scifimath said:
on spaceship and fly out a couple light speed seconds to try the entangled speed experiment.
https://www.technologyreview.com/s/428328/super-physics-smackdown-relativity-v-quantum-mechanicsin-space/
For example, physicists routinely measure the quantum phenomenon of entanglement by sending entangled pairs of photons from one location to another. In these experiments, the sender and receiver must both measure the polarisation of the photons, whether vertical or horizontal, for example. But that can only happen if both parties know which direction is up.
That’s easy to specify when they are close together. But it becomes much harder if they are separated by distances over which the curvature of spacetime comes into play. The problem here is that the answer is ambiguous and depends on the path that each photon takes through spacetime.
The experimenters can work this out by tracing the path of each photon back to their common source, if this is known. But then, how does each photon ‘know’ the path that the other has taken? Theorists can only guess.
Another problem arises when these kinds of experiments are done with the sender and receiver traveling at relativistic speeds. This introduces the well known problem of determining the order of events, which Einstein famously showed depends on the observers’ points of view.
That’s in stark contrast to the prediction of quantum mechanics. Here the measurement of one entangled photon instantly determines the result of a future measurement on the other, regardless of the distance between them.
If special relativity ensures that the order of events is ambiguous, what gives? Once again, theorists are at a loss.
Of course, the way to answer these questions is to test them and see.
Today, David Rideout at the University of California, San Diego and a few friends outline various ways to crack these nuts and they say these kinds of experiments ought to be possible in the near future.
That’s largely because the required experimental gear is standard in many optics laboratories, so qualifying it for use in space should be straightforward.
Two groups have already proposed to do these kinds of experiments in space. One group wants to put a package capable of producing entangled photons on the International Space Station, for beaming back to Earth. Another wants to keep the quantum equipment on the ground and bounce photons off a simple microsatellite in low Earth orbit, an option they say will be cheaper, easier and better.
Fundamental quantum optics experiments conceivable with satellites—reaching relativistic distances and velocities
http://iopscience.iop.org/article/1...8A9901A43D8B8271136.c2.iopscience.cld.iop.org
https://arxiv.org/pdf/1206.4949v2.pdf
Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an effective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 m (Dimopoulos 2007
Phys. Rev. Lett. 98 111102; 2008
Phys. Rev. D 78 042003). In contrast, quantum theory provides an effective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, ~10−20 m, up to that of hundreds of kilometres (Ursin
et al 2007
Nature Phys. 3 481–6). Yet, such tests fall short of the scales required to investigate potentially significant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena. In particular, we review a wide variety of potential tests of fundamental physics that are conceivable with artificial satellites in Earth orbit and elsewhere in the solar system, and attempt to sketch the magnitudes of potentially observable effects. The tests have the potential to determine the applicability of quantum theory at larger length scales, eliminate various alternative physical theories, and place bounds on phenomenological models motivated by ideas about spacetime microstructure from quantum gravity. From a more pragmatic perspective, as quantum communication technologies such as quantum key distribution advance into space towards large distances, some of the fundamental physical effects discussed here may need to be taken into account to make such schemes viable.
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