Comment by hazrmard
6 hours ago
A breakdown of why the awarded work, Ice Cube, is significant:
- A neutrino is an elementary subatomic particle. Neutrinos are produced by nuclear reactions inside stars, supernovae, radioactive decay. They are one of the most abundant particles in the universe.
- Neutrinos are known as "ghost particles". They have 0 charge and near-zero mass. They only react with the weak nuclear force and gravity. Incredibly hard to detect. Trillions can pass through a whole planet without hitting a single atom!
- Neutrinos give us a pristine snapshot into the origin of the universe. They have travelled billions of years and trillions of miles without interacting with anything. Unless...we catch them!
- Ice Cube does this. Located in Antarctica, the project turns a cubic kilometer of ice into a neutrino detector. How? Scientists drilled boreholes 2.5km deep into the ice and placed 5000 optical detectors to catch a neutrino interaction.
- When a neutrino, rarely, collides with an atom, it produces charged particles. In ice - not vacuum! - certain particles can travel faster than light. This produces something similar to a sonic boom. A faint, blue glow known as Cherenkov radiation (see it in action https://youtube.com/watch?v=hSuSG19Pcoc).
- IceCube was first to detect neutrinos coming from outside the solar system, establishing the source of high energy cosmic radiation. It also opened a whole new chapter of neutrino astronomy.
" - When a neutrino, rarely, collides with an atom, it produces charged particles. In ice - not vacuum! - certain particles can travel faster than light."
That confused me for a moment so it seems worth clarifying: in ice, certain particles can travel faster than light does in ice.
Thank you, I lost my mind, briefly, reading that part.
Light slows down in dielectric materials because as an em wave it interacts with the polarization of molecules. Neutrino has very little interaction with matter, OTOH.
This is also the source of the classic blue glow in water cooled nuclear reactors. Electrons move through the water faster than light and leave behind a kind of 'sonic boom' of photons in its wake.
>Neutrinos give us a pristine snapshot into the origin of the universe. They have travelled billions of years and trillions of miles without interacting with anything. Unless...we catch them!
I assume this is not a hard, totalizing law since it seems we're able to get samples of neutrino collisions in just a kilometer sized chunk of ice on Earth (meaning that the probability of collision is not absolutely zero and there's no way to know the full neutrino travelogue through the universe)
Correct, they do have a probability of interacting, but it's extremely low, depends of the energy of the neutrino (its momentum) but basically it can go through 1 light year of lead and still have only a 50/50 chance of interacting.
to put things to scale 1 ly is 9,460,730,472,580,800 meters, or 63,241.077 astronomical units, the distance from the Earth to the Sun.
Needless to say, it's pretty weakly interacting as far as interaction goes...
> neutrinos coming from outside the solar system How do we know this and why do we care where they came from?
Since neutrinos don’t interact with much of anything, its path doesn’t deviate from its origin. Different origins emit neutrinos with different levels of energy. When a neutrino hits a nucleus, the blue light emitting particle in ice follows closely the same direction. Measuring the direction and the magnitude (lighting energy) of the vector we can classify its origin. Collecting a bunch of the same signature we know there's an object at that direction emitting at that energy level. From the vector and energy we kind of know whether it’s from the solar system or not.
Identifying the origin let us see objects behind dust clouds or other obstacles.
> When a neutrino hits a nucleus, the blue light emitting particle in ice follows the same direction.
How does this not violate conservation of momentum? Are you saying every single collision is head-on?
1 reply →
We know this because
- In the beginning, for the first couple of events, only because they have way higher energies than anything in the solar system could produce - By now, with enough data collected, their origin correlates very well with the milky way - we are close to identifying several far away galaxies as well
This is the significance. Contrary to some statements published today, IceCube was not primarily built to study Neutrinos, it was built to study the universe using Neutrinos.
That's why we care where they are coming from, we want to learn about the astrophysical objects that produce them.
what is so special about ice?
H2O is the key, not ice. Ice is nice because it's rigid, so you don't need a boat [1]. They're also working on making detector under the sea [2].
[1] https://www.amusingplanet.com/2015/07/the-surreal-world-of-n...
[2] https://news.cnrs.fr/videos/detecting-neutrinos-at-the-botto...
Didn’t the big bang theory show have an episode about this?
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