Top all-time · #401
Tom Murphy
Personal blog · dothemath.ucsd.eduscienceeconomics
Tom Murphy writes Do the Math, a personal blog at dothemath.ucsd.edu about science and economics. Since 2017, 136 different Hacker News readers have linked it 287 times, most often “Exponential Economist Meets Finite Physicist (2012)”. It is still writing: the last post was on 2026-10-20, and you can follow it by feed.
Sometimes recommended · 7 of 40 sampled comments recommend it?
Why HN links it
Linked for its energy-growth posts, which argue that waste heat and finite resources limit growth. Commenters call the blog the best resource in its area.
- Recommended for · 7 comments
- called it the best resource in its area and really good; a sobering look at growth limits; a nice graph
Summarised by Claude from a sample of 40 HN comments that link here. Each comment is marked recommending, critical or neutral (citing without judging); how this works.
Most-linked posts?
- Exponential Economist Meets Finite Physicist (2012)40 people · 69 mentions · first linked 2017-04-17
- Galactic-Scale Energy (2011)22 people · 37 mentions · first linked 2017-11-28
- The Energy Trap (2011)10 people · 10 mentions · first linked 2018-02-19
- Pump Up the Storage8 people · 12 mentions · first linked 2018-10-07
- /7 people · 8 mentions · first linked 2020-01-02
- Can Economic Growth Last?7 people · 7 mentions · first linked 2017-10-24
- A Nation-sized battery (2011)6 people · 7 mentions · first linked 2018-03-28
- /2012/03/space-based-solar-power/5 people · 17 mentions · first linked 2017-04-26
- Heat Pumps Work Miracles5 people · 5 mentions · first linked 2019-02-27
- Why Not Space? (2011)4 people · 4 mentions · first linked 2017-07-13
What Hacker News says?
It's interesting to look at things from a controls perspective. An economy (any kind of economy!) is just a feedback control system. Generally, when you're choosing a feedback controller, you have two options: PID, where you have a set of 3 "dumb" rules, and all you have to do is tune the gains on those dumb rules. Or MPC, where you need to actually build a model of the system you are controlling, and then you can o…
Comment linking /2011/07/galactic-scale-energy/
on “100 years of whatever this will be”Submitted Heat Pumps Work Miracles as a story · 251 points
HN discussion> Fusion is in theory something that could give us true energy abundance. Well, at least for a few hundred years but then: > if you plot the U.S. energy consumption in all forms from 1650 until now, you see a phenomenally faithful exponential at about 3% per year over that whole span. The situation for the whole world is similar. […] the Earth has only one mechanism for releasing heat to space, and that’s via (infra…
Comment linking /2012/04/economist-meets-physicist/
on “MIT-designed project achieves major advance toward fusion energy”Submitted Death by hockey sticks as a story · 184 points
HN discussionMaria Popova https://www.brainpickings.org/ Tom Murphy https://dothemath.ucsd.edu/ Cathy O'Neil https://mathbabe.org/ Peter Woit (Not Even Wrong) https://www.math.columbia.edu/~woit/wordpress/ Autumn Gearhart Rain https://rainintheforecast.wordpress.com/
Comment linking /
on “Ask HN: Favorite Blogs by Individuals?”Submitted Exponential Economist Meets Finite Physicist (2012) as a story · 133 points
HN discussionThere's waste heat from our power plants today, but it's an extremely minor factor compared to carbon emissions. However, if we were to continue our current rate of exponential energy growth on this planet, we would boil the oceans in 400 years. https://dothemath.ucsd.edu/2012/04/economist-meets-physicist... On the other hand, compact fusion power would make for some great rockets, so by the time it's common it woul…
Comment linking /2012/04/economist-meets-physicist/
on “Radical hydrogen-boron reactor leapfrogs current nuclear fusion tech?”Submitted Galactic-Scale Energy (2011) as a story · 75 points
HN discussionAnd pumped hydro isn't a panacea either. https://dothemath.ucsd.edu/2011/11/pump-up-the-storage/
Comment linking /2011/11/pump-up-the-storage/
on “Finland starts much-delayed nuclear plant, brings respite to power market”Submitted Burning Desire for Efficiency (2012) as a story · 39 points
HN discussionYeah. This blog post [0] has a nice graph showing that at continued exponential growth of energy consumption, we have less than a few hundred years until the planet would become uninhabitable simply due to the amount of additional heat. In particular, in about 400 years, the energy demand would equal the total solar energy flux hitting the planet. [0] https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/
Comment linking /2011/07/galactic-scale-energy/
on “Korean nuclear fusion reactor achieves 100M°C for 30 seconds”Submitted Peak Population Projections as a story · 34 points
