Author Topic: Neutrinos  (Read 1508 times)

Offline jazzba

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Neutrinos
« on: April 14, 2014, 09:18:14 PM »
Neutrinos....are they faster than light?
They detected a neutrino from a supernova three hours before it's light hit earth.
Cern said they were FTL ...then took it back.
Inflation ....that was faster than light...wasn't it? Can we say that?

Offline scikopas

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Re: Neutrinos
« Reply #1 on: April 14, 2014, 09:45:17 PM »
You should watch this week's episode 6 of Cosmos, NGT explains that!  And it was explained on an episode of TiPhy too if I remember correctly... I think this one: http://titaniumphysicists.brachiolopemedia.com/2012/04/15/episode-13-that-which-lies-beneath-the-ice/

Tl;dr:  neutrinos don't travel faster than the speed of light in a vacuum.   The reason we were able to detect neutrinos from a supernova much sooner than we saw the light is because the light that is "produced" in a star does not immediately escape the sun! it is created way in the center, all surrounded by mass, and then it flys a little bit and bumps into some mass and is reflected and re-absorbed and re-emitted many many many many times.  It takes a really long time for it to escape the star in the first place, many (thousands? millions of?) years in the case of a regular sun, or in the case of a supernova, it takes until the explosion actually rips apart the matter in the star (closer to the speed of sound) and allows the light to escape.

Neutrinos on the other hand don't interact with matter, so they have no problem escaping from the center of the sun at some fraction of the speed of light! Because they had a "head start" on the photons, we are able to detect them first.


Cern's thing was a mistake about two clocks that were miscalibrated. I had a professor who worked there who told us that one of the atomic clocks was actually unplugged... but thats apocryphal so I would just go with the official story.


Inflation happened sort-of faster than the speed of light, but the rule is no particle can go faster than the speed of light, and in this case it was space itself that was expanding, not any particle, so thats allowed still.  I think that's discussed on the most recent TiPhy: http://titaniumphysicists.brachiolopemedia.com/2014/03/28/episode-45-the-thumbprint-of-creation-with-ryan-north/  and the first episode of TiPhy if I remember right, http://titaniumphysicists.brachiolopemedia.com/2011/11/08/episode-1/  I would (re)listen to both of them just to be safe, and because ryan north is the super great guest on both those shows.

PhD student in Materials Science at Arizona State University currently working on high-temperature superconductors and quantum computers or something.
my (materials) science podcast: LASER (Let's Agree Science and Engineering are Rad!) twitter @scikopas

Offline CollapsedPsi

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Re: Neutrinos
« Reply #2 on: April 17, 2014, 10:40:20 AM »
I've heard the unplugged atomic clock story as well. In my (apocryphal?) version it was plugged in and looked good but not tightly enough to make a real connection (I'm imagining a BNC cable not twisted into position?)

Offline scikopas

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Re: Neutrinos
« Reply #3 on: April 17, 2014, 11:52:41 AM »
I've heard the unplugged atomic clock story as well. In my (apocryphal?) version it was plugged in and looked good but not tightly enough to make a real connection (I'm imagining a BNC cable not twisted into position?)

That's actually what my professor said, I had just simplified it... those stupid BNC cables...  That someone else has heard the same story makes me think twice that it might have actually happened, yikes. 
PhD student in Materials Science at Arizona State University currently working on high-temperature superconductors and quantum computers or something.
my (materials) science podcast: LASER (Let's Agree Science and Engineering are Rad!) twitter @scikopas