In 1927 the Belgian Catholic priest and former engineer Georges Lemaître was the first person to propose that the universe was expanding (1, 2) rather than being in a steady state. This was grounded in his own mathematical reasoning, derived from Einstein’s General Theory of Relativity. Einstein was initially highly dismissive, reportedly saying “Your calculations are correct, but your physics is atrocious.” Nevertheless Lemaître’s idea was indeed confirmed experimentally just two years later by Edwin Hubble through observations made with the Hooker Telescope at Mount Wilson Observatory, measuring the redshift of light from distant galaxies.
Jumping forward to 1998 two independent teams in America discovered that not only is the universe expanding, it is expanding at an accelerating rate (3). A discovery that was recognised in 2011 with the award of the Nobel Prize in Physics (4). Now, one would intuitively think that the energy density of ’empty’ space is zero, but to account for the accelerated expansion this self-evidently cannot be so; there has to be a force pushing things apart. The name given to this force by physicists is ‘Dark Energy’. Modern physics rests on two beautifully successful models, the Standard Model and General Relativity. General Relativity explains the behaviour of the universe as a whole; of gravity and the nature of space and time. Conversely the Standard Model applies to the sub-atomic world of particles and the nature of quantum physics. Both models work phenomenally well and have been confirmed to immense precision through experimental results at their relative scales; the universe and the atom. Equally, both models can be used to derive the force required, per cubic metre of empty space, to account for the observed accelerating expansion of the universe. Observations consistent with General Relativity suggest the energy density of dark energy is equivalent to about four hydrogen atoms per cubic metre. By contrast, quantum field theory—built on the Standard Model—predicts a vacuum energy density larger by a staggering factor of 10¹²⁰. (5). To grasp the scale of this discrepancy, consider that the known universe contains only about 10⁸⁰ atoms.
So, what does one make of this? If you are a scientist? A philosopher? A cleric? Or anyone else for that matter. To my mind there are three scenarios that might account for this mind-bending discrepancy at the heart of our understanding of reality. First, our physics – our very conception of spacetime – may be flawed or at least incomplete. Second, some might conclude that the nature of the universe is fundamentally unknowable by the human mind and thus must be the result of a mathematical god, or mathematics itself. And third, as proposed by Nick Bostrom and many philosophers before him, we might be living in a simulation. I find this third idea deeply unsatisfying: if we are simulated, then there must be a deeper reality in which the simulation runs—and we are left chasing the recursion. The old ‘turtles all the way down’ problem (6).
For me, when I reach the limits of what I can reason, the only sensible response is to take my dog for a long walk, and then go to the pub with friends. Still, I cannot help but speculate: what if reality is fundamentally informational — and computational? What if matter and spacetime are emergent—illusions born of interference patterns, field effects, or something stranger still? A line of thought that, I think, leads us back to Cantor, to Hilbert, to Maxwell, to Boltzmann.
And what of consciousness — our irreducibly first-person experience of being? Classical physics assumes objectivity, but that assumption now wobbles. John Bell’s brilliant theorem showed that no theory based on local realism can account for quantum behaviour — a truth confirmed in exquisite detail by the experiments recognised in the 2022 Nobel Prize in Physics. Bell, who died too early, left us with a deep wound in the heart of classical thought. And consciousness — the so-called Hard Problem — remains untouched by equations.
But that’s for another day. Time for that walk.
Selected references, notes and links
1 Lemaître, G. 1927. Un univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques. Annales de la Société Scientifique de Bruxelles, A47, pp. 49-59.
2. The expanding universe theory is commononally now known as ‘The Big Bang’, a term that was first coined mockingly on 28th March 1949 in a BBC radio broadcast by the English astronomer Fred Hoyle who vehemently opposed the theory.
3. Riess, A.G., Filippenko, A.V., Challis, P., Clocchiatti, A., Diercks, A., Garnavich, P.M., Gilliland, R.L., Hogan, C.J., Jha, S., Kirshner, R.P., Leibundgut, B., Phillips, M.M., Reiss, D., Schmidt, B.P., Schommer, R.A., Smith, R.C., Spyromilio, J., Stubbs, C., Suntzeff, N.B. and Tonry, J., 1998. Observational evidence from supernovae for an accelerating universe and a cosmological constant. The Astronomical Journal, 116(3), pp.1009–1038. doi:10.1086/300499.
4. https://www.nobelprize.org/prizes/physics/2011/summary/ . The Prize was divided, one half awarded to Saul Perlmutter, the other half jointly to Brian P. Schmidt and Adam G. Riess “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae”.
5. PBS Space Time (2023) The Worst Prediction in Physics [online video], 7 July. Available at: https://www.youtube.com/watch?v=M8Ao_oZnbe4 (Accessed: 23 May 2025).
6. https://en.wikipedia.org/wiki/Turtles_all_the_way_down.