By Paul Sutter/
In the beginning, there was… But maybe there never was a beginning. Perhaps our Universe has always existed, and a new theory of quantum gravity reveals how it might work. “There are so many things to reality that most people would associate with science fiction or even fantasy,” he says. Bruno Bento, a physicist who studies the nature of time at the University of Liverpool in Great Britain.
In his work, he used a new theory of quantum gravity, called causal set theory, in which space and time are divided into separate parts of spacetime.
According to this theory, at one level, there is a fundamental unit of space-time.
Bento and his collaborators used this causal approach to explore the beginnings of the Universe. They found that the Universe likely did not have a beginning, that it has always existed in the infinite past, and that it only recently evolved into what we call the Big Bang.
A quantum of gravity
Quantum gravity is perhaps the most frustrating problem facing modern physics. We have two extremely effective theories of the universe: quantum physics and general relativity. Quantum physics has produced a successful description of 3 of the 4 fundamental forces of nature (electromagnetism, the weak force, and the strong force) down to microscopic scales. On the other hand, General Relativity is the most powerful and complete description of gravity ever created.
But for all its strengths, General Relativity is incomplete. In at least two distinct places in the Universe, the mathematics of general relativity breaks down, failing to produce reliable results: at the centers of black holes and at the beginning of the Universe.
These regions are called “special zones”, which are points in space-time, and where our current laws of physics break down. However, they are mathematical warning signs that General Relativity is tripping over itself. Within both of these “special zones”, gravity becomes extremely strong on very small length scales.
As such, to solve the mysteries of these 2 areas, physicists need a microscopic description of strong gravity, otherwise known as a quantum theory of gravity. And there are many contenders out there, including string theory and curved quantum gravity.
Meanwhile, there is another approach that completely rewrites our understanding of space and time.
The theory of causal elements
In all current theories of physics, space and time are continuous. They form a “smooth fabric” which underlies all reality. In the continuum of space and time, two points can be located very close to each other in space, and two events can occur at approximately the same time.
But another approach, called the theory of causal elements, imagines space-time as a series of separate pieces, or “atoms” of space-time. This theory would place tighter limits on how close events can be in space and time, since they cannot be closer than the size of an “atom”.
For example, if you look at your computer screen while reading this article, everything looks smooth and continuous. But if you were to look at the same screen through a magnifying glass, you could see the pixels sharing the space, and you’d see that it’s impossible to get two images on your screen closer than a single pixel.
This theory greatly excited Benton. “It tries not only to be as basic as possible, but to give a central role to time and what the passage of time means physically, how physical your past is, and whether the future already exists or not.” Bento said to Live Science. Space-time is made up of discrete chunks or “atoms” of space-time, similar to pixels in a computer image.
The beginning of time
The theory of causal elements has important implications for the nature of time. “A big part of the philosophy of this theory is that the passage of time is something physical, and it should not be attributed to some kind of illusion appearing or something going on inside our brains that makes us think time is passing. In itself this transition is a demonstration of physical theory. So in the theory of causal elements, a group of such elements will become bigger and bigger” – emphasizes Bento.
The approach of this theory carefully avoids the problem of the singularity of the Big Bang, since singularities cannot exist in theory. It is impossible for matter to condense down to infinitesimally small points. They can become no smaller than the size of a space-time atom.
So what could the beginning of our universe look like without a singularity like the Big Bang? In this case Bento and his collaborator, Stav Zalel, a graduate student at King’s College London, explored what the theory of causal elements has to say about the early moments of the Universe.
“In the formulation and dynamics of the original causal community, such a group of elements grew out of nothing into the Universe we see today. In our study, there was no Big Bang in the beginning, as the causal elements have always existed” – emphasizes Bento.
Their study implies that the Universe may not have had a beginning. But that he has always existed. What we perceive as the Big Bang may have been only a particular moment in the evolution of this ever-existing cluster of causal elements, but not a true beginning. / “Livescience”