Thanks for sharing this, I upvoted it. It's cool to see efforts aimed at moving the overton window on nonhuman sentience. In general I feel positively about this article and have a lot of respect for your work. 

One worry I have about this type of public communication is that it runs the risk of distracting people from the more glaring problem of factory farming.

Caring about pigs is already way outside the overton window. If we spill a lot of ink on really speculative claims in public-facing media, there's a risk that people will conflate two very different phenomena:

1. An extreme moral catastrophe that we know is happening (factory farming) 
2. An important but very speculative area of academic philosophy (microbe sentience etc.)

The former has a clear solution (eat plants), the latter might be completely intractable. The former involves lives that are almost certainly net-negative, the latter involves lives of unknown quality. The former is robustly terrible according to any sane worldview, the latter may hinge on population ethics and your approach to Pascal's Mugging.

I think you could have better communicated this distinction, perhaps by having a paragraph early in the article that states in very clear terms how bad factory farming is.

Thanks for sharing!

At least until the scale of arthropods, it does seem like the scale of the welfare of populations of smaller beings tends to be larger. I do not know where this tendency stops, but I would not be surprised if it continued all the way to bacteria or even fundamental physics. One could argue there is nothing we can do now to improve the welfare of small beings. I agree that is mostly the case now, but we can still do research to do better in the future.

It also appears that smaller beings can produce welfare more efficiently.

The title of your post is very provocative and gets right to the point. 

A typical human has about 40 trillion microbes, presumably large mammals have similar quantities, numbers which are beyond our ability to comprehend. 

If we treat each microbe as sentient, then unless we can somehow demonstrate that my feelings are more than 40 trillion times more important than those of a microbe - very tough, because we have 500 times fewer neurons in our brains, so even if every neuron were united in suffering, how could we justify a factor of 40 trillion? - we could end up just calculating the importance of different species and their suffering purely in terms of the number of microbes they contain, on the assumption that if a mammal suffers and dies some fraction of the microbes in and on their body will also suffer and some will die. 

In such a calculus, it seems highly unlikely that we could justify the continued existence of humans, if only based on the number of animals we harm, directly and indirectly, and the microbes in and on those animals.

I believe we will resolve this dilemma sometime in the future (existential risks permitting) with some experimentally and theoretically derived scale by which we can estimate sentience and the potential for suffering based on some quantitative, measurable parameters.

I tend to believe (without evidence) that there is a point below which suffering is not possible, possibly based on the minimum complexity required to create consciousness as an emergent phenomenon. (yes, I realise that sounds like a list of big words cobbled together randomly to give the illusion of understanding). 

We're not there yet, but we will reach a point where we can fully understand the workings of the simplest microbes in terms of chemical equilibria and chemical potential and thermodynamics - what appears as their "desire" to do X or Y will be shown to be no different to the "desire" of a positive ion to approach a negative ion, but without any reason to evolve consciousness. 

The assumption behind this is that one day we will understand consciousness in something other than a hand-waving manner. Right now, given that we don't, it is very difficult to quantify anything, and so we need to err on the side of caution. 

Is there evidence on the effects of extreme claims on moral circle expansion? 

I am relatively aware of the potential benefits (eg. talking about shrimp sentience might encourage people to start reflecting on the welfare of farm animals more broadly).
But it feels like there is also a potential failure mode with this current approach, where talking about extremely non-mainstream ideas such as stopping boiling vegetables or refraining from using antibacterial deodorant (as per the article) might make readers less likely to engage with similar arguments in the future.

Curious to hear if anyone has more insights on that!

Well, the main problem here is that we don't know and cant know, for reasons explained here:

https://forum.effectivealtruism.org/posts/cFDGyFGhiW3JeCrd4/freedom-under-naturalistic-dualism

Laplace's demon could know the exact future evolution of each neuron in Descartes's brain without this giving him the slightest information about whether Descartes thought and existed as a conscious subject. In fact, the demon himself would not even know whether computing Descartes's future evolution would generate the realization of his conscious experience. If the answer were affirmative, only the “simulated Descartes” himself would know it (!), and if it were negative then nobody would. In naturalistic dualism consciousness is the ultimate noumenon.

In fact, the “neural correlates of consciousness” research agenda (Koch, Massimini, Boly and Tononi, 2016) substantially depends on our trust on human subjective reporting. The extension of this methodology to animals is undermined for their lack of language, which limits reporting.  On the other hand, for computers, even superhuman cognitive and linguistic skills would be not enough to guarantee conscience, because the specific physical implementation of a neural network (and not only her outputs) is likely important for the emergence of conscience (see Marshall, Albantakis, Mayner, Koch, and Tononi, 2019). 

Reading this made me realize how the view that all suffering matters is quite well-represented in Jainsm - https://en.wikipedia.org/wiki/Ahimsa_in_Jainism. 

Thanks for writing this. Some time ago, I also wrote on the possibility of microorganism suffering. Feel free to reach out if you'd like to discuss the topic :) From the intro:

At any given moment, around 10³⁰ (one thousand billion billion billion) microorganisms exist on Earth.^[2] Many have very short lives, resulting in massive numbers of deaths. Rough calculations suggest 10²⁷ to 10²⁹ deaths per hour on Earth.^[3] Microorganisms display aversive reactions, escape responses, and/or physiological changes against various fitness-threatening phenomena: harmful chemicals, extreme temperatures, starvation, sun damage, mechanical damage, and predators and viruses.

Separately, the hyperlink in this sentence seems to be incorrect:

And if they can suffer, as Jeff Sebo, a philosophy professor at NYU, argues in a prescient new paper, we should probably try to prevent that pain.

Unless the first thing stated after a clickbait title like this is “no, microbes don’t matter more than humans…but now that I have your attention…here’s a valuable point” then first I have no time for it and second it’s silliness like this that makes me take the whole movement of EA less seriously .