The document discusses several topics related to zero point energy and vacuum fluctuations:
1) It explains how the Heisenberg uncertainty principle leads to zero point energy, which is the lowest possible energy of a quantum system in its ground state.
2) It describes vacuum fluctuations as quantum fluctuations of fields even in their lowest energy state. These fluctuations can be thought of as virtual particles being created and destroyed in the vacuum.
3) Several phenomena are discussed that demonstrate the effects of zero point energy and vacuum fluctuations, including spontaneous emission, the Casimir effect, and the Lamb shift.
11. Zero Point Energy The origin of zero-point energy is the Heisenberg uncertainty principle. It is the lowest possible energy that a quantum mechanical system may have; it is the energy of its ground state. The most famous such example of zero-point energy is πΈ=12βπ associated with the ground state of the quantum harmonic oscillator. It is the expectation value of the Hamiltonian of the system in the ground state. Β
12. Zero Point Energy π»=β22πΒ β2+π(π,π‘) πππΈ=π»=Ξ¨ππππ’πππ»Ξ¨ππππ’ππ Β
13. Vacuum Fluctuations In quantum field theory, the fabric of space is visualized as consisting of fields, with the field at every point in space and time being a quantum harmonic oscillator. The zero-point energy is again the expectation value of the Hamiltonian; here, however, the phrase vacuum expectation value is more commonly used, and the energy is called the vacuum energy. Vacuum energy can also be thought of in terms of virtual particles (also known as vacuum fluctuations) which are created and destroyed out of the vacuum. The concept of vacuum energy was derived from energy-time uncertainty principle.
14. Vacuum Fluctuations The vacuum state |π£ππ> of the field is the state of the lowest energy. The expectations values of both πππ and πππ + vanish in the vacuum state, because: πππ |π£ππ>Β =0=<π£ππ|πππ + Vector πΉ(π,π‘), which may be the electric or magnetic or the vector potential, having a mode expansion of the general form: πΉπ,π‘=1πΏ32π,π πππππ πππ πππβπβππ‘+h.π Β
15. Vacuum Fluctuations Where ππ is some slowly varying function of frequency which is different for each field vector. Expectation value of πΉπ,π‘ in the vacuum state: <π£πππΉπ,π‘π£ππ>Β =0 However, the expectation of the square of the field operator does not vanish, as we will show soon. This implies that there are fluctuations of the em field, even in its lowest energy. Β
16. Vacuum Fluctuations If we use the mode expansion and make use of the fact that: π£πππππ +ππβ²π β²π£ππ=0 π£πππππ +ππβ²π β²+π£ππ=0 π£πππππ ππβ²π β²π£ππ=0 We find that: π£πππΉ2(π,π‘)π£ππ==1πΏ3ππ πβ²π β²πππβ(πβ²)π£πππππ ππβ²π β²+π£ππ(πππ βππβ²π β²β)βππ[πβπβ²πβπβπβ²π‘] Β
18. Vacuum Fluctuations So that: π£πππΉ2(π,π‘)π£ππ=1πΏ3π,π ππ2=2πΏ3πππ2Β Β βΆΒ 22π3ππ2π3π This is clearly non-zero, and indeed is infinite for an unbounded set of modes. As it is know: π£ππβπΉ2π£ππ=π£πππΉ2π£ππΒ Β Β ,Β Β Β Β βπΉ=πΉβπΉ βπΉ β the deviation from the mean This shows us that the field fluctuates in the vacuum state. Β
19. Vacuum Fluctuations The effects of vacuum energy can be observed in various phenomena such as spontaneous emission, the Casimir effect and the Lamb shift, and are thought to influence the behavior of the Universe on cosmological scales.
20. Spontaneous Emission Quantum electrodynamics shows that spontaneous emission takes place because there is always some electromagnetic field present in the vicinity of an atom, even when a field is not applied. Like any other system with discretely quantized energy, the electromagnetic field has a zero-point energy. Quantum electrodynamics shows that there will always be some electromagnetic field vibrations present, of whatever frequency is required to induce the charge oscillations that cause the atom to radiate 'spontaneously'.
21. The Casimir Effect One of the more striking examples is the attractive force between a pair of parallel, uncharged, conducting plates in vacuum. This force is also referred to as a Van der Waals attraction and has been calculated by Dutch physicists Hendrik B. G. Casimir and Dirk Polder (1948).
