Wikipedia:Reference desk/Archives/Science/2014 April 29

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

April 29

How can a universe have properties as a whole, how can it live in a time realm not of its own making?

I miss (in the Big bang lemma) a discussion about the following problem:

A universe only can be said to expand if it has a finite inside dimension –which in increases in time.

Not to mention that Big Bang cosmology in speaking about its age, asserts that the universe lives in a time realm not of its own making, doesn’t a (finite) inside dimension imply a finite outside size –even though it obviously cannot be measured from the outside as space and time, the meter and second aren’t defined outside of it?

Put differently, what is the significance of statements about the size and age of the universe if by definition there is nothing outside of it with respect to which its size and age matters, physically?

Can someone explain how a universe can have particular properties and evolve as a whole if there is nothing outside of it with respect to which it can have properties, can interact with and express such properties? Antonquery (talk) 00:25, 29 April 2014 (UTC)

You've got a false premise there: the measurement of the size and age of the universe does not imply the existence of any exterior thing relative to which that measurement must be made. All the measurements are made with respect to things inside the universe that are - of necessity - younger and smaller than it. When we say the universe is 13.7 million years old, we do not mean that anything at all happened or existed 14 million years ago - we just mean that the universe has existed a bit more than two and a half times as long as the earth has. And the expansion of the universe means that we can determine that all objects were closer together long ago. It doesn't mean there's a space they've expanded into, and it doesn't mean there's a centre they've expanded from. AlexTiefling (talk) 00:34, 29 April 2014 (UTC)

Psst... billion, not million, right? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:15, 29 April 2014 (UTC)

A million years here, a million years there, pretty soon you're talking about a real long time. —Tamfang (talk) 03:42, 29 April 2014 (UTC)

Ehh, what's a factor of a thousand between colleagues? AlexTiefling (talk) 11:32, 29 April 2014 (UTC)

The OP calls the Big Bang theory a lemma which is a philosophical statement that one accepts as true in order to find out whether another statement is true. This rightly characterizes the theory as a hypothetical model that strives to put an explanation to our observation that the universe is expanding. The idea began with Edwin Hubble's observation that all distant galaxies and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity, regardless of direction. Assuming that we are not at the center of a giant explosion, it must seem that all observable regions of the universe are receding from each other. Big Bang theory proposes that it has "always" been doing that, where the quotes show that such a simplistic assumption creates the paradox that everything originated from an abstract singular point. The implication is that if one could rewind in time our view of the universe and see it shrink, its outer border would come into view. For the moment, the popularity of the Big Bang model relies on Albert Einstein's general relativity and on simplifying assumptions such as homogeneity and isotropy of space. Since Copernicus, scientific thought has insisted that Earth is not in a central, specially favored position in the universe nor that humans are privileged observers of the universe. Thus we can do no more than theorize about what limits might exist, or existence itself, beyond our particular Cosmological horizon as in the OP's question about the Size of the universe. 84.209.89.214 (talk) 11:26, 29 April 2014 (UTC)

Lemma can also denote a headword in a dictionary or something similar. That's how the OP was using it—as a (somewhat confusing) way of saying "the article with 'Big Bang' as its title", not to refer to "a philosophical statement that one accepts as true in order to find out whether another statement is true". Deor (talk)

• I'd just like to add a pointer to Mach's principle, which is relevant to this discussion even if it doesn't apply directly. Looie496 (talk) 14:36, 29 April 2014 (UTC)

Is it true that eating burned food is not good for you?

^Topic ScienceApe (talk) 00:54, 29 April 2014 (UTC)

Shonuff. --Jayron32 01:39, 29 April 2014 (UTC)

For refs on WP, see Cooking#Cooking_and_carcinogens, and Heterocyclic_amine_formation_in_meat. SemanticMantis (talk) 13:10, 29 April 2014 (UTC)

From an Epicurean standpoint, it's terrible waste. Even if it doesn't kill you, you're never really "living" on char. InedibleHulk (talk) 00:20, 4 May 2014 (UTC)

Well, there you have it. After 20 years of people yammering at us to cook our meat until it's brown and flavorless to avoid E. coli, now they're turning around and snickering at us and saying ha, we gave you cancer. People should reject newfangled and dangerous inventions like partial dehydrogenation, but when it comes to an ancient practice like cooking, or which foods you choose to eat, a few thousand years of modern-era evolution of both genes and culture should give us some confidence that no matter what you do, you'll face a certain small risk of death. Wnt (talk) 04:43, 5 May 2014 (UTC)

Hans Meyer and Ernest Overton in Lund

Greetings. A photo of Hans Meyer and Ernest Overton taken in Lund, Sweden between 1907 and 1911 exists on Wiki. I have seen it twice but cannot find it again. Any suggestions? I have looked on wikis in various languages but I can' locate the page with that photo. — Preceding unsigned comment added by 2602:30A:C08C:F440:0:0:0:41 (talk) 01:42, 29 April 2014 (UTC)

Milk gone off but doesn't smell bad?

