In
2007 astronomers detected a new class of radiation signal from deep
space – what are called fast radio bursts. Fast radio bursts are
highly energetic but very short-lived bursts of radio energy,
typically lasting less than a hundredth of a second. Fewer than
twelve of these bursts have been detected. For years, all of the
detections came from a single telescope in Australia, but now the
Arecibo Observatory in Puerto Rico has also detected such a fast
radio burst.
Where
are the signals coming from? Based on something called dispersion
measures, an astronomer named Dan Thornton estimates that the signals
come from between five and ten billion light years away. But other
astronomers disagree. One team of astronomers estimates that the
signals are coming from nearby stars inside our galaxy. But their
reasoning is based on a “5% coincidence” argument that isn't very
convincing (considering that 5% coincidences are not very
improbable).
Based
on the number of fast radio bursts that have been detected,
astronomers have estimated that our planet could be receiving as many
as 10,000 of these radio bursts per day. What could be causing the
signals? Astronomers don't know. Some astronomers speculate that the
fast radio bursts could be caused by various exotic types of stellar
events, such as unusual solar flares or two neutron stars
colliding with each other.
There
is, however, a general problem with such explanations. A scientific paper on the fast radio bursts says this (which I'll “translate”
in a moment):
Let
me clarify this rather opaque comment. The highly energetic freak
events imagined as the source of the fast radio bursts would probably
have produced other types of radiation such as gamma ray radiation,
x-rays, or visible light. But no one has detected a flash of any of
these types of radiation with a position in space (and time of
origin) matching any of the fast radio bursts. To give an analogy,
it's kind of as if you felt the ground shaking, and assumed it was
something heavy falling to the ground, but you didn't hear any noise
at the same time. That would throw doubt on your explanation.
The
same paper discusses various theories to explain the fast radio
bursts. The paper mentions the possibility of neutron star mergers
(two nearby neutron stars interacting with each other), but it notes
that this extremely rare phenomenon would not occur often enough to
explain the estimated occurrence rate of the fast radio bursts. The
paper also notes the hypothesis of black hole evaporation being the
source of the fast radio bursts, but notes that the expected energy
from such an event would be much less than the energy coming from a
fast radio burst. The paper notes that there is no way to get a fast
radio burst merely from a core-collapse supernova event, but says that
conceivably if a supernova was next to a neutron star, it might
produce a fast radio burst. But a supernova occurs only about once
every 50 years in our galaxy, and a supernova very close to a
neutron star is very, very rare – probably too rare to explain the
phenomenon.
In
short, we seem to have no really good astrophysical explanations for
the fast radio bursts. Given the fact that short radio bursts have
been postulated as one means by which extraterrestrial civilizations
could announce their existence, there would seem to be a very real
possibility that some or many of these short radio bursts are coming
from extraterrestrial civilizations.
Hypothetical extraterrestrial radio transmitter
I
may note that even if the signals are coming as far away as five
billion light years, that does not rule out the possibility that they
are artificial signals from extraterrestrial civilizations. The
universe is believed to be about 13.7 billion years old. If a radio
signal came from five billion light-years away, it would have come
from a time when the universe was about 8.7 billion years old. Was
there enough time for intelligence to appear by that date? There
might well have been. Recent telescopic observations show that when
the universe was only a few billion years old, it already had
surprisingly mature galaxies. We know of no reason why intelligence
could not have arisen in other galaxies between five and seven
billion years ago.
I
may note the astonishing difference between the way astronomers have
reacted to two different cases of unexplained new radiation
observations: the fast radio bursts and the b-mode polarization
signals detected recently by the BICEP2 team. The two cases are quite
similar in some respects. In both cases we have a type of signal
observation that might be explained through a relatively mundane
explanation, and which might also be explained by imagining something
monumental. In the case of the fast radio bursts, the mundane
explanations are things like solar flares and star collisions, and
the monumental explanation is to imagine deliberate signals from
extraterrestrial civilizations. In the case of the b-mode
polarization observations, the quite plausible mundane explanations
are things like cosmic dust, synchrotron radiation, and gravitational
lensing; the monumental explanation is to assume something coming from cosmic inflation in the universe's
first second.
In
the case of the fast radio bursts, astronomers have reacted with the
greatest caution and circumspection. Their accounts merely report the
observations, without speculating about any possible monumental
explanation. In the case of the b-mode polarization signals reported
by the BICEP2 team, astronomers and cosmologists instantly threw
caution and circumspection out the window, and enthusiastically
jumped the gun by calling the signals proof of cosmic inflation,
seemingly before the public had even had time to scrutinize the
scientific paper. I suspect that this case will be recorded as one of
the great cases of over-enthusiastic gun-jumping hype, similar to the
1990's “life on Mars fossils” announcement that didn't pan out. A
few weeks after the BICEP2 announcement, a scientific paper appeared
reporting that a certain type of cosmic dust (not considered by the
BICEP2 team) could be the source of their observations.
Can
we imagine if astronomers had reacted to the fast radio bursts the
way they reacted to the findings of the BICEP2 team? In that case
they would have announced we had received the smoking gun of alien
civilizations.
What
is the proper way to consider both of these cases? An intelligent
outlook is to say that some interesting signals have been discovered,
and to cautiously note the fact that they could possibly be due to an
epic, monumental explanation – while at the same time saying that
the matter is very much undecided, because the universe has a
thousand surprises up its sleeves, because there are almost always a dozen
different ways to explain any very distant thing we see in our telescopes,
and because our knowledge of the universe is shaky and fragmentary.
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