The short answer is yes and no.
As Geoffrey Greene points out in The Sixth Paper, you’d have to corral a tremendous amount of energy to convert it into mass. Doing so is not possible with our current technologies and scientific knowledge. However, as Greene likes to say: 1904.
This is a term Greene coined in the story to mean never say never, and that we should keep an open mind. 1904 was the year before Einstein published the four papers that changed science as we knew it. In 1904, people were absolutely certain about a lot of things that a year later Einstein proved not to be. For example: time. In 1904, if you told the average person that a minute of time for someone standing at the base of a mountain moved slower than a minute for someone at the top of that mountain, they would have said you were crazy. However, Einstein proved that to be true in his theory of special relativity, his third published paper in 1905.
Geoffrey Greene is fond of saying that Einstein made the impossible possible, but what he actually did was much simpler: he corrected and broadened our understanding of physics.
So while a nuclear shield might not be constructable today, Einstein’s 1905 mass-energy equivalence paper showed that reverse conversion is possible — on paper, if not yet in practice.
Arguably the most famous equation in history, it states that the energy of a system equals its mass (matter) multiplied by the speed of light squared. This concept was set forth in Einstein’s mass-energy equivalence paper, his fourth and final paper in 1905.
Two things of great interest in this. First, the formula quantified the immense amount of energy contained with matter; and second, it showed that mass and energy are different forms of the same thing, that they are interchangeable. This led scientists to discover nuclear weapons and nuclear power, using fission to break apart atoms and release the strong force energy in the process. The strong force is the most powerful of the four known natural forces, the other three being gravity, electromagnetism, and the weak force (a quantum energy like the strong force, but a million times weaker).
However, it wasn’t until the year 2021, in an experiment at Brookhaven National Laboratory, when scientists were finally able to prove that reverse conversion was possible.
Scientists from the Department of Energy crashed gold ions moving at nearly the speed of light into each other. As that speed, the gold ions formed photons, which is energy, that traveled with the ion. After the collisions, scientists detected electrons, which are matter. The photons had turned into electrons, energy into matter. Earlier experiments showed that reverse conversion was possible, but those experiments were multi-stepped. This experiment at Brookhaven directly converted the photon-energy into electron-matter for the first time.
The laws of physics allow for reverse conversion. Perhaps one day we will find the treasure of knowledge that allows us to do so and we will be able to turn a deadly nuclear blast back into a few grams of matter.
