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February 14

How could the universe be infinite?

Apparently the universe could be finite or infinite. I'm curious how it could be infinite given the universe has an age and finite speed of expansion? — Preceding unsigned comment added by 2.102.184.32 (talk) 03:23, 14 February 2017 (UTC)[reply]

Simple. It was always infinite <added>at any positive time after the Big Bang</added>. In an infinite universe, the Big Bang was ~~not~~ a moment of zero size, ~~but rather~~ <added>and also</added> of infinite (or maximum) density. We have some discussion of this at size of the universe and shape of the universe. Someguy1221 (talk) 03:29, 14 February 2017 (UTC)[reply]

So the Universe at the time of the Big Bang was just a tiny area, but in that tiny area there was an infinite density of stuff, and when it exploded the infinite stuff expanded to an infinite area?— Preceding unsigned comment added by 2.102.184.32 (talk • contribs)

<added>Yes</added>~~Not quite. The theory would go that at the time of the Big Bang, the universe was infinite in both density and extent. It never went from finite to infinite~~. You might ask how something infinite can get bigger... well, it can. In the case of the universe, an expanding and infinite universe is merely one in which though the total size is always "infinity", the bits inside are getting further apart from one another at all times. Someguy1221 (talk) 04:42, 14 February 2017 (UTC)[reply]

It's not clear that it's meaningful to talk about the exact moment of the Big Bang. Cosmologists can tell all sorts of things about what happened 100,000 years after the Big Bang, or 1 second after it, or 10⁻³⁵ seconds after it, but you'll basically never see them say anything about exactly 0 seconds.

That said, it's possible to make sense, at least mathematically, of the universe having infinite extent at any positive time after the Big Bang, but zero extent at the exact moment of the Big Bang. I'll elaborate below. --Trovatore (talk) 04:46, 14 February 2017 (UTC)[reply]

You know what, Trovatore, I think you have to be right, and I have to be wrong. Thanks for throwing me the "any positive time after the big bang" life raft :) Someguy1221 (talk) 05:03, 14 February 2017 (UTC)[reply]

(edit conflict)Just a bit more on how something infinite can get bigger, a lot of people have trouble thinking about infinity as mathematicians do. Take an example. There are infinity numbers between 0 and 1, because you can write nonrepeating decimal expansions forever. There are also infinity numbers between 0 and 10. Are there more numbers between 0 and 10, than between 0 and 1? All numbers between 0 and 1, are also between 0 and 10. But the interval from 0 to 10 also has numbers that aren't between 0 and 1. So you'd like to say that there are more numbers in the larger span. But it's definitely true that both spans contain infinity numbers. If you accept that this is logical, then you may also accept that a universe that was always infinite in size can get bigger, defined as the average space between particles at least. Someguy1221 (talk) 04:48, 14 February 2017 (UTC)[reply]

(edit conflict) Wikipedia has an article titled shape of the universe which discusses some of the geometric possibilities that could produce an infinite universe. You aren't the first person to wrestle with such issues; see Olbers' paradox for one such famous issue with infinity. --Jayron 32 03:31, 14 February 2017 (UTC)[reply]

Actually its all still unknown. The Big Bang is an widely agreed assumption, not a proven fact! The universe may be much older or maybe it was always here. Neither the "age of the universe" nor "its rate of expansion" are really "given" facts in scientific sense, so your basic assumption is already wrong. Both are infact also "just" widely agreed on assumptions aswell. Astrophysics still has allot of homework to do on what has been discovered by astronomy and astronomy is barley started. Remember Hubble Space Telescope is just 26 years young and it is a very restricted instrument, atleast compared to the new James Webb Space Telescope, that will start collecting new facts in 2 years.

Likely there are some groundbraking discoveries about to be made in the near future and it will not be the first time big theories get dumped into history books as nice try but proven to be wrong if they find stuff that doesnt add up. --Kharon (talk) 04:25, 14 February 2017 (UTC)[reply]

Saying the Big Bang is "not a proven fact" is disingenuous. It is enormously well-supported by evidence. Scientific theories, especially well-tested theories like the Big Bang, aren't just guesses. (I'm reminded of the frequent creationist canard that "evolution is only a theory!") It's true that theories are adjusted to account for new evidence, but that doesn't mean learning anything new requires us to throw them out and start over from scratch. As Lawrence Krauss is quoted as stating in our Big Bang article, "[The] big bang picture is too firmly grounded in data from every area to be proved invalid in its general features." --47.138.163.230 (talk) 06:45, 14 February 2017 (UTC)[reply]

To concur with 47.138, it should be noted that you are not a proven fact. However, the Big Bang is as well accepted as anything else, so there's no need to say that it "isn't a proven fact". If you demanded more proof for the Big Bang than currently exists, then you probably don't believe anything has ever been proven ever. --Jayron 32 12:01, 14 February 2017 (UTC)[reply]

