10
A. Balbi and M. M. ´
Cirkovi´ c
for locations within the Milky Way. For example, one can think of an electromagnetic signal of some sort emitted from a location a thousand light-years from the
Sun: if such communication ceased before a thousand years ago, we cannot observe
it any more. This implies that any technological civilization of which we might find
empirical evidence must either be very long-lived or almost coeval to ours [3, 4].
It also implies that the chances of discovering intelligent life outside Earth depend
on how life was distributed in time over the course of cosmic history. If we are
latecomers, and most other civilizations went already extinct, we may now be alone.
Otherwise, if life only started appearing very recently, and the universe is waking
up right now, we may be just one of the many examples of infant technological
civilizations.
Relaxing the assumption of our temporal typicality can also impact interpretations
of the so-called Fermi paradox, i.e. the apparently puzzling fact that we have not
encountered any evidence of advanced civilizations in the universe. If the universe
was not as life-friendly in the past as it is today, then the puzzle can dissolve, or at
least be mitigated. In general, evaluating the outcomes of SETI searches, or even
interpreting negative results, needs to assume a knowledge of how the propensity
for life of our universe changed over time, a perspective that is inseparable from the
historical and evolutionary aspects of the cosmological scenario.
2.4 Conclusions
We have outlined a few reasons that make the definition of average temporal conditions problematic in cosmology and astrobiology. Such problems should suggest
the adoption of a more modest, deflationary account of temporal Copernicanism:
we cannot really say whether we are living in a typical cosmological epoch and we
should therefore refrain from assuming our typicality in this respect and deriving
any conclusion from such an assumption. This, of course, does not mean abandoning Copernicanism in general, or, even worse, adopting a ‘chronocentric’ view of
the universe, revolving around the present epoch. Typicality in time can still be welldefined by focusing on subsets of the history of the universe where we might expect a
reasonably uniform behavior of some variable quantity relevant to the problem under
investigation. For example, when discussing the chances that life evolved on other
planets, one might restrict the time interval only to the period when star formation
rate is around its peak value (the so-called ‘stelliferous’ era). But this is precisely
the main caveat introduced in [9], that we summarized here: there is no straightforward way in which our typicality in time can be assumed, without accompanying the
assumption with some knowledge of the temporal evolution of key factors involved
in the habitability of the universe and in the appearance of life. So, at the very least,
further work would be necessary to understand the complicated variation in time of
the conditions that make the presence of observers possible.
A. Balbi and M. M. ´
Cirkovi´ c
for locations within the Milky Way. For example, one can think of an electromagnetic signal of some sort emitted from a location a thousand light-years from the
Sun: if such communication ceased before a thousand years ago, we cannot observe
it any more. This implies that any technological civilization of which we might find
empirical evidence must either be very long-lived or almost coeval to ours [3, 4].
It also implies that the chances of discovering intelligent life outside Earth depend
on how life was distributed in time over the course of cosmic history. If we are
latecomers, and most other civilizations went already extinct, we may now be alone.
Otherwise, if life only started appearing very recently, and the universe is waking
up right now, we may be just one of the many examples of infant technological
civilizations.
Relaxing the assumption of our temporal typicality can also impact interpretations
of the so-called Fermi paradox, i.e. the apparently puzzling fact that we have not
encountered any evidence of advanced civilizations in the universe. If the universe
was not as life-friendly in the past as it is today, then the puzzle can dissolve, or at
least be mitigated. In general, evaluating the outcomes of SETI searches, or even
interpreting negative results, needs to assume a knowledge of how the propensity
for life of our universe changed over time, a perspective that is inseparable from the
historical and evolutionary aspects of the cosmological scenario.
2.4 Conclusions
We have outlined a few reasons that make the definition of average temporal conditions problematic in cosmology and astrobiology. Such problems should suggest
the adoption of a more modest, deflationary account of temporal Copernicanism:
we cannot really say whether we are living in a typical cosmological epoch and we
should therefore refrain from assuming our typicality in this respect and deriving
any conclusion from such an assumption. This, of course, does not mean abandoning Copernicanism in general, or, even worse, adopting a ‘chronocentric’ view of
the universe, revolving around the present epoch. Typicality in time can still be welldefined by focusing on subsets of the history of the universe where we might expect a
reasonably uniform behavior of some variable quantity relevant to the problem under
investigation. For example, when discussing the chances that life evolved on other
planets, one might restrict the time interval only to the period when star formation
rate is around its peak value (the so-called ‘stelliferous’ era). But this is precisely
the main caveat introduced in [9], that we summarized here: there is no straightforward way in which our typicality in time can be assumed, without accompanying the
assumption with some knowledge of the temporal evolution of key factors involved
in the habitability of the universe and in the appearance of life. So, at the very least,
further work would be necessary to understand the complicated variation in time of
the conditions that make the presence of observers possible.