Astronomy
Astrophysics - specifically things such as the speed of light, which generates the
starlight problem. In order for the universe (YEC usually has the entire universe pop into existence, rather than just the planet) to be seen, either the speed of light has to be changing or light had to have started en route to Earth already. The former is not supported by modern science or any observational evidence, and even semi-coherent theories regarding an
anisotropic synchrony convention or
C-Decay can't account for the massive change needed. The latter is a case of
special pleading and can lead to
Last Thursdayism.
Electromagnetism - Since the speed of light can be derived from the
vacuum permeability and the
vacuum permittivity, unpredictable changes in speed of light pretty much renders the predictive power of the whole branch of electromagnetism to be thrown out of the window.
Cosmology - The Cosmic Microwave Background (CMB) - a background level of very cold, low frequency radiation, predicted to exist by the "Big Bang" model and discovered and researched intensively throughout the latter half of the 20th century.
General physics
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Mechanics - including Newtonian mechanics with gravity.
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Nuclear physics - the decay rates of certain isotopes are known and are used in
radiometric dating. YEC beliefs often require these well established rates to change by, for lack of a better term, stuff.
Transport phenomena
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Fluid mechanics -
momentum transfer is pretty much incompatible with the idea of a global flood.
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Heat transfer - pretty much incompatible with all the variations of ideas that require
water under earth's crusts, or in case of radiative heat transfer,
White hole cosmology and anything that involves different speed of light or radioactive meterial giving radiation at a significantly different rate.
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Mass transfer - also would have to be ignored, due to phenomena such as
diffusion of impurities or crystal/sediment formation