Wikipedia:Reference desk/Archives/Science/2014 November 13

= November 13 =

Mitochondrial DNA questions

 * 1) Please, in the least number of words and in the simplest way you can - Except for ATP production, what is the other main function of the Mitochondria?
 * 2) What is the prevalence, in general, of known\defined Mictochondrial disorders? - What is the Ratio of Disorder\Births?

I guarantee these are not homework questions; Thank you, Ben. Ben-Natan (talk) 03:03, 13 November 2014 (UTC)


 * There are many different functions, really - biological structures and genes don't actually "know" what they are "for". The article mitochondria does list quite a few of them.  If I were going to answer I might have talked about apoptosis, but the article seems to prefer uncoupled energy production (as per heat generation in brown fat) as the more important second function, and I can't really argue it.
 * The article mitochondrial disorders actually does list those stats currently, and cites its sources - 1 in 4000 births, but only about 15% of the diseases due to mitochondrial DNA proper. I haven't looked at such stats in a long time, but they sound plausible enough. Wnt (talk) 04:04, 13 November 2014 (UTC)


 * 1. I never said or even clued that "Biological structures and genes know what they are for". I asked the question because I once read at a discussion here that Mitochondria have to main functions, 1 is ATP production and the other - well, that wasn't very clear from the text...


 * 2. I couldn't understand what you meant at "about 15% of the diseases due to mitochondrial DNA proper"; did you mean that 0.0000375 births (15%/4000) are Mitochondrial proper? Ben-Natan (talk) 05:07, 13 November 2014 (UTC)

Question About the Reversibility of Gene Therapy
I apologize for my ignorance in regards to this, but is gene therapy theoretically always (fully) reversible or not? Futurist110 (talk) 03:46, 13 November 2014 (UTC)


 * As practically implemented, gene therapy is almost never truly reversible; it generally involves inserting bits of DNA into the cell; in theory this may be in a specific location (see adeno-associated virus), but in practice (as the deaths from leukemia attest) it can be less predictable. A clever approach might tend to pop out the preceding alteration, or be targeted to disrupt something that was added, but with varying degrees of success.  It is however possible to make gene therapy that is designed from the beginning to be capable of being shut off; a laboratory mechanism in mouse studies involves using tetracycline to control transcription of an added gene.  In theory such control mechanisms could be arbitrarily elaborate and sophisticated.  In practice, it is still far too rare to see gene therapy even attempted in even the most straightforward situations where it should help. Wnt (talk) 04:11, 13 November 2014 (UTC)


 * Don't apologize for that!
 * At present gene therapy is not permanent, when the modified cells die the new ones don't have the therapy. So in a way it's reversible. However there is no direct way to reverse the effects, if you wanted to do that you would essentially need more Gene Therapy. So it's also not reversible. Ariel. (talk) 08:24, 13 November 2014 (UTC)

The Lactose has a sweet taste
Maybe that's what gives the sweet taste to the milk. Am I right? and does it raise the glucose in the blood - generally? (not for a medical advice, but to the facts about Lactose) 5.28.177.33 (talk) 06:14, 13 November 2014 (UTC)
 * Yes, and slightly old milk is sweeter since the lactose gets hydrolysed into smaller sugars, which are sweeter. Yes, it does raise glucose since it has glucose in it, but not very much. Ariel. (talk) 08:27, 13 November 2014 (UTC)
 * Thank you 5.28.177.33 (talk) 12:11, 13 November 2014 (UTC)

Thermodynamics properties of chemical substances
If the chemical and physical properties of the chemical substances are always dependent on their valence and their molecular structure of the chemical substance, so that did the thermodynamic properties of the chemical substances to been defined by valence of this chemical substances?

