August 17, 2019

XKCD Web Comic #1017: Backward in Time (described)

A web comic of romance, sarcasm, math, and language.


[BG note: If you click on the comic panel at the xkcd site, it takes you to a spread sheet that enables you to use the formula.]

Scene: Caption

When I have a boring task to get through–a three-hour lecture, a giant file download, or a long-term goal in fitocracy–I use this formula to convert the percentage completed (p) into a date:

( the formula has a box around it)

T =(Current Date) – (e^(20.3444p^3 + 3)-e^3)years


When the task is 0% done, it gives today’s date, and as I make progress, I move further and further back in time.

(a grayed-out formula in a box)

Inverse: p = sqrt[ln((T+e^3)/20.3444)]

(a timeline)

0% / New 10% /Sept. 2011 30%/1997 40%/1958  50%/1776 60% 405AD 70%/22,000 years ago 80%/671,000 years ago 90%/55 million years ago 100%/138 million years ago


It moves slowly through the past few years, then steadily accelerates. I tuned the formula so the time spent in each part of the past is loosely proportional to how well I know it. This means I hit familiar landmarks with each bit of progress, giving me a satisfying sense of movement.

(Six boxes are stacked in a 3×2 pattern)

Top Left Box: 7.308%/December 18, 2011 Around this time: Kim Jong-Il dies. U. S.  leaves Iraq.

Top Right Box: 31.12% February 1995 Around this time: Windows95 debuts. O J found not guilty.

Middle Left Box: 47.91%/1844 Around this time: Rubber vulcanized, bicycle invented, wrench patented.

Middle Right Box: 70.33%/24,000 years ago Around this time: Caves painted, ceramic art made. Neanderthals extinct.

Bottom Left Box: 90.42%/68 million years ago Around this time: First flowering plants. Chicxulub impact kills off most dinosaurs.

Bottom Right Box: 100%/13.76 billion years ago Around this time: Universe begins. First stars ignite Download complete

Two stick figures are talking. One holds up a laptop and is looking at it  and the other has dark hair.

Person 1: Swoosh! Watching all that time blur past is such a rush!

Person 2: So…you’ve tried to make an extreme sport out of…waiting.

Person 1: Swoosh!

Hover text: People tell me I have too much time on my hands, but really the problem is that there’s too much time, PERIOD.


Warning: This comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors). Comic by Described by BlindGadget under the Creative Commons license

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