THE SOUTHWORTH PLANETARIUM 207-780-4249 www.usm.maine.edu/planet
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70 Falmouth Street Portland, Maine 04103 43.6667° N
70.2667° W Altitude: 10 feet below sea level Founded January 1970 Julian
Date: 2459361.18
2020-2021: CXXXVII
THE DAILY ASTRONOMER
Wednesday, May 26, 2021
How Aliens Will Find Earth
__________________________________________________________
*A hopefully helpful primer: Binary numbers*
Consider this a brief primer on binary numbers, which is a base two system
In the base 10 system, a single digit represents numbers 1 - 9. The next
number after 9 is 10, which requires two digits.
In the base 2 system, the first number after 0 is 1. The next number is
10, which equals 2, in our base two system. The next number in binary
is 11, which equals 3 and then 100, equivalent to 4. 101 is 5, 110 is 6,
111 is 7, 1000 = 8; and so forth.
The binary system is the simplest of them all and is likely to be known to
other races around the galaxy....we think
________________________________________________________________
*"If aliens do capture a Pioneer probe, how will they know its solar system
of origin?" '*
The strange thought arrived, appropriately, on a night so crystal clear,
even the diffuse Milky Way seemed distinctly luminous. While admiring
the boundless, I suddenly thought of the Pioneer 10 and 11 probes traveling
inexorably away from Earth. They are now approaching the heliosphere (the
'bubble' enclosing the solar system) and are destined to continue soaring
through the infinitude for millions, if not billions of years, provided
they either don't collide with anything or aren't eventually captured by an
alien race.
Perhaps they won't have any idea from which star system the probe was
deployed. It could be like one of the translucent wraiths that suddenly
dive out from the clouds, leaving only mocking laughter behind.
This question proved so bothersome, that I sought and found an answer.
Unfortunately, though the basic idea is simple, the devil and 90% of all
its nastiest minions were in the details.
The simple idea is that the Pioneer probes each contain a golden record on
which a "pulsar map" has been inscribed. This map shows the position of
the Sun relative to fourteen pulsars located throughout the galaxy. It
also shows the distance of the pulsars from the galaxy's center. The map
designers, including radio astronomer Frank Drake of SETI fame, obviously
hoped that any extra terrestrial race would be able to pinpoint the Sun's
location simply by noting the positions of these pulsars. Refer to the
following image to see this map. After the image, we'll delve deeply into
the details.
[image: cid:image002.jpg@01D21BFB.1ECB31E0]
*"The Pioneer Plaques."** The Pioneer 10 and 11 probes each contain a
golden record onto which the images above have been etched. At the upper
right,*
*two conjoined circles depicting the two lowest states of the hydrogen atom*
*(explanation in the article). Just under these circles -and to the left
of the*
*Abercrombie and Fitch sales associates- is the pulsar map, which shows*
*the Sun's location relative to 14 different pulsars. An outline of the*
*Voyager probe is in the background, so as to show the average size of
humans relative to the vessel. The Solar System is drawn at the bottom.
It points to the planet from which the probe originated. *
Pulsars are rapidly spinning neutron stars. They are formed when some
highly massive stars explode as supernovae. (Other highly massive stars
leave black holes behind when they explode.) Pulsars spin very quickly
and with periods so precise they can serve as highly accurate clocks.*
Moreover, pulsars have different rotation rates, so they all are
distinctive and can serve as galaxy markers. For instance, let's assume
you're standing in a wide field which contains hundreds of weird tops
spinning at different rates. We could pinpoint your precise location if
you told us your distance from the nearest tops and the rates at which
these tops spin. It would work the same way if you were floating in space
and could somehow tell us the spin rates of nearby pulsars and your
distances from them.
However, dire complications arise when trying to communicate this
information to aliens. First of all, aliens most likely don't speak
English (unless they're Star Trek aliens who speak a highly cultivated form
of English that we can't understand, anyway.) Also, their time keeping
system is most assuredly different from ours. Seconds, minutes and hours
are specific to our cultural history and are not universal throughout the
galaxy. We know how quickly pulsars are spinning when measured in
seconds. How can we specify the spin rates of these pulsars so that alien
beings who are neither conversant with any human language nor our
horological system will understand it? The key is at the upper right hand
corner of the above image: those two circles represent the two lowest
states of the hydrogen atom. Here, the circle represents the single
proton within the hydrogen nucleus. Astronomers assume that aliens will be
familiar with hydrogen, as it is the most abundant element in the
Universe. They will also know that a hydrogen nucleus contains precisely
one proton.
We say that these circles represent "neutral hydrogen." Now, without
descending four fathoms deep into these details, scientists know that when
an electron within this neutral hydrogen atom goes through an energy level
transition, it will emit a specific type of radiation at a frequency of
1420 MHz (1 Hz, or one Hertz, is one cycle per second; 1 MHz, or one
mega-Hertz, is a million cycles per second.) This atom serves as the
time keeping standard because each pulsar spin rate can be specified
according to this radiation frequency. Yes, of course we'll explain:
First, many astronomers assume that this atom will be of particular
significance to other races, just as it is to us. Hydrogen is not only
the Universe's most abundant element, but it is also one of the two
constituents of water. Water is essential to Earth life. Nothing
survives without it. Many astrobiologists assume that extra terrestrial
races will be just as reliant on water as we are and will recognize the
neutral hydrogen atom in the double circles. Now, if the aliens realize
that we're etched a neutral hydrogen atom on the record, perhaps they will
also know about the frequency of this radiation. After all, some
scientists believe that it is along this wavelength that civilizations
around the galaxy will exploit for communication.**
So, let's assume they know these circles represent the hydrogen atom and
also surmised that the significance of the atoms is the emitted radiation.