Valence of what chemical substances is always been much, the valence of the carbonaceous gases or valence of the alkalic vapour and acid vapour (chemical vapours)?--Alex Sazonov (talk) 09:59, 13 November 2014 (UTC)


 * It is unclear what you mean by valence? Valence is a property of an element in a chemical compound that refers to the number of electrons that participate in chemical bonding.  The way you are using the word here does not make sense.  Perhaps you mean something different than what you are asking, but you have such a poor use of the English language it is hard to follow your questions.  It may be best for you if you asked questions at a website where the other users spoke your native language.  -- Jayron  32  11:35, 13 November 2014 (UTC)
 * I’m sorry for my English. I heard that the industrial use of all chemicals is always dependent on their calorie content which is always determined by the valence of these chemicals. Did the thermal properties of chemical substances depend on of the valence of these chemical substances?--Alex Sazonov (talk) 18:34, 13 November 2014 (UTC)


 * When referring to 'valence', do you mean 'bond enthalpy'? Plasmic Physics (talk) 20:29, 13 November 2014 (UTC)
 * I think, that ordinary chemical valence always gives an idea (concept) about the chemical and physical properties of chemical substances.--Alex Sazonov (talk) 11:17, 14 November 2014 (UTC)
 * Valence is a hueristic tool used in chemistry. It applies only to chemical elements, and not to all substances, and valence really only tells you how different elements will form bonds to other elements to form compounds.  There is some alignment between the valence of an element and other properties of that element, but the effect is not truly causative, as you seem to imply.  Valence doesn't cause an element to have its properties, valence is just a concept like oxidation number which allows us to make specific predictions about specific ways in which elements come together to form compounds.  For example, all of the elements in the alkali metals group have a valence of 1, and are highly chemically reactive; they all form very soluble salts, they all react explosively with water, etc.  But having a valence of 1 does not cause them to be highly reactive.  Silver also has a valence of 1, and is relatively unreactive; it doesn't do anything remarkable in water, it doesn't form particularly soluble salts, etc.  Valence as a concept is something taught to introductory chemistry students so the understand how to figure out chemical formulas and things like that, so they can reasonably predict what the formula for calcium chloride or sodium nitrate would look like.  But as you get deeper into studying chemistry, it's a heuristic you'll leave behind as you get a deeper, more complex understanding of chemical bonding.  -- Jayron  32  12:45, 14 November 2014 (UTC)
 * I believe, that the chemical valence always characterizes the electronic charge and the molecular structure of chemical substances, so I done this conclusion.--Alex Sazonov (talk) 14:36, 14 November 2014 (UTC)

Note:I believe, that in natural nature always been only once electronic charges (single electronic charges or charges of the electron pairs), so that I would argue that the valence always determines the chemical and physical properties of all chemicals, but this did not negate the fact, that in natural nature are always been a chemical substances which had complex valence - complex chemical substances and chemical substances which had simple valence - simple chemical substances.--Alex Sazonov (talk) 15:00, 14 November 2014 (UTC)
 * If in natural nature been other elementary particles except for electrons, in natural nature the negative charge could been exists as a positive charge, however, that in natural nature none done.--Alex Sazonov (talk) 15:18, 14 November 2014 (UTC)
 * Due to the fact that electrons did not change their electric charge in natural nature been an electric current!--Alex Sazonov (talk) 15:25, 14 November 2014 (UTC)
 * Under the influence of the forces of magnetism (electromagnetism) electric current (electrons) could change the direction of its motion in natural nature and electrical circuits, however, this did not negate what I told.--Alex Sazonov (talk) 16:04, 14 November 2014 (UTC)

Gases and valence
What natural gases in natural nature always had a lot, the natural gases which had a much valence or natural gases which had a small valence?--Alex Sazonov (talk) 11:16, 13 November 2014 (UTC)


 * What do you mean by natural gases? Also, your use of English is so idiosyncratic that it makes it difficult for people to understand you well enough to know how to answer your questions.  You should consider finding a website in your native language to answer these questions instead. -- Jayron  32  11:35, 13 November 2014 (UTC)


