China to Tune in to the Music of Dark Energy

BEIJING—China is about to join the hunt for dark energy. At a cosmology workshop held here on 20 March, scientists unveiled Tianlai, or "Sound of Heaven," a project to listen to radio emissions from deep space that may reveal the nature of dark energy.

Dark energy is the mysterious force driving the accelerating expansion of the universe. Although not directly observable, the phenomenon "can be studied by observing the expansion rate of the universe at different epochs," says Tianlai project leader Chen Xuelei, a cosmologist at National Astronomical Observatories of China here. The principle idea is to use a radio telescope to map neutral hydrogen, which emits or absorbs radio waves with a wavelength of 21 centimeters. They will be able to peer back to earlier ages in the universe by looking for redshifted radio waves. The distribution of hydrogen offers a way to more precisely measure the universe's expansion rate.

Detecting the cosmic 21-centimeter signal is notoriously hard, as it is swamped by radiation from our own Milky Way galaxy. The radiation must be measured to a precision of one in 100-thousandths to see the signal. "Many colleagues have doubts about whether it will ever work," says Chen. In collaboration with Canadian, French, and U.S. researchers, Chen's group has just launched a pilot project to build a prototype cylinder radio telescope. After a few years of experiments, the team should know whether the new instrument can detect dark energy. If successful, the project would be expanded to make a three-dimensional map of hydrogen in the universe.