The vacuum isn’t empty. Even where there is no matter and no radiation, there is structure – and we may be able to use the structure of the vacuum itself to send and receive messages.
No matter how empty space gets, the fundamental laws of physics dictate that it is always teeming with energy from the quantum fluctuations of various fields, like the electric and magnetic fields. “Empty space is something dynamical,” says Achim Kempf at the Perimeter Institute in Canada. “It’s not really empty. Space and time are actually something, and that something can vibrate.”
We already expected we can use electromagnetic fields to probe the structure of the vacuum and also to make it vibrate. Charles Su and Rainer Grobe at Illinois State University calculated that these vibrations in the structure of the vacuum itself can be used to communicate.
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The method in their thought experiment uses electromagnetic fields to manipulate the vacuum, but does not actually send any photons of light from the sender to the receiver. “If there were a photon moving there, that would just be normal wireless communication like a cell phone,” says Grobe. “There is no matter or charge being transported.”
Something from nothing
Instead, it uses one of the strangest properties of the vacuum: in theory, if you apply a strong enough electromagnetic field, you can rip pairs of electrons and their antimatter twins positrons from what seems to be thin air in what’s called the Schwinger effect. The field then blasts the two particles in opposite directions so that they cannot come back together and annihilate, which would see them fade back into the vacuum.
Su and Grobe calculated that a weaker electromagnetic field applied to an area of vacuum can create ripples in its structure, and these ripples can be measured via the energies of the particle pairs generated by the Schwinger effect.
The ripples from the weaker field propagate outward through the vacuum, effectively like the water ripples generated by dropping a pebble into a pond. Then, when the extremely powerful field is applied to the rippling vacuum, the energy distributions of the stream of electrons and positrons that it creates change depending on the size of the ripples.
This means that by then tweaking the weaker field to change the size of the ripples, it is possible to use the very fabric of the vacuum to send a message – for example, by correlating each particle energy distribution resulting from a particular size of ripple to a letter. “You can think of it as a sort of Morse code,” says Kempf.
Into the abyss
The researchers emphasize that these calculations are very preliminary. It is not yet clear over what distances these messages could be sent or in what contexts they might be useful.
“There are numerous challenges, both theoretically and practically,” says Grobe. “We are beginning to maybe see how one could manipulate the vacuum itself, but we are very far away from any practical applications.”
Perhaps the most basic challenge is that we do not yet have lasers strong enough to produce the Schwinger effect. “The Schwinger effect has been around the corner for decades now,” says Kempf. The main problem is that a laser strong enough to rip particles from the vacuum is also strong enough to destroy just about anything else, including the machinery that’s generating it.
“This is just a first step to explore something unknown,” says Grobe. If we do eventually succeed in building a powerful enough laser, we may be able to create messages in what appears to be absolutely nothing, and receive them by ripping matter from the fabric of the vacuum.
Physical Review Letters
