Well, this could change things (neutrinos)

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Yakk
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Re: Well, this could change things (neutrinos)

Postby Yakk » Wed Nov 23, 2011 1:20 am UTC

You'd need to accelerate an LHC and neutrino detector to near light speed to transmit information into the past, then communicate between said LHC and a stationary LHC + detector.

Note that the only neutrino detectors we have require something closer in mass to the Earth to shield out the noise than the mass of things that we can accelerate to relativistic speeds. And there might be a range problem.

There might be an easy refinement, but that is the most "direct" way to send information into the past from this experiment.
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Re: Well, this could change things (neutrinos)

Postby ibgdude » Wed Nov 23, 2011 6:18 am UTC

Couldn't the break in causality be caused by just a single ship w/neutrino dectector moving at near lightspeed, and the LHC on earth, because velocity is relative? So, not really that hard. You use light for spaceship-earth, and FTL back again. This second ship only needs to have a heavy metal, photographic film and a laser, so it could be pretty small. Launch it off a ring accelerator on the moon, not too hard. We could be there in 100-1000 years.
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Re: Well, this could change things (neutrinos)

Postby eSOANEM » Wed Nov 23, 2011 7:31 am UTC

IIRC, for FTL to give signals going back in time, doesn't the relativistic observer have to be moving towards the non-relativistic observer (which limits the stability of such systems).
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Re: Well, this could change things (neutrinos)

Postby Tass » Wed Nov 23, 2011 9:47 am UTC

Yakk wrote:You'd need to accelerate an LHC and neutrino detector to near light speed to transmit information into the past, then communicate between said LHC and a stationary LHC + detector.


Minor nitpick: The CNGS (and by extension OPERA) uses the SPS not the LHC. Slightly easier to accelerate, although still beyond our means.

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Re: Well, this could change things (neutrinos)

Postby gmalivuk » Wed Nov 23, 2011 3:06 pm UTC

ibgdude wrote:Couldn't the break in causality be caused by just a single ship w/neutrino dectector moving at near lightspeed, and the LHC on earth, because velocity is relative?
That doesn't make it much easier, considering how big typical neutrino detectors are.

eSOANEM wrote:IIRC, for FTL to give signals going back in time, doesn't the relativistic observer have to be moving towards the non-relativistic observer (which limits the stability of such systems).
No, they have to be moving apart.
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Re: Well, this could change things (neutrinos)

Postby mfb » Wed Nov 23, 2011 3:07 pm UTC

ibgdude wrote:Couldn't the break in causality be caused by just a single ship w/neutrino dectector moving at near lightspeed, and the LHC on earth, because velocity is relative? So, not really that hard. You use light for spaceship-earth, and FTL back again. This second ship only needs to have a heavy metal, photographic film and a laser, so it could be pretty small. Launch it off a ring accelerator on the moon, not too hard. We could be there in 100-1000 years.

- You need FTL in both directions.

- To shield cosmic rays, you need some hundred meters of rock (or less with heavy metals) in front of the detector, and unless you have a really good way to handle noise you probably need it in all directions.

- You need an accelerator for ~500 GeV (estimated from SPS capacity), a target and some beam handling. Interesting thing: With wakefield accelerators, the 500 GeV could be achieved within ~10m, together with ~50m pre-acceleration the system is quite compact.

- Let's assume that this high-tech system in the ship can be accelerated with 1000g. Don't try this with any part of the SPS...
Even with non-relativistic formulas, you need an acceleration track of 30 AU (4 light hours). But you need at least ~(1-10-5)c (gamma=200), I think a relativistic calculation will give you acceleration tracks which exceed the size of the solar system by some orders of magnitude.

- The CNGS is able to detect 1 neutrino per 10^16 accelerated protons with a distance of 730km. Fun fact: Scale the rate down according to the 30 AU distance calculated before, and you need the energy equivalent of 1 million megatons of TNT per detected neutrino. At that distance, each round-trip could transmit the bit ~100ms in the past, so you have to send that amount (more realistic: some multiple of it) 10 times per second for a "1", which requires ~10^23W or ~1/1000 of the total power output of the sun. Remember: You need that on the ship, too ;).
It is obvious that the neutrino detector and the beam profile would need a lot of work to reduce these numbers by several orders of magnitude. However, note that the distance is too low by several orders of magnitude as well.

- With a shield of 1km^3 of water density, you need 10^27W to accelerate the ship within 8 hours (the classical 1000g from above). That is ~10 times the power of the sun.

Funny numbers. Maybe we should stay at the theory, as any application is far away from our current knowledge of physics.

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Re: Well, this could change things (neutrinos)

Postby eSOANEM » Wed Nov 23, 2011 3:34 pm UTC

gmalivuk wrote:
eSOANEM wrote:IIRC, for FTL to give signals going back in time, doesn't the relativistic observer have to be moving towards the non-relativistic observer (which limits the stability of such systems).
No, they have to be moving apart.


*sketches diagram* yup, sorry. I remembered something about them having to be moving in a specific direction and, it seems, didn't quite think which direction through properly. Thanks.
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Re: Well, this could change things (neutrinos)

Postby Game_boy » Wed Nov 23, 2011 4:38 pm UTC

@mfb

Thanks for the numbers. AYou'd only need one logic-bit of information to be sent back by a fraction of a second to set up a causality paradox we could test, so perhaps it could be done once. A very expensive once.
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Re: Well, this could change things (neutrinos)

Postby Randomizer » Thu Feb 23, 2012 12:10 am UTC

I saw this article come up today: Faster-Than-Light Neutrino Results May Be Due to Bad Cables

Aw, how sad. I was hoping for faster-than-light telecommunications. :(

Looks like they're going to re-test neutrino speeds in March.
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Re: Well, this could change things (neutrinos)

Postby mfb » Sat Feb 25, 2012 6:52 pm UTC

Well, no negative ping for your internet connection.

I think the two issues they found settle this discussion. Even if they would report "we investigated these cables, and we still see some effect" after a new measurement, who would believe them?
It is not possible to make a measurement without any chance to have an error (which is different from an uncertainty) inside. Errors can happen, and I think a lot of publications have them in various magnitude. The OPERA collaboration was just unlucky to have one of this size at such a fundamental measurement, and did not find it before they went to the public with their result.

Looks like the SPS is already running again and sending neutrinos to Gran Sasso.


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