What is wrong with our understanding of the universe?

[JDługosz]

I just watched the latest episode of "The Universe", on the History Channel.

Yipes, they made a lot of gross errors!

They explained why matter is solid when it's composed of mostly empty space: Using an electric box fan, they showed that pingpong balls go through it when the blades are not moving. They said the hub is like the positive nucleus, and the blades are the electrons. It was said that "standing still" they don't keep anything out, but when spinning (he turns on the fan) it now fills out the space and prevents the balls from passing through.

When they said that matter is mostly empty space, they showed an illustration of simple planetary-model atoms, far far apart like a diffuse gas. In reality, those electron shells are touching or bound together to make the solid. The "emptiness" was portrayed at the wrong level!

The Earth was morphed-in from a bar magnet, showing the magnetic field is like the Earth is a big magnet. But they showed the N at the Earthly north pole. If the Earth were a big bar magnet, the S would be at the top, so the N's on our compass needles are attracted to it.

Particles from solar flares are radioactive? I thought they were mainly protons and electrons.

They said that the plasma is magnetic, and that's why it's deflected via the Earth's magnetic field.

They said that if the geomagnetic field faded or reversed, our compasses would not work, and GPS would not work either.

Sunspots are holes where the sun dimples down, and a solar flare is where material rushes out of this central bore (the body of the black spot) like a geyser! The "solar flare" arcs across and somehow connects with another one (it didn't say if they both squirt and meet in the middle, or of the first plume dives back down the other hole) to form the loops you see at the edge of the sun.

Jupiter's magnetic field extends out for 4 million miles.

The classic picture of iron filings around a magnet: this was explained as a way to visualize the "lines" that are really there. They got the basics wrong, but I can see how they were leading up to the way magnetic lines behave in the sun.

I don't remember what else -- it just kept on going, with almost every scene being incorrect somehow. Anyone have more?

 

[zhermes]

Almost everything in your above list is correct. The ones that aren't are completely fair simplifications for the general public.

 

[diazona]

I don't know, I think they could at least have showed the Earth's magnetic field in the proper orientation, and maybe colored in some electron clouds in the atom model. But to be fair, "solidness" is not exactly the easiest thing to explain in non-technical terms.

Then again, I didn't see the show, so maybe I should keep my mouth shut

 

[zhermes]

I don't know, I think they could at least have showed the Earth's magnetic field in the proper orientation, and maybe colored in some electron clouds in the atom model. But to be fair, "solidness" is not exactly the easiest thing to explain in non-technical terms.

Then again, I didn't see the show, so maybe I should keep my mouth shut

lol, I don't think that's a necessary prerequisite.

But I really disagree about the magnetic field, if anything the scientific convention of magnetic fields is what's incorrect, not the Earth's field--which is based on historically clad nomenclature. The "top" of the Earth is 'north,' so the magnetic pole on that side is also 'north.' Some genius just decided that whichever direction of a bar magnet points towards that pole is also 'north.' ;P

 

[diazona]

But I really disagree about the magnetic field, if anything the scientific convention of magnetic fields is what's incorrect, not the Earth's field--which is based on historically clad nomenclature. The "top" of the Earth is 'north,' so the magnetic pole on that side is also 'north.' Some genius just decided that whichever direction of a bar magnet points towards that pole is also 'north.' ;P

Well, yeah, I can agree with you there, that the convention is confusing. It probably would have made more sense to use other terms that aren't related to geographical direction.

But actually, what came first was people deciding that the end of a bar magnet which points north should be labeled "north." It made perfect sense for several centuries, until (according to Wikipedia) William Gilbert first postulated that the Earth itself was a giant magnet in 1600. I'm sure after that happened, it didn't take too long for someone to realize that the north end of the Earth had to have the same polarity as the end of a bar magnet which points south. Of course, by that time they were pretty much stuck with the "north" and "south" labels, so they had to say that the Earth's south magnetic pole was the one at the north end of the planet. The alternative would have been decreeing that the end of a bar magnet which points north should actually be relabeled the "south" end, and that would have confused a lot of people. Probably even more than the current system.

 

[JDługosz]

Almost everything in your above list is correct. The ones that aren't are completely fair simplifications for the general public.

How is the balls and fan bit "correct" or at least "fair simplification"?

 

[alxm]

On a related historic note, 'B' for the magnetic field comes from borealis.