 * As the world industrial history always told, that at first was developed a mineral raw sources which had a low cost of raw material production, as well as had a natural raw sources material which had a low cost of industrial processing, so that I believe that natural gases which had a much valence was developed in the first place!--Alex Sazonov (talk) 15:52, 13 November 2014 (UTC)
 * You appear to be using the word 'valence' in a different way than it is used in English, so that many of us can't understand your questions. Perhaps by natural gases you mean diatomic nitrogen, diatomic oxygen, carbon dioxide, and water vapor, but compounds do not have valence.  If you really want to ask questions here, I suggest that you try automated translation from your native language into English, rather than writing the questions in your attempt at English.  Robert McClenon (talk) 21:04, 13 November 2014 (UTC)
 * As world economic history always told us, that the costly spending sources economic models always had economy of spending costs, so that the starting of costly spending sources economic models always had start from the low cost of raw sources materials and low cost of industrial processing of this raw sources materials, that’s why I believe, that the natural raw sources materials which had a much valence was developed in the first place! --Alex Sazonov (talk) 13:38, 14 November 2014 (UTC)
 * You are making what appears to be the same statement again, after being advised that it doesn't make sense, because you persist in using the word 'valence' in a way that is inapplicable in English. We can't answer your questions when we don't understand them.  Please either find a reference desk service in your native language or use automated translation from your native language to English before posting here.  If you continue to post questions that don't make sense, you may be topic-banned from posting here.  Robert McClenon (talk) 16:33, 14 November 2014 (UTC)
 * I think, that anyone practical model of the economics always done start only from a low cost.--Alex Sazonov (talk) 19:46, 14 November 2014 (UTC)

cushing's syndrome
A person suffering from Cushing’s syndrome will have symptoms that include rapid weight gain, particularly of the trunk and face (moon face) with sparing of the limbs. Why & how does the syndrome affect the body in this way? b.Could the consumption of hydrocortisone of 20mg daily to alleviate adrenal insufficiency also cause a “moon face” effect? — Preceding unsigned comment added by 113.210.35.128 (talk • contribs) 14:24, 13 November 2014
 * Sensitivity to hydrocortisone, which is what we call medically-administered cortisol, varies greatly from person to person (so it's not possible to give an accurate, simple answer to your question - the effects are too variable). The differential sensitivity of various types of adipose tissue (visceral and peripheral, among others - see some listed in that linked article) to the opposing effects of cortisol vs. elevated insulin levels that cortisol can stimulate, probably determines the pattern of fat redistribution. -- Scray (talk) 20:06, 13 November 2014 (UTC)

Looking for further reading on cosmic body physics particularly comets/soft bodies type and collisions
First is the bit I understand and what made me curious.

Was looking at, which shows the Lutetia big side up and marks the circles of their craters.

And then this one, which gives a sort of impression of two comets that collided and did not quite make escape velocity. So, I was think about the gravity and friction of when two bodies collide. Obviously the two had collided and caused a temporarily plastic surface, like, or even as, a wet blob, and eventually friction and other stuff brings it to a halt as the new single body.

However... Would the internal friction alone be enough to bring the surface to a settling halt? I assume the external tidal forces, such as the pull of the sun, would be the cause of the surface in the absence of any absorber of the collision force. Can anyone say a subject with particular focus on cosmology that will tell me stuff like if stuff outside the suns area of effect actually settles into a constant steady surface some time after impact, as the Lutetias is, and stuff about how that settling actually works out there?

I searched up stuff like collisions and gravity but of course it's a very specific item. There's probably not an article in it but aren't half of us wondering about comets and that today? :)~ R.T.G 15:32, 13 November 2014 (UTC)


 * The escape velocity of 67P/Churyumov–Gerasimenko is 1 m/s, less than walking speed. If it formed through two bodies colliding, it was an incredibly minor crash. Rmhermen (talk) 15:52, 13 November 2014 (UTC)


 * And it would also take a very long time for the two to approach each other at those speeds, maybe thousands of years ? StuRat (talk) 16:36, 13 November 2014 (UTC)


