Nuclear Fusion and Energy

[Ostronomos]

It was in the 1930s that Szilard and other Physicists discovered that nuclear fusion, as opposed to fission, proved to be the sun's power source. Because of the complex interplay of forces, when two nuclei fuse to form a heavier one it gives off energy. Similar to fission except it's the opposite.

My question: can energy be produced from literally nothing?

I realize that the Joint European Torus (JET) produces conditions on earth for nuclear fusion to occur but is there a source of energy with never-ending power that can be found in the fabric of the universe itself? What of pair production and annihilation?

The Wikipedia article on Gibbs Free energy explains this as follows:

In thermodynamics, the Gibbs free energy (or Gibbs energy) is a thermodynamic potential that can be used to calculate the maximum reversible work that may be performed by a thermodynamic system at a constant temperature and pressure. The Gibbs free energy (Δ G = Δ H − T Δ S {\displaystyle \Delta G=\Delta H-T\Delta S}

, measured in joules in SI) is the maximum amount of non-expansion work that can be extracted from a thermodynamically closed system (one that can exchange heat and work with its surroundings, but not matter). This maximum can be attained only in a completely reversible process. When a system transforms reversibly from an initial state to a final state, the decrease in Gibbs free energy equals the work done by the system to its surroundings, minus the work of the pressure forces.[1]

Gibbs free energy - Wikipedia

Thoughts?

 

[Subduction Zone]

It was in the 1930s that Szilard and other Physicists discovered that nuclear fusion, as opposed to fission, proved to be the sun's power source. Because of the complex interplay of forces, when two nuclei fuse to form a heavier one it gives off energy. Similar to fission except it's the opposite.

My question: can energy be produced from literally nothing?

I realize that the Joint European Torus (JET) produces conditions on earth for nuclear fusion to occur but is there a source of energy with never-ending power that can be found in the fabric of the universe itself? What of pair production and annihilation?

The Wikipedia article on Gibbs Free energy explains this as follows:

In thermodynamics, the Gibbs free energy (or Gibbs energy) is a thermodynamic potential that can be used to calculate the maximum reversible work that may be performed by a thermodynamic system at a constant temperature and pressure. The Gibbs free energy (Δ G = Δ H − T Δ S {\displaystyle \Delta G=\Delta H-T\Delta S}

, measured in joules in SI) is the maximum amount of non-expansion work that can be extracted from a thermodynamically closed system (one that can exchange heat and work with its surroundings, but not matter). This maximum can be attained only in a completely reversible process. When a system transforms reversibly from an initial state to a final state, the decrease in Gibbs free energy equals the work done by the system to its surroundings, minus the work of the pressure forces.[1]

Gibbs free energy - Wikipedia

Thoughts?

Gibbs free energy refers to chemical reactions. It does not refer to nuclear reactions.

 

[Polymath257]

Pair production and annihilation is a result of the uncertainty principle. In this case, it allows for a violation of the conservation of energy for a brief period of time. The amount of time allowed decreases as the amount of the energy violation increases (the product of the two is Planck's constant). Macroscopic violations can thereby only happen for very brief periods of time. For example, the energy associated with the mass of a proton can only be allowed for femptoseconds.

Note that Gibb's free energy is associated with the *usable* energy and is ultimately related to the total entropy change of the system and surroundings (under constant pressure). you don't get 'free' energy this way.

 

[Polymath257]

Gibbs free energy refers to chemical reactions. It does not refer to nuclear reactions.

Not 100% true. But it does have an assumption of constant pressure. And, for statistical mechanics to be relevant, you would need a LOT of nuclear material. So, the nuclear version might be relevant for plasma confinement, the cores of stars, and neutron stars.

One problem is that for fusion, there is a *decrease* of entropy (fewer particles after than before) and the temperature tends to be high, so the second term is large and positive. That means there has to be a large energy production (first term) for the reaction to be spontaneous. Fortunately, fusion gives such a large return.

 

[exchemist]

It was in the 1930s that Szilard and other Physicists discovered that nuclear fusion, as opposed to fission, proved to be the sun's power source. Because of the complex interplay of forces, when two nuclei fuse to form a heavier one it gives off energy. Similar to fission except it's the opposite.

My question: can energy be produced from literally nothing?

I realize that the Joint European Torus (JET) produces conditions on earth for nuclear fusion to occur but is there a source of energy with never-ending power that can be found in the fabric of the universe itself? What of pair production and annihilation?