Is it possible for milk to curdle without smelling bad? I just poured milk on my cereal and it was all nasty and lumpy but there was no smell. Is that possible naturally or is my housemate trying to kill me? --78.148.106.196 (talk) 07:47, 29 April 2014 (UTC)

Sure it's possible naturally -- that's how they make cheese! As for smelling bad, that has to do with milk going sour, which is a different process altogether. 24.5.122.13 (talk) 10:15, 29 April 2014 (UTC)

That curdling is caused by growth of bacteria in the milk. The bacteria produce acids, and the acids cause the milk to curdle. You can also cause milk to curdle by adding acid directly, for example lemon juice or vinegar. Whether the curdling is harmful depends on what type of bacteria are growing. If they are the same types used to produce buttermilk or yogurt, then the milk can be perfectly healthy and good-tasting even after it curdles. But other types of bacteria will make it nasty-smelling and harmful. Looie496 (talk) 14:27, 29 April 2014 (UTC)

So what happened to my milk? Did I throw away some good cheese? I've never had milk go lumpy and not stink before. --129.215.47.59 (talk) 20:00, 29 April 2014 (UTC) (formerly known as 78.148.106.196 (talk)

It's probable that you could have made good cheese from your lumpy milk, but commercial cheese is made using rennet and a cultured bacterial mix (so that they know the bacteria are harmless). I think I would have thrown it away as you did, just in case there were some nasties amongst the bacterial mix that came from the environment. Dbfirs 21:20, 29 April 2014 (UTC)

If you drained most of the whey from your curdled milk, and scrambled up what is left, you would have cottage cheese. Looie496 (talk) 01:31, 30 April 2014 (UTC)

Fast walking in the heat

Do people with good levels of fitness not sweat or feel out of breath after walking fast in hot weather? 194.66.246.11 (talk) 11:26, 29 April 2014 (UTC)

For sweat, it seems to be the opposite of what you suggest. Here are two sources that say that people who are fit will start to sweat sooner, and more easily [1] [2]. No comment there on "out of breath". As for heat, note that humans change when living in different environments, see Acclimatization#Humans, and here [3]. Basically, people who spend more time in heat and exercise at higher heat respond differently than people who are not used to it. SemanticMantis (talk) 13:07, 29 April 2014 (UTC)

People with good aerobic fitness are less likely to feel out of breath in almost any situation. Regarding sweating, that's more directly a function of weight than aerobic fitness. Light people have a higher ratio of body surface to body mass than heavy people, so they don't need to sweat as much to stay cool. However, there is an additional factor: people who have gotten used to exercising in hot weather are less likely to notice that they are sweating than people who are not adapted to it. Looie496 (talk) 14:32, 29 April 2014 (UTC)

I'm sure your first sentence is right, but it's a rather tricky think to find a WP:RS to cite, isn't it? If anyone has one, please add. As for the weight, that is surely a big factor as well. My (admittedly not great) links above indicate that for two people of the same weight, the more aerobically fit one will sweat more during the same exercise conditions. SemanticMantis (talk) 14:41, 29 April 2014 (UTC)

Are been, a telephone links had been a powerful electric volts

Is it been, a powerful electric volts are beening in a telephone links, because a some transformation of a powerful electric volts always had been saved a incoming amplitude frequency of a powerful electric volts after a transaction of it?--Alex Sazonov (talk) 12:11, 29 April 2014 (UTC)

Landline covers the technical aspects of over-wire telephone service. I think that's what you are asking about. --Jayron32 13:11, 29 April 2014 (UTC)

Thanks for you. Is it been, a nets of these telephone links which I’m asked may been doing a level of logical as a level of logical of a nets of a computers?--Alex Sazonov (talk) 13:50, 29 April 2014 (UTC)

There are very complicated switches in a telephone network. See Public_switched_telephone_network and Switching_center#Technologies. There are indeed some analogies to the logic gates that form the basis of computer processing. There are similarities, but they are not the same thing. (I hope that helps. I understand English is not your native language, but you will get better answers here if you can spend a little more time going over your wording.) SemanticMantis (talk) 14:36, 29 April 2014 (UTC)

A Plain old telephone service uses a nominal 48 volts. "The subscriber loop typically represents an electrical load of about 300 ohms, and does not pose a threat of electrocution to humans, although shorting the loop may be felt as an unpleasant sensation." Modern networking equipment like Router_(computing) are designed to work with these voltages. 196.214.78.114 (talk) 14:12, 29 April 2014 (UTC)

Thanks for all in our discussion. I been thinking that a logically level of a telephone links of a telephone nets of a powerful electric volts always must been doing as a more much logically level of a telephone links than a simple logically level of a telephone nets of a computers in the USA, thats it they always been be bestly.--Alex Sazonov (talk) 15:19, 29 April 2014 (UTC)

