Ask a physicist anything. (6)

[Chalnoth]

Are the spirals in this picture anything to do with particle "spin"? What about the dots and lines?

Ahhh, bubble chambers Cool stuff!

What happens here is that you have a liquid that is kept right at the boiling point. So when you have some sort of disturbance, such as a charged particle zipping through the liquid, it creates a bunch of bubbles. Eventually the chamber fills with bubbles and it has to be "reset" which involves compressing it to turn it back into a liquid.

In order to obtain a bit more information than just whether or not a particle passed through the chamber, they make it very thin and apply a magnetic field to the chamber. The magnetic field causes charged particles to go in circles. But as they pass through the bubble chamber, they also lose energy, so instead of a circle we see a spiral. The size of the spiral provides us with a relationship between the mass/kinetic energy and the charge of the particle. For particles like electrons with small mass compared to their charge that lose energy very rapidly, you see small, tight spirals. If the particle is more massive, its track won't be bent as much, and it will produce a larger spiral. Or, if it is massive enough, it may pass through the entire chamber without appearing to bend at all.

Additionally, there are particles which may pass through the chamber that have no charge. An uncharged particle isn't going to show any track, because it won't interact very much with the matter in the chamber. But if that particle decays into a pair of charged particles, we can see the tracks of the two particles it decays into: this is the V-shaped track you see: an uncharged particle came into the chamber from the bottom and decayed into two charged particles (probably a pair of pions).

 

[GrowingSmaller]

So its not spin then? I got the idea from L Krauss' new book on Feynman ("Quantum Man") where he says electrons behave like spinning tops.

 

[Chalnoth]

So its not spin then? I got the idea from L Krauss' new book on Feynman ("Quantum Man") where he says electrons behave like spinning tops.

Yes, in a way. But that fact doesn't come into play here.

Edit: where the spin of electrons does come into play, at least the most noticeable place, is in chemistry. If you remember your chemistry, you may remember the electron orbitals, the orbitals that determine the layout of the periodic table. And you may also remember the Pauli exclusion principle that states that not two electrons can be in the same state at the same time.

The Pauli exclusion principle stems from the fact that these particles are spin 1/2. The half-integer spin forces electrons to form anti-symmetric wavefunctions. That is, if I have two electrons in two states, a and b, and I swap the states, the result comes up with a minus sign. But if a=b, then swapping a and b changes nothing, so that the only function that can match this is zero: the amplitude for two electrons being in the same state is always zero.

When we apply this to the atom, the first thing we find is that, for example, for the S-orbital, there is only one possible spatial distribution of the electrons. So you'd think there would be only one state. But this isn't the case: the electrons also have spin, and with spin = 1/2, there are two possible spin states the electrons can hold (up and down). So you can actually put two separate electrons in the same S orbital. Similar with the P orbital: there are three different spatial distributions for the P orbitals, but you can fit six electrons into them. And it goes on increasing like this. Atoms in the periodic table are grouped by their valence electrons, those electrons that are least tightly bound to the atom. The S-orbital valence elements form the two leftmost columns (as well as Helium). The P-orbital valence elements form the six rightmost columns (except Helium, of course). The ten columns in the center have D-orbital valence electrons. The 14 columns in the actinide/lanthinide series have F-orbital valence electrons.

 

[GrowingSmaller]

What about the idea (IIRC) that positrons are electrons travelling back in time? Is that actually regarded as a valid model?

Also where can I find some pimped out feynman diagrams to put on a t-shirt?

 

[Chalnoth]

What about the idea (IIRC) that positrons are electrons travelling back in time? Is that actually regarded as a valid model?

Well, sort of. Quantum mechanics, as we know it, satisfies what is known as the CPT symmetry. This is the conjugation of the charge, parity, and time symmetries.

The charge symmetry just switches the charge with its negative. The electron has a charge of -e, and a positron has a charge of +e.

The parity symmetry is a left/right symmetry. A clockwise-spinning particle acts like a counterclockwise-spinning anti-particle.

The time symmetry is a time reversal symmetry: an electron moving forward in time behaves like a positron moving backward in time.

