A Difficulty in the Concept of Social Welfare
A Difficulty in the Concept of Social Welfare
- Event time: 11:30am until 12:30pm
- Event date: 5th April 2019
- Speaker: Professor Graeme Ackland (School of Physics & Astronomy, University of Edinburgh)
- Location: Room 2511, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
Event details
You may have noticed some difficulties reaching an agreement in recent political debate. In part, this is because it is impossible to have a fair, democratic vote when there are more than two options. Unlike the normal usage (i.e. "In accordance with my personal prejudices") "Democratic Fairness" has to be defined rigorously for a voting system, as follows.
Democratic - no one individual is guaranteed to get their preference
Deterministic - if the process is run again with the same voter preferences, it gives the same answer
Universal - the process should provide a complete ranking of all options.
Independence of irrelevant alternatives - the fact that option A is preferred to option B, cannot be changed by including/excluding some other option C in the vote
Unianimity - if everyone prefers A to B, then the system must rank A above B
Unrestricted - for any possible outcome some set of voting preferences exists which will give it.
The impossibility to devise a fair voting system was elegantly proved by Arrow in 1950, and is one of the things "everyone should know, but nobody does". I'll go through the proof.
Event resources
About Condensed Matter journal club
Given the diversity of research in the CM group, chosen topics vary widely. We tend to stick to high-impact journals - Nature, Science, PNAS and PRL have been popular - but this is not prescriptive..