[imatfaal]

Two distances involved - not sure which you are asking about. 

Distance to satellite. You do need to know where the satellite is and the distance (and more importantly the error) to each of the base-stations; but the speed of the signal is so damn high that even estimates with high ephemeris error will lead to a nano-second error at such a short baseline

Distance on baseline.  As you know the distance to a common known point (the gps sat) then you do know the baseline - but it is not part of the calculation

I am not aware of the error algorithms - but everything I have read suggested that at over 3000km you need to start being careful of errors close to 10ns.  But 730km is actually quite a short baseline distance for this technique and the max error is 2.3ns.  The subtraction of one data set from the other means that errors are cancelled not accrued - most of the error in a signal coming from a satellite 22000 km away to two posts 730km apart will be the same.

Thanks!

What I'm (sort of) getting at is that, for this experiment, both the distance and time have to be very accurately known.

  Completely - it's the be all and end all

However, if I understand properly how this works, the accuracy of the time synchronization depends on a very accurate measurement of the baseline. If the baseline is a bit off I think it will introduce an error into the time synchronization, although it's probably very small.

You need to know the 3d coordinates of each basestation very accurately.  This the GPS system, using multiple view, is very good at this and there is a claimed accuracy - that I do not think many experts in the field argue with - of 2cm. This allows you to calculate your baseline.  It also allows you to calculate the errors in the common single view time synchronization of the two clocks

It's probably highly unlikely that would account for the observed results, but it might be a contributing factor.

The bulk of the acknowledged error - and possibly the source for more - is the measurement from the GPS basestation to the actual receivers.  This was old fashioned manual survey and the 10km is uncertain by 20cm m/l.  But the time difference between estimated arrival and actual arrival was 60ns which dwarfs the error margins .

BTW, you only know the distance from the satellite to the receiver if they have a common view of time, and the speed of the signal really has nothing to do with it.

  - it means that errors in position of the gps basestations and the ephemeris error of the gps-sat do not translate into large differential time lags that screw up your common view synchronization

[CliffordK]

How easy would it be to move either the transmitter or receiver to New Zealand & repeat the experiment?

[yor_on]

Then you will have to consider tectonic movements too
And sheep's getting in the way (or is that kangaroos?)

[imatfaal]

How easy would it be to move either the transmitter or receiver to New Zealand & repeat the experiment?

You could start again from scratch.  You need a hi-power proton synchrotron - a graphite block and a km long tunnel - the tunnel is directional so pointing it through the earth would not be easy.  The receptors are also not moveable.  You could rebuild new ones with a longer baseline - but there is really no need; if the experiment methodology was misconceived then that can be shown in CERN/OPERA, and will also be shown when FermiLab/MINOS give their results next year.  If the accuracy was poor - this can be rechecked with different protocols and other staff.  The error was small compared to the difference found - the problem isn't with significance of results , its the results themselves.  A longer baseline would be great - but not necessary yet.

Then you will have to consider tectonic movements too
And sheep's getting in the way (or is that kangaroos?)

Sheep in NZ Roos in OZ
Tectonic movement will not make a difference.  The positions of the GPS basestations is calculated as a point in three dimensional space - the distance between them can be calculated very accurately at an almost instantaneous rate.  The baseline distance is not worked out by plotting each basestation on a globe and then working out the cord distance - the system of GPS-sats create a 3d coordinate system and you can work out a distance. 

You will need to take into account the rotation of the earth - which will affect the position of the basestations - but not the straightness of the neutrino beam. 

[Geezer (OP)]

Two distances involved - not sure which you are asking about. 

Distance to satellite. You do need to know where the satellite is and the distance (and more importantly the error) to each of the base-stations; but the speed of the signal is so damn high that even estimates with high ephemeris error will lead to a nano-second error at such a short baseline

Distance on baseline.  As you know the distance to a common known point (the gps sat) then you do know the baseline - but it is not part of the calculation

I am not aware of the error algorithms - but everything I have read suggested that at over 3000km you need to start being careful of errors close to 10ns.  But 730km is actually quite a short baseline distance for this technique and the max error is 2.3ns.  The subtraction of one data set from the other means that errors are cancelled not accrued - most of the error in a signal coming from a satellite 22000 km away to two posts 730km apart will be the same.

