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Talk:Galaxy formation and evolution

structure and scale
Some questions this article needs to address: a. Why are most galaxies 1,000 to 100,000 parsecs in diameter when the process of formation described here could operate on almost any scale? b. Is the process of galaxy formation equivalent (on a different scale) to that of protoplanetary disc formation and of supercluster formation? c. If so, then why do galaxies have structures such as spirals, not observed in the disc structures at other scales? --Tediouspedant (talk) 20:07, 6 February 2010 (UTC)

some comments
Almost all galaxies have an extrememly large black hole at their center, or many tightly-packed neutron stars formed from collapsing supernovas over billions of years. All of the stars in the galaxy rotate around this massive center.

It has been suggested that the universe will end with neutrons as well, when all stars have collapsed into neutron stars and planets have been pulled into black holes. However, this may not happen for many billions of years.

 * Maybe true, but it doesn't belong in Galaxy formation and evolution, and is not very well formulated.

rmulated are terms as top-down and bottom-up process models, Zel'dovich's pancake (originally crepe paper). Do someone have enow (an 'old' enough) time to define them better? After all 'at least' our Galaxy must have 'developed' from somewhere. XJam [2002.03.26] 2 Tuesday (0) - The article currently claims that M31 has a lower mass than the Milky Way; I was fairly sure that it's the other way round, with M31 being about twice the MW's mass. Does anyone know for sure? Will check up on this when I get a chance. --Bth 01:28 Oct 1, 2002 (UTC)

M31 = Andromeda Galaxy ( >4.1 E11 solar masses), Milky Way (5 E11 solar masses) &  --mav

The masses seem to be comparable, I really don't know how much effect a 20% diff or so can have, so I eliminated sentence about M31 being affected the most, for precaution. If somebody is familiar with simulations and is really sure of it, you are welcome to put the sentence back.--AN

The future of galaxies
For an article claiming to be complete, why does it include nothing on the future of galaxies? For example what happens when the Milky Way collides with Andromeda? What happens when galaxies are depleted of gas. Are there white (or even red dwarf or "degenerate matter" galaxies? This needs to be added to the article IMO. John D. Croft 19:38, 4 February 2007 (UTC)

Galaxy formation
Is it not accepted now that most galaxies form around a massive black hole as the result of starburst triggered by quasar activity? This is not mentioned in the article.

Alan Stafford

 * Um, I think it is accepted that galaxies form around gravitationally unstable fluctuations in the initial distribution of mass in the universe. As these structures collapse, they become dense enough for stars to form, and the centre of the more dense of such collapsing structures could well form massive black holes. Quasars are thought to be one of the manifestations of the accretion of mass onto such an object.

 * In your picture, how do the massive black holes form? What causes the black holes to become quasars?  How do the quasars trigger starburts?  And how do the starbursts create galaxies?  -- ALoan (Talk) 20:53, 23 January 2006 (UTC)

Its not my model. I saw a television program about it. The program was, "Supermassive Black Holes" : 'Horizon', it is a Horizon documentary on the "UKTV Documentary" channel.

Found the transcript: http://www.bbc.co.uk/science/horizon/2000/massivebholes_transcript.shtml

The bulge relation is in this paper http://arxiv.org/abs/astro-ph/0107134 authors David Merritt and Laura Ferrarese (Rutgers Uni). I think it was Martin Rees who calculated how the quasar would turn off to give the quiet galaxies we see lower than redshift ~6.

The television can be wrong, for example there was one where someone claiming a time machine design based on lasers. But this theory seemed more definite.

PS I found this paper http://arxiv.org/abs/astro-ph/9912346

The theory buzzword is "coevolution" or "co-evolution".

 * Thanks for your interesting links. Merritt and Ferrarese's paper is about the apparent link between the mass of a central black hole and the mass of the galaxy bulge within which they are located, and the correlation between the mass of the black hole and the velocity dispersion of stars in the bulge.  They talk about models of formation without drawing any concrete conclusions.  Similarly, Rees' paper suggests that black holes could form directly from coalescing gas without stars forming first, or by runway evolution of dense star clusters.

In the program above they were quite definite that the SMBH were responsible for forming galaxies. The reverse of the standard view.

 * The papers at the symposium also look very intersting but I am unable to open .ps.gz here. -- ALoan (Talk) 19:19, 26 January 2006 (UTC)

see http://www.ociw.edu/ociw/symposia/series/symposium1/proceedings.html

If I remember correctly Joseph Silk and Martin Rees said the starburst is triggered by temperature differences in the gas surrounding the quasar caused by the quasar. I think it was the starburst that also helps the quasar become dormant after time but my memory may be faulty here.

This paper summarizes the scenario. http://arxiv.org/abs/astro-ph/0511034.

The Future of Galaxies
This article on the formation and evolution of galaxies contains only a tiny fraction of the story - about 1010 years of the story. What happens to galaxies in 10100 years? Has the evolution of galaxies stopped. This is a fundamentalist belief that has no place in an article on the formation and evolution of galaxies.

Regards

John D. Croft 00:11, 21 February 2006 (UTC)

Galaxy Formation due to He++ to He+ Phase Transformation
Most scholars agree that the galaxies formed in the epoch of recombination. Calculation shows that the galaxies formed as a consequence of the He++ to He+ phase transformation in the expanding and cooling Big Bang fireball, assuming that the universe had expanded to point where its density was down to the average density of the present Milky Way galaxy, $$2.67 x 10^{-21} kg/m^3$$. At that time it had cooled to the He++ to He+ phase transition temperature, $$6.31 x 10^5$$ degrees Kelvin, which is determined by the binding energy of singly-ionized helium at 54.39 eV. The sudden reduction in particle number n per unit volume due to the recombination of electrons with helium nuclei caused a shattering pressure jog in P = nkT, allowing gravitation to gather bound clouds of galactic dimensions with the precise dimensions and masses determined by the cloud geometry, which was a function of internal angular momentum in sectors of the turbulent Big Bang fireball relic. These clouds had to be massive enough to prevent evaporation of material from their surfaces in order to be stably bound objects, which can be used to determine the absolute dimensions from an assumed geometry at the transition temperature and overall mass density of the Milky Way. The predicted dimensions and masses of these model galaxies for assumed geometries match observations well enough for us to recognize that the galaxies formed like this. The key event was the first major phase transformation featuring a pressure jog due to the formation of the first bound atomic systems in the Big Bang, the singly-ionized helium atoms. Heavier species were not then abundant, but created later on in supernova explosions. Thus the galaxies were forged at the same time the first bound atoms were formed in the first major recombination event. For details, see Galaxy Formation by James A. Green from Greenwood Research at http://greenwood.s5.com/galaxy.html, and also see further details at http://greenwood.s5.tripod.com/m51gal.html. According to this phase-transformation galaxy formation theory, the barred spiral galaxies such as NGC 1365 in Fornax are considerably smaller than the 88,060 light-year in diameter flat spirals, the barred spirals measuring just 3/2 Jeans lengths along the bar, or 48,070 light-years. A typical 88,060 light-year in diameter flat spiral averaging about 10,200 light-years thick is thought to have been formed from pressure waves featuring an integer number 7 of Jeans half-lengths across and 11 complete waves azimuthally around at the mass-averaged expection radius, automatically excluding most possible initial forms in the flat spiral class by initially requiring integer numbers of pressure wavelets both radially across and azimuthally around. The numbers 7 & 11 come up, like something from a cosmic game of dice, except that all is determined by a pressure wave-mechanical process triggered by a quantum-mechanically fixed atomic transition between He++ and He+. The pressure waves are due to the pressure jog induced by the associated phase transformation He++ to He+ in the cooling Big Bang fireball, which takes place at a well-defined temperature. On the other hand, a galaxy formation process based on the H+ to H recombination event would produce galaxies with linear dimensions reduced by 1/2 and masses down by (1/2)3 = 1/8, no longer matching observations well. The time of galaxy formation may be determined by universe dynamics and the observed dimensions of galaxies. According to the equations for a universe of constant density, the solution for the radius of the universe should vary like $$r = a*[t]^{2/3}$$. From observations, if the universe were shrunken by a factor of Z = 100, the galaxies would all be touching. Let $$r_B$$ be the radius of the universe at that time. Then if r is the current radius of the universe,

$$ Z = r/r_B = (t/t_B)^{2/3} = 100.$$

Then $$t/t_B = (100)^{3/2} = 1000$$, and

$$ t_B = t/1000 = 13.5 x 10^9$$ years/1000 = 13.5 million years.

This is on the time-scale associated with the matter-dominated era, but it shows that the galaxies formed quite early.

Many of the results of the sophisticated theory based on pressure waves at the Jeans wavelength associated with the He++ to He+ transition phase transformation can be obtained from flocule theory based on models of gas evaporation from galactic surfaces. In flocule theory one considers the escape of a gas particle working against the gravitational potential for the cloud, and from this derives the dimensions of the cloud if the density is assumed to be the average Milky Way density. This density is assumed to be a relic of the Big Bang fireball at the He++ to He+ transition temperature. Using flocule theory, one can then derive the dimensions of spherical galaxies, ellipitical galaxies, and flattened ellipicals. The results agree well with observations of galaxies in clusters, and with the predictions of the model using Jeans length pressure waves. Using the gravitational potential associated with a flat plate, one may estimate the thickness of flattened spiral galaxies using bound flocule theory, which turns out to be 10,200 light-years, although no limit is specified then for the galactic diameter, which is determined by the more elaborate model involving Jeans length pressure waves due to the jog associated with the He++ to He+ phase transformation. This flat spiral galaxy thickness is determined by the thickness required to create a gravitational field strong enough to prevent the escape of particles from its surface to infinity at the transition temperature of $$6.31 x 10^5$$ degrees Kelvin from a body of Milky Way density. The Jeans theory based on pressure waves must be used to find the flattened spiral radius, however, which is not determined by the bound-cloud flocule theory. A perfectly uniform spherical galaxy formed under these conditions must have a radius of 8.8 Kilolightyears and a mass of $$0.328 x 10^9$$ solar masses. A disk with a thickness of 10,200 light-years determined by this bound-cloud theory and having a radius of 51 KLY has a mass of $$9.47 x 10^{10}$$ solar masses, about right for a typical flattened spiral galaxy, usually estimated at $$10^{11}$$ solar masses. An flattened-ellipsoid bound-cloud flocule model along these lines gives a central thickness of 14,400 LY, a little thicker than the Jeans model.

