December 13, 2012
Proton-to-Electron Mass Ratio Has Hardly Changed Over Course Of Time
Lee Rannals for redOrbit.com - Your Universe Online
This fundamental constant of nature has changed by a maximum of one hundred thousandth of a percent over cosmic history.
Scientists from VU University Amsterdam and the Max-Planck-Institut fÃ¼r Radioastronomie (MPIfR) used the Effelsberg 100-m radio telescope to make accurate measurements of the methanol absorption at several characteristic frequencies.
Methanol is the simplest form of the family of alcohol molecules, and it was observed in a distant galaxy toward the quasar system PKS 1830-211.
The results from the measurements show that stringent limit on the proton-to-electron mass ratio shows that molecules and molecular matter are the same now as 7 billion years ago.
A fundamental constant like proton-to-electron mass ratio cannot be calculated from any currently known theory, and can only be measured. Scientists say there is a possibility that the proton-to-electron mass ratio was different in other places in the universe or at separate durations in cosmic history.
The methanol molecule is a sensitive probe for detecting a shift of the proton-electron mass ratio, so the scientists pointed to it for their research. Some of the lines in the microwave spectrum of this molecule would undergo a rather late shift upon a variation of the proton-to-electron mass ratio, while other lines are not affected.
The scientists found that the hindered internal rotational motion in molecules like methanol can give rise to very high sensitivity coefficients. The sensitivity of each spectral line can be expressed in a value K.
“This idea makes the methanol molecule an ideal probe to detect a possible temporal variation in the proton-electron mass ratio”, said Wim Ubachs, Professor at VU University Amsterdam and Head of its Department of Physics. “We proposed to search for methanol molecules in the far-distant universe, to compare the structure of those molecules with that observed in the present epoch in laboratory experiments.”
The team investigated a galaxy known as a "molecular factory" in the line-of-sight of a strong radio source. The molecule factory is known to be at a distance of 7 billion light-years from Earth.
“Coming from optical astronomy it was an interesting experience to perform observations at such long wavelengths”, said Julija Bagdonaite, a PhD student at VU University Amsterdam and lead author of the paper. “The absorptions of the radio waves have occurred 7 billion years ago, and the radio waves traveling to Earth carry the fingerprint of the methanol molecules in the distant past.”
The researchers concluded that the structure of molecular matter is almost the same as it was 7 billion years ago.
“If you see any variations in that fundamental constant, then you would know that something is wrong in our understanding of the foundations of physics”, wrote Karl Menten, Director at MPIfR and head of the Institute´s Millimeter and Submillimeter Astronomy Department. “In particular, it would imply a violation of Einstein´s Principle of Equivalence which is at the heart of his General Theory of Relativity.”
Image 2 (below): Picture of the methanol molecule (CH3OH); the black ball represents a C-atom, red an O-atom and grey H-atoms; the yellow arrow indicates the internal rotational motion, which is hindered, giving rise to quantum tunneling. Credits: Paul Jansen, VU-UniversitÃ¤t Amsterdam