HN discussionEventually, yes. Right now waste heat is a tiny fraction of excess greenhouse heating, but if we kept multiplying our energy usage by a couple percent per year, we'd boil the oceans in four centuries. https://dothemath.ucsd.edu/2012/04/economist-meets-physicist... If we invent fusion, I think we could grow exponentially for quite a while, but it'll mostly happen in space. Controlled fusion makes a really great rocke…
Comment linking /2012/04/economist-meets-physicist/
on “Korean nuclear fusion reactor achieves 100M°C for 30 seconds”Submitted A Climate Love Story as a story · 32 points
HN discussionThis article by a Berkeley physicist does the math on fusion fuel: https://dothemath.ucsd.edu/2012/01/nuclear-fusion/ Deuterium fuel is the most abundant. There's enough in your morning shower to supply all your energy needs for a year. There's enough in the oceans to last for billions of years. Fusion is as close to renewable as anything, because it'll last until the sun goes out. Right now most projects are also u…
Comment linking /2012/01/nuclear-fusion/
on “Korean nuclear fusion reactor achieves 100M°C for 30 seconds”Submitted Galactic-Scale Energy (2011) as a story · 13 points
HN discussion"Actually the one sweating should be Russia, because on the long haul (10-20 years), Germany is going to be energy independent due to massive investments (also subsidies) into renewable energy." ROTFL Edit: Yes, please feel free to show your ignorance and lack of basic math skills and downvote this comment. For all others: https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/ I am sure Russia is not scared. Who…
Comment linking /2011/07/galactic-scale-energy/
on “EU bans Belarusian airlines from European skies”Submitted Inexhaustible Flows? as a story · 7 points
HN discussionThere has been some work in this area: https://www.motherjones.com/politics/2010/07/peter-victor-de... “We’ve had 125,000 generations of humans, but it’s only been the last eight that have had growth,” Victor told me. “So what’s considered normal? I think we live in very abnormal times. And the signs are showing up everywhere that the burden we’re placing on the natural environment can’t be borne.” See also, the phy…
Comment linking /2012/04/economist-meets-physicist/
on “After rising for 100 years, electricity demand is flat”Submitted Confessions of a Disillusioned Scientist as a story · 6 points
HN discussionThe latest thinking is that with the seasonality of solar insolation and the current demand curve, a complete move to solar will require massive overprovisioning. (5x, 10x capacity at solar noon?) The price curve in 2050 or so would look funny to modern eyes: power would be free around noon, but expensive at night. Charge your car for nothing during the day, and enjoy endless hot water, but the minute the sun sets y…
Comment linking /2012/03/home-heating-for-the-hardy/
on “What went wrong with the Texas power grid?”Submitted The Energy Trap (2011) as a story · 5 points
HN discussionWe would literally boil the Earth in 450 years ! https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/
Comment linking /2011/07/galactic-scale-energy/
on “A new heat engine with no moving parts is as efficient as a steam turbine”Submitted Exponential Economist Meets Finite Physicist (2012) as a story · 5 points
HN discussionYeah. Well. That's a fun math game and not much more. Other view on "energy growth rate": https://dothemath.ucsd.edu/2011/07/galactic-scale-energy/ Energy growth is due to end sooner or later. First, in the real world, any long term exponential growth is actually the upward branch of an S (that plateau at some point) or of a bell curve (that falls down after a peak). Second, with such an energy growth rate we'll boi…
Comment linking /2011/07/galactic-scale-energy/
on “Water found on a potentially life-friendly alien planet”Submitted Exponential Economist Meet Finite Physicist: Energy growth cant continue forever as a story · 4 points
HN discussionAs much as I'm in favor of moving towards renewables, we are still destroying our biosphere, and the resources needed for renewables are not renewable ... > Energy transition aspirations are similar. The goal is powering modernity, not addressing the sixth mass extinction. Sure, it could mitigate the CO2 threat (to modernity), but why does the fox care when its decline ultimately traces primarily to things like defo…
Comment linking /2022/09/death-by-hockey-sticks/
on “Carbon capture more costly than switching to renewables, researchers find”Submitted A Mind-Blowing Leap as a story · 3 points
HN discussionHere is a pretty good one IMO (loooong read): https://jancovici.com/en/readings/societies/the-limits-to-gr... Another article that explains well what the model does, that economists do as if matter and laws of physics didn't exist (unless they're of the rare breed of Georgescu-Roegen's disciples): https://jancovici.com/en/energy-transition/societal-choices/... Another article from another source: https://dothemath.u…
Comment linking /2011/09/discovering-limits-to-growth/
on “Up to one million species are on the verge of extinction, U.N. panel says”Submitted Exponential Economist Meets Finite Physicist as a story · 3 points
HN discussion