But the February 2017 Scientific American has an article by 3 astrophysicists, 2 from Princeton and 1 from Harvard, saying that in their opinion the latest data strongly refutes the Big Bang, and they favor a Big Bounce from a previously contracting universe as an alternative theory consistent with the data. Loraof (talk) 17:36, 14 February 2017 (UTC)[reply]

We have an article on the Big Bounce theory. It's actually conceptually very similar to the Big Bang, in that ~13.7 billion years ago the universe was contracted into an immensely dense, tiny volume. They differ fundamentally in that Big Bounce posits a "before". Big Bounce could be true, possibly while keeping true most of the Big Bang theory. Someguy1221 (talk) 01:16, 15 February 2017 (UTC)[reply]

Per Someguy1221, the story is clearly "Some scientists have proposed refining current theories about the origin of the universe" and not "SCIENTISTS NOW SAY EVERYTHING YOU KNOW IS WRONG!" Science works this way by small incremental changes to established theories. Complete rejection of established, well-supported theories are exceedingly rare, instead most of the major work is in refinement. The popular press (and/or the Intelligent Design crowd) latch on to these refinements and blow them way out of proportion to say "SCIENCE SAYS X IS WRONG" or "SCIENTISTS DON'T KNOW WHAT THEY ARE DOING" when, in reality, these sorts of tweaks and changes to theories happen continuously, and don't prove that older scientific theories were wrong, just that we get better results with more accumulated knowledge. --Jayron 32 13:16, 15 February 2017 (UTC)[reply]

Here's a silly toy example that is absolutely not a picture of the actual universe, but might give some insight into how such a thing could be logically possible.

Suppose the universe is laid out on a standard 3-dimensional Cartesian coordinate system, where at any fixed comoving time, every point has a set of coordinates (x, y, z) for some real numbers x, y, z.

Now suppose that all particles go exactly with the Hubble flow, and that each particle has three coordinates x₀, y₀, z₀ that tell you where it is at one second after the Big Bang.

Suppose further that, at any time t seconds after the Big Bang, said particle is at position (tx₀, ty₀, tz₀).

Then you can easily check that, at any positive time t, there are particles arbitrarily far apart from one another.

However, at the exact moment of the Big Bang, namely t=0, all particles are at location (0, 0, 0). --Trovatore (talk) 04:54, 14 February 2017 (UTC)[reply]

I found your toy example extremely useful. I got it wrong above at first, but I found your argument excellent when thinking of the problem backwards. Instead of asking what happens after the Big Bang, asking what happens starting from the present and working back. Now of course if the universe is finite in size, you can compress it as much as you want, and it won't reach infinite density as long as its volume is non zero. Well, if you start with an infinite universe, it's actually still really hard to get infinite density. As long as there is space between particles (assumed to be points), you can keep compressing forever. You can get any two particles, arbitrarily far apart in the universe, to be arbitrarily close, without ever hitting infinite density. In this thought experiment, you don't reach infinite density unless every particle is touching every other particle. Now this started with an infinite extent, infinite mass, finite density universe. If we work forward from my initial (and now I think wrong) assumption of a universe with infinite extent, mass and density, I'm not sure you ever get a universe that is not all of the above. I won't drone on about a counterfactual, but I don't think logic (let alone physics) even works. So thanks again. Someguy1221 (talk) 05:18, 14 February 2017 (UTC)[reply]

Suggested videos from PBS Space Time: [1] [2] [3] --47.138.163.230 (talk) 06:45, 14 February 2017 (UTC)[reply]

I suspect the toy example leads astray. The molecules are not expanding neatly at kx, ky, kz. They are moving all over the place, smashing against each other. A second after the Big Bang every molecule was colliding with some unimaginable number of other molecules, so in that "short" amount of time, a whole lot of stuff was going on. I don't know if simply taking ln t = "tau" is really an accurate way to look at it, but I think we can put an infinite amount of history into a finite amount of time - under regimes of physics that used ever smaller Compton radii for ever larger masses for particles stable on ever smaller time scales the further back you look. Eventually they get down the Planck radius, particles that are black holes, nobody knows what happens - but this is not a guarantee that physics before that point was boring or nonexistent ... it gives quite a hint to the contrary. Wnt (talk) 17:52, 14 February 2017 (UTC)[reply]

Well, it was an example with a very limited purpose, to show that it's logically possible to have a universe with finite (actually zero) extent at one instant, and infinite extent at all later moments. You can't ask too much of it.

