You will be surprised to hear that our universe is actually quite simple - it is our cosmological theories that turn out to be unnecessarily complex, says one of the world's leading theoretical physicists. Such a conclusion may seem illogical: in the end, in order to understand the true complexity of Nature, one has to think wider, study things on smaller and smaller scales, add new variables to equations, come up with "new" and "exotic" physics. Someday we will figure out what dark matter is, get an idea of where the unusual gravitational waves are hiding - if only our theoretical models become more developed and more … complex.
This is not the case, says Neil Turok, director of the Perimeter Institute for Theoretical Physics in Ontario, Canada. According to Turok, if the universe, on the largest and smallest scales, tells us anything, it is about its incredible simplicity. But in order to fully understand this, we need a revolution in physics.
In an interview with Discovery, Turok noted that major discoveries of recent decades have confirmed the structure of the Universe on cosmological and quantum scales.
“On a large scale, we mapped the entire sky - the cosmic microwave background - and measured the evolution of the universe, how it changed, how it expanded … and these discoveries show that the universe is startlingly simple,” he says. "In other words, you can describe the structure of the Universe, its geometry, the density of matter with just one number."
The most exciting takeaway from this reasoning is that describing the geometry of the universe with just one number is easier than describing numerically the simplest atom we know of, the hydrogen atom. The geometry of the hydrogen atom is described by three numbers that follow from the quantum characteristics of an electron in its orbit around a proton.
“This tells us that the universe is smooth, but has a small level of fluctuation, which is described by this number. And that's all. The universe is the simplest thing we know."
Somewhere on the opposite end of the scale, something similar happened when physicists explored the Higgs field using the most complex machine ever built by humans, the Large Hadron Collider. When physicists historically discovered the Higgs mediator particle - the Higgs boson in 2012 - it turned out to be the simplest type described by the Standard Model of particles.
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“Nature uses the smallest solution, the smallest mechanism imaginable, to give particles their mass, their electrical charge, and so on, says Turok.
20th century physicists taught us that if you increase precision and delve deeper into the quantum world, you will find a zoo of new particles. Because the experimental results produced a lot of quantum information, theoretical models predicted more and more particles and forces. But we have now reached a crossroads where many of our advanced theoretical ideas about what lies “beyond” our current understanding of physics are awaiting some experimental results that will support unusual predictions.
“We are in a strange situation where the Universe is talking to us; it tells us that it is extremely simple. At the same time, the theories that have been popular (the last 100 years of physics) are becoming more complex, arbitrary and unpredictable,”he says.
The Turk points to string theory, which has been billed as the "ultimate unification theory," packing all the secrets of the universe into a neat package. And also looking for evidence of inflation - the rapid expansion of the Universe that it experienced almost immediately after the Big Bang some 14 billion years ago - in the form of primordial gravitational waves engraved against the cosmic microwave background, the "echo" of the Big Bang. But as we seek experimental evidence, we grasp at straws; the experimental evidence simply does not agree with our unbearably complex theories.
Our cosmic origins
Turok's theoretical work is devoted to the origin of the universe, a topic that has received a lot of attention in recent months.
Last year, the BICEP2 collaboration, which uses a telescope at the South Pole to study the CMB, announced the detection of primary gravitational wave signals. This is a kind of "holy grail" of cosmology - the discovery of gravitational waves generated by the Big Bang can confirm inflationary theories of the Universe. Unfortunately for the BICEP2 team, they announced the "discovery" even before the European Planck Space Telescope (which also maps the microwave background) showed that the BICEP2 signal was caused by dust in our galaxy, not ancient gravitational waves.
What if the primordial gravitational waves never find it? Many theorists who have pinned their hopes on a Big Bang followed by a period of rapid inflation may be disappointed, but, according to Turok, “this will be a powerful hint” that the Big Bang (in the classical sense) may not be the absolute beginning of the universe.
“The hardest thing for me is to describe the Big Bang itself mathematically,” adds Turok.
Perhaps a cyclical model of the evolution of the universe - when our universe collapses and starts over - would better fit observations. Such unusual models do not need to produce primordial gravitational waves, and if these waves are not detected, perhaps our inflationary theories need to be improved.
Regarding the gravitational waves predicted to be generated by the rapid motion of massive objects in our modern universe, Turok is confident that we have reached such a degree of sensitivity that our detectors should soon detect them, confirming one of Einstein's predictions about spacetime. "We expect to see gravitational waves from colliding black holes in the next five years."
The next revolution?
From the largest scales to the smallest, the universe appears to be "scaleless" - in other words, no matter what spatial or energy scale you look at, there is nothing "special" about the scale. And this conclusion speaks in favor of the fact that the universe has a much simpler nature than modern theories suggest.
“This is a crisis, but a crisis at its best,” Turok says.
Thus, in order to explain the origin of the universe and come to terms with some of the most mysterious mysteries of our universe, like dark matter and dark energy, we may have to look at space completely differently. This will require a revolution in the understanding of physics, a revolutionary approach comparable in strength to Einstein's realization that space and time are two sides of the same coin, when general relativity was formed.
“We need a completely different view of fundamental physics. The time has come for radically new ideas,”concludes Turok, noting that now is a great time for young people to study theoretical physics, since it is the next generation that will most likely turn our understanding of the Universe.
Ilya Khel