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On Dec 28, 2014, at 1:11 AM, Adam Crowl <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:
Hi Jack
This one specifically:
On a fatal error in tachyonic physics
Edward Kapuścik
(Submitted on 10 Aug 2013)
A fatal error in the famous paper on tachyons by Gerald Feinberg is pointed out. The correct expressions for energy and momentum of tachyons are derived.
Subjects: General Physics (physics.gen-ph)
Cite as: arXiv:1412.6010 [physics.gen-ph]
(or arXiv:1412.6010v1 [physics.gen-ph] for this version)
For some reason it has sat in the arXiv dungeon since last year.
Another paper of interest is this:
Six observations consistent with the electron neutrino being a tachyon with mass: m2νe=−0.11±0.016eV2
Robert Ehrlich
(Submitted on 20 Jul 2014 (v1), last revised 18 Dec 2014 (this version, v7))
Six observations based on data and fits to data from a variety of areas are consistent with the hypothesis that the electron neutrino is a m2νe=−0.11±0.016eV2 tachyon. The data are from areas including CMB fluctuations, gravitational lensing, cosmic ray spectra, neutrino oscillations, and 0ν double beta decay. For each of the six observations it is possible under explicitly stated assumptions to compute a value for m2νe, and it is found that the six values are remarkably consistent with the above cited νe mass (χ2=2.73). There are no known observations in clear conflict with the claimed result. Three checks are proposed to test the validity of the claim, one of which could be performed using existing data.
On 28/12/2014 11:15 AM, JACK SARFATTI wrote:
Tachyons follow spacelike geodesics. I don’t think anyone has calculated them in a gravity lens situation?
The conventional wisdom in QFT is that tachyon excitations destabilize the vacuum, i.e. spontaneous symmetry breaking as in Higgs mechanism and many other systems including such mundane things as crystal formation.
E^2 = p^2c^2 - m^2c^4  for tachyon free particles.
Also tachyons have opposite spin statistics.
spin 1 tachyon is a fermion and will act like dark matter in random virtual ZPF form off-mass-shell
spin 1/2 tachyon a boson and will act like anti-gravity dark energy in random ZPF virtual pair form off-mass-shell.
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On Dec 27, 2014, at 2:35 PM, Adam Crowl <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:
Using gravitational lensing to minimise power requirements of signals means the whole Galaxy could be networked and it'd be undetectable by any conceivable planet-based SETI. 
A recent paper has revived tachyons as a possibility, by pointing out an error in Feinberg's original paper. 
reference please
I wonder how tachyons respond to gravity lenses? If they deflect in a similar manner to luxons then there's no impediment for a Galactic civilisation to be aware of the whole galaxy in close to real time.
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On 28 Dec 2014, at 6:53 am, JACK SARFATTI <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:
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They did quite a good job IMO.
1. Cocteau's estimate of how many highly advanced civilizations may exist in the galaxy was very good and almost exactly how I've tried to articulate the problem at times. I'll probably now use this as a reference. I was surprised at the estimate of 100 million advanced civilizations/average spacing of 10 light years between advanced civilizations. My estimates tended to be an order or two of magnitude lower, but his methodology seems solid even ~45 years later. Of course we now know for certain that most, if not almost all, stars do develop planetary systems, but observing earth sized planets is difficult, so we're still not sure how abundant they are. We do know that a fair number of stars appear to have planets too close or too far to be in a habitable zone, but even that is already taken into account by Cocteau; he estimates 1000 million sun-like stars out of 100 billion stars and drops the number with planets in acceptable orbits to somewhere around 600 million.
Interestingly recent observations and computer models seem to suggest that binary and trinary star systems can have planets in stable orbits around each star, so long as the stars orbit a common barycenter at a sufficient distance; indeed some studies claim to have detected planets circling the two main Alpha Centauri stars (the third smaller star would circle the whole system outside of the two local systems). So perhaps Cocteau's estimate is even conservative.
To get ~10 LY average spacing we should expect‎ civilizations in at least two of the following three systems with reasonably sun-like stars: Epsilon Eridani (though it's probably too young), Tau Ceti and Alpha Centauri. To maintain the spacing places like Gleise 86 would probably have to be inhabited too. So, either there should be loads of activity out there, or else: (a) correctly sized planets in habitable zones are very infrequent for some reason we don't yet understand; (b) for some reason we don't yet understand life fails to get started or to evolve beyond relatively small, simple forms; (c) civilizations tend to destroy themselves.
I keep an open mind but in the absence of data all I can say is that my instincts suggest that (a), (b), and (c) are wrong, which should mean that Cocteau's methodology holds and that there is a lot going on around the galaxy.
2. Another point where we now have a bit more to go on - the old light speed limit discussion further down in the paper. We now have the Thorne wormhole and Alcubierre warp metrics and the associated requirement for negative energy or mass, and we also have the accelerating expansion of the universe, which suggests that negative energy does exist in the universe. This is much more than having no clue as to how interstellar travel might work. Possibly we've actually already figured out generally how it works, but not the details yet. Obviously we can't build anything like this until we know how to generate and control negative energy.
Things like Jack's idea about changing the flexibility of spacetime by changing the speed of light might be techniques that further augment FTL travel or reduce the negative energy requirements.