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afterburner
2006-Aug-09, 04:42 PM
There is still one(well, maybe more) thing that I dont understand...So please help me!!!

How can it be that neutrinos apparently have no mass whatsoever, yet they interact through the weak force, which is mediated by massive particles? In other words...Does the massless neutrino "spontaneously" create more massive particles than itself for weak interaction? If so, how can this be? where are these particles coming from?

And in one of my other threads, I asked how can particles spontaneously create force carrier particles out of nothing? no one answered

Also, the force carrier particles "spontaneously" appear, so when they dissapear... is it also spontaneous and absolutely no trace of them is left? *puf* so to speak?

Is it possible to create force carriers by themselves? What I want to know is...if force cariers for an electron and positron are exactly the same...if we create just force carriers without the electron/positron pair, what will the force carriers do? attract of repell?

Thought experiment...if we have a charged particle travelling at c, will the force carriers appear in front of it? or will they trail behind it?

Is it correct to say that the idea behind a wave function is that... if we have a particle with known energy, we dont know its position exactly, so we spread that energy over a probable volume. So, when the particle interacts with another particle, the wave function becomes a point at the place of interaction within the wave function? (with all of the energy that was previously spread out, in one point)

trinitree88
2006-Aug-10, 01:56 AM
Afterburner. The business of virtual particles is attributable to Einstein. It comes out of Heisenberg's Uncertainty Principle. The Uncertainty Principle was formulated after Heisenberg considered the effects of a photon striking an electron.

Picture an electron stealthily moving along at some velocity v, but unseen by you in a darkened room. You are given a laser pointer that emits single photons of visible light, at one second intervals (it's arbitrary). When your photon hits the electron, it's absorbed and re-emitted in your direction, you"see" it (technically not true for the retina, but we labor for simplicity here). However, the photon carries momentum E/c...so the electron may have it's original velocity vector affected by the impact...it may gain energy and momentum from the photon. This bothered Heisenberg. If you don't fire a photon, you can't "see" the electron, but when you do...you change the momentum of the object you are looking for.
There is no way out here. In order to measure the position of the electron you need to input your measuring method, and the consequence of that is you affect the system you are measuring. Heisenberg expressed this numerically as ....(delta x)(delta p) = or > h/2pi delta x is the uncertainty in the position of the object delta p is the uncertainty in the momentum of the object (p=mv) h is Planck's constant h/2pi is sometimes written as h with a bar over it It has units of action (energy times time) in erg-sec or Mev-sec...
Einstein hated this. He thought he could devise a thought experiment wherein one could determine both the position and momentum with arbitrary uncertainty simultaneously. While you can improve either quantity....whatever you do to better one...worsens the other. For example you could use a violet photon with a smaller wavelength, to fix the position more precisely....but it's increased momentum means you now know the momentum of the struck electron more vaguely. Bohr argued with Einstein over this for a long time...pointing out every time how Heisenberg was right. Finally Einstein accepted it, but he didn't like it.
Soon Einstein realized something else was up....if you replace delta x, the position with c delta t...for a particle moving at ~ c AND... if you replace delta (mv) with delta (mc) in delta p ...for that same particle, then you get (mc)(c delta t) = or > h/2 pi Rearranging the algebra delta mc2 (delta t) = or > h/2 pi. Now you have E=mc2....so you can replace the delta mc2 with delta E

This yields (delta E)(delta t) = or > h/2 pi This equation says the energy (E) of an object is uncertain in the same way that the momentum and position are ...and the uncertainty is time dependent. What it means physically is that the energy of a photon may increase briefly over small time intervals. The larger the interval, the smaller the increase....but for sufficiently small intervals the fluctuation may be quite large, and the object may "use" this energy to create short-lived particle/antiparticle pairs. Like Cinderella, they must return to a state of annihilation by "Midnight"...delta t'
massive pairs are very short-lived. Massless ones much longer (Z/anti-Z)

Enter Hideki Yukawa. He reasoned that the time for a force carrier to traverse the width of a proton...~ one Fermi was so short that the particle should have a mass of ~ 250 Mev. Eventually, after a misidentification of the muon as the strong force carrier, the pion fit the bill. Nobel Prize for Yukawa.