I do have a sort of a similar picture to yours; a universe that actually has no first instant, but just has a time coordinate that converges when you look backwards in time. As to whether there's anything interesting to say about the pre-Planck-time epoch, who knows. --Trovatore (talk) 19:39, 14 February 2017 (UTC)[reply]

Feynman Lectures. Lecture 48. Ch.48-3 [4]

...
The television problem is more difficult. As the electron beam goes across the face of the picture tube, there are various little spots of light and dark. That “light” and “dark” is the “signal.” Now ordinarily the beam scans over the whole picture, 500 lines, approximately, in a thirtieth of a second. Let us consider that the resolution of the picture vertically and horizontally is more or less the same, so that there are the same number of spots per inch along a scan line. We want to be able to distinguish dark from light, dark from light, dark from light, over, say, 500 lines. In order to be able to do this with cosine waves, the shortest wavelength needed thus corresponds to a wavelength, from maximum to maximum, of one 250th of the screen size. So we have 250×500×30 pieces of information per second. The highest frequency that we are going to carry, therefore, is close to 4 megacycles per second. Actually, to keep the television stations apart, we have to use a little bit more than this, about 6 mc/sec; part of it is used to carry the sound signal, and other information. So, television channels are 6 megacycles per second wide. It certainly would not be possible to transmit tv on an 800 kc/sec carrier, since we cannot modulate at a higher frequency than the carrier.

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

How did he derived the number 250 and why must it be the wavelength? So I assume that the maximum of modulating signal amplitude is converted to the increasing electron emission from CRT and so white spot; the minimum of amplitude is the decreasing emission and dark spot. These spots are within the same line (one of 500), are adjacent , situated horizontally (as lines are horizontal) and have a diameter = 1 line width. Is it correct? Can the equipment modulate the carrier wave like this png so on the screen we see only one spot? Username160611000000 (talk) 05:23, 14 February 2017 (UTC)[reply]

A white spot adjacent to a black spot represents one cycle of the highest video frequency required, which is half the number of spots scanned per second. Assuming that the transition from spot to spot is a sine (or cosine) wave means that no higher frequency is needed (whereas abrupt black/white changes as in a chequerboard image would involve squarewaves and much higher harmonic frequencies). He calculates "4 megacycles per second" which is better expressed as 4 MHz. The 4 MHz video signal can be modulated on any higher frequency carrier for broadcasting. Simple Amplitude modulation would transmit sideband frequencies (F_c - 4) and (F_c + 4) MHz however this wastes precious bandwidth so the lower sideband is mostly suppressed and receivers are designed to demodulate the resulting vestigial sideband signal. The explanation serves as an introduction to the NTSC#Transmission modulation scheme that occupies a total bandwidth of 6 MHz. Blooteuth (talk) 19:14, 14 February 2017 (UTC)[reply]

Nuclear fallout

If terrorists detonate an atom bomb in the area of Wichita, KS, what amount of food and non-food crops would be contaminated by the fallout? Would that result in actual food shortages in the USA (to the point where some people would have to go without certain foods or where rationing would have to be put in place), or would it only cause increases in the price of food? If the latter, approximately how much of an impact would it have? In either case, for how long would the land remain contaminated and unusable for growing crops (i.e. how long would it be before agriculture in the area could return to normal again)? (Assume that the explosive yield of the bomb is 45 kt (the biggest nuke which those vermin could realistically obtain at present), that the detonation is at ground level (worst-case scenario in terms of radiation), and that prevailing winds prevail.) 2601:646:8E01:7E0B:9076:92A3:E19C:2F76 (talk) 06:38, 14 February 2017 (UTC)[reply]

"We don't answer requests for opinions, predictions or debate." See the page header. --47.138.163.230 (talk) 07:00, 14 February 2017 (UTC)[reply]

Would you have answered the question if I specified the location as Broken Arrow, OK? 2601:646:8E01:7E0B:9076:92A3:E19C:2F76 (talk) 10:28, 14 February 2017 (UTC)[reply]

There is a gem of an answerable question in there. Someone should be able to find references on how much agricultural land around a nuclear blast is expected to become unusable in the short term. This was once a very hot topic of research. Someguy1221 (talk) 08:21, 14 February 2017 (UTC)[reply]

Well, I've actually done the first part of the research -- I've played out this scenario on Nukemap, and it shows that with 15 knots of wind from the southwest (which may or may not actually be the prevailing wind, I don't know), the fallout plume would stretch almost as far as Topeka: http://www.nuclearsecrecy.com/nukemap/ So, with the fallout plume as shown, how much farmland would be contaminated, and how long would it stay that way -- and how much would it hurt food production? 2601:646:8E01:7E0B:9076:92A3:E19C:2F76 (talk) 10:41, 14 February 2017 (UTC)[reply]

We can generate a pretty good answer from history, and that answer is "nationwide food production and price changes would be negligible". The US has detonated over 600 kilotons of surface-level nuclear weapons within the continental US, with over 500 kilotons additionally detonated over the US at airburst levels. This is of much higher magnitude than the suggested range for a single terrorist bomb, and no widespread fallout (to the degree that it materially impacted the availability of food) was observed. Any single low-yield nuclear detonation can be safely characterized as being local in scope (however horrific that local scope may be), and the food production of the US is not constrained to any particular local scope. At most, you might find some highly-localized specialty crop that could be substantially disrupted, but not staples. — Lomn 15:42, 14 February 2017 (UTC)[reply]

