Chasing a theory of everything

TODAY I FOCUS my feeble mind on a deep question. Will science ever fully explain the fundamental nature of physical reality and formulate a Theory of Everything (Toe)? In this regard I recommend a fascinating article by Marcelo Gleiser in the New Scientist on May 10th. Gleiser argues that there are fundamental reasons why science can never reveal the total knowledge of physical reality at its most basic level.

Science has made spectacular progress in explaining the natural world over the past 500 years. We are conditioned to think that this progress will continue indefinitely until eventually we will know everything about physical reality. Obviously, science will continue making new discoveries about the world, but Gleiser argues that two fundamental barriers will forever prevent it from reaching the Holy Grail of Toe. These two barriers are, first, the First Cause problem, and second, the limit of knowledge caused by indeterminacy.

What was the first cause of everything that exists – how did the world and life come to be? Every culture has pondered this question and has traditionally answered it by postulating a transcendent force not constrained by physical laws – God. This explanation is not, of course, open to science.

The conventional scientific description of origins is that the world began about 14 billion years ago in a massive explosion called the Big Bang, and current understanding of what happened in the Big Bang requires a marriage of the theory of relativity with quantum theory. As I understand the matter, this marriage cannot yield a reliable answer because, to formulate an answer, we must push these theories far beyond the range where they are known to work.

You might argue that future developments will eventually resolve the problem but Gleiser argues that this cannot happen because of the conceptual structure of science itself. Science can never explain the first cause because science cannot fully explain itself. Certain untestable philosophical propositions must be assumed before you can do science, eg that the world is rationally understandable and operates on laws and processes that are uniform across time and space.

Stephen J Gould expressed this memorably: “You cannot go to a rocky outcrop and observe either the constancy of nature’s laws nor the working of unknown processes. You must first assume these propositions and then you go to the outcrop of rock”.

Science has made great progress in explaining how the world has unfolded over time, but Gleiser argues that it will never satisfactorily uncover the first cause because “the first cause is an a priori limitation of any rational explanation of reality”.

The second barrier to formulating a Toe is indeterminacy. Ultimately in science we only know what we can measure and here we face a fundamental limitation – the uncertainty principle of quantum mechanics. Quantum mechanics is the science of the very small – atomic level and below – but the information we can extract in our measurements at this level is limited because our measuring device interacts with the system being measured and selects its behaviour – “to measure is to corrupt”.

Werner Heisenberg (1901-1976) formulated the uncertainty principle. This states that, in the quantum world you can never simultaneously know both the position and the velocity of a particle. If you measure the position, the velocity is a complete unknown, and vice-versa.

Gleiser offers an analogy to illuminate the quantum interaction of measuring device and system being measured. Consider an anthropologist observing a new tribe from a hidden vantage point. One day a tribesman sees the anthropologist and, after some hubbub, the tribe agrees to allow the scientist to remain in their midst and to continue his observations.

But the behaviour of the tribe is now somewhat different. Through his interaction with the tribe, the anthropologist has affected their behaviour. This analogy is imperfect because the anthropologist retains his notes of the tribe’s behaviour while he remained hidden. The scientist can have no such information about a quantum system – he/she can know only what they see when they are in plain sight.

Science can continue to improve the accuracy of its measurements but it can never exceed what is allowed by the Heisenberg uncertainty principle. We will never therefore be able to measure the totality of reality and we can never really know if a theory is final.

The fact that we can never know everything should not dismay us. In fact, it is good news. Science is a voyage of discovery and if nothing remained to be discovered we would surely miss the adventure and the imaginative pleasures of speculation.

William Reville is professor of biochemistry and public awareness of science officer at UCC – understandingscience.ucc.ie