For the mythology of the celestial sphere alluded to above, see http://greenwood.s5.com/orionsky.html. Also see http://greenwood.s5.com/galaxyformationlinks.html.

Updated April 23, 2007. - James A. Green, March 25, 2006, http://greenwood.s5.com/home.html. --JamesAGreen 23:10, 25 March 2006 (UTC)

"Spiral galaxies cannot be built up by mergers of already existing smaller galaxies." This sentence is verging on incorrect. See "A Merger-Driven Scenario for Cosmological Disk Galaxy Formation," http://xxx.lanl.gov/abs/astro-ph/0503369

 * More importantly, it is written as a statement of fact, not verifiability, hence it is not written in NPOV style. --Iantresman 07:32, 2 May 2006 (UTC)

Spiral formation
Can someone provide a reference for this statement. It also contradicts the rest of the text which talks about how the Milky Way is absorbing other galaxies.

Spiral galaxies cannot be built up by mergers of already existing smaller galaxies. When galaxies collide, the individual stars barely notice. The stars themselves never collide with each other because of the enormous distances between them, compared to their size. So when galaxies collide, they actually simply pass through each other, but the gravitational effects disrupts their structure as this happens. As they separate, gravity slows them down and, if they are gravitationally bound, will eventually bring them back together for another collision. After several collisions their individual structures are so changed, with many stars mixed up between them, that we identify the result as a single merged object. So after a merger, most of the stars originally belonging to both galaxies remain to form the new merged galaxy (a small fraction will have been thrown out entirely). If either galaxy were a spiral before the merger, the violence of the event would disrupt the delicate structure of the disk. The existing stars cannot afterwards change their orbits to form a new disk. The stellar disk must essentially form in place; a dense rotating disk of gas forms first, then stars are born inside it.

Roadrunner 22:44, 2 June 2006 (UTC)

Can someone add a citation
This is so vague that it is impossible for me to figure out what it is referring to.

 * Recent data strongly suggests that the first galaxies formed as early as 600 million years after the Big Bang, much earlier than astronomers had previously believed. That leaves hardly enough time for the tiny primordial instabilities to grow sufficiently forming protogalaxies into galaxies.

Roadrunner 22:44, 2 June 2006 (UTC)

Hubble Tuning Fork
Article incorrectly states that Hubble believed the Fork to be an evolutionary sequence. This is a myth, see the Wiki article for the Tuning Fork itself. — Preceding unsigned comment added by 130.113.172.251 (talk) 03:04, 25 May 2016 (UTC)

Galaxy formation conflicts with observation
Key Theory Of Galaxy Formation No Longer Conflicts With Observations

This article states: "Astrophysicists led by the University of Chicago's Andrey Kravtsov have resolved an embarrassing contradiction between a favored theory of how galaxies form and what astronomers see in their telescopes."

I can't seem to find any mention of this in the article, which would appear to be a vital criticism. Oversight? Cover-up? Simplification? Uninformed editors? --Iantresman 22:49, 12 June 2006 (UTC)

Indeed, the dwarf galaxy problem is mentioned elsewhere but deserves mention here. --ScienceApologist 01:34, 13 June 2006 (UTC)

Galactic vs extragalactic astronomy
"A great deal of the research in this area is focused on components of our own Milky Way, since for us it is the easiest galaxy to observe"

This is wrong: actually our own Galaxy is the most difficult galaxy to observe because we're sat right in the middle of it, looking through a lot of dust and gas. Also since galaxy evolution is a slow process, a single galaxy doesn't tell you a whole lot. In fact most research in this area is focused on very distant galaxies, where you have a range of ages and types of galaxy to compare. Cosmo0 03:23, 16 June 2007 (UTC)

DIDN'T HELP
This article needs some serious primping and pampering. 71.212.121.155`~

71.212.121.155 23:53, 4 October 2007 (UTC)

Ellipticals "most evolved"
"Astronomers now see elliptical galaxies as some of the most evolved systems in the universe." Would "entropic" be a better term than "evolved" (this coming from a biological sciences major)? 69.243.168.118 (talk) 01:08, 29 April 2008 (UTC) (logged out User:Formerly the IP-Address 24.22.227.53

Tone tag
I removed the tone tag that was added in July. Since that time, some of the concerns of the original tagger were met, while others were not. This article may be an exception to the recommended guideline ("editorial feel. Avoid writing with "we must" and "We see that..." etc...) The scale is so vast, the language almost requires it. Viriditas (talk) 13:01, 25 October 2008 (UTC)

Pea galaxies
I have added a link in the "See also" section to the "Pea galaxy" article as I'm sure that it is relevant to this subject. I also put a citation query next to the amount of star-formation in mergers, as these figures seem optimistic. Great article though Richard Nowell (talk) 11:09, 25 January 2010 (UTC)

Galaxy evolution
Please note that most of this article discusses how galaxies form, not how they evolve or will be like in the future. I am doing a paper on this topic, and I am a big fan of Wikipedia. As we all know this article is called "Galaxy formation and evolution" and not just "Galaxy formation", please add more information. Thanks for your contributions. ~ Wimpy Fan boy ''' my talksign! 22:59, 30 May 2011 (UTC)

--Oldest galactic clusters found: In case these articles are useful to the authors: 1. General Science news article http://news.nationalgeographic.com/2015/04/150406-baby-galaxy-cluster-planck-herschel-sky-watching-virgo/?sf8415306=1

2. The Research paper for item 1 above http://www.aanda.org/articles/aa/pdf/forth/aa24790-14.pdf Jcardazzi (talk) 13:04, 7 April 2015 (UTC)jcardazzi

Galaxy evolution II
I am aware that balancing the needs of the different viewers' levels of interest and expertise, in order to be concise but not missing important content. That's why we have discussions. With that as preamble, I propose these additions. Such as why spiral arms contribute to star formation, that they are composed of shock waves whose leading edges entrain matter in "front" of them, etc. Likewise, I would wish not to see development between two merging galaxies; which will produce an elliptical galaxy, so simplified as here. Surely, it is worth describing as a multi-phase process. The process of cold dust condensation, star formation, supernova warming, resulting in dust warming and dispersion, etc. all this should be worth presenting. In addition re elliptical galaxies as being the end product of galactical evolution, then there should be a wealth of metallics, and thus a greater richness of planets in star orbits than in other galaxy types? Doesn't that provide a good link to other issues of interest to we humans, ie the existence of life? Perhaps my suggestions are already covered elsewhere in Wikipedia, in which case there might be feeder text with links. Just a few newbie comments. Hope they help. Idealist707 (talk) 21:05, 9 June 2011 (UTC)

Galaxy mergers and the formation of elliptical galaxies
I shortened the "Galaxy mergers and the formation of elliptical galaxies" section, pasting the content in the galaxy merger article, which has only been linked from the aforementioned sectioned.

This way, we give an overview of what a galaxy merger is, but for additional information the reader is redirected to the main article.

RickV88 (talk) 12:46, 5 January 2012 (UTC)

The globular cluster system and the formation of the galactic halo
Evolution of globular clusters and the origin of galactic halo stars The globular cluster system and the formation of the galactic halo Just granpa (talk) 01:20, 17 July 2013 (UTC)

Cosmology
I've added 'Cosmology' to the 'See also' section because "Galaxy formation and evolution" is part of 'cosmology'. As a one-word term, I didn't see 'cosmology' mentioned in the article here when I did a 'Find' within the article. — Charles Edwin Shipp (talk) 09:36, 28 February 2014 (UTC)

wwwcosmophysics.blogspot.com Arunprasadramadoss (talk) 18:38, 22 January 2021 (UTC)

Arunprasad Arunprasadramadoss (talk) 15:21, 24 May 2021 (UTC)

Commonly Observed Properties - problems.
As I read down through the common properties, there are a number of obvious and less obvious problems: The first is "notable" is NOT even close to being the same as "common"; they are (in some contexts) opposites. The section title is Common Properties, but the first sentence describes it as a partial list of notable properties. Second; "Spiral galaxies and the galactic disk are quite thin" seems to be a clumsy typo. I don't know if the author meant "Sprial and disk galaxies" or "Spiral galaxies' disks" or "Spiral galaxies and their disks are quite thin and ...". Third; it is, imho, a huge mistake to equate the shape of the VISIBLE galaxy with the shape of the galaxy. With our current understanding we can OBSERVE the emr from the normal matter and describe its shape and we infer the bulk of every galaxy is composed of Dark Matter in the shape of a sphere with density diminishing with radius. That is, the "shape" of most galaxies is spherical while their appearance tends to be lenticular (disk, sprial). A clear distinction should be made about what we are talking about. Fourth, the statement that Dark Matter "might not interact through any means except gravity" is a real problem. It almost certainly (if it exists) interacts with itself. So it does interact. I suppose the author meant to say it might not interact with normal matter and electromagnetic radiation, but this needs a citation, since it is my understanding that its not a question of zero interaction, rather a question of the magnitude of the cross-section (the probability of a collision occurring). That said, its also true that we have no clear idea what kind of 'stuff' it is, so talking about any of its positive properties isn't really possible. We can set limits on how much it interacts with normal matter, how much it interacts with emr, and how much it interacts with itself, but we know very little about it other than that. Fifth; "clouds of neutral hydrogen are "raining" down on the galaxy"... THE galaxy?? what is meant by THE galaxy? clouds are either raining down (this is a really poor choice of words, rain suggests 'precipitation from' rather than 'falling down of' the (entire) cloud) on galaxies (on large galaxies?) or they aren't a common property of galaxies. Two other problems with this section: one is that it has zero numbers. Estimates of the rotation speeds, proportions of dark matter, proportions of spiral, elliptical and globular galaxies, estimates of ratio between the two types of galaxies can and should be included. Second, a distinction between old galaxies (at high red-shift) and young ones (near by) should be made since galaxies change with time. It should be made clear which properties change with age and which don't.Abitslow (talk) 17:43, 16 January 2015 (UTC)

Formation of spiral galaxies - error
"As a galaxy gained mass (by accreting smaller galaxies) the dark matter stays mostly on the outer parts of the galaxy. This is because the dark matter can only interact gravitationally, and thus will not dissipate." this is just so WRONG! First, if galaxies are combining, then it makes little sense to talk about dark matter staying anywhere (the structures are merging, nothing is "staying"). Second, it is absolutely wrong to speak of dark matter "dissipating". Dark matter, we believe, interacts very little with itself or normal matter hence there is no good mechanism for its condensation (normal matter can condense because it can radiate away some of its kinetic energy as a result of collisions). Since dark matter doesn't radiate and doesn't collide, it tends to maintain its velocity and so has little propensity to fall into smaller orbits. Speaking about this as being "mostly on the outer parts" needs a citation, I'd say it tends to be uniform in distribution, certainly more uniform, but I also haven't seen the dynamics simulations which quantify that.Abitslow (talk) 18:13, 16 January 2015 (UTC)

