Thinking Physics?

[Cap'n Refsmmat]

I recently got a book called "Thinking Physics" which is a book demonstrating physics with cartoony examples and such (it's fun).

However I noted a few problems, and I'm not sure if I'm right or not.

The first one, on which I know I am right, is that he claims that energy has mass. This is demonstrated by the following example:

 

You have a box strong enough to withstand a nuclear explosion and keep all the energy inside of it (not likely, but say you have it). You detonate a nuclear bomb inside it. Then you weigh it. According to physics, some of the mass will have simply vanished and turned to energy (remember e=mc2?). But he says that it will still weigh the same, because that energy has mass.

Of course, energy does not have mass.

 

For the next one he gives this example:

 

You are in a spacecraft going very fast (not any specific speed, just fast) and you are passing a constellation of 3 stars, which you call A, B and C, all an equal distance apart.

A B C

you (going right)

Suddenly, B explodes. Because you are going to the right, he says, the light from the explosion will appear to reach C first. This goes against my understanding of relativity, which states that light always appears to be going the speed of light relative to the observer. Who is right?

oops...

I figured it out now, but still, is that right?

 

One more:

 

He says:

 

If a proton and an electron collide (in a vacuum) you'd think they'd cancel each other out electrically. Instead, he says, the electron (not the proton!) would envelope the PROTON, not the other way around. He says electrons are very big, so it would swallow up the proton. And then, the resulting particle would still have energy! Even though protons and electrons carry the EXACT same amount of energy (except one is negative) the thing would still have energy!

Is that right either?

 

That's all for now... I'm not too good at this, so tell me if he is right, please.

[JaKiri]

I'm going to comment on q3:

 

The protons and electrons don't have the same amount of energy. A proton is several thousand times 'larger' in the only measurable quantity, mass. The only way they are equal is electronic charge, which has little to do with 'energy' as an abstract concept.

 

Neither protons nor electrons have 'size' in any conventional sense. They're not balls of stuff, they just are. As far as I can remember, they may even be point masses.

 

The only difference is that the electron generally travels faster, because it is less massive, and it's more 'spread out' as a result.

[Cap'n Refsmmat]

Who told me they had the same amount of energy?

 

grrrr...

[Cap'n Refsmmat]

Hold on, I just thought it over 6 minutes.

 

If they were to have varying amounts of energy, then wouldn't atoms have positive or negative energy? It has to be equal!

 

I'm not saying you're wrong, because normally you're right, and I just don't understand it.

[JaKiri]

If they were to have varying amounts of energy, then wouldn't atoms have positive or negative energy? It has to be equal!

 

Atoms have positive energy. A LOT of positive energy.

 

Can I reiterate:

 

Charge =! Energy

[Cap'n Refsmmat]

 

So... you're saying just because it has energy doesn't mean it's charged?

I suppose e=mc² supports that, because it can't have no energy at all...

I get it now.

[JaKiri]

So... you're saying just because it has energy doesn't mean it's charged?

 

A neutron has energy and isn't charged. Ditto light, and everything apart from electrons and some quarks (and their varients)

[jordan]

So then what gives the particles their charge?

[JaKiri]

So then what gives the particles their charge?

 

In what sense?

 

Charge is an innate property, like mass, but it's invarient, unlike mass. You don't add energy to something to make it more charged, for instance.

[swansont]

In what sense?

 

Charge is an innate property' date=' like mass, but it's invarient, unlike mass. You don't add energy to something to make it more charged, for instance.[/quote']

 

Rest mass is invariant, too. That's why one generally uses that in a discussion rather than "relativistic mass," which often tends to confuse things.

[jordan]

In what sense?

What makes the proton and electron different from the neutron, and each other for that matter? What causes one to have positive charge, one negative and one no charge?

[JaKiri]

Rest mass is invariant, too. That's why one generally uses that in a discussion rather than "relativistic mass," which often tends to confuse things.

 

It's pretty evident rest mass is invarient given the name. However, as far as I know, there is no physical operation which affects the charge of a particle.

[JaKiri]

What makes the proton and electron different from the neutron, and each other for that matter? What causes one to have positive charge, one negative and one no charge?

 

Because they do. Why do they have different masses? Because they do.

 

Hopefully, at some point some coherent theory will come along to explain all this*, but at the moment it's the anthropic principle for us.

 

*Neutrons and protons are made of quarks. Neutrons are made of 2x - 1/3 and 1x +2/3 (summing to 0), Protons are made of 2x 2/3, 1x -1/3 (summing to 1).

[ydoaPs]

wat determines an elementary particle's charge, mass, spin, ect. is thier vibrational frequency.

 

baryons are composed of quarks

[JaKiri]

wat determines an elementary particle's charge, mass, spin, ect. is thier vibrational frequency.

 

Only in String Theory, which as of yet is unproven, untested and unfinished, and should not be used as an answer to any question not about string theory.

[jordan]

Because they do.

 

So what you're saying is that if I were to examine every aspect of a proton and nuetron, I wouldn't find anything different that could possibly lead to one being positive and one being neutral? Is this because we don't have the technology to analyse this in-depth yet or because there is just some yet-undiscovered difference still eluding scientists? Or am I misiterpreting your answer?

[JaKiri]

So what you're saying is that if I were to examine every aspect of a proton and nuetron, I wouldn't find anything different that could possibly lead to one being positive and one being neutral? Is this because we don't have the technology to analyse this in-depth yet or because there is just some yet-undiscovered difference still eluding scientists? Or am I misiterpreting your answer?

 

The main problem here is that the only physical things (ignoring stuff like half life, and so forth) you can measure of a particle are mass and charge. An electron is indivisible; once you know the mass and the charge, you know everything about a generic electron that you can possibly know. There isn't some finer structure, it isn't made of anything else, it just is. We can't even be sure it has volume in the conventional sense, aside from its probability shell. The only thing particles are made of are other, smaller, particles, and there's only so far this goes on for before you hit the bottom of the well; they're not like rocks, you can't cut them up and see what they're like inside; they're the way they are because... they're the way they are.

 

Addendum:

 

Protons and neutrons (and all hadrons) are made up of Quarks, but so far quarks have been found to be indivisible, so that's where the buck stops for the moment.

[Cap'n Refsmmat]

So we're saying we don't know why it has charge, we just say, "That's the way it is"?

[JaKiri]

So we're saying we don't know why it has charge, we just say, "That's the way it is"?

 

Aside from the anthropic principle, yep.

[TheProphet]

Aside from the anthropic principle, yep.

 

JaKiri: Spank me if it's just for me being Swedish.. But what is the Anthropic principle about? links?

[JaKiri]

JaKiri: Spank me if it's just for me being Swedish.. But what is the Anthropic principle about? links?

 

There's 2 basic interpretations.

 

The weak anthropic principle:

 

'We find information (the balance of charges, the four forces) because if these were not so, there would not be any life to measure them'

 

The strong anthropic principle:

 

'We find information because they were designed for us to measure them'

 

Noone much cares for the latter.

[TheProphet]

There's 2 basic interpretations.

 

The weak anthropic principle:

 

'We find information (the balance of charges' date=' the four forces) because if these were not so, there would not be any life to measure them'

 

The strong anthropic principle:

 

'We find information because they were designed for us to measure them'

 

Noone much cares for the latter.[/quote']

 

Thanks... it atleast gave me a good laugh, i did thought there was something much bigger behind that name..