Universe Today
Since the 1990s, astrophysicists have known that for the past few billion years, the Universe has been experiencing an accelerated rate of expansion. This gave rise to the theory that the Universe is permeated by a mysterious invisible energy known as "dark energy", which acts against gravity and is pushing the cosmos apart. In time, this energy will become the dominant force in the Universe, causing all stars and galaxies to spread beyond the cosmic horizon.
At this point, all stars and galaxies in the Universe will no longer be visible or accessible from any other. The question remains, what will intelligent civilizations (such as our own) do for resources and energy at this point? This question was addressed in a
recent paper
by Dr. Abraham Loeb - the Frank B. Baird, Jr., Professor of Science at Harvard University and the Chair of the Harvard Astronomy Department.
The paper, "
Securing Fuel for our Frigid Cosmic Future
", recently appeared online. As he indicates in his study, when the Universe is ten times its current age (roughly 138 billion years old), all stars outside the Local Group of galaxies will no be accessible to us since they will be receding away faster than the speed of light. For this reason, he recommends that humanity follow the lesson from Aesop's fable, "The Ants and the Grasshopper".
https://svs.gsfc.nasa.gov/vis/a020000/a020200/a020246/WFIRST_Dark_Energy_Expansion_H264_1080p.webm
This classic tale tells the story of ants who spent the summer collecting food for the winter while the grasshopper chose to enjoy himself. While different versions of the story exist that offer different takes on the importance of hard work, charity, and compassion, the lesson is simple: always be prepared. In this respect, Loeb recommends that advanced species migrate to rich clusters of galaxies.
These clusters represent the largest reservoirs of matter bound by gravity and would therefore be better able to resist the accelerated expansion of the Universe. As Dr. Loeb told Universe Today via email:
Dr. Loeb also indicated where humanity (or other advanced civilizations) should consider relocating to when the expansion of the Universe causes the stars of the Local Group to expand beyond the cosmic horizon. Within 50 million light years, he indicates, likes the Virgo Cluster, which contains about a thousands times more matter than the Milky Way Galaxy. The second closest is the Coma Cluster, a collection of over 1000 galaxies located about 336 million light years away.
[caption id="attachment_138057" align="aligncenter" width="580"]
Diagram showing the Virgo Supercluster. Credit: Wikipedia Commons/Andrew Z. Colvin
[/caption]
In addition to offering a solution to the accelerating expansion of the Universe, Dr. Loeb's study also presents some interesting possibilities when it comes to the search for extra-terrestrial intelligence (SETI). If, in fact, there are already advanced civilizations migrating to prepare for the inevitable expansion of the Universe, they may be detectable by various means. As Dr. Loeb explained:
This paper is similar to a study Dr. Loeb conducted back in 2011, which appeared in the
Journal of Cosmology and Astroparticle Physics
under the title "
Cosmology with Hypervelocity Stars
". At the time, Dr. Loeb was addressing what would happen in the distant future when all extragalactic light sources will cease to be visible or accessible due to the accelerating expansion of the Universe.
This study was a follow-up to a 2001 paper in which Dr. Loeb addressed what would become of the Universe in billions of years - which appeared in the journal
Physical Review Letters
under the title "T
he Long–Term Future of Extragalactic Astronomy
". Shortly thereafter, Dr. Loeb and Freeman Dyson himself began to correspond about what could be done to address this problem.
[caption id="attachment_102586" align="aligncenter" width="580"]
An artist's conception of a hypervelocity star that has escaped the Milky Way. Credit: NASA
[/caption]
Their correspondence was the subject of an article by
Nathan Sanders
(a writer for
Astrobites
) who recounted what Dr. Loeb and Dr. Dyson had to say on the matter. As Dr. Loeb recalls:
At the time, Dr. Loeb indicated that data gathered by the
Sloan Digital Sky Survey
(SDSS) indicated that attempts at "super-engineering" did not appear to be taking place. This was based on the fact that the galaxy clusters observed by the SDSS were not overdense, nor did they exhibit particularly high velocities (as would be expected). To this, Dr. Dyson wrote: "That is disappointing. On the other hand, if our colleagues have been too lazy to do the job, we have plenty of time to start doing it ourselves."
A similar idea was presented in a
recent paper
by Dr. Dan Hooper, an astrophysicist from the
Fermi National Accelerator Laboratory
(FNAL) and the University of Chicago. In his study, Dr. Hooper suggested that advanced species could survive all stars in the Local Group expanding beyond the cosmic horizon (100 billion years from now), by harvesting stars across tens of millions of light years.
[caption id="attachment_139126" align="aligncenter" width="580"]
Artist impression of the 14 galaxies detected by ALMA as they appear in the very early, very distant universe. These galaxies are in the process of merging and will eventually form the core of a massive galaxy cluster. Credit: NRAO/AUI/NSF; S. Dagnello
[/caption]
This harvesting would consist of building unconventional Dyson Spheres that would use the energy they collected from stars to propel them towards the center of the species' civilization. However, only stars that range in mass of 0.2 to 1 Solar Masses would be usable, as high-mass stars would evolve beyond their main sequence before reaching the destination and low-mass stars would not generate enough energy for acceleration to make it in time.
But as Dr. Loeb indicates, there are additional limitations to this approach, which makes migrating more attractive than harvesting.
While this may seem like a truly far-off concern, it does raise some interesting questions about the long-term evolution of the Universe and how intelligent civilizations may be forced to adapt. In the meantime, if it offers some additional possibilities for searching for extra-terrestrial intelligences (ETIs), then so much the better.
And as Dr. Dyson said, if there are currently no ETIs preparing for the coming "cosmic winter" with cosmic engineering projects, perhaps it is something humanity can plan to tackle someday!
Further Reading: arXiv, Journal of Cosmology and Astroparticle Physics, astrobites, astrobites (2)
