# Decode Voyager's Message to Aliens

As a matter of fact, humanity sent a message to aliens with Voyager spacecrafts on 1977. Aliens suppose to decode the message without knowing anything about human race and be able to play attached videodisk.

But is it that simple task for a human? I think this can be an excellent decode-puzzle for you: explain each of 8 pictures from the message.

Click image for better resolution.

Big hint:

According to wiki the message should contain a instructions in binary code, indicate the location of the solar system relative to the 14 powerful pulsars. As a "dipstick" the hyperfine structure of the hydrogen molecule (1420 MHz) is given.

• Ah! This would be very interesting to solve... If I hadn't already seen the "solution" some time ago. My advice is to use the full resolution version of the image to try to solve it... – Narmer Jan 12 '16 at 14:03
• @Narmer, I think all the details is visible there (though small dash can be blur, but you need to know only their orientation). You need to click on the photo or stretch the picture in your browser. – klm123 Jan 12 '16 at 14:14
• Yes, that's exactly why I'm advicing to use the full resolution pic to solve it ;) – Narmer Jan 12 '16 at 14:15
• there was a video on it by vsauce...but i cant recall all the explaination. but as much as i remember, the circle at the upper left shows the way to play this disc. Many kind of songs were stored in it just to show the diversities of our culture. There is a morse code too but not sure why. And hydrogen atom is the fundamental atom so its there too. – manshu Jan 12 '16 at 14:16
• Are we allowed to answer if we already know the explanation? – 2012rcampion Jan 12 '16 at 21:41

# Part 1

This is one of the more difficult parts. This portion of the record is supposed to pictorially represent

the transition between two states of the hydrogen atom: in particular, the two hyperfine levels of the ground state. The difference between the two states is in the alignment of the electron's spin and angular momentum; on the right the two are parallel, and on the left the two are antiparallel.

The transition between these two states happens at a very precise frequency. The bar between the two states is labeled with a | (1), indicating that this frequency defines the units of time used on the rest of the record:

\begin{align}1~\text{TU}&=\frac{1}{1420.4~\text{MHz}}=7.04\cdot 10^{-10}~\text{s}\end{align}

# Part 2

The meaning of these images is relatively simple, they are

top and side views of the record itself, as well as the stylus included alongside the record. They are intended to demonstrate how the record is played.

The dashes are

binary numbers, with | representing 1 and - representing 0. Both encode a duration using the time unit from Part 1.

The number wrapping around the record (|--||----||--|-------------------) represents $9753\times 2^{19}~\text{TU}$, or $3.600~\text{s}$, the duration of one rotation. (This makes it a $16\frac{2}{3}$ record, half the speed of a typical $33\frac{1}{3}$ record.) It is read in the direction the stylus moves over the record (counterclockwise as seen from above).
The number below the side view (||-|----|----------------------------------) represents $139\times 2^{34}~\text{TU}$, or about $84~\text{min}$, approximately the duration of the record. It is read in the direction the stylus moves over the record, from the outer edge to the inside.

The audio contents of the record (which I listened to while writing this) consist of greetings in 55 languages, as well as a couple longer snippets from members of the United Nations; whale song (really!); "sounds of the Earth," including natural sounds (e.g. a thunderstorm), as well as manmade sounds (e.g. a rocket launch); and a variety of music from different cultures.

# Part 3

This part is a schematic depiction of

a TV signal, intended to assist in decoding the images stored on the record.

The first row shows

the signal itself, going from left to right. It begins with a beep (probably a vertical synchronization pulse that separates images), then shows three complete lines and the start of one more. The lines are numbered sequentially, | (1), |- (2) and || (3).

Each line begins with a horizontal blanking interval (low period) and then a horizontal sync pulse, followed by the analog video signal representing the image intensity along that line. The first line is marked with |-||-|--||--------------, $723\times 2^{14}~\text{TU}$ or $8.3~\text{ms}$, the duration of one line. (This is several orders of magnitude slower than ordinary video, whose frequencies are too high to record on a record.)

The second row shows

The horizontal location on the screen, going slowly from one side of the screen to the other during the active part of the signal, and quickly returning back during the blanking interval. I'm not exactly sure what the dots are; possibly they indicate the three color components (RGB) of the video signal, or that the video signal is interleaved?

The third row shows

The scan pattern on the screen. They seem to have interchanged the horizontal and vertical components of the signal, since ordinary TV scans the lines horizontally, not vertically. The two numbers (|--- and |---------) indicate the 8 lines shown, and the total of 512 lines per frame.

Finally, the fourth row shows

The first image on the record: a circle (meant as a test pattern).

The images on the record start off with basic mathematical definitions (Arabic numerals in base-10, addition, and fractions); then basic units (including centimeters, meters, and kilometers, seconds, days, and years); a schematic of the solar system; and finally a wide range of humans and human activities. (I based one of my puzzles off of the beginning part of the record's message, actually!)

# Part 4

This is another hard one. The spiky object on the lower-left depicts

A map of the solar system's location relative to a number of pulsars. A pulsar is a class of neutron star, the ultra-dense remnant of a massive supernova. When the neutron star forms, it retains the angular momentum of the original star; but since it is so small (on the order of 10 kilometers), this means that it spins very fast (think of a figure skater pulling in their arms when they spin). For example, the Crab pulsar spins at around 30 rotations per second! A pulsar has a "hot spot" that comes into view once per rotation, so the star appears to flash very quickly. Since neutron stars are still around five times as massive as the Sun, their rate of rotation is very stable over time. This allows us to use them as "beacons," identifiable by the frequency of their flashes.

The lines emanate from the solar system at the center, and represent the relative distance and direction to various pulsars. The numbers on each line encode the period of the pulsar's rotation. In most images of the record it's hard to make out the map very well, so if you're interested in more details about it you should look at this page (in which the author shows that it is possible to use the map to determine very accurately not only the position, but also the date at which the map was produced).

• Yes, the dots in part 3 indicate that the video is interlaced. – squeamish ossifrage Jan 13 '16 at 20:48
• Please explain -- how does a shift in the even line[s] (presumably due to the shortened sync pulse) indicate interlace, and why would you interlace still images anyway? (is the raster an analog luminance?) – amI Nov 23 '18 at 6:11