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120 years ago, people thought that experimental results on wave propagation in continuous media could be used to make statements about wave propagation in elect
by genug 11y ago
120 years ago, people thought that experimental results on wave propagation in continuous media could be used to make statements about wave propagation in electrodynamics. That's how we ended up with ether theories, which were eventually falsified with interferometric experiments.
To my mind, we should take this as a lesson that the notion of analogue systems (e.g., using results from fluid dynamics to make statements about gravitation) is bogus. The ether episode seems to indicate that if we want to make statements about gravitational Hawking radiation, we need to do tests on a system where the gravitational dynamics are important (e.g., a black hole), not an unrelated system that just happens to be governed by an identical set of equations in some regime.
Another example of people incorrectly conflating properties of an analogue system with the real system of interest is the Nature monopole paper: http://www.nature.com/nature/journal/v505/n7485/full/nature12954.html http://www.nature.com/nature/journal/v505/n7485/full/nature1...
The actual result contained in the paper is that you can make a BEC whose vorticity field has regions of nonzero divergence. It is mathematically similar to (but fundamentally unrelated to) actual magnetic monopoles. Nonetheless, the paper contains the phrase "Dirac monopoles" in the title and then spends half the abstract talking about actual magnetic monopoles, as if the result is somehow relevant to actual magnetic monopole searches (which it isn't).
- Ono-Sendai 11y agoAll ether theories weren't really falsified, just discarded on a metaphysical basis as being redundant.
- CamperBob2 11y agoI wouldn't say that. The Michelson-Morley experiment demonstrated that if there was a luminiferous ether, it had no measurable inertia. That pretty much falsified the ether as anything that we'd recognize as "real."
- Ono-Sendai 11y agoI've never read about the ether needing to have inertia. Also, a modern version of the ether is pretty well accepted - quantum fields that occupy all of space. Particles etc.. are disturbances in this field. Ether is something of a tainted term these days so quantum fields are not referred to as ether.
- chc 11y agoQuantum field theory doesn't seem very much like the luminiferous ether. This seems like finding a new species of grasshopper that lives on a mountain, and saying, "Ah-ha, I've found Zeus! Zeus is a thing that lives on a mountain and has never been seen before, so this must be Zeus!"
- deleted 11y ago[deleted]
- chakademus 11y agoAs a counterpoint: what about the efficacy of condensed matter physics informing developments in quantum field theory? Of course analog systems must be treated carefully, but I think we shouldn't rush to do away with the practice entirely. Naturally, we do want to study black holes directly (with experiments like LIGO, LISA, etc.), but this is very expensive, difficult, and time consuming. If a small lab wants to try out some gravitationally analogous system, why not?
- trhway 11y ago>not an unrelated system that just happens to be governed by an identical set of equations in some regime. that is exactly the point of analogue systems - identical equations have identical solutions, and thus analogue system allows to observe and explore the solutions (which in many cases aren't that easy/possible to obtain mathematically/numerically)
- genug 11y agoWe have no experimental evidence that the calculations for gravitational Hawking radiation (or their physical interpretation) are valid. The notion that dumb holes exhibit all the same properties as black holes is conjectural.