Spooky Action At A Distance - Albert Einstein

August 09, 2004

Artist's rendition of an atom. Image credit: NSF

Essay by Mark Waldron

Once derided by Einstein as "spooky action at a distance", quantum entanglement could hold out the promise of a novel means of space propulsion, perhaps even making interstellar travel feasible.

Astrobiology Magazine -- In 2001, researchers at the University of Aarhus' Quantum Optics Center in Denmark successfully applied a phenomenon of physics known as quantum entanglement to two specimens of cesium measuring in the trillions of atoms apiece, transferring the quantum state of one group of atoms to the other. Such a transfer is called "quantum teleportation," though it is hardly teleportation of the Star Trek variety.

The success in Denmark was noteworthy due to the scale of the experiment; previously the quantum states of only a handful of atoms at a time had been successfully entangled. In addition to whole atoms, there have also been multiple quantum teleportations of laser beams beginning with a successful experiment in such teleportation conducted by the Australian National University in 2002.

At present, the primary application of quantum teleportation is viewed as being the development of quantum computing, in which the logic gates of a computer processor are integrated at the atomic level and the logic state of one of the processor's bits would be denoted by the quantum state of an individual atom. (Such a representation of computer logic can be applied to computer's memory as well, creating, in effect, quantum RAM.) In addition, a field of quantum cryptography is being developed from the ability to teleport laser beams, which are capable of carrying information. A teleported laser beam that conveys data would provide an ultrasecure, essentially unbreakable means of encoding sensitive information.

This author would like to propose a third (and even a fourth) application of quantum teleportation, an application with implications at least as far-reaching as the two mentioned above: propulsion. It should be possible to apply quantum teleportation to the problem of deep-space propulsion; not only is such an application possible, but, if implemented, would revolutionize space travel, even to the point of making interstellar travel (both manned and unmanned) truly feasible for the first time. Interestingly, the initial steps of applying teleportation as a propulsion method can be taken using present-day technology.

In brief, the idea is to apply quantum entanglement to ion propulsion. An ion drive system is a form of rocket propulsion which uses a stream of charged particles, or ions, as a rocket exhaust. Ion drives typically yield far lower thrust-to-weight ratios than traditional chemical rockets, but because of their much slower fuel burn rate they can gradually accelerate a spacecraft to speeds that no chemical rocket can reach.

Ion propulsion was used on NASA's highly successful Deep Space 1 probe, in the form of a solar-electric drive, that is, an ion drive in which solar panels provide the electrical power that is used to excite the fuel material to produce the ion stream that propels the craft. Interestingly, cesium is one of the materials that has been used as a fuel in ion rockets.

While quantum entanglement and quantum teleportation experiments have to date been confined to entangled specimens of materials within the same laboratory, there is no theoretical limitation on how great a distance quantum entanglement can operate across. In other words, once two groups of atoms have been entangled, that entanglement would still be in effect were one of the entangled specimens moved to the other side of the earth.or the solar system.

Therefore, were two specimens of cesium (to take one example; other materials would also work) to be entangled on earth, then one of the specimens lofted into space, exciting the earthbound cesium sample to produce ions would result in the space-traveling cesium sample becoming energetically excited and producing ions like its earthbound counterpart. A resulting ion stream, produced without the benefit (or hindrance, for that matter) of any form of internal engine system onboard the spacecraft, could propel the craft through space. It would be a kind of engineless drive system, which I am calling the teleportation drive. The actual engine and, even more importantly, its power source-a nuclear reactor, a solar array, or other form of power generation-would remain on earth along with the earthbound, entangled fuel sample.

The benefits of a teleportation drive are most apparent when one considers the various forms of nuclear-electric propulsion that are currently in vogue among NASA researchers. A nuclear-electric drive is a form of ion drive which uses a nuclear reactor to produce the electricity needed to generate its ion exhaust stream.

Because of the far higher power levels a nuclear reactor can yield versus solar power, the nuclear-electric drive has risen to the forefront of NASA's ion drive design options in the last few years; being the centerpiece of its Project Prometheus, a long-range research effort into nuclear propulsion systems for spacecraft. For example, the space agency's Jupiter Icy Moons Orbiter (JIMO) project, an offshoot of Project Prometheus, is to be powered by a nuclear-electric drive system.

