Neutrinos

[THX1138]

Boy neutrino's are some strange stuff
I have lots and lots of questions I'd like to ask about these things right now..........
I'll try to keep that number down to two or three right here right now
The / a neutrino is created and then automatically starts moving at c in some certain direction or another, why?
It's moving because the supernova explosion that created it has blown or pushed it some certain direction ?
Such as, and or, ( say if one were to make one single neutrino ) It would fly away from them at c, why would it and what would determine the direction it would take considering a light year of lead is probably not enough to give you any interaction with it (even if one wanted to steer one) I guess the same goes for a photon, why does it automatically start moving as soon as it's comes in to existence..........At C ?
How about, Do they stop, can you stop a neutrino or a photon and look at it.
Is that too many questions........Sorry

[Chris Peterson]

The / a neutrino is created and then automatically starts moving at c in some certain direction or another, why?

Keep in mind that neutrinos may not move at c, because they are probably not massless. They certainly have an extremely small mass, however, and move very close to c, if not at it.

I think you are falling into what I call the billiard ball fallacy here... the tendency to try and force the world to behave the way you have observed it to in everyday cases. The quantum world behaves differently, and there's nothing odd about that. It's just different. Particles come into existence with some momentum- a mass and a velocity (the latter a vector, meaning both speed and direction). The mass is intrinsic to the type of particle. The velocity (which will always have a speed component of c if the particle is massless) may be determined by the characteristics of the collision or interaction that produced the particle, or may be (apparently) random in the case of spontaneous particle production.

It's moving because the supernova explosion that created it has blown or pushed it some certain direction ?

Not at all. It doesn't interact with the supernova. It's moving because neutrinos don't exist without a nonzero velocity.

How about, Do they stop, can you stop a neutrino or a photon and look at it.

You certainly can't stop a photon. Massless particles only exist at c. Whether a neutrino could be stopped rests on whether it has mass. It it could be trapped, nobody has a clue how to do it.

[neufer]

The / a neutrino is created and then automatically starts moving at c in some certain direction or another, why? It's moving because the supernova explosion that created it has blown or pushed it some certain direction ?

Not at all. It doesn't interact with the supernova. It's moving because neutrinos don't exist without a nonzero velocity.

Around 1% of the neutrinos might interact with core collapse supernovae:

(Note: 250 meters of neutron core has the neutrino stopping power of 1 light-year of lead.)

<<There is a fundamental difference between the balance of energy production in the different types of supernova. In type Ia white dwarf detonations, most of the explosion energy is directed into heavy element synthesis and kinetic energy of the ejecta. In core collapse supernovae, the vast majority of the energy is directed into neutrino emission, and while some of this apparently powers the main explosion 99%+ of the neutrinos escape in the first few minutes following the start of the collapse.

In lower mass cores the core collapse is stopped and the newly formed neutron core has an initial temperature of about 100 billion kelvin, 6000 times the temperature of the sun's core. 'Thermal' neutrinos form as neutrino-antineutrino pairs of all flavors, and total several times the number of electron-capture neutrinos. About 10⁴⁶ joules, approximately 10% of the star's rest mass, is converted into a ten-second burst of neutrinos which is the main output of the event. The suddenly halted core collapse rebounds and produces a shock wave that stalls within milliseconds in the outer core as energy is lost through the dissociation of heavy elements. A process that is not clearly understood is necessary to allow the outer layers of the core to reabsorb around 10⁴⁴ joules (1 foe) from the neutrino pulse, producing the visible explosion, although there are also other theories on how to power the explosion.

Core collapse supernovae are on average visually fainter than type Ia supernovae, but the total energy released is far higher. This is driven by gravitational potential energy from the core collapse, initially producing electron neutrinos from disintegrating nucleons, followed by all flavours of thermal neutrinos from the super-heated neutron star core. Around 1% of these neutrinos are thought to deposit sufficient energy into the outer layers of the star to drive the resulting explosion, but again the details cannot be reproduced exactly in current models. Kinetic energies and nickel yields are somewhat lower than type Ia supernovae, hence the reduced visual luminosity, but energy from the ionisation of the many solar masses of remaining hydrogen can contribute to a much slower decline in luminosity and produce the plateau phase seen in the majority of core collapse supernovae.>>

[Chris Peterson]

Not at all. It doesn't interact with the supernova. It's moving because neutrinos don't exist without a nonzero velocity.