But yes, the whole 'atoms are mostly empty space' stuff is pretty lousy if you ask me. The is no meaningful distinction between 'empty' and 'occupied' when you're talking about particles that have no definite location.

Besides being the truth, that's a far more interesting fact than the claim that atoms are 'mostly empty'.

 

[Naty1]

Their magnetic reference is no more odd than using current flow conventions to reflect "positive" current movement.

The only one I did not get was the GPS comment...I can tell you from first hand experience navigating a boat in magnetically anamolous areas of Maine (US east coast) my two GPS systems continued to provide my correct position and heading...

They implied compass navigation would be interrupted by a pole reversal...but did not explain ...I suspect they meant the new (reversed) N and S poles would likely be in different relative positions from the opposite ones today...the inner Plasma would likely move and shift about...

 

[zhermes]

How is the balls and fan bit "correct" or at least "fair simplification"?

You see, they weren't actually saying that atoms are "balls and fans." They were using what we call an "analogy." See: http://en.wikipedia.org/wiki/Analogy. Analogies have been used since the ancients to explain difficult concepts. The use of analogies is similar to that of "comparisons," "metaphors," "similes," "allegories," and "parables." They can all be used to produce insight in otherwise obscure subjects.

Note that here, I neglected to employ an "analogy," so as to not confuse you further.

 

[johng23]

I really can't see a way in which the ball-and-fan thing is helpful under any circumstance. I used to think that's why material was solid, I don't know who told me it. What's the analogy? A mostly empty space can impart a force? It's completely misleading.

 

[zhermes]

On a related historic note, 'B' for the magnetic field comes from borealis.

I've actually always wondered that, thanks!

But yes, the whole 'atoms are mostly empty space' stuff is pretty lousy if you ask me. The is no meaningful distinction between 'empty' and 'occupied' when you're talking about particles that have no definite location.

The significance of 'mostly empty space' is exactly that particles don't have a definite location, and more importantly, that the entire concept of "size" and the pool-ball notion of particle physics is entirely subjective.

