prism
© Chris Rogers-Rainbow/Science Faction/CorbisSpacetime is often discussed as a unified mechanism—but what if were actually that different particles felt its existence in a different way, creating a ‘rainbow’ composed of many forms of spacetime? Physicists from the University of Warsaw have used quantum theory to develop a model that supports this idea.
  • Researchers have suspected that spacetime is sensed in different ways
  • Physicists' model reveals different interactions based on particle energy
  • Thus, classical spacetime structure depends on energy of varying particles
Spacetime is often discussed as a unified mechanism—but what if were actually that different particles felt its existence in a different way, creating a 'rainbow' composed of many forms of spacetime?

Earlier hypotheses on this idea were formed from guesses, but now, physicists from the University of Warsaw have used quantum theory to develop a model that supports ideas of a structure based on the energies of different particles. When white light is passed through a prism, the rainbow on the other side reveals a rich selection of colours - and spacetime works in the same way, the researchers claim.

Just as a normal rainbow can be described in terms of varying wavelength, the physicists suggest the 'spacetime rainbow,' reflects the measure of energy differences.

The researchers explain the phenomenon in terms of a common experiment: white light passes through a prism, splitting to form a rainbow. This could be explained by saying that photons of different energies 'sense' the prism as having slightly different properties, the researchers write. In quantum universe models, theorists have suspected a similar behaviour, that particles of different energies sense spacetimes with slightly different structures.

'Two years ago we reported that in our quantum cosmological models, different types of particles feel the existence of spacetimes with slightly different properties,' said Professor Jerzy Lewandowski, who led the study. 'Now it turns out that the situation is even more complicated. We have discovered a truly generic mechanism, whereby the fabric of spacetime felt by a given particle must vary depending not only on its type, but even on its energy.'

To create a model, the researchers focused on two components: gravity, and one type of matter. The physicists then quantized the model, converting continuous values to discrete values that could only differ by specific intervals. 'Today there are many competing theories of quantum gravity. Therefore, we formulated our model in very general terms so that it can be applied to any of them,' said PhD student Andrea Dapor.

'Someone might assume the kind of gravitational field—which in practice means spacetime—that is positied by one quantum theory, and someone else might assume another. Some mathematical operators in the model will then change, but this will not change the nature of the phenomena occurring in it.'

Using the quantum theory, the researchers found that the processes showed the same behaviour as when the theory is applied to a classical continuous spacetime, like the one we experience.

'This result is simply astonishing. We start with the fuzzy world of quantum geometry, where it is even difficult to say what is time and what is space, yet the phenomena occurring in our cosmological model still look as if everything was happening in ordinary spacetime!' said PhD student Mehdi Assanioussi.

When looking at the scalar field, the particles of matter, calculations revealed that particles that differ in energy interacted differently with quantum spacetime. The researchers say this means even the structure of classical spacetime must depend on the energy of the individual particles. This relationship can be explained in terms of a 'beta function,' which measures the extent to which the classical structure is changed based on the different particles. According to the research, this function reflects the degree of 'non-classicalness' of quantum spacetime.

In a classical-like setting, the function would have a value close to zero, while it would have a value close to one in quantum conditions. This means that the rainbow would expand as the beta function moves closer to one. In the classical-like state of our Universe, the value suggests support for the theory, with a figure below .01.

So, while the spacetime rainbow may exist, it is so narrow it cannot be detected in an experiment.