Would that mean that even though the pressure in the blast chamber is greater than the vortex pressure on the target, it is over a much smaller area so is not as effective at moving the whole system backwards. A similar example would be a ship on water, if i set off an explosion on a small part of a ship, it may destroy a part of the ship, but the whole thing will not move across the water, but the much smaller pressure of the wind on the sale, which is a significantly larger area, can move the whole ship across the water. Do you think the vortex launcher works something like that, more pressure but in a smaller area at the launcher, so it experiences a jolt, but less pressure but more area at the target so it is moved backwards (knocked over)

Does that make sense or have I missed something.

Many thanks. —Preceding unsigned comment added by 62.3.99.14 (talk) 11:11, 21 November 2010 (UTC)

It is not necessary that all the momentum comes from the "vortex launcher" since the vortex interacts with the surrounding air. Also the shouter can maybe seek support while the target are unprepared. Even given this I have difficulties in seeing that it could be a practical weapon in most situations. --Gr8xoz (talk) 01:07, 22 November 2010 (UTC)

Is it safe to drive after drinking cough syrup?

I feel euphoric and other pleasant senses. There's something about cough syrup that just alters the way I feel and etc.

But I have this gut feeling about driving that caused me to ask you here: Is it safe to drive after having had cough syrup? Please let me know ASAP, and don't forget to cite sources. --70.179.178.5 (talk) 13:28, 21 November 2010 (UTC)

Are you talking about a normal dose, or intentional abuse of dextromethorphan, or something else? There are many different cough syrups with different active ingredients. Do you want to specify one in particular? Wnt (talk) 13:33, 21 November 2010 (UTC)

Edit conflict - It is policy here not to answer medical advice questions. Please read the package insert of your cough syrup to find out if you can safely drive under medication from its contents, which as user:Wnt pointed out we cannot know. Please ask a qualified Pharmacist or Medical Doctor near your location for their advice regarding this matter. --79.219.104.60 (talk) 13:36, 21 November 2010 (UTC)

I have added back the above response which was removed by the OP [9] with the claim it was 'unconstructive' Nil Einne (talk) 18:11, 21 November 2010 (UTC)

Regardless of that, do you really want to trust some randomers on the internet about this? Maybe ask you doctor! SmartSE (talk) 13:56, 21 November 2010 (UTC)

SmartSE, my doctor is not in on weekends. Otherwise I would've called him already. --70.179.178.5 (talk) 14:46, 21 November 2010 (UTC)

Wasn't there a leaflet in the box? If so, read it carefully. If not, and you can't get advice anywhere else, be safe and don't drive. No-one here can help you any further because we don't know what is in that particular cough syrup. Don't take medicines for a sense of euphoria, only for the medical conditions they are meant for. Itsmejudith (talk) 17:20, 21 November 2010 (UTC)

Words of wisdom: when a question says "please let me know ASAP, and don't forget to cite sources", it should be treated as trolling. Looie496 (talk) 17:21, 21 November 2010 (UTC)

More so when the OP removes helpful answers. Nil Einne (talk) 18:11, 21 November 2010 (UTC)

Most UK medicines in this class have the following warning - "Warning. May cause drowsiness. If affected do not drive or operate machinery." Exxolon (talk) 20:00, 23 November 2010 (UTC)

In the US, the standard warning is "do not drive or operate heavy machinery while using this product". This was amusing when placed on a bottle of children's cough syrup ... so can we assume it's OK for toddlers to drive and operate heavy machinery after they get over their colds ? :-) StuRat (talk) 20:14, 23 November 2010 (UTC)

Limits on number of channels in MIMO wireless

In my answer to the question Wireless v Fibre on the 16/11 [10] I assumed that the maximum number of independent MIMO- channels in future wireless internet connections is limited to 10. This question got me thinking on what the physical limits really are and how they depends asymptotically to the size of the antenna arrays. I has not been able to find any work on this, maybe be course I do not know the terminology.