Thanks!

What I'm (sort of) getting at is that, for this experiment, both the distance and time have to be very accurately known.

  Completely - it's the be all and end all

However, if I understand properly how this works, the accuracy of the time synchronization depends on a very accurate measurement of the baseline. If the baseline is a bit off I think it will introduce an error into the time synchronization, although it's probably very small.

You need to know the 3d coordinates of each basestation very accurately.  This the GPS system, using multiple view, is very good at this and there is a claimed accuracy - that I do not think many experts in the field argue with - of 2cm. This allows you to calculate your baseline.  It also allows you to calculate the errors in the common single view time synchronization of the two clocks

It's probably highly unlikely that would account for the observed results, but it might be a contributing factor.

The bulk of the acknowledged error - and possibly the source for more - is the measurement from the GPS basestation to the actual receivers.  This was old fashioned manual survey and the 10km is uncertain by 20cm m/l.  But the time difference between estimated arrival and actual arrival was 60ns which dwarfs the error margins .

BTW, you only know the distance from the satellite to the receiver if they have a common view of time, and the speed of the signal really has nothing to do with it.

  - it means that errors in position of the gps basestations and the ephemeris error of the gps-sat do not translate into large differential time lags that screw up your common view synchronization

I thought I read that they actually did a survey transit to determine the positions. Surely that could introduce some serious errors, or did I get that wrong?

[CliffordK]

You will need to take into account the rotation of the earth - which will affect the position of the basestations - but not the straightness of the neutrino beam. 

Ahhh...  so if you aligned it on the equator, say from South America to New Guinea, then measured the deflection due to the Coriolis effect, you could make an exceptionally accurate real-time geo-clock.  That is, assuming everything could be monitored in real-time.

[Geezer (OP)]

I think Syhprum may have cracked it!

http://www.thenakedscientists.com/forum/index.php?topic=42298.msg374847#msg374847

[imatfaal]

I thought I read that they actually did a survey transit to determine the positions. Surely that could introduce some serious errors, or did I get that wrong?

The survey was merely to determine the offset of the detectors and the sources from the two GPS base-stations.  It was about 10km of the total of 730km - but the error in that survey was the vast majority of the entire error of the set up.

re Syhprum's unit post - I hope and pray that, for the sake of scientific dignity, that it doesn't turn out that one bozzo was using mm and the other bozzo was using cm and that if they had both used the same unit the 60ns/18m disappears

[Geezer (OP)]

I thought I read that they actually did a survey transit to determine the positions. Surely that could introduce some serious errors, or did I get that wrong?

The survey was merely to determine the offset of the detectors and the sources from the two GPS base-stations.  It was about 10km of the total of 730km - but the error in that survey was the vast majority of the entire error of the set up.

re Syhprum's unit post - I hope and pray that, for the sake of scientific dignity, that it doesn't turn out that one bozzo was using mm and the other bozzo was using cm and that if they had both used the same unit the 60ns/18m disappears

Perhaps the surveyors were distracted by a flock of particularly attractive sheep?

I think I figured the difference comes out at around 27 ppm, so a little bit of extra coax here or even a few kinks in a cable there and Bob's your uncle, although I'm sure they've gone over this till they are completely sick of it.

BTW, it would only take about 6m of cable (even less if it's optical fibre) to account for that time difference.

[syhprum]

BTW I think information travels faster in the type of optical cable used for long distance circuits that it does in coaxial cable. best check

[Geezer (OP)]

BTW I think information travels faster in the type of optical cable used for long distance circuits that it does in coaxial cable. best check

You're right. I'm being a bit pessimistic.

[Bill S]

I voted for "There is only one neutrino that travels infinitely fast and is thus everywhere at once" because I like the idea of someone else bringing infinity into the discussion.  []

However, I also quite like the thought that they may have found the long soughtafter tachyon.  Can we be sure that neutrinos don't always travel just a little faster than light.

Hang on, though, shouldn't that mean they travel backwards through time?

