Quantum physicists in the Netherlands, Spain, and the UK have confirmed in the lab that the weird instant correlations between remote “entangled” particles are real. The question that comes to mind is, can quantum weirdness be used to send instant message across space-time, faster than light?
The new experimental conformation of instant entanglement – not the first, but the strongest to date – is published on arXiv with the title “Experimental loophole-free violation of a Bell inequality using entangled electron spins separated by 1.3 km.” See also my summary and Zeeya Merali’s summaries published at Foundational Questions Institute (FQXi) website and Nature News.
The researchers measured the spins of hundred of entangled particles in two University of Delft labs, located 1.3 km apart, and confirmed that the entangled correlations are still observed when there is not enough time for light to travel from the first lab to the second, which means that entanglement isn’t limited by the speed of light.
If the correlations between entangled particles aren’t limited by the speed of light, is it possible to send instant messages faster than light (FTL), or across time, or do even weirder forms of quantum magic?
The cover image is taken from the scientific documentary “What the Bleep Do We Know!?” – a controversial “quantum mysticism” cult film that intriguingly hints at the possibility that quantum weirdness might eventually provide a solid scientific framework for spiritual beliefs.
To be entirely honest, I want quantum physics to be weird. In “The Lifebox, the Seashell, and the Soul,” Rudy Rucker astutely observes that many people find quantum mysticism appealing because it seems to offer a scientific escape from death. “If the world is fundamentally random, then surely I’m not a robotic machine, and if I’m not a machine, then perhaps I have an immortal soul, so death isn’t so frightening.”
I plead guilty as charged – and why not? I realize that the universe doesn’t have to agree with my hopeful thinking… but perhaps it does. Time will tell.
Faster than light communications based on entanglement: No Can Do
The awesome scientific history book “How the Hippies Saved Physics,” by David Kaiser, tells the fascinating story of the Fundamental Fysiks Group – quantum physics and the psychedelic youth culture of the seventies rolled together – and shows some of the colorful scientists who dedicated years to developing schemes for FTL messaging via entanglement.
“Nick Herbert and Jack Sarfatti [liked] to talk about the quantum physics and the possibilities of time travel,” wrote R.U. Sirius in his book review. “It is clear that hip young scientists in the 1970s broke through an extant taboo against exploring theoretical physics. And even if some may find their theories flakey in the extreme, we can thank them for busting open the exploration of big physics ideas.”
“And who knows. Maybe Jack Sarfatti will yet build that time machine.”
Nick Herbert’s (highly recommended) book Quantum Reality, acclaimed as one of the best popular books on quantum physics, is still very much worth reading 30 years after its first publication in 1985. Contrary to some books by other members of the Fundamental Fysiks Group, such as the very successful The Tao of Physics by Fritjof Capra, Herbert’s book doesn’t emphasize quantum mysticism but sticks to solid – though open-minded and imaginative – physics, including a very clear explanation of Bell’s theorem. Kaiser tells the story of Herbert’s imaginative and apparently solid – but ultimately unsuccessful – schemes with names like QUICK and FLASH to use entanglement for FTL communications.
John G. Cramer, a professor of physics at the University of Washington in Seattle, who also authored the excellent science fiction novels Twistor and Einstein’s Bridge, proposed schemes for spacetime communication via quantum entanglement, often discussed in his Alternate View columns on Analog Science Fiction & Fact Magazine.
Unfortunately, according to our current understanding of quantum physics, entanglement can’t be used to send FTL instant messages. Measuring the spin of one of a pair of entangled particles always gives a random result – even if the results of the two measurements are correlated – and any attempt to preset the spin of a particle would break the entanglement. A good analogy is two decks of “magic” cards that are always in the same order, but the magic only works if both decks are well shuffled first, and cheating breaks the magic.
In the image above I illustrate another good analogy, due to physicist David Bohm. Two screens in different places seem to show two fishes that exhibit weird, instantly correlated behaviors – when one turns left the other also turns left – but the screens are really showing two images of the same fish. Of course, an observer at one screen can’t send an instant message to an observer at the other screen. Nothing – zooming in, increasing the luminosity, switching the screen off – will work short of persuading the real fish to turn in one direction, which the observer can’t do.
It’s interesting that, despite the simple no-can-do analogies above, the FTL schemes devised by Herbert and Cramer seem solid and almost correct. Spotting the design flaws requires subtle reasoning, giving the impression that the universe tries to protect itself from FTL signaling.
Recently, Cramer and Herbert wrote a joint paper titled “An Inquiry into the Possibility of Nonlocal Quantum Communication” with a negative conclusion. A few days ago, Herbert criticized yet another new scheme for FTL messaging via entanglement, and concluded:
“Despite the FTL nature of the Theory that represents the World, despite the FTL nature of the Reality which underlies the World, the World Herself displays not a speck of evidence for any FTL connections.”
In summary, according to our best (current) understanding of the quantum world, entanglement can’t be used to send instant FTL messages.
Non-linear quantum physics to the rescue?
FTL fans and adepts of quantum mysticism can still hope that future non-linear versions of quantum physics might allow for FTL communications, and who knows what else.
“This idea was studied in the early 1990s as a consequence of a particular nonlinear variant of quantum mechanics due to [Steven] Weinberg,” explained Barak Shoshany, a graduate student at Perimeter Institute for Theoretical Physics. “Later it was argued that any nonlinear formulation of quantum mechanics (not only in Weinberg’s framework) necessarily leads to the possibility of superluminal communication.”
Shoshany gives a list of references, all easy to find online in full text. “I show that Weinberg’s nonlinear quantum mechanics leads either to communication via Einstein-Podolsky-Rosen correlations, or to communications between branches of the wave function,” reads the abstract of one of the references, by Joseph Polchinski. In other words, either FTL instant messages to the stars, or messages to parallel universes.
“Any attempt to generalize quantum mechanics by allowing small nonlinearities in the evolution of state vectors risks the introduction of instantaneous communication between separated observers,” noted Weinberg in his “Lectures on Quantum Mechanics.”
Time will tell, and experiment will decide. In the meantime, I certainly want to read more about these fascinating topics.
Image from “What the Bleep Do We Know!?” and a PPT presentation by the author.