The joke appears in the SMBC comic dated May 14, 2025, here.
The strip is hilarious (I do understand enough about quantum mechanics to get it), but the caption, which invokes Einstein-Landauer culinary units is just a bit beyond my grasp.
TIA
Einstein established the equivalence between mass and energy, Landauer established that information storage takes a finite amount of energy. So you could ask for a certain mass of flour using units of information- if you were being terribly passive-aggressive
I would have answered, “Okay, but you have to give me some time to count it out.”
The number “five hundred sextillion terabytes” really grates me. Just say “5×1035”.
How much flour is that in HDD?
Gifted student to Bart Simpson: “I’ll trade you 1,000 picoliters of my milk for 4 gills of yours.”
In short, Landauer’s principle is that all information is energy. Einstein’s E=MC^2 tells us that energy and mass are equivalent. So, “Einstein-Landauer” refers to the fact that there is an equivalency between information and mass. All information is energy; All energy is Mass; therefore all information is mass.
So, with that in mind, someone could make an attempt at quantifying mass using the same units of measure typically associated with information (bytes). Therefore, a cup of flower or a teaspoon of sugar could be expressed as a certain number of bytes. These would be Einstein-Landauer culinary units. Not sure what the converstion is between terabytes and gallons, but the point of the joke is that it can be meaningfully converted at all.
Well, “information” multiplied by temperature has units of energy, via Boltzmann’s Constant, which I do not see mentioned in this thread. And energy = mass via the speed of light.
I would describe Landauer’s Principle in terms of computational limits (classical computation requires a certain amount of energy), not so much “information = energy”. In fact, I am not sure how you mean to go directly from “1 bit” to an amount of energy, without taking into account something like the temperature?
Presumably the current room temperature? Bearing in mind that the person asking for the flour is being deliberately difficult
The real joke is that “cup” is a unit of volume, not mass.
You don’t. Landauer’s principle establishes the need to dissipate a certain minimal energy to the environment for irreversible operations, like deleting a bit. The usual logic is that you take a system which has a single degree of freedom that can be in either of two states, e.g. a box containing a particle that can either be in the left (l) or the right half (r). Then you ‘reset’ that system to a known state, say l. You do that by inserting a piston and compressing the system such as to be present in the left half only. Since that reduces the available state space by a factor 2, you get an entropy increase proportional to ln(2) (with the proportionality constant being the Boltzman factor), which yields a heat energy of Tln(2) provided the bath is at temperature T.
So it’s really the case that deleting the amount of information in the comic yields at a certain temperature a dissipation of heat equal to the mass-energy of a cup of flour. Which however doesn’t make for quite such a snappy joke.
I assume it works in the other direction, too. I dare anyone here to go to Microcenter and ask for a two-pound hard drive.
Yeah, I know.