Editing to add: Here's a map of fallout from the Nevada Test Site. It's clearly quite extensive over the Great Plains, so it's not as if major farming regions didn't experience the effects of several hundred kilotons of nuclear detonations. — Lomn 15:48, 14 February 2017 (UTC)[reply]

Thanks! So I understand the answer is, not much of an impact on food supplies, right? 2601:646:8E01:7E0B:64B4:64AD:FCBF:2883 (talk) 09:04, 15 February 2017 (UTC)[reply]

Here's a 70-page book, available at no cost, from the RAND Corporation: Technical Report 391, Considering the Effects of a Catastrophic Terrorist Attack (2006). If you're the sort who likes to read about these things, it's good to learn a few good sources: RAND publishes a huge library of very professional-quality research on science and policy topics like this one, and the overwhelming majority of their library is available at no cost (!) because some famous historical guy figured that the cost-benefit of an informed public, educated by free, free information, outweighed the risk of controversial information "leaking out."

On the topic of vermin, a senior member of the White House staff was recently ousted for being overly-friendly with our nation's arch-nuclear-rival.... It was his published opinion that Islamic terrorist group Al Qaeda remains as-strong-as-ever. I wonder if we can believe him!

One of my professors and a fellow pilot, Martin Hellman, worked with a few senators and politicians and researchers to found Nuclear Risk, a very alarmist organization whose primary objective, apparently, is turning intellectuals into insomniacs. They publish a lot of information on realities and speculations of 21st-century nuclear war. I find that experienced glider pilots tend to see things that we often cannot see from ground-level.

And lastly, if you haven't yet read The Bulletin, have a glance at their motives for moving their metaphorical "doomsday clock" to its most desperate setting since the invention of the hydrogen bomb in 1953. "...intemperate statements, lack of openness to expert advice, and questionable cabinet nominations have already made a bad international security situation worse."

To quote disenfranchised Arab musician Ghassan Rahbani, we're all chickens and there are foxes guarding the hen house.

Nimur (talk) 15:46, 14 February 2017 (UTC)[reply]

First of all, even if Flynn was in cahoots with the Russians (which is probably just lies created by rogue elements in our intelligence services in any case), it DOES NOT invalidate his assessment of Al-Qaida -- read Ad hominem fallacy, for God's sake! Second of all, President Trump's cabinet nominations, with a couple of exceptions, have been THE BEST in recent history -- in fact, they are THE FIRST cabinet nominees IN HISTORY to take the threat of Islam seriously! And why would ANYONE believe some raghead musician (i.e. a self-evident NON-expert, and moreover one with a VESTED INTEREST in HARMING our nation) over MULTIPLE EXPERTS in matters of NATIONAL SECURITY?! 2601:646:8E01:7E0B:64B4:64AD:FCBF:2883 (talk) 09:12, 15 February 2017 (UTC)[reply]

I'm not familiar with Ghassan Rahbani or his music. Can you explain in what way he has a vested interest in harming the US? (Preferably without resorting to racial slurs or excessive use of capitalization). Iapetus (talk) 10:26, 15 February 2017 (UTC)[reply]

Incidentally, the slur seems even sillier here than normal since AFAICT, Ghassan Rahbani does not generally wear a turban or keffiyeh. Nil Einne (talk) 14:39, 15 February 2017 (UTC)[reply]

My OpInIoN iS MoRe iMPoRtanT anD cORReCt beCAUse I usE randOm caPiTal letters? --Stephan Schulz (talk) 10:23, 15 February 2017 (UTC)[reply]

The Lebanese do not wear rags on their heads. That's a pretty impolite thing to insinuate; and in my neighborhood, it's a poor life-choice to become impolite with a Lebanese individual. Regarding headwear: there is a long and complex tradition of ~~Taqiya~~ Taqiya that is rooted in some important political history, and some of the young people are bringing it back to make an ironic statement. It might serve you well to expand your cultural horizons: here's the music in question - a hip-hop song about the difficulties of pacifism - but you kind of have to come from a rough neighborhood to appreciate that kind of music. Nimur (talk) 14:45, 15 February 2017 (UTC)[reply]

Note the answer would deeply involve human psychology. That is, how many people would be unwilling to feed their family food that is "only slightly contaminated but deemed to be safe by the government". Considering the level of distrust of government in the US, I suspect many people wouldn't believe the US government. And, if food wasn't labelled as coming from the contaminated area, that might cause people to avoid all food that might possibly be from there, instead preferring foods that were canned before the event or that don't grow in that region.