The Russian Wikipedia article on the Telephone may help. 84.209.89.214 (talk) 16:15, 29 April 2014 (UTC)

Thanks welly. Did a computers nets of a telephone links always been use a electrical telephone transformation of a electric telephone signals?--Alex Sazonov (talk) 16:38, 29 April 2014 (UTC)

Alex, perhaps you want an explanation of the differences between analog communication originally used in telephone links and digital signals used in data networks and inside computers. Please say what is your own language and someone will find a reference for you to read. 84.209.89.214 (talk) 18:56, 29 April 2014 (UTC)

Thanks. My native language is been Russian, but ofcourse I see that a electrical transformation in telephone links always is been own, but is been not another.--Alex Sazonov (talk) 19:25, 29 April 2014 (UTC)

Is it been, a telephone electronics always been use a powerful electric volts in a long telephone trunk line of a telephone links?--Alex Sazonov (talk) 06:53, 30 April 2014 (UTC)

The high voltage (48v) was needed in the old days to transmit signals reliably over miles of copper wire. Modern computer systems usually run on a much lower voltage, but there are still lots of older telephones connected with miles of copper, so the high voltage is still kept. Dbfirs 07:32, 30 April 2014 (UTC)

Thanks. But I always been mean in our discussion a 220-380 Volts of a powerful electric in a long telephone trunk line of a telephone links or a 550-580 Volts of a powerful electric in a old long telephone trunk line of a telephone links.--Alex Sazonov (talk) 09:33, 30 April 2014 (UTC)

No one except perhaps the poseur Antonio Meucci ever proposed using high voltage for a telephone. (By the way if you use Google translate the English will probably be far more intelligible than the word salad you have been posting here. It generally makes no sense at all and people try to figure out what you mean based on a word here and there.) Edison (talk) 14:32, 30 April 2014 (UTC)

Is it been, a tone of a voice speaking by a telephone links of a powerful electric volts been modify from a electrical telephone transformation?--Alex Sazonov (talk) 14:17, 30 April 2014 (UTC)

Why in the USSR always been make a telephone links of a powerful amplitude frequency of a signals but in the USA always been make a telephone links of a none powerful amplitude frequency of a signals?--Alex Sazonov (talk) 14:46, 30 April 2014 (UTC)

The Tsarist government of Russia issued its first decree on the development of urban telephone networks in 1881 and the first exchanges in the Empire opened the following year. Telephones played a significant role during the upheavals of 1917. According to the last tsarist Chief of Police, 'neither the military authorities nor the mutineers thought of occupying the Telephone Exchange'; consequently it continued to function, serving both sides, until the operators finally left their positions amidst the growing confusion'. In 1919, Sovnarkom nationalized all telephone systems in the Russian Republic. Until the end of the USSR in 1991, the sole fixed-line telephone operator in the country was the Ministry of Communications of the USSR. Today Russian landline telephony employs modern network elements such as digital telephone exchanges, mobile switching centres, media gateways and signalling gateways at the core, interconnected by a wide variety of transmission systems using fibre-optics or Microwave radio relay networks. Our article reports that services are still outdated in rural areas but says nothing about unusual high line voltages that could only create problems for Telephone exchanges. 84.209.89.214 (talk) 16:30, 30 April 2014 (UTC)

I been very thanks for yours explain of a history of the Russian telephone links, and as I been know a telephone links of the USSR always made as a powerful aggregation of a electric volts.--Alex Sazonov (talk) 18:17, 30 April 2014 (UTC)

Could anyone say me is been a multiplier of a amplitude frequency in a powerful electric volts?--Alex Sazonov (talk) 18:20, 30 April 2014 (UTC)

Ваш английский язык является недостаточным. Пожалуйста, попросите еще раз в русском языке. 84.209.89.214 (talk) 19:07, 30 April 2014 (UTC)

(A Google translation of the above is:"Your English is inadequate. Please ask again in the Russian language.") Edison (talk) 01:34, 1 May 2014 (UTC)

Well. Может ли кто-нибудь сказать мне, существует ли умножение (шаг) амплитудной частоты в силовых электросетях?--Alex Sazonov (talk) 20:22, 30 April 2014 (UTC)

Нет -- частота переменного тока не меняется при трансформации. 24.5.122.13 (talk) 19:47, 3 May 2014 (UTC)

A everyone new electric transformer in a nets of a electrical including always been done a new amplitude frequency of a electric volts, because a everyone new electric transformer in a nets of a electrical including always been done a new electric potential of a electric transformation.--Alex Sazonov (talk) 20:11, 4 May 2014 (UTC)

