Today the much-hyped film, “The Fourth Kind,” debuts in
theaters with a predictable poster of a pair of other-worldly eyes staring out.
Sci-fi film buffs will remember Steven Spielberg’s sappy
1977 film “Close Encounters of the Third Kind” where flying saucers outfitted
with disco lights buzz lone cars and farmhouses, and in a messianic ending aliens
carry a few chosen people skyward in a “mothership” that looks more like a
chandelier.
“The Fourth Kind” goes one step further and supposedly
presents “real footage” clips from alleged alien abduction cases – the
so-called “fourth kind” of encounter with extraterrestrials.
This post is part of our in-depth look at how astronomers have caught dark energy in the act of slowing down the universe's development. For much, much more of our series The Wide Angle, click around in the box at the end of this post.
We all thought that George Lucas was being melodramatic when he had Obi Wan Kenobi give a soliloquy about the dark side of “The Force” in the original 1977 Star Wars film.
Little might coldly rational scientists have imagined that 21 years after the Star Wars debut, astronomers would be confronting the reality of such a spooky property of nature. Since 1998 we’ve known that the vacuum of space is more than nothingness, it is a reservoir of a tiny amount of latent energy that grows irrevocably stronger as the universe gets bigger.
A report today from NASA’s Chandra X-Ray Telescope provides compelling observational evidence that the growth of large clusters of galaxies essentially stopped about 5 billion years ago when the universe began to accelerate under the increasingly strong push of dark energy.
Chandra measured how clusters grew over time, like plotting the grown chart of a child. But about 5 billion years ago the clusters were forced into full maturity because dark energy kicked into high gear and started to accelerate the universe. The universe was flying apart too fast to gravitationally pull material together to grow even larger galaxy clusters.
Though this “arrested development” affects the large-scale structure of the universe it does not inhibit the ongoing formation of stars, planets or the onset of life within a galaxy.
We’re safe for at least a trillion years according to the Chandra measurements, and earlier observation by the Hubble Space Telescope. Whatever it is, dark energy looks stable, as Einstein had postulated when he first conceived of a “repulsive” form of gravity to keep the universe from collapsing like a house-of-cards.
If dark energy were unstable, it might exponentially grow in its repulsive force and lead to the so-called “Big Rip” where everything in the universe flies apart. In the universe’s final moments Earth would be pushed farther from the sun and finally the atoms making up our planet, and our bodies would come apart. The universe would evaporate into oblivion.
Instead, a more likely scenario which is bolstered by this latest evidence, is that space will just keep stretching and stretching forever. Eventually it will be expanding faster than the speed of light (that’s OK, only something with mass cannot travel at the speed of light). This means that the photons of light from external galaxies will be “swimming upstream” against the expansion and no longer be able to reach the Earth.
The disappearance of the rest universe will be a gradual process. Distant galaxies will grow dimmer and dimmer as light it stretched to longer wavelengths, or redshifted. This means that our far descendants’ ability to know about the universe will decrease with time as everything beyond our Milky Way rushes away from us.
When the expansion velocity reaches the speed of light, galaxies will appear to "freeze." They will never seem to get older, they will just continue dimming. About 150 billion years from now all of the galaxies in the universe will be receding fast enough to be invisible from the Milky Way. We will be surrounded by an ever-encroaching event horizon, a boundary beyond which all information is irretrievable.
The two dozen or so galaxies in our local group will have burned out and been largely assimilated into the “super-galaxy,” the elliptical-shaped galaxy that resulted from the merger of the Milky Way and the Andromeda galaxy 6 billion years from now.
The night sky will only be filled with dim aging red stars floating in an inky blackness. Astronomers of that epoch will be as sorely ignorant about cosmology as the Greek philosophers were. They will be clueless as to whether the universe ever had a beginning or if such a thing as “space” is expanding or collapsing.
Imagine one of them uncovering an ancient archive of deep-sky photographs of galaxies from our era. He shows them to his colleagues, and hypothesizes that these are baby pictures of what is now an infinitely redshifted universe. He’s immediately burned to death as a heretic...
So we live in a very special time in the universe’s history. A time where its origin and evolution is knowable. What is unsettling is that the universe switched gears from decelerating to accelerating about 5 billion years ago. That’s close to the time the sun and Earth formed. This is patently anti-Copernican because it means that we came into existence in a very, very special intersection in time, at the definitive moment that dark energy won the arm-wrestling match with gravity.
To be honest this leaves me with a nagging uncertainty over dark energy. Maybe it is a manifestation of something else entirely, that is so exotic, the answer lies far beyond our feeble imaginations.
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