Galileo Galilei - and his mechanics and motion
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'Dialogues concerning Two New Sciences' (1638),Translated by H Crew and A De Salvio
Galileo stated that he himself had not sought the publishing of
this his major work on mechanics and motion. It is part Italian and part Latin, and it had a 1914 English translation and also a much more recent 'modern science' translation. It largely deals with
mechanical strength under gravity, motion generally and especially
motion under gravity including motion on inclined planes,
projectile motion and pendulum motion. Its dialogue style (between
Salviati, Sagredo and Simplicio) made the presentation of its
science somewhat more difficult for readers, but partly suited the
nasty religious and legal requirement that Galileo was under to publish his ideas as 'only ideas'.
Some key extracts follow ;
So on motion, Page 154 ;
"Uniform Motion.
In dealing with steady or uniform motion, we need a single
definition which I give as follows.
DEFINITION. By steady or uniform motion, I mean one in which the
distances traversed by the moving particle during any equal
intervals of time, are themselves equal."
And Page 169 ;
"Sagrado.
... it would seem that up to the present we have established the
definition of uniformly accelerated motion, which is expressed as
follows ;
A motion is said to be equally or uniformly accelerated when,
starting from rest, its momentum receives equal increments in equal
times."
And Page 215 ;
"... Furthermore we may remark that any velocity once imparted to a
moving body will be rigidly maintained as long as the external
causes of acceleration or retardation are removed ..."
And expressing a Newton-like blackbox view on different theories of gravity, Pages 166-167 ;
"Salviati.
The present does not seem to be the proper time to investigate the
cause of the acceleration of natural motion concerning which
various opinions have been expressed by various philosophers, some
explaining it by attraction to the centre, others to repulsion
between the very small parts of the body, while still others
attribute it to a certain stress in the surrounding medium which
closes in behind the body and drives it from one of its positions
to another. Now all these fantasies, and others too, ought to be
examined ; but it is not really worth while. At present it is the
purpose of our author merely to demonstrate and to investigate some
of the properties of accelerated motion (whatever the cause of this
acceleration may be) - meaning thereby a motion, such that the
speed goes on increasing after departure from rest, in simple
proportionality to the time ..."
Of course Galileo basically took Earth's gravity as constant since its strength varies very little over moderate distances from Earth's surface,
despite Gilbert having repeatedly noted that the strength of forces including magnetic and electric forces decreased with distance from their source.
And supporting the existence of a vacuum, Page 81 ;
"... in the previous experiment we weighed the air in vacuum and
not in air or other medium."
Galileo claimed to have a Universal Law of Gravitation covering
both terrestrial gravity and the motion of planets which he was
afraid to discuss. But this looks more an aspiration than
a reality, as he seems not to have considered gravitational force
as decreasing with distance from its source, which was central to
Newton's later Universal Law of Gravitation and had been considered
earlier by others and was demonstrated earlier by Gilbert for
magnetic and electrical forces at least. But Earth's gravitational
force does not decrease much if the highest you test from is the
top of a Pisa tower, and worse was his testing gravity by the
acceleration it produced on bodies using a gravity clock to measure
it. He used a water version of the sand hour-glass or egg-timer -
but if gravity was weaker and actually produced less acceleration,
then his gravity clock would run proportionately slower so that the
acceleration, and gravity strength, would appear constant. Clearly
a clock must be independent of the event it is measuring, so
Galileo should maybe have used iron filings and a magnet
horizontally for a magnetic clock - he is known to have certainly
have been acquainted with magnetism although the copy of Gilbert's 'De Magnete ...' that Galileo studied
may have excluded Book 6, where Gilbert included a basically correct theory of Earth's tides (detailed later in his De Mundo), as Galileo then
put much effort into producing his own quite incorrect mechanical theory of tides. And
many kinds of clock are of course possible as using astronomical,
physical, chemical, biological or possibly even mental processes of
determinate duration, and time measurement was perhaps also an issue even later
for Einstein ?
Yet on Pages 261-262 ;
"Sagrado.
(if each planet had started from rest at particular heights under
gravity and) fall with naturally accelerated motion along a
straight line, and were later to change the speed thus acquired
into uniform motion, the size of its orbit and its period of
revolution would be those actually observed.
Salviati.
I think I remember him having told me that he once made the
computation and found a satisfactory correspondence with
observation. But he did not wish to speak of it ..."
It seems that at least in two 1615 private letters, Galileo supported the basics of Gilbert's magnetical or attraction physics
but feared that if he publicly supported such the Catholic church might burn him to death as it had done to Bruno in 1600. He guardedly admitted that he believed that 'the Sun can be described as the soul of the world and transmits a spirit all around that gives life and movement to all things'.