First of all, amplitude and frequency are two different things; second of all, in a power grid all power sources have the same frequency and are synchronized in phase -- so if the power generators output their current at 60 hertz (as they do in my country), then it will be the same 60 hertz everywhere without any kind of modulation; third of all, the transformers feeding power into the grid are also standardized in output voltage, so if the grid is designed for 500 kilovolts (a typical voltage for the US national power grid), then all the transformers feeding into it will output 500 kilovolts (plus or minus a few percent) -- this is EXTREMELY IMPORTANT because (1) many consumers of electricity depend on getting their power at a constant voltage, which in turn depends on maintaining a constant voltage in every power line, and (2) a transformer which outputs at a lower voltage than the others could allow the higher-voltage electricity in the power line (as much as 500,000 volts, remember?) to "backfeed" into the transformer and the upstream power generator, with consequences you would not want to contemplate. Am I making myself clear here? 24.5.122.13 (talk) 18:22, 5 May 2014 (UTC)

Unfortunately the Russian version makes no more sense than the English one. 84.209.89.214 (talk) 20:47, 30 April 2014 (UTC)

Excellent. InedibleHulk (talk) 21:10, 30 April 2014 (UTC)

A Google translation of Alex Sazonov's Russian text is "Well. Can anyone tell me if there is a multiplication (step) amplitude frequency power electric? " Gibberish? Edison (talk) 01:34, 1 May 2014 (UTC)

What a sense always is been mean a contours of a electrical transformation? Same it, in a Russian - Какое значение всегда имеют контуры трансформации электрического тока?--Alex Sazonov (talk) 08:01, 1 May 2014 (UTC)

Is it been, a ways of a electrical including for a electric transformer are been a contours of a electrical transformation? Same it, in a Russian – Являются ли способы включения трансформатора в электрическую сеть контурами трансформации электрического тока?--Alex Sazonov (talk) 18:38, 1 May 2014 (UTC)

Чо? 24.5.122.13 (talk) 19:48, 3 May 2014 (UTC)

"What a sense always is been mean a contours of a electrical transformation?" could mean: "What is the standard value of transformation contours of electrical current?" although it also could mean: "What is the meaning of contours of transformation of electrical current."

The next paragraph could mean: "Are the ways/manners of connection of electrical transformers into the electric circuit contours of transformation of electric current?" A variant of this sentence in the affirmative would sound like: "The manners of connection of electrical transformers into electric circuit are contours of transformation of electrical current."

Either way it sounds gibberish to me. — Preceding unsigned comment added by 168.178.73.124 (talk) 16:18, 7 May 2014 (UTC)

What is be a contours of a electrical transformation?--Alex Sazonov (talk) 14:50, 8 May 2014 (UTC)

I've figured out that "contours" is a poor machine translation of "контурами", which is more appropriately translated as "circuits" in this context. At least, Google Translate gives "contours" and "circuits" as the top two possible translations of "контурами".

If I'm understanding correctly, I think the basic question here is whether anyone has created a telephone system in which a mains power grid was used to double as the medium for the transmission of the telephone signals. I.e., whether anybody has essentially used frequency-division multiplexing to combine mains power transmission and telephony. I at least haven't been able to find evidence of such a system having been used, with a few minutes of searching. Red Act (talk) 19:31, 8 May 2014 (UTC)

point particle

do elementary particles warp empty space the same way that black holes do? I am imagining two very similar objects with one of their properties in common being "has no empty space 'inside'"?66.87.116.12 (talk) 13:56, 29 April 2014 (UTC)

All particles that have mass have gravitational fields. Albert Einstein predicted that gravity is due to curvature of the space around masses. In 1919 Arthur_Stanley_Eddington made the first empirical test of Einstein's theory by measuring the deflection of star lights by the sun's gravitational field. However the gravitational attraction between ordinary masses does not accelerate them beyond the speed of light, as occurs entering a black hole. 84.209.89.214 (talk) 15:30, 29 April 2014 (UTC)

Is that just for rest mass, or do those objects with only relativistic mass also warp space ? StuRat (talk) 16:23, 29 April 2014 (UTC)

Yes, also. Whenever the stress–energy tensor is nonzero, the geometry of space will be affected according to the Einstein field equations. I have seen a paper on exact solutions for the case of an intense electromagnetic field propagating through otherwise empty space. —Quondum 17:01, 29 April 2014 (UTC)

You can also see that this must be the case without invoking the intricate details of general relativity. Just consider the fact that a big mass like the Sun will bend light. So, a photon with some initial momentum will after passing close to the Sun hend up having a different momentum (it will have changed in direction). Since total momentum must be conserved, this means that the Sun must have changed its momentum to compensate for the change in the momentum of the photon. Therefore the photon must have a gravitational field. Using just the formula for the bending angle, you can easily compute the effective gravitational potential of a beam of light. Count Iblis (talk) 17:05, 29 April 2014 (UTC)

because the infinity grab in small scal , because the secend degre of R , it sqewez to a point flip the derection of time and mulltiply by three , and make the three visibel dimention space . Thanks water — Preceding unsigned comment added by 192.116.142.154 (talk) 13:42, 30 April 2014 (UTC)

