The infinitesimally low concentration of homeopathic preparations, which often lack even a single molecule of the diluted substance, has been the basis of questions about the effects of the preparations since the 19th century. Modern advocates of homeopathy have proposed a concept of "water memory", according to which water "remembers" the substances mixed in it, and transmits the effect of those substances when consumed. This concept is inconsistent with the current understanding of matter, and water memory has never been demonstrated to exist, in terms of any detectable effect, biological or otherwise. James Randi and the 10:23 campaign groups have highlighted the lack of active ingredients in most homeopathic products by taking large 'overdoses'. None of the hundreds of demonstrators in the UK, Australia, New Zealand, Canada and the US were injured and "no one was cured of anything, either". Outside of the alternative medicine community, scientists have long considered homeopathy a sham or a pseudoscience, and the mainstream medical community regards it as quackery. There is an overall absence of sound statistical evidence of therapeutic efficacy, which is consistent with the lack of any biologically plausible pharmacological agent or mechanism. Abstract concepts within theoretical physics have been invoked to suggest explanations of how or why preparations might work, including quantum entanglement, quantum nonlocality, the theory of relativity and chaos theory. Contrariwise, quantum superposition has been invoked to explain why homeopathy does not work in double-blind trials. However, the explanations are offered by nonspecialists within the field, and often include speculations that are incorrect in their application of the concepts and not supported by actual experiments. Several of the key concepts of homeopathy conflict with fundamental concepts of physics and chemistry. The use of quantum entanglement to explain homeopathy's purported effects is "patent nonsense", as entanglement is a delicate state that rarely lasts longer than a fraction of a second. While entanglement may result in certain aspects of individual subatomic particles acquiring linked quantum states, this does not mean the particles will mirror or duplicate each other, nor cause health-improving transformations. Plausibility The proposed mechanisms for homeopathy are precluded from having any effect by the laws of physics and physical chemistry. The extreme dilutions used in homeopathic preparations usually leave not one molecule of the original substance in the final product. A number of speculative mechanisms have been advanced to counter this, the most widely discussed being water memory, though