Around 1% of the neutrinos might interact with core collapse supernovae:

Yes, of course. There's always a finite possibility of a neutrino interacting with another particle. The point, however, is that the velocities of the neutrinos produced in an supernova don't result from any interaction with the supernova material. They aren't being bounced around or having their speeds altered.

[neufer]

Not at all. It doesn't interact with the supernova.

Around 1% of the neutrinos might interact with core collapse supernovae:

Yes, of course. There's always a finite possibility of a neutrino interacting with another particle. The point, however, is that the velocities of the neutrinos produced in an supernova don't result from any interaction with the supernova material. They aren't being bounced around or having their speeds altered.

Not at all (necessarily):

<<Around 1% of these neutrinos are thought to deposit sufficient energy into the outer layers of the star to drive the resulting explosion.>>

[Chris Peterson]

Not at all (necessarily):

<<Around 1% of these neutrinos are thought to deposit sufficient energy into the outer layers of the star to drive the resulting explosion.>>

Not sure of your point. The neutrinos that deposit the energy are being absorbed. They are not the neutrinos we observe coming from a supernova.

I did not say that neutrinos don't interact with the supernova. What I said is that the neutrinos we observe from a supernova are not having their velocities altered by interactions with the supernova material.

[neufer]

Not at all (necessarily):

<<Around 1% of these neutrinos are thought to deposit sufficient energy into the outer layers of the star to drive the resulting explosion.>>

Not sure of your point. The neutrinos that deposit the energy are being absorbed. They are not the neutrinos we observe coming from a supernova. I did not say that neutrinos don't interact with the supernova. What I said is that the neutrinos we observe from a supernova are not having their velocities altered by interactions with the supernova material.

Quasi-elastic (QE) scattering dominates for neutrino energies less than 1 Gev:

• . http://asterisk.apod.com/viewtopic.php? ... 05#p227172

(Note: Neutrinos detected from SN1987A ranged in energy from 6 to 39 MeV.)

I presume that quasi-elastic scattering has more effect upon neutrino velocities than upon their numbers.

I just think that the previous discussion about neutrino transparency shouldn't leave the wrong impression that neutrino/supernova core interactions aren't important (; which is what I was taking away from your comments). Neutrino/supernova core interactions might be very important. (Note: Supernova cores are ~ 4 x 10¹³ times denser than lead.)

[THX1138]

Thank you, both of you for trying to clear that up for me
I'm afraid I'm going to have to read and re-read your replays a number of times over the next ? week, month ? before i can fully grasp what you guys said, nonetheless thank you
This may be slightly off topic..........But when you mentioned that you cannot stop a photon it got me thinking along this line.
The universe is expanding / Is it expanding at C then ? / And if so now that we know the the universe is not slowing down and that it is actually speeding up would it be correct to assume that it is expanding faster than C ?

[Chris Peterson]

The universe is expanding / Is it expanding at C then ? / And if so now that we know the the universe is not slowing down and that it is actually speeding up would it be correct to assume that it is expanding faster than C ?

You can't place any single speed on something that is expanding uniformly- including the Universe. Expansion can only be understood as a rate between any two points. When you blow up a balloon, two close points on its surface are moving apart slowly compared with two points that are widely separated. The expansion of the Universe is described by Hubble's law, v = H₀D, which describes the apparent velocity between two points separated by D. The Hubble constant, H₀, has a value of about 70 km s⁻¹ Mpc⁻¹.

That means there is some distance beyond which points in space are moving away from each other at greater than c. That distance is what defines the size of the observable universe (or any observable universe, since every point in space has its own).

[THX1138]

Thank you Chris, Well it going to be awhile before I'll be posting another question because I'll be busy making sence out of both this one and the last few replies.
It's fun though......I love this stuff