Well that explains everything. Justin15w (talk) 15:19, 30 April 2014 (UTC)

Thanks, water. Thwater. AlexTiefling (talk) 15:42, 30 April 2014 (UTC)

The classical idea of a black hole does have empty space inside. An event horizon marks a point of return, but is supposed to have nothing locally special visible to someone falling in. Everything gets crushed in a singularity at the center. However, the fuzzball idea does suppose the hole is packed with string theory objects. A particle, by contrast, has a much more poorly defined position (Compton radius) and contains a space within that radius that may be shared with other particles. (See Bose-Einstein condensate, for example) Wnt (talk) 19:35, 30 April 2014 (UTC)

Alien Worlds???...

Do any Biologist or Biochemist know what are the problems for Humans when they find in the Future a Planet with Life???...

First Question: WHAT must be right to be a Planet with Life Human-friendly???...

Second Question: WHAT must be wrong to be a Planet with Life Human-enemy???...("a forbidden Paradise!!!...")

Third Question: Could it be a Si₁₄-World in place of our C₆-World???!!!...

THANK you VERY-VERY much!!!...

"Have a nice Day/Night!!!..."

SPYROU Kosta - Greece - Honeycomp (talk) 14:56, 29 April 2014 (UTC)

As a minimum for life as we understand it, a planet should be in the habitable zone; planets outside it are automatically unfriendly to Earth-based life forms. But beyond that, a lot is speculation - there are so many ways a planet's biome could be harmful to humans, it's hard to know where to start - huge predators, virus- or bacteria-like pathogens, poisonous creatures, all life existing in places (glacial trenches, volcano margins) that are naturally bad for humans... AlexTiefling (talk) 15:03, 29 April 2014 (UTC)

You might also want to read up on planetary habitability.--Shantavira|^{feed me} 15:30, 29 April 2014 (UTC)

All scientists, not just bio-scientists, know that an eventual discovery of an extraterrestrial planet with life will force a review of everything we know about our own origins. — Preceding unsigned comment added by 84.209.89.214 (talk) 16:16, 29 April 2014 (UTC)

That's very dubious. Suppose that 10 years from now, someone takes the spectrum of an Earth-like planet and sees oxygen and methane--a very strong indicator of life. How would that force a review of the African origin of humans, of early conditions on Earth, or of any of the geological record? Suppose that tomorrow, someone discovers a radio signal from an exoplanet that's undeniably artificial. How does that force a review of evolutionary history? Of course discovering life on other planets could radically change everyone's philosophical outlook, but it might have little effect on existing science. --Bowlhover (talk) 16:52, 29 April 2014 (UTC)

If the philosophy of science were already perfected beyond criticism, there would be no need for the many science fiction writers who have addressed the implications of contact with alien beings. Now on Earth we cannot isolate the scientific hypotheses that we test from the influence of the theories in which our observations are grounded (see Kuhn). Therefore, if someone communicates by radio or other means with life on another planet, they should listen in order to learn, rather than reiterate their favourite theory-laden observations that are circumscribed by their own theoretical presuppositions. 84.209.89.214 (talk) 15:36, 30 April 2014 (UTC)

First Question: The Rare Earth Hypothesis uses the Goldilocks principle in the argument that a planet must neither be too far away from, nor too close to a star and galactic center to support life, while either extreme would result in a planet incapable of supporting life. It considers the likelihood that something we recognize as life might have evolved on a yet unknown planet; however the probability can be greater if we envisage possible Extremophile life forms, and much less probable that we ever find another "human friendly" planet. The prospect of Terraforming a planet to this end has arisen in science fiction.

Second Question: The more human friendly a planet with life turns out to be, the more likely it is to have predators or parasites that will like to dine on humans, and on Earth our experience has shown unfortunate results for a civilisation that contacts a more advanced one.

Third Question: This calls for speculation. 84.209.89.214 (talk) 16:00, 29 April 2014 (UTC)

Two comments:

A) Habitable zone is defined as distance from a star, but a large planet might provide enough tidal heating to keep a moon warm. So, the habitable zone around a star can be extended outward for some moons around large planets.