Fossil Galaxy
In case this article is useful to the authors http://news.nationalgeographic.com/news/2014/05/140510-fossil-galaxy-astronomy-science-space-stars/ Jcardazzi (talk) 13:00, 7 April 2015 (UTC)jcardazzi

dark matter
Under "top-down theories", there is " clumps that consisted mostly of dark matter". This isn't dark matter in the modern sense, is it? Bubba73 You talkin' to me? 02:49, 4 July 2019 (UTC)

Possible merger?
I wonder if Stellar archaeology should be merged/redirected here. MaryMO (AR) (talk) 20:10, 4 August 2022 (UTC)

Wiki Education assignment: Astroparticle Physics
— Assignment last updated by Ghusheng (talk) 05:07, 23 April 2023 (UTC)

title: Talk:Galaxy formation and evolution


text:
Talk:Great Depression

First Sentence Wrong
The current version says: "The Great Depression was a severe worldwide economic depression that took place mostly during the 1930s, beginning in the United States". This is wrong. Trouble started in London/England/GB and continuously affected other places. On the other hand side, damage done to the U.S. economy was so bad that other economies e.g. in South America and on continental Europe were badly affected as well at this point, while the initial British failure of stock markets and related bank collapses were not able to do such enormous harm. In fact, it needed the leading economy to collapse to create such a global crisis, and the leading economy of these days had been the U.S.A. So the article should be re-written/ corrected to tell the actual story and to reflect all relevant facts in a precise and sufficient way. 188.99.107.40 (talk) 11:20, 14 June 2021 (UTC)

 * The Great Depression only happened in the United States,not worldwide. Luke Skywalker 350 (talk) 16:14, 15 December 2023 (UTC)
 * That is incorrect. Read Great Depression. Regards, Thinker78  (talk) 04:22, 16 December 2023 (UTC)
 * Sorry about that. I just learned that it happened in the U.S. Luke Skywalker 350 (talk) 16:34, 18 December 2023 (UTC)

Vietnam
The first phase of the Vietnamese revolution began in 1930 partly because the world depression then began to hit the Indo-Chinese export economy while simultaneous crop failures and famines intensified the popular suffering in the crowded delta regions. The Vietnam Nationalist Party attempted a military rising, starting in February with a mutiny of troops at Yen Bai on the Chinese border, which the French crushed with such severity that the party was all but destroyed. The newly unified Communist network, however, receiving a great influx of ardent revolutionaries, proceeded to stir up many strikes, demonstrations, incidents, and even peasant risings. The French used their Foreign Legion in a small-scale war to get the situation under control in 1931, and as a result thousands were killed, tried, executed, or deported.

Myanmar

 * From the Great Depression to Riots and Rebellions — Preceding unsigned comment added by 122.52.197.131 (talk) 08:12, 27 December 2022 (UTC)

Chart colors
The chart has a line that is red and blue, but the coloring is not explained. What does it mean? Kdammers (talk) 23:04, 27 January 2023 (UTC)

Semi-protected edit request on 16 May 2023
Yes October 24, 1929 fell on a Thursday not Tuesday meaning it would have been October 22 which was known as “black Tuesday” as the author states and therefore it should be edited to reflect the actual date of the event. 2603:8090:103:1E00:919A:F646:73A9:B84 (talk) 11:19, 16 May 2023 (UTC)
 * ✅ switched back to Black Thursday as the date is correct. Tuesday would've been the following Tuesday and the 29th Cannolis (talk) 14:59, 16 May 2023 (UTC)
 * I believe the Great Depression started on October 29th, not the 24th — Preceding unsigned comment added by 69.254.140.77 (talk) 23:14, 18 January 2024 (UTC)

the depression of 20th century
how great depression still plays a role in this century 41.116.194.249 (talk) 12:23, 30 October 2023 (UTC)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Talk:Great Depression


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Talk:Gamma function

Proof of equivalence of the three definitions
Is there value in using this instead or additionally?: $$\begin{align} & \int_0^\infty t^{z-1} e^{-t} dt \\ & = \lim_{n\rightarrow\infty} \int_0^{n+1} t^{z-1} \left(1-\frac{t}{n+1}\right)^n dt \\ & = \lim_{n\rightarrow\infty} \frac{1}{z(z+1)\ldots(z+n-1)}\frac{n!}{(n+1)^n} \int_0^{n+1} t^{z+n-1} \left(1-\frac{t}{n+1}\right)^0 dt \\ & = \lim_{n\rightarrow\infty} \frac{n!}{z(z+1)\ldots(z+n-1)}\frac{1}{(n+1)^n} \frac{(n+1)^{z+n}}{z+n} \\ & = \lim_{n\rightarrow\infty} \frac{n!}{z(z+1)\ldots(z+n)} (n+1)^{z} \\ & = \frac{1}{z} \prod_{n=1}^{\infty} \frac{(1+1/n)^z}{1 + z/n} \end{align}$$ where the second equality is integration by parts $n$ times. — Q uantling (talk | contribs) 22:42, 27 May 2023 (UTC)

 * This proves it only for $$\Re (z)>0$$. And as noted by Plusjeremy, that alone is insufficient for proving the reflection formula. Can you show that the infinite product is analytic for $$z\in\mathbb{C}\setminus\mathbb{Z}_0^-$$? (We're assuming the integral definition together with $$\Gamma (z+1)=z\Gamma (z)$$). A1E6 (talk) 09:18, 28 May 2023 (UTC)

I suggest adding it. Hawkeye7  (discuss)  00:02, 28 May 2023 (UTC)

are all these definitions shown?
are all these defenitions of $$\Gamma(x)$$ shown? $$\begin{align} \Gamma(x)=\int_{0}^{\infty}t^{x-1}e^{-t}dt\\ \Gamma(x)=\int_{0}^{1}(-\ln(t))^{x-1}dt\\ \Gamma(x)=\lim_{n\to\infty}n^{x-1}\prod\limits_{k=1}^{n}\frac{1}{k+x-1} \end{align}$$ Erikgobrrrr (talk) 21:50, 1 October 2023 (UTC)

Euler's definition as an infinite product
The reference for Euler's infinite product says that the limit goes to n!, not 1. 104.187.53.82 (talk) 16:21, 6 November 2023 (UTC)

 * I believe that you are talking about two different expressions. Both of these are true:
 * $$\lim_{n \to \infty} \frac{n! \, \left(n+1\right)^z}{(n+z)!} = 1$$
 * $$\lim_{n \to \infty} \frac{1}{z} \prod_{k=1}^n \left[ \frac{1}{1+\frac{z}{k}} \left(1 + \frac{1}{k}\right)^z \right] = \Gamma(z)$$ — Q uantling (talk | contribs) 16:41, 6 November 2023 (UTC)

log vs ln
I don't care much about which, but the article should be consistent. Do we want to use "$log$" or "$ln$" to indicate a natural logarithm? We could use one or the other throughout. Or, if we mostly go with "$ln$", we could nonetheless use "$log$" in those fewer cases where the expression works regardless of the base of the logarithm. What do you prefer? — Q uantling (talk | contribs) 17:06, 10 June 2024 (UTC)

 * I've made it consistent. Since I had to choose one, I chose log, with a notation on first use that it is the natural logarithm. I think this is the more common style for mathematical analysis and analytic number theory, the main subfields of mathematics for this topic. —David Eppstein (talk) 18:18, 10 June 2024 (UTC)

Equation appears wrong
The equation immediately following the words "Laplace transform" appears wrong.

The number log(π) has a positive sign in the previous equation, on the right of the equals sign.

So when it is brought to the left of the equals sign as in the equation following "Laplace transform", it should have a negative sign.

But it does not.

If this observation is correct, I hope someone familiar with this subject can fix this.

title: Talk:Gamma function


text:
GNU Compiler Collection

The GNU Compiler Collection (GCC) is a collection of compilers from the GNU Project that support various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free software under the GNU General Public License (GNU GPL). GCC is a key component of the GNU toolchain which is used for most projects related to GNU and the Linux kernel. With roughly 15 million lines of code in 2019, GCC is one of the largest free programs in existence. It has played an important role in the growth of free software, as both a tool and an example.

When it was first released in 1987 by Richard Stallman, GCC 1.0 was named the GNU C Compiler since it only handled the C programming language. It was extended to compile C++ in December of that year. Front ends were later developed for Objective-C, Objective-C++, Fortran, Ada, D, Go and Rust, among others. The OpenMP and OpenACC specifications are also supported in the C and C++ compilers.

GCC has been ported to more platforms and instruction set architectures than any other compiler, and is widely deployed as a tool in the development of both free and proprietary software. GCC is also available for many embedded systems, including ARM-based and Power ISA-based chips.

As well as being the official compiler of the GNU operating system, GCC has been adopted as the standard compiler by many other modern Unix-like computer operating systems, including most Linux distributions. Most BSD family operating systems also switched to GCC shortly after its release, although since then, FreeBSD and Apple macOS have moved to the Clang compiler, largely due to licensing reasons. GCC can also compile code for Windows, Android, iOS, Solaris, HP-UX, AIX and DOS.

History
In late 1983, in an effort to bootstrap the GNU operating system, Richard Stallman asked Andrew S. Tanenbaum, the author of the Amsterdam Compiler Kit (also known as the Free University Compiler Kit) for permission to use that software for GNU. When Tanenbaum advised him that the compiler was not free, and that only the university was free, Stallman decided to work on a different compiler. His initial plan was to rewrite an existing compiler from Lawrence Livermore National Laboratory from Pastel to C with some help from Len Tower and others. Stallman wrote a new C front end for the Livermore compiler, but then realized that it required megabytes of stack space, an impossibility on a 68000 Unix system with only 64 KB, and concluded he would have to write a new compiler from scratch. None of the Pastel compiler code ended up in GCC, though Stallman did use the C front end he had written.