The public reaction to the food supply following the Fukushima Daiichi nuclear disaster may also be relevant. StuRat (talk) 17:30, 14 February 2017 (UTC)[reply]

The form of resulting ground contamination would be very dependent on weather conditions. Dry weather with strong winds could spread the contamination in a stripe over a hole continent. Enough rain would keep it a very local ground contamination. If the catastrophy would happen right at or near the shore of an Ocean, like in Fukushima, and the wind direction would transport most of the fallout away from the landmass, it would be minimal. --Kharon (talk) 14:46, 15 February 2017 (UTC)[reply]

It's highly unlikely that any terrorist group could gain access to a nuclear weapon and the means to deploy it. They would be much more likely get hold of some nuclear waste and make a dirty bomb - the detonation of which would have different consequences from that of an atom bomb. Richerman (talk) 17:38, 16 February 2017 (UTC)[reply]

They could buy one from the pakis (which is the scenario I had in mind, hence my specification of a 45-kt yield), or they could make their own! 2601:646:8E01:7E0B:3CD9:5D5C:57CE:D50B (talk) 10:49, 17 February 2017 (UTC)[reply]

North Korea seems more likely to sell atom bombs, as they already have just about every possible sanction on them, and are low on cash, so they have little to lose. StuRat (talk) 18:57, 17 February 2017 (UTC)[reply]

You've described a "question" that requires some pretty fair modelling with data we don't really have here, but here are some sources that may make your simulation more realistic:

It's good you're familiar with Nukemap, because that would give you an estimate of the fallout plume from a ground burst at any yield you care to simulate.

A 45 kiloton-yield weapon, unless it was unusually "dirty" (which a Pakistani nuclear device might be, since their mathematical physicists were probably not as skilled as, say, Freeman Dyson or Theodore Taylor) would not pose a strategic contamination problem. Its fallout would probably be limited to a hundred or so miles downwind of ground zero and be very light compared to the fallout from a thermonuclear weapon (current thinking is that the Pakistani nuclear arsenal is mostly fusion boosted fission weapons, not thermonuclear weapons). The United States has actually detonated several such devices in ground and air bursts before the ban on above-ground nuclear testing was negotiated with the Soviet Union. The resulting impact on food production was minor (although the public was less aware of the biological effects of even small amounts of fallout at that time and there could be more reluctance to eat food grown in a fallout plume).
The Rice University Web site "Estimated Strategic Nuclear Weapons Inventories (September 2004)" shows what warheads at what yields our most credible nuclear threat, Russia, has. The largest weapon yields (according to our treaty information from Russia) in that force are 1-2 megatons. A realistic assessment of the cropland damage you're asking about really ought to use current warheads aimed at our nation which are on proven delivery systems - that is a graver concern than terrorist nuclear devices, which are unlikely to reach or exceed 100 kilotons yield.
For a more realistic estimate of fallout on Kansas cropland, I'd simulate several ground bursts upwind from Kansas.

Warren Air Force Base near Cheyenne, Wyoming is the US Strategic Command ICBM base from which average prevailing winds would carry nuclear fallout to Kansas. It's reasonable to expect several 1-2 megaton ground bursts there in a counterforce nuclear strike to attempt to destroy those ICBMs and/or prevent future launches if the silos at Warren AFB are reloaded.

Other large point sources of fallout possibly falling on Kansas cropland are:

Airbursts in the megaton range over Denver, Colorado metropolitan area, a high priority defense and civilian government hub, and Buckley Air Force Base which hosts part of NORAD's missile tracking network and might get hit pre-emptively
Ground bursts in the megaton range at Schriever Air Force Base, Peterson Air Force Base, and Cheyenne Mountain Air Force Station near Colorado Springs, Colorado, all of which are known counterforce targets.

All those areas are going to be hit hard by Russian nuclear weapons in a nuclear war. Those are the fallout plumes I'd simulate to get a good idea of cropland damage by fallout from a nuclear attack.

Please note, however, that deposition of fallout is almost never uniform within the contours of a fallout plume. The plumes you see in a NukeMap simulation imply worse and more widespread contamination than would occur in practice. Actual experience with above-ground tests shows fallout will fall in "hot spots" of concentrated activity, while surrouding areas get little or no fallout and can be used with few or no precautions. That fact is documented in Chapter IX of The Effects of Nuclear Weapons by Samuel Glasstone and Philip Dolan. In practical terms, you'd have to actually monitor the farmland in the fallout plume (which as you've doubtless noticed, can stretch for hundreds of miles) to see where the fallout actually fell.

If I were you, I'd avail myself of Technical Report 391, Considering the Effects of a Catastrophic Terrorist Attack, but also find a copy of Herman Kahn's On Thermonuclear War, which might fill in some conceptual gaps in how widespread nuclear contamination of crop land in the United States would affect availability of food, and the practical steps available to best manage the risk of contaminated foods (he suggested a rationing scheme in which older survivors of a nuclear attack would be allowed to eat food that was safe as far as acute radiation was concerned but was contaminated enough to increase cancer risk - the reasoning being that such risk is cumulative over many years and older survivors would likely not suffer cancers or other long-term effects before they died of the normal effects of aging). Kahn's discussion of how to manage cropland contamination by fallout is important because it's the "why" to that RAND Corporation document's "how" - if you'd like a full understanding of the problem. On Thermonuclear War was written while Kahn worked at the RAND Corporation. loupgarous (talk) 10:23, 18 February 2017 (UTC)[reply]

What to call '2A "self-cleavage" peptide?

