News & Views | Published:

50 & 100 years ago

    Naturevolume 440page286 (2006) | Download Citation

    Subjects

    50 YEARS AGO

    “The Arrow of Time” — It is widely believed that all irreversible mechanical processes involve an increase of entropy, and that ‘classical’ (that is, non-statistical) mechanics, of continuous media as well as of particles, can describe physical processes only in so far as they are reversible in time. This means that a film taken of a classical process should be reversible, in the sense that, if put into a projector with the last picture first, it should again yield a possible classical process. This is a myth, however, as a trivial counter-example will show. Suppose a film is taken of a large surface of water initially at rest into which a stone is dropped. The reversed film will show contracting circular waves of increasing amplitude. Moreover, immediately behind the highest wave crest, a circular region of undisturbed water will close in towards the centre. This cannot be regarded as a possible classical process. (It would demand a vast number of distant coherent generators of waves the co-ordination of which, to be explicable, would have to be shown, in the film, as originating from one centre. This, however, raises precisely the same difficulty again, if we try to reverse the amended film.)

    K. R. Popper

    From Nature 17 March 1956.

    100 YEARS AGO

    Journals dealing with the chemical aspects of physiological and pathological research have long been current in Germany; but up to the present time English-speaking workers have had to rely on periodicals dealing with all branches of physiology and pathology for the publication of their results... the need has for long been felt of a special journal, and we have to chronicle the advent of one — the Bio-chemical Journal... In America also a similar want has been met by the issue of the first numbers of what is there called the Journal of Biological Chemistry.

    From Nature 15 March 1906.

    About this article

    Publication history

    Published

    Issue Date

    DOI

    https://doi.org/10.1038/440286a

    Comments

    By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

    Newsletter Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing