# Units used on Voyager golden record

Lojzek
I would like to understand how units of distance, time and mass are defined on
the golden record on Voyager spacecraft.

I suppose the units are similar to natural units (speed of light=Planck constant=1), except that the basic unit is not GeV:

The unit of energy is the energy difference between two lowest states of hydrogen atom. I think the unit of frequency can be calculated from the unit of energy using Planck constant. The unit of time follows from unit of frequency. Unit of distance is the distance traveled by light in one unit of time.
Unit of mass follows from unit of energy and mass-energy equivalence.

Questions:
1. Is the above consideration correct?
2. How big is the energy difference between two lowest hydrogen energy states?
3. Does the length of the line between scheme of two hydrogen energy states on the record have any meaning? How long is it? Is it equal to the unit of distance?
4. Do you know any good links to information about this topic?

## Answers and Replies

Science Advisor
Gold Member
Dearly Missed
This is not a direct answer to your question.
http://en.wikipedia.org/wiki/Pioneer_plaque

You may recall that the earlier Pioneer spacecraft had a plaque depicting a man a woman standing in front of an outline of the spacecraft, a sketch of the solar system, etc.

The 21 cm unit was used. binary numbers were attached to lengths on that plaque, to show scale.

The H hyperfine transition was depicted, to give some physical basis for the 21 cm unit.
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The voyager mission came later, with its "golden record".
I gather that images were encoded on record as well as music.
Presumably some of these images would have displayed units.
As you suggest, some of the units might have been Planck units.
I suppose they might have also used other reference quantities. Perhaps a la Pioneer?

Lojzek
I think I understand the units now.

The unit of distance/the difference between two lowest energy states of hydrogen atoms is:

E0=5.9*10^-6 eV

A quantum particle with this energy has a frequency:

f0=E/h=1.4*10^9 Hz

The unit of time corresponds to this frequency:

t0=1/f=7*10^-10 s

The unit of distance is path traveled by light in this time:

s0=c*t0=0.21 m

The small line connecting the pictures of hydrogen atoms is much smaller than 21 cm, so it's length probably doesn't have any meaning. It seems the unit of distance can only be calculated from hydrogen energy levels.
I wonder why the unit wasn't drawn on the record, since it could easily fit the record size.