Other particles can emit virtual pairs transiently, but are similarly restricted by the time interval. Like Cinderella, they must disappear by Midnight...delta t to conserve mass and energy. It's not true that the neutrino can only interact via massive force carriers in the weak interaction, the W+, W-, or Z0. The Z can be a photon/ anti-photon ...it is it's own anti-particle...or a neutrino/antineutrino pair. They are both massless and have infinite range.

No charged particle will ever travel at c...SR forbids it. However if an electron is exchanging virtual photons with a proton in hydrogen, binding them in the elctromagnetic interaction....and you "kick" the atom with heat, or photons...you can promote some of the virtual photons into reality...the hydrogen spectrum.

With regards to the wave function collapsing...yes that's how your radio works too. Hope this helps. Pete.

afterburner
2006-Aug-11, 12:50 AM
Thank you for the explanation trinitree88.

However, I just dont see why the energy of a photon (or any particle) would increase even slightly over small intervals of time. :wall: It just doesnt make sence in my head.

I can see why Einstein had problems with the Uncertainty Principle. Although we cant measure the electrons position and momentum at the same time, it does not necessarily mean that the particle experiences an uncertainty. If we were to ask the particle, it would tell us all what we want to know (the electron does something when its in the electron cloud, its not uncertain about what its doing, it just doesnt want to "tell", and we have no way of getting the information out of it so to speak). Similarly, if we were to ask the Universe, it would also tell us what we want to know, assuming it can account for every particle that exists in it (and the language problem :silenced: )

:shifty: :eh:

Ufonaut99
2006-Aug-11, 02:02 PM
However, I just dont see why the energy of a photon (or any particle) would increase even slightly over small intervals of time. :wall: It just doesnt make sence in my head.
How about this: We accept every particle has an uncertainty in position - right? Well, a photon's energy is inversely proportional to its wavelength (shorter wavelength = higher energy). Well, if we're not certain of position, then the crest of one wave may be nearer or further than expected to the previous crest - hence, the photon has more or less energy.


In order to measure the position of the electron you need to input your measuring method, and the consequence of that is you affect the system you are measuring.
I've always wondered about this. While it's undoubtedly true that hitting something with a more powerful bullet means that you affect the thing you're measuring more, there's got to be more to it than that. The uncertainty principle limits natures own knowledge of the particle, not just our ability to measure - otherwise we're left with the particle really going through one slit.

Or have I got the wrong end of the stick about what you're saying?

trinitree88
2006-Aug-13, 12:31 AM
RobA...snippet:
I've always wondered about this. While it's undoubtedly true that hitting something with a more powerful bullet means that you affect the thing you're measuring more, there's got to be more to it than that. The uncertainty principle limits natures own knowledge of the particle, not just our ability to measure - otherwise we're left with the particle really going through one slit.

Or have I got the wrong end of the stick about what you're saying?[/QUOTE]

Take the case of a pot of warm water. You pick up a thermometer, put it in the water up to it's calibrated immersion level. You wait for thermal equilibrium. You read the thermometer. 40 degrees + or -...right? Well, Yes and NO. It's pretty close, with an error bar....but was the thermometer warmer than the water, or colder? If it was warmer...then there's added heat from the thermometer, if it was colder there's subtracted heat (MCdelta T). So you have the equilibrium temperature of the two objects, not the water alone. You can reduce the size of the thermometer, but you can't make it disappear....so you never get the temperature of the water only....you only get the equilibrium temperature of the water-thermometer system. They're not the same. There's no way out of this. Your measuring device affects what you are measuring...hence Heisenberg. Only the supernatural can "know" perfectly. I'm not arguing against what nature knows. ....or seems to know. Pete

Jeff Root
2006-Aug-13, 12:43 AM
Pete,

What if I don't care about the temperature of the water -- I want
to know the temperature of the thermometer!

-- Jeff, in Minneapolis

trinitree88
2006-Aug-13, 01:54 AM
Pete,

What if I don't care about the temperature of the water -- I want
to know the temperature of the thermometer!