In theory it should be possible to place any number N antennas in a arbitrary small area on the transmitter and receiver and get N independent channels but if the antennas are to closely spaced the problem with separating the independent channels will be very ill-conditioned. It will be a hard inverse problem that will get very bad signal to noise ratio.

So the question is: How will the number of possible independent channels depend on the size of the antenna arrays given that the separation of the channels should be a reasonable well-conditioned problem?

This should be the same as to say that the needed power at the sender should scale linearly in the number of channels.

In the case of free space communication my guess based on intuition and calculation of the angular resolution of the antennas are:

$N<C\left({\frac {D_{t}D_{r}}{\lambda L}}\right)^{2}$

Where N is the number of independent channels, C is a small constant depending on how well-conditioned the system should be, $D_{t}$ is the diameter of the transmitter array, $D_{r}$ is the diameter of the receiver array, $\lambda$ is the wave length and L is the distance between the transmitter and the receiver. I think this should be valid for $\lambda <<D_{t}$, $\lambda <<D_{r}$, $D_{t}<<L$ and $D_{r}<<L$.

Is this correct?

An example $D_{t}=3m$, $D_{r}=3m$, $L=1000m$ and $\lambda =0.003m$ (100 GHz) would give 9 C channels.

There are much hype around Orbital Angular Momentum (OAM) [11] but I do not think it will make any difference for this limit, is this correct?

In the presence of reflectors the number of channels can be increased and in the extreme case when the transmitter and the receiver are in the focal points of a reflective ellipsoid cover the limit should be something like: $N<C\min \left(\left({\frac {D_{t}}{\lambda }}\right)^{2},\left({\frac {D_{r}}{\lambda }}\right)^{2}\right)$

In a network the capacity can be increased by using more than one base station.

Any ideas of what number of MIMO- channels that can be used in the future for fixed data-links (point to point), stationary roof mounted antennas in a cellular system and in portable devices? --Gr8xoz (talk) 14:19, 21 November 2010 (UTC)

If you try to pack too many antennas in a small space, the power required will grow exponentially with the number of antennas. Totally negating the benefit, as you could get that by having more bits per symbol anyway. You can try to imagine how many antennas on a portable device. At the wavelengths used you could get about two, and if you allow diverse polarization as well, perhaps you can get 4 independent signals on your handheld device. For larger implementations, it is going to be mostly 2 dimensional on the surface of the earth. In a stationary application, you can have a tradeoff with independent antennas, or getting gain with a directional antenna and increasing the bits per symbol. remember also that the cost will be proportional to the number of antennas, so having 1000 antennas in a circle to get 1000 times the bit rate may not be economical, it may be better to run in an optical fibre. Graeme Bartlett (talk) 09:53, 22 November 2010 (UTC)

Thank you for the answer. How many antennas is to many in a given space? I assume it is the number of independent channels that is limited, many antennas sending the same signal does not require more power. I also think that about 4 channels on a hand-held device at today's frequencies is around the maximum but the trend are for frequencies to go up over time, from 415 MHz NMT to 2.6 GHz 4G and 5 GHz WiMAX, the question is where does it stop and how many independent channels can be used then.

My impression was that as long as you do not pack the antennas to tight the power rises linearly with the number of channels and the capacity while the power rises exponentially with the number of bits/s/Hz/channel. See Shannon–Hartley theorem.

For the same reason the needed surface-area of a directional antenna will increase exponentially with the number of bits/s/Hz/channel while the needed surface area for a antenna array in a MIMO-system only should increase by the square-root of the needed capacity.

Antenna arrays aligned with the surface of the earth is of curse the way to go for radio astronomy and deep-space communication. I think that in order to get 2D MIMO you will need a projected area perpendicular to the direction of communication, for communication along the surface of the earth it will become a 1D MIMO-system. I was thinking more of integrated antennas on printed circuit-boards in the size of a normal satellite dish operating at high frequencies (10-300 GHz). The current fastest data-link operates at 85 GHz. I do not see the cost of the antennas as important in such an installation but of curse the transceivers and signal processing will cost a loot today but they follow Moore's law.

