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Astronomers Measure Universe Expansion, Get Hints of ‘New Physics’

By Andy Fell on January 26, 2017 in Science & Technology

Quick Summary

  • Hubble constant measures rate at which universe is expanding
  • ‘Traffic delay’ in light passing through massive galaxies gives new estimate of Hubble constant
  • Differences between estimates could point to new discoveries in physics


The Hubble constant allows astronomers to measure the scale and age of the universe and measure the distance to the most remote objects we can see, said Chris Fassnacht, a physics professor at UC Davis and a member of the international H0LiCOW (H0 Lenses in COSMOGRAIL's Wellspring) collaboration, which carried out the work.


“The Hubble constant is crucial for modern astronomy as it can help to confirm or refute whether our picture of the universe — composed of dark energy, dark matter and normal matter — is actually correct, or if we are missing something fundamental,” Suyu said.

Dark energy is a mysterious force that makes up about three-quarters of the universe and drives cosmic expansion. Dark matter makes up about a quarter of the universe and exerts a gravitational pull on visible, “normal” matter and light.

Gravitational lenses bend light from quasar

The H0LiCOW astronomers measured the Hubble constant by exploiting massive galaxies that act as “gravitational lenses,” bending light from a yet more distant object.


Because mass is not evenly distributed through these massive galaxies, some areas bend or slow light more than others. So light from the quasar will arrive at slightly different times depending on the route it takes through the lens, just as drivers who set off from one city to another at the same time, but travel by different routes, will arrive at different times. By analyzing that “traffic delay,” the researchers could arrive at a figure for the Hubble constant.


“These three things allow us to get a precise measure of the Hubble constant,” Fassnacht said.

Hint of new physics

The Hubble constant estimate from H0LiCOW, 71.9±2.7 kilometers per second per megaparsec, is accurate to 3.8 percent. The figure is in close agreement with measurements by other astronomers based on observations of supernovae, or of variable stars called Cepheids. But these estimates are rather different from that obtained from the Planck space telescope, which measured radiation from the cosmic microwave background.

The Planck measurement does rely on some assumptions, for example that the universe is flat, Fassnacht said. Or, the difference could be a statistical fluctuation that will disappear as the estimates get better — or it could be something more exciting.

“If you still see something when the error bars shrink, maybe it’s new physics, beyond the Standard Model of cosmology,” Fassnacht said.


Suyu is also Max Planck @TUM professor at the Technical University Munich. The team also included Nick Rumbaugh, junior specialist in the UC Davis Department of Physics, and researchers at UCLA; UC Santa Barbara; Stanford University; École Polytechnique Fédérale De Lausanne, Switzerland; National Astronomical Observatory of Japan, Japan; Academia Sinica Institute of Astronomy and Astrophysics, Taiwan; University of Cambridge, U.K.; Beijing Normal University, China; Ludwig-Maximilians-Universität, Germany; Kavli Institute for the Physics and Mathematics of the Universe, Tokyo; The University of Tokyo; Argelander-Institut für Astronomie, Germany; European Southern Observatory, Germany; University of Groningen, The Netherlands; Osservatorio Astronomico di Capodimonte, Italy; University of Portsmouth, U.K.; and the Max Planck Institute for Astrophysics, Germany.

The Hubble Space Telescope is a project of international cooperation between the European Space Agency and NASA.

Media contact(s)

Chris Fassnacht, UC Davis Physics, (530) 754-4419,


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