-- Jeff, in Minneapolis

Jeff. Yah. Yah. Yah......:D Pete.

swansont
2006-Aug-13, 04:22 PM
Thank you for the explanation trinitree88.

However, I just dont see why the energy of a photon (or any particle) would increase even slightly over small intervals of time. :wall: It just doesnt make sence in my head.

I can see why Einstein had problems with the Uncertainty Principle. Although we cant measure the electrons position and momentum at the same time, it does not necessarily mean that the particle experiences an uncertainty. If we were to ask the particle, it would tell us all what we want to know (the electron does something when its in the electron cloud, its not uncertain about what its doing, it just doesnt want to "tell", and we have no way of getting the information out of it so to speak). Similarly, if we were to ask the Universe, it would also tell us what we want to know, assuming it can account for every particle that exists in it (and the language problem :silenced: )

:shifty: :eh:

Einstein wasn't the only one who struggled with it, but the Bell's inequality measurements seem to have shown that there are not "hidden variables." That is, if a particle can be in one of two states, it really is in those two states, as opposed to really being in one state all along, and we just didn't know until we measured it.

The quantum world really is different than the classical one with which we are familiar. It's not just a miniaturized version with similar concepts and behaviors.

trinitree88
2006-Aug-22, 12:15 AM
:clap:
Thank you for the explanation trinitree88.

However, I just dont see why the energy of a photon (or any particle) would increase even slightly over small intervals of time. :wall: It just doesnt make sence in my head.

I can see why Einstein had problems with the Uncertainty Principle. Although we cant measure the electrons position and momentum at the same time, it does not necessarily mean that the particle experiences an uncertainty. If we were to ask the particle, it would tell us all what we want to know (the electron does something when its in the electron cloud, its not uncertain about what its doing, it just doesnt want to "tell", and we have no way of getting the information out of it so to speak). Similarly, if we were to ask the Universe, it would also tell us what we want to know, assuming it can account for every particle that exists in it (and the language problem :silenced: )

:shifty: :eh:


Afterburner, ...very Einsteinian of you...lol.:lol: Interrogating the particle would require a communication.Even a single photon of communication will carry away some energy and momentum....hence, object changed, just as in a collision. Some things we have to accept...like it or not. Ciao. Pete

Cougar
2006-Aug-22, 01:14 AM
Even a single photon of communication will carry away some energy and momentum...
Of course this is true, but most of the treatments I've read on this topic include the school of thought that Heisenberg Uncertainty is not simply a limitation in our ability to measure, as RobA and swansont have indicated. It's a more fundamental limitation....

swansont
2006-Aug-22, 02:09 AM
Of course this is true, but most of the treatments I've read on this topic include the school of thought that Heisenberg Uncertainty is not simply a limitation in our ability to measure, as RobA and swansont have indicated. It's a more fundamental limitation....

In QM, the wave function of conjugate variables, like momentum and position, are Fourier transforms of each other. The uncertainty is inherent in that.

Jeff Root
2006-Aug-22, 03:22 AM
if a particle can be in one of two states, it really is in those
two states, as opposed to really being in one state all along,
and we just didn't know until we measured it.

In QM, the wave function of conjugate variables, like
momentum and position, are Fourier transforms of each other.
The uncertainty is inherent in that.
Can we go into this?

Assume that I know nothing about "the wave function of
conjugate variables" or "Fourier transforms". Can you
explain why anyone should think that a particle really is
in two mutually-exclusive states simultaneously, rather
than simply being in an unknown state?

-- Jeff, in Minneapolis

Nereid
2006-Aug-22, 02:25 PM
Can we go into this?

Assume that I know nothing about "the wave function of
conjugate variables" or "Fourier transforms". Can you
explain why anyone should think that a particle really is
in two mutually-exclusive states simultaneously, rather
than simply being in an unknown state?

