One of the most challenging aspects of astrobiology and the search for extraterrestrial intelligence (SETI) is predicting what extraterrestrial life and civilizations will look like, the report says. www.universetoday.com.
Invariably, we only have one example of a planet that supports life (Earth) and one example of a technologically advanced civilization (humanity) on which to base our theories. When it comes to more advanced civilizations, which seems statistically more likely, scientists limit themselves to forecasts of our own development. However, these same projections place limits on what SETI researchers should look for and provide clues about our future development.
In a series of articles led by the Blue Marble Space Institute of Science (BMSIS), a team of researchers examines what the level of technological development of the Earth (the so-called “technosphere”) will look like in the future.
In the latest installment, they offer a reinterpretation of the Kardashev Scale, which suggests that civilizations expand to take advantage of greater levels of energy (planet, host star, and galaxy). Instead, they suggest that the Kardashev Scale sets upper limits on the amount of stellar energy a civilization can harness (the “luminosity limit”), and that civilizations can circumvent this by directly exploiting stellar mass.
As with the previous study in this series, the study was led by Jacob Haqq-Misra, senior researcher at the Blue Marble Space Institute of Science. The paper “Projections of the Earth's technosphere: luminosity and mass as limits to growth” is under review for publication in the journal Acta Astronautyka.
The Kardashev scale, named after the Soviet-Russian astrophysicist and radio astronomer Nikolai Kardashev (1932–2019), was first proposed in his seminal paper “Transmission of Information by Extraterrestrial Civilizations” published in 1964.
In it, Kardashev suggested what types of radio frequencies (and at what energies) scientists should look for to detect possible extraterrestrial civilization (ETC) transmissions. Consistent with the idea that there may be civilizations billions of years older than humanity, he concluded that these civilizations could harness energy levels beyond human capabilities.
To characterize the level of development of ETCs, Kardashev proposed a three-level scale based on the amount of energy they can exploit.
However, this scale reflected the assumption that civilizations and their energy needs would grow exponentially. This is consistent with observations of humanity's “technosphere,” which refers to human-made infrastructure, machines, communications, and other signs of technological activity (aka “technosignatures”). This essentially reflects our confined perspective when it comes to the types of behaviors that advanced ETCs exhibit. As Haqq-Misra told Universe Today via email:
“Earth is our only known example of a technology-enabled planet, so the search for extraterrestrial civilizations must begin by considering how to look for analogues to Earth's technosignatures today and possible technosignatures that may emerge in Earth's future.
We should also try to stretch our minds to consider other, extraterrestrial and more exotic possibilities, but even such imaginations will always either start with (or contrast with) what we know is possible based on existing or known physics on Earth. . “
Traditional applications of the Kardashev Scale predict that growth will be exponential, and it has even been contemplated how this could lead to a civilization capable of harnessing the energy produced by all the stars in the Universe – a Type IV space civilization!
This application has motivated many searches for civilizations that have achieved the scale of enormous energy use, as indicated by megastructures (e.g. Dyson Spheres, Clarke Bands, etc.) and other advanced technospheres. In their research, Haqq-Misra and his colleagues took a different approach:
“Our study re-examines these assumptions, noting that civilizations may follow different trajectories for their expansion in space and energy consumption. This involves a trade-off between “exploration” and “exploitation”, and there are many opportunities for civilization to develop in these two dimensions.
“Some civilizations can prioritize physical-distance exploration without having to increase energy consumption to the Kardashev scale of Type I or II. Other civilizations may focus on exploitation and increase energy consumption more locally. Some civilizations may try to find the optimal balance between exploration and exploitation.
“We also point out that the Kardashev scale is better treated as the theoretical limit of a civilization using the energy of stars (luminosity). Rather than describing the trajectory that advanced civilizations will follow, the Kardashev scale represents an upper limit on a civilization's energy consumption as it relates to increasing physical distance, but a limit that may never be reached due to limits on thermodynamic efficiency.
“In other words, the Kardashev scale describes the upper limit of the trade-offs between exploration and exploitation, and a civilization that depends on the luminosity of stars for its energy needs will always fall below the energetic and spatial limits described by the Kardashev scale.”
The scenario proposed by Haqq-Misra and his colleagues presents several new and interesting possibilities for advanced civilizations. Suppose, for example, that humanity ever reaches a limit on the amount of energy it can extract from our Sun. In this case, it may decide not to explore and settle other star systems (with the intention of using the energy of more planets and stars). Instead, they can start collecting the stellar mass itself.
“Such star-consuming civilizations, which we call 'stellivores,' would be able to enhance their energy consumption beyond the Kardashev scale luminosity limits,” Haqq-Misra said.
“As a civilization on Earth, we are not yet at that level, but we can at least think about the possibility that accumulating mass and converting it into energy (as described by Einstein's famous equation) will enable civilization to achieve scales of energy use beyond those predicted by the Kardashev scale.”
Like all predictions about future human development, this study also has implications for future SETI research. This is consistent with the assumption that ETCs in our galaxy would be older and more advanced than humanity at this point.
It is also consistent with the principle that “if we can imagine it, someone has probably already done it.” As Haqq-Misra explained, future SETI studies should study “accretionary binaries,” closely orbiting binary stars whose mass flows from one star to another.
Maqq-Misra and his colleagues recommend that scientists monitor accreting binaries for abnormal behavior that could indicate technological activity:
“If some civilizations do evolve into carnivores, then some of them may look like such accreting binaries. We cannot claim that all or even most accreting binaries are actually technological civilizations, but we also cannot rule out the possibility that some of them may actually be technological in nature. It's worth keeping an open mind and actually looking for such evidence of advanced and exotic civilizations, rather than ruling them out before we start looking.”
Image Source: Pixabay.com
