Putting aside the term God, would you agree?

[Polymath257]

Yes fair enough. That just goes to show how hard it is for a chemist to set aside QM thinking!

In fact, the specific heat of gases is one of the classic results of Stat TD - but based, as you rightly remind me, on QM assumptions about energy level spacing in the various degrees of freedom and how they are populated: ε >> kT vs. ε << kT .

In fact, the *wrong* prediction of specific heats for larger molecules was one of the first hints of quantization. Classical descriptions worked reasonably well for monatomic and diatomic gases, but got increasingly bad for gases like methane. In a classical setting, methane would have a very large number of degrees of freedom, each with average energy kT. This would make the specific heat much smaller than what was observed.

The resolution? Energy levels with E>>kT are not populated at all, so the average energy is NOT kT in the quantum version.

Moreover, the Maxwell distribution exp(-kT/E) is replaced by either the Fermi or the Bose distribution (depending on total spins). This is more relevant for solid state physics, though, as opposed to gas state.

 

[9-10ths_Penguin]

Of course... but none of them is the hammer or the metal.
It has many causes that follow one another until the main "event" (the hit itself)
It is not 20 events happening in the same time (although such things do happen )

But you agree that this one event can be traced back to many independent causes.

Okay - since it seems you understand how an event can have more than one cause, let's get back to the question you still haven't answered: can you name any event that had a single cause?

 

[exchemist]

In fact, the *wrong* prediction of specific heats for larger molecules was one of the first hints of quantization. Classical descriptions worked reasonably well for monatomic and diatomic gases, but got increasingly bad for gases like methane. In a classical setting, methane would have a very large number of degrees of freedom, each with average energy kT. This would make the specific heat much smaller than what was observed.

The resolution? Energy levels with E>>kT are not populated at all, so the average energy is NOT kT in the quantum version.

Moreover, the Maxwell distribution exp(-kT/E) is replaced by either the Fermi or the Bose distribution (depending on total spins). This is more relevant for solid state physics, though, as opposed to gas state.

Surely the spec heat for diatomic gases goes wrong too, doesn't it, as rotation and then vibration modes kick in with rising temperature?

(And by the way I'd have thought the rotation about the axis of the molecule corresponds to an electronic excitation, so that too is degree of freedom of a sort but not excited thermally, obviously.)

 

[Polymath257]

Surely the spec heat for diatomic gases goes wrong too, doesn't it, as rotation and then vibration modes kick in with rising temperature?

(And by the way I'd have thought the rotation about the axis of the molecule corresponds to an electronic excitation, so that too is degree of freedom of a sort but not excited thermally, obviously.)

Actually, rising temperature brings things more in line with the classical result because more energy levels are available.

I had to go check, but you are correct. Diatomic molecules don't have quite the correct specific heats with hydrogen the worst off and bromine almost agreeing with classical theory. In other words, mass (actually moment of inertia) has an effect on the spacing of the energy levels for rotation. A higher mass leads to smaller spacing, so more levels are occupied, leading to a result closer to the classical one.

Rotation about an axis can be considered both ways, actually. It depends on what basis you use to expand your wave function. Typically, it is easier to consider rotational degrees separately from electronic levels, but at base they are all just ways of getting *all* the energy levels in some fashion.

 

[exchemist]

Actually, rising temperature brings things more in line with the classical result because more energy levels are available.

I had to go check, but you are correct. Diatomic molecules don't have quite the correct specific heats with hydrogen the worst off and bromine almost agreeing with classical theory. In other words, mass (actually moment of inertia) has an effect on the spacing of the energy levels for rotation. A higher mass leads to smaller spacing, so more levels are occupied, leading to a result closer to the classical one.

Rotation about an axis can be considered both ways, actually. It depends on what basis you use to expand your wave function. Typically, it is easier to consider rotational degrees separately from electronic levels, but at base they are all just ways of getting *all* the energy levels in some fashion.

Sorry that's what I meant, just expressed badly. It is the ε >>kT you don't get in a classical world, i.e. the suppression of degrees of freedom that can't be excited, due to the large size of the minimum quantum needed. Agreed.

The thing about rotation along the molecular axis is a personal niggle, as the facile undergrad explanation was that considering atoms as point masses there is no energy in this rotation. But of course they aren't quite point masses. However it is only the electrons that are contacted in a thermal collision, so if one thinks about it, one is really considering transferring angular momentum to the electron cloud......which would in effect be an electronic excitation. ε>>kT up to very high temperatures indeed.

 

[Segev Moran]

But you agree that this one event can be traced back to many independent causes.

Okay - since it seems you understand how an event can have more than one cause, let's get back to the question you still haven't answered: can you name any event that had a single cause?

I don't think you understood my OP.
I didn't say everything has only one cause entirely, rather everything has a chain of events (many events following each other) you can trace the events back until you get to a root event that starts everything.
It all depends far back you want to look. as i see it, "somewhere" back far far in the history of our universe or existence there is an event that started this enormousness chain of other events.
My OP was dealing with the question of whether it is logical to think that indeed there was such one event or that reality simply became without a cause (an event that made it become).

 

[Polymath257]

I don't think you understood my OP.
I didn't say everything has only one cause entirely, rather everything has a chain of events (many events following each other) you can trace the events back until you get to a root event that starts everything.
It all depends far back you want to look. as i see it, "somewhere" back far far in the history of our universe or existence there is an event that started this enormousness chain of other events.
My OP was dealing with the question of whether it is logical to think that indeed there was such one event or that reality simply became without a cause (an event that made it become).

