Sorry! De informatie die je zoekt, is enkel beschikbaar in het Engels.
This programme is saved into My study choice.
This programme cannot be saved.
You are not logged in yet to My study choice Portal. Login or create an account to save your programmes.
Something went wrong, try again later.

Are fundamental physical constants indeed always constant?

5 August 2021
VU physicist Wim Ubachs, together with international experts from Sweden, Germany and India, investigated how constant the proton-to-electron mass ratio really is, by observing methanol in a distant galaxy.

The research was done with the Atacama Large Millimetre Array (ALMA) in Chili, currently the most sensitive radio telescope in the world. The research is published in the scientific journal Astronomy and Astrophysics.

Our understanding of the Universe relies on scientific laws that describe, for example, the motions of planets around their stars or the propagation of electromagnetic waves. The basic assumption that the scientific laws are valid everywhere, and at any time, can be challenged. In particular, are the fundamental physical constants, like the speed of light or the Newton gravitational constant, indeed constant, or can their values change with time and space or with local properties?

Looking at methanol in a distant galaxy
Searches for varying constants can be done with various methods, including spectroscopic observations toward high redshift objects in the Universe. The methanol molecule is the most sensitive spectroscopic probe of hypothetical variations of the dimensionless proton-to-electron mass ratio. 

Unfortunately, to date only one single high-redshift object, a galaxy located at a look-back time of about 7 Gyr illuminated by the background quasar PKS1830-211, has been found with methanol absorption. The system is a very complex one (a gravitational lens, where the background source has a high time variability in intensity and structure), thus causing systematic problems in the precise analysis of absorption frequencies.

With ALMA, Ubachs and his co-authors have now observed multiple lines of methanol in absorption toward PKS1830-211, they investigated the dominant systematic effects, and included them in an analysis constraining the drift of the proton-to-electron mass ratio. They conclude that the proton-to-electron mass ratio in this distant galaxy does not differ from its value today on Earth by more than 0.00004%, a tight constraint suggesting that it may indeed be constant. Or varying, but at a rate still below our perception.

Photo: ALMA radio telescope. Photo credits: Christoph Malin