A modern computer makes billions of calculations per second. The calculations have a "forward direction". For example, if the result of x + y is 4, you cannot "compute backwards" and find out what x and y are equal to.
But calculations can be reversible. For instance one could say that x is 3, and then have enough information to run the calculation backwards. This is particularly interesting because physics dictates that computers based on reversible calculations use less energy than ones based on non-reversible calculations.
Lecturer: Postdoc Holger Bock Axelsen from the Department of Computer Science, University of Copenhagen