So when we do quantum field theory calculations, we can simplify our calculations by, instead of having two different kinds of particle (an electron and positron), we can consider only one type (the electron), and say that the positron is the electron moving backward in time, with opposite charge and spin.

Now, the positron in this example really is moving forward in time. It has the same arrow of time as the rest of us. But we can, mathematically, exchange its arrow of time, charge, and spin to instead describe it as an electron and simplify our calculations.

Also where can I find some pimped out feynman diagrams to put on a t-shirt?

Sorry, no clue

 

[razeontherock]

You can't divide by zero, but you can have infinities. Density isn't a 'real' thing, so even though we define it as mass over volume, and thus mass distributed over zero volume has a meaningless density, that doesn't invalidate the concept of density, nor does it negate the possibility that a finite (or, indeed, infinite) amount of matter can't be distributed over zero volume. Just because density approaches infinity as volume approaches zero, doesn't mean volume can't be zero.

I prefer to think of science as descriptive, not prescriptive. If infinite densities can exist, we have to allow for them.

Doesn't a singularity have non-zero volume? A single point is till volume, is it not?

 

[razeontherock]

[Total de-rail]

So we always have to be careful to not take our theories too seriously in all cases. It's important to have a good feel for where they are valid, and where they are not.

Just imagine what adopting this attitude would do for the Ev / Cr debate
[/Total de-rail]

 

[razeontherock]

I trust that my partner loves me, not because it is a statement of faith for which I have no proof, but because I do have evidence. Thus, I am confident, and thus, I have trust. Trust, after all, is earned.

Faith, on the other hand, doesn't appear to be based on anything at all. Whenever a religious person says they have faith, they mean they believe regardless of anything else. It's a badge of pride, they can say, "Look, God! I believed in you even when everything said not to!". It strikes me as... desperate.

Here you have created a false dichotomy. You provided a perfect illustration to understand the majority of people around you, (your partner's love) but for that to help you need to realize said majority has a partner you do not perceive. They (we) have a basis for the same kind of trust you write about in your partner. And each of us truly do have to recognize that G-d has indeed earned said trust.

 

[Chalnoth]

[Total de-rail]



Just imagine what adopting this attitude would do for the Ev / Cr debate
[/Total de-rail]

Scientists have a very proportionate attitude towards the validity of evolutionary theory: the evidence that all life on Earth shares a common ancestry is utterly overwhelming. So stating that fact with confidence is precisely what I was talking about with regard to having a good feel where our theories are valid.

Now, I don't want to get embroiled in an evolution discussion here, but if you really wanted to investigate it, here is the set of steps I would suggest:
1. Think of an objection to evolution.
2. Search for that objection over at talkorigins.org. The site is quite comprehensive, so chances are you'll find it (hint: if you don't find it quickly at the FAQ page, try a Google search with site:talkorigins.org added to the query).
3. Have a pen and paper in hand when you go over the article. Carefully write down the primary points and primary supporting evidence. Note whether or not the supporting evidence directly addresses the primary points.
4. Look for a rebuttal to the talk origins article. Many rebuttals are available at various creationist websites, such as answers in genesis.
5. Do the same analysis of the rebuttal, but also check to see if the main points of the article that you already wrote down are addressed, and whether or not they are addressed directly.

If you do this, and do it honestly, what you will find is that the talkorigins articles, by large, do a very good job of presenting a variety of evidence that directly addresses the points made. But the creationist rebuttals will not: you will see a lot of peripheral swipes, attempts to cast doubt. But no actual direct arguments that aren't clearly fallacious.

 

[Chalnoth]

Doesn't a singularity have non-zero volume? A single point is till volume, is it not?

No, a singularity actually has zero volume. This is one of the reasons why I say it is mathematical nonsense that cannot exist in reality.

 

[Chalnoth]

And each of us truly do have to recognize that G-d has indeed earned said trust.

Why? Based upon what?

 

[razeontherock]

Scientists have a very proportionate attitude towards the validity of evolutionary theory: the evidence that all life on Earth shares a common ancestry is utterly overwhelming. So stating that fact with confidence is precisely what I was talking about with regard to having a good feel where our theories are valid.