 * I think you're looking for information about hydrostatic equilibrium.
 * On Earth, we use hydrostatic equilibrium to describe, say, water in a pipe; or oil-and-vinegar that have separated out into layers based on their different densities.
 * In planetary science, we can use the models and terminology of fluid dynamics to study all matter. Everything is a fluid on a sufficiently long time-scale!
 * One of the current elements in the definition of a planet is that the object's matter has enough self gravitation to achieve hydrostatic equilibrium. That means two things: there's enough material - and it's made of chemicals that are soft enough relative to its own mass - to squish into a spherical object.  This process can take thousands, millions, billions of years.
 * Comets are made of water and carbon dioxide ice, among others (methane and ammonia for some comets). They sometimes also contain a lot of other harder materials: to use the terminology of comet scientists, there are also "metallic" and "chondritic" (rock-like) chemicals.  Depending on which theory applies to any specific comets, those chemical compounds are primitive - they evolved directly out of stellar nucleosynthesis products - so they have never been subject to processes of geological evolution.  That means that the iron in a meteoroid or a comet was never "refined" by heat and pressure; the "rock" and "dust" have never been subjected to the usual earth-style "igneous rock"/"metamorphic rock" progression; and although exposed to the harsh environments of space, there's not a whole lot of physical erosion action.  These materials are kind of strange!  Over a long time - billions of years - the materials have been subjected to direct, unfiltered stellar radiation, and extremes of temperature and heat.  This actually can chemically change some of their materials.  Over billions of years, exposure to sunlight has an erosive effect, softening "rock" and turning it into dust!  (Solar Wind and Micrometeorite Effects in the Lunar Regolith, (1977).
 * Add on top of this that the comet's elliptic orbit cycles it through a variety of solar distances, ranging across several AU. Methane and ammonia and water and carbon dioxide - all of which might be gravitationally bound to the comet - can turn from liquid, to solid, to gas, depending on the effective planetary temperature of the comet.  So, one day the comet might be a bunch of sand and gravel that's  glued together by rigid ice - and the next, it might be a swampy clump of wet sand and metal fragments!  When that happens, the material can re-shape.
 * Last, but not least, there is a stronger force than gravity: ''electrostatics. The comet, and all of its gas and solid components, are blasted by highly energetic solar wind.  Some of the atoms become ionized.  When this happens, the material in the planet is subject to electrostatic attraction - or repulsion - and the strength of these forces can be orders of magnitude larger than the attractive force of gravity.
 * If there is enough matter, gravity will win: the self-gravitation of all these particles will, over the long run, cause the materials to smush together into a nearly perfect sphere. For a comet the size of Comet 67P/Churyumov–Gerasimenko, this hasn't happened yet - and very likely won't happen for a very very long time, comparable to the lifetime of the solar system.  It will always be irregular!
 * Let me close with a pitch for one of my favorite books on planetary formation - one that doesn't pull any punches or leave out any equations! de Pater and Lissauer, Planetary Sciences - it was written by the scientists who worked on the extrasolar planetary mission of the  Kepler Space Telescope - and it has an entire chapter on comets and meteoroids; and another entire chapter on planetary models of hydrostatic equilibrium!
 * Nimur (talk) 16:42, 13 November 2014 (UTC)
 * Brilliant by User:Nimur. ~ R.T.G 00:00, 14 November 2014 (UTC)

What is the farthest you can communicate with an unlicensed (and legal) radio?
--Senteni (talk) 17:18, 13 November 2014 (UTC)
 * According to whose laws? -- Jayron  32  17:20, 13 November 2014 (UTC)
 * Well, US, Europe, although I suppose there must be an international aggreement on this, so all countries will let the same wavelength free.--Senteni (talk) 17:35, 13 November 2014 (UTC)
 * For starters, see Amateur radio, International_Amateur_Radio_Union, and pirate radio. maybe DXing has some interest as well. SemanticMantis (talk) 17:42, 13 November 2014 (UTC)
 * Note that it's not just a matter of what wavelength. Maximum transmission power, antenna size and other factors will be dependent on local laws. Also as those articles illustrate, it will depend on time of day and other factors. Additionally, "unlicensed and legal radio" is unclear. AFAIK, in many countries amateur radio operators can operate in frequencies and possibly with greater power without a specific licence for the radio, but they do need a licence themselves. Nil Einne (talk) 18:04, 13 November 2014 (UTC)


