“Are we alone in the Universe?”
This is one of the most fascinating questions ever, and I personally ask it to myself every
time I watch the sky at night.
While we cannot give a precise answer to this question yet, you may be surprised to hear
that we may have already received a communication from space… in fact, in 1977, astronomers
detected a signal that may have been sent from an alien civilization!
Do you want to hear more about that?
Watch this video and I will tell you!
Our story starts in 1973, at the Ohio State University, where the radio telescope named
‘Big Ear’ was assigned to look at the sky searching for signs of extraterrestrial
life, as part of the SETI project.
A radio telescope is like a giant antenna able to detect radio waves, the electromagnetic
waves with longest wavelength.
About four years later, on the night of August 15, 1977, something unexpected happened: the
radiotelescope detected a signal that was different from any other previously observed.
The first person who realized this was the astronomer Jerry Ehman, a few days later.
While he was analyzing the data from Big Ear, Ehman observed a sudden jump in the intensity
of the signal recorded by the telescope at 22:16 Eastern Time Zone, on the night of August
15.
The signal recorded by the detector was measured over an interval of 12 seconds, and then printed
out as a single character corresponding to the average of the intensity of the signal
over each interval.
Therefore, the output analyzed by Ehman was a sequence of characters, each of them representing
the average intensity of the signal every 12 seconds.
The characters used in this system were the following: a space indicated a signal intensity
of zero, numbers between 1 and 9 indicated increasing intensity, while signals with intensity
of 10 or above were represented using letters: ‘A’ corresponded to a signal intensity
of 10, ‘B’ to a signal intensity of 11, and so on.
Normally, the printouts analyzed by Ehman only contained a mix of space characters together
with the digits 1 and 2, representing low-intensity signals corresponding to background noise.
However, while checking the data from August 15, Ehman was shocked by finding a sequence
of 6 consecutive characters very different from the rest: ‘6EQUJ5’.
He was so surprised when he found this sequence that he circled it and he wrote the word “Wow!”
next to it: consequently, this signal later became known as “Wow! signal”.
As we said before, each character represents the average intensity of the signal over 12
seconds: so, this sequence of 6 characters corresponds to a signal of 72 seconds in total.
However, this doesn’t mean that the real signal coming from space lasted 72 seconds.
In fact, Big Ear was configured to “watch” towards a fixed direction, relying on the
rotation of the Earth to scan across the sky.
Considering the speed of the Earth’s rotation and the size of the telescope, this means
that Big Ear could observe a given point in space only for 72 seconds.
So the Wow sequence, 6EQUJ5, was recorded during the time window in which the telescope
was observing the region of space where this signal came from.
72 seconds later, Big Ear was already pointing to another portion of sky, and so the signal
disappeared.
The recorded intensity increases in the first half of the sequence (6-E-Q) and then decreases
in the second half (U-J-5), with a peak of 30 at the centre, in correspondence of the
letter ‘U’.
These two facts together mean that the signal observed by Big Ear was continuous, and with
a duration of at least 72 seconds, possibly more.
However, we also know that the signal lasted less than 3 minutes.
In fact, Big Ear consisted of two ‘feed horns’ observing the same portion of the
sky three minutes apart from each other.
The Wow signal, however, was detected by one of the two horns only: if it was longer than
3 minutes, both horns should have observed it.
Where did this signal come from?
Given the design of the telescope, it was not possible to determine which of the two
horns detected the signal, so there is a small ambiguity in the determination of the precise
location.
However, we know for sure that it came from somewhere in the direction of the constellation
Sagittarius, very close to the plane of the ecliptic (which is the plane that contains
both the Sun and the Earth’s orbit).
Ehman and others later tried several times to “watch” again that same portion of
the sky, but the Wow signal was never detected again.
What is so special about this signal, and why is it a possible candidate for an alien
radio transmission?
To answer this question, we need to look at the characteristics of this signal.
First of all, its frequency.
The frequency of the Wow signal is approximately 1420 Megahertz.
This value is very special in nature, because it corresponds to the frequency of the radio
waves emitted by neutral hydrogen gas in space.
Since hydrogen is the most abundant element in the Universe, scientists believe it is
natural for any civilization to choose this frequency to transmit a message into space.
In reality, the frequency of the Wow signal was slightly higher than the frequency of
emission of the neutral hydrogen.
It is possible that this discrepancy is due to a blue-shift.
This is a phenomenon that occurs when the object emitting the signal is moving towards
us: in that case, the frequency of the signal as observed on the Earth is higher than the
real frequency.
If that was the case, scientists calculated that the source of this signal should have
been moving towards the Earth at a speed of 10 kilometres per second, about 36,000 kilometres
per hour.
