#46 – Philosopher Hilary Greaves on moral cluelessness, population ethics, probability within a multiverse, & harnessing the brainpower of academia to tackle the most important research questions

The barista gives you your coffee and change, and you walk away from the busy line. But you suddenly realise she gave you $1 less than she should have. Do you brush your way past the people now waiting, or just accept this as a dollar you’re never getting back? According to philosophy professor Hilary Greaves – Director of Oxford University’s Global Priorities Institute, which is hiring now – this simple decision will completely change the long-term future by altering the identities of almost all future generations.
How? Because by rushing back to the counter, you slightly change the timing of everything else people in line do during that day — including changing the timing of the interactions they have with everyone else. Eventually these causal links will reach someone who was going to conceive a child.
By causing a child to be conceived a few fractions of a second earlier or later, you change the sperm that fertilizes their egg, resulting in a totally different person. So asking for that $1 has now made the difference between all the things that this actual child will do in their life, and all the things that the merely possible child – who didn’t exist because of what you did – would have done if you decided not to worry about it.
As that child’s actions ripple out to everyone else who conceives down the generations, ultimately the entire human population will become different, all for the sake of your dollar. Will your choice cause a future Hitler to be born, or not to be born? Probably both!
Some find this concerning. The actual long term effects of your decisions are so unpredictable, it looks like you’re totally clueless about what’s going to lead to the best outcomes. It might lead to decision paralysis — you won’t be able to take any action at all.
Prof Greaves doesn’t share this concern for most real life decisions. If there’s no reasonable way to assign probabilities to far-future outcomes, then the possibility that you might make things better in completely unpredictable ways is more or less canceled out by the equally plausible possibility that you might make things worse in equally unpredictable ways.
But, if instead we’re talking about a decision that involves highly-structured, systematic reasons for thinking there might be a general tendency of your action to make things better or worse — for example if we increase economic growth — Prof Greaves says that we don’t get to just ignore the unforeseeable effects.
When there are complex arguments on both sides, it’s unclear what probabilities you should assign to this or that claim. Yet, given its importance, whether you should take the action in question actually does depend on figuring out these numbers.
So, what do we do?
Today’s episode blends philosophy with an exploration of the mission and research agenda of the Global Priorities Institute: to develop the effective altruism movement within academia. We cover:
- What’s the long term vision of the Global Priorities Institute?
- How controversial is the multiverse interpretation of quantum physics?
- What’s the best argument against academics just doing whatever they’re interested in?
- How strong is the case for long-termism? What are the best opposing arguments?
- Are economists getting convinced by philosophers on discount rates?
- Given moral uncertainty, how should population ethics affect our real life decisions?
- How should we think about archetypal decision theory problems?
- The value of exploratory vs. basic research
- Person affecting views of population ethics, fragile identities of future generations, and the non-identity problem
- Is Derek Parfit’s repugnant conclusion really repugnant? What’s the best vision of a life barely worth living?
- What are the consequences of cluelessness for those who based their donation advice on GiveWell style recommendations?
- How could reducing global catastrophic risk be a good cause for risk-averse people?
- What’s the core difficulty in forming proper credences?
- The value of subjecting EA ideas to academic scrutiny
- The influence of academia in society
- The merits of interdisciplinary work
- The case for why operations is so important in academia
- The trade off between working on important problems and advancing your career
Get this episode by subscribing to our podcast on the world’s most pressing problems and how to solve them: type 80,000 Hours into your podcasting app. Or read the transcript below.
The 80,000 Hours Podcast is produced by Keiran Harris.















