I shouldn’t have to say it. But I do.
Nuclear reactors can use “control rods” to control the reaction. Push them in all the way, they’ll slow the reaction so much it will quickly die out. Pull them all the way out, the reaction grows so fast it goes critical — but before it can “go nuke” it melts. Still a disaster.
The “basic” epidemiological model (the SIR model) makes some very basic assumptions, and treats the spread of a disease like COVID-19 in a straightforward manner. It gives rise to the “bell-shaped” curve (the one everyone wants to flatten) we’ve seen in so many news stories.
Of course it’s not “right” — there are too many unaccounted-for factors to believe that. But they also encompass certain purely logical ideas which are known to be correct. Added bonus: the equations are not unlike what you see when you study how neutrons keep the reaction going in a nuclear reactor. The reactor equations are likewise imperfect, but they too encompass some undeniable logical ideas. The most impressive thing they have in common: experience has shown that they both work.
And now to the real point of this post. Pay attention, because this is the real message and it’s worth it. Here it is:
Part 1: How fast a nuclear reaction grows or shrinks depends on where you set the controls.
Part 2: How fast an epidemic grows or shrinks depends on where you set the controls.
Do you think you can remove the control rods from a nuclear reactor and NOT see the reaction grow?
There’s one way you can. Let the reaction run wild. Pull out the control rods enough that it runs hot, but not hot enough to melt, and let it run until it exhausts its fuel. Then you can remove the control rods because there’s not enough fissile material left to sustain a reaction.
You can do the same with an epidemic. Pull out the controls, let it run its course, and eventually there aren’t enough people left to get sick and sustain the epidemic. You may have heard of it: it’s called “herd immunity.” The catch is: nearly everybody gets it, nearly everybody who can die from it does. In the USA, that means maybe about three million people. I don’t like that solution.
Governors Ron Desantis of Florida and Greg Abbott of Texas act like they can re-open their states’ economies, removing restrictions but not suffer an immediate reaction. When the immediate reaction follows, they blame it on anything but removing the control rods from the nuclear reactor. It’s the fault of “young people” in Texas — it’s the fault of migrant workers in Florida — and it’s the “fault” of more testing. They act like there aren’t really more cases — we just found more because we tested more. I’ve already shown how stupid that is.
And these two republican governers have failed to pay attention to what their own data say — because the data for an epidemic (or a nuclear reactor) tells you when it’s safe to remove some of the controls. The Florida data and the Texas data gave a clear answer: NO. But they opened anyway. Florida even pressured one of their own data scientists to change the data and make it look like they were ready when they weren’t — then fired her when she refused.
State governors should look at the data for their own states. They should know it like the back of their own hand. If the reaction is growing (the case load is rising) it will keep rising unless you push in some control rods. If it’s slowing it will keep slowing unless you pull out some control rods. Every time you change the controls, it will change how fast the reaction grows or dies.
The only way to re-open safely is to wait until the rate is low enough AND it’s not growing hotter, then remove controls slowly while remaining constantly vigilant. If the reaction grows fast enough or far enough, restore controls. If not, then it might be safe to try the next small step.
My advice to governors in all states:
— Don’t remove controls until the rate is very low (well below 50 cases per day per million population) and either steady or going down. When you remove controls, the rate will go up — if we’re lucky, not too fast or too far.
— Don’t loosen too many things at once, or you won’t know which controls are working and which aren’t.
— When the reaction heats up, don’t blame hipsters or gen-X or millenials or migrant workers or testing. It sounds like the dog ate your homework.
In the next post (or at least, soon) I’ll explain and run the SIR model, and show you the control rods in action. There will be math. But not too much.
This blog is made possible by readers like you; join others by donating at My Wee Dragon.
Open Mind 
Ignorance can be a very scary thing, particularly with nuclear fuel. Scary monsters.
BTW, typo: DeSantis (title).
Excellent post and a fantastic analogy. On some denier sites (very reminiscent of climate change denier sites) they try to claim that pushing in the control rods had no effect or may have made it worse. They even try to point to research which proves their point. I’ve tried in vain to educate them but it just won’t happen. It is very difficult to convince people of anything they don’t want to be convinced of.
When you do talk about the SIR model, is James Annan’s model worth comparing. I gather it is slightly different and the most recent incarnation looks very impressive.
The question I have is how do you decide that a change has occurred (as with Germany recently I gather). I presume that new cases, or new ‘community acquired’ case numbers indicate a higher rate of transmission. Death rate seems too late an indicator.
Thank you for your posts. Interesting from a NZ POV, where we are concerned with implications of a handful of new cases imported here.
Henry
Reblogged this on Don't look now and commented:
Open minds: excellent again.