There's this short peptide sequence that when it's translated from mRNA results in a break in the nascent peptide and it's called '2A'. It was or is commonly called a "self-cleavage" peptide because, I think, that was how it was once supposed to function but that is now known not to be the case. If it's not a "self-cleavage" peptide, what kind of peptide can it be called? --129.215.47.59 (talk) 14:19, 14 February 2017 (UTC)[reply]

The preferred terminology appears to be self-cleaving peptide. --Jayron 32 15:06, 14 February 2017 (UTC)[reply]

But it's not self-cleaving. --129.215.47.59 (talk) 16:13, 14 February 2017 (UTC)[reply]

But that's what it's called in the literature, so that's "what it's called" or at least a common and recognizeable term among those in the field. And what wikipedia would call an article, for the same reason. It's known that it's a misnomer (see for example doi:10.1186/s13068-017-0710-7 and references therein), but also hardly the first time a now-disproven idea has persisted in nomenclature. DMacks (talk) 16:33, 14 February 2017 (UTC)[reply]

This calls it the 2A self-processing peptide, FWIW. While this paper just calls it "2A peptide" in many places, and says (citing this, which looks likely to be the original skip paper): "2A and 2A-like sequences are now referred to as CHYSELs (cis-acting hydrolase elements) rather than self-cleaving peptides". As an article title I'd prefer the phrase in words - the acronym seems too clever by half. Wnt (talk) 17:28, 14 February 2017 (UTC)[reply]

What is subcloning? I think article might be wrong

According to the article subcloning is "a technique used to move a particular gene of interest from a parent vector to a destination vector in order to further study its functionality". What if you don't want to study its functionality? What if you just want the expression cassette out of one reporter to put in another? Is that not subcloning? --129.215.47.59 (talk) 15:04, 14 February 2017 (UTC)[reply]

I believe that's just cloning. --Jayron 32 15:07, 14 February 2017 (UTC)[reply]

The definition is wrong (well not wrong, just too specific). Moving any genetic material from one vector to another is generally referred to as subcloning. Amplifying the genetic material from its native environment (DNA, mRNA etc) into vector-based cDNA is molecular cloning. Fgf10 (talk) 15:37, 14 February 2017 (UTC)[reply]

I agree the "in order" should be a different sentence; "this might be done in order...". Cloning is to subcloning as letting (renting out) an apartment is to subletting it. So long as you are growing up many identical copies of the genetic sequence, and you started with something you'd already cloned, it's subcloning. (But subcloning is still a kind of cloning, just as subletting is a kind of letting, as after all (as the Jurassic Park novel famously pointed out) many "cloning" experimental sequences have turned out to have started inadvertently with plasmid DNA!) Wnt (talk) 17:43, 14 February 2017 (UTC)[reply]

How long does a fecal transplant last?

I was in a seminar recently and it was discussed that after an effort is made to change a person's microbial flora it reverts back to the original state and is based on their genetics. I've heard of fecal transplants as treatments for people with some gastrointestinal diseases and I've heard of these causing obesity when fecal material was sourced from an obese donor. Does the microflora return to the disease state and/or patient to original body weight? --129.215.47.59 (talk) 16:26, 14 February 2017 (UTC)[reply]

Wikipedia has an article titled Fecal microbiota transplant which covers the procedure. According to the Wikipedia article, obesity is only mentioned in passing as a "potential" application. It does not mention the mechanism by which it may work to treat obesity. --Jayron 32 16:56, 14 February 2017 (UTC)[reply]

The Q was about it causing obesity, not treating it. StuRat (talk) 17:34, 14 February 2017 (UTC)[reply]

Note that the gut microbiome also greatly depends on what the person eats, and specifically probiotics and prebiotics. A transplant won't last long if the intestinal environment does not allow for the survival of those organisms, or could last a lifetime, if it does. StuRat (talk) 17:38, 14 February 2017 (UTC)[reply]

Is that a guess, or could you give us a reference for both parts of your last sentence? Loraof (talk) 02:10, 15 February 2017 (UTC)[reply]

You want a source for the statement that organisms won't survive in an environment that doesn't allow for their survival, and could survive in an environment that does allow for their survival ? StuRat (talk) 03:30, 15 February 2017 (UTC)[reply]

I want a source for the notion that it can happen that a fecal transplant might not last too long, and a source for the notion that it could last for a lifetime. I genuinely would like a source for these, but I have no idea whether you're just guessing. Loraof (talk) 16:46, 15 February 2017 (UTC)[reply]

