[time-nuts] Fast than light neutrino

[Javier Serrano]

On Mon, Sep 26, 2011 at 12:41 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 9/25/11 3:26 PM, Hal Murray wrote:
>
>>
>> javier.serrano.pareja at gmail.**com <javier.serrano.pareja at gmail.com> said:
>>
>>> A fiber-based time-transfer would be nice complementary as it would
>>>> provide
>>>> an independent timing path.
>>>>
>>> Any ideas on how to proceed? This is unknown territory for me.
>>>
>>
>> You can get a lot of good ideas from the radio astronomers.  It's been
>> discussed here in the past, but I don't know what terms to use when
>> searching
>> the archives.  I think it was mostly pointers to their papers.  They were
>> interested is much shorter distances.  I think it was 10-20 km.
>>
>>
>> The idea is to send a signal in both directions over the same fiber.  If
>> it's
>> the same fiber, the transit times are likely to be the same in both
>> directions.  If you send a pulse out and back, you can assume the time the
>> pulse arrived at the far end was half the round trip time after it left
>> the
>> start.
>>
>>
>> Whatever you do, it will require a lot of cooperation from the people who
>> own
>> the fibers.
>>
>>
> The Deep Space Network do lots of this kind of thing for interferometry.
>
>
>
I did not express myself correctly. We know how to do accurate two-way sync
over a few km of fiber. See e.g.
http://dl.dropbox.com/u/13409775/pac2011/WEOAN1.pdf or
http://dl.dropbox.com/u/13409775/wrapper.pdf (our contribution to the CLIC
Conceptual Design Report). What is new for us is going through more than
1000 km of fiber (only neutrinos have the luxury of going in a straight line
through the crust of the Earth, 732 km). I wonder who one calls for fibers
and also more technical things like optical amplifier technology with
typical ranges, etc. What I gather from the discussion so far is that 100 km
is within reach of available optical transceivers. I wonder how far one can
go with EDFAs. One thing we could do is establish a fiber link between METAS
in Bern and CERN, and then look for a good metrology place in Rome (the
national one in Italy is in Torino I believe) and have a link between them
and Gran Sasso. Then we could use their UTC data sets to establish a paper
link between CERN and Gran Sasso which would be independent of the current
link.

Cheers,

Javier