22. The Casimir Effect One can account for this force (also known as Casimir force), and obtain an approximate value of its magnitude, by assuming that the force is a consequence of the separation-dependent vacuum field energy trapped between the two plates. If the plats are squares of side L and are separated by a distance z, we may suppose that the system constitutes a βcavityβ that supports modes with wave number k down to about 1/z. the vacuum field energy trapped between the plates may therefore be written approximately as: π=π,π 12βπβπΏ2π§1π§πΎβππΒ π2ππβ14πΏ2βππ§πΎ4β1π§3=ππ’ππππβππππ€ππ Β
23. The Casimir Effect we have introduced a high frequency cut-off K to make the energy finite. We can think of the negative rate of change of the lower cut-off energy ππππ€ππ with separation z as constituting a force of attraction, whose magnitude F per unit are is given by: πΉ=β1πΏ2πππππ€ππππ§~βππ§4 Β
24. The Casimir Effect It is interesting to note from the structure of F that the force is proportional to β and is therefore quantum mechanical. Because the strength of the force falls off rapidly with distance, it is only measurable when the distance between the objects is extremely small. On a submicrometre scale, this force becomes so strong that it becomes the dominant force between uncharged conductors. Β
25. The Casimir Effect At separations of 10 nmβabout 100 times the typical size of an atomβthe Casimir effect produces the equivalent of 1 atmosphere of pressure (101.325 kPa), the precise value depending on surface geometry and other factors. In modern theoretical physics, the Casimir effect plays an important role in the chiral bag model of the nucleon; and in applied physics, it is significant in some aspects of emerging micro technologies and nanotechnologies.
26. The Lamb Shift The Lamb shift, named after Willis Lamb (1913β2008), is a small difference in energy between two energy levels 2S1 / 2 and 2P1 / 2 of the hydrogen atom in quantum electrodynamics. According to Dirac, the 2S1 / 2 and 2P1 / 2 orbitals should have the same energies. However, the interaction between the electron and the vacuum causes a tiny energy shift on 2S1 / 2. Lamb and Robert Retherford measured this shift in 1947. Lamb won the Nobel Prize in Physics in 1955 for his discoveries related to the Lamb shift.
28. The Lamb Shift In 1948 Welton succeeded in accounting for the Lamb shift between the s and p energy levels of atomic hydrogen in terms of the perturbation of the electronic orbit brought about by vacuum fluctuations. A perturbation πΏπ in electronic position in general causes a change of potential energy πΏπ given by: πΏπ=ππ+πΏπβππ=βπβπΏπ+12ππππππππππΏπππΏππ+β― Β
29. The Lamb Shift When we average this over the random displacements π, the term in πΏπ2 is the leading non-zero term and we find that: πΏπ=16β2πΒ πΏπ2 In order to calculate the value of πΏπ2 resulting from the fluctuations of the vacuum field, we observe that, under the influence of an electric field πΈπ of frequency π, the electronic position r obeys the equation of motion: ππ=βππΈπcosππ‘ Β
32. The Lamb Shift If we take the potential energy π(π) to be: ππ=βπ24ππ0πΒ then: β2ππ=π2π0πΏ3(π) and the volume integral reduces to: π2π0π02 Β
33. The Lamb Shift This vanishes for a p-state but gives a finite value for an s-state. The difference between the s and p energy levels is therefore: βπΈ=βπ412π2π02π2π3ππ 02lnππ2βπ0 Β
34. The Lamb Shift This leads to: βπΈβ~1040Β ππ»π§ For the 2s-state of hydrogen, and is in reasonable agreement with measurements by Lamb and Retherford (1947). Β
36. The Beam Splitter After decomposing all fields into plane-wave modes in the usual way, we consider a single incident mode labeled 1, which gives rise to a reflected mode 2 and a transmitted mode 3. r, t are the complex amplitude reflectivity and transmissivity for light incident from one side. πβ²,Β π‘β² for light coming from the other side there are no losses in the beam splitter Β
37. The Beam Splitter Then these parameters must obey the following reciprocity relations (due to Stokes, 1849): π=πβ²Β Β ,Β Β