-- Jeff, in MinneapolisA clarification if I may - are you asking for a walk-through of the theory (crudely, what does all this "the wave function of
conjugate variables" or "Fourier transforms" stuff mean, in simple language)? Or how an experiment (or series of experiments) could rule out 'hidden variables'? Or, perhaps, what the experiments were that actually produced the results we interpret as 'no hidden variables' (and cause Einstein to spin in his grave, no doubt)?

afterburner
2006-Aug-23, 12:34 AM
Some time ago, I asked whether or not there is a limit to how much or how litle energy a photon can have. The answer was no.

Would this not mean that we could technically use photons that have extremely small energy levels (I'm talking really small here) to interrogate the particle, so that the energy lost/gained is so insignificantly small, that we would be satisfied?

(Scenario for above: We have large bubble Universe, (100 billion light year redius) at the center of this large, empty space, we have some particle. From the outside of this bubble, we send a photon with a wavelength of 30 billion light years straight at the particle. IT HITS!!! My question is...whats going to happen? Would this kind of communication be effective for interrogating the particle and having it tell us what we want to know?)

Just as a side note...All things cast a shadow in the neutrino sea..right? Do subatomic particles also have their own shadow in this sea, or is it only larger objects?

And another thing...Are there even any advantages to knowing the precise position and momentum of a particle?...As in, if we knew the position and the momentum at the same time...what could we potentially do differently? New technologies perhaps? Or is there no point to it at all?


Thanks.

Ufonaut99
2006-Aug-23, 12:52 AM
Would this not mean that we could technically use photons that have extremely small energy levels (I'm talking really small here) to interrogate the particle, so that the energy lost/gained is so insignificantly small, that we would be satisfied?

Small energy levels mean a long wavelength, and the longer the wavelength means the lower the resolution. So, if you get a hit, all you know is that the particle you're observing is somewhere within that wavelength.

So you've got a choice :
- high energy photon, which tells you precisely where something was before you sent it barrelling away, or
- low energy photon, which tells you roughly where something is


(Scenario for above: We have large bubble Universe, (100 billion light year redius) at the center of this large, empty space, we have some particle. From the outside of this bubble, we send a photon with a wavelength of 30 billion light years straight at the particle. IT HITS!!! My question is...whats going to happen?

You know that the particle is somewhere in a 30 billion light year region :)



And another thing...Are there even any advantages to knowing the precise position and momentum of a particle?...As in, if we knew the position and the momentum at the same time...what could we potentially do differently? New technologies perhaps? Or is there no point to it at all?

If it were possible, there would be a lot of point. Yes, we could develop new technologies and materials, and it would give us a sharp view into whats happening in nature in our laboratories.
Unfortunately, that's all predicated on "If it were possible". QM says that even nature itself doesn't "know" the precise position and momentum, so we never will.

Jeff Root
2006-Aug-23, 01:08 AM
Some time ago, I asked whether or not there is a limit to how
much or how litle energy a photon can have. The answer was no.

Would this not mean that we could technically use photons that
have extremely small energy levels (I'm talking really small
here) to interrogate the particle, so that the energy lost/gained
is so insignificantly small, that we would be satisfied?
There is no limit to how little energy a photon can have, but
there are limits to how little energy a photon can have and
yet be able to interact with a particle or a detector.



(Scenario for above: We have large bubble Universe, (100 billion
light year redius) at the center of this large, empty space, we
have some particle. From the outside of this bubble, we send a
photon with a wavelength of 30 billion light years straight at
the particle. IT HITS!!! My question is...whats going to happen?
Would this kind of communication be effective for interrogating
the particle and having it tell us what we want to know?)
I don't understand the reason for the scenario, but the photon
would not hit the particle. The wavelength needs to be about
the same size as a particle, or smaller, in order to interact
with the particle. For the same reason, there would be no way
to detect such a photon. The longest-wavelength photon which
can be detected as an individual is probably in the infrared
part of the spectrum, with a wavelength less than a millimeter.
Longer wavelengths, such as microwaves and radio waves, can
only be detected by the combined effects on a detector of very
large numbers of photons acting together.



Just as a side note...All things cast a shadow in the neutrino
sea..right? Do subatomic particles also have their own shadow in
this sea, or is it only larger objects?
If a subatomic particle can and does interact with a neutrino,
then the neutrino ceases to exist (something else is formed),
and you will have a "shadow". I don't see that this fact is
of any practical value.



