An armillary sphere - before telescopes these were used to determine celestial positions.
Interesting article from Cosmos - is the search for a unified theory of everything (the elusive Grand Unified Theory) little more than wishful thinking?
Giving up the ghost
Are physicists wasting their time hunting for a theory that unites the forces of nature? Marcelo Gleiser, once an enthusiast in the quest, wonders if it’s just wishful thinking.
IN THE 1990S, I was a physicist hunting for a theory that would unify two of the four forces – gravity and electromagnetism – as manifestations of a single force. There was good reason to hope, and the great and the good were committed.
More than 10 years on, are we any closer? Is the search fundamentally misguided? Could belief in a physical theory that unifies the secrets of the material world – a ‘hidden code’ in nature – be the scientific equivalent of the religious belief in oneness?
In Ancient Greece, Pythagoras and his followers believed nature was a mathematical puzzle, constructed through ratios and patterns that combine integers, and that geometry was the key to deciphering it.
The idea re-emerged in the late Renaissance, although Galileo Galilei, Johannes Kepler and Isaac Newton believed the mathematical description of nature could be found through the painstaking application of the scientific method, where hypotheses are tested by experiments and observations, and then accepted or rejected.
But that’s really only half the story. According to Newton, God was the supreme mathematician and the mathematical laws of nature were Creation’s blueprint.
And while the notion that God interfered with natural phenomena faded with the march of science, the idea that nature’s hidden code lay in wait to be discovered did not.
Modern incarnations of unified field theories come in two flavours. The more traditional version, the so-called Grand Unified Theory, seeks to describe electromagnetism and the weak and strong nuclear forces as a single force, and the first of these theories was proposed in 1974 by Howard Georgi and Sheldon Glashow.
The more ambitious version seeks to include gravity in the unification framework. Superstring theory tries to do this by abandoning the age-old paradigm that matter is made of small, indivisible blocks, substituting them with vibrating strings that live in higher-dimensional spaces.
Like all good theories in physics, grand unified theories make predictions. One is that the proton, the particle that inhabits all atomic nuclei, is unstable. But for decades, experiments of increasing sensitivity have looked for decaying protons and failed to find them.
As a consequence, the models have been tweaked so that protons decay so rarely as to be outside the current reach of detection. Another prediction fared no better: bundled-up interacting fields called magnetic monopoles have never been found.
For superstrings, the situation is even worse: in spite of its mathematical elegance, the theory is so detached from physical reality that it is difficult to determine what a measurable string effect might be.
I now think it is the very notion of a final theory that is faulty. Even if we succeed in unifying the known forces, our instruments have limits. Since knowledge of physical reality hangs on the measureable, we will never know all there is to know.
Who is to say there are only four fundamental forces? Science is full of surprises. Much better to accept our knowledge of physical reality is incomplete.
This way, science is understood as a human enterprise, and the idea of finding a theory of everything – what Stephen Hawking has called equivalent to “seeing the mind of God” – can be exorcised once and for all.
Particle physics experiments have shown us that our hopes for perfection are just that – hopes. Symmetries are violated left and right; in nature, unlike in John Keats’s famous poem, beauty isn’t always truth.
Perhaps fundamental asymmetries are necessary. The universe had to have very special properties to keep expanding for 13.7 billion years; and particles of matter had to dominate those of antimatter soon after the Big Bang, or the universe would consist mostly of radiation.
Life itself is a product of imperfections, from the spatial asymmetry of amino acids to mutations during reproduction.
Asymmetries forged the long, complex and erratic path from particles to atoms to cells, from simple prokaryotic cells to more sophisticated eukaryotic cells, and from unicellular to multicellular organisms.
The history of life is deeply enmeshed with the Earth’s environmental changes, from the increase of oxygen availability, to the advent of plate tectonics that help regulate carbon dioxide. Life – not to mention intelligence – is probably quite rare, a product of asymmetries, imperfections and accidents.
In the end, giving up on a final theory won’t make doing physics – or science – less exciting. Nature has plenty of mysteries to keep us busy for a very long time.
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