Earlier this year, we wrote about the theoretical possibility of using black holes as batteries. In this approach, a small primordial black hole (one formed around the time of the Big Bang) can be charged until it begins repelling the charge, effectively making it a battery.
The concept is theoretical since questions such as how we charge a black hole and transport its energy back to the Earth are largely unanswered. But that does not stop theoretical physicists from thinking about other energy storage possibilities.
Last month, a paper in published in High Energy Density Physics spoke about the use of micro black holes as batteries. Coffee Table Science got in touch with its authors, Espen Haug and Gianfranco Spavieri, to know more about it.
Espen Haug is a researcher at the Norwegian Institute of Life Sciences, while Gianfranco Spavieri is a Professor Emeritus at the Universidad de Los Andes, Centro de Fisica Fundamental, in Venezuela.
Professor Espen Haug, one of the authors of the micro black hole battery paper.
Coffee Table Science (CTS): Scientists have previously discussed accessing energy from black holes. Since they are far from Earth, how can this energy be transferred back?
Espen Haug (EH): This approach is interesting, but we believe it to be highly unrealistic, as it requires transporting energy over enormous distances. Even reaching any known black holes would likely be impossible in the foreseeable future. Nonetheless, such ideas are intriguing, as they prompt consideration of distant possibilities for the future. However, at present, they seem more akin to science fiction than to practically implementable science.
How old is the concept of black holes as batteries? Who first thought of this idea?
To our knowledge, Mai and Yang have first proposed the concept of a black hole battery. We have gone further and explored the potential of micro black hole cellular batteries, leveraging the distinctive properties of what is known as the extremal solution to the Reissner-Nordström exact solution of Einstein’s field equations.
Einstein introduced his theory of general relativity in 1916, which remains the cornerstone of contemporary gravitational theories. Reissner and Nordström solved Einstein’s equations to describe charged black holes, within which the extremal solution represents a specific mathematical solution. We have found that these extremal micro black holes exhibit unique characteristics, making them ideal candidates for exceptionally powerful batteries—at least, that is the implication of Einstein’s theory.
Einsten and Markov proposed micro black holes in 1960s. Image credit: Dee/Pixabay
Your recent paper talks about micro-black holes. What classifies as a micro black hole?
A micro black hole is the smallest possible type of black hole.
Stephen Hawking and the less-known physicist Markov were the first to suggest the existence of micro black holes in the late 1960s to early 1970s. They theorized that these black holes would be approximately the size of the Planck mass. The concept of the Planck mass was proposed by the renowned physicist Max Planck in 1899, and it is about 10^(-8) kg, roughly the mass of a fly’s egg.
However, for this mass to form a black hole, it needs to be compressed within the radius of the shortest possible length considered in quantum gravity, namely the Planck length. The Planck length, also introduced by Max Planck in 1899, is extremely short (small), on the order of 10^(-35)meters. This is much shorter (smaller) than anything we can measure directly today, though it has been measured indirectly through gravitational observations.
How will a micro black hole battery work? What would be its advantages?
First of all, micro black holes are exceptionally adept at storing energy. Unlike large, standard astrophysical black holes, these micro black holes do not emit Hawking radiation. Furthermore, they do not continuously absorb matter and energy, which is beneficial since a black hole used as a battery that engulfs its surroundings would be problematic. The mathematics suggests a perfect equilibrium between the electrostatic and gravitational forces within these micro black holes, rendering them 100 percent stable.
This stability implies that they do not lose energy and can store it indefinitely. Moreover, the energy density of micro black holes is enormous. For instance, a battery weighing just one kilogram could provide approximately 470 million times the energy of the most efficient 200-kilogram lithium battery. This means that a family could rely on a single charge for their lifetime or multiple generations, using it to heat their homes, fuel their car, and even power their private drone helicopter.
However, to utilize this battery, one must also be able to release the stored energy. This can be achieved simply by bringing together negatively and positively charged micro black holes. It is likely that they would annihilate each other upon contact, releasing all the stored energy. This would necessitate incredibly small containers to hold the positively and negatively charged micro black holes separately. When energy is needed, a couple of them are released for a micro black hole annihilation.
The significant advantage of micro black hole batteries over other black hole energy storage concepts is their feasibility of being created on Earth, their extreme compactness, and their unparalleled energy density, making them potentially the most efficient energy storage ever conceivable.
A single micro black hole battery could serve a family for their lifetime and even beyond.Image credit: Gerd Altmann/ Pixabay
Could one possibly generate a micro black hole in the lab? How would that be achieved?
This endeavor could potentially be carried out in large particle accelerators. However, the Large Hadron Collider (LHC) does not appear powerful enough, providing another reason to build and design particle accelerators that are even more powerful than those currently at CERN. Some theories of quantum gravity also suggest that these micro black holes could be hidden everywhere around us, but they are so small that detecting them is almost impossible.
Nevertheless, there are laboratories planning to work on detecting them. My lab has initiated the construction of a laboratory equipped with gravity-measuring devices ordered from Germany, aiming to detect micro black holes. Others have proposed that they could be detected in high-energy cosmic rays. The truth is, we simply do not know yet, but there will certainly be laboratories exploring the various possibilities to find them.
On a lighter note, it is unlikely that a black hole battery will be discovered in our lifetimes. Why do scientists entertain such outlandish ideas in the first place?
Researchers hold varying opinions on this matter. Some believe it is impossible, while others, like us, think it could be possible. However, even if it turns out to be impossible to build such batteries and they can only be studied theoretically, they still seem to define the ultimate limit on battery energy density achievable in the future, based on the laws of physics. The energy density is vastly higher than today’s batteries, indicating that we are just at the very early stages of a battery revolution.
This ongoing revolution in battery capacity could be akin to the revolution witnessed in computing. Just as computers have become significantly more powerful every few years, we might see a similar trend with batteries. For those old enough to remember the first computers, the progression to increasingly powerful machines has been nothing short of amazing.
We anticipate a similar evolution with batteries. Naturally, if micro black holes become a reality, they would revolutionize clean energy storage, marking a significant breakthrough in the field.
These are indeed very exciting times.
(The interview was conducted via email, and the responses have been edited lightly for clarity)
