Why this macro thing having quantum behaving but other not?

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In summary: Thermodynamics is classically,universally describle theory of aggregate matter,so that we can use intact classical notion of temperature in Quantum Mechanics.E.g the Bose-Einstein and Fermi -Dirac quantum statistic distributions use classical temperature in their formula.And in Quantum Field (e.g electromagnetic radiation) Theory we use quantum entropy to construct the notion of temperature.Is that right?Then I think Thermodynamics is classically,universally describle theory of aggregate matter,so that we can use intact classical notion of temperature in Quantum Mechanics.E.g the Bose-Einstein and Fermi -Dirac quantum statistic distributions use classical temperature in their formula.And in Quantum
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fxdung
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Why some macro phenomena have not quantum behaviour,but other phenomena have quantum behaviour?Why notions of temperature and heat are successfully in classical model and non-relativistic condition,despite they relate with energy and entropy that directly concern with quantum state ensemble?Whether do the notions of temperature and heat change when we consider effect of quantum and relativistic character of nature?What does control the self-cancelation quantum character in classical physics?
 
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fxdung said:
Why some macro phenomena have not quantum behaviour,but other phenomena have quantum behaviour?Why notions of temperature and heat are successfully in classical model and non-relativistic condition,despite they relate with energy and entropy that directly concern with quantum state ensemble?Whether do the notions of temperature and heat change when we consider effect of quantum and relativistic character of nature?What does control the self-cancelation quantum character in classical physics?
This is a very long story usually treated in books on statistical mechanics.

Usually, the heavier the more classical. A quantum system with weight 1 gram is already very classical. Even if it is a superconductor. Though superconductivity is a quantum effect, but so is the fact that solids are hard. Treated in a phenomenological way, both facts can be handled in a completely classical way for engineering purposes.
 
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To behave quantum mechanically, the crucial requirement is to keep quantum coherence for a long time. For that purpose, the system is better to have a small number of active degrees of freedom. There are two ways how can that be achieved:
- By containing a small number of particles. (atom, few photons, ...)
- By containing a large number of particles in the same quantum state. (superfluid, superconductor, laser beam, ...)
In the latter case, it helps a lot if the temperature is low.
 
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I hear that there is Thermal Quantum Field Theory,then what are the notions of temperature and heat in QFT and QM?Is that it bases on entropy so then on statistic quantum state ensemble or the classical notions of temperature and heat(basing on classical chaos motion of classical particles) still be able to use in QM and QFT?Does the book of QFT of Zinn-Justin say about this topic?
 
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fxdung said:
I hear that there is Thermal Quantum Field Theory,then what are the notions of temperature and heat in QFT and QM?Is that it bases on entropy so then on statistic quantum state ensemble or the classical notions of temperature and heat(basing on classical chaos motion of classical particles) still be able to use in QM and QFT?Does the book of QFT of Zinn-Justin say about this topic?
Quantum statistical mechanics uses entropy and temperature in analogy to (but not equivalent with) classical mechanics.
I recommend the book on statisitcal physics by Linda Reichl. On a more advanced level the book by Calzetta and Hu on nonequilibrium QFT.
 
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Then I think Thermodynamics is classically,universally describle theory of aggregate matter,so that we can use intact classical notion of temperature in Quantum Mechanics.E.g the Bose-Einstein and Fermi -Dirac quantum statistic distributions use classical temperature in their formula.And in Quantum Field (e.g electromagnetic radiation) Theory we use quantum entropy to construct the notion of temperature.Is that right?
 
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fxdung said:
Then I think Thermodynamics is classically,universally describle theory of aggregate matter,so that we can use intact classical notion of temperature in Quantum Mechanics.E.g the Bose-Einstein and Fermi -Dirac quantum statistic distributions use classical temperature in their formula.And in Quantum Field (e.g electromagnetic radiation) Theory we use quantum entropy to construct the notion of temperature.Is that right?
There is no difference between classical temperature and quantum temperature, since upon quantization, temperature (just like time) does not become an operator.

In each case, the quantum version is obtained from the classical version by replacing the classical extensive quantities by their operator version and the phase space integral by a trace. See Chapter 8 of my online book.
 
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Why are only extensive quantities to be replaced by operators but not for other quantities e.g intensive quantities?
 
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fxdung said:
Why are only extensive quantities to be replaced by operators but not for other quantities e.g intensive quantities?
Because intensive quantities are just parameters in the description of the state.
This is immediate for parameters such as temperatures, which directly go into the expression for the density matrix (in a canoncal ensemble, say).

But it holds generally. For example, to go from an extensive quantity to the corresponding normalized intensive quantity one needs to divide by the mean mass or a similar expectation, and hence depends on the state.
 
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Time is a coordinate and not a thermodynamic quantity. But it is intensive, as having 1000 objects at time ##t## doesn't multiply the time by 1000.
 
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So,the state depend on time.Then time is a parameter.
 

1. Why do certain macroscopic objects exhibit quantum behavior?

The behavior of macroscopic objects is governed by the laws of classical physics, which do not account for the principles of quantum mechanics. However, at the quantum level, objects can behave differently and exhibit properties such as superposition and entanglement. This behavior can be observed in certain macroscopic objects under specific conditions, such as extremely low temperatures or in highly controlled environments.

2. How can macroscopic objects simultaneously exist in multiple states?

This phenomenon, known as superposition, is a fundamental principle of quantum mechanics. At the quantum level, particles can exist in multiple states or locations at the same time. This concept has been observed in experiments with macroscopic objects such as buckyballs, which are made up of thousands of atoms. However, superposition is not typically observed in everyday objects due to the effects of decoherence, where external interactions cause the object to "collapse" into a single state.

3. Can macroscopic objects be entangled?

Entanglement is the phenomenon where two or more particles become connected in such a way that the state of one particle is dependent on the state of the other, regardless of the distance between them. While entanglement is most commonly observed at the quantum level, it has also been observed in macroscopic objects such as diamonds and superconductors. This phenomenon has potential applications in quantum computing and secure communication.

4. What are the implications of macroscopic quantum behavior?

The discovery of macroscopic quantum behavior has challenged our understanding of the world and opened up new possibilities for technology and scientific research. It has also raised questions about the boundary between the classical and quantum worlds, and the role of consciousness in the measurement process. Further research in this field could lead to advancements in areas such as computing, communication, and energy efficiency.

5. Is it possible to observe quantum behavior in everyday objects?

While quantum behavior is typically observed at the microscopic level, scientists have found ways to observe it in larger objects under specific conditions. For example, in 2019, a team of researchers were able to observe quantum behavior in a human-made object consisting of trillions of atoms. However, this behavior is usually fleeting and difficult to observe due to the effects of decoherence. It is not yet possible to observe quantum behavior in everyday objects in our daily lives.

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