GCC was first released March 22, 1987, available by FTP from MIT. Stallman was listed as the author but cited others for their contributions, including Tower for "parts of the parser, RTL generator, RTL definitions, and of the Vax machine description", Jack Davidson and Christopher W. Fraser for the idea of using RTL as an intermediate language, and Paul Rubin for writing most of the preprocessor. Described as the "first free software hit" by Peter H. Salus, the GNU compiler arrived just at the time when Sun Microsystems was unbundling its development tools from its operating system, selling them separately at a higher combined price than the previous bundle, which led many of Sun's users to buy or download GCC instead of the vendor's tools. While Stallman considered GNU Emacs as his main project, by 1990 GCC supported thirteen computer architectures, was outperforming several vendor compilers, and was used commercially by several companies.

EGCS fork
As GCC was licensed under the GPL, programmers wanting to work in other directions—particularly those writing interfaces for languages other than C—were free to develop their own fork of the compiler, provided they meet the GPL's terms, including its requirements to distribute source code. Multiple forks proved inefficient and unwieldy, however, and the difficulty in getting work accepted by the official GCC project was greatly frustrating for many, as the project favored stability over new features. The FSF kept such close control on what was added to the official version of GCC 2.x (developed since 1992) that GCC was used as one example of the "cathedral" development model in Eric S. Raymond's essay The Cathedral and the Bazaar.

In 1997, a group of developers formed the Experimental/Enhanced GNU Compiler System (EGCS) to merge several experimental forks into a single project. The basis of the merger was a development snapshot of GCC (taken around the 2.7.2 and later followed up to 2.8.1 release). Mergers included g77 (Fortran), PGCC (P5 Pentium-optimized GCC), many C++ improvements, and many new architectures and operating system variants.

While both projects followed each other's changes closely, EGCS development proved considerably more vigorous, so much so that the FSF officially halted development on their GCC 2.x compiler, blessed EGCS as the official version of GCC, and appointed the EGCS project as the GCC maintainers in April 1999. With the release of GCC 2.95 in July 1999 the two projects were once again united. GCC has since been maintained by a varied group of programmers from around the world under the direction of a steering committee.

GCC 3 (2002) removed a front-end for CHILL due to a lack of maintenance.

Before version 4.0 the Fortran front end was, which only supported FORTRAN 77, but later was dropped in favor of the new GNU Fortran front end that supports Fortran 95 and large parts of Fortran 2003 and Fortran 2008 as well.

As of version 4.8, GCC is implemented in C++.

Support for Cilk Plus existed from GCC 5 to GCC 7.

GCC has been ported to a wide variety of instruction set architectures, and is widely deployed as a tool in the development of both free and proprietary software. GCC is also available for many embedded systems, including Symbian (called gcce), ARM-based, and Power ISA-based chips. The compiler can target a wide variety of platforms, including video game consoles such as the PlayStation 2, Cell SPE of PlayStation 3, and Dreamcast. It has been ported to more kinds of processors and operating systems than any other compiler.

Supported languages
GCC includes front ends for C, C++ , Objective-C and Objective-C++, Fortran , Ada (GNAT), Go , D ( , since 9.1), and Modula-2 ( , since 13.1)  programming languages, with the OpenMP and OpenACC parallel language extensions being supported since GCC 5.1. Versions prior to GCC 7 also supported Java, allowing compilation of Java to native machine code.

Regarding language version support for C++ and C, since GCC 11.1 the default target is gnu++17, a superset of C++17, and gnu11, a superset of C11, with strict standard support also available. GCC also provides experimental support for C++20 and C++23.

Third-party front ends exist for many languages, such as Pascal, Modula-3, and VHDL. A few experimental branches exist to support additional languages, such as the GCC UPC compiler for Unified Parallel C or Rust.

Design

GCC's external interface follows Unix conventions. Users invoke a language-specific driver program ( for C,   for C++, etc.), which interprets command arguments, calls the actual compiler, runs the assembler on the output, and then optionally runs the linker to produce a complete executable binary.

Each of the language compilers is a separate program that reads source code and outputs machine code. All have a common internal structure. A per-language front end parses the source code in that language and produces an abstract syntax tree ("tree" for short).

These are, if necessary, converted to the middle end's input representation, called GENERIC form; the middle end then gradually transforms the program towards its final form. Compiler optimizations and static code analysis techniques (such as FORTIFY_SOURCE, a compiler directive that attempts to discover some buffer overflows) are applied to the code. These work on multiple representations, mostly the architecture-independent GIMPLE representation and the architecture-dependent RTL representation. Finally, machine code is produced using architecture-specific pattern matching originally based on an algorithm of Jack Davidson and Chris Fraser.

GCC was written primarily in C except for parts of the Ada front end. The distribution includes the standard libraries for Ada and C++ whose code is mostly written in those languages. On some platforms, the distribution also includes a low-level runtime library, libgcc, written in a combination of machine-independent C and processor-specific machine code, designed primarily to handle arithmetic operations that the target processor cannot perform directly.

GCC uses many additional tools in its build, many of which are installed by default by many Unix and Linux distributions (but which, normally, aren't present in Windows installations), including Perl, Flex, Bison, and other common tools. In addition, it currently requires three additional libraries to be present in order to build: GMP, MPC, and MPFR.

In May 2010, the GCC steering committee decided to allow use of a C++ compiler to compile GCC. The compiler was intended to be written mostly in C plus a subset of features from C++. In particular, this was decided so that GCC's developers could use the destructors and generics features of C++.

In August 2012, the GCC steering committee announced that GCC now uses C++ as its implementation language. This means that to build GCC from sources, a C++ compiler is required that understands ISO/IEC C++03 standard.

On May 18, 2020, GCC moved away from ISO/IEC C++03 standard to ISO/IEC C++11 standard (i.e. needed to compile, bootstrap, the compiler itself; by default it however compiles later versions of C++).

Front ends

Each front end uses a parser to produce the abstract syntax tree of a given source file. Due to the syntax tree abstraction, source files of any of the different supported languages can be processed by the same back end. GCC started out using LALR parsers generated with Bison, but gradually switched to hand-written recursive-descent parsers for C++ in 2004, and for C and Objective-C in 2006. As of 2021 all front ends use hand-written recursive-descent parsers.

Until GCC 4.0 the tree representation of the program was not fully independent of the processor being targeted. The meaning of a tree was somewhat different for different language front ends, and front ends could provide their own tree codes. This was simplified with the introduction of GENERIC and GIMPLE, two new forms of language-independent trees that were introduced with the advent of GCC 4.0. GENERIC is more complex, based on the GCC 3.x Java front end's intermediate representation. GIMPLE is a simplified GENERIC, in which various constructs are lowered to multiple GIMPLE instructions. The C, C++, and Java front ends produce GENERIC directly in the front end. Other front ends instead have different intermediate representations after parsing and convert these to GENERIC.

In either case, the so-called "gimplifier" then converts this more complex form into the simpler SSA-based GIMPLE form that is the common language for a large number of powerful language- and architecture-independent global (function scope) optimizations.

GENERIC and GIMPLE
GENERIC is an intermediate representation language used as a "middle end" while compiling source code into executable binaries. A subset, called GIMPLE, is targeted by all the front ends of GCC.

The middle stage of GCC does all of the code analysis and optimization, working independently of both the compiled language and the target architecture, starting from the GENERIC representation and expanding it to register transfer language (RTL). The GENERIC representation contains only the subset of the imperative programming constructs optimized by the middle end.

In transforming the source code to GIMPLE, complex expressions are split into a three-address code using temporary variables. This representation was inspired by the SIMPLE representation proposed in the McCAT compiler by Laurie J. Hendren for simplifying the analysis and optimization of imperative programs.

Optimization
Optimization can occur during any phase of compilation; however, the bulk of optimizations are performed after the syntax and semantic analysis of the front end and before the code generation of the back end; thus a common, though somewhat self-contradictory, name for this part of the compiler is the "middle end."

The exact set of GCC optimizations varies from release to release as it develops, but includes the standard algorithms, such as loop optimization, jump threading, common subexpression elimination, instruction scheduling, and so forth. The RTL optimizations are of less importance with the addition of global SSA-based optimizations on GIMPLE trees, as RTL optimizations have a much more limited scope, and have less high-level information.

Some of these optimizations performed at this level include dead-code elimination, partial-redundancy elimination, global value numbering, sparse conditional constant propagation, and scalar replacement of aggregates. Array dependence based optimizations such as automatic vectorization and automatic parallelization are also performed. Profile-guided optimization is also possible.

C++ Standard Library (libstdc++)
The GCC project includes an implementation of the C++ Standard Library called libstdc++, licensed under the GPLv3 License with an exception to link non-GPL applications when sources are built with GCC.

Other features
Some features of GCC include:

 * Link-time optimization
 * Link-time optimization optimizes across object file boundaries to directly improve the linked binary. Link-time optimization relies on an intermediate file containing the serialization of some Gimple representation included in the object file. The file is generated alongside the object file during source compilation. Each source compilation generates a separate object file and link-time helper file. When the object files are linked, the compiler is executed again and uses the helper files to optimize code across the separately compiled object files.

 * Plugins
 * Plugins extend the GCC compiler directly. Plugins allow a stock compiler to be tailored to specific needs by external code loaded as plugins. For example, plugins can add, replace, or even remove middle-end passes operating on Gimple representations. Several GCC plugins have already been published, notably:
 * The Python plugin, which links against libpython, and allows one to invoke arbitrary Python scripts from inside the compiler. The aim is to allow GCC plugins to be written in Python.
 * The MELT plugin provides a high-level Lisp-like language to extend GCC.
 * The support of plugins was once a contentious issue in 2007.

 * C++ transactional memory
 * The C++ language has an active proposal for transactional memory. It can be enabled in GCC 6 and newer when compiling with.

 * Unicode identifiers
 * Although the C++ language requires support for non-ASCII Unicode characters in identifiers, the feature has only been supported since GCC 10. As with the existing handling of string literals, the source file is assumed to be encoded in UTF-8. The feature is optional in C, but has been made available too since this change.

 * C extensions
 * GNU C extends the C programming language with several non-standard-features, including nested functions and  expressions.

Architectures

The primary supported (and best tested) processor families are 64- and 32-bit ARM, 64- and 32-bit x86_64 and x86 and 64-bit PowerPC and SPARC.