 * For the purposes of this question... does the radio signal need to propagate wirelessly? Nimur (talk) 19:19, 13 November 2014 (UTC)
 * I think I know what you're getting at, but radio says "Radio is the radiation (wireless transmission) of electromagnetic signals through the atmosphere or free space." (emphasis mine) - Do you really commonly refer to signals sent through a wire as "radio signals"? SemanticMantis (talk) 19:33, 13 November 2014 (UTC)
 * Actually I was thinking of a similar thing. Namely whether the OP was truly restricing the question to parts of the EM spectrum generally considered radio which includes some stuff also sometimes considered microwave and other things, but generally never stuff called light. Because high powered laser laws are still often limited albeit increasingly getting more stringent thanks to pressure from idiots misusing such lasers (and even then, some countries restrict readymade laser devices much more heavily than the diodes). Of course this illustrates another point, you can theoretically communicate quite far with lasers depending I think on atmospheric conditions and other factors. Possibly further than with an unlicenced radio even one designed to send to space (although I'm not sure). However there's no one to actually receive your line of sight signal somewhere in outerspace. Nil Einne (talk) 13:44, 14 November 2014 (UTC)
 * If you are talking 2-way Line-of-sight radio the Marine VHF radio article mentions some ranges. I do not see refs to support all the info though. I would imagine radios at sea would be more consistent in performance since there is no unpredictable terrain. It mentions 111 km with 25 watt transmitter. I went through some ads for handheld high powered 2-way radios and they went up to 5 watts.  Richard-of-Earth (talk) 19:36, 13 November 2014 (UTC)
 * Looking around some more that article has to be wrong. This mentions line of sight on a curved earth max range is 13.3 miles (21.4 km). Richard-of-Earth (talk)
 * I think the article might still be right. The marine VHF article says ~100 km for tall ships or antennae mounted on hills. Your recent link says 13 miles for a 100 ft antenna. Surely large commercial vessels will have much higher antennae, and consequently longer range, as described by the equations at line-of-sight propagation. (I did not check all the math, just saying that the two pieces of info are not necessarily contradictory) SemanticMantis (talk) 20:04, 13 November 2014 (UTC)
 * Larger ships that travel far from land will also have access to HF radio (which is not limited to line of sight), or ultra-high-frequency radio (or microwave radio) satellite uplink (which is line-of-sight to an orbital digital radio repeater). Nimur (talk) 20:07, 13 November 2014 (UTC)
 * Hmm. The OP really does need to give more specifics. this article mentions the different types of radios, their ranges and needs for licenses (in the US I am sure). If you are transmitting for an aircraft, up to 200 miles! So you have to buy or charter a plane too. Of course, you can walk into a store, buy a disposal cell phone and communicate via radio to anywhere on planet, no licence needed. Richard-of-Earth (talk) 20:31, 13 November 2014 (UTC)
 * In many countries, the mobile phone or its transceivers will however need to be appropriately licenced. (At the very least, in most cases the spectrum they are operating can only be used because whoever's network your connecting to paid the government good money to be allowed to use said spectrum. And said operator usually sets standards which you are required to follow, failing which they may ask you to stop using their network or even take legal action against you.) Nil Einne (talk) 13:28, 14 November 2014 (UTC)


 * Technically you can communicate around the world, just use a low frequency. Looks like below 9khz is unlicensed (not certain though). But your bandwidth will be tiny. Some links to check: ELF SLF ULF VLF Ariel. (talk) 20:40, 13 November 2014 (UTC)
 * Technically, it is prohibitively difficult for an amateur on a limited budget to broadcast a strong signal at VLF or lower frequency. A quarter-wave antenna at 30 kHz would be 2.5 kilometers high.  VLF and lower frequency transmitters tend to be operated by scientific researchers and by well-funded governments.  Nimur (talk) 00:17, 14 November 2014 (UTC)
 * ???? The OP is asking about unlicensed but legal transmitters. Hams (with legal licensed transmitters) have been doing EME (that's about all most half a million miles) since about the 1960 and all without a government grant of billions of dollars. For lower frequencies,  a British and New Zeeland ham duo were able to communicate at 2 (two) watts, by careful frequency and phase matching and signal period. A technique, later adopted many decades later by JPL in order to pull in the very weak 20 watt transmissions from Voyager one & two (and they added a bit of computerized statistical analysis as well, to speed things up, and to help  filter out the signal from the background noise). Most unlicensed but legal  transmitters are in the upper frequency range so don't travel much further than the visible horizon during time of normal propagation.  During time of tunnelling however, US police VHF communications have been hear in the UK.  I have also received VHF from a guy whilst walking his dog on the shores of Holland who had only a 5 Watt transceiver but due to atmospheric tunneling he came in loud and clear. Sea water (being conductive) can create a dielectric wave guide taking the signal way beyond the radio horizon.  So lets not hear any more of this “Technically, it is prohibitively difficult for an amateur on a limited budget“ nonsense.  --Aspro (talk) 14:37, 14 November 2014 (UTC)
 * Most HAMs aren't transmitting below 50 kHz - ergo, "VLF", "ELF", and so on. "VHF" and "VLF" are one letter and many hundreds of thousands of dollars of equipment apart.  Nimur (talk) 16:04, 14 November 2014 (UTC)
 * Most HAMs may not be transmitting below 50 kHz but some do and quite successfully without billion dollar grants. But this is with legal licensed  equipment. Most no-licensed-required legal equipment (as asked by the OP)  uses VHF and above.--Aspro (talk) 16:29, 14 November 2014 (UTC)