Johnson/Cummings do note this.
You don’t understand something simple. The Trumpublicans have figured out that the people most likely to die or suffer severe illness from COVID-45 are old people of color. SO THEY DON’T CARE.
While I mostly agree with your conclusions and recommendations, your analogy falls down in the very first paragraph. Reactors go critical all the time; all “critical” means is “steady state”; in layman’s terms, “on”. In the terms of a physicist, keff=1. Reactors even go SUPERcritical; that’s the only way to raise power. Also, if by “go nuke” you mean “undergo a nuclear detonation”, it’s incredibly irresponsible to even bring such an event up in the context of a nuclear reactor. The enrichment levels alone preclude such an occurrence, to say nothing of the insanely precise geometry required to construct a nuclear weapon that bears NO resemblance to the geometry of a reactor.
[Response: Be as pedantic as you like.]
Your analogy is apt but your terms are a little off. All reactors operate normally while critical.
https://en.m.wikipedia.org/wiki/Critical_mass#Explanation_of_criticality
You seem to forget Henry McMaster of South Carolina. His position essentially seems to be that there’s nothing to be done with *his* control rods, because economy. But he’s very happy to chide South Carolinians, particularly young ones, for not taking care of *their* control rods–social distancing and mask-wearing. (Haven’t seen him wear one once, by the way.) He’s not wrong about Carolinian compliance, if my observations on our once-a-week foray into the world, but it hardly seems the acme of gubernatorial responsibility to take that stance. In fact, I’d call it hypocritical.
But what I or anyone else calls isn’t the crucial thing: that would be that we are currently at 1k new cases daily, with every prospect of growth, no prospect of new restrictions, and planning in full process for the reopening of schools in August. (I spent a fair amount of time last year substitute teaching; no way are you going to see me doing that this school year.)
So, I say to Brazil: do your worst! America will continue to be #1!
Uh, I may have gotten a little bitter there. Sorry.
Doc, Having spent a fair amount of time in Brazil, I would not write them off. When I was down there last Summer, I was only half-way through my taxi ride from the airport before I witnessed the deep divisions that fracture that country over the Bolsonaro regime. The guy who was sharing the taxi with me almost got into a physical altercation with the driver–while the taxi was in motion!
The political class in Brazil has a long and inglorious history of corruption, and that corruption has sunk deep roots into the society. People are fed up, and some wanted a strong man to clean things up. Unfortunately, authoritarians are piss poor judges of character and they elected Trump’s Mini-Me, Bolsonaro. Some of the state governors have stepped in to fill the leadership vacuum, but again, the machismo in the culture and political division, coupled with poor education for many lead to a very combustible mix. Too bad. It is a beautiful country.
Well, they won yesterday’s mano-a-mano (or whatever the Portugese phrase would be) on daily cases–despite a national third-‘best’-ever 36,015 by the US–when the Brazilians uncorked a second-‘best’-ever-anywhere-by-anybody 40,131.
So your point is very definitely taken.
I am posting a link to an involved economist – someone who not only gets it but dishes it out – with access to a tool that you might find useful. It is a long watch but I think you will find it worth the time.
I’m working on the economics aspect of this myself now, but I wanted to introduce this to people who understand that the climate is breaking and have the technical background to be able to grab this tool (*FREE BETA*) and use it. Serious math managed here – Keen has a background in math.
It models the COVID infections and it models the economics of the great recession and he has many things to say about Nordhaus and Tol and their economic incompetence.
Reason I am here? He asked for real scientists to invade the sacred turf of the economists and tear their blithe assumptions to shreds. I figured this is one of the places where such people – particularly including you Tamino, may be found. I imagine you finding this more interesting than most.
This is also a bit of a pull back towards the nasty difficult problem in the area of climate change. Easier for me to think about because I am in Wellington, NZ and don’t have to think about COVID too very much.
On the subject, I could do nothing but display my layperson ignorance, though perhaps acknowledging that I don’t know enough is better than not doing so.
But I can’t help thinking of the Santa Fe Institute, which was formed partly to bring “real scientists to invade the sacred turf of the economists and tear their blithe assumptions to shreds.” Does it still do so (if you know?).
Don’t have time right now but will be interested in your video though I suspect it will be over my head.
I can’t tie this in, but since I’m here, a friend pointed me to Tamsin Edwards in the Guardian, and we had a very polite argument about the subtle way she understates the case where she should be beginning to grok how events are overtaking scientific predictions. https://www.theguardian.com/commentisfree/2020/jun/25/arctic-heatwave-38c-siberia-science – OT for this post, but every time I look at her material I find myself agreeing with those who think it is unhelpful to exaggerate on the low end, uncertainty not being our friend.