Its important to realize that when you touch something, its not nano-scopic billiard-balls colliding and therefore not moving further. Instead its E&M interactions between elusive collections of energy we term 'particles.'

~~~~~~~~~~~~~~
As for everyone who's suggesting that 'mostly empty space' isn't even accurate: that's ridiculous. The covalent radius of a hydrogen atom is something like
[tex]
R_H \approx 10^{-11} \textrm{ - } 10^{-10}
[/tex]
The charge radius of a proton, on the other hand, is
[tex]
R_p \approx 10^{-15}
[/tex]
Thats a factor of a hundred million difference in 'volumes.'
Now, the electron's radius
[tex]
R_e \lesssim 10^{-22}
[/tex]
in advance of objections (see: http://iopscience.iop.org/1402-4896/1988/T22/016/).

So the 'size' of the electron, which generates the effective barrier between atoms, is a whopping 22 orders of magnitude smaller in effective volume than a hydrogen atom. So how exactly is it inaccurate to say that what we think of as 'matter,' if you look at the constituent particles, is 'mostly empty space'?

 

[pallidin]

I didn't know there was a "size" of an electron.
Thought that all fundamental particles are essentially "size-less"

 

[sophiecentaur]

Well, yeah, I can agree with you there, that the convention is confusing. It probably would have made more sense to use other terms that aren't related to geographical direction.

But actually, what came first was people deciding that the end of a bar magnet which points north should be labeled "north." It made perfect sense for several centuries, until (according to Wikipedia) William Gilbert first postulated that the Earth itself was a giant magnet in 1600. I'm sure after that happened, it didn't take too long for someone to realize that the north end of the Earth had to have the same polarity as the end of a bar magnet which points south. Of course, by that time they were pretty much stuck with the "north" and "south" labels, so they had to say that the Earth's south magnetic pole was the one at the north end of the planet. The alternative would have been decreeing that the end of a bar magnet which points north should actually be relabeled the "south" end, and that would have confused a lot of people. Probably even more than the current system.

At School, were were told that the end of a bar magnet that pointed to the North was called a "North Seeking Pole", not a "North Pole". There could be no confusion that way because the South Pole of the Earth is also a NSP.

 

[JDługosz]

You see, they weren't actually saying that atoms are "balls and fans." They were using what we call an "analogy." See: http://en.wikipedia.org/wiki/Analogy. Analogies have been used since the ancients to explain difficult concepts. The use of analogies is similar to that of "comparisons," "metaphors," "similes," "allegories," and "parables." They can all be used to produce insight in otherwise obscure subjects.

Note that here, I neglected to employ an "analogy," so as to not confuse you further.

You don't have to be condescending. I certainly know what Analogy is. I just don't see how this analogy is useful or valid. Electrons don't repel other atoms because they are moving rapidly around the nucleus. Are you saying that is the case?

 

[JDługosz]

So the 'size' of the electron, which generates the effective barrier between atoms, is a whopping 22 orders of magnitude smaller in effective volume than a hydrogen atom. So how exactly is it inaccurate to say that what we think of as 'matter,' if you look at the constituent particles, is 'mostly empty space'?

But the "size" of the bound electron is exactly that of the resulting atom. It is the concept of size that is funny. In no cases do we really have the same concept of size like we use in our familiar world. It's more like the territory of a lion: it's staked out a zone of space, and affects things that overlap that space.

 

[zhermes]

I certainly know what Analogy is. I just don't see how this analogy is useful or valid. Electrons don't repel other atoms because they are moving rapidly around the nucleus. Are you saying that is the case?

What if the motion of the fan blades is an "analogy" for the delocalization of the electrons--mostly due to QM effects, but yeah, a classical concept of velocity can't be entirely excluded from that. As I showed earlier (above), the fundamental "size" of an electron is (in this context) negligible. If electrons weren't delocalized around nuclei, the effective size of atoms would be many orders of magnitude smaller and therein their interactions with other atoms.

 

[zhermes]

But the "size" of the bound electron is exactly that of the resulting atom.

That's just not the case. That would be the same as saying the "size" of Jupiter is that of its orbit (even though the Bohr model is incorrect), because its tidal and gravitational interactions over large time scales extend that far.

An electron "cloud" or "occupied orbital" is not the same as an electron.

 

[alxm]

The significance of 'mostly empty space' is exactly that particles don't have a definite location, and more importantly, that the entire concept of "size" and the pool-ball notion of particle physics is entirely subjective.

That's a charitable interpretation to say the least. Most people hearing the claim that 'atoms are mostly empty space' aren't learning quantum mechanics. Most people's image of the atom is that of the Bohr model, which most certainly does give people the idea that there's nothing 'between' the electron and the nucleus.

As for the rest of your objections, that was handled by JDługosz already.

That's just not the case. That would be the same as saying the "size" of Jupiter is that of its orbit (even though the Bohr model is incorrect), because its tidal and gravitational interactions over large time scales extend that far.

That is the case. And it underlines what JDługosz said, 'size' on the macroscopic scale has no meaning at the subatomic scale. There is no 'shell' around the atom giving it a particular radius, and any definition of such radius is merely a convention or convenience (such as the Bohr radius, or charge radius), with no real resemblance to macroscopic 'size' which is quite definite.

An electron "cloud" or "occupied orbital" is not the same as an electron.

It certainly is, as far as the electron's "size" and location and every single observable property of it are concerned. What's the 'size' of a delocalized electron? It can be detected in several places simultaneously.

 

[Naty1]

And it underlines what JDługosz said, 'size' on the macroscopic scale has no meaning at the subatomic scale.

seriously misleading...Of course "size" has meaning on the sub atomic scale...not the same as our classical macroscopic understanding...but clearly observables which makes such things "real"...

For a particle in a bound state, there is a vanishing probability of finding the particle at infinity...the particle is localized in a finite region; in a unbound state, that particle does not remain localized in a finite region...the eigenfunctions do NOT vanish at infinity...

Another interpretation of "size" comes from scattering observations...

and yet another, perhaps less direct, in nulcear reaction calculations via nuclear cross sections...http://en.wikipedia.org/wiki/Nuclear_cross_section

 

[alxm]

seriously misleading...Of course "size" has meaning on the sub atomic scale...not the same as our classical macroscopic understanding...but clearly observables which makes such things "real"...

I don't see how this is 'seriously misleading' when I made the point in the same post that 'sizes' are used. But I disagree that they are not clearly 'observable'. They're calculated from observed values in accordance with some definition that was defined into existence.

E.g. The Bohr radius is the radius of greatest total electronic density in the non-relativistic hydrogen atom, not accounting for reduced mass effects. You could define it as the radius that encloses 90% of the electronic density or 50% or whatever you like.

 

[zhermes]

That's a charitable interpretation to say the least.

We're not talking about feynman lectures or something; we're talking about a history (or discovery or whatever) channel special--the kind of thing my nephew watches while he plays with action figures. Yes, I'm giving them a little slack and taking a charitable interpretation, i think that's called for.

Most people hearing the claim that 'atoms are mostly empty space' aren't learning quantum mechanics.

Its really okay that the lay-person isn't learning quantum mechanics (personally I think it would be better if they were, but that's a separate issue). All they need to get from this TV special is that there is a discongruities between their classical way of viewing the world, and the physic-al way.

That is the case. And it underlines what JDługosz said, 'size' on the macroscopic scale has no meaning at the subatomic scale. There is no 'shell' around the atom giving it a particular radius, and any definition of such radius is merely a convention or convenience (such as the Bohr radius, or charge radius), with no real resemblance to macroscopic 'size' which is quite definite.

That doesn't make any sense. The Bohr radius is the radius which explains macroscopic sizes. That's why it appears in so many equations. The charge radius--which isn't especially useful in quantitative analysis--is similarly effective for thinking about macroscopic objects. But we're digressing.

[electron is not the same as an occubied orbital] --> It certainly is, as far as the electron's "size" and location and every single observable property of it are concerned. What's the 'size' of a delocalized electron? It can be detected in several places simultaneously.

If that were true, then the answer to the question, "whats the size of an electron in benzene?" would be, 'the size of benzene.' The answer to, "whats the size of an electron in a sheet of metal?' would be, 'the size of the sheet of metal.' Which is clearly not the case, irrelevant, and unhelpful to an explanation.