(see Alberto Martinez, http://notevenpast.org/giordano-bruno-and-the-spirit-that-moves-the-earth/)
But later in his polemical 'Il saggiatore' (The Assayer) 1623, Galileo was seemingly supporting greek Atomist mechanical push physics
against Gilbert attraction physics in claiming that science should
concern itself only with the size, shape and relative motion of
objects - a clearly unreasonable narrow view but supported by some Jesuits and
Rene Descartes and many others. Galileo praised
Gilbert while opposing his attraction physics with no actual
disproofs or even discussion being provided, and seemed to
use bits of trickery at times especially to try to avoid the
scary anti-heresy and anti-science Catholic Inquisition. Some may have felt that attacking a
Protestant scientist might help placate the then very scary Catholic
church. But early science was competitive as with Galileo refusing to help Kepler obtain a telescope (see Philip Ball http://aeon.co/essays/science-is-becoming-a-cult-of-hi-tech-instruments) and also unreasonably rejected Kepler's proof that
planet orbits are elliptical and are not circles. He may possibly also have pressured Kepler to drop his early support of William Gilbert's action-at-distance signal-response physics. And Galileo in his 1623 'The Assayer' also publicly condemned the German astronomer Simon Marius wrongly as being a plagiarist, but also as being a Protestant and not a good Catholic !
And he did also note that 'He who slings the most mud wins !'.
While the Catholic church strongly opposed Galileo's post-1609 moving-Earth astronomy, they did back Galileo's push-physics against William Gilbert's action-at-distance physics. But that may have been chiefly rather because of Gilbert's published 1600 support of a moving-Earth astronomy.
Galileo's 'invention' of the telescope (really more its improvement and use in astronomy) maybe led him to seeing
astronomy as more important than physics, and to wanting to advance that quickly
despite astronomical evidence at the time being to many less convincing than experiment evidence.
But beginning his telescope studies Galileo basically in 1610 abandoned Experimental Physics for Observational Astronomy.
He produced an awful wrong mechanical push theory of Earth tides as later did
Descartes, and Kepler produced a mechanical-field push theory of Earth
tides - but all were easily disproved later by Newton who correctly developed Gilbert's
better attraction theory of Earth tides (useable field or continuum mechanical
push explanations of tides may well be possible but seem hard to find).
Kepler, but not Galileo, correctly had gravity decrease as the square of
the distance from its source and a better mathematics of planet motion
within his own pseudo-Gilbert physics. But Galileo's motion under gravity
experiments did basically show how planet ellipse type motion in nature could
derive from linear motion. He was just not himself very strong on such theory.
And 2024 still sees some of Galileo's writings not yet translated from their Italian to English,
though he did publish some of his work in Latin like his 1610 Sidereus Nuncius.
Science and churches.
Early science in Europe faced sometimes fierce opposition from churches that often
dominated governments, with Bruno being burnt at the stake in catholic Rome
in 1600 (the year that Gilbert after much hesitation finally
published his work in a then only slightly less intolerant protestant England under
Queen Elizabeth who however died just months before Gilbert's death
in 1603). But churches generally preferred to control dissent and science more often by reasoning and by nasty threats and less often by extreme nasty action. The catholic church executing Bruno in 1600 acted as a strong threat to all dissidents and emerging scientists,
and its Jesuit Order which was founded to counter non-Catholic ideas soon began pushing an acceptable greek-Atomist physics that was basically taken up as a self-perpetuating mainstream physics that Newton considered 'prejudice'.
The catholic church also ensured that Galileo faced legal restriction and also pressured Descartes strongly,
maybe encouraging them both to attack protestant Gilbert's physics. In Galileo's 1633 Catholic Inquisition trial the one book condemned besides his 1632 Italian 'Dialogue Concerning the Two Chief World Systems' was Gilbert's 1600 Latin 'De Magnete ...',
though the Catholic Church had already banned that and some other books including Copernicus and some other Galileo.
When Copernicus published his astronomy it was a fairly good theory backed by only a little evidence and, though Galileo and others did then add some further supporting evidence, it was only later that Newton was to tie together such evidence with a stronger theory which really proved it.
The catholic Jesuit 'scholars' who had strongly opposed William Gilbert were also involved in Galileo's catholic inquisition trial which was perhaps really directed more at the long-dead Copernicus.
