A Hologram for All Theories

When I am not editing Holography News for Reconnaissance International, I volunteer as an online maths and science tutor. Nowadays, I tutor students from age 15 to 18, but I have previously taught children as young as 11.

One of the strangest experiences I am constantly amazed by is the ease with which students accept the idea of gravity. In the UK, the concept of gravity is introduced through the story of Sir Isaac Newton (1642-1727) sitting underneath a tree, when suddenly, without any apparent projectile being thrown, an apple falls from the tree and lands on his head.

Its gravity – stupid!

And that’s it. From that point on if you ask a child what is the non-contact force that acts between two masses at a distance, you should get the answer ‘gravity’ – that is if the student has been paying attention! If you get a question in an exam ‘what is the force that holds the Earth in orbit around the Sun’ – you should answer ‘gravity’: ‘what holds a person to the surface of the Earth’ – answer ‘gravity’ (although I did get one answer from a student that it is the force of ‘atmospheric pressure’ pressing us to the surface which got me thinking that it wasn’t such a silly counter-hypothesis – but even then it is gravity that holds the atmosphere to the Earth).

The Newtonian model and equations that have survived for 300 years are simple and elegant. The force of gravity between two objects is always attractive and is related (through the so-called gravitational constant) to their masses and the reciprocal of the distance (squared) between them.

But just because we continue to teach this simplistic but highly accurate (on an everyday macroscopic scale) explanation of gravity to students doesn’t mean that physicists have stopped thinking about better models to describe the phenomenon of why two seemingly unconnected objects should fall towards one another and in so doing bring into being the planets, stars and galaxies that make up the known universe.

Holograms as models of the universe

And so it is that Quanta Magazine has recently published an article ‘Symmetries Reveal Clues About the Holographic

Universe’ ¹,which describes physicists’ attempts to use quantum field theories to describe gravity, and that one of the most promising of those efforts treats gravity as something like a hologram – a threedimensional (3D) effect that pops out of a flat, two-dimensional (2D) surface.

In the Quanta article, the notion that a thin and flat emulsion on a plate can store and then replay a real image of a 3D object complete with all of the optical information that described the original object is used to model the universe as largely flat and contained within a sphere of infinite radius.

It’s not the first time that various properties of optical holograms have been used to model evolving theories of the universe involving quantum gravity.

On his staff page on the University of Southampton (UK) website, Prof Kostas Skenderis Professor of Theoretical Physics, Head of Applied Mathematics & Theoretical Physics, sets out that his research interests include relativity, cosmology, quantum field theory and string theory. In particular, he has worked extensively on holographic dualities which he claims, if correct, would change the paradigm for physical reality.

A significant part of his work has been devoted to developing and extending the holographic dictionary. Specifically, he has developed the method of holographic renormalization, which ultimately could lead to a manifestly holographic reformulation of physics.

Another example of academic use of holograms as a model for the universe came when Prof Stephen Hawking (theoretical physicist and cosmologist who passed away in 2018), working with Belgian colleague Prof Thomas Hertog, extended the notion of a holographic reality to explain how the universe came into being from the moment of the Big Bang.

His theory embraced the concept that the universe is like a vast and complex hologram. In other words, 3D reality is an illusion, and that the apparently ‘solid’ world around us - and the dimension of time - is projected from information stored on a flat 2D surface.

The model-maker

And so, what is it that makes the hologram such a useful model-making tool to theorists? Firstly, it should be noted that the theories don’t run ‘the universe is a hologram’ but rather ‘the universe is like a hologram’. Current theories, as I understand them, don’t postulate that the physical world we inhabit is a store of interference patterns between a signal and a reference wave. Its closer to the idea that what we perceive as 3D and solid may be the image of 2D processes on a huge cosmic horizon – the so called ‘holographic principle’.

Humans are accustomed to seeing the 3D solid world we inhabit squashed onto the 2D plane of a photograph, TV screen, movie theatre or computer monitor. We are less accustomed to witnessing 2D surfaces manifesting 3D real images – except for the holograms on credit cards and banknotes we handle – making them an obvious candidate to help explain complex 2D to 3D transformations to non-specialists.

Fast forward a further 300 years, and in the same way that gravity is currently ingrained in students as the answer to what holds objects to each other over distance, so it might be that the stock answer to ‘how would you describe the universe’ might just be ‘it’s a hologram, of course’.

Editor’s note. I am embarrassingly aware that this article is very UK-biased, so I’d really love to hear from other holographers with examples of where holographic principles have been used to model scientific theory.