A joint Fermilab/SLAC publication

Are the laws of physics the same throughout the universe?

06/19/08

Observations of a quasar about 6 billion light years from Earth have shown that one of the fundamental properties of physics is the same there as here. Astrophysicists measured the ratio of the electron mass to the proton mass in the distant quasar and found the protons there are 1836.15 more massive than the electrons, the same value as here on Earth now.

The work, published this afternoon online in Science magazine, was done by an international team of astrophysicists and astronomers, led by Michael Murphy of Swinburne University of Technology in Australia. Murphy's work has received a lot of attention in the past over his investigations of whether what we assume are fundamental constants of the universe are indeed constant throughout time and space.

In this research, the astrophysicists looked at light coming from a quasar called B0218+367. In particular, they looked at the frequency of light coming from the quasar and passing through ammonia gas in a galaxy between the quasar and Earth. That gas absorbs some of the quasar light at a frequency that depends on the properties of the atom, including the ratio of the electron mass to the proton mass. To measure the ratio of proton to electron masses precisely, the astrophysicists had to compare the ammonia frequency measurement with that of light coming from other molecules. Having completed those measurements, they could put a precise value on the ratio of the masses.

It might not seem all that interesting to show that the laws of physics are the same everywhere, but it is a fundamental assumption of physics and all assumptions need to be tested. Furthermore, there had been some evidence that the assumed "constants" of nature had changed over time. Murphy and colleagues point out that this new result is inconsistent with previous results that hinted at changes in this ratio over time.

The result is not the end of the exploration as the precision of the measurement can be improved significantly, and there is still wiggle room for some change to have occurred. As theories of physics become more precise, physicists need to test their assumptions more precisely.

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