High energy physics experiments attempt to re-create conditions immediately after the big bang, by searching back in time for evidence of elusive short lived particles. The linked study by Bhaskaran and colleagues (doi:10.1136/bmj.d5531) reports findings from a case crossover analysis of very short term effects of air pollution on myocardial infarction in England and Wales. This state of the art analysis tests the epidemiological (as opposed to physical) limits of detection.1

The effects of air pollution on death and morbidity from cardiorespiratory disease on daily and longer time scales are now well established.2 The largest effects are seen after years or decades of chronic exposure, as shown by cohort studies.3 However, such studies are logistically demanding, requiring high quality data on spatial patterns of exposure and long follow-up of large populations or linkage of routinely collected datasets.4 For this reason, most epidemiological studies have analysed the acute effects of air pollution, using daily time series of exposure to air pollution and health outcomes available from routinely collected data. …