 * I have no doubt that some amateur radio enthusiasts may try to transmit VLF; but they probably fail to generate very strong signals. This is what a VLF transmitter looks like: NAA as viewed from two miles away.  That is not a grouping of several dozen different VLF aerials: all of those towers are the radiating elements for one single VLF transmitter.  The wavelength of the center-frequency is about eight miles.  So, if you wanted to build a crappy, inefficient, barely functional amateur-grade whip antenna (instead of one of these sophisticated multi-element radiator arrays that the Navy uses), you'd still need a piece of wire five miles long, and you'd need to somehow attach it to a tower that would be taller than the tallest structure ever built by humans.  At wholesale prices, the wire-runs alone would cost upwards of $60,000, but the engineering and construction costs would be ... a little more complicated to estimate!  That's at 24 kHz.  Lower frequency radio, like ELF, corresponds to even longer wavelengths.
 * In March 2014, HAM operator W2ZM claimed to transmit trans-Atlantic signal at 29.499kHz on WH2XBA. I would go so far as to say, this level of equipment is non-amateur.  In fact, it is actually regulated as radio licensed for scientific research.
 * Let me re-iterate: I have no doubt that some amateur radio enthusiasts may try to transmit VLF; but they probably fail to generate very strong signal that would be suitable for long-distance propagation. It is much much much more efficient for a HAM to use an HF transmitter and use the skywave effect to transmit over the horizon.  Nimur (talk) 18:36, 14 November 2014 (UTC)
 * Oh Boy! Allow me re-iterate. The OP is asking about Legal but unlicensed apparatus. What has power got to do with it? See Shannon–Hartley theorem. The VLF image you referred to, is that high, because it is more efficient than it would be lower down,  but a lower antenna is still going to radiate . Have you heard of antenna that are λ/2,  λ/4,  λ/8 high and in length etc. Right. So why oh why, does one need five miles of very expensive sleeved cable cable costing $60,000 like you linked to? It is up in the air -it does not need to be copper or have any insulation (use plain aluminum)  and just a mile will do. $500,000 dollar towers ? Answer: String the antenna from tree to tree. If one has  to have all ones  teeth veneered by a dentist because one  drank too much coke and soda pop as a child, then in comparison, the cost of an amateur VLF antenna and associated equipment  is hardly astronomical- is it?  -Finally, the OP asks about Legal frequency but unlicensed'.  Most frequencies above 9 kHz have been  allocated by the ITU. So in answer to the OP's question its about 3800 miles in normal day/night conditions  with current practices; unless one is doing EME work but one will probable require a license for that in many countries as the side lobes could cause interferance. See and I quote:McIntyre needed no FCC license to transmit on 8.971 kHz, since the Commission has not designated any allocations below 9 kHz.--Aspro (talk) 21:25, 15 November 2014 (UTC)


 * PS. Do you know what a whip aerial is and why they are used, together with their efficiency and suitability in the right application?  You say “barely functional amateur-grade”?  Look at the specs and compare them to commercial (cheap (?) and cheerful) whips that cost an arm and a leg. Then see if you can find the  fallacies you're using from this List of fallacies. Just asking  (¬)--Aspro (talk) 21:59, 15 November 2014 (UTC)


 * The article you really need to read is Tropospheric propagation and the short answer is several thousand miles under ideal conditions. For the purposes of this post I am assuming the OP is referring to unlicensed UHF hand-held transceivers that operate near 460 MHz in most countries (where they are legal). Roger (Dodger67) (talk) 14:16, 14 November 2014 (UTC)


