Em 23/9/2011 12:07, Kerry Wentworth escreveu:
> Isaac Marino Bavaresco wrote:
>> Em 23/9/2011 10:48, smplx escreveu:
>>  =20
>>> On Fri, 23 Sep 2011, IVP wrote:
>>>
>>>    =20
>>>>> http://www.bbc.co.uk/news/science-environment-15017484
>>>>>        =20
>>>> I think the neutrinos just get excited by a trip to Italy
>>>>
>>>> The figure I've seen is 20ppm faster than light. They allegedly
>>>> arrived 60ns before light would have, with an accountable
>>>> error of 10ns
>>>>
>>>> One scientist asked why neutrinos haven't been observed (for
>>>> whatever reason) ahead of supernovae, which they should do
>>>> by a significant time period if at least one flavour of neutrino is
>>>> 20ppm faster than light
>>>>
>>>> 20ppm of 1 year is 10.5 minutes. Even 1ppm faster than light
>>>> would be 30s per lightyear distance
>>>>
>>>> Joe
>>>>      =20
>>> 60ns measured between 2 points lets you plot one point on a curve. If y=
ou=20
>>> don't know what shape the curve is, assuming it's a straight line and=20
>>> looking for other points on that line isn't going to get you anywhere :=
-)
>>>
>>> Regards
>>> Sergio Masci
>>>    =20
>>
>> The neutrinos traveled from Swiss to Italy inside rock (and perhaps
>> magma) in a straight line. For neutrinos that's easy.
>> In the 60ns the light travels approximately 18m.
>>
>> My question is: Did they know the exact distance with a precision of a
>> few meters between two points separated by 732km? Both buried under
>> hundreds of meters of rock?
>>
>> I'm sure they could not send anything else through the same path to comp=
are.
>> Another challenge would be the synchronization of the two clocks at such
>> distance.
>>
>> Perhaps they are simply using a distance which is not that precise.
>>
>>
>> Isaac
>>
>>  =20
> With GPS, both time and distance should be known accurately enough, I=20
> would think.


Perhaps, but we are talking about sub-microsecond times (less than 1/16us).

This one seem too obvious, but only perhaps: Did they remember to take
in account the curvature of the surface of the earth? The GPS
measurements are surely on the surface of the earth. They would need to
extrapolate to the underground site the equipments are located. At a
distance of 732km the radii of the earth cannot be considered parallel.
The deeper you go, the closer two points on those radii are.


>   The important thing to remember is that they are not=20
> measuring the speed in a vacuum.  The speed of light in a vacuum is a=20
> constant (and a limit?), but the speed of light through other media is no=
t.
> The speed of light through a medium is (speed of light in a=20
> vacuum)/(index of refraction of medium)
> The index of refraction is dependent on the wavelength of the light.
> Neutrinos are not light.
> So:
> Is the index of refraction known for the entire path?
> Is the index of refraction for light the same as for neutrinos?
> Is the wavelength of neutrinos known to sufficient accuracy?

These points are important also.


Isaac

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.