GCC target processor families as of version 11.1 include:

 * AArch64
 * Alpha
 * ARM
 * AVR
 * Blackfin
 * eBPF
 * Epiphany (GCC 4.8)
 * H8/300
 * HC12
 * IA-32 (x86)
 * IA-64 (Intel Itanium)
 * MIPS
 * Motorola 68000
 * MSP430
 * Nvidia GPU
 * Nvidia PTX
 * PA-RISC
 * PDP-11
 * PowerPC
 * R8C / M16C / M32C
 * RISC-V
 * SPARC
 * SuperH
 * System/390 / zSeries
 * VAX
 * x86-64

Lesser-known target processors supported in the standard release have included:

 * 68HC11
 * A29K
 * C6x
 * CR16
 * D30V
 * DSP16xx
 * ETRAX CRIS
 * FR-30
 * FR-V
 * IBM ROMP
 * Intel i960
 * IP2000
 * M32R
 * MCORE
 * MIL-STD-1750A
 * MMIX
 * MN10200
 * MN10300
 * Motorola 88000
 * NS32K
 * RL78
 * Stormy16
 * V850
 * Xtensa

Additional processors have been supported by GCC versions maintained separately from the FSF version:

 * Cortus APS3
 * ARC
 * AVR32
 * C166 and C167
 * D10V
 * EISC
 * eSi-RISC
 * Hexagon
 * LatticeMico32
 * LatticeMico8
 * MeP
 * MicroBlaze
 * Motorola 6809
 * MSP430
 * NEC SX architecture
 * Nios II and Nios
 * OpenRISC
 * PDP-10
 * PIC24/dsPIC
 * PIC32
 * Propeller
 * Saturn (HP48XGCC)
 * System/370
 * TIGCC (m68k variant)
 * TMS9900
 * TriCore
 * Z8000
 * ZPU

The GCJ Java compiler can target either a native machine language architecture or the Java virtual machine's Java bytecode. When retargeting GCC to a new platform, bootstrapping is often used. Motorola 68000, Zilog Z80, and other processors are also targeted in the GCC versions developed for various Texas Instruments, Hewlett Packard, Sharp, and Casio programmable graphing calculators.

License
GCC is licensed under the GNU General Public License version 3. The GCC runtime exception permits compilation of proprietary programs (in addition to free software) with GCC. This does not impact the license terms of GCC source code.

Official

 * GCC Release Timeline
 * GCC Development Plan
 * GCC Development Plan

Other

 * Collection of GCC 4.0.2 architecture and internals documents at I.I.T. Bombay
 * From Source to Binary: The Inner Workings of GCC, by Diego Novillo, Red Hat Magazine, December 2004
 * A 2003 paper on GENERIC and GIMPLE
 * Marketing Cygnus Support, an essay covering GCC development for the 1990s, with 30 monthly reports for in the "Inside Cygnus Engineering" section near the end
 * EGCS 1.0 announcement
 * EGCS 1.0 features list
 * Fear of Forking, an essay by Rick Moen recording seven well-known forks, including the GCC/EGCS one
 * EGCS 1.0 features list
 * Fear of Forking, an essay by Rick Moen recording seven well-known forks, including the GCC/EGCS one

title: GNU Compiler Collection


text:
Talk:Film genre

This article needs some TLC and fresh eyes
I have tagged this article for OR and needing more RS for verification. It has gone mostly unedited for years and IMO become quite sad. Jump in and let's edit the F out of it. —አቤል ዳዊት?(Janweh64) (talk) 07:38, 6 July 2017 (UTC)

Here is my proposed re-write
— Preceding unsigned comment added by Anon, a mouse... (talk • contribs) 4:49, 31 December 2018 (UTC)
 * I deleted the text that "Anon, a mouse" had pasted here because all the formatting displayed wrong, and I included a permalink to their sandbox which properly displays the correct formatting. Secundus Zephyrus (talk) 16:38, 31 December 2018 (UTC)
 * I think the rewrite is a really great start, and I especially like the lead section because it's clear and easy to understand. However I do think there is a lot of good information on the current page, and I think that whole sections from the current article could be added to your rewrite (e.g. "History" "Pure and hybrid" "Categorization"), even though they as well need to be significantly edited. Also, maybe some information from the article's current lead section can be incorporated into other sections of the new draft? -Secundus Zephyrus (talk) 17:18, 31 December 2018 (UTC)

Possible misplacement
Shouldn't Thriller be placed separately outside of Drama? Anubhab030119 (talk) 23:34, 2 January 2021 (UTC)

second chance 154.57.200.174 (talk) 17:11, 13 January 2024 (UTC)

The Film Genre article has issues
On the template it said that the article referenced in the title had multiple issues. I am a child, and I probably should not be doing this, but can someone older fix it please? 101.98.24.246 (talk) 04:04, 22 January 2024 (UTC)

You are not logged in. To be notified when someone replies and receive attribution with your name instead of your IP address, you can log in or create an account.@ 2402:AD80:11E:8E86:1:0:A58C:7FBC (talk) 13:32, 20 April 2024 (UTC)

title: Talk:Film genre


text:
Galen

Aelius Galenus or Claudius Galenus (Κλαύδιος Γαληνός; September 129 – 216 AD), often anglicized as Galen or Galen of Pergamon, was a Roman and Greek physician, surgeon, and philosopher. Considered to be one of the most accomplished of all medical researchers of antiquity, Galen influenced the development of various scientific disciplines, including anatomy, physiology, pathology, pharmacology, and neurology, as well as philosophy and logic.

The son of Aelius Nicon, a wealthy Greek architect with scholarly interests, Galen received a comprehensive education that prepared him for a successful career as a physician and philosopher. Born in the ancient city of Pergamon (present-day Bergama, Turkey), Galen traveled extensively, exposing himself to a wide variety of medical theories and discoveries before settling in Rome, where he served prominent members of Roman society and eventually was given the position of personal physician to several emperors.

Galen's understanding of anatomy and medicine was principally influenced by the then-current theory of the four humors: black bile, yellow bile, blood, and phlegm, as first advanced by the author of On the Nature of Man in the Hippocratic corpus. Galen's views dominated and influenced Western medical science for more than 1,300 years. His anatomical reports were based mainly on the dissection of Barbary apes. However, when he discovered that their facial expressions were too much like those of humans, he switched to other animals, such as pigs. While dissections and vivisections on humans were practised in Alexandria at this time, Galen did not have Imperial permission to perform his own, and had to use animals instead. Galen would encourage his students to go look at dead gladiators or bodies that washed up in order to get better acquainted with the human body. His anatomical reports remained uncontested until 1543, when printed descriptions and illustrations of human dissections were published in the seminal work De humani corporis fabrica by Andreas Vesalius, where Galen's physiological theory was accommodated to these new observations. Galen's theory of the physiology of the circulatory system remained unchallenged until c. 1242, when Ibn al-Nafis published his book Sharh tashrih al-qanun li' Ibn Sina (Commentary on Anatomy in Avicenna's Canon), in which he reported his discovery of pulmonary circulation.

Galen saw himself as both a physician and a philosopher, as he wrote in his treatise titled That the Best Physician Is Also a Philosopher. Galen was very interested in the debate between the rationalist and empiricist medical sects, and his use of direct observation, dissection, and vivisection represents a complex middle ground between the extremes of those two viewpoints. Many of his works have been preserved and/or translated from the original Greek, although many were destroyed and some credited to him are believed to be spurious. Although there is some debate over the date of his death, he was no younger than seventy when he died.

Biography
Galen's Greek name Γαληνός (Galēnós) comes from the adjective γαληνός (galēnós) 'calm'. Galen's Latin name (Aelius or Claudius) implies he had Roman citizenship.

Galen describes his early life in On the affections of the mind. He was born in September 129 AD. His father, Aelius Nicon, was a wealthy patrician, an architect and builder, with eclectic interests including philosophy, mathematics, logic, astronomy, agriculture and literature. Galen describes his father as a "highly amiable, just, good and benevolent man". At that time Pergamon (modern-day Bergama, Turkey) was a major cultural and intellectual centre, noted for its library, second only to that in Alexandria, as well as being the site of a large temple to the healing god Asclepius. The city attracted both Stoic and Platonic philosophers, to whom Galen was exposed at age 14. His studies also took in each of the principal philosophical systems of the time, including Aristotelian and Epicurean. His father had planned a traditional career for Galen in philosophy or politics and took care to expose him to literary and philosophical influences. However, Galen states that in around 145 his father had a dream in which the god Asclepius appeared and commanded Nicon to send his son to study medicine.

Medical education
Following his earlier liberal education, Galen at age 16 began his studies at the prestigious local healing temple or asclepeion as a θεραπευτής (therapeutes, or attendant) for four years. There he came under the influence of men like Aeschrion of Pergamon, Stratonicus and Satyrus. Asclepiea functioned as spas or sanitoria to which the sick would come to seek the ministrations of the priesthood. Romans frequented the temple at Pergamon in search of medical relief from illness and disease. It was also the haunt of notable people such as the historian Claudius Charax, the orator Aelius Aristides, the sophist Polemo, and the consul Cuspius Rufinus.

Galen's father died in 148, leaving Galen independently wealthy at the age of 19. He then followed the advice he found in Hippocrates' teaching and traveled and studied widely including such destinations as Smyrna (now İzmir), Corinth, Crete, Cilicia (now Çukurova), Cyprus, and finally the great medical school of Alexandria, exposing himself to the various schools of thought in medicine. In 157, aged 28, he returned to Pergamon as physician to the gladiators of the High Priest of Asia, one of the most influential and wealthy men in Asia. Galen claims that the High Priest chose him over other physicians after he eviscerated an ape and challenged other physicians to repair the damage. When they refused, Galen performed the surgery himself and in so doing won the favor of the High Priest of Asia. Over his four years there, he learned the importance of diet, fitness, hygiene, and preventive measures, as well as living anatomy, and the treatment of fractures and severe trauma, referring to their wounds as "windows into the body". Only five deaths among the gladiators occurred while he held the post, compared to sixty in his predecessor's time, a result that is in general ascribed to the attention he paid to their wounds. At the same time he pursued studies in theoretical medicine and philosophy.

Rome

Galen went to Rome in 162 and made his mark as a practicing physician. His public demonstrations and impatience with alternative views on medicine brought him into conflict with other doctors practicing in the city. When the Peripatetic philosopher Eudemus became ill with quartan fever, Galen felt obliged to treat him "since he was my teacher and I happened to live nearby". He wrote: "I return to the case of Eudemus. He was thoroughly attacked by the three attacks of quartan ague, and the doctors had given him up, as it was now mid-winter." Some Roman physicians criticized Galen for his use of the prognosis in his treatment of Eudemus. This practice conflicted with the then-current standard of care, which relied upon divination and mysticism. Galen retaliated against his detractors by defending his own methods. Garcia-Ballester quotes Galen as saying: "In order to diagnose, one must observe and reason." This was the basis of his criticism of the doctors who proceeded alogos and askeptos."

