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Comment by zipstudio | Hacker News Reader

So if it's the gravitational pull that makes the clocks different, it seems obvious that doing the experiment in the other direction is the next step. Measure the time in both directions to average out this effect.

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The equipment necessary for generating versus detecting neutrinos is vastly different (and entirely immobile, to all intents and purposes).

Calling half time and changing ends is a nice idea, but utterly impractical. Finding/building an alternative neutrino source and pointing it at the detector is (I think) the best approach to reproducibility, but it still leaves open the possibility of systematic errors in the detection mechanism causing the same issues. A different distance should give a different delay though, which would be one test.

Another might be to try and use photons as a reference/synchronisation mechanism, but that's hindered by the fact that everything is in underground caverns.

I wonder if MINOS (a Fermilab experiment, http://en.wikipedia.org/wiki/MINOS) could be repurposed to provide collaborating evidence. It's an experiment that detects neutrinos both close up and after a 730-ish km flight. Maybe if they run both detectors on the same beam and can sync the results they can provide great enough accuracy to verify the result?

Yes it would probably cost millions for such a thing to be done if it's even possible.

So all they need to do is build an enormous particle accelerator and the other bits required to turn it into a neutrino source at the Gran Sasso site, and an enormous neutrino detector at CERN, and they can go right ahead and do that. Too bad it'll take decades and $billions.

Figuring out the appropriate clock corrections very, very carefully seems like a better approach...

From what I understand, the equipment needed to emit the neutrinos and then detect them amounts to enormous hunks of metal, circuitry, and plumbing, not mention vacuum- or water-filled cavities, neither of which are readily interchangeable. Not a trivial task by any measure.

If synchronized clocks are a problem, I wonder why they don't race the neutrino against a photon. Obviously the photon would have to take a different path - maybe bouncing off a satellite.

I wonder how accurate the GPS synchronization is too. I'm wondering if it takes into account different atmospheric conditions and the index of refraction of radio waves in air.

Time measurements are interestingly difficult when you start to care about high accuracy or long times. There's a kind of hard-to-read but interesting running log on the state of the leap second at http://www.ucolick.org/~sla/leapsecs/onlinebib.html. (What, you didn't know there were leap seconds? See http://en.wikipedia.org/wiki/Leap_second)

How about two pairs atomic clocks. One paired at the start point, one paired at the end point then a start- and an end-clock being used in both locations? Or use a neutral third frame of reference by timing from a pulsar.

This probably wouldn't work, time dilation under gravity makes my head hurt!

>If synchronized clocks are a problem, I wonder why they don't race the neutrino against a photon. Obviously the photon would have to take a different path - maybe bouncing off a satellite.

how about just inside the fiber. How good is the ping between CERN and Gran Sasso ? :)

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