An optical fibre is of curse a good alternative in many cases.--Gr8xoz (talk) 11:48, 22 November 2010 (UTC)

Your sensible limit will be determined by diffraction limits, and will be about a square half wavelength per antenna. Also double that to get the alternate polarization. You could print the antenna on a circuit board, but as you say a 1D arrangement is probably the best that you will do for an earth surface system. If you can scatter bases over buildings or vehicles then you may be able to take advantage of 2D patterns. I was thinking that if you can have an electrically controlled hologram, you could send a coherent beam of light off in different directions to your base stations. The electric control would enable to beams to be steered to keep them on target as your mobile moved. However you really need a clear line of site for this to work. At your 300GHz you could get 4 per mm (Vertical and Horizontal for two half wavelengths). So with a meter of length of antenna you could have 4000 beams. Graeme Bartlett (talk) 11:51, 24 November 2010 (UTC)

As I understand it those 4000 beams will be in all directions only a few will hit the receiver if it is small compared to the distance. That was the idea behind the formula $N<C\min \left(\left({\frac {D_{t}}{\lambda }}\right)^{2},\left({\frac {D_{r}}{\lambda }}\right)^{2}\right)$ where I asume that there are a useful path in any direction, this is the 2D-case, remove the square to get the 1D case. As I understand it is your sugestion is that C=4.

I was maybe unclear in my first post, the formula $N<C\left({\frac {D_{t}D_{r}}{\lambda L}}\right)^{2}$ is based on the diffraction-limited angular resolution of each antenna. The angular resolution of the transmitter are $1.22\left({\frac {D_{t}}{\lambda }}\right)$, the receiver takes an angle of ${\frac {D_{r}}{L}}$ that means that the transmitter can point out $N=C\left({\frac {D_{t}D_{r}}{\lambda L}}\right)^{2}$ points on the receiver. You can of curse use the receiver to resolve the transmitting antennas in stead if you want to. The same formula apply if you divide both antenna arrays in to directional sub arrays. Lets say the transmitter can resolve 9 by 9 points on the receiver (81 channels), if we divide both the transmiter and receiver in 3 by 3 sub-arrays, each sub-array on the transmitter can now resolve the 3 by 3 sub-arrays on the receiver and the sub-arrays of the receiver can resolve and separate the signals from the sub-arrays of the transmitter. Each sub-array of the transmitter can send 9 signals, one to each sub-array of the receiver and there are 9 transmitter sub-arrays so the total number of channels are still 81.

Is this the right way to think of it or can the other beams (4000 in your case) be used by some holographic trick to get significantly more channels?

I also think a hologram is a good way to think of a fully controlled antenna array. When you say "light" do you mean visible light (400 to 800 THz) or more generally electromagnetic radiation including microwaves? Why do I need a clear line of sight for this to work? I would think that this would work even for reflections as long as they are "mirror like" (at the relevant frequencies) and that multiple "mirrors" should increase the capacity by simulating more receivers/transmitters. Of curse the problem of channel estimation becomes harder in a environment with unknown reflections such as a city. --Gr8xoz (talk) 14:03, 24 November 2010 (UTC)

Origin of particle diversity

What is the origin of such a diverse world of elementary particles (if you exclude the divine one)? As the vacuum state says, the default vacuum has a zero-point energy, so (if I'm not mistaken) it can support only Higgs boson or photon annihilation at best. How can low-energy Higgs bosons or photons produce so many different particles if they were the original stuff for annihilation? (leaving aside the Big Bang as the high energy origin, because the explosion reason and the origin of pre-Bang ingredients are unclear so far) Twilightchill t 14:33, 21 November 2010 (UTC)