However, Eudemus warned Galen that engaging in conflict with these physicians could lead to his assassination. "Eudemus said this, and more to the same effect; he added that if they were not able to harm me by unscrupulous conduct they would proceed to attempts at poisoning. Among other things he told me that, some ten years before, a young man had come to the city and had given, like me practical demonstrations of the resources of our art; this young man was put to death by poison, together with two servants who accompanied him." When Galen's animosity with the Roman medical practitioners became serious, he feared he might be exiled or poisoned, so he left the city.

Rome was engaged in foreign wars in 161; Marcus Aurelius and his then co-Emperor and adoptive brother Lucius Verus were in the north fighting the Marcomanni. During the autumn of 169 when Roman troops were returning to Aquileia, a great plague, most likely one the first appearances of smallpox (then referred to as the Antonine Plague) in the Mediterranean world, broke out, and the emperor summoned Galen back to Rome. He was ordered to accompany Marcus and Verus to Germany as the court physician. The following spring Marcus was persuaded to release Galen after receiving a report that Asclepius was against the project. He was left behind to act as physician to the imperial heir Commodus. It was here in court that Galen wrote extensively on medical subjects. Ironically, Lucius Verus died in 169, and Marcus Aurelius himself died in 180, both victims of the plague.

Galen was the physician to Commodus for much of the emperor's life and treated his common illnesses. According to Dio Cassius 72.14.3–4, in about 189, under Commodus' reign, a pestilence occurred which at its height killed 2,000 people a day in Rome. This was most likely the same plague (the so-called "Antonine Plague" and most likely smallpox) that struck Rome during Marcus Aurelius' reign. Galen was also physician to Septimius Severus during his reign in Rome. He complimented Severus and Caracalla on keeping a supply of drugs for their friends and mentioned three cases in which they had been of use in 198.

The Antonine Plague
The Antonine Plague was named after Marcus Aurelius' family name of Antoninus. It was also known as the Plague of Galen and held an important place in medicinal history because of its association with Galen. He had first-hand knowledge of the disease, and was present in Rome when it first struck in 166, and was also present in the winter of 168–69 during an outbreak among troops stationed at Aquileia. He had experience with the epidemic, referring to it as very long lasting, and described its symptoms and his treatment of it. His references to the plague are scattered and brief. Galen was not trying to present a description of the disease so that it could be recognized in future generations; he was more interested in the treatment and physical effects of the disease. For example, in his writings about a young man afflicted with the plague, he concentrated on the treatment of internal and external ulcerations. According to Niebuhr, "this pestilence must have raged with incredible fury; it carried off innumerable victims. The ancient world never recovered from the blow inflicted upon it by the plague that visited it in the reign of M. Aurelius." The mortality rate of the plague was 7–10 percent; the outbreak in 165–168 would have caused approximately 3.5 to 5 million deaths. Otto Seeck believes that over half the population of the empire perished. J. F. Gilliam believes that the Antonine plague probably caused more deaths than any other epidemic during the empire before the mid-3rd century. Although Galen's description is incomplete, it is sufficient to enable a firm identification of the disease as related to smallpox.

Galen notes that the exanthema covered the victim's entire body and was usually black. The exanthem became rough and scabby where there was no ulceration. He states that those who were going to survive developed a black exanthem. According to Galen, it was black because of a remnant of blood putrefied in a fever blister that was pustular. His writings state that raised blisters were present in the Antonine plague, usually in the form of a blistery rash. Galen states that the skin rash was close to the one Thucydides described. Galen describes symptoms of the alimentary tract via a patient's diarrhea and stools. If the stool was very black, the patient died. He says that the amount of black stools varied. It depended on the severity of the intestinal lesions. He observes that in cases where the stool was not black, the black exanthema appeared. Galen describes the symptoms of fever, vomiting, fetid breath, catarrh, cough, and ulceration of the larynx and trachea.

Later years
Galen continued to work and write in his final years, finishing treatises on drugs and remedies as well as his compendium of diagnostics and therapeutics, which would have much influence as a medical text both in the Latin Middle Ages and Medieval Islam.

The 11th-century Suda lexicon states that Galen died at the age of 70, which would place his death in about the year 199. However, there is a reference in Galen's treatise "On Theriac to Piso" (which may, however, be spurious) to events of 204. There are also statements in Arabic sources that he died in Sicily at age 87, after 17 years studying medicine and 70 practicing it, which would mean he died about 216. According to these sources, the tomb of Galenus in Palermo was still well preserved in the tenth century. Nutton believes that "On Theriac to Piso" is genuine, that the Arabic sources are correct, and that the Suda has erroneously interpreted the 70 years of Galen's career in the Arabic tradition as referring to his whole lifespan. Boudon-Millot more or less concurs and favors a date of 216.

Medicine
Galen contributed a substantial amount to the understanding of pathology. Under the Hippocratic bodily humors theory, differences in human moods come as a consequence of imbalances in one of the four bodily fluids: blood, yellow bile, black bile, and phlegm. Galen promoted this theory and the typology of human temperaments. In Galen's view, an imbalance of each humor corresponded with a particular human temperament (blood – sanguine, black bile – melancholic, yellow bile – choleric, and phlegm – phlegmatic). Thus, individuals with sanguine temperaments are extroverted and social; choleric people have energy, passion, and charisma; melancholics are creative, kind, and considerate; and phlegmatic temperaments are characterised by dependability, kindness, and affection.

Galen was also a skilled surgeon, operating on human patients. Many of his procedures and techniques would not be used again for centuries, such as the procedures he performed on brains and eyes. His surgical experiments included ligating the arteries of living animals. Although many 20th-century historians have claimed that Galen believed the lens to be in the exact center of the eye, Galen actually understood that the crystalline lens is located in the anterior aspect of the human eye.

At first reluctantly but then with increasing vigor, Galen promoted Hippocratic teaching, including venesection and bloodletting, then unknown in Rome. This was sharply criticized by the Erasistrateans, who predicted dire outcomes, believing that it was not blood but pneuma that flowed in the veins. Galen, however, staunchly defended venesection in his three books on the subject and in his demonstrations and public disputations. Galen's work on anatomy remained largely unsurpassed and unchallenged up until the 16th century in Europe. In the middle of the 16th century, the anatomist Andreas Vesalius challenged the anatomical knowledge of Galen by conducting dissections on human cadavers. These investigations allowed Vesalius to refute aspects of Galen's theories regarding anatomy.

Anatomy

Galen's interest in human anatomy ran afoul of Roman law that prohibited the dissection of human cadavers since roughly 150 BC. Because of this restriction, Galen performed anatomical dissections on living (vivisection) and dead animals, mostly focusing on primates. Galen believed that the anatomical structures of these animals closely mirrored those of humans. Galen clarified the anatomy of the trachea and was the first to demonstrate that the larynx generates the voice. In one experiment, Galen used bellows to inflate the lungs of a dead animal. Galen's research on physiology was largely influenced by previous works of philosophers Plato and Aristotle, as well as from the physician Hippocrates. He was one of the first people to use experiments as a method of research for his medical findings. Doing so allowed him to explore various parts of the body and its functions.

Among Galen's major contributions to medicine was his work on the circulatory system. He was the first to recognize that there are distinct differences between venous (dark) and arterial (bright) blood. In addition to these discoveries, Galen postulated much more about the nature of the circulatory system. He believed that blood originated in the liver, which follows the teachings of Hippocrates. The liver converted nutrients gathered from ingested food into blood to be used in the circulatory system. The blood created in the liver would eventually flow unidirectionally into the right ventricle of the heart via the great vein. Galen also proposed a theory on how blood receives air from the lungs to be distributed throughout the body. He declared that the venous artery carried air from the lungs into the left ventricle of the heart to mix with created blood from the liver. This same venous artery allowed for an exchange of waste products from the blood back into the lungs to be exhaled. In order to receive air from the lungs in the left ventricle, the new blood needed to get there from the right ventricle. Thus, Galen asserted that there are small holes in the septum dividing the left and right sides of the heart; these holes allowed the blood to pass through easily to receive air and exchange the aforementioned waste products. Although his anatomical experiments on animal models led him to a more complete understanding of the circulatory system, nervous system, respiratory system, and other structures, his work contained scientific errors. Galen believed the circulatory system to consist of two separate one-way systems of distribution, rather than a single unified system of circulation. He believed venous blood to be generated in the liver, from where it was distributed and consumed by all organs of the body. He posited that arterial blood originated in the heart, from where it was distributed and consumed by all organs of the body. The blood was then regenerated in either the liver or the heart, completing the cycle. Galen also believed in the existence of a group of blood vessels he called the rete mirabile in the carotid sinus. Both of these theories of the circulation of blood were later (beginning with works of Ibn al-Nafis published c. 1242) shown to be incorrect.

Galen was also a pioneer in research about the human spine. His dissections and vivisections of animals led to key observations that helped him accurately describe the human spine, spinal cord, and vertebral column. Galen also played a major role in the discoveries of the central nervous system. He was also able to describe the nerves that emerge from the spine, which is integral to his research about the nervous system. Galen went on to be the first physician to study what happens when the spinal cord is transected on multiple different levels. He worked with pigs and studied their neuroanatomy by severing different nerves either totally or partially to see how it affected the body. He even dealt with diseases affecting the spinal cord and nerves. In his work De motu musculorum, Galen explained the difference between motor and sensory nerves, discussed the concept of muscle tone, and explained the difference between agonists and antagonists.

Galen's work on animals led to some inaccuracies, most notably his anatomy of the uterus which largely resembled a dog's. Though incorrect in his studies of human reproduction and reproductive anatomy, he came very close to identifying the ovaries as analogous to the male testes. Reproduction was a controversial topic in Galen's lifetime, as there was much debate over if the male was solely responsible for the seed, or if the woman was also responsible.

Through his vivisection practices, Galen also proved that the voice was controlled by the brain. One of the most famous experiments that he recreated in public was the squealing pig: Galen would cut open a pig, and while it was squealing he would tie off the recurrent laryngeal nerve, or vocal cords, showing they controlled the making of sound. He used the same method to tie off the ureters to prove his theories of kidney and bladder function. Galen believed the human body had three interconnected systems that allowed it to work. The first system that he theorized consisted of the brain and the nerves, responsible for thought and sensation. The second theorized system was the heart and the arteries, which Galen believed to be responsible for providing life-giving energy. The last theorized system was the liver and veins, which Galen theorized were responsible for nutrition and growth. Galen also theorized that blood was made in the liver and sent out around the body.