It has been noted that "Soon after 1600, when William Gilbert published his famous book on magnetism, a copy was given to Galileo by an Italian professor of natural philosophy at Padua, probably Cesare Cremonini … Galileo remarked that the professor seemed afraid that Gilbert's work might infect the other books on his shelves (or that Galileo believed he wanted to free his library of its contagion)."
Galileo was probably joking in a somewhat insulting manner, but the more theory inclined Cremonini may well have thought 'De Magnete ...' of more interest to the experimentalist Galileo and may have given him friendly advise that the catholic inquisition might investigate anyone caught owning it. Cremonini himself was an atheist Aristotlean and had survived several investigations by the catholic inquisition and he did have a healthy fear of them and considered limited accommodation necessary. Galileo generally thought likewise.
see 'Galileo at Work, His Scientific Biography' Stillman Drake 2003 p.62-63 - or - http://www-spof.gsfc.nasa.gov/earthmag/demagadd.htm
Around 1602, on studying 'De Magnete...', Galileo did some magnetic experiments with Sarpi and Sagredo but produced nothing new on magnetism beyond what Gilbert had, as later Newton also did with basicly similar result.
Hence basically Galileo did Gilbert's magnetic experiments but did not commit to interpreting the results as Gilbert had, while later Newton did Gilbert's magnetic experiments and accepted the Gilbertian interpretation of the results as Gilbert had but also allowed of some unspecified Galileo-Descartes push-physics explanation being maybe possible. Experiments can be interpreted differently, and Galileo was probably less well acquainted with Gilbert's interpretation than Newton. It seems that Galileo's copy of 'De Magnete ...' contained just one note by Galileo but many underlinings relating to Gilbert's experiments, indicating that he closely studied Gilbert's experiments but not Gilbert's theory as indeed many at the time probably did.
He certainly was not the 'honest reader' to which Gilbert's preface addressed 'De Magnete...', which
was written chiefly as new science for the more intelligent reader but to also entertain and hold all readers and so included a deal of entertaining chat not intended to be taken seriously, so it was easy to take his experiments as his only serious science though Gilbert undoubtedly hoped that much of his basic physics theory would also be taken seriously.
It is not clear if Galileo and friends also replicated Gilbert's electrical experiments though some others did, but it was to be only after the 1820 Oersted discovery that electric currents also produce magnetism that real further progress was made in magnetism or electromagnetism, and certainly Galileo entirely failed to incorporate any of it into his physics as later Einstein was also to fail to incorporate electromagmetism into his relativity physics.
While Gilbert's 1600 Latin work had no translation till hundreds of years later, Galileo's
1632 Italian astronomical 'Dialogue Concerning the Two Chief Systems of the World – Ptolomaic and Copernican' or 'Dialogo ...' had published 1635 Latin and 1661 English translations.
Unlike this, Galileo's physics was not promoted as much as his astronomy was.
Churches being inclined to the view of God as the cause of
everything, led many early scientists to omitting causal theory
from their science. Yet churches generally really saw God as at least largely
an imaginary unseen that science would never be able to fully prove or disprove.
And the churches were in fact less concerned
about what caused day to day events, than with science
contradicting some particular words in their holy books. So their
real opposition was to science claiming that the Earth is not the
centre of the universe but is just one planet of several orbiting
the Sun, and to science claiming that humans were not specially
created but evolved from apes.
So early scientists even claiming that almost everything was caused by God,
could still be in trouble. Of course Descartes basically did just get away
with claiming that everything was caused by God AND that nothing was
caused by God. But in the end physics survived, in a maybe highly prejudiced form, chiefly because the power of
religion in Europe gradually weakened and science was increasingly
seen as being of practical use - especially for war weapon development.
Still there were complaints against Galileo that, in supposedly following his
religious and legal requirement to publish his ideas as 'only ideas', he made competing Bible and Catholic Church ideas regarding astronomy and physics look simplistic and ridiculous.
But to be fair there have always been some scientists concluding that science theories are often claimed to be proven when their 'proofs' are really weak. Maybe reletivity
theory, string theory and other modern science theory should be better seen as possible truths or likely truths rather than as proven truths ?
Maybe all scientists have a tendency to overstate their claims to at least some degree, often with somewhat vague theory not all rigorously defined ?
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(The fictional time-travel and multi-universe type ideas of modern physics theory have long totally discouraged certain lines of physics experiment despite there being strong reasons to believe them to be very promising if not essential lines of experiment. Some such lines of experiment considered here identified as early as the 1960s seem still to have had no work done on them and there is maybe not much more time here for this. Science funding both government and private unfortunately now all goes to basically safe standard mainstream science, and no money at all goes to any really innovative risky science though that might pay a thousand times greater.)
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