In addition to being a staple of science fiction, the concept of megastructures has long been the subject of serious scientific studies. As famed physicist Freeman Dyson originally proposed in 1960, “Malthusian pressures will ultimately drive an intelligent species” to occupy an “artificial biosphere which completely surrounds its parent star.” In short, he theorized that advanced civilizations would disassemble their planet (or planets) to create a structure (which has since come to be called a “Dyson Sphere” that would harness all the energy from their star and provide immense living space.

Over time, scientists have proposed many variations on this structure, collectively known as “Dyson Structures.” However, considerable research has countered these proposals, arguing that such megastructures would be unstable. In a new study, famed engineer Colin R. McInnes demonstrates how two specific megastructures – Dyson Bubbles and Stellar Engines – could be built in such a way that they would be passively stable over time. These findings could aid the Search for Extraterrestrial Intelligence (SETI) by constraining the technosignatures these structures could produce.

Colin R. McInnes is a Professor of Engineering Science at the University of Glasgow and the chair of the James Watt School of Engineering. His findings are presented in a paper that appeared in the Monthly Notices of the Royal Astronomical Society. While the concept is several decades old, megastructures have received renewed attention thanks to the discovery of Boyajian’s Star and other cases where stars exhibited periodic dimming, were low in luminosity, or were “missing.”

In addition to being a leading figure in the field of solar sails, reflectors, and satellites, McInnes has also previously authored a paper on the subject of megastructure stability. As he summarized in this latest study, megastructures have been proposed for a range of ventures, including asteroid orbit modification, climate engineering (i.e., solar shields), terraforming (a la Ken Roy’s Shell World concept), and planetary orbit modification (moving them into the star’s habitable zone).

At larger scales, scientists have considered how massive swarms of reflectors could enshroud a star, known as a Dyson Swarm, Bubble, or Matrioshka Brain, or be used to alter a star’s orbit, known as a Stellar Engine or Shkadov Thruster. In the case of the former, the reflective surface ensures that radiation pressure will levitate the swarm (which could support habitats) above the star. In the latter, a flat reflective disk remains bound to a star through gravitational coupling, causing the star to move.

Much like Dyson proposed in his original paper, these studies assume that advanced civilizations will experience exponential growth and rising energy demands as they age. “Freeman Dyson imagined a swarm of energy-collecting elements enveloping a central star as an endpoint for a civilisation with continuously growing energy demands,” McInnes told Universe Today via email. “It’s clearly difficult to infer motivations. However, the universality of the laws of physics means that we can at least speculate on how such structures could be engineered.”

While a popular idea among scientists, considerable research by physicists and structural engineers has cast doubt on the existence of megastructures. In short, they have argued that such structures would be, by their very nature, gravitationally unstable. But as McInnes explained, it is possible that megastructures could be built in a way that would ensure long-term passive stability:

Many concepts, such as a rigid Dyson sphere or Ringworld, are not in orbit, and so a small displacement can cause the structure to drift and collide with the central star. They would therefore need active control measures to stabilise them. However, my interest is in understanding ways in which ultra-large structures could be engineered so that they are passively stable. We can imagine that engineers, terrestrial or otherwise, would prefer passive stability to more complex active control measures.

The simplest design (he notes) for a Stellar Engine would likely be a flat reflective disk. Using an ultra-large disk as a starting point, he calculated the structure’s stability from first principles using a simplified model of a perfectly reflecting rigid disc. He then employed the functional forms of gravitational and radiation-pressure forces to investigate the stability of a stellar engine and of orbiting reflectors (making up a Dyson’ Bubble) in different configurations. Said McInnes:

Stability analysis involves adding a small displacement to the equations of motion describing such structures and then determining if the displacement grows with time. Then, by considering ways to engineer the structure’s properties, for example, its geometry or mass distribution, we can determine if it can be stabilized such that small displacements do not grow and are bounded. There isn’t a set process as such; it’s a case of looking at the equations of motion and considering how the forces acting could be modified, for example, through changes in the geometry or mass distribution of the structure.

In the end, his analysis showed that while an ideal stellar engine comprising a uniform, reflective, rigid disc is unstable, a reflective disc whose mass is concentrated at its edge can (in principle) be passively stable. By balancing the gravitational and radiation pressure forces, such a design would also maximize the stellar engine’s propulsion. Meanwhile, a self-stabilizing Dyson Bubble or Swarm would avoid (or minimize) collisions among the cloud’s elements and maintain equilibrium, provided the right configuration and design considerations were taken into account.