And the response is
1. There is seldom a *chain* of causes. Instead, there is usually a *network* of causes with no 'root event'.
2. There is no reason to eliminate an infinite regress.
3. We have examples of uncaused events, so even the general argument fails.

 

[Segev Moran]

And the response is
1. There is seldom a *chain* of causes. Instead, there is usually a *network* of causes with no 'root event'.
2. There is no reason to eliminate an infinite regress.
3. We have examples of uncaused events, so even the general argument fails.

Can you elaborate on number 3 with the exception of quantum physics vacuum particles?

 

[Polymath257]

Can you elaborate on number 3 with the exception of quantum physics vacuum particles?

Why make that exception?

But sure. The timing of radioactive decays is usually uncaused (stimulated decay can be caused).

The vast majority of quantum events are technically uncaused. Their probabilities are determined, but not the actual events.

 

[Segev Moran]

Why make that exception?

Because we simply don't know if there is a cause, this does not mean that there is none.

But sure. The timing of radioactive decays is usually uncaused (stimulated decay can be caused).

Can you please explain what you mean by uncaused?
Is it a random process? no (although we cannot anticipate which atom decays, we know they do and we can use it to measure the age of substances as there is an order to things)
Has it ever been that the radioactive decay didn't take place?
Do some materials decay and some not?
If there is a pattern and prediction, i can't see how you assume this is really uncaused?

The vast majority of quantum events are technically uncaused. Their probabilities are determined, but not the actual events.

The word technically here is very important.
I can say for example that gravity is technically uncaused. Yet we know that something causes it (whatever it is)
Quantum fluctuations, intriguing as they are, are still bound to physics. These are btw not really pieces of matter.
Although they seem to be random and uncaused, they are formed to some sort of disturbance. this means that something causes these disturbances.
As particles are always in motion, wouldn't you say something causes them to move?
The assumption of these disturbances is considered uncaused as there is not way to measure what makes them happen in the vacuum. this is not something we can determine as a proof for uncausality.

 

[exchemist]

Because we simply don't know if there is a cause, this does not mean that there is none.

Can you please explain what you mean by uncaused?
Is it a random process? no (although we cannot anticipate which atom decays, we know they do and we can use it to measure the age of substances as there is an order to things)
Has it ever been that the radioactive decay didn't take place?
Do some materials decay and some not?
If there is a pattern and prediction, i can't see how you assume this is really uncaused?

The word technically here is very important.
I can say for example that gravity is technically uncaused. Yet we know that something causes it (whatever it is)
Quantum fluctuations, intriguing as they are, are still bound to physics. These are btw not really pieces of matter.
Although they seem to be random and uncaused, they are formed to some sort of disturbance. this means that something causes these disturbances.
As particles are always in motion, wouldn't you say something causes them to move?
The assumption of these disturbances is considered uncaused as there is not way to measure what makes them happen in the vacuum. this is not something we can determine as a proof for uncausality.

Introducing "proof" is, with due respect, a red herring here. Nobody has been asserting that lack of causality is "proved". No theory of science is "proved".

What we have been explaining is that current models of physics treat the world as having uncaused events. Examples have been given, both of experimental phenomena, such as radioactive decay, and of theories, such as quantum theory, with its probabilities and its indeterminacy.

It is always possible that our models may change but as yet there is no evidence that they are wrong in this respect. You will, therefore, not get people familiar with the science to assent to the proposition that everything must have a cause, because there is evidence that this is untrue.

 

[Polymath257]

Because we simply don't know if there is a cause, this does not mean that there is none.

I agree. There is a difference between not knowing a cause and knowing there is not a cause. In the case of quantum mechanics, we know there is not a cause.

Can you please explain what you mean by uncaused?
Is it a random process? no (although we cannot anticipate which atom decays, we know they do and we can use it to measure the age of substances as there is an order to things)
Has it ever been that the radioactive decay didn't take place?
Do some materials decay and some not?
If there is a pattern and prediction, i can't see how you assume this is really uncaused?

Actually, the individual decays *are* random. The averages of quintillions of individuals is what gives the predictability for dating methods. There would be no way to use radioactive decay to date things if there were only 5 atoms of the isotope used.

Once again, we can predict *probabilities* but not individual events. Which of the possibilities becomes real and when it does so are not caused.

The word technically here is very important.
I can say for example that gravity is technically uncaused. Yet we know that something causes it (whatever it is)
Quantum fluctuations, intriguing as they are, are still bound to physics. These are btw not really pieces of matter.
Although they seem to be random and uncaused, they are formed to some sort of disturbance. this means that something causes these disturbances.

That is your *assumption*. But that assumption has been shown to be wrong.

The point is that there being causes in and of itself has consequences for how events are correlated. We can measure those correlations and find that causality is ruled out.

As particles are always in motion, wouldn't you say something causes them to move?

No. In fact, quite the opposite. Nothing causes them to move, but there can be causes for *changes* of motion.

The assumption of these disturbances is considered uncaused as there is not way to measure what makes them happen in the vacuum. this is not something we can determine as a proof for uncausality.

It isn't an assumption that these things are uncaused. It is *your* assumption that they are. But that assumption is contradicted by the actual evidence (not just the limitations of the current theory).