JIMO will require a 100-foot boom section to separate the craft's instrument payload from its nuclear reactor; large radiator fins will also be mounted on the reactor section to dissipate excess heat generated by the drive. These two requirements-physical separation of the drive from the rest of the craft and radiator fins for heat dissipation-are two distinctive hallmarks of traditional nuclear-driven propulsion system designs.

From the standpoint of a government-funded space agency, there are also political drawbacks to placing a nuclear reactor in space. With a teleportation drive, there are no radiator fins or separator sections needed on the spacecraft; furthermore, the negative political issues surrounding nuclear space propulsion systems vanish. These, however, are all secondary benefits, as important as they are. The primary benefit of the teleportation drive is that it effectively removes all limitations on how much power can be generated to propel the spacecraft.

The need for a high-yield yet compact power source has been the bane of nuclear propulsion designs in the past; it is, for instance, a major technical barrier to seeing the realization of NASA's VASIMR (Variable Specific Impulse Magnetoplasma Rocket) drive, under development at the Johnson Space Center in Houston under the direction of Dr. Franklin Chang-Diaz. Because the power source of a teleportation drive is earthbound, it can be arbitrarily large.

A very large nuclear reactor-which now of course does not need to be flown into space-can provide the power for propelling a very small spacecraft. Such a craft could enjoy a very high thrust-to-weight ratio, potentially greater than that of chemical rockets, with obvious benefits in terms of maximum attainable speed when combined with the teleportation drive's inherently high fuel efficiency (high specific impulse, in rocketry parlance).

The new thrust levels attainable by a teleportation drive might also allow for the craft to take off directly from the earth's surface, without the need for chemical rockets to place it in space, something never before attainable with any form of ion drive. Finally, in the past only two forms of power source have been put forward for ion drives: solar and one or another form of nuclear power.

Since a teleportation drive's power source remains earthbound, any method of generating electricity can be applied to power the drive, including hydroelectric power (imagine Hoover Dam generating the power for a deep space probe's engine). There is also an economy of scale that applies to the earthbound power source in that the same source can be used to excite multiple entangled fuel specimens: the same plant can therefore be used to accelerate multiple spacecraft.

There is another propulsion application for quantum entanglement which, while probably requiring more R&D investment than the teleportation drive, would have even greater (as in, several orders of magnitude greater) speed benefits for a spacecraft: applying quantum entanglement to produce the first viable photon drive.

A photon drive system uses nothing but a beam of photons (a beam of light if the photons fall in the frequency spectrum of visible light) to propel a spacecraft. The photon drive is a theoretical possibility that has been talked about for decades but has never been practical due to the immense power requirements it would take for such a drive to generate sufficient thrust to propel a spacecraft.

An example of the simplest photon drive imaginable has been given in the past: if a flashlight were to be turned on in space and left there by an astronaut, its light beam would provide a miniscule amount of thrust to the flashlight, but not nearly enough to accelerate it to any noteworthy speed before the battery burned out. A photon drive requires essentially no fuel, only power. In other words, a photon drive has an extremely high specific impulse but a very low thrust-to-weight ratio.

The great advantage to a photon drive is that if its power requirements were to be overcome, a photon drive system could eventually accelerate a spacecraft up to very high speeds-even, theoretically, close to the speed of light. However, both nuclear fission and nuclear fusion fall short in terms of generating the necessary power, at least from a reactor small enough to be realistically carried onboard a spacecraft.

A matter-antimatter reaction of a sufficient size could generate the required power, but antimatter is exquisitely expensive to produce at the time of this writing, and containment and manipulation technologies for it are still in early stages of development. Thus, a photon drive powered by matter-antimatter reaction is currently not a viable option. There is another option.

Applying quantum teleportation to a photon drive (to produce what I am dubbing the telephotonic drive) would remove the one great engineering obstacle (i.e., power generation) to producing a viable photon drive system. Recall from earlier in this article that laser beams (i.e., concentrated streams of photons) have been successfully teleported.