Nobody knows what the origin of particle diversity is. One of the ambitious goals of string theory and other Theories of Everything is that, if correct, one of these theories will clear up why things are the way they are — it'll turn out that logically they have to be the way they are. (An analogy — in 1913, it was a good question to ask, why are the Bohr atom electron orbits exactly where they are? Doesn't that seem arbitrary? But in 1924 De Broglie showed that their orbits are absolutely necessary according to the idea that the electron was actually a standing wave that could not cancel itself out. What seemed arbitrary at first was really just an imperfect understanding of the nature of the physical universe itself, which really did not allow alternatives.) It's certainly the most ambitious goal of modern physics to figure out why things are as they are, and not some other way. There are some who believe that universes pop into and out of existence all the time (e.g. in the multiverse), and so what we have is a quasi-Darwinian situation where of course the only universe that we happen to have come into existence in happens to be not only stable but contain a mixture of things that are allowable for the formation of suns and planets and water and life (see anthropic principle). For some that's a good enough answer, for others it isn't. --Mr.98 (talk) 14:40, 21 November 2010 (UTC)

"The default vacuum has a zero-point energy, so it can support only Higgs boson or photon annihilation at best" makes no sense to me, and I think it's simply wrong. In modern physics the vacuum effectively supports everything; we are perturbations of the vacuum. It's also not true that photons and Higgs bosons were the first particles. What determines the particle types is the various ways in which the vacuum can vibrate, so the question is why the vacuum can vibrate in those ways and not others. The various grand unified theories are about finding a simple vacuum "structure" that can vibrate in those ways and not others. For example, in SO(10) grand unification you can imagine there's a 10-dimensional sphere attached to every point in spacetime, and the various Standard Model bosons (except the Higgs) arise as rotations of the spheres, while the different fermions are more or less different spherical harmonics of the spheres. These models predict additional bosons arising from other rotational motions of the spheres, so one has to find a way to explain why those bosons haven't been seen. But that's not too difficult; you can invent a mechanism similar to the one that makes the weak force so weak. Unfortunately, these theories are difficult to test, so we remain ignorant about what's really going on. Hopefully data from the LHC will finally clarify things, but it might not. -- BenRG (talk) 02:22, 22 November 2010 (UTC)

Electroplating With Lemon Juice?

The other day I decided to clean some extremely corroded and grimy coins that I had laying around my room. One was a United States nickel and the other a US penny. In order to clean the coins, I placed them in a small container of lemon juice in hopes that the acid would help remove some of the grime. After a day, I removed them from the container and to my surprise, the penny was delightfully shiny, while the nickel had turned copper as well! I assumed that some sort of electroplating had occurred, but the container was never exposed to an electrical field. Could someone please help explain to me what has happened to these coins? Thanks! Stripey the crab (talk) 14:51, 21 November 2010 (UTC)

There was an electrical field, which was set up by the battery you inadvertently created. See Galvanic cell. Going from metallic nickel and copper ions to metallic copper and nickel ions is chemically favorable (see electromotive series and Standard electrode potential (data page)), like going from metallic zinc and copper ions to metallic copper and zinc ions. It's just that, instead of having two separate electrodes with a wire between, you have different parts of the same coin acting as the two electrodes and the wire. -- 174.24.198.158 (talk) 19:26, 21 November 2010 (UTC)

Waste of lemon juice. --90.219.114.59 (talk) 23:16, 21 November 2010 (UTC)

I want to repeat this experiment. Will vinegar work for the acid? Will it help to put some table salt in it? Should the coins be touching or not? —Bkell (talk) 05:01, 22 November 2010 (UTC)

Those are good experiments to try. If we told you what the results would be, they wouldn't be experiments. Cuddlyable3 (talk) 09:08, 22 November 2010 (UTC)

Heh, okay. :-) —Bkell (talk) 14:23, 22 November 2010 (UTC)

I don't think that the coins have to touch. The copper(II) oxide and carbonate on the penny coin dissolves in the acid to make copper(II) acetate. The copper(II) acetate reacts with the nickel in the nickel coin to make nickel(II) acetate and copper metal. Sorry for ruining your experiment, do it anyway! --Chemicalinterest (talk) 15:28, 22 November 2010 (UTC)

Enema washes aren't enough; will taking many laxatives help lose substantial weight?

