How does Replaceability applies to overcrowded academic areas that have an oversupply of PhDs slaving away in postdocs never to find a permanent job? This glut of PhDs must mean the actual impact of me joining a field like Particle Physics would be very low. Is that correct?

How is that different to one of the recommended career paths by 80000 Hours, Biomedical Research, which is also competitive, but is marked as high impact?

For context, I must mention that Biomedical Research seem to tackle more 'solvable' problems while Theoretical Physics has been mostly stagnated since the standard model (little progress has been made in several decades). For example, a few scientists predicted the Higgs boson within a short time of each other, Higgs was merely the first to do so. It should also be added that Biomedical Research positions exist in Big Pharma, while Theoretical Physics is limited to academia.

I have read many articles about replaceability. In special, the 80000 Hours 3-part series "How many lives does a doctor save?" about the impact of new doctors, as well as the Rational Altruist blog on Replaceability ( But I still have this question.

I believe the answer may be in the post "What does economics tell us about replaceability?" ( but I am no economist and most of it flew over my head. I guess I need someone to dumb it down a little for me.


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Hauke Hillebrandt

Jan 25, 2022


The paper "Are ideas getting harder to find?" might be relevant.

According to the law of logarithmic utility—which has been applied to research funding—a simple rule of thumb is that $1 is worth 1/X times as much if you are X times richer (doubling someone's income is worth the same amount no matter where they start). 

Past the point of increasing returns to scale, the next dollar donated say at the $100M funding mark might have 10x as much impact as the dollar donated after the $1B mark (which is ~basic physics funding in the US— though total physics-related public R&D seems more like $100B and maybe 2x that globally). 

So all else being equal (e.g. personal fit) by switching to a field like AI safety which has even less $100M / y you have that sort of strong multiplier on your side.

These neglectedness/crowdness considerations map onto some fundamental cognitive biases, like scope insensitivity (we aren't very sensitive if a research field receives $1B vs. $10B) and also the sort of counterfactual thinking (people rarely think about the fact that if they don't take that job as a doctor or physics postdoc someone else who's just marginally less qualified will).

Having said that, Einstein is probably a contender of “who did the most good?”, as he revolutionized physics, paved the way for lasers, GPS, and the microelectronics/computers, which in turn transformed modern economies (though some physics might have dual-use risks c.f. nuclear energy and atomic bombs). My read is that Einstein pushed the field forward by many years, so if you think you have strong personal fit for physics, maybe it's worth becoming a physicist.

To synthesize your point, you believe that replaceability and economics of scale ensure that individual impact in Theoretical Physics is small, unless you are able to be revolutionary, like Einstein?

I don't have access to the first paper you linked, though I can get an idea of what it debates by reading the abstract. The projects in science have been getting bigger, and that is specially true in Physics. A multi-billion dollar project, the Large Hadron Collider (LHC), was needed to test the Higgs Boson. Now, some Physicists want an even bigger one. Papers ... (read more)

Charles He
Here is your paper: []
Charles He
You should bookmark sci-hub (or rather mentally bookmark the name sci-hub, as the url get knocked around a bit)
Hauke Hillebrandt
  I'm not saying that you necessarily present day adjusted  Einstein-level to be a physicist. If you have strong personal fit and are very motivated then maybe still consider it. You could also do some other physics (see for instance Toby Ord's astrophysics papers []).  I'm just saying everyone who goes to university is implicitly exposed to the ‘basic research is the most noble / high impact pursuit ever’ meme... and I think that's not true... so if you have other interests then you could just pursue those, and all else being equal, you would have more impact because they're likely more neglected in terms of raw IQ than particle physics. But then some argue that society pushes too much raw IQ into the financial sector and not enough into science.