The new theory of quantum gravity shows that perhaps our universe had no beginning and has always existed.
The causal set theory assumes that space and time are broken down into discrete chunks of space-time, suggesting the existence of a fundamental unit of space-time.
Physicists in their new work have shown that it is likely that the universe had no beginning-it could have always existed in the infinite past and only recently evolved into what we call the Big Bang.
Quantum gravity is probably the most unpleasant problem facing modern physics. We have two extremely effective theories describing the universe: quantum physics and general relativity.
Quantum physics has successfully described three of the four fundamental forces of nature (electromagnetism, weak interaction and strong interaction) down to microscopic scales.
The General Theory of Relativity (GTR), for its part, is the most powerful and complete description of gravity ever developed, but for all its strengths, the GTR is incomplete.
In at least two specific places in the Universe, the mathematics of GR simply breaks down without giving reliable results: at the centers of black holes and at the beginning of the Universe. These areas are called "singularities," which are points in space-time where our current laws of physics collapse. Within both of these singularities, gravity becomes incredibly strong on very small length scales, which is all we know.
We need a quantum theory of gravity to describe the singularities. There are many contenders, including string theory and loop quantum gravity, but there is one approach that completely rewrites our understanding of space and time.
In all modern theories of physics, space and time are continuous and form the "fabric" underlying all reality. Causal set theory, redefines space-time as a series of discrete fragments, or "atoms" of space-time. by imposing stricter limits on how close events in space and time can be, since they cannot be closer than the size of an "atom."
The clearest analogy here is the display through which you read this text. It consists of pixels and the minimum possible distance between the objects filling the pixels is actually one pixel.
The causal set theory neatly eliminates the Big Bang singularity problem, because there can be no singularities in it. Matter cannot shrink to infinitely tiny points, because there is a minimum possible size - one "atom" of space-time.
What does the beginning of our Universe look like without a Big Bang singularity?
It doesn't. It didn't happen. According to the conclusions from the paper, the implication is that the universe may have just always existed, and that what we perceive as the Big Bang may have been just a certain point in the evolution of this always-existing causal set, rather than a true beginning.
This is just an interesting new hypothesis for now. It remains to be seen whether this causal approach can allow us to create physical theories with which we can work to describe the complex evolution of the universe, including the moment we call the Big Bang.
In other words, this is... is just the beginning of the work.
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