"Somewhere, something incredible is waiting to be known" Carl Sagan
sábado, 12 de noviembre de 2011
Astrobiology - Is life on Earth due to a quirk in the laws of physics?
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.
If the signs are right, fundamental equations of cosmology may need altering [Credit: waljoris]
It suggests one of the fundamental laws of physics, electomagnetism, is not constant throughout the universe and may change depending on where you are.
Big claims? Yes, they are. The discovery we have made is radical. Onlookers are skeptical and it may take years to show whether we are right or wrong.
And, yes, who am I to speak?
I lead a research group at the University of New South Wales 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. My work sits at the boundary between fundamental physics and astronomy.
In general terms, I investigate what the universe was like when it was very young and how it has evolved over the 14 billion years since it spontaneously appeared.
When my colleagues and I looked at the spectra of gas clouds in the early universe and compare with the same elements measured in laboratories on Earth, we saw very slight but significant differences.
A simple analogy might help explain this:
Consider a barcode on an every-day 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 as we do with the barcode, where the relative positions of the lines uniquely identify the elements present.
These relative positions in the distant cloud of gas can be measured with impressive precision and what we have found 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 we are actually measuring electromagnetism, the force that binds electrons and nuclei together in atoms. This is because relative positions of the lines in the spectrum are determined by the strength of the electromagnetic force.
We only know of four forces in nature: electromagnetism, gravity, and the strong and weak forces acting within atomic nuclei themselves. And at least one of them, in other regions of the universe, now appears to be different from that on Earth.
But the story gets stranger still.
My colleagues and I have looked out into the universe all over the sky, probing physics in 300 different places. We’ve found the strength of electromagnetism changes gradually from one “side” of the universe to another – a slow spatial gradient in physics.
The implications for science are profound. All “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 my colleagues and I are right, this may now need to be demoted to the “Equivalence Approximation”. The fundamental equations of cosmology may need altering, with important 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, even though its nature is entirely unknown.
How we got here
Some 11 years ago, my Russian colleague Victor Flambaum and I made a breakthrough. We came up with an idea that allowed 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, the “Many-Multiplet" method. It has now become the default technique used by most competing research groups in universities around the world.
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 as much as a thousand billion times the energy of our sun. This energy is generated by the efficient conversion of matter into energy according to the Einstein’s well-oiled E=mc2 equation.
That means quasars can be seen at enormous distances, and we can study them in great detail using the worlds’ biggest telescopes – the Keck telescope in Hawaii and the Very Large Telescope in Chile.
By employing such 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.
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.
But if the laws of physics gradually change from one region of the universe to another, 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.
And since we see only a very small change in the strength of electromagnetism over cosmological scales, that change may continue unabated for a spatial eternity. In other words, space is infinite. This is my preferred interpretation.
As I said at the start of this article, no-one believes us yet, and we are in for a long battle. 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 remind myself that, for now, I’m alive and kicking and working on it.