Title text: Bonus points if you can identify the science in question
This comic is available on a t-shirt from the xkcd stores.
On the front of the t-shirt it says
- It works, bitches."
And on the back of the t-shirt is the drawing of the graph from the comic (with a little more details, and without the text written on the front of the shirt)
On the xkcd store there is both an explanation for the title:
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.
And specifically an explanation for the graph:
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.
The only Wiki link that was actually part of the original text on xkcd in the above two excerpts (which are direct copy paste, with possible errors), is the one to the COBE mission. But the link on xkcd is now "broken" since there are now several other wiki pages with COBE in them.
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 written as "v" and the temperature T is included in "I(f)" so it becomes "I(v,T)", but it still represents the energy density. For the record, 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 GHz (Giga (or billion) Herz). 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 in fact the universe at the point when it had cooled down enough to allow photons to escape, and the fact that this light is now in the microwave range is due to the extreme redshift which becomes stronger the further apart astronomical objects are from each other, due to the expansion of the universe; The back-ground radiation "light" has been traveling since "close" (380,000 years) to the beginning of the universe, so that which is reaching us right now came from very far indeed (13.8 billion light years minus the 0.00038 billion light years, so it was pretty close in comparison).
The title text praises viewers who can identify where this equation and corresponding graph come from (without consulting this wiki, of course).
- [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 point, which the curve fits perfectly. The Y-axis are labeled. Along the X-axis the zero point and the frequency where the peak has it's maximum are labeled 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.
- This is the 48th comic originally posted to livejournal. The previous comic was 50: Penny Arcade, the next is 51: Malaria.
- This comic is available on a t-shirt at the xkcd store.
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