These structures would also produce telltale technosignatures that SETI researchers could look for in the future. While a Stellar Engine would scatter light reflected from its star, a Dyson Bubble would appear as a dense cloud enclosing a star, thus modifying its spectral characteristics. For a static cloud, there would be no flickering apparent to observers, unlike a swarm of orbiting reflectors, which would pass in front of the stellar disc. And as Dyson first predicted, e a solid Dyson sphere would be discernible from the infrared excess produced by radiated heat.

However, as McInnes added, this study is not the final word on megastructures and their potential stability. “The analysis in the paper is simplified and makes a number of assumptions,” he said. “However, it’s a starting point to begin to understand how ultra-large structures could be engineered to be passively stable. For example, a dense Dyon bubble can apparently be self-stabilising due to light pressure falling faster than gravity as we move out through the cloud of elements. Perhaps by understanding how such structures can be engineered to be passively stable, we can better predict the technosignatures associated with them.”

Further Reading: MNRAS

The city of Riverside is trying to fire three of its police officers because they’re using license plates for disabled veterans on their personal vehicles despite having no apparent problems performing their jobs, the officers’ attorney has claimed.

The department’s logic for firing the officers, their attorney Matthew McNicholas said, was that they must have lied to the California Department of Motor Vehicles in order to obtain the specialized plates, which exempt drivers from paying registration fees and allow them to use disabled parking spots and park in metered spots for free.

That logic is broken, McNicholas said, because under federal law, to get a 100% disability rating — which each of the officers obtained — a veteran doesn’t have to be fully disabled. A veteran can get that disability status through a combination of partial disabilities, such as partial hearing loss, post-traumatic stress disorder or a back injury. To obtain plates for veterans rated as 100% disabled, a person must submit a certificate from a medical professional or a county, state or federal veterans’ agency confirming their disability.

“The department said it’s a bad look” for the officers to come to work in their personal cars carrying plates for veterans with a 100% disability rating, McNicholas said in an interview Tuesday.

The Riverside Police Department declined to comment on the case or the officers’ status with the agency, citing employee confidentiality. But McNicholas said that the department is acting out of concern about public perception and to punish the officers for refusing to remove the plates when asked to do so by their superiors.

Officers Timothy Popplewell, Richard Cranford and Raymond Olivares were put on administrative leave and informed of an internal investigation into their use of veteran plates on May 21. They sued the agency about two months later, claiming in a complaint filed July 17 in Riverside County Superior Court that it had discriminated against them and harassed them based on their veteran and disability status. On Feb. 24, the Riverside City Council met in closed session to discuss whether to settle the case and voted against doing so, said Saku Ethir, the Riverside Police Officers’ Assn. attorney representing the officers. The day after that vote, the officers received notices of termination, Ethir said.

The city moved to fire the officers because despite having special veteran plates stemming from their war injuries, they “showed up to work” and “were completely fit and satisfactory,” McNicholas said in a video posted to Instagram March 2. All three had been asked by their superiors to replace the plates on their cars but refused, McNicholas said. A fourth officer with veteran plates agreed to remove them and has not faced termination, he said.

Through a spokesperson, the Riverside Police Department declined to answer questions about the officers, “due to the confidential nature of the personnel action which has not completed its process.”

In an Oct. 16 response to the officers’ lawsuit, the department said it “acted in good faith with reasonable belief that its actions were lawful and further did not directly or indirectly perform any acts whatsoever which would constitute a breach of any duty owed to Plaintiffs.”

Popplewell, Cranford and Olivares will still have a chance to argue to the department that they shouldn’t be fired, Ethir said. They’ve already been provided with documents the department relied on in its decision to fire them, but a hearing to appeal their termination has not yet been scheduled, she said. Ethir said she believes the department has not provided all the records it is legally obligated to give the officers.

Popplewell served in the military from 2008 to 2011 and was deployed in Iraq, McNicholas said. Olivares was in the Marines from 2013 to 2019 and was deployed in the Middle East and Africa. Cranford served in the Army from 2010 to 2014 and was deployed to Iraq. All three joined the Riverside Police Department in 2019, according to the lawsuit.