The Wikipedia article on Gibbs Free energy explains this as follows:

In thermodynamics, the Gibbs free energy (or Gibbs energy) is a thermodynamic potential that can be used to calculate the maximum reversible work that may be performed by a thermodynamic system at a constant temperature and pressure. The Gibbs free energy (Δ G = Δ H − T Δ S {\displaystyle \Delta G=\Delta H-T\Delta S}

, measured in joules in SI) is the maximum amount of non-expansion work that can be extracted from a thermodynamically closed system (one that can exchange heat and work with its surroundings, but not matter). This maximum can be attained only in a completely reversible process. When a system transforms reversibly from an initial state to a final state, the decrease in Gibbs free energy equals the work done by the system to its surroundings, minus the work of the pressure forces.[1]

Gibbs free energy - Wikipedia

Thoughts?

No energy can't be produced from nothing. The First Law of Thermodynamics forbids this and Emmy Noether has proved the 1st Law has to be true, at least so long as the laws of physics don't change with time (I think?), as they appear not to.

Gibbs Free Energy, as others have pointed out, is a standard term used in school level chemistry and is not about getting energy from nothing. That much is obvious from the definition you have posted.

 

[Subduction Zone]

No energy can't be produced from nothing. The First Law of Thermodynamics forbids this and Emmy Noether has proved the 1st Law has to be true, at least so long as the laws of physics don't change with time (I think?), as they appear not to.

Gibbs Free Energy, as others have pointed out, is a standard term used in school level chemistry and is not about getting energy from nothing. That much is obvious from the definition you have posted.

What about "zero point energy". Surely there must be something I can get for free from there

 

[Polymath257]

No energy can't be produced from nothing. The First Law of Thermodynamics forbids this and Emmy Noether has proved the 1st Law has to be true, at least so long as the laws of physics don't change with time (I think?), as they appear not to.

There are a couple of caveats to this.

1. Noether's results assume commutativity of the basic variables. This is violated in quantum mechanics. There *are* versions of Noether's theorem that work in QM, but because of the non-commutativity, they do allow for *brief* violations. Yes, it is time/energy that are linked, just like momentum/position.

2. In General Relativity, the basic equations *can* and often *do* have the 'time' variable in them explicitly. This depends, to some extent, on the coordinates chosen and the geometry of spacetime, but conservation of energy is tricky in GR. In particular, conservation of energy happens *locally*, but talking about the 'total energy in a region' requires translating the energy-momentum 4-vectors to a common location. The results of this translation can depend on the path used because of curvature.

Gibbs Free Energy, as others have pointed out, is a standard term used in school level chemistry and is not about getting energy from nothing. That much is obvious from the definition you have posted.

 

[exchemist]

What about "zero point energy". Surely there must be something I can get for free from there

AARGH! Don't you start.

That has just got to be cobblers. The whole point is zero point energy is the energy of the ground state. By definition, there is no lower state than the ground state. So the energy remaining in the ground state is ipso facto unextractable. I really don't understand why this crazy notion has so much traction. But maybe @Polymath257 has a view on that.

Anyway, full marks for knowing how to put a dime in my slot and getting me to light up.

 

[exchemist]

There are a couple of caveats to this.

1. Noether's results assume commutativity of the basic variables. This is violated in quantum mechanics. There *are* versions of Noether's theorem that work in QM, but because of the non-commutativity, they do allow for *brief* violations. Yes, it is time/energy that are linked, just like momentum/position.

2. In General Relativity, the basic equations *can* and often *do* have the 'time' variable in them explicitly. This depends, to some extent, on the coordinates chosen and the geometry of spacetime, but conservation of energy is tricky in GR. In particular, conservation of energy happens *locally*, but talking about the 'total energy in a region' requires translating the energy-momentum 4-vectors to a common location. The results of this translation can depend on the path used because of curvature.

Yes the QM short-term thing I knew - and it really is short term and only at the atomic scale. The GR one is interesting and subtle. However, as regards the possibility of "free energy", one would need that locally, so the notion can safely be dismissed. (I just thought I'd add that, to prevent any readers from going off the deep end and claiming "GR says free energy is feasible".)

 

[Polymath257]

Yes the QM short-term thing I knew - and it really is short term and only at the atomic scale. The GR one is interesting and subtle. However, as regards the possibility of "free energy", one would need that locally, so the notion can safely be dismissed. (I just thought I'd add that, to prevent any readers from going off the deep end and claiming "GR says free energy is feasible".)

To go a bit further.

There are two main expressions for the conservation of energy: a local (differential equation) version and a global (integral) version. In flat geometry, the two can be interconverted by the divergence theorem from calculus III.

In essence, the integral form says that the rate of change of the total energy in a region is the same as the rate at which energy is entering (or leaving) the region through the boundary.

But, in a curved geometry, the divergence theorem no longer holds. There are 'extra terms' in the differential version that do NOT have counterparts in any integral version. The upshot is that there can be local energy conservation, but even *defining* total energy of a region is problematic in curved space, let alone trying to state something like the law of conservation of energy.