There's certainly not a lack of theories about the end of the world. You can find completely unbelievable ones, or some that start with a scientific fact but blow it out of proportion. For example, just last week I had to reassure my mom that she had been the victim of one of the wacky ones in a TV show mysteriously named “Infinito abre tu mente” (infinite-open-your-mind). A pseudo scientist was claiming he’d discovered the five stages of the universe, and that it’d end in a reverse Big-bang 100 millions years from now, when we’d all end up as deconfined protons. However, a couple of weeks ago I also ran across a much more plausible ending for life as we know it, and thus I quote from a non other a source than Science magazine [1]:

"Only 7.6 billion years from now, it'll be the end of the line for Earth. Two astronomers who suggested that our planet might escape the fireball as the dying sun expands have changed their minds: Earth will be engulfed and vaporized after all. In 2002, Robert Smith of the University of Sussex in the U.K. and colleague Klaus-Peter Schroeder calculated that a strong solar wind would eventually reduce the sun's mass, weakening its gravitational hold on Earth. The planet would then drift outward far enough to remain intact. But since then, Schroeder, now at the University of Guanajuato in Mexico, has revised the stellar mass-loss formula that astrophysicists have been using for decades. The new formula shows that the sun's gravity will be stronger than he and Smith thought [....] The results spell ultimate doom. None of this matters much to human beings: Increased solar radiation will turn Earth into a lifeless rock about a billion years from now."

Billons of years sound un-human, but I have to admit the article caught my attention, in part because I didn't know more radiation from the sun was the next threat our beloved star would present us with. Also because I realized it's never too early to consider the fate of mankind, especially if our doomsday is predicted by such a well established theory as that of stellar evolution (we are certain the sun will grow incredibly large in its way to become a red giant).

Thus, I dug the paper from Smith & Schroeder [2], and to my surprise I found they only considered a linear and stable problem, i.e. they don't allow for chaotic solutions to the problem (please bear with me if this gets a little too technical). My preliminary calculations demonstrated the adding a perturbative term to their description of the tydal interaction of the sun (eq. 1), we could possibly set the orbit in an unstable solution of the 4 dimensional (space + time) Riemann manifold of allowed solutions for the gravitationally bound motion. In simple terms, we'd separate the Earth from the Sun.

My calculations also hint at an amplification of the effects if the perturbation is applied at a moment when the innermost planets are aligned, which also gives the possibility to, at least in first order, chose the direction of the path the Earth would follow in its trip away from the solar system (circumstantially, this could be the first time the discipline of Astrology has direct incidence in mainstream science, since astrologers have perfected the art of predicting planetary alignments during the ages).

However, this solution to the problem also illustrate why the urge to tackle this problem now: the sudden perturbation I considered, and the only one large enough I can think of, corresponds to the act of vaporizing the Moon through a nuclear explosion. That has been estimated to require the equivalent to a 179 GigaTon nuclear weapon [3], which would consume about two thirds of the estimated Uranium reserves that exist in geological deposits (5.70 x 10^14 grams of U [4]) . In an age where considering the future energy needs of humanity means thinking about how many degrees the global temperature will rise in the next century, or whether we'll run out of oil in 40 or 50 years, we have to start acting now to create the social conscience to provide generations to come with enough resources to address such an extreme situations.

A less severe solution might involve using a gigantic solar sails - radiation reflecting devices that have already been proposed as a propulsion mechanism for spaceships [5][6]. Considered the expected increase of the solar wind in a billion years, this could be an alternative way to get unlocked from the Lagrangian orbit that ties us to the sun, sparing the Moon in that way. The Moon could be a heavy piece of luggage to carry with us, but it could prove to be a useful one in the unfortunate case that at the end of our journey we find ourselves in a collision course towards our new home star (the same chaotic mathematics that make our escape possible make it almost impossible to exactly predict the orbit we'd fall into). Also, it is easily demonstrated that a solar sail of ~10^13 square meters could provide enough acceleration to reach a escape velocity of ~0.001c. Such speed would put within our reach several stars in the solar neighborhood: it would take 'only' 100 thousand years for the journey to a star 100 light years away. Such an interstellar trips would certainly have some tough requirements. For example, if we assume in the future everybody adapts an Italian lifestyle where population growth is almost negligible and we limit ourselves to 4 billion inhabitants for our planet, then a diet based on pasta (500 kcal= 1 rammen noodle+tablespoon of butter) would require that we pack 1.2x10^18 packages of rammen noodles for the trip. A tough upper limit, which again serves as an illustration of the daunting task ahead, and why, once again, we as scientists in a globalized civilization have a moral obligation to create awareness of the big tasks facing humanity, and direct the vision of our human race beyond the mundane woes that currently distracts our most gifted minds.

A paper with the details of this analysis will be published soon [7], but I thought this is a good venue to start discussing the subject and bring together people from different fields in the interdisciplinary approach we'd certainly need to resolve this issue. We are also currently working in the creation of a group in modern social networking tool to increase awareness in such issues: be ready to join “1,000,000 strong for Earth Space Travel!” on facebook....

Stars in the solar neighborhood.

[1] "Out of the Frying Pan", Science Vol. 319. no. 5869, (2008) p. 1465
[2] Schröder, K.-P.; Connon Smith, Robert, “Distant future of the Sun and Earth revisited”, Monthly Notices of the Royal Astronomical Society, 2008
[3] “Satelite deconfinement by nuclear techniques”, J. K. Lopez, Jour. of Pyrotech. 234 (2003) 1456.
[4] “Lanthanides in submersive tectonic plates”, Jong-il, K. et al., IX Proc. of the Soc. of Metal Hunters (1985).
[5] “Reflexion and Thermal Properties of Sails for Solar Sail Spacecraft”, Michaela Benda, 55th International Astronautical Congress of the International Astronautical Federation (2004)
[6] A New Scientist article: http://www.newscientist.com/article/dn3895-solar-sailing-breaks-laws-of-...
[7] A. Estrade and J. Montero Castillo, to be published, Perpetuus Motus Machinae Ephemeridis (2008).