Myths in the history of Physics As an example of such a historical myth that we all learned, there is the story that in his confrontation with Cardinal Bellarmine in 1632, Galileo had all the evidence on his side, won the intellectual argument by the weight of that evidence, and was defeated only by the ignorant prejudices the trial judges.   However, historical studies have also advanced as more detailed information was obtained and reflected upon.  
The actual situation was much more nuanced.   The version of Copernican theory defended by Galileo assumed 1. a very small solar system, the size of which should clearly be seen by measurements of planetary parallax and 2. circular orbits, not elliptical (although Galileo knew of the work of Kepler, but declined to incorporate it).  Both Copernicus and Galileo had attempted to measure parallax in the solar system, and failed to get a result > 0.  (It was only measured by Bessell in 1838.)   Furthermore, because it used circles for orbits, the Copernican model was actually less accurate than the old Ptolemaic epicycle system of approximations.  In addition, Galileo predicted only a single tide/day, not the actual two.  
On the other hand his unambiguous observation of Venus in all four phases in 1610 definitely ruled out the Aristotelian model of heavens, since in this model the sphere of the sun was always beyond the sphere of Venus, although the Tychonic, Capellan and Extended Capellan models were still possible, each either with or without a daily rotating Earth. These latter models had the virtue of explaining the phases of Venus without the vice of the 'refutation' of full Copernican heliocentrism’s prediction of stellar parallax.  From Wikipedia's article on Galileo, confirmed by Weinberg.
Conclusion: on the basis of the evidence available to them, the Church had a pretty strong case on the evidence against Copernican heliocentrism, arguably stronger than Galileo.  Furthermore, on the basis of contemporary documents and doctrines going back to Augustine and the 4th century, if the church had seen conclusive proof in favor of the Copernican system, it was already formally committed to changing its interpretation.   The Church, being engaged in a power struggle during the reformation, would likely have followed conclusive evidence had it been presented.
Refs: see the historically accurate and nuanced video at http://online.itp.ucsb.edu/online/colloq/tutino1/rm/qt.html, for slides see http://online.itp.ucsb.edu/online/colloq/tutino1/, book at Google.  This is not an obscure, idiosyncratic view of the Galileo affair, but rather the generally accepted view of knowledgeable scholars. 
What other famous oversimplified or false myths of this sort do you know and can document and or reference corrections to?
 A: I'll add the popular myth that Special relativity was made "in response" to Michelson–Morley experiment. Actually, Einstein never mentioned the experiment in his work, as well as he didn't mention aether.  
The point is that new theory must not be constructed "in response" to some new experiment. New theory should embrace all existent experimental evidence. 
A: The biggest myth in the history of physics is that the great physicists did all their great work in their 20s, and their later work is nonsense which can be ignored. The reason this is said is because the truly revolutionary work of the great physicists, often done in their 30s and 40s, took a much longer time to be appreciated. The early work was always easier to accept, because the arguments were less ideosyncratic, and more in tune with the spirit of the times.
Einstein's 1905 work was certainly revolutionary, but pales in comparison to the work of 1915-1917, GR and cosmology. He was then in his mid 30s. General relativity was so advanced, that it took about 50 years to be fully accepted. Einstein's work in the period 1917-1926 on quantum mechanics was about as revolutionary as the 1905 work. The work of the older Einstein on EPR entanglement, wormholes, the focusing properties gravity, gravitational lensing, and second order phase transitions also took decades to be apprediated and completed.
Pauli's earliest celebrated work is a review of relativity, but his original discoveries include the spin of the electron and the exclusion principle, discovered in his 20s. These discoveries are important, but again, they pale in comparison with the full analysis of all relativistic wave equations, a program he pursued with Fierz in the 1930s, which culminated in the spin-statistics relation. His contributions to quantum field theory include the theory of the quantum spin-2 field, which unlike the exclusion principle, which is a foundational rock, still yields surprises today.
The myth might be most true for the young Heisenberg. He did develop quantum mechanics at the age of 22, which was the most revolutionary of his accomplishments. But in later years, he developed the theory of Isospin, the theory of turbulence, and launched S-matrix theory, and developed the notion of spontaneous symmetry breaking. S-matrix theory is still actively pursued as string theory. His latest work was on self-interacting fermi fields and their condensates, which was universally heckled as an overreaching theory of everything (which it was), but it was a siginificant source of inspiration for the Nambu-Jona-Lasinio model of quark condensates.
Dirac's contributions in his 20s were so enormous, that it is probably correct to say that they could not be overshadowed by his later career. This includes the Dirac equation, antimatter, and monopoles, the transformation theory of quantum mechanics, and the theory of distributions. His later contributions were important too, the quantization of constrained systems.
Feynman's contributions of his late 20s, early thirties, also are hard to overstate. The path integral is revolutionary. Still, his later work on liquid helium, parton model, gauge vacuum, and quantum computing, are very active today. The diagrams were more in the spirit of the time, since they had an antecedent in Stueckelberg's prescient work in the 1930s.
