13:28 14 April 2015 by Jacob Aron
Planets weren't built using magnets. That's the latest finding from Philae, the European Space Agency lander that touched down on comet 67P/ChuryumovGerasimenko last year.
The probe shut down a few days after its bumpy landing, and ESA's mission scientists still haven't been able to find it. But they have been busy analysing the data gathered during while Philae was active.
Today they presented results from the spacecraft's magnetic sensors at the European Geosciences Union General Assembly in Vienna, Austria. These show that Philae and its mothership Rosetta, which is currently in orbit around 67P, detected similar readings throughout Philae's descent. The results are also published in the journal Science.
"You see almost no difference", said Karl-Heinz Glassmeier, who is in charge of the magnetometer on Rosetta, during a press conference. In other words, the comet has almost no discernible magnetic field if it had one, Philae would have seen a different signal to the more distant Rosetta.
That's a surprise, because it was thought that magnetic forces played a role in assembling cometary material into larger planetary-building blocks during the formation of the solar system.
These readings of the weak magnetisation on 67P suggest that magnetic forces were too small to bring together building blocks larger than a metre in size, although they may have played a role on smaller scales. "We feel that the fields must have been much smaller in the earlier solar system than previously thought," said Glassmeier.
"If this comet is representative of all the others, there is no chance you can have accretion with magnetic forces," said Hans-Ulrich Auster, who is in charge of Philae's magnetometer. Instead, it is likely that collisions between smaller particles led to one particle growing larger by chance, eventually building up enough bulk for gravitational forces to dominate and pull more material together.
an entangled state has both the electric and magnetic fields associating mass.
Photoluminescence under applied electric fields
The exciton PL emissions from two representative dots (dot A and dot B as indicated in Fig. 1d) were observed with their redshift in the presence of the electric field. Here we focused on the result of dot A, where four emissionsan exciton (X), biexciton (XX), negatively charged exciton (X−) and positively charged exciton (X+)were detected. In addition to the linear and the superlinear responses of their PL intensities to the excitation power, the exciton and the biexciton emissions were assigned according to their opposite linear polarization (Fig. 1e). Thus, the exciton and the biexciton can be easily distinguished from X− and X+. The PL intensity dropped by 45% when E increased from 0 to 29.2 kV cm−1, most probably owing to an increase of the field-assisted carrier tunnelling. Above E=29.2 kV cm−1, the PL became significantly weak and broadened, which makes it difficult to determine ΔFSS at E>30 kV cm−1 (at these fields, I increases progressively above 10 nA (Fig. 1c)). The observed dependence of the PL spectra on the electric field for other dots was similar to that represented in Figure 1d.
Changes in polarization and FSS with the electric field
The in-plane asymmetry of GaAs QDs is reflected in the polarization anisotropy exhibited by the integrated PL spectra of the exciton and the biexciton. By carefully following the evolution of the exciton and the biexciton PL energies with the polarization angle, we obtained a clear behaviour that could be fitted with a sinusoidal function, from which we extracted ΔFSS. The polarization axis of the PL was determined by the angle that represents the maximum splitting energy, and ΔFSS was measured with an accuracy of 23 μeV. Figure 2a shows a clear nonlinear change of ΔFSS with the electric field, where ΔFSS decreased from 38 μeV at E=0 to below our detection limit when the field approached 30 kV cm−1. We studied five quantum dots; three of them showed a similar FSS suppression behaviour with the increase in the electric field. Moreover, on tuning ΔFSS over the measured range of the electric field, we observed a clear rotation of the exciton polarization axis. Figure 2b summarizes the relationship between the electric field and ϕ, which describes the orientation of the exciton polarization axis relative to the crystal axis . We found that as the field increased, the exciton polarization axis continuously rotated from ϕ=90°, where it aligned with the crystal axis  at E=−45 kV cm−1, until it approached 45°, and it became independent of the polarization axis at E=29.2 kV cm−1, where ΔFSS was minimized within our detection limit (Fig. 2c). Similar results have recently been reported for InAs/GaAs QDs using a large electric field of up to a few hundred kV cm−1 (ref. 12).
The above results demonstrate that the two-photon state emitted from the same GaAs QD can be manipulated from the polarization-correlated state to a polarization-entangled state by applying a vertical electric field. Because these GaAs island QDs emit light at a short wavelength (~750 nm), they will be useful for efficient detection of photons with silicon detectors. The reduction in ΔFSS for these dots, caused by the forward bias voltage, may also allow the fabrication of an efficient visible light-emitting diode, which can emit entangled photons with a high emission probability that is suitable for qubit-based optical30 and spin31 quantum computation applications
Gravity itself, is the entanglement of em between points in time.
It's coming (unveiling), slowly but surely.