You must have misinterpreted what I said, so I will clarify. The purpose of the fecal transplant is to deliver microbes to improve the mix in the gut flora. However, whether those microbes flourish and reproduce, or die out in short order, depends on whether the intestinal environment is conducive to their survival. I didn't get into exactly what conditions are good for those microbes, and which are bad for them, but I see a note on artificial sweeteners has been added, with sources, at the bottom of this post, so you can take a look at those. StuRat (talk) 18:18, 15 February 2017 (UTC)[reply]

And is there any chance that the intestinal environment won't be conducive to the transplanted microbes' survival, as you extremely strongly implied could be the case? Citation needed. Loraof (talk) 21:49, 15 February 2017 (UTC)[reply]

Yes. I provided four articles from respectable journals, all of which make it very clear that consuming artificial sweeteners makes it difficult for healthy intestinal bacteria to survive. Can you explain why you believe that transplanted bacteria will survive any better than the person's own bacteria? 209.149.113.5 (talk) 12:56, 16 February 2017 (UTC)[reply]

To me, "a [fecal] transplant won't last long if ..." means that its intended effect, such as crowding out an infection of C. difficile, will soon fail. There appears to be nothing in the four linked articles about that. What I'd like is a reference that says something about fecal transplants and how long they last in the sense of their being effective. Thanks if you can find some—I'd appreciate it. Loraof (talk) 17:30, 16 February 2017 (UTC)[reply]

Actually some of the sources in the fecal transplant article address the success rate (upwards of 80%), though this doesn't say whether failure is due to the transplanted microbes failing to survive or just failing to overwhelm the C. diff. Loraof (talk) 17:50, 16 February 2017 (UTC)[reply]

Yes, you misunderstood me. I wasn't talking about "crowding out an infection of C. difficile", at all. StuRat (talk) 19:26, 16 February 2017 (UTC)[reply]

As far as which microbes survive and which die out, in any environment, it depends on many factors, like temperature and acidity, as well as the presence or absence of other microbes. I believe at least one of those 4 sources mentioned that the genetics of the person also control which microbes can survive, by altering the intestinal environment. StuRat (talk) 22:35, 17 February 2017 (UTC)[reply]

personal dispute

The following discussion has been closed. Please do not modify it.

A source for anything you say ever would be a nice start. --Jayron 32 04:00, 15 February 2017 (UTC)[reply]

Let's see a source for your claim that I've never provided a source for anything I've ever said. I've provided many sources to debunk that lie, now it's your turn to defend it. StuRat (talk) 04:28, 15 February 2017 (UTC) [reply]

An example of the claim that what you consume affects your gut flora... Many (too many to list) studies have concluded that consumption of artificial sweeteners negatively impacts gut bacteria and most of these studies correlate the altered gut bacteria with a predisposition to weight gain. [5] [6] [7] [8] (is that enough references to support the claim?) 209.149.113.5 (talk) 14:56, 15 February 2017 (UTC)[reply]

Thanks for the info. StuRat (talk) 18:21, 15 February 2017 (UTC)[reply]

According to this "Patients' gut bacteria remained healthy for up to 21 weeks after FMT" Richerman (talk) 18:31, 16 February 2017 (UTC)[reply]

Nanobots slowing aging

Will nanobots be eventually able to actually reverse aging, or will they just slow it down?Uncle dan is home (talk) 18:11, 14 February 2017 (UTC)[reply]

The article Ageing explains what we theorize about it, that it is a combination of accumulated damage (such as DNA oxidation) and programmed processes (such as DNA oxidation). Nanorobotics is an emerging technology that has potential medical applications such as directed drug delivery e.g. to cancer cells, and even assisting White blood cells protect the body. However the Ref. Desk will not give the OP a prediction about achieving Immortality (see article). Blooteuth (talk) 18:35, 14 February 2017 (UTC)[reply]

There is potential to repair DNA, such as lengthening telomeres on chromosomes and fixing errors within the DNA. Not sure if nanobots or programmed viruses would be the method. Note that fixing errors requires a "correct" version of the DNA to compare with, so cells from that individual, frozen at birth, might be useful there. Otherwise you would need to compare many damaged DNA samples to try to determine what the original undamaged version was. StuRat (talk) 18:40, 14 February 2017 (UTC)[reply]

Blood type distribution by country

Our article at Blood type distribution by country has been tagged "factual accuracy is disputed" since 2012. Does anyone have a source that can be used to either correct the article or remove the tag? --Guy Macon (talk) 18:26, 14 February 2017 (UTC)[reply]

Some possible leads to follow: [9], [10], [11], [12]. All of these were found on the first page of a Google search with the phrase blood type distribution. If you try that yourself, you may find more references you can use. --Jayron 32 18:51, 14 February 2017 (UTC)[reply]

Does porn change the sexual preferences?

