“Dark energy is incredibly strange, but actually it makes sense to me that it went unnoticed,” said Noble Prize winning physicist Adam Riess in an interview. “I have absolutely no clue what dark energy is. Dark energy appears strong enough to push the entire universe – yet its source is unknown, its location is unknown and its physics are highly speculative.”
Physicists have found that for the last 7 billion years or so galactic expansion has been accelerating. This would be possible only if something is pushing the galaxies, adding energy to them. Scientists are calling this something “dark energy,” a force that is real but eludes detection.
One of the most speculative ideas for the mechanism of an accelerating cosmic expansion is called quintessence, a relative of the Higgs field that permeates the cosmos. Perhaps some clever life 5 billion years ago figured out how to activate that field, speculates astrophysicist Caleb Scharf in Nautil.us. How? “Beats me,” he says, “but it’s a thought-provoking idea, and it echoes some of the thinking of cosmologist Freeman Dyson’s famous 1979 paper “Time Without End,” where he looked at life’s ability in the far, far future to act on an astrophysical scale in an open universe that need not evolve into a state of permanent quiescence. Where life and communication can continue for ever.
Once we start proposing that life could be part of the solution to cosmic mysteries, Scharf concludes, “there’s no end to the fun possibilities. Although dark-matter life is a pretty exotic idea, it’s still conceivable that we might recognize what it is, even capturing it in our labs one day (or being captured by it). We can take a tumble down a different rabbit hole by considering that we don’t recognize advanced life because it forms an integral and unsuspicious part of what we’ve considered to be the natural world.”
There are several theories for the identity of dark energy: it may be energy generated by ghostly subatomic particles that appear out of nothing before annihilating; it may associated with the recently confirmed Higgs Field, which gives certain kinds of matter mass; or it may be explained by string theory by which extra invisible dimensions of space get compressed into sizes much smaller than atoms. Some theorists believe it’s an example of fine-tuning that demands the existence of a multiverse to explain it.
“The multiverse may be the most dangerous idea in physics” argues the South African cosmologist George Ellis. The multiverse may be an artifact of a deeper reality that is comprehensible and unique.
Almost all physicists agree that if the amount of dark energy in the universe were slightly different, life could never have emerged. The amount of dark energy is astoundingly small compared to the theoretically large range it could be (it has been measured to be about one-hundred-millionth of an erg per cubic centimeter). We happen to live in a universe with a small dark energy value, allowing for expansion rather than contraction, and for the emergence of life.
Scientists have established that the universe is expanding at a rate 20 percent faster than it was 5 billion years ago. In 1929, Edwin Hubble first demonstrated that the universe was expanding by showing that galaxies outside the Milky Way, in which earth’s solar system resides, were moving away from each other. Only about 5 percent of the universe is composed of planets, stars and gaseous structures, with the remaining 95 percent comprising dark matter and dark energy.
Hubble’s law is the first observational basis for the expansion of the Universe, and provides strong evidence for the Big Bang model. The value of the expansion rate is called the Hubble constant. Hubble constant is a critical parameter in cosmology and the measurement of Hubble constant is a key task for the astrophysicists and cosmologists.
“The galaxies are kind of like the raisins, and as the loaf rises, the raisins, which are far apart to begin with, rush apart even faster, Reiss observed. “It doesn’t matter where you are in this loaf; everything looks like it’s moving away from everything else.”
Riess, who is a researcher at the Space Telescope Science Institute in Baltimore, Maryland, and a professor at Johns Hopkins University was one of the recipients of the 2011 Nobel Prize in physics for the discovery that the universe is expanding at an accelerating rate using images of very distant supernovae to derive what was considered the most accurate measurement to date of cosmic speed.
“We know there is gravity because apples fall from trees. We can observe gravity in daily life. If we could throw an apple to the edge of the universe, we would observe it accelerating,” Reiss said. “Until the 1990s, there were few reliable observations about movement at the scale of the entire universe, which is the only scale dark energy effects. So dark energy could not be seen until we could measure things very, very far away.”
Before his and his colleagues’ discovery, many scientists had posited the rate at which the universe was expanding was decreasing. Riess was awarded the Nobel Prize in conjunction with Brian Schmidt, who like Riess was a member of the High-Z Supernova Search Team, and Saul Perlmutter, head scientist of the Supernova Cosmology Project, a competitor to Riess’ team which published a paper in 1999 corroborating the results of Riess’ 1998 paper.
Image credit: With thanks to PBS, What Does Dark Energy Look Like