[imatfaal]

I voted for "There is only one neutrino that travels infinitely fast and is thus everywhere at once" because I like the idea of someone else bringing infinity into the discussion.  []

However, I also quite like the thought that they may have found the long sought after tachyon.  Can we be sure that neutrinos don't always travel just a little faster than light.

Hello Bill - welcome back. 

The neutrinos from Supernova SN1987a got to earth at the correct predicted time - ie a few hours (not years) earlier than the light; the light has to contend with the gas/dust cloud surrounding a huge exploding star, the neutrinos whip straight through.  So at present we think neutrinos travel at a significant proportion of the speed of light  (99.9 and more nines)

Hang on, though, shouldn't that mean they travel backwards through time?

You cannot have Special Relativity, Faster than Light, and Causality all at the same time.  So we would say that for some reason these neutrinos do not seem governed by Special Relativity - this is a bit of a blow, but not too bad.  Sr is already limited to flat space so another limit ain't that bad

[Bill S]

You cannot have Special Relativity, Faster than Light, and Causality all at the same time.

Confused!!! Are you saying that if something could travel faster than light, it would not travel backwards through time?

Thanks for the "welcome back".  I hope to have a little more spare time for asking silly questions, at least for a while.

[simplified]

I exactly don't  know how scientists create right formulae.But now I think it is impossible to create formula of energy of  such fast massive object, because we are  captives of relative kinematic slowing of time. Development needs an experiment with a synchronization of atomic clocks on a satellite.

[imatfaal]

You cannot have Special Relativity, Faster than Light, and Causality all at the same time.

Confused!!! Are you saying that if something could travel faster than light, it would not travel backwards through time?

Thanks for the "welcome back".  I hope to have a little more spare time for asking silly questions, at least for a while.

What I am saying is that the failure of causality, ie the travelling backwards in time, is a result of plugging FTL speeds into the ideas of special relativity.  BUT SR does not deal with massive objects going light speed and deals with nothing going FTL.  You cannot extrapolate SR into a realm of FTL travel because SR has an axiom that speed limit is that of light.  I do not know what happens if you could get a massive object above SoL - but I am sure that you cannot use SR to predict it. 

Personally I think that FTL travel is not feasible and OPERA Gran Sasso has made a mistake.  The Yanks are repeating the experiment in Fermilab/MINOS - and iff that comes in with agreement to OPERA then all bets are off - but I just don't think it will

[simplified]

You cannot have Special Relativity, Faster than Light, and Causality all at the same time.

Confused!!! Are you saying that if something could travel faster than light, it would not travel backwards through time?

Thanks for the "welcome back".  I hope to have a little more spare time for asking silly questions, at least for a while.

.  The Yanks are repeating the experiment in Fermilab/MINOS - and iff that comes in with agreement to OPERA then all bets are off - but I just don't think it will

Your forecast  may be wrong again.Because massive object with very high energy can move some space.

[simplified]

Hi Imatfaal. Let's consider Einstein's formula of speed
          v=[c (E^2+2Emc^2)^1/2]/(E+mc^2)
v - speed of massive object
E - kinetic energy of the massive object
m - mass of the object
c - light speed

I suspect that if we  insert  very big energy and very small mass then speed can be more than light speed. But my calculator is unable precisely to count such numbers .

[simplified]

    I am wrong because
                                 ( E^2+2Emc^2)^1/2 < (E^2+2Emc^2+m^2c^4)^1/2

[CliffordK]

I tried to figure out which were actually bigger, neutrinos, or photons thinking that speed was related to mass.  However, I think the neutrinos are actually slightly larger than the photons.

With stellar phenomena, different energy photons (wavelengths) including Gamma all arrive at Earth at the same time.  So energy alone doesn't account for the difference of speed.

There also seems to be a rather high error rate in the measurements.  One question related to other discussions.  Essentially all of our current measurements of the speed of light are "2-way" measurements.  The speed from the source to a mirror and back. 

One should be able to do good one-way speed of light experiments using geosynchronous satellites, but I'm not sure if these have been done. 

Anyway, perhaps the neutrino experiments are one-way speed experiments that would be biased by the time of day they are being collected (and thus Earth's orientation in space).