Does porn change the sexual preferences? If people are given access to different types of porn, which they find appealing, would that result in a different sexual preferences? Would they ignore the types they don't have access to?--Llaanngg (talk) 19:39, 14 February 2017 (UTC)[reply]

Some good faith answers on sexual orientation, but OP was interested in sex acts. Also some meta-discussion on conduct. Collapsed for clarity.

Wikipedia has an extensive article titled Sexual orientation which discusses a myriad of factors that may or may not affect a person's sexual preferences. It does not mention any effect of pornography generally, but does contain several statements from respected organizations and researchers to the effect of " mechanisms for the development of a particular sexual orientation remain unclear" and " there is no scientific consensus about the specific factors that cause an individual to become heterosexual, homosexual, or bisexual" and "No one knows what causes heterosexuality, homosexuality, or bisexuality." and " [there is no] conclusion based in sound science at the present time as to the cause or causes of sexual orientation". So, take that as you may. --Jayron 32 19:49, 14 February 2017 (UTC)[reply]

Note that the age at which the exposure occurs may well be critical, as sexual orientation tends to be more flexible at an earlier age. Also note that if someone was exposed to homosexual porn at an early age, and became a homosexual adult, there are at least 3 possible conclusions:

They were heterosexual, and the gay porn "turned them gay".

They were genetically predisposed to be homosexual, but would have repressed this tendency if they had no "gay role models".

They would have become a homosexual adult in any case.

So, the exact nature of the cause and effect, if indeed there is any, is open for debate. StuRat (talk) 20:53, 14 February 2017 (UTC)[reply]

Do you ever read anything about actual research in this area, by actual experts who study it, or do you just make shit up as you go along as usual. "gay porn turned them gay"? Do you have any idea how absolutely backwards and bigoted that sounds given what we know about this? This is why we don't tell people what "we know" here at the reference desk. Give them reading material and let them figure it out. Jeez Stu, you've reached a new low here today. --Jayron 32 03:59, 15 February 2017 (UTC)[reply]

Do YOU have any idea how absolutely STUPID you sound accusing StuRat of being "bigoted" just for bringing up a possibility of gay porn turning someone gay? BTW, there HAVE been in fact cases of straight people becoming gay and vice versa, so this possibility is not even that far out! 2601:646:8E01:7E0B:64B4:64AD:FCBF:2883 (talk) 09:18, 15 February 2017 (UTC)[reply]

there HAVE been in fact cases of straight people becoming gay and vice versa ^{[citation needed]} - It sounds plausible enough to me, but that doesn't mean it's true. Tigraan^{Click here to contact me} 13:56, 15 February 2017 (UTC)[reply]

Well, sure, there is fluidity of sexual orientation, but recognizing that is different then the sort of "we can just make him straight" or "X made him gay" sort of thinking. A person's sexuality can be fluid, and can change throughout someone's life, but the idea that sexuality can be reliably controlled by outside factors is what leads to bullshit like conversion therapy. Yes, sexuality can change. No, you cannot make it change. --Jayron 32 14:48, 15 February 2017 (UTC)[reply]

I'm pretty sure he was just talking about how, logically, a correlation can have multiple possible explanations, and showing that there are alternatives to the theory that watching it changed them. Its analogous to saying: "If someone claims they were abducted by aliens, there are at least 3 possible conclusions: 1) They were abducted by aliens; 2) They're just making it up; 3) They imagined it". Listing an implausible explanation alongside more reasonable ones doesn't mean you support it, and is often done to emphasize how unlikely it is. Iapetus (talk) 10:37, 15 February 2017 (UTC)[reply]

My point exactly, and I added the scare quotes to emphasize that this is not what I believe. But Jayron probably knew that, as his reading comprehension skills can't possibly be that poor. He just lies about everything I do to try to make me look bad. StuRat (talk) 14:42, 15 February 2017 (UTC)[reply]

(EC) A selection of relevant scholarly articles that may be of interest:

The Influence of Pornography on Sexual Scripts and Hooking Up Among Emerging Adults in College[13] (freely accessible)

“Bareback” Pornography Consumption and Safe-Sex Intentions of Men Having Sex with Men[14](paywalled).

Does Pornography Influence Sexual Activities?[15](accessible)

Does pornography influence young women’s sexual behavior?[16](paywall)

As indicated in our article, and mentioned by Jayron, there is no general consensus of any strong effect of pornography on sexual orientation, but many researchers have documented some effects of pornography consumption on sexual preference (in a non-orientation sense), sexual acts, etc. SemanticMantis (talk) 20:57, 14 February 2017 (UTC)[reply]

Yes, I meant sexual preference in the sense @SemanticMantis used the word, that is, not as sexual orientation (homo, hetero, and so on), but as a preference for sexual activities.Llaanngg (talk) 21:31, 14 February 2017 (UTC)[reply]