Lancaster physicist Dr Jonathan Gratus is challenging a core assumption of the current model of the universe using mathematical pictures of the cosmos.

His joint paper with Lancaster alumnus and Nottingham PhD student Sam Close is entitled “Infinite Blueshift as a Challenge to Past Eternal Inflation” published in Classical and Quantum Gravity.

They began their investigation with the Penrose diagram of de Sitter space, which models eternal inflation. Named after the eminent physicist Roger Penrose, a Penrose diagram is a two-dimensional diagram capturing the causal relations between different points in spacetime.

Dr Gratus said: “Our current best model of the universe requires a period of rapid growth called inflation in order to explain, among other things, why the universe appears so flat. We know the minimum period of inflation, but few constraints on the maximum period of inflation, which in some models is eternal.”

The physicists’ powerful method of representing the universe is to add mathematical ‘metric hyperbolae’ to the Penrose diagram to transform it into a tool which, in addition to capturing the causal relations, also describes the geometry and, in this case, the nature of light from distant objects.

Using these pictures, they showed that, in an eternally inflating universe, an observer will see flashes of high intensity blue light from sources that are rushing towards them.

“In our work, we find that in such a universe which had past eternal inflation, one would see almost everything rushing towards us, becoming bigger in the sky and being infinitely bright and infinitely blue shifted. This is a Doppler effect where photons become more energetic.”

However, there has never been any observation of such intense flashes of blue light.

“In reality, we see most objects rushing away from us, and their light is increasingly red shifted. Explaining this discrepancy opens some interesting questions about our universe.

“Using our results, we know the universe could not have been eternally inflating in the past and we can estimate the maximum number of times the universe doubled in size during inflation, which is of a similar order of magnitude as other values found in the literature.”

Dr Gratus is currently writing an introduction to relativity based on this visual approach.

“This may open the door to a greater appreciation of the power of visual reasoning, which may improve lay understanding of ‘complicated’ physics.”