~~~
Summary:

1) The point of my posts was to say that their presentation of these ideas is sufficient for the audience they're addressing.

2) The 'mostly empty space' statement is completely valid. Its not a quantitative statement, its a qualitative statement that reflects the nature of atomic behavior. With a given scattering event (e.g.) an electron will localize to a very specific location, confined to a size orders of magnitude smaller than the atom is belongs to. The atom's size is defined by a large 'region' of effective interaction based on interatomic bonds/interactions, which end up composing the overall structure and therein size of a macroscopic object.

 

[Naty1]

alxm: Perhaps we can agree that "size has a different meaning on the subatomic scale than the macroscopic.." and I could have posted "size has no meaning on the subatomic scale" could be misleading...because all observables have a different meaning at subatomic scales.

 

[Naty1]

alxm:

There is no 'shell' around the atom giving it a particular radius...with no real resemblance to macroscopic 'size' which is quite definite.

I don't think we KNOW that...do we? What we can say, I think, is that such a "shell" and a corresponding radius has never been experimentally observed.

Insofar as macroscopic size is concerned, I'm sure glad you said "quite" definite...but I'd prefer "appears more" definite...given issues in general relativity and even Heisenberg uncertainty along with "most atoms being empty space" what we think we observe (as in planetary motions for example) and are superficially confident about has proven through history to be as much illusion and appearance rather as "reality"...

Palladin:

I didn't know there was a "size" of an electron.
Thought that all fundamental particles are essentially "size-less"

Fundamental particles have been treated as point particles via classical theory and mathematics as approximations...I don't think anyone "knows" the size of any particle but we do have experimental evidence of maximum possible sizes...that was discussed recently in another thread...and those maximum sizes can be found in Wikipedia.

Lugosz:

But the "size" of the bound electron is exactly that of the resulting atom.

Zhermes:

That's just not the case.

Zhermes correction is accurate. The "size" of a bound electron" is reflected in my earlier post indicating a vanishing probability of finding the electron at infinity...but a thousand miles from the nucleus, for example, there IS a finite probability of finding that electron...small,of course, but NOT zero probability.

An electron "cloud" or "occupied orbital" is not the same as an electron

.

alxm:

It certainly is, as far as the electron's "size" and location and every single observable property of it are concerned

alxm's comment is absolutely correct...they ARE the same...in contrast, as I posted, a free (unbounded) electron has a wave probability extending to infinity...that is there is a finite probability or a bounded probability of finding the electron ANYWHERE.

Having said all that, we all need to remember quantum mechanics which we are discussing here is NOT the final theory of everything...so something may be quite wrong with anyone the statements being made here; all we can say, is that so far experimnetal observation within the limits we can observe, confirms the (correct) statements made.

If we adopt the view of string theory, then there is no "matter", just one dimensional energy vibrations, some of which come with with observables that we mortals associate with "matter". So if you want to get into confusing discussions about the size of "particles", go there.

That's a good illustration why I like the maxim "The more we know the less we understand."