Los Angeles | Humans may be more aligned with the universe than thought, say scientists who found that the structures of our cell cytoplasm and neutron stars are similar, both resembling helical multistory parking garages.
Researchers from the University of California, Santa Barbara in the US, explored the biophysics of shapes – helices that connect stacks of evenly spaced sheets – in a cellular organelle called the endoplasmic reticulum (ER).
These structures named ‘Terasaki ramps’ were thought to be unique to soft matter (like the interior of cells) until researchers happened upon the work of nuclear physicist Charles Horowitz at Indiana University in the US.
Using computer simulations, Horowitz and his team had found the same shapes deep in the crust of neutron stars.
Nuclear physicists have an apt terminology for the entire class of shapes they see in their high-performance computer simulations of neutron stars: nuclear pasta.
These include tubes (spaghetti) and parallel sheets (lasagna) connected by helical shapes that resemble Terasaki ramps. However, differences can be found in the underlying physics.
Typically matter is characterised by its phase, which depends on thermodynamic variables: density (or volume), temperature and pressure – factors that differ greatly at the nuclear level and in an intracellular context.
“For neutron stars, the strong nuclear force and the electromagnetic force create what is fundamentally a quantum-mechanical problem,” said Greg Huber, physicist at the University of California, Santa Barbara.
“In the interior of cells, the forces that hold together membranes are fundamentally entropic and have to do with the minimisation of the overall free energy of the system. At first glance, these could not be more different,” said Huber.
Another difference is scale. In the nuclear case, the structures are based on nucleons such as protons and neutrons and those building blocks are measured using femtometres.
For intracellular membranes like the ER, the length scale is nanometres. The ratio between the two is a factor of a million, yet these two vastly different regimes make the same shapes.
“This means that there is some deep thing we do not understand about how to model the nuclear system,” Huber said.
The similarity of the structures is riveting for theoretical and nuclear physicists alike.
“Seeing very similar shapes in such strikingly different systems suggests that the energy of a system may depend on its shape in a simple and universal way,” said Horowitz.
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