Expansion of the Universe Calculated with Unprecedented Accuracy
Scientists have now measured the rate of expansion of the universe with astonishing accuracy.
Two teams of physicists have studied more galaxies than ever before in order to generate a more precise measurement of the expansion of the universe. Using the Baryon Oscillation Spectroscopic Survey (BOSS), they studied more than 140,000 particularly bright galaxies (quasars) and yielded an expansion rate of 42 miles (68 kilometers) per second per 1 million light-years, with an error rate of a mere plus or minus a kilometer and a half per second. Their measurement was not only more exact, but looked twice as far back in time as the most comprehensive studies on the subject.
The new research "explores a region of the universe that was not explored before," said Andreu Font-Ribera of the U.S. Department of Energy's Lawrence Berkeley National Laboratory, who led one of the two teams.
Approximately a century ago, astronomer Edwin Hubble determined that other galaxies were moving farther away from the Milky Way as a direct result of the expansion of the universe. So when measuring this expansion, researchers use the distance between the Milky Way and certain quasars, as well as their distance from each other, as a standard length "ruler" for the rate of expansion. They measure the distances between galaxies by observing Baryon acoustic oscillations (BAOs), or oscillations similar to sound waves that are imprinted in the galaxies of the early universe. When the light from galaxies is filtered through the dust surrounding the galaxy, the imprint can be observed.
Because galaxies grow fainter at greater distances, previous studies were only able to study galaxies from the past 6 billion years, while the universe has existed for 13.8 billion years. Font-Ribera and his team took a significant step towards solving this problem by observing the BAOs in quasars. Since the quasars are much brighter than normal galaxies, quasars from much earlier in the universe were able to be studied.
"If we looked back to the universe when it was less than a quarter of its present age, we'd see that a pair of galaxies separated by a million light-years would be drifting apart at a velocity of 68 kilometers a second as the universe expands," Font-Ribera said in an accompanying press release.
This research may allow physicists to better understand the nature of the expansion of the universe, especially its relationship to dark energy, which is considered to be one of the greatest remaining mysteries of the universe. After observation of supernova in the 1990's, researchers concluded that the expansion of the universe was not slowing down, but rather accelerating. This is difficult to reconcile with the known laws of the universe; as a result, it is often compared to a ball accelerating after it is thrown in the air. "[The universe's] acceleration is like you throw the ball up, and it starts going up faster and faster," said Patrick McDonald of the Canadian Institute for Theoretical Astrophysics. "No normal attractive gravity will do that."
The prevailing explanation for this consistency is the existence of "dark energy." Although scientists are not 100% certain of the exact nature of dark energy, the general consensus is essentially that the curvature of spacetime is dependent on the amount of energy in the universe, which means that the universe will expand at a fixed rate. This is not to be confused with a fixed speed, it simply means that the universe will take a fixed amount of time to double in size. As a result, it is expanding at an exponential rate, and the speed at which it expands is accelerating.