Localization of function
One of Galen's major works, On the Doctrines of Hippocrates and Plato, sought to demonstrate the unity of the two subjects and their views. Using their theories, combined with Aristotle's, Galen developed a tripartite soul consisting of similar aspects. He used the same terms as Plato, referring to the three parts as rational, spiritual, and appetitive. Each corresponded to a localized area of the body. The rational soul was in the brain, the spiritual soul was in the heart, and the appetitive soul was in the liver. Galen was the first scientist and philosopher to assign specific parts of the soul to locations in the body because of his extensive background in medicine. This idea is now referred to as localization of function. Galen's assignments were revolutionary for the time period, which set the precedent for future localization theories.

Galen believed each part of this tripartite soul controlled specific functions within the body and that the soul, as a whole, contributed to the health of the body, strengthening the "natural functioning capacity of the organ or organs in question". The rational soul controlled higher level cognitive functioning in an organism, for example, making choices or perceiving the world and sending those signals to the brain. He also listed "imagination, memory, recollection, knowledge, thought, consideration, voluntary motion, and sensation" as being found within the rational soul. The functions of "growing or being alive" resided in the spirited soul. The spirited soul also contained our passions, such as anger. These passions were considered to be even stronger than regular emotions, and, as a consequence, more dangerous. The third part of the soul, or the appetitive spirit, controlled the living forces in our body, most importantly blood. The appetitive spirit also regulated the pleasures of the body and was moved by feelings of enjoyment. This third part of the soul is the animalistic, or more natural, side of the soul; it deals with the natural urges of the body and survival instincts. Galen proposed that when the soul is moved by too much enjoyment, it reaches states of "incontinence" and "licentiousness", the inability to willfully cease enjoyment, which was a negative consequence of too much pleasure.

In order to unite his theories about the soul and how it operated within the body, he adapted the theory of the pneuma, which he used to explain how the soul operated within its assigned organs, and how those organs, in turn, interacted together. Galen then distinguished the vital pneuma, in the arterial system, from the psychic pneuma, in the brain and nervous system. Galen placed the vital pneuma in the heart and the psychic pneuma (spiritus animalis) within the brain. He conducted many anatomical studies on animals, most famously an ox, to study the transition from vital to psychic pneuma. Although highly criticized for comparing animal anatomy to human anatomy, Galen was convinced that his knowledge was abundant enough in both anatomies to base one on the other. In his treatise On the usefulness of the parts of the body, Galen argued that the perfect suitability of each part of the body to its function indicated the role of an intelligent creator. His creationism was anticipated by the anatomical examples of Socrates and Empedocles.

Philosophy

Although the main focus of his work was on medicine, anatomy, and physiology, Galen also wrote about logic and philosophy. His writings were influenced by earlier Greek and Roman thinkers, including Plato, Aristotle, the Stoics, and the Pyrrhonists. Galen was concerned to combine philosophical thought with medical practice, as in his brief work That the Best Physician is also a Philosopher he took aspects from each group and combined them with his original thought. He regarded medicine as an interdisciplinary field that was best practiced by utilizing theory, observation, and experimentation in conjunction.

Galen combined his observations of his dissections with Plato's theory about the soul. Plato believed that the body and the soul were separate entities, rivaling the Stoics. Plato proclaimed that the soul is immortal, so it must exist before one is born, beyond the human body. This influenced Galen's thinking that the soul had to be acquired because the soul does not always reside within the human body. Plato's influence in Galen's model showed itself most prominently in what Galen dubbed arterial blood, which is a mixture of nutritious blood from the liver and the vital spirit (the soul) which was attained from the lungs. The vital spirit within this medium was necessary for the body to function and eventually completely absorbed. This process was then repeated indefinitely, according to Galen, so that the body could be replenished with the soul, or the vital spirit.

Several schools of thought existed within the medical field during Galen's lifetime, the main two being the Empiricists and Rationalists (also called Dogmatists or Philosophers), with the Methodists being a smaller group. The Empiricists emphasized the importance of physical practice and experimentation or "active learning" in the medical discipline. In direct opposition to the Empiricists were the Rationalists, who valued the study of established teachings in order to create new theories in the name of medical advancements. The Methodists formed somewhat of a middle ground, as they were not as experimental as the Empiricists, nor as theoretical as the Rationalists. The Methodists mainly utilized pure observation, showing greater interest in studying the natural course of ailments than making efforts to find remedies. Galen's education had exposed him to the five major schools of thought (Platonists, Peripatetics, Stoics, Epicureans, Pyrrhonists), with teachers from the Rationalist sect and from the Empiricist sect.

Opposition to the Stoics
Galen was well known for his advancements in medicine and the circulatory system, but he was also concerned with philosophy. He developed his own tripartite soul model following the examples of Plato; some scholars refer to him as a Platonist. Galen developed a theory of personality based on his understanding of fluid circulation in humans, and he believed that there was a physiological basis for mental disorders. Galen connected many of his theories to the pneuma and he opposed the Stoics' definition of and use of the pneuma.

The Stoics, according to Galen, failed to give a credible answer for the localization of functions of the psyche, or the mind. Through his use of medicine, he was convinced that he came up with a better answer, the brain. The Stoics only recognized the soul as having one part, which was the rational soul and they claimed it would be found in the heart. Galen, following Plato's idea, came up with two more parts to the soul.

Galen also rejected Stoic propositional logic and instead embraced a hypothetical syllogistic which was strongly influenced by the Peripatetics and based on elements of Aristotelian logic.

Mind–body problem
Galen believed there is no sharp distinction between the mental and the physical. This was a controversial argument at the time, and Galen agreed with some Greek philosophical schools in believing that the mind and body were not separate faculties. He believed that this could be scientifically shown. This was where his opposition to the Stoics became most prevalent. Galen proposed organs within the body to be responsible for specific functions. According to Galen, the Stoics' lack of scientific justification discredited their claims of the separateness of mind and body, which is why he spoke so strongly against them. There is an intense scholarly debate about soul-body relations in Galen's psychological writings. In his brief treatise Quod animi mores, Galen says both that the soul "follows" the mixtures of the body, and that the soul is a bodily mixture. Scholars have offered ways of reconciling these claims, arguing for a materialist reading of Galen's philosophy of mind. According to this materialist reading, Galen identifies the soul with the mixtures of the body.

Psychotherapy
Another one of Galen's major works, On the Diagnosis and Cure of the Soul's Passion, discussed how to approach and treat psychological problems. This was Galen's early attempt at what would later be called psychotherapy. His book contained directions on how to provide counsel to those with psychological issues to prompt them to reveal their deepest passions and secrets, and eventually cure them of their mental deficiency. The leading individual, or therapist, had to be a male, preferably of an older, wiser, age, as well as free from the control of the passions. These passions, according to Galen, caused the psychological problems that people experienced.

Published works

Galen may have produced more work than any author in antiquity, rivaling the quantity of work issued from Augustine of Hippo. So profuse was Galen's output that the surviving texts represent nearly half of all the extant literature from ancient Greece. It has been reported that Galen employed twenty scribes to write down his words. Galen may have written as many as 500 treatises, amounting to some 10 million words. Although his surviving works amount to some 3 million words, this is thought to represent less than a third of his complete writings. In 191, or more likely in 192, a fire in the Temple of Peace destroyed many of his works, in particular treatises on philosophy.

Because Galen's works were not translated into Latin in the ancient period, and because of the collapse of the Roman Empire in the West, the study of Galen, along with the Greek medical tradition as a whole, went into decline in Western Europe during the Early Middle Ages, when very few Latin scholars could read Greek. However, in general, Galen and the ancient Greek medical tradition continued to be studied and followed in the Eastern Roman Empire, commonly known as the Byzantine Empire. All of the extant Greek manuscripts of Galen were copied by Byzantine scholars. In the Abbasid period (after 750) Arab Muslims began to be interested in Greek scientific and medical texts for the first time, and had some of Galen's texts translated into Arabic, often by Syrian Christian scholars (see below). As a result, some texts of Galen exist only in Arabic translation, while others exist only in medieval Latin translations of the Arabic. In some cases scholars have even attempted to translate from the Latin or Arabic back into Greek where the original is lost. For some of the ancient sources, such as Herophilus, Galen's account of their work is all that survives.

Even in his own time, forgeries and unscrupulous editions of his work were a problem, prompting him to write On His Own Books. Forgeries in Latin, Arabic or Greek continued until the Renaissance. Some of Galen's treatises have appeared under many different titles over the years. Sources are often in obscure and difficult-to-access journals or repositories. Although written in Greek, by convention the works are referred to by Latin titles, and often by merely abbreviations of those. No single authoritative collection of his work exists, and controversy remains as to the authenticity of a number of works attributed to Galen. As a consequence, research on Galen's work is fraught with hazard.

Various attempts have been made to classify Galen's vast output. For instance Coxe (1846) lists a Prolegomena, or introductory books, followed by 7 classes of treatise embracing Physiology (28 vols.), Hygiene (12), Aetiology (19), Semeiotics (14), Pharmacy (10), Blood letting (4), and Therapeutics (17), in addition to 4 of aphorisms, and spurious works. The most complete compendium of Galen's writings, surpassing even modern projects like the Corpus Medicorum Graecorum/Latinorum, is the one compiled and translated by Karl Gottlob Kühn of Leipzig between 1821 and 1833. This collection consists of 122 of Galen's treatises, translated from the original Greek into Latin (the text is presented in both languages). Over 20,000 pages in length, it is divided into 22 volumes, with 676 index pages. Many of Galen's works are included in the Thesaurus Linguae Graecae, a digital library of Greek literature started in 1972. Another useful modern source is the French Bibliothèque interuniversitaire de médecine (BIUM).

Late antiquity

In his time, Galen's reputation as both physician and philosopher was legendary, the emperor Marcus Aurelius describing him as "Primum sane medicorum esse, philosophorum autem solum" (first among doctors and unique among philosophers Praen 14: 660). Other contemporary authors in the Greek world confirm this including Theodotus the Shoemaker, Athenaeus and Alexander of Aphrodisias. The 7th-century poet George of Pisida went so far as to refer to Christ as a second and neglected Galen. Galen continued to exert an important influence over the theory and practice of medicine until the mid-17th century in the Byzantine and Arabic worlds and Europe. A few centuries after Galen, Palladius Iatrosophista stated in his commentary on Hippocrates that Hippocrates sowed and Galen reaped.