And another thing...Are there even any advantages to knowing the
precise position and momentum of a particle?...As in, if we knew
the position and the momentum at the same time...what could we
potentially do differently? New technologies perhaps? Or is there
no point to it at all?
All I can think is that it would allow measurements of some
other things to be more precise, and less noisy. So that it
might be possible to measure some things that currently can't
be measured at all because the signal can't be distinguished
from noise. But I can't come up with a specific example.

-- Jeff, in Minneapolis

Jeff Root
2006-Aug-23, 01:23 AM
Assume that I know nothing about "the wave function of
conjugate variables" or "Fourier transforms". Can you
explain why anyone should think that a particle really is
in two mutually-exclusive states simultaneously, rather
than simply being in an unknown state?
are you asking for a walk-through of the theory (crudely, what
does all this "the wave function of conjugate variables" or
"Fourier transforms" stuff mean, in simple language)?
Or how an experiment (or series of experiments) could rule out
'hidden variables'? Or, perhaps, what the experiments were that
actually produced the results we interpret as 'no hidden
variables' (and cause Einstein to spin in his grave, no doubt)?
Wow. I knew I was asking for a lot, but yeah, I just want
a complete explanation of quantum mechanics and quantum
electrodynamics, written for a twelfth-grade reading
comprehension.

Seriously, maybe the thing to do would be to start with a
specific and work toward the more general, basic ideas.

Here, I'll start by just asking what measurements swansont
referred to:



the Bell's inequality measurements seem to have shown that
there are not "hidden variables." That is, if a particle can
be in one of two states, it really is in those two states, as
opposed to really being in one state all along, and we just
didn't know until we measured it.
After I know what is measured and how it is measured, we can
get into what those measurements imply.

-- Jeff, in Minneapolis

Nereid
2006-Aug-23, 03:11 AM
This thread (http://www.bautforum.com/showthread.php?t=35006), from late last year, may be a good place to start - it covers the general topic, and includes a lot of reference material.

trinitree88
2006-Aug-27, 11:30 PM
[QUOTE=Jeff Root;809971] snippet:


If a subatomic particle can and does interact with a neutrino,
then the neutrino ceases to exist (something else is formed),
and you will have a "shadow". I don't see that this fact is
of any practical value.

Jeff, Not quite true. The three branches of neutrino interactions are W+, W-, and Z0. The neutral current, carried by the Z0, allows the emitting particle to convert some of it's energy and momentum into a particle/ anti-particle pair. The original neutrino would not cease to exist....it is redshifted. The Z, so created, can transfer it's energy and momenta of the pair to any collision that follows.
In the first bubble chamber photographs to show the effect...a neutrino slips in, unseen, creates a knock-on electron, and slips out unseen, as if by magic...no trail (Gargamelle...C.E.R.N.) circa 1979. Pete.

ZaphodBeeblebrox
2006-Aug-28, 06:01 AM
snippet:


If a subatomic particle can and does interact with a neutrino,
then the neutrino ceases to exist (something else is formed),
and you will have a "shadow". I don't see that this fact is
of any practical value.
Jeff, Not quite true. The three branches of neutrino interactions are W+, W-, and Z0. The neutral current, carried by the Z0, allows the emitting particle to convert some of it's energy and momentum into a particle/ anti-particle pair. The original neutrino would not cease to exist....it is redshifted. The Z, so created, can transfer it's energy and momenta of the pair to any collision that follows.
In the first bubble chamber photographs to show the effect...a neutrino slips in, unseen, creates a knock-on electron, and slips out unseen, as if by magic...no trail (Gargamelle...C.E.R.N.) circa 1979. Pete.
Yeah ...

Not ONLY That, But The Discovery of Said Neutral Current, in Which a Neutrino Interaction Occurs But Does Not Produce a Muon or Another Charged Lepton ...

Provided The Proof That Led to The Awarding of The 1979 Nobel Prize in Physics (http://nobelprize.org/nobel_prizes/physics/laureates/1979/), to Sheldon Lee Glashow, Abdus Salam, and Steven Weinberg!