Science

BACKGROUNDER: The laws of Nature

John Webb
Monday, 31 October, 2011
John K. Webb*

A radical discovery by my colleagues and I – reported this week in Physical Review Letters – could help explain why it was possible for life (at least as we know it) to develop on Earth, but not in other parts of the universe.

Our work sits at the boundary between fundamental physics and astronomy. In general terms, we are finding out what the universe was like when it was very young and how it has evolved over the 14 billion years since it spontaneously appeared out of absolutely nothing – the ultimate free lunch.

I lead a research group here at UNSW focusing on one very specific question: have the laws of physics always been as we know them today on Earth, or were they different in the early universe?

Eleven years ago, my Russian colleague, Victor Flambaum, and I, made a breakthrough in the field. We came up with a new idea allowing us, literally overnight, to improve the precision with which we could measure the physical laws elsewhere in the universe --‐ by a factor of 10.

We named this new method, perhaps unattractively, but informatively, the “Many-Multiplet" method. It has now become the default technique used by most competing research groups in universities around the world today.

We applied the new idea to astronomical observations of distant “quasars”. Quasars are relatively small objects in astronomical terms, probably about the size of the solar system, or less than 1000th the size of a galaxy and yet they are the most energetic objects known in the universe.

They emit vast amounts of energy, as much as a thousand billion times that of our Sun, from a tiny volume of space. This energy is generated by the efficient conversion of matter into energy according to the Einstein’s well-oiled E=mc^2 equation.

So quasars can be seen at enormous distances, and we can study them in great detail using the worlds’ biggest telescopes, the Keck telescope on Mauna Kea, Hawaii, and the VLT in Paranal in the Atacama desert in Chile.

As the light from a distant quasar makes its way to us, it inevitably passes through the outer regions or halos of very distant galaxies, similar to our own Milky Way, but “seen” at much earlier stages of their lives. By using high precision instrumentation we can use the spectrum of the quasar to measure the detailed physical conditions in the galactic gas intersecting the sight line to the background quasar.

Frozen in time

The light-travel time to the most distant quasars is more than 90% of the age of the universe and the information contained in the quasar light remains thereafter “frozen in time” - a snapshot of the universe at a distance of say 10 billion light years from Earth.

About 5.5 billion light years after the light leaves the distant gas cloud, our Earth forms. About 0.7 billion years after that, primitive life forms on Earth. Add another 3.8 billion years and the Earth is teaming with humans, technology, and eager scientists armed with large optical and radio telescopes.

So what have we found and why is it interesting? When we look at the spectra of gas clouds in the early universe and compare with the same elements measured in laboratories on Earth, we see very slight but significant differences. A simple analogy to help explain: consider a barcode on an everyday item on a supermarket shelf. The relative positions of the strips in the barcode form a unique identifier to the item in question.

Similarly, in the spectra of distant gas clouds, we see distinct lines caused by various elements such as magnesium, iron, aluminium, nickel, chromium, zinc, and many others. We can visualise the spectrum of this gas just like the barcode, where the relative positions of the lines uniquely identify the elements present.

The relative positions of these lines in the distant cloud of gas can be measured with impressive precision and what we find is amazing; the unique patterns of lines for the same elements seen in laboratory measurements today are slightly different to that seen in distant galaxy halos. In fact, when we make measurements of this sort, it turns out that what we are actually measuring is the electromagnetic force, the force which binds electrons and nuclei together in atoms – the relative positions of the lines in the spectrum are determined by the strength of the electromagnetic force.

We only know of 4 forces in nature; electromagnetism, gravity, and the strong and weak forces acting within atomic nuclei themselves. So we seem to be finding that the laws of physics, or at least one of them, in other regions of the universe are not the same as on Earth!

But the story is stranger still. For various reasons my colleagues and I have been able to study more data, by a factor of more than 10, than any other competing group, and there are quite a few in universities across the US and Europe, and elsewhere. We have looked out into the universe all over the sky, probing physics in 300 different places in the universe.

What we find is that the strength of electromagnetism changes gradually from one “side” of the universe to another – a slow spatial gradient in physics.

Profound implications

The implications for science are profound. All of “textbook” physics rests on the assumption of constancy of the laws of physics. One example is Einstein’s theory of general relativity, which embodies this assumption in something called the “Equivalence Principle”. If we are right, this may now need to be demoted to the “Equivalence Approximation”. The fundamental equations of cosmology may need altering, with important physical re-interpretations for a multitude of experimental data, potentially even including the seemingly mysterious “dark energy”, which is currently thought to provide 70% of the energy content of the universe, and yet the nature of which is entirely unknown.

Another interesting consequence concerns the so-called “fine-tuning problem”. For decades scientists have puzzled over the fact that the laws of physics seem to be mysteriously tuned to favour our existence. No explanation at the fundamental level exists. The “hand of God” is preferred by some as the explanation for fine-tuning. Others prefer the “Anthropic Principle”; we shouldn’t be surprised to find the universe is apparently finely tuned for our presence in it, otherwise we wouldn’t be here to discuss the matter in the first place.

Our observed values of the laws of physics are then put down to mere chance. However, the new results I describe above solve all this in one sweep; if the laws of physics gradually change from one region of the universe to another, then it may simply be that we happen to reside in that part of the universe where the local “by-laws” are perfect for life as we know it. Elsewhere that may not be the case and the universe may be radically different, with a different periodic table, different chemistry and biology, or even no biology at all.

Moreover, since we see only a very small change in the strength of electromagnetism over cosmological scales, it may well be the case that that change continues unabated for a spatial eternity, in other words, space is infinite. This is my preferred interpretation.

The discovery I have outlined is radical. No-one believes us yet. It will take years to show whether it is right or wrong. Some days I doubt I shall be living when the proof comes in. The work is technical, laborious, very difficult, requires a great deal of data from extremely expensive scientific facilities, and the analyses take a lot of time and effort. But on other days I’m more optimistic and I am, at least currently, still alive and kicking and working on it.

*John Webb is Professor of Astrophysics in the UNSW School of Physics.

Related news story here.