is the 'big bang' a hoax?: the theory which pushes physics to its uppermost limits 

The origin of our universe has forever intrigued physicists. Did our universe begin in a black hole? Are we just one of infinite universes in a network of universes, i.e., a multiverse? The theory which is taught and accepted by most is known as the 'big bang' theory. This idea states the universe expanded from an initial state of infinite density and temperature. However, it is important to establish that this theory arises from a mathematical singularity and not physical observation. We came up with this theory by extrapolating Einstein's theory of general relativity back to the early universe, where his theory may very well not be valid anymore.

Edwin Hubble first noticed the expansion of our universe by observing nearby galaxies. Einstein's theory of relativity explains this by proposing that space responds to the matter and energy within itself by expanding. However, if the universe is currently expanding, then at some point in the past it must've been much much more densely packed. Well what was going on before this high density period? Here's where the issues start piling in; we cannot test at these higher densities, so we simply don't know what works and what doesn't yet. We can ignore this inconvenience and continue to work with Einstein's equations, and in doing so, we find that the density of matter must've been infinite at some point in the past - 13.7 billion years ago (the 'Hubble constant'), with the universe expanding from this singularity. Most physicists however believe that this so called 'big bang' is a mathematical artefact and not what really happened physically. It is quite likely that Einstein's theory stops working and so we must look for other theories to complete the jigsaw. One flaw to consider is that Einstein's theory does not take into account the quantum nature of space. Physicists are currently working towards a 'theory of everything' which harmoniously links relativity to the quantum world (a theory of 'quantum gravity'). In other words, we currently don't truly know how the universe began!

Why do physicists put forward so many ideas of how our universe began when we simply don't know? In all honesty, us physicists cannot accept the scientifically honest answer. Instead, we extrapolate with a different combination of equations and that leaves us with infinitely many crazy theories as to how we came into existence. The entire study of cosmology is using the universe's initial state, its final state (i.e., the universe as it currently is), and a set of governing equations which allow the initial state to transition to its current state. We know that Einstein's theory of relativity accurately describes the space-time we currently live in from redshift data and from the perihelion position of Mercury (just to name a couple pieces of evidence). In cosmology, we make further assumptions, including the cosmological principle - the idea that the universe is homogeneous and isotropic - or ones about dark matter/energy (the most simple one being the Lambda-CDM model). We can slightly tweak our current set of equations as we please, or use a different initial state (like one without a big bang) to give us numerous plausible cosmological models. In doing this, though, we aren't really getting anywhere; we aren't improving upon our current explanation of the standard cosmological model. We're essentially just adding unnecessary complication to explain what we observe. 

We can see an example of what we've just discussed in Popławski, N., 2021. A nonsingular, anisotropic universe in a black hole with torsion and particle production. General Relativity and Gravitation, 53(2). In this paper, Popławski proposes a change to general relativity by adding a new 'torsion' term to the governing equations to replace the big bang singularity with a 'bounce', similar to an emergence from a black hole. Another popular theory is one called 'no boundary', put forward by Hawking himself. It proposes that our universe has no origin; space has always existed with time being finite. The maths is totally valid and these theories could very well be true, but we have no real way to test them. 

When we try to answer the question at hand, we come face to face with the limits of physics itself. It's a question which we may never be able to answer. The big bang is the simplest explanation which works mathematically and fits current observations, but it is probably wrong physically. That's all we know at the moment. 

published: 20/09/22 by kaan evcimen