effective as opposed to a tax subsidy. >> final question. how far can this go? i mean, is this a substitute for legislation? in a way, it would be ideal if it could organically shift people's choices. >> it won't do anything. it's not going to solve global warming by itself or stop war, but there are many areas where it can be effective. in relation to health, most years of healthy life lost are behavior, we don't exercise enough, eat well enough. the same is true for crime, for economic growth. economies bounce up and down because of what we think other people are doing. we're often wrong in those perceptions. there have been great successes in the uk, but it's also that we think we're still scratching the surface. there's a long way still to go. >> best of luck. fascinating ideas. >> next on gps, the queen just became the longest serving british monarch. but who's got the crown for the whole world? find out when we come back.