Hi, the Enema Wash on my BioBidet BB-i3000 ( http://www.BioBidet.com ) isn't doing enough of a job at forcing weight out of my system. It has improved my weight loss, but not by enough in my opinion. I currently weigh 178 lbs. at 5'11.5", but will try to get down to a nice, round 150 lbs. (below 135 is underweight.)

So if I take a lot of laxatives, how much will that help me lose more weight? Also, what ill side-effects might it have?

Besides, what ill side effects will giving myself extra enema-washes from bidet-seats give me? --70.179.178.5 (talk) 14:56, 21 November 2010 (UTC)

Request for medical advice removed. Please consult an appropriate physician for advice on any aggressive weight loss scheme. 71.228.185.250 (talk) 15:05, 21 November 2010 (UTC)

Mass of energy?

Something is wrong with this set-up, but I'm not sure what. Let's say I turn a kilogram of mass into (1kg)*c^2 energy. If energy is massless, I should be able to lift it up ten metres for free. I then turn it back to matter and run in through a watermill and generate free energy. Is the problem in my assumption that energy is massless? I'm guessing so given that black holes can attract light. 142.244.236.20 (talk) 22:06, 21 November 2010 (UTC)

If you can turn a Kilogram of mass into energy, why are you bothering with watermills? AndyTheGrump (talk) 23:11, 21 November 2010 (UTC)

Because I don't want my kilogram consumed in the process; it has sentimental value. 142.244.236.20 (talk) 23:13, 21 November 2010 (UTC)

And because antimatter is really expensive... Googlemeister (talk) 15:08, 22 November 2010 (UTC)

It turns out that moving your equivalent-to-one-kilogram-of-matter chunk of energy up a gravity gradient costs exactly the same amount of energy as moving the original one-kilogram mass. For example, if you point a flashlight straight up, the photons will get (ever-so-slightly) redder as they gain altitude. (See gravitational redshift for more details.) Your kilogram mass at ground level will be just a little bit lighter once you've lifted it up ten meters, whether you convert it to energy or leave it as matter during the trip. Each time you repeat the cycle, you lose a little bit of mass/energy — that's where the energy coming out of the watermill in your thought experiment is coming from. TenOfAllTrades(talk) 23:30, 21 November 2010 (UTC)

What do you mean when you say my kilogram will be lighter after the trip even if I leave it as matter? Does something with more potential energy have less mass? Where did that mass go, did it lose a very small number of atoms? 142.244.236.20 (talk) 02:11, 22 November 2010 (UTC)

For light to climb out of a gravity well it cannibalizes some of its own energy to do so, so it ends up massing less (compared to other object also out of the gravity well). On the other hand, if you compare that mass to something at the ground you will find no change in the mass because the potential energy of the gravity adds to the mass (so it traded light-energy into gravitational potential energy). Yes, I know it's complicated. If you carry matter up against gravity, you have to add energy externally to do it, since you can't steal energy from the mass itself, this energy you added will, of course, add to the mass of the matter. No atoms are gained or lost, the change in mass (and weight) is entirely due to change in potential energy. Potential energy from gravity is particularly hairy to calculate since it's totally relative to what you are measuring against. There is a reason scientists usually deal only with rest mass when possible, since calculating the true mass of something is not just hard, it's also not a single number - it depends on what you compare to. Ariel. (talk) 02:52, 22 November 2010 (UTC)

The fundamental assumptions in the question are flawed, mass is identical to energy mass can not be turned in to energy, it is energy and 1 kg will be 1 kg = 9e16 J regardless of what form of energy it is. Energy is not massless, it is mass so the OP:s suspicion of the flaw is correct. Matter is a category of energy that covers almost everything we normally think of as mass, it is not an entirely well defined category. --Gr8xoz (talk) 00:58, 22 November 2010 (UTC)