Galen summarized and synthesized the work of his predecessors, and it is in Galen's words (Galenism) that Greek medicine was handed down to subsequent generations, such that Galenism became the means by which Greek medicine was known to the world. Often, this was in the form of restating and reinterpreting, such as in Magnus of Nisibis' 4th-century work on urine, which was in turn translated into Arabic. Yet the full importance of his contributions was not appreciated until long after his death. Galen's rhetoric and prolificity were so powerful as to convey the impression that there was little left to learn. The term Galenism has subsequently taken on both a positive and pejorative meaning as one that transformed medicine in late antiquity yet so dominated subsequent thinking as to stifle further progress.

After the collapse of the Western Empire the study of Galen and other Greek works almost disappeared in the Latin West. In contrast, in the predominantly Greek-speaking eastern half of the Roman empire (Byzantium), many commentators of the subsequent centuries, such as Oribasius, physician to the emperor Julian who compiled a Synopsis in the 4th century, preserved and disseminated Galen's works, making them more accessible. Nutton refers to these authors as the "medical refrigerators of antiquity". In late antiquity, medical writing veered increasingly in the direction of the theoretical at the expense of the practical, with many authors merely debating Galenism. Magnus of Nisibis was a pure theorist, as were John of Alexandria and Agnellus of Ravenna with their lectures on Galen's De Sectis. So strong was Galenism that other authors such as Hippocrates began to be seen through Galen's eyes, while his opponents became marginalised and other medical sects such as Asclepiadism slowly disappeared.

Greek medicine was part of Greek culture, and Syrian Christians came in contact with it while the Eastern Roman Empire (Byzantium) ruled Syria and western Mesopotamia, regions that were conquered in the 7th century by the Arabs. After 750, these Syrian Christians made the first translations of Galen into Syriac and Arabic. From then on, Galen and the Greek medical tradition in general became assimilated into the medieval and early modern Islamic Middle East. Job of Edessa is said to have translated 36 of Galen's works into Syriac, some of which were later translated into Arabic by Hunain ibn Ishaq.

Medieval Islam
Galen's approach to medicine became and remains influential in the Islamic world. The first major translator of Galen into Arabic was the Arab Christian Hunayn ibn Ishaq. He translated (c. 830–870) 129 works of "Jalinos" into Arabic. Arabic sources, such as Muhammad ibn Zakarīya al-Rāzi (AD 865–925), continue to be the source of discovery of new or relatively inaccessible Galenic writings. One of Hunayn's Arabic translations, Kitab ila Aglooqan fi Shifa al Amrad, which is extant in the Library of Ibn Sina Academy of Medieval Medicine & Sciences, is regarded as a masterpiece of Galen's literary works. A part of the Alexandrian compendium of Galen's work, this 10th-century manuscript comprises two parts that include details regarding various types of fevers (Humyat) and different inflammatory conditions of the body. More important is that it includes details of more than 150 single and compound formulations of both herbal and animal origin. The book provides an insight into understanding the traditions and methods of treatment in the Greek and Roman eras. In addition, this book provides a direct source for the study of more than 150 single and compound drugs used during the Greco-Roman period.

As the title of Doubts on Galen by al-Rāzi implies, as well as the writings of physicians such as Ibn Zuhr and Ibn al-Nafis, the works of Galen were not accepted unquestioningly, but as a challengeable basis for further inquiry. A strong emphasis on experimentation and empiricism led to new results and new observations, which were contrasted and combined with those of Galen by writers such as al-Rāzi, Ali ibn Abbas al-Majusi, Abu al-Qasim al-Zahrawi, Ibn Sina (Avicenna), Ibn Zuhr, and Ibn al-Nafis. For example, Ibn al-Nafis' discovery of the pulmonary circulation contradicted the Galenic theory on the heart.

The influence of Galen's writings, including humorism, remains strong in modern Unani medicine, now closely identified with Islamic culture, and widely practiced from India (where it is officially recognized) to Morocco. Maimonides was influenced by Galen, whom he cited most often in his medical works, and whom he considered to be the greatest physician of all time. In India many Hindu physicians studied Persian and Urdu languages and learnt Galenic medicine. This trend of studies among Hindu physicians began in the 17th century and lasted until the early 20th century (Speziale 2018).

Middle Ages

From the 11th century onwards, Latin translations of Islamic medical texts began to appear in the West, alongside the Salerno school of thought, and were soon incorporated into the curriculum at the universities of Naples and Montpellier. From that time, Galenism took on a new, unquestioned authority, Galen even being referred to as the "Medical Pope of the Middle Ages". Constantine the African was amongst those who translated both Hippocrates and Galen from Arabic. In addition to the more numerous translations of Arabic texts in this period, there were a few translations of Galenic works directly from the Greek, such as Burgundio of Pisa's translation of De complexionibus. Galen's works on anatomy and medicine became the mainstay of the medieval physician's university curriculum, alongside Ibn Sina's The Canon of Medicine, which elaborated on Galen's works. Unlike pagan Rome, Christian Europe did not exercise a universal prohibition of the dissection and autopsy of the human body and such examinations were carried out regularly from at least the 13th century. However, Galen's influence was so great that when dissections discovered anomalies compared with Galen's anatomy, the physicians often tried to fit these into the Galenic system. An example of this is Mondino de Liuzzi, who describes rudimentary blood circulation in his writings but still asserts that the left ventricle should contain air. Some cited these changes as proof that human anatomy had changed since the time of Galen.

The most important translator of Galen's works into Latin was Niccolò di Deoprepio da Reggio, who spent several years working on Galen. Niccolò worked at the Angevin Court during the reign of king Robert of Naples. Among Niccolò's translations is a piece from a medical treatise by Galen, of which the original text is lost.

Renaissance
The first edition of Galen's complete works in Latin translation was edited by Diomede Bonardo of Brescia and printed at Venice by Filippo Pinzi in 1490.

The Renaissance, and the fall of the Byzantine Empire (1453), were accompanied by an influx of Greek scholars and manuscripts to the West, allowing direct comparison between the Arabic commentaries and the original Greek texts of Galen. This New Learning and the Humanist movement, particularly the work of Linacre, promoted literae humaniores including Galen in the Latin scientific canon, De Naturalibus Facultatibus appearing in London in 1523. Debates on medical science now had two traditions, the more conservative Arabian and the liberal Greek. The more extreme liberal movements began to challenge the role of authority in medicine, as exemplified by Paracelsus' symbolically burning the works of Avicenna and Galen at his medical school in Basle. Nevertheless, Galen's pre-eminence amongst the great thinkers of the millennium is exemplified by a 16th-century mural in the refectory of the Great Lavra of Mt Athos. It depicts pagan sages at the foot of the Tree of Jesse, with Galen between the Sibyl and Aristotle.

Galenism's final defeat came from a combination of the negativism of Paracelsus and the constructivism of the Italian Renaissance anatomists, such as Vesalius in the 16th century. In the 1530s, the Flemish anatomist and physician Andreas Vesalius took on a project to translate many of Galen's Greek texts into Latin. Vesalius' most famous work, De humani corporis fabrica, was greatly influenced by Galenic writing and form. Seeking to examine critically Galen's methods and outlook, Vesalius turned to human cadaver dissection as a means of verification. Galen's writings were shown by Vesalius to describe details present in monkeys but not in humans, and he demonstrated Galen's limitations through books and hands-on demonstrations despite fierce opposition from orthodox pro-Galenists such as Jacobus Sylvius. Since Galen states that he is using observations of monkeys (human dissection was prohibited) to give an account of what the body looks like, Vesalius could portray himself as using Galen's approach of description of direct observation to create a record of the exact details of the human body, since he worked in a time when human dissection was allowed. Galen argued that monkey anatomy was close enough to humans for physicians to learn anatomy with monkey dissections and then make observations of similar structures in the wounds of their patients, rather than trying to learn anatomy only from wounds in human patients, as would be done by students trained in the Empiricist model. The examinations of Vesalius also disproved medical theories of Aristotle and Mondino de Liuzzi. One of the best known examples of Vesalius' overturning of Galenism was his demonstration that the interventricular septum of the heart was not permeable, as Galen had taught (Nat Fac III xv). However, this had been revealed two years before by Michael Servetus in his fateful "Christianismi restitutio" (1553) with only three copies of the book surviving, but these remained hidden for decades; the rest were burned shortly after its publication because of persecution of Servetus by religious authorities.

Michael Servetus, using the name "Michel de Villeneuve" during his stay in France, was Vesalius' fellow student and the best Galenist at the University of Paris, according to Johann Winter von Andernach, who taught both. In the Galenism of the Renaissance, editions of the Opera Omnia by Galen were very important, beginning from the Aldine Press' editio princeps in Venice in 1525. It was followed in Venice in 1541–1542 by the Giunta. There were fourteen editions of the book from that date until 1625. Just one edition was produced from Lyon between 1548 and 1551. The Lyon edition has commentaries on breathing and blood streaming that correct the work of earlier renowned authors such as Vesalius, Caius, or Janus Cornarius. "Michel De Villeneuve" had contracts with Jean Frellon for that work, and the Servetus scholar-researcher Francisco Javier González Echeverría  presented research that became an accepted communication in the International Society for the History of Medicine, which concluded that Michael De Villeneuve (Michael Servetus) is the author of the commentaries of this edition of Frellon, in Lyon.

Another convincing case where understanding of the body was extended beyond where Galen had left it came from these demonstrations of the nature of human circulation and the subsequent work of Andrea Cesalpino, Fabricio of Acquapendente, and William Harvey. Some Galenic teaching, such as his emphasis on bloodletting as a remedy for many ailments, however, remained influential until well into the 19th century.

Contemporary scholarship
Galenic scholarship remains an intense and vibrant field, following renewed interest in his work, dating from the German encyclopedia Realencyclopädie der Classischen Altertumswissenschaft.

Copies of his works translated by Robert M. Green are held at the National Library of Medicine in Bethesda, Maryland.

In 2018, the University of Basel discovered that a mysterious Greek papyrus with mirror writing on both sides, which is in the collection of Basilius Amerbach, a professor of jurisprudence at the university in the 16th century, is an unknown medical document of Galen or an unknown commentary on his work. The medical text describes the phenomenon of "hysterical apnea".

title: Galen