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Entanglement Makes Quantum Particles Measurably Heavier, Says Quantum Theorist
KentuckyFC writes: Physicists have long hoped to unify the two great theories of the 20th century: general relativity and quantum mechanics. And yet a workable theory of quantum gravity is as far away as ever. Now one theorist has discovered that the uniquely quantum property of entanglement does indeed influence a gravitational field and this could pave the way for the first experimental observation of a quantum gravity phenomenon. The discovery is based on the long-known quantum phenomenon in which a single particle can be in two places at the same time. These locations then become entangled — in other words they share the same quantum existence. While formulating this phenomenon within the framework of general relativity, the physicist showed that if the entanglement is tuned in a precise way, it should influence the local gravitational field. In other words, the particle should seem heavier. The effect for a single electron-sized particle is tiny — about one part in 10^37. But it may be possible to magnify the effect using heavier particles, ultrarelativistic particles or even several particles that are already entangled.
FWIW, it appears from the paper that this extra "mass" is an artifact of analyzing entangled particles in a linearized gravity framework and observing a stress-energy tensor term that seems to appear higher for entangled particles and radiated away as particles move to decoherence. This perhaps might be considered the mass of the entanglement.
On the other hand, wouldn't it be cool if the reason for the observed equivalency of gravitational mass and inertial mass was somehow related to quantum entanglement? (yes I know this is unrelated to this phenomena, but still)...
So I think this means that either the no-communication theorem is wrong, or the change in mass of an entangled particle cannot be measured.
That's an interesting point, but on my reading of the paper (which was pretty cursory, admittedly) the extra mass term comes from the joint wavefunction, which means both particles would have to be measured. It looks like the pair has greater mass, not the individual particles.
This makes sense because insofar as they are entangled it doesn't even make sense to talk about the individual particles. Furthermore, if one were to measure either of the particles individually, that would break the entanglement and the extra mass term would fall to zero.
Thing of the highly idealized experiment of two sources on a balance beam, one that emits pairs of non-entangled particles, one that emits pairs of entangled particles. The theory says that the balance will tip toward the side of the entangled pairs, but it does not follow from this that measurements on any of the individual particles will reveal increased mass.
Blasphemy is a human right. Blasphemophobia kills.
The photon has zero rest mass, yes.
E = mc**2 is a nice popularization; it's also wrong. It's actually E**2=(mc**2)**2 + (pc)**2, where p is the momentum. When momentum is zero, you can usually simplify this to E=mc**2, but a photon's existence is defined mostly by its momentum. Since m is zero for a photon, this means the energy of a photon is given by entirely by E=pc.
Hope this helps!