Schwinger's early calculation of the magnetic moment of the electron introduced 1 loop methods in QED which worked to renormalize it without an explicit well-defined regulator. His work on Schwinger terms, and anomalies also dates to this period, as well as the foundational formalism of modern quantum field theory. This is his most celebrated work. But Schwinger's work of his 30s and 40s is definitely more important in my view, although it is less recognized. Schwinger was the first to propose that there is an electroweak interaction, unifying the photon with two W bosons. This was in the late 1950s, when he was in his late 30s, and nobody took the idea seriously at the time, but this is the birth of the standard model. His student Glashow proposed the Z boson, and the rest is well known.
Schwinger discovered the 1+1 Schwinger model, the prototype for quark confinement, in the 1960s. He also proposed a generational structure for leptons, as part of the SU(2) unified model which is so close to correct. These are all later discoveries.
t'Hooft's work on renormalization of gauge theories completed a program of Veltman, who was not so young then. Veltman wrote the first algebraic manipulation computer code, Schoonship, to establish renormalizability, and this is an unsung but important contribution to mathematical physics. But t'Hooft's discovery of the holographic principle, however, in my mind overshadows all the mathematical contributions of his youth. The holographic principle was so vague and difficult to make precise, that it was mocked by many people. I talked to a physicist in 1996 (!) who had seen a talk about holography and told me that t'Hooft was all washed up, and not to expect great things from him anymore.
Schrodinger was in his late 30s when he discovered the equation that bears his name. He wasn't as distinguished as a young man.
Anyway, the point here is that one should read all the papers of the great physicists, even the ones that are laughed at, because the idea that these people went crazy later in life is mostly a myth.
A: Maxwell's equations
This isn't so much a myth, as a misnomer! The four equations commonly called Maxwell's equations should in fact be attributed to Gauss, Faraday, and Ampere. Maxwell added the important displacement current term to Ampere's equation, which then allowed him to derive and explain electromagnetic waves - his true achievement. The equations however, were a joint work over almost a century of physics.
A: Mark Eichenlaub asked in a comment 2 days ago- "Also, did Galileo actually drops rocks off that damn tower or not?!!"    As you may now it's iffy, and furthermore the dropping different weights experiment had been done and published several times before Galileo.
Additionally, from Wikipedia, Galileo reasoned as follows from one of the first thought experiments:
Imagine two objects, one light and one heavier than the other one, are connected to each other by a string. Drop this system of objects from the top of a tower. If we assume heavier objects do indeed fall faster than lighter ones (and conversely, lighter objects fall slower), the string will soon pull taut as the lighter object retards the fall of the heavier object. But the system considered as a whole is heavier than the heavy object alone, and therefore should fall faster. This contradiction leads one to conclude the assumption is false. 
A: MYTH:
The (L)arge (H)adron (C)ollider will destroy the earth. High energy collisions will create a black hole and it will swallow the earth. 
I read this in a newspaper. It was also mentioned there that this is myth and physicist are pretty/damn sure that this won't happen. 
NOTE: I don't know enough about LHC and particles to debunk this one. But I am sure that no sane physicist would want to commit suicide. 
A: All of the physical laws are $C$, $P$ and $T$ symmetric.
This is actually not that far from truth, which is why it took so long to notice it doesn't hold. Only weak interactions violate these symmetries. In 1950s it was indeed realized that while then known electromagnetic and strong processes were tested to be $P$-symmetric, weak processes were omitted. And indeed as soon as experiments were conducted (on a certain beta decay), violation has been found.
$C$-symmetry is violated by the fact that we only observe left-handed neutrinos and right-handed antineutrinos. But $C$-symmetry would imply also right-handed neutrinos and left-handed antineutrinos.
As for $T$-symmetry, this is the same as $CP$-symmetry, by $TCP$ theorem (and this is no blind belief anymore because this theorem is an immediate consequence of any reasonable quantum field theory). This symmetry was proposed after the discovery of $P$-symmetry and later found to be violated because $K_L$, a long-lived kaon eigenstate, can decay into two pions (which would be forbidden if $CP$-symmetry held). Today, these violations are understood in terms of CKM matrix.
Also our intuition about violations is by now completely reversed: besides $TCP$-symmetry (which has been verified to a very large degree) people became actually suspicious when some system obeys some additional symmetry. This is best illustrated on strong $CP$ problem because strong interactions obey this symmetry and there is no a priori reason why they should.
A: That nuclear bombs are fission powered, but thermonuclear bombs are fusion powered. Although thermonuclear bombs do use fusion as a secondary reaction, this is used to produce vast amounts of energy through fission, which produces around 50% of the energy output.
A: That Heisenberg did not know about Matrices ... If he read Weyl  then he would have known.