 * There are also some frequencies that have unlimited radiation regulations. 13.56MHz used to be a frequency that was chosen for certain equipment because it wasn't regulated.  --DHeyward (talk) 00:05, 15 November 2014 (UTC)

Why are we able to see light from almost the time of the big bang, should it not have got passed us?
I know that the further away an object is, the further back in time you're looking at that object, it's simply because light takes time to reach us, and as a result we are able to see objects that are over 10 billions years now, to almost to the time of the big bang itself. The question I have is how come we are able to see that light given that everything started from a single point and that everything escaped from that point, and given that light goes faster than us, us made of matter, that light should have passed us almost right from the beginning and should now be impossible to see, so my question is why are we able to see light that came from almost the time of the big bang given that that light should be out of reach? Joc (talk) 19:55, 13 November 2014 (UTC)


 * That is because space is glowing like a cooling ember. We cannot see the fire before the ember though. Plasmic Physics (talk) 20:21, 13 November 2014 (UTC)


 * That doesn't really answer the question. Vacuum or space can not radiate light (even if you had the energy, where would the momentum go?). So what is glowing? Ariel. (talk) 21:44, 13 November 2014 (UTC)


 * You are taking my metaphor too literally, I mean that even though it's not the honest truth, space itself may as well be glowing. The CMB was caused by the gas in the early universe cooling down. However, the rate of expansion out-paced the speed of light, and so the light from the glow is delayed. It is effect as hearing a lightning strike sometime after the matter, due to the difference between the speed of light, and speed of sound. Plasmic Physics (talk) 01:04, 14 November 2014 (UTC)


 * First, it's not accurate that everything escaped from a point. A better analogy is that of an expanding balloon, with two dimensional creatures living on the surface of the balloon.  To the 2D creatures, there is no third dimension.  Their universe is expanding, but there's no point in space that everything is escaping from.
 * We can see almost to the Big Bang because at that time, we were moving nearly at the speed of light relative to the point we now see. The speed of light was so close to the speed of expansion that light only managed to catch up after 14 billion years.  --Bowlhover (talk) 21:55, 13 November 2014 (UTC)


 * See Inflation (cosmology) for why light got left behind.   D b f i r s   23:21, 13 November 2014 (UTC)
 * No, inflation is not really it. The balloon analogy is better. Imagine a constantly growing balloon (ok, there is some inflation ;-). We are living on and looking along the surface of the balloon in this reduced dimension. But no matter how far you look, there is always a piece of the balloon that is that far away, and from which light has travelled for a corresponding amount of time. --Stephan Schulz (talk) 00:04, 14 November 2014 (UTC)
 * OK, point taken. Also, inflation happened before photons of light came to exist, and long before there were stars to shine, so the balloon started partially inflated.  Perhaps a constantly stretching flat rubber sheet would be a better analogy if you believe that space is flattish.    D b f i r s   00:27, 14 November 2014 (UTC)

Bowlhover: I agree that matter was going at almost the speed of light at the moment of the big bang but now we are going much slower, it seems to me that the light from the big bang should have passed us long ago.

Plasmic Physics: I agree that the CMB (Cosmic Microwave Background) is like the amber of the "explosion", an ambient light all around us that came from the big bang, but unless I'm mistaken, what we are actually seeing are very old galaxies that existed almost at the beginning of the universe, and again, how come we can see them, how come the light has not passed us and make them impossible to see???

Stephan Schulz: the balloon analogy seems to best answer to my question; both me and the far away galaxy are moving apart, that means that light has a longer distance to travel, which allows me to see further in the past. It seems like a race condition, the speed of the expansion of the universe against the speed of light. Would be nice to get details on that. Joc (talk) 22:14, 14 November 2014 (UTC)


 * See Metric expansion of space for details of the race. The expansion is currently accelerating.  My point was that space had a head start.  Matter as we know it (three states of atoms) didn't exist immediately after the Big Bang.   D b f i r s   22:28, 14 November 2014 (UTC)


