#### Mk

Neutrons don't have charge you remember, thus neutrons and anti-neutrons cannot have opposite charges, but they do have two other significant things diffrent (I don't know what).

ZapperZ is refering to it as pop-sci, due to its layman's nature, that happens to cause some things to be wrong in it, and due to it was written a fairly long time ago - in theoretical physics, stuff changes a lot.

#### ZapperZ

Staff Emeritus
2018 Award
A pop-sci (short for "popular science") is a text meant for the GENERAL PUBLIC and people with very little physics and/or mathematics background. While such books are quite valuable in introducing people to various ideas and concepts in physics, they all lack RIGOR and thorough treatment of the subject. This is because (i) they can't introduce too much mathematics (ii) they have to explain things superficially and (iii) they have to use examples and analogies to illustrate ideas, rather than present the idea RAW and UNADULTERATED. This means you get snippets of the whole picture, rather than the whole picture themselves.

This is why one should NOT use such books in any physics arguments. We certainly do not use them to teach physics to physics majors.

Zz.

#### Norman

Stefan Udrea said:
Norman,you said :

<<an antiparticle has the same mass and spin as its mate, but has opposite charge>>

I don't pretend to understand these things profoundly,but I wil quote from Feynman's "Lectures on Physics" :

<<The most important characteristic [of antimatter] is that when a proton and anti-proton come together they can anihilate each other.The reason why we accentuate this is because people don't understand when we say that there is a neutron and an anti-neutron,because they say "a neutron is a neutron,so how can it have opposite opposite charge".The rule of "anti" is not that it has opposite charge,but that it has a lot of other properties which are opposed.The anti-neutron distinguishes itself from a neutron this way : if we bring together two neutrons,they remain two neutrons,but if we bring together a neutron and an anti-neutron,they anihilate each other with a big explosion of released energy,with many $$\pi$$ mesons , gamma rays and many others.>>

(actually it was a romanian translation that I've put back into english )
If you would have quoted my exact statement you would understand that the so-called qualities that the anti-particles have (opposite lepton charge (or number), opposite baryon charge, and on and on...) that Feynman mentioned, were exactly what I was refering to in the parantheses after the statement you quoted. I was not just refering to the electric charge- that is why I put the examples after my original statement, including lepton number. I suppose it wasn't completely clear if you misunderstood.
Cheers,
Ryan

#### Stefan Udrea

Oh,I see.
Sorry Norman.
I mean, of course you knew those things

#### eNathan

What exactly is the decaying of a proton? I though sub atomic particles were constant :|

#### lawtonfogle

ZapperZ said:
A pop-sci (short for "popular science") is a text meant for the GENERAL PUBLIC and people with very little physics and/or mathematics background. While such books are quite valuable in introducing people to various ideas and concepts in physics, they all lack RIGOR and thorough treatment of the subject. This is because (i) they can't introduce too much mathematics (ii) they have to explain things superficially and (iii) they have to use examples and analogies to illustrate ideas, rather than present the idea RAW and UNADULTERATED. This means you get snippets of the whole picture, rather than the whole picture themselves.

This is why one should NOT use such books in any physics arguments. We certainly do not use them to teach physics to physics majors.

Zz.
Thank you for explaining that.

#### Mk

eNathan said:
What exactly is the decaying of a proton? I though sub atomic particles were constant :|
Subatomic paticles fall apart all the time, and that's what radiation is.

I thought radiation was subatomic particles breaking away from a cluster of particles, ie an alpha particle breaking free from the nucleus. Do protons and neutrons spontaneously break into their constituent quarks without any outside interference?

#### Norman

I thought radiation was subatomic particles breaking away from a cluster of particles, ie an alpha particle breaking free from the nucleus. Do protons and neutrons spontaneously break into their constituent quarks without any outside interference?
No, free quarks do not occur in nature. Maybe that is a little misleading given that so many people are looking for the quark-gluon plasma. Anyways, the situation is this: The forces between quarks are such that as you bring them farther apart it takes more and more energy until there is enough energy that a quark-antiquark pair can be created and these bind together to produce new hadrons. This is called confinement and is applicable at lower energies. Confinement is the reason we see protons, neutron, pions, kaons, etc., instead of up, down, anti-up, anti-down, strange quarks, etc.