TenOfAllTrades gave you the correct answer, but I wanted to add that energy is not massless. Not only does it have mass, it also has weight. So if you had the energy in 1kg all as light (photons), somehow stored in a box, that box would actually weigh 1kg just from the energy. Ariel. (talk) 01:47, 22 November 2010 (UTC)

If photons have mass, how can they travel at the speed of light? 142.244.236.20 (talk) 02:11, 22 November 2010 (UTC)

Because although a so-called massless particle like a photon has mass, it has a rest mass of zero. See mass in special relativity. Red Act (talk) 02:35, 22 November 2010 (UTC)

The fundamental flaw in the question is the assumption that matter can be turned into "pure" energy. You can't. Energy is no substance, it is a quantity that has to be ascribed to a material system depending on its mass and state of motion. Indeed, mass and energy are not the same thing, however often you write down $E=mc^{2}$ (that equation is only valid/useful in the rest frame of the mass m - there is the alternative interpretation of "relativistic mass" advocated by Gr8xoz but that is not useful (because it hides the physical difference between mass and energy) and is not used in physics any more). Radiation is not "pure energy" either, it is better viewed as a substance, i.e. matter in a broad sense. A single photon always has zero mass, but a collection of photons (say, a photon gas confined within a box of negligible mass) can have an effective mass. May sound strange, but that's how special relativity works. --Wrongfilter (talk) 10:06, 22 November 2010 (UTC)

I'm sorry, but this is incorrect. A single photon has mass, and so does a collection of them. Matter CAN be turned into "pure" (as you call it) energy. For example you can convert matter into kinetic energy (assuming you have some anti-matter, but anti-matter is still matter). Mass and energy are in fact the same thing, it's impossible to make a logically consistent distinction between them. You can distinguish between zero rest mass and non zero, but that's all. Ariel. (talk) 11:40, 22 November 2010 (UTC)

As I said, there are two conventions. The one that is in use in theoretical physics (have a look at a current text book on relativity) uses mass for the invariant length of the 4-momentum vector, and energy for its time component (3-momentum gives the three spatial components). The full equation is $mc^{2}={\sqrt {E^{2}-p^{2}c^{2}}}$. Energy and mass (and 3-momentum) are intricately linked, of course, but they are not the same. If you annihilate matter and anti-matter you don't get pure energy. You get radiation, which has energy. --Wrongfilter (talk) 12:49, 22 November 2010 (UTC)

Ummm ... if energy and mass are not the same, then perhaps you can demonstrate this by giving an example of a system that has energy without mass, or mass without energy - or a process that changes a system's mass without changing its energy, or vice versa ? Gandalf61 (talk) 13:49, 22 November 2010 (UTC)

A single photon that has energy $E=h\nu$ has momentum $p=h\nu /c$ and zero mass. If I switch reference frame, the photon's frequency, and thus its energy and momentum, will change (Doppler effect in SRT) but the mass will remain at 0. A system of two photons (of equal frequency) that are moving in opposite spatial direction has energy 2E, and total momentum p=0, hence mass $2E/c^{2}$. That's why a box containing a gas of photons whose momenta cancel each other (so that the box as a whole stays at rest in my reference frame) will have effective mass which is (numerically) equal to the sum of their energies. There is no system with non-zero mass and zero energy - this is precisely the meaning of $E=mc^{2}$. For a system that is in motion as a whole, the energy will always be larger than its mass (multiplied by c²). Mass is an intrinsic property of a system which is invariant with respect to changes of reference system, energy is not. The mass of a particle tells you what states of motion are possible for it; the energy (and the momentum) tell you what the actual current state of motion of the particle is. --Wrongfilter (talk) 15:14, 22 November 2010 (UTC)

Locally, incidentally, any process conserves 4-momentum, hence energy and (ordinary) momentum, hence also mass. That's the shortest answer to OP's question. --Wrongfilter (talk) 15:16, 22 November 2010 (UTC)