B) Conditions needed for life to begin might be considerable different from those needed for humans to exist there now. The early Earth would have been quite inhospitable to humans, due to lack of atmospheric oxygen, toxic gases in the air, high volcanism and meteor impacts, and obviously a lack of plants and animals to eat. However, using modern technology, we might be able to live in places not well suited to primitive humans. StuRat (talk) 16:20, 29 April 2014 (UTC)

It occurs to me that question three, i.e. whether it's possible, could be answered by someone smarter than me (which is most of you) looking at what it is that makes Carbon so special as the "anchor" of organic life as we know it. That is, does Silicon have the potential to interact with other elements in pretty much the same way that Carbon does? One possible side issue: The basic organic compounds often include elements with low atomic numbers. Do scientists believe that the larger atomic numbers were created later? That is, would Silicon have turned up well after Carbon, and if so, could primitive life forms or almost-life forms have already gotten started before Silicon came along? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:21, 29 April 2014 (UTC)

The thing that makes carbon "special" is the ability to form long-chain and complex structures. Silicon can also form chains, but nowhere near as long as carbon can. --Carnildo (talk) 01:43, 30 April 2014 (UTC)

Another element substitution I asked about here some time ago is substituting F for O (Wikipedia:Reference_desk/Archives/Science/2013_October_10#Fluorine_planet). Granted, it's not very plausible, given the relative abundances of these elements.

Hypothetical types of biochemistry gives many more substitutions. Possible substitutions for C include B, Si (this is the one you are proposing), P, S, and metal oxides. O₂ could be substituted by Cl₂ (and maybe F₂? That's the one I asked about.). P could be substituted by As. H₂O could be substituted by NH₃, HF (the one I asked about), CH₄, H₂S, HCl, H₂SO₄, HCONH₂, CH₃OH, N₂ (l), H₂ (l), a mix of H₂O and H₂O₂, etc. Double sharp (talk) 16:14, 3 May 2014 (UTC)

Hmmm, a fun one ought to be to substitute carbon with boron nitride, which apparently allows for analogs of things as complex as naphthalene and biphenyl. [4] Wnt (talk) 05:16, 4 May 2014 (UTC)

@Honeycomp:: See especially this book for your third question: Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, by Robert A. Freitas Jr. You want section 8.2.3 (and for substitutions in biochemistry in general, the whole of chapter 8). @Wnt:: Boron nitride might be slightly problematic, though it is a beautiful parallel to carbon: according to Xenology, "While some B-N polymers are known to be stable to high temperatures, many such substances turn out to be less stable with heat. Borazine, the boron-nitrogen analogue to benzene, is more susceptible to chemical attack because of its greater reactivity. The presence of water tends to degrade most B-N polymeric compounds." Double sharp (talk) 13:14, 5 May 2014 (UTC)

The high temperature degradation might not be a problem, on a planet where temperatures are more stable than on Earth. On Earth, temperatures are more stable in the ocean, so a planet without any land should have a more even temperature, as it's more able to distribute heat by convection. The ocean need not be water, as any liquid can do the same thing. Similarly, a thick atmosphere, like on Venus, can distribute heat more evenly, although you'd want it to be farther from the Sun to avoid the entire planet getting too hot, as on Venus, due to the greenhouse effect. A short day would also help to keep the daylight heating/nighttime cooling cycle to a minimum, while a lack of tilt would prevent the summer/winter cycle. Tidal heating, say of a moon around a large planet, should also provide more evenly distributed heat, rather than just on the surface, as sunlight does. StuRat (talk) 14:18, 5 May 2014 (UTC)

@StuRat: The reactivity problem might also require an atmosphere that's less oxidizing than O₂, but that's also not really a problem. OK, I think I've convinced myself that it could work out!

I've still been thinking about the F-for-O substitution a lot, though, because it fits very well: F₂ is very reactive, like O₂, so you could have the planetary surface passivated. HF and H₂O both support acid-base chemistry, are polar molecules, and have reasonably large liquid ranges. Therefore you could have photosynthesis where plants take up HF and transpire F₂. It would require more energy, to be sure, but getting UV photons would do the job, and for that you just need the right kind of sun. (The downside is that the planet may not last as long.) Fluorine's rarity seems the biggest obstacle to this. Now, is there some way to get around this? Double sharp (talk) 11:17, 6 May 2014 (UTC)

@Honeycomp: Here is an attempt to answer your original question about silicon-based life. Most of this information was obtained from Freitas' book Xenology, section 8.2.3.

Silicon-based life is an idea that has been advanced many times (one of the first mentions of the possibility is that of Sir Harold Spencer Jones in 1940), because Si and C are chemical homologues. While Si is about one order of magnitude less common than C in the universe, the issue is more of its abundance in the planetary crust – and even on Earth, C atoms are outnumbered on the crust by Si atoms by about two orders of magnitude.

The Si-Si bond is readily broken in the presence of oxygen, so presumably an oxygen atmosphere is out of the question. (If it is not, the silicon organism in an oxygen atmosphere must excrete SiO₂ (quartz), which is not really a problem if it does not breathe it out.) And while SiO₂ is quite stable, it is the starting material for synthesis of many organosilicon compounds, so presumably life could get started even if most silicon became bound as parts of SiO₂ macromolecules. SiH₄ and silicon halides could work as solvents, anologously to liquid methane on a cold world.