As far as the decay of particles, most subatomic particles are unstable. Take for instance the cosmic ray showers. An incident cosmic ray (say a proton) collides with a nucleus in the earths atmosphere- it creates a bunch of particles, we will track the progress of one of these particles- a kaon, lets say it is a positive kaon. The kaon travels a distance on the order of a meter and decays into a positive pion and a neutral pion. The neutral pion decays very quickly (on the order of $10^{-17} s$) into two photons. The positive pion lives a little longer ( $10^{-8} s$) but then decays into a positive muon and muon neutrino. The muon neutrino is stable and lives until it interacts with another particle. The muon eventually decays into a positron, electron neutrino, and a muon anti-neutrino- all of which are stable particles. So a kaon has decayed (eventually) into 6 stable particles. I have assumed here that the intermediate states, the pions and muon do not scatter off any other atmospheric particles.

So we have seen that in fact, most of our particles, even fundamental ones like the muon, decay (at least can decay) into other particles. Have a look at a particle physics book, like Griffiths "Introduction to Particles Physics" for a much better introduction.
Cheers

E

#### elas

Griffiths also states:
"Ordinarily the procedure is to guess a form for the interaction and compare the resulting theoretical calculations with the experimental data"

"Quantum theory emerges largely unscathed, only serving to reinforce the point that the theory remains the most powerful framework for explaining observations of the quantum world, but its orthodox interpretation continues to offer little in the way of understanding in terms of underlying physical processes"

Martin Veltman puts it this way:

"There is one truth the reader should be fully aware of. Trying to explain something is a daunting endeavour. You cannot explain the existence of certain particles much as you cannot explain the existence of this universe. In addition, the laws of quantum mechanics are sufficiently different from the laws of Newtonian mechanics which we experience in daily life to cause discomfort when studying them. Physicist usually cross this barrier using mathematics: you understand something if you can compute it. It helps indeed if one is at least capable of computing what happens in all situations. But we cannot assume the reader to be familiar with the mathematical methods of quantum mechanics, so he will have to swallow strange facts without the support of equations".

The truth is that we have a brilliant predictive theory and a lousy, incomplete model. No one understands quantum theory, but if your really clever you can learn how to use it. If your absolutely brilliant you can try and explain it, but beware, read what others say about Hawkin's 'Brief History of Time'. The price of brilliance is often derision.

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#### AntonVrba

A contribution to the matter anti-matter debate

Why should it be that the positron is the anti-electron, OK they have opposite charge and the positron does not like an electron and vica versa because when they meet they end up as gamma rays and their mass is annilated or rather cinverted into another energy form. Is this really conclusive proof to say that the positron is the anti matter of the electron?

When the positron is part of a larger mass i.e the proton, and the proton and electron meet then we have what is called electron capture and no burst of gamma rays and the proton changes to a neutron and instead of mass-annilation we have mass-unification.

Could it be that matter and anti-matter actually co-excist within the same particle (nucleus). If this could be true then the problem of where all the anti-matter hides, is solved.

If on the other hand if anti-matter is accumulated at an alternate point in space then surely huge fields would be excist between the matter and anti-matter.

My guess is that we will not know the answer for a long time and my statements above are as speculative as the statements that anti-matter should excist elsewhere.

#### ZapperZ

Staff Emeritus
2018 Award
AntonVrba said:
A contribution to the matter anti-matter debate

Why should it be that the positron is the anti-electron, OK they have opposite charge and the positron does not like an electron and vica versa because when they meet they end up as gamma rays and their mass is annilated or rather cinverted into another energy form. Is this really conclusive proof to say that the positron is the anti matter of the electron?
You seem to have completely ignored HOW we often create positrons. Most of the centers that use positron sources create them via pair production, i.e. by creating electron-positron pairs via gamma rays (typically impinging on Be). We simply do not call something a "positron" simply because it has a positive charge!

Zz.

E

#### elas

AntoVrba

Why should it be that the positron is the anti-electron, OK they have opposite charge and the positron does not like an electron and vica versa because when they meet they end up as gamma rays and their mass is annilated or rather cinverted into another energy form. Is this really conclusive proof to say that the positron is the anti matter of the electron?

QT is essentially a predictive theory that tells us what will, or has, happened; it makes no attempt to tell us how or why. Richard Morris summed up the current predicament in "Achilles in the Quantum Universe” with the following statement:
"They (physicists) feel a complete explanation of the subatomic world will not have been attained until it is known why particles have the charge, masses and other particular properties they are observed to possess"

There is no accepted (or Standard model) explanation of why things are the way they are. Take for example proton:proton collision which produces new quarks, they are said to be created out of the energy of the collision; but why should the energy of the collision form quarks? why not some other particle or an entirely new particle; the Standard model does not tell us.

#### cosmos seeker

Re: antimatter

does it exist any way to use antimatter as fuel . for the spaceships so they can fly very fast

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