This is a point in common with special creation.

 

[razeontherock]

Why? Based upon what?

This is a personal (and therefore subjective) thing. As someone else pointed out
many professing Christians never make it to that point, but as an unbeliever you would have no basis - by definition.

 

[Chalnoth]

This is a point in common with special creation.

Yeah, um, not even close. The evidence in favor of evolution fills libraries, while there just isn't any evidence whatsoever that favors special creation. The two couldn't be more different.

 

[Chalnoth]

This is a personal (and therefore subjective) thing. As someone else pointed out
many professing Christians never make it to that point, but as an unbeliever you would have no basis - by definition.

Except you said:

And each of us truly do have to recognize that G-d has indeed earned said trust.

If it's a subjective thing, then each of us absolutely don't have to recognize it.

 

[razeontherock]

Yeah, um, not even close. The evidence in favor of evolution fills libraries, while there just isn't any evidence whatsoever that favors special creation. The two couldn't be more different.

You completely missed the point. Simply reducing to the LCD via knee-jerk reaction?

Everything about the Biblical account points to a common ancestor, regardless of the variety of views.

 

[razeontherock]

Except you said:

If it's a subjective thing, then each of us absolutely don't have to recognize it.

Notice the word, "us." You are allowed to exclude yourself from that, and I never said otherwise. (This really is all implied. Why would you make that so difficult?)

 

[Chalnoth]

You completely missed the point. Simply reducing to the LCD via knee-jerk reaction?

Everything about the Biblical account points to a common ancestor, regardless of the variety of views.

Huh? Special creation is the diametric opposite of common ancestry. Pretty sure you won't find many creationists claiming that trees are our (extremely distant) cousins.

I assume you're attempting to, by analogy, talk about a "common creator" as if it were the same thing? Because it isn't. Not even close.

 

[chris4243]

Scientists have a very proportionate attitude towards the validity of evolutionary theory: the evidence that all life on Earth shares a common ancestry is utterly overwhelming. So stating that fact with confidence is precisely what I was talking about with regard to having a good feel where our theories are valid.

Now, I don't want to get embroiled in an evolution discussion here, but if you really wanted to investigate it, here is the set of steps I would suggest:
1. Think of an objection to evolution.
2. Search for that objection over at talkorigins.org. The site is quite comprehensive, so chances are you'll find it (hint: if you don't find it quickly at the FAQ page, try a Google search with site:talkorigins.org added to the query).
3. Have a pen and paper in hand when you go over the article. Carefully write down the primary points and primary supporting evidence. Note whether or not the supporting evidence directly addresses the primary points.
4. Look for a rebuttal to the talk origins article. Many rebuttals are available at various creationist websites, such as answers in genesis.
5. Do the same analysis of the rebuttal, but also check to see if the main points of the article that you already wrote down are addressed, and whether or not they are addressed directly.

If you do this, and do it honestly, what you will find is that the talkorigins articles, by large, do a very good job of presenting a variety of evidence that directly addresses the points made. But the creationist rebuttals will not: you will see a lot of peripheral swipes, attempts to cast doubt. But no actual direct arguments that aren't clearly fallacious.

On the other hand, you can also do an analysis of literal genesis, of which the Flood would be the easiest to understand. What are the consequences of a worldwide flood, specifically with respect to genetics, patterns of species distribution, the effects on plants and on aquatic animals requiring a specific salinity range. There's gonna be some very specific consequences that would leave definite evidence.

Since this subject is almost never worth discussing, I'll just leave it at that. The evidence is clear for those who wish to follow it, but those who wish to cover their eyes and believe what they want to believe will continue to do so.

 

[Chalnoth]

On the other hand, you can also do an analysis of literal genesis, of which the Flood would be the easiest to understand. What are the consequences of a worldwide flood, specifically with respect to genetics, patterns of species distribution, the effects on plants and on aquatic animals requiring a specific salinity range. There's gonna be some very specific consequences that would leave definite evidence.

Yup. As well as a huge number of other things. Evidence that isn't seen. A global flood is, quite simply impossible.