Quantum Theory...help!

John W. Kelly · Post by **John W. Kelly** » Mon May 12, 2008 11:21 pm

I just picked up a book dealing with this subject. I couldn't get past the first several pages before I was as lost as lost could be. Can anyone give me some pointers on how to begin to understand this subject? Maybe an outline of the very basics?

Arising_uk · Post by **Arising_uk** » Tue May 13, 2008 12:09 am

Hi John,
QED by R. Feynman.
Does not deal with QM but gives you the understanding of where it came from.

John W. Kelly · Post by **John W. Kelly** » Tue May 13, 2008 5:02 am

I have that book somewhere. Now to sift through this rat's nest I call home.

Arising_uk · Post by **Arising_uk** » Sun May 18, 2008 11:30 am

Oo! Oo! Just checked my shelves and Quantum Mechnics for Beginners is a great introduction. Comic book form but covers the whole history in an informative and interesting way.

John W. Kelly · Post by **John W. Kelly** » Sun May 18, 2008 6:19 pm

Thank you. I might have to take a trip down to the college bookstore. Who is the author? Joseph McEvoy by any chance?

Arising_uk · Post by **Arising_uk** » Sun May 18, 2008 7:37 pm

That'll be the one.

John W. Kelly · Post by **John W. Kelly** » Mon May 19, 2008 5:49 am

Thankyou.

John W. Kelly · Post by **John W. Kelly** » Tue May 20, 2008 3:51 am

Found McEvoy's book at the library. Might have a few questions later.

Arising_uk · Post by **Arising_uk** » Wed May 21, 2008 1:56 am

Bet I have more.
p.s.
Yah wanna go page by page or some combination thereof?

John W. Kelly · Post by **John W. Kelly** » Wed May 21, 2008 2:34 am

Arising_uk wrote:Bet I have more.
p.s.
Yah wanna go page by page or some combination thereof?

Sounds like a plan. I'm on page 18 where Clausius describes entropy (S). We know that the 2nd law states a hot to cold flow of heat. Why would entropy max out at thermal equilibrium? Wouldn't the higher-entropy cold object and lower-entropy hot object average out at any point before equilibrium?

Arising_uk · Post by **Arising_uk** » Wed May 21, 2008 6:15 pm

Hi John,
I'm still unclear about what exactly Entropy is?
I think I understand the ideas on pages 16 & 17 about Thermal equlibrium and how Energy can be described(formalised?) as the exchange of Work and Heat and that there is a Law called The Conservation of Energy, i.e. Energy is a constant that can be equal or unequal amounts of Work and Heat. If I understand right, Clausius's idea is that some heat is 'wasted' or non-useful in the process of a hot object effecting a cold one until they are both at the same temperature. This means that the total energy of the combined objects when at the same temperature will be slightly less
than the sum of energy of the two objects measured seperately. I think this is what he means by Entropy, the 'missing' energy.

With respect to your questions. The way I'm trying to understand it is that we have two containers of the same liquid. Joined but with a gate between them one is coloured, the other clear. We heat the coloured one and then open the gate. Apparently the coloured one will rush into the clear one. It is the process that 'creates' the Entropy by losing Heat out of the system thereby reducing the level of Energy at the end. So it will at its maximum(?) when the process is complete, i.e. when Thermal Equlibrium(TE) is reached.
Sorry if this misses the point of your questions but if you could explain more about this idea of the hot and the cold objects averaging out before TE it might help me.
(If any Physicists out there want to drop in to correct our ideas I think JWK and I would be delighted)
a_uk

John W. Kelly · Post by **John W. Kelly** » Wed May 21, 2008 9:53 pm

What I see is that the flow of energy has a limit in the direction it can go, like a diode. Nothing new here. Could it be that once we have TE, entropy is maximum because no work can be done? Wasted (unavailable) energy is easily found in a car engine. Engines create heat and noise that do nothing to get us down the road, but energy is conserved. As we look at page 20, statistical averaging is introduced. I looked up entropy up in my dictionary and found "(in statistical mechanics) a measure of the randomness of the microscopic constituents of a thermodymanic system." There's a connection here I'm having trouble seeing.

Arising_uk · Post by **Arising_uk** » Wed May 21, 2008 11:17 pm

Hi JWK,

John W. Kelly wrote:What I see is that the flow of energy has a limit in the direction it can go, like a diode. Nothing new here.

Whoa! There Kemo Sabe. I do not have a great understanding of Electronics. A diode is what? I'm guessing that it sounds like an incarnation of C's second law?

Could it be that once we have TE, entropy is maximum because no work can be done?

I think that it is exactly this as Entropy appears to be the loss of 'total' energy through 'wasteful' heat.

Wasted (unavailable) energy is easily found in a car engine. Engines create heat and noise that do nothing to get us down the road, but energy is conserved.

I can go with this image. And I can go with the idea of the 'wasted heat' being the friction heat and noise created by using a mechanical means to produce Work from Heat. And I think I get that Entropy is the difference between the TE endstate and the summed pre-joined individual objects. But I'm guessing that C's idea of Entropy was based upon ideal containers, i.e. perfect null-things, i.e. no interaction between container and components and I'm guessing that he'd still say that some Heat is always 'wasted'. How I cannot understand because in a perfect container all heat would be contained so I can't think where it goes?

As we look at page 20, statistical averaging is introduced. I looked up entropy up in my dictionary and found "(in statistical mechanics) a measure of the randomness of the microscopic constituents of a thermodymanic system." There's a connection here I'm having trouble seeing.

I think this Boltzmann geezer on page 24 may get into the connection here and I'm not sure you are missing anything, just that its a slippery concept.

With respect to page 20. I'd need a Physicist to explain to me if a gas could retrospectively be understood to be a black-body that expands and contracts at its boundries according to some kind of non-particular wave thermodynamics, i.e. were atoms a necessity? As so far it appears that Maxwells equations would not have appeared unless he had this metaphysical belief. Although I'll need to check the refs for Perrin and Einstein(page 19) as they appear to have proved that Atoms are a fact so J.C. would have been working with a fact rather than a metaphysical idea.
a_uk
p.s.
Shout! If I ramble to far from topic, bad habit.

John W. Kelly · Post by **John W. Kelly** » Thu May 22, 2008 5:17 am

A diode lets current flow in one direction only. I thought it was a good example of the 2nd law. Good guess! As far as entropy goes, the best I can do is say TE maximizes our ignorance of the system's previous state.

John W. Kelly · Post by **John W. Kelly** » Thu May 22, 2008 5:12 pm

I think Max Planck will answer many of our questions. They didn't name a crater on the Moon after him for nothing!