54: Science

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LiveJournal title: Science
Bonus points if you can identify the science in questionLiveJournal caption: Bonus points if you can identify the science in question.
Title text: Bonus points if you can identify the science in question

LiveJournal caption: Bonus points if you can identify the science in question.


This was the forty-eighth comic originally posted to LiveJournal. The previous one was 50: Penny Arcade, and the next one was 51: Malaria. It was among the last eleven comics posted both on LiveJournal and on xkcd.com after the new site was launched. This comic wasn't published on the same day across both sites, but most of them shared the same posting day. It was released on xkcd.com on January 25, 2006, seven days after originally being posted on LiveJournal. See the trivia section below.

The solid line represents the theoretical radiation for a blackbody at 2.73 K according to Planck's Law (derived as early as 1900 by Max Planck). The formula, almost as written in the graph, can be found here. The only changes are that on Wikipedia, the frequency f is represented by the Greek letter ν (nu) and the temperature T is included as an independent variable, so I(f) becomes I(v,T). However, I(v,T) still represents the spectral radiance (similar to energy density). In this formula, h is the Planck constant, c is the speed of light in a vacuum, and k is the Boltzmann constant. The frequency (f or v) along the x-axis is measured in gigahertz. The curve peaks at 160.4 GHz. There is no scale or unit on the energy density on the y-axis.

The theory is that the blackbody in question was the universe at the point when it had cooled down enough to allow photons to escape, 0.38 million years into its 13.8 billion years history. The photons that reach us today are the ones that have been travelling to us at lightspeed since then. As the light from astronomical objects suffers from redshift due to the expansion of the universe, and this shift becomes more pronounced with distance from the observer, this light displays in the infrared range.

The title text praises viewers who can identify where this equation and corresponding graph come from (without consulting this wiki, of course).

T-shirt explanation

This comic was made into a T-shirt but is no longer available. On the xkcd store, there was an explanation both for the title and for the graph in the comic:

Science: We finally figured out that you could separate fact from superstition by a completely radical method: observation. You can try things, measure them, and see how they work! Bitches.
The babydoll shirt is a slightly lighter green. The graph on the back of the shirt is data from theCOBE mission which looked at the background microwave glow of the universe and found that it fit perfectly with the idea that the universe used to be really hot everywhere. This strongly reinforced the Big Bang theory and was one of the most dramatic examples of an experiment agreeing with a theory in history -- the data points fit perfectly, with error bars too small to draw on the graph. It's one of the most triumphant scientific results in history.


[A graph with a curve that begins at zero, then peaks at a given frequency, indicated via a thin vertical line, and then fades down towards zero. It is possible to see the data points, which fit the curve perfectly. The y-axis is labelled. Along the x-axis, the zero point and the frequency where the peak has its maximum are labelled and close to the arrow the unit of this axis is written.]
y-axis: Energy Density
Along the x-axis:
[Above the graph to the right is the following formula, with the last inner parentheses only included to make the formula clear, since in the drawing the fractions are written above and below horizontal lines:]
I(f) = (2hf3/c2)(1/(ehf/kT-1))
[Below the graph is written the following:]
It works, bitches.


  • For unknown reasons, on January 18, 2006, this comic was posted on LiveJournal on the same day that 51: Malaria was released on xkcd.com. Three days later, on January 21, 2006, 51: Malaria was posted on LiveJournal, thus forcing the next two comics (52: Secret Worlds and 53: Hobby) to be released on xkcd.com two days before LiveJournal. Four days later, on January 25, 2006, this comic was finally posted on xkcd.com, which fixed the date discrepancies and allowed the next comic, 55: Useless, to be published on the same day across both sites.
  • This comic used to be available as a T-shirt at the xkcd store.

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It's also commonly called "Microwave Background Radiation" because where the radiation peaks at 160.4 GHz is in the microwave range of the electromagnetic spectrum. --Dangerkeith3000 (talk) 18:02, 13 March 2013 (UTC)

Error - Inverted graph!

Am I the only one who came here confused because the graph is wrong? The shape of the graph is clearly that of blackbody radiation - on a wavelength axis! However Randall titles the axis GHz (pointing right) which is the inverse of wavelength (of course on a wavelength axis, the curve should not extend down to zero). But look up the graph on Wikipedia, and notice that it's on a wavelength scale and looks exactly like this - even better, google "black body radiation" images, and notice how ~95% of them show the radiation on a wavelength scale for some reason. But scroll down, and eventually you'll see one on a frequency scale. It looks quite different! Also, the blackbody radiation is known for its rather sharp high frequency cutoff (or low wavelength), which Randall accidentally got inverted here, and placed at zero... It shows much more dramatically on frequency axis, which is why you can very clearly see that this graph is NOT a radiation graph on a frequency axis - it goes on to infinity. Anyway, sorry for the rant - but it's Science bitches, and axis' matter! Especially if you are going to invert one of them! - Richard 22:56, 28 June 2018 (UTC)

I don't think it's inverted. We are not plotting against -wavelength but 1/wavelength, so it's plausible to have the sharp drop on the left. I haven't plotted it for myself, but see for example https://www.researchgate.net/figure/A-plot-of-the-intensity-of-the-radiation-of-a-blackbody-versus-frequency-for-temperatures_fig2_259735413. 14:30, 29 April 2022 (UTC)

Title Text Meaning

As can easily be seen from the page's history, Dgbrt and I have been locked in a minor edit war over the meaning of the title text. I claim that Randall is simply complimenting the readers who happen to know what the formula and curve mean. Dgbrt thinks otherwise; I will let him explain his interpretation.

Please add to this discussion so we may come to a consensus on its meaning. Thanks. --Quicksilver (talk) 23:18, 25 August 2013 (UTC)

Glad to oblige. I think we need to draw a distinction between what Randall means and what some people might like him to mean. Many people don't agree that the universe started with a Big Bang, whether because they're cosmologists who support an alternative scientific theory, or because they're young earth Creationists who hold that God created the universe about 6000 years ago, or because they're philosophers who hold it self-evident that something can't come out of nothing, or for whatever reason.

Now, I'm not going to say which of those (if any) I believe, because it really doesn't matter in this context - and neither is it important (in this context) what Quicksilver or Dgbrt believes. What we have to keep clear in our minds is that this site is about explaining the cartoons, not projecting particular philosophical standpoints onto Randall's mildly ambiguous phrasing. (When he wrote it, I doubt very much whether he realised he was writing ambiguously.)

The xkcd series, throughout its history, shows not only Randall's firm belief in the scientific method for establishing plausible explanations of the way the universe works, but also his antipathy towards historical explanations that seem to be at odds with observable evidence and even historical record. See #803 and #1255 for obvious examples.

Given Randall's known love of science and the absence of any firm clues that he was being heavily ironic and running massively against type, I think we have to conclude that he was either praising those who could identify the science he was talking about, or just possibly was trying to cause a Wikipedia search spike! --BinaryDigit (talk) 07:17, 8 April 2014 (UTC)

So no one's gotten the bonus points yet?! He was asking to identify the science in question. When he says "It works", I'm sure he was not meaning that blackbody radiation works. This graph was the key to one of the biggest leaps in human understanding.--ChrisfromHouston (talk) 06:23, 8 September 2014 (UTC)

He meant that Science in general works. And this is just an example that proves this point. And he has explained what the graph is on his own page in the shop. --Kynde (talk) 20:16, 30 April 2015 (UTC)

Is the description supposed to say 273 Kelvin? I don't see the significance of 2.73 Kelvin.

-- Terry (talk) 23:38, 17 August 2022 (please sign your comments with ~~~~)