X-ray pulses that last for less than a femtosecond – or 10^-15 seconds – have been created for the first time by physicists in Austria. Ferenc Krausz of the University of Vienna and colleagues have used the ultra-short bursts of X-rays to probe the ionization of krypton – a process that takes place too quickly for existing techniques to detect. The breakthrough marks the transition from tracking fast molecular processes to monitoring the ultra-fast dynamics of a whole range of sub-atomic events on an attosecond – 10^-18 seconds – time-scale (M Hentschel et al 2001 Nature 414 509).