Although this may seem a huge value, this is very similar to the speed of some of the
space probes that we sent in space.
The two Voyagers, for example, are currently travelling at a speed of just above 15 kilometres
per second.
Another interesting characteristics of the Wow signal is that it is very narrowband.
Generally, natural sources in space emit radio waves across different frequencies: this is
called ‘broad spectrum’.
But this is not true for the Wow signal.
In fact, Big Ear had a receiver containing 50 different channels, each of them able to
detect a different frequency: still, only one channel “saw” the signal, indicating
that it was very narrow and concentrated around a single frequency.
It is interesting to note that this is more similar to the kind of signals emitted by
radio stations for communications on Earth, which are indeed narrowband.
It is not clear what kind of natural source can emit such narrow-band signal.
At this point, one may wonder whether this Wow signal may have actually originated on
Earth, and perhaps reflected towards the radiotelescope by a satellite.
This is very unlikely, essentially for two reasons.
First: the frequency of 1420 Megahertz is a “protected frequency”, because of its
important connection to hydrogen.
This means that no radio communications on Earth are allowed to use this frequency, to
let radioastronomers do their studies without interference.
So it is very unlikely that somebody on Earth was transmitting messages at this frequency
in 1977.
Second: given the shape of the signal detected by Big Ear, scientists calculated that the
source of the signal must have been at least as distant from the Earth as the Moon.
So, even if we assume that somebody broadcasted this message from the Earth at a frequency
of 1420 Megahertz, this should have been reflected by a satellite at least as distant from the
Earth as the Moon: this is very unlikely, since all satellites that we know orbit the
Earth much closer than that.
So, now that we have seen the characteristics of the Wow signal, we may ask: what are possible
explanations of its nature?
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So, what are possible explanations about the origin of the Wow signal?
One hypothesis is that the signal was just a result of an interstellar scintillation.
This is a phenomenon that occurs when radio waves produced by some celestial object are
randomly scattered and amplified by the interstellar medium.
It’s like the twinkling of the light of a star at night when we watch the sky, but
with radio waves instead of visible light.
If that was the case, it is possible that one of the two feed horns of Big Ear was “watching”
the right part of the sky just at the right time, but the signal was no longer amplified
when the other feed horn observed the same patch of sky.
However, this explanation does not entirely convince scientists, especially because such
a signal should have been observed also by the Very Large Array observatory in New Mexico
(already operating at that time), which is much more sensitive than Big Ear to this type
of signal.
Another hypothesis is that the signal is just the result of a gravitational lensing.
According to the theory of general relativity by Einstein, massive objects creates strong
gravitational fields, producing a curvature in the space-time.
As a result, the path followed by light (or any other electromagnetic radiation, such
as radio waves) passing nearby a massive object is not straight, but curved: this phenomenon
is known as gravitational lensing.
So, it is possible that the Wow signal actually came from a different direction than the one
in which Big Ear was observing, and it was quickly gravitationally lensed by a natural
object passing in between.
But this hypothesis doesn’t sound very likely either, because it’s very unlikely that
this effect lasted that briefly, and the signal should have been observed by the second feed
horn as well.
A third possible explanation was proposed more recently, in 2017: perhaps the Wow signal
originated by the hydrogen cloud surrounding two comets, namely 266P/Christensen and 335P/Gibbs,
that were not catalogued at that time yet.
However, scientists are also skeptical about this possibility.
In fact, the two comets didn’t seem to be located in the right direction at the time
of the observation of the Wow signal.
Moreover, it is not clear how they could produce a signal visible in only one of the two feed
horns of the telescope.
As we also explained earlier, any Earth-related origin for the Wow signal seems also not very
likely.
So, what is it?
The truth is, we don’t know.
There are dozens of other possible hypotheses, but none of them sound very convincing to
scientists.
The Wow signal may have been produced by a natural source in rotation around its axis,
so that the signal was pointing in our direction only for a limited time; or a source producing
signals of variable frequency, and so on.
But after all, the most fascinating hypothesis still holds: it is possible that the signal
was not produced by any natural source, and its origin was artificial instead.
If this is the case, we can say that the Wow signal may have been the first successful
communication we ever received from an alien civilization.
And in this case, that short sequence of six characters represents the answer to one of
the greatest questions: are we alone in the Universe?
"This video ends here!
Thanks for watching everyone!
Did you find the story of the Wow signal fascinating?
Do you believe it was really a message sent by an alien civilization, or it was just the
result of some unknown natural process?
Do you want to know more about this topic?
Let me know in the comments below, be sure to subscribe, and I'll see you next time on
the channel!"