Without knowing it, the researchers who accomplished this feat created a basic telephotonic drive in the course of their experiments. In the case of a telephotonic drive powerful enough to propel a spacecraft, earthbound electric plants (nuclear or otherwise) would generate the power for a laser beam which would then be teleported to a spacecraft.

While even a dedicated nuclear power plant may not generate sufficient power to create a laser powerful enough to realistically provide propulsion for a spacecraft, there is no reason why a single spacecraft would need to be powered by a single entangled laser beam; multiple power plants, perhaps widely spread geographically over the earth's surface, could generate multiple laser beams which would then be teleported to adjacent "cells" to the rear of the spacecraft, producing an array of high-power laser beams that would collectively propel the craft...potentially to near the speed of light. Incidentally, since entanglement information is itself conveyed (either by laser or radio waves) at the speed of light, and since even a telephotonic drive could never, according to relativity theory, propel a craft up to the speed of light, a spacecraft propelled by a telephotonic drive could never "outrun" its lasers' required entanglement information.

A variation on the telephotonic drive concept involves using entangled lasers, generated on the earth's surface, to create a laser fusion drive. The idea behind the laser fusion drive (which, like the photon drive, has been talked about for years but has never been developed) is that pellets of frozen hydrogen fired out of the rear of a spacecraft like a machine gun are individually struck by powerful laser beams, igniting each one in an individual fusion reaction; the resulting series of energy bursts push the craft forward.

There is an engineering obstacle in creating lasers powerful enough to fuse the hydrogen pellets; as in the case of the telephotonic drive, teleporting entangled laser beams from earthbound power plants to the spacecraft would overcome this obstacle. While an entangled laser fusion drive would not accelerate a spacecraft to the speeds attainable by a telephotonic drive, or even a teleportation drive, I suspect that it is more immediately realizable from a practical engineering standpoint than either of those propulsion concepts.

The first step, of course, towards implementing any of these drive schemes is to test them on the ground. As stated before, the theory of the telephotonic drive has, in effect, already been proven; it only needs scaling up (though vastly so) in order to become a viable propulsion method. The successful entanglement of lasers also proves the conceptual soundness of the entangled laser fusion drive.

The teleportation drive could be proven, in concept, for relatively little cost or resources. There are commercially available small ion rockets designed for use as maneuvering thrusters on satellites and space probes.

An experiment to prove the theoretical soundness of the teleportation drive would involve taking one of these commercial thrusters and entangling its fuel to another specimen of the same element. If, upon activation of the thruster, the entangled second specimen generated an ion stream, the theory would be proven. Such an experiment is well within the resources of even small government or university physics laboratories.

Spacecraft propulsion is therefore a third practical application of quantum teleportation, in addition to quantum computing and quantum cryptography. There is, however, a fourth application, one which deserves its own treatment in a separate paper but which I will briefly introduce here because of its relevance to the propulsion systems outlined above. That application is wireless power transmission.

NASA and the U.S. Department of Energy have, over the last three decades, studied various concepts for generating electric power in space and then beaming it (via microwave in most design concepts) to the earth's surface for public use. In the late 1970s the DoE, under the Carter Administration, studied the possibility of orbiting large satellites that would collect solar energy and beam it to earth.

The idea was unviable due to the immense size of the solar arrays involved (on the order of tens of square kilometers). There is also a problem presented by beaming energy to earth in this manner, as such a beam would have a tendency to diffract in the earth's atmosphere.

However, aided by advances in solar cell technology, much smaller solar arrays could today be placed in orbit around the sun, perhaps within the orbit of Mercury (naturally the arrays would need to be designed to withstand intensive bombardment by heat and radiation; the upside would be that the proximity to the sun would also allow for greater power collection).

A resulting microwave beam generated with the energy collected could be quantum-teleported directly to the earth's surface. Aside from the obvious immediate benefits of such an efficient power generation system, these satellites could also provide the power input for a telephotonic or entangled laser fusion drive. Thus quantum teleportation could provide an "end-to-end solution" for propelling a craft up to near-light speeds.

Einstein was uncomfortable with the idea of quantum entanglement, referring to it as "spooky action at a distance". By applying quantum teleportation to deep-space propulsion, that element of distance may be measurable in light-years.