# If neutrinos travel faster than light, how much lead time would we have over detecting supernovas?

In light of the recent story that neutrinos travel faster than photons, I realize the news about this is sensationalistic and many tests still remain, but let's ASSUME neutrinos are eventually proven to travel "60 ns faster than light". If so, how much lead time would they have over light from local supernovas (e.g. SN 1987A) and distant (e.g. SN 2011fe)?

What does the math look like to calculate this?

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You have a lead time over detecting the rising light curve anyway (every large, low background neutrino detector has a "supernova trigger" these days for just this event...the hope being to get a IAU telegram out so that the optical scopes can get busy as early as possible.), because the neutrinos get out of the core faster than the light does. The talk at CERN is just ending as I type this, but you can read the pre-print at arxiv.org/abs/1109.4897 . – dmckee Sep 23 '11 at 15:08
What do you mean by "The talk at CERN is just ending as I type this"? – Sony Nov 20 '11 at 18:27
@Sony: He meant the OPERA collaboration first presented this result in public at a CERN colloquium which was webcast live to the whole world (word of the result had leaked into the physics blogosphere and been picked up by the mainstream media; and there was a paper on the arXiv). I had a important phone conference at the same time so I only got to see part of it. – dmckee Nov 21 '11 at 23:12
It is possible (/has been thought) that the ability of the neutrinos to travel faster than light is linked to their energy, as the neutrinos in the OPERA experiment have much more energy than those that reach of from supernovas. – Jonathan. Dec 5 '11 at 18:32
Conference recording from the original presentation (September 2011) is available at CERN's Indico webcast/meetings/slides system: indico.cern.ch/conferenceDisplay.py?confId=155620 – jbatista Dec 10 '11 at 0:22

The calculation is done for 1987A here. Basically, the neutrinos' fractional speed increase from the new paper is $2.48\pm0.28\pm0.30\times10^{-5}$ (statistical / systematic errors, respectively) . SN1987a was $166\,912\pm10.1$ ly away, so multiplying the fraction by the travel time gives $4.14\pm0.97$ years. In reality, we got the neutrinos a few hours beforehand, but mostly because the light had to scatter out.

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Please clarify what you mean by "the light had to scatter out." Surely scattering cannot account for a difference of 2-3 years time gap. – Dale Oct 6 '11 at 5:59
The four year difference would be if neutrinos travel faster than light. If they don't, then we would naively expect the light and the neutrinos to reach us at the same time. But the material around the collapsing stellar core isn't perfectly transparent, which means that, on average, the light is slowed because it interacts with a few ions/atoms along the way, changing its course and slowing it down relative to the neutrinos that hardly interact at all. – Warrick Oct 6 '11 at 7:13
We got the neutrinos a few hours ahead eh? That fact would seem to contradict the recent findings at CERN. – Dale Oct 6 '11 at 17:50
Is scattering really the answer? My understanding is that the core collapse is a quick event that generates a blortload of neutrinos; the neutrinos travel through the material of the star (and anything else in their path) and reach us without delay. Meanwhile, the core collapse and rebound emits energy in forms that's absorbed by the body of the star, causing it to head up. We don't see the visible light until that energy (1) reaches the surface of the star, causing it to glow more brightly, and/or (2) blows away most of the star's mass, exposing the bright core. – Keith Thompson Nov 18 '11 at 21:00
(ran out of characters) The bulk of the star isn't significantly transparent at all. We don't see the light from the blast until most of the star is blown away -- which happens in a matter of a few minutes or hours. – Keith Thompson Nov 18 '11 at 21:01

If light is interacting with ions/atoms and neutrinos do not, that would mean that light has a variable speed no? Therefore neutrinos are more constant at the "speed of light". If this is true, then can we devise an experiment that slows light? It is energy and has mass, why not? If this is correct, then wouldn't nuetrinos be affected too and we should be able to slow them down? Do they change state? Interesting questions.

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This argument would be viable if you were measuring the difference in arrival time of a light pulse and the neutrino pulse traversing a medium. But that is not what they are doing. The neutrinos are traveling though the Earth and the are measuring $\Delta x/\Delta t$ for the neutrinos and comparing to the known speed of light in vacuum. With the recent announcement of the short-pulse data conforming to the long pulse data, interest is now focused on the distance and time measurements. Many people think the time comparison is being done incorrectly. – dmckee Nov 18 '11 at 19:32

I would think that if neutrinos travel faster than light the first thing one would need to know is their velocity.

Yesterday or today the Opera folks announced that they had found a loose cable connection and had calculated that the error it caused was the same as the discrepancy between the expected time of arrival and the time recorded by the experiment. It's all to be confirmed, of course.

Here's a link: http://www.iol.co.za/scitech/science/news/was-einstein-s-theory-of-relativity-wrong-1.1240964 Use a search engine such as Google to find more.

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They announced that they had two candidates for problems with their equipment and calculations and that they pulled in opposite directions. The issue is not settled yet. – dmckee Feb 24 '12 at 17:49