Unlike C, Si cannot form long-chain polymers easily. However, many organic molecules used in Earth life don't need very long C chains, such as proteins, carbohydrates, and nucleic acids. So you could use a stable silicon polymer like polydimethylsiloxane (and quite a lot of the silicones). Such stable polymers even exist for the heavier group 14 elements – Ge, Sn, and Pb (ignoring the severely unstable and superheavy Fl). The problem here is that Si-Si bonds are unstable at high temperatures, where the threat of oxygen is largely mitigated by O's role being replaced by S. At these temperatures (300–350°C), silicones also tend to decompose. (At low temperatures, the threat from NH₃, H₂O, and O₂ becomes the problem.) Si-C and Al-Si combinations can get to substantially higher temperatures (500–600°C), but introducing carbon creates a problem of competition: why should the C atoms form polymers with Si, when they can do so by themselves?

It must also be remembered that Si is not the only alternative to C. Ge, Sn, and Pb are also in the same group, although they're even less likely. More distantly, B, P, and S are possible alternatives. As Wnt suggested, another plausible carbon substitute is boron nitride: one could also include its relatives boron phosphide and boron arsenide.

And even these substitutions are not the only ones. You could substitute H with F or Cl to create halogen-based life. F or Cl could also replace O. The ubiquitous solvent H₂O could be replaced by its close analogues NH₃ and HF (the latter would work well as a full substitution of F for O), or by more distant analogues like H₂SO₄ or HCONH₂. Even H₂ or N₂ could work as solvents at cryogenic temperatures. And there are different possibilities even using the terrestrial carbon/water system (see xenobiology).

But polymerization possibilities, though a significant step forward, isn't yet enough complexity to support life.

The relevant chapter of Freitas' book closes with the statement:

“ The evidence admittedly is against the existence of silicon-based life-forms: The evolutionary mechanisms and planetary conditions appear much too unwieldy. Ammonia life seems far more feasible, if for no other reason than it is so closely analogous to terran biochemistry.

It would also appear that carbon is the backbone element of choice in Earthlike environments, although this should impose no real restriction on diversity. One must agree with Shklovskii and Sagan when they assert: "It is quite premature to conclude that ours is the only, or even the best of all possible, biochemistries."

In spite of the difficulties, there probably exist many different kinds of life in our Galaxy, including some very exotic forms based on different physical interactions than ours. But we cannot be certain of this until we travel into space and seek them out. ”

(Do note though that Freitas' book is from the late 1970s and advances have certainly been made since then.)

Here's another interesting book on the topic. Double sharp (talk) 12:06, 6 May 2014 (UTC)

Some more thoughts:

C) Chemical instability isn't always bad. After all, oxygen tends to oxidize and destroy many types of molecules, yet life on Earth has adapted to live with it. However, on Earth at least, an initial environment without free (diatomic) oxygen was needed for life to evolve. So, perhaps as long as those other planets have a "nursery", they can adapt, too. That nursery may be an early time period, as on Earth, and/or a different physical location on the planet, like underwater on Earth.

D) Ammonia lakes do seem likely to exist, so that's a good place to start looking for life.

E) A variety of environments may also be helpful to the development of life. Here on Earth, for example, we have black smokers, with a very different chemistry than most of the rest of the planet. Land also seems to have played an important role in the development of intelligent life. Without land based animals, like mammals and birds, the next most intelligent creatures on Earth are probably cephalopods, and that's a big step backwards. Even cetaceans seem to have needed a history on land to develop their intelligence, as their "never on land" analogues, the sharks, seem downright stupid in comparison. StuRat (talk) 14:37, 6 May 2014 (UTC)

It looks like we're closer to ammonia life than we think! Apparently, according to the abstract of [5] some bacteria can survive 35% ammonia at -80C or room temperature! It would be fun to get busy selecting some bacteria that can survive and grow in higher and higher levels, turning the temperature further and further down... Wnt (talk) 18:47, 6 May 2014 (UTC)

Alien Earth-like World...

SORRY but I made the FALSE Question earlier...

Imagine that we find a Planet with Earth-like life:

1). with Atmosphere like ours...

2). with water H2O...

My Questions are Biology-Questions:

If the D.N.A. is like ours - or NOT...

If the Amino-Acids are like ours - or NOT...

If the Molecules of Life have the same Hirality - or NOT...

a). WHAT of them will be Human-friendly???...

b). WHAT of them will be Human-enemy???...

THANK you VERY-VERY much!!!...

"Have a nice Day/Night!!!..."

