[ExI] Faster than light??

Anders Sandberg anders at aleph.se
Wed Sep 28 09:45:20 UTC 2011

Stefano Vaj wrote:
> 2011/9/27 Tomaz Kristan <protokol2020 at gmail.com>:
>> B - c is a little higher and photons are a bit slower than c. Neutrinos
>> travel with a velocity between those two. Minor revisions, something like
>> Anders seems to think.
> I am confused here. Particles with a mass travelling faster than
> electromagnetic or gravitational waves?

Actually, this ought to be observationally ruled out for all *charged* 
faster-than-photon particles, because of Cherenkov radiation. The 
Frank-Tamm formula produces a divergent result since in vaccum the speed 
will be greater than the speed of light for the medium for all 
velocities. So presumably you cannot accelerate a charged particle 
beyond photon speed because of energy losses. Cute.

Neutrinos are fine, of course.

A universe with a vacuum index of refraction slightly above 1 is not 
really problematic for SR, it would just look odd (there is an exercise 
in Rindler's "Essential Relativity" about this).

However, if you could move particles with mass faster than gravity waves 
then you would presumably get an analogous divergence of gravitational 
Cherenkov radiation ("gravity shockwaves"). This likely precludes 
neutrinos from going faster than the speed of gravity waves, given that 
they have been observed to have mass.

Anders Sandberg,
Future of Humanity Institute 
James Martin 21st Century School 
Philosophy Faculty 
Oxford University 

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