So with that definition of mass, two photons of equal frequency travelling in opposite directions have a joint energy of 2E and a joint mass of $2E/c^{2}$ - but if you consider each photon individually, it has an energy of E but a mass of 0 ? Gandalf61 (talk) 16:55, 22 November 2010 (UTC)

That's weird, isn't it? I think it has to do with the fact that the concept of "opposite directions" is not invariant. If you go to another reference system the angle between the directions changes. --Wrongfilter (talk) 17:17, 22 November 2010 (UTC)

See Mass in special relativity for a discussion of the distinction between "invariant mass" and "relativistic mass" which is what this argument comes down to. Which is the true "mass" is a question of semantics. Rckrone (talk) 18:19, 22 November 2010 (UTC)

This is one of the reasons that I think the concept of relativistic mass deserves a little more respect than it sometimes gets. Intuitively, the mass of the whole should be the sum of the mass of the parts. That's true for relativistic mass, not true for invariant mass. --Trovatore (talk) 18:17, 22 November 2010 (UTC)

Pre-mitochondrial eukaryote

How did eukaryotes process energy before merging with mitochondria? 142.244.236.20 (talk) 22:08, 21 November 2010 (UTC)

See Mitochondrion#Origin and Endosymbiotic_theory. The pre-eukaryotic cells would have probably used biochemical pathways like glycolysis and fermentation (biochemistry). --- Medical geneticist (talk) 22:26, 21 November 2010 (UTC)

Evolution without Cretaceous–Tertiary extinction event

Would there be major evolutionary disruptions if the Cretaceous–Tertiary extinction didn't occur? I think the evolution would have take much more time at best and the man would have little chances to pop out and survive... —Preceding unsigned comment added by 89.77.158.172 (talk) 23:36, 21 November 2010 (UTC)

This is very hypothetical. Still, I should point out that mammals filled the ecological niches left by the extinction, for example, by producing megafauna. I think the question here is whether dinosaurs or mammals would have better adapted to the climate changes over the last 65 millions years, such as the ice ages. —Arctic Gnome (talk • contribs) 23:47, 21 November 2010 (UTC)

Of course the life on earth would be very different if the CT extinction didn't take place. Essentially what you are asking is if life evolved differently, would it be different?.. How different is impossible to say from our perspective. Every evolutionary biologist would love to have a machine that could replay evolution from a chosen point in earth's history, that kind of machine would answer a lot of questions. I would also just point out that "evolution would have taken much more time" is a meaningless statement. Evolution doesn't have a "vector" or purpose except for fitness, the vectors can only be drawn in post hoc. Unlike Star Trek might have you believe, bipedal tetrapods with big brains are not the ultimate goal of evolution. Vespine (talk) 02:38, 22 November 2010 (UTC)

How many feet do bipedal tetrapods have? --Lgriot (talk) 12:38, 22 November 2010 (UTC)

Two. WikiDao ☯ (talk) 15:38, 22 November 2010 (UTC)

It is 100% certain that our species would NOT exist. Cause and effect could not conceivably have led to our species, given such a fundamentally different foundation. It is literally inconceivable. 63.17.93.42 (talk) 04:24, 22 November 2010 (UTC)

Our article on the extinction (a featured article, no less) mentions that there is not universal support for the exact cause of the extinction, which makes it extremely difficult to figure out how "it" (the cause of the extinction) not happening might affect everything else. In terms of dinosaurs, the article confirms my recollections of the current state of evidence: "The dinosaur fossil record has been interpreted to show both a decline in diversity and no decline in diversity during the last few million years of the Cretaceous..." and "Whether the extinction occurred gradually or very suddenly is debatable, as both views have support in the fossil record." The point being that if non-avian dinosaurs were declining in numbers for whatever reason anyway, their continued existence may not have played much of a part in affecting the survival of birds and mammals that were around at the time. Matt Deres (talk) 14:52, 22 November 2010 (UTC)