Is there really a unified theory of physics which describes the world we live in? Or are we just chasing a mirage? There seem to be 3 logical possibilities:

1) There is a unified theory (or a collection of overlapping formulations) which we'll eventually discover someday

2) There is no ultimate theory of the universe -- just an infinite sequence of theories which describe the universe more and more accurately

3) There is no theory of the universe; events can only be predicted to a certain extent and on a large scale occur in a random and arbitrary manner

Some would argue for the third possibility by pointing out that a unified theory would infringe on God's freedom to change his mind and intervene in the world. It kinda links back to the old paradox: "can God create a stone so heavy that he can't lift it?" However, you could counter this statement by pointing out that a God would not experience time in the same way we do. After all, God probably knew exactly what he wanted when he initially set up the universe and began the the ticking of time 13.7 billion years ago!

We know from quantum mechanics that events cannot be predicted with complete accuracy -- there is always some element of uncertainty. Nowadays, we have essentially eliminated the third possibility above by redefining the aim of physics research: to formulate a set of laws which enable us to predict events only up to the limit set by the uncertainty principle.

The second possibility agrees with all our experience so far. In essence: we increase the sensitivity of our measurements/make new observations, discover new phenomena not predicted by existing theory, then come up with modified theories to account for the new data. For example, it wouldn't surprise me if we eventually find several new layers of structure more basic than the quarks and electrons we currently regard as the most 'elementary' particles. It's also possible that gravity provides an upper limit to this endless sequence of improved theories. If you had a particle with an energy above what is known as the Planck energy, its mass would be so concentrated that it'd cut itself off from the rest of the universe and form a mini black hole. So as we reach higher and higher energies, there seems to be some limit beyond which things would break down -- this limit could be thought of as approaching some ultimate theory of the universe. We are very very very far away from generating energies as high as the Planck energy in laboratories, so we won't be reaching this limit anytime soon! We'd expect energies comparable to this so-called Planck energy at the early stages of the universe's formation. Therefore, the study of the early universe is probably what'll lead us to a theory of everything (if it ever does happen).

Uncovering a theory of everything would bring the long chapter of humanity's struggle to understand the universe to a close, and it would also revolutionise the ordinary (someone with a non-physics background) person's understanding of the laws governing our universe. In Newton's time, it was possible for someone well educated to have a brief grasp of all knowledge discovered by humanity. Since then, the pace of scientific development has made this impossible. As theories are continually being changed due to new observations, they're never properly digested or simplified so that the ordinary person can understand them. You have to be a specialist, and even then you can only hope to have a proper grasp of a small portion of scientific theories. The rate of progress is so rapid that what you learn at school or university is always a bit outdated. Only a few people can keep up with the rapid advancement of knowledge in a given field, and in return, they must dedicate their whole life to the study of that said field. 70 years ago, only a few people understood the general theory of relativity. Nowadays, thousands of university graduates do, and millions of people are at least familiar with the idea. If we eventually discover a unified theory, it'll soon after be digested and simplified in the same way that relativity is today. We would all then be able to have some understanding of the laws which govern the universe and are responsible for our existence.

It's important to understand that a complete unified theory would not mean that we're able to predict events in the universe for 2 reasons. Firstly, the uncertainty principle sets strong restrictions on our powers of prediction. Secondly, we will never be able to solve the equations of the theory exactly without making a bunch of simplifications/assumptions. We can't even solve exactly for the motion of 3 bodies in Newton's theory of gravity, and the difficulty only increases as you add more bodies. We already understand the basic laws which underlie all of chemistry and biology -- yet we've had little success in predicting human behaviour from these mathematical equations. Similarly, if we do eventually find a complete set of unifying laws, there still exists the challenge of developing relevant approximations to begin grasping the cosmos.

We find ourselves in a strange world. We want to make sense of what we see around us and to do so we ask questions: why is the universe the way it is? What is our place in the universe? Why does the universe exist?... A complete, consistent unified theory is the first step in answering these questions.

published: 22/04/23 by kaan evcimen