Well, we can then specify the rotation speeds of each of the 14 pulsars
relative to the frequency of this atom. Of course, we can't use 1420
MHz, itself, because that number is based on cycles per second. We've
already established that the aliens will not be familiar with seconds.
They will be familiar with the amount of time required for this emission of
radiation to complete one cycle, which is 7.04024183647 x 10-10 sec. (Or
0.000000000704024183647 second) That is not a particularly long time.
However, this time was chosen as the "clock," because the duration of one
cycle will be the same for them as it will be for us or anybody else.
So, a pulsar's spin can be measured as multiples of this cycle.
Perfect time for an example.
One of the pulsars, J1731-4744, has a period of 0.8296830003 seconds.
The amount of time required for one rotation therefore equal to 1178486506
cycles of this radiation. ( One can derive this value by dividing
0.8296830003 by 0.000000000704024183647.) One might notice the precision
of these values. Pulsar J1731-4744 is the only one which has this
rotation period. The other 13 pulsars also have unique rotation periods
and so can be readily identified by them. Moreover, each pulsar point
also includes the pulsar's distance from the galactic center.
Here, unfortunately, we encounter another complication -and it won't be the
last. These numbers derive from the base-ten system, which is specific to
our culture. (Remember that the Babylonians used a base-60 system, which
explains the 360 degrees in every circle.) We cannot assume that aliens
will know the base 10 number system anymore than they would know seconds,
minutes or hours. Moreover, they certainly won't know the Arabic
numerals such as 1, 2, 3.... Instead, the map designers indicated
the periods in binary notation. We've stuck the catacombs bit in the
article now for those who need information about binary numbers
The pulsar map shows the frequency of each pulsar expressed in binary
notion. Also, the length of the lines specifies the pulsars distance
relative to the Sun. We're supposed to be in the center of the cluster.
(See image below)
*The Pulsar mapThe lines show the distances of the pulsars relative to the
Sun and each line contains a binary representation of the pulsar's
frequency in terms of the cycle of radiation from that special neutral
hydrogen atom. This map has also been printed on the golden record that
was placed on each Voyager probe.*
Therefore, if the aliens know that the lines represent the distances of
these pulsars from the Sun and if they know that we have printed the binary
representation of their rotational periods relative to the neutron hydrogen
atom radiation emission. And, if they even know the fourteen objects are
pulsars, then, perhaps, just maybe, they'll realize that we're trying to
tell them where in the galaxy they will find the solar system from which
the probe was deployed.
Now, we realize that people stopped reading this article about ten
paragraphs ago, but we have still other complications. One, the pulsars
and our solar system are all moving through outer space and by the time any
alien finally captures a probe, these pulsars and the Sun will have moved
relative to the galactic nucleus and two each other. Moreover,, the spin
rates will have all decreased in that time period. And, a long time,
indeed, might elapse. Mission scientists estimate that the Pioneer probe
will swoop by Aldebaran, in Taurus the Bull, in about two million years.
Even this encounter won't exactly be a close one, Steven. The
hope is that the aliens will know the map depicts pulsars and will be able
somehow find a few of them and will be able to extrapolate back in time the
spin periods of these pulsars and will then know where they were originally
because they will also know the space velocities of all of them..
The astronomers who designed this map made quite a few assumptions about
the aliens who might one day capture the probes and decipher the plaques
that have been attached to them. Even the most optimistic scientist
acknowledges that they won't be able to know our origin precisely.: maybe
within 10 - 20 light years. Of course, if the plaques are found hundreds
of millions of years in the future, then the pulsar map will be no good
whatsoever.
How will the aliens find us?
Well, if they are using the Pioneer plaques to search for us, they probably
won't. That might be to our benefit, especially if the aliens are well
armed and have severe anger/frustration issues.
*Some millisecond pulsars -those that complete more than a thousand
rotations a second- have proven even more chronologically accurate than
atomic clocks.
**Frake Drake and Phillip Morrison, the two SETI pioneers suspected that
this hydrogen line would serve as the Moroccan bazaar of the Milky Way
Galaxy. All the races, being all dependent on water, would choose this
frequency for their communications, Hydrogen pervades the galaxy and this
frequency is neatly tucked away in a "quiet" zone within radio. This
assumes that the race is using radio for its communication, that it is
dependent on water and that they are thinking like we're thinking, which is
a bold assumption because we don't know they exist and they presumably
don't know we exist, or if they do know we exist, they're not trying to
communicate with us and, like the downcast lover who looks longingly at the
phone that hasn't rung once for 62 hours, 23 minutes and 12 seconds -not
that he's counting-, maybe we should stop trying and find another hobby.
Here, we can see the complications inherent in talking to
extraterrestrials of unknown mind, body, location, inclination or even
existence.
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