SPYROU Kosta - Greece - Honeycomp (talk) 17:38, 29 April 2014 (UTC)

• You may find the Wikipedia articles titled Extraterrestrial life and Astrobiology useful to start your research. --Jayron32 17:42, 29 April 2014 (UTC)

• You mean chirality, which might well be reversed. Also, some evolutionary "mistakes", like the one that causes our blind spot, might not be repeated. And if bipedal locomotion developed earlier there, they might have evolved a spine that actually works properly when walking upright, unlike ours which is prone to all sorts of problems (I think a thick, rubbery spinal cord with no nerves would make sense inside the spine, with the nerves in front of the spine, in a notochord.) StuRat (talk) 18:25, 29 April 2014 (UTC)

There is some evidence that amino acids (Urey-Miller experiment), RNA (RNA world), and metabolism ([6]) date back to the origin of life, or before the origin of life. The solution our cells contain is closely based on the primordial sea. If this is true, then many characteristics of modern Earth life may be very similar to the environment of the early Earth, and the biochemistry of Earth life should not be seen as an evolved optimum. Nonetheless, some important evolution has occurred, most notably the oxygen catastrophe that replaced the primordial reducing atmosphere with a highly oxidizing environment. The presence of oxygen continues to be stressful to life to this day - the activity of genes like superoxide dismutase appears to be important in trying to stave off a process of aging that is partially due to reactive oxygen species. And yet, of course, we now cannot do without oxygen, nor can we tolerate ammonia. To answer your question, you would need to know how many planets have something like Earth's early chemistry, and whether other life is more prone to evolve away from its original biochemistry, but we don't know either of these things. Wnt (talk) 11:35, 30 April 2014 (UTC)

SPYROU Kosta: My Questions are specific!!!:

Same D.N.A. = Human-friendly Or Human-hostile???...

Same Aminoacids = Human-friendly Or Human-hostile???...

Same Chirality = Human-friendly Or Human-hostile???...

THANK you... - Honeycomp (talk) 14:09, 1 May 2014 (UTC)

"Human-friendly" or hostile could mean a vast range of things:

1) Can they cause bacterial or viral diseases in humans ? Here more similar life forms are more likely to causes diseases, although prions are an interesting exception.

2) Could they hunt humans ? Here a very different biology might not prevent them from hunting humans. Even if they can't digest us, they might kill us anyway, not knowing that.

3) Warfare involving intelligent aliens ? Here I wouldn't think biological similarity would make much difference, although they might tend to sympathize more with similar life forms. Here on Earth, for example, you will got a lot more donations to save the chimps than to save the centipedes.

However, a very different life form might not even perceive us as alive, or interact with us in any way. For example, perhaps crystals are alive, and grow and reproduce over millions of years, never knowing there is any other form of life. StuRat (talk) 15:50, 2 May 2014 (UTC)

SPYROU Kosta: THANK you StuRat for your Help!!!... - Honeycomp (talk) 00:01, 4 May 2014 (UTC)

You're quite welcome. StuRat (talk) 16:17, 4 May 2014 (UTC)

Math. function

Hi, What function gives 1,7,13,25,49,97,... It begin's with (6+1) then (2*6+1) and (2*12+1) to infinity. It's for Flower of life article. Thx --YB ^✍ 20:42, 29 April 2014 (UTC)

1 + (2^x * 6)

- Eron^Talk 20:58, 29 April 2014 (UTC)

Simple indeed. What if it start at one? --YB ^✍ 21:09, 29 April 2014 (UTC)

The 1 simply doesn't follow your rule; it ought to be (3+1) so that the next term can be (2*3+1). --Tardis (talk) 00:45, 1 May 2014 (UTC)

It might not make that much sense to you, but that sequence has an official name in the OEIS, you can cite this page [7] if/when you add it to the article. SemanticMantis (talk) 21:27, 29 April 2014 (UTC)

I had the feeling it had something to do with Fibonacci number and fractals. Thanks for the ref. --YB ^✍ 23:15, 29 April 2014 (UTC)

That's not the same sequence; they diverge after 769 ($x=7$). (Similarly, the 2, 3, 5 part of the standard Fibonacci sequence matches $1+2^{n}$ for n 0, 1, and 2, but not afterwards.) --Tardis (talk) 00:45, 1 May 2014 (UTC)

Why didn't you post this to the Math Desk ? StuRat (talk) 03:39, 30 April 2014 (UTC)

I haven't examined the connection to Flower of Life but the natural thing would be to include 3+1 = 4 so it goes 1, 4, 7, 13, 25, 49, 97. That's OEIS:A004119: 3×2ⁿ+1. A Thabit number is 3×2ⁿ−1. PrimeHunter (talk) 17:25, 1 May 2014 (UTC)

Sorry, the sequence is 1,7,19,37,61,... [8]. Anyway, thanks for the link. --YB ^✍ 01:33, 2 May 2014 (UTC)

Then I guess you want Centered hexagonal number which already has a see also link to Flower of Life. PrimeHunter (talk) 00:24, 4 May 2014 (UTC)