Einstein's quest to "know the thoughts of God" could take millennia

In 1925, Einstein went on a walk with a young student named Esther Salaman. While they wandered, he shared his main intellectual principle: "I want to know how God created this world, I'm not interested in this or that phenomenon, in the range of this or that element. thoughts, the rest are just details. "

The expression "thoughts of God" is a metaphor perfectly suited to the ultimate goal of modern physics, which is to develop a perfect understanding of the laws of nature – what physicists call "a theory of everything" or TOE. Ideally, a TOE would answer all the questions, leaving nothing unanswered. Why is the sky blue? Covered. Why gravity exists? It's covered too. In more scientific terms, a TOE would ideally explain all phenomena with a single theory, a single building block and a single force. In my opinion, finding a TOE could take hundreds, even thousands of years. To understand why, let's take stock. [The 18 Biggest Unsolved Mysteries in Physics]

We know two theories that together give a good description of the world around us, but both are light-years away from the TOE.

The first is Einstein's theory of general relativity, which describes the gravity and behavior of stars, galaxies and the universe at larger scales. Einstein described gravity as the literal bending of space and time. This idea has been validated several times, especially during the discovery of gravitational waves in 2016.

The second theory is called the standard model, which describes the subatomic world. It is in this area that scientists have made the most obvious progress towards a theory at all.

If we look at the world around us – the world of stars and galaxies, poodles and pizza – we may wonder why things have the properties they have. We know that everything consists of atoms and that these atoms are made of protons, neutrons and electrons.

And, in the 1960s, researchers discovered that protons and neutrons were made up of even smaller particles, called quarks, and that the electron was part of the class of particles called leptons.

Finding the smallest building blocks is only the first step in developing a theory at all. The next step is to understand the forces that govern how building blocks interact. Scientists know four fundamental forces, of which three – electromagnetism and strong and weak nuclear forces – are understood at the subatomic level. Electromagnetism keeps the atoms together and is responsible for the chemistry. The strong force holds together the nucleus of the atoms and keeps the quarks inside protons and neutrons. The weak force is responsible for certain types of nuclear disintegration.

Each of the known subatomic forces has an associated particle or particles that carry this force: the gluon carries the strong force, the photon governs the electromagnetism and the bosons of W and Z control the weak force. There is also a ghostly energy field, called the Higgs field, which permeates the universe and gives a mass to quarks, leptons and some of the force-carrying particles. Taken together, these constituent elements and forces constitute the standard model. [Strange Quarks and Muons, Oh My! Nature’s Tiniest Particles Dissected]

By using quarks and leptons and particles carrying known forces, we can build atoms, molecules, people, planets and, in fact, all the known matter of the universe. This is undoubtedly a remarkable achievement and a good approximation of a theory at all.

And yet it is really not the case. The goal is to find a single building block and a single force that can explain the matter and the movement of the universe. The standard model comprises 12 particles (six quarks and six leptons) and four forces (electromagnetism, gravity and strong and weak nuclear forces). In addition, there is no known quantum theory of gravity (that is, our current definition only covers gravity involving larger objects than, for example, ordinary dust), so the gravity is not even part of the standard model. Physicists therefore continue to search for an even more fundamental and underlying theory. To do this, they must reduce the number of building blocks and forces.

It will be difficult to find a smaller building block because it requires a more powerful particle accelerator than the one humans have ever built. The time horizon for commissioning a new accelerator installation is several decades and this installation will only bring about a relatively modest incremental improvement over existing capabilities. Scientists must therefore speculate on what a smaller building block might look like. A popular idea is called supercord theory, which postulates that the smallest building block is not a particle, but rather a small and vibrant "chain". In the same way that a cello string can play more than one note, the different vibration patterns are the different quarks and leptons. In this way, only one type of chain could be the ultimate building block. [Top 5 Reasons We May Live in a Multiverse]

The problem is that there is no empirical evidence of the actual existence of supercords. In addition, the expected energy required to view them is called Planck Energy, which is a quadrillion times (10 times the power 15) higher than what we can currently generate. Planck's great energy is closely related to what is known as Planck's length, an unfathomable length beyond which quantum effects become so important that it is literally impossible to measure anything smaller. . Meanwhile, go smaller than Planck's length (or larger than Planck's energy), and the quantum effects of gravity between photons, or light particles, become important and relativity no longer works. This makes it likely that it is on this scale that quantum gravity will be understood. This is, of course, very speculative, but it reflects our current best prediction. And, if this is true, the supercorders will have to remain speculative in the foreseeable future.

The plethora of forces is also a problem. Scientists hope to "unify" the forces, showing that they are just different manifestations of the same force. (Sir Isaac Newton did just that when he showed that the force that made things fall on Earth and that the force that governed the movement of the heavens was one and the same thing, James Clerk Maxwell showed that Electricity and magnetism were really different behaviors of a unified force called electromagnetism.)

In the 1960s, scientists were able to show that the weak nuclear force and electromagnetism were actually two different facets of a combined force called electroweak force. Researchers now hope that the electroweak force and strong force can be unified into a so-called unified force. Then they hope that the great unified force can be unified with gravity to make a theory of everything.

However, physicists suspect that this final unification would also take place at Planck's energy, again, because this is the energy and size at which quantum effects can no longer be ignored in the theory of relativity. And, as we have seen, this is a much higher energy than we can expect to achieve inside a particle accelerator. To give an idea of ​​the gulf between current theories and a theory of everything, if we represent the energies of particles, we can detect that the width of a cell membrane, Planck energy is the size of the Earth. Although it is conceivable that a person with extensive knowledge of cell membranes can predict other structures within a cell – elements such as DNA and mitochondria – it is inconceivable to be able to accurately predict the Earth. What is the probability that they can predict volcanoes, oceans or the Earth's magnetic field?

The simple fact is that with such a gap between the energy currently achievable in particle accelerators and Planck's energy, it seems unlikely to correctly design a theory of everything.

This does not mean that physicists should all retire and embark on landscape painting – there is still a lot of work to be done. We still need to understand unexplained phenomena such as Dark Matter and Dark Energy, which make up 95% of the known universe, and use this understanding to create a newer and more complete theory of physics. This new theory will not be a TOE, but will be progressively better than the current theoretical framework. We will have to repeat this process again and again.

Disappointed? I am too. After all, I've spent my life trying to reveal some of the secrets of the cosmos, but maybe some perspective is in order. The first unification of forces was carried out in the 1670s with Newton's theory of universal gravitation. The second was in the 1870s with Maxwell's theory of electromagnetism. Electroweak unification was relatively recent, only half a century ago.

Given that 350 years have passed since our first great success in this process, it may be less surprising that the path ahead is even longer. The notion that a genius will have an idea that will lead to a fully developed theory of everything in the next few years is a myth. We will have to go a long way – and even the grandchildren of today 's scientists will not see the end.

But what a trip it will be.

Don Lincoln is a physics researcher at Fermilab. He is the author of "The Large Hadron Collider: The Extraordinary Story of the Higgs Boson and Other Things That Will Blow Your Mind"(Johns Hopkins University Press, 2014), and produces a series of science education videos. Follow him on Facebook. The opinions expressed in this comment are his.

Don Lincoln contributed this article to Live Science Expert Voices: Op-Ed & Insights. Originally published on live science.