DIRAC'S STRING PROBLEM  
Curriculum Vitae
Mathematics

Translation of the front of the bag A bottle opener is attached to two posts (e.g. two table legs) by elastic strings (or loose strings) as shown in Figure 1 [see below]. The bottle opener is now turned one full turn as shown in Figure 1. This leads to Figure 2, where the strings are twisted. Now keep the bottle opener fixed and try to see whether it is possible to manipulate the elastic strings so that the twisting is removed. If you do not succeed it is not surprising. Mathematically it can in fact be proved that it is impossible. Now turn the bottle opener another full turn, so that altogether we have made two full turns (Figure 3). In Figure 3 everything looks a bit more twisted. Again keep the bottle opener fixed and see whether the twisting can now be removed by taking the strings over and around the bottle opener. This time it is possible to do it. If you give up, the solution can be found on the other side of the bag. 