 * Joc, the thing to understand is that the Big Bang didn't happen at a place. From our perspective, it happened at all places.  All of space originated from the Big Bang, and consequently, all of space was filled with hot plasma in the initial moments after the Big Bang.  In essence, when we look deep into space in one direction and see the cosmic microwave background, we are seeing what the after effects of the Big Bang looked like in that particular location a long time ago, and when we look in a different direction, we are seeing the after effects of the Big Bang somewhere else a long time ago.  The Big Bang affected all of space, so if you look a great enough distance in any direction, you'll eventually see light that originated from the era shortly after the Big Bang itself.  And the light you'll see reflects the impact of the Big Bang on that specific region of space far, far away (it's nearly the same in all direction, but people who study the cosmic microwave background can gain big insights from small difference depending on where you look in space).  Also, the cosmic microwave background was created by the glow of recombination (cosmology), a side-effect of the universe cooling after the Big Bang and forming the first atoms (instead of ionized plasma).  It predates the formation of galaxies and stars.  Dragons flight (talk) 23:07, 14 November 2014 (UTC)


 * That it happen in "all places" implies that the universe is infinite, that also implies that light has an infinite amount of space to travel, and so it implies that we could look an infinite amount of time in the past, even before the big bang! Now I know that's wrong, but I don't know how it's wrong. I'm NOT interested by the CMB, what we measure is it's temperature and it glows everywhere; what I'm interested is that I read that we can actually see galaxies from very near the time of the big bang, and that we can see them clearly enough to be able to tell they they are "primitive", that they didn't have the time to form structures such as spirals for example, this is not the diffuse light of the CMB but light from a very precise point in space and time, the thing I don't understand is how those photons didn't get passed us since they are faster than us, given that everything came from the same point (if everything is moving away, reversing the time arrow, implies that everything came from the same point).


 * The universe may be infinite, or it may simply be far, far bigger than the part of it that we can see. Either theory is consistent with cosmology and the shape of the universe as we know it.  The expansion of the universe makes many things confusing, but lets ignore that for a moment.  Ignoring expansion, we would assume that the oldest galaxies formed ~13 billion years ago, in a region of space ~13 billion light years away, using matter and energy the Big Bang left in their local region of space.  As far as we can see, the Big Bang left a nearly uniform density of matter everywhere, and it did so as far back in time as we can see.  In practical terms, that's what it means that the Big Bang affected all of space, it deposited nearly uniform matter everywhere we can see at the very beginning.  That may continue literally forever (an infinite universe), or it may stop somewhere beyond the visible universe that we can see, but either way all of space for as far away as one can choose to look, is filled with matter.  Incidentally, the CMB is the limit of how far one can look.  At that point you are seeing the glow of the Big Bang, and no light older than the CMB survived.


 * For a slightly more nuanced description, that includes expansion, one would say that the earliest galaxies formed ~13 billion years ago in a region of space that is now ~40 billion light years away. The extra ~30 billion light years is associated with the expansion of space, but the light only traveled ~13 billion years to reach us because at the time it departed the two regions of space were much closer.  Even accounting for expansion though, the far away region of space 13 billion years ago already had a similar density of matter as the region of space we presently live in had 13 billion years ago.  The Big Bang deposited matter everywhere we can see during the very earliest moments of time (e.g. inflation), well before those early galaxies formed.


 * To return to the balloon analogy, the universe is like the surface of a balloon, and the density of matter can be thought of as like the thickness of the rubber. As the balloon expands, all points get farther away from one another and the local density of matter (i.e. rubber) decreases.  The universe stretches and thins.  However, the balloon always had rubber everywhere, it was created that way.  No matter how you shrink or expand the balloon, there is no point in time where the rubber vanishes, it simply becomes more or less dense.  On cosmological scales, the matter in the universe is the same way.  The instant of the Big Bang created the universe (i.e. the balloon) with matter everywhere.  The matter was then stretched and expanded, becoming less dense, but there was no region of space (as far as we can see) that ever lacked for matter.  Dragons flight (talk) 20:23, 16 November 2014 (UTC)


 * A slight improvement on the balloon analogy would have galaxies stuck onto the expanding surface in a rigid material, so that only the rubber between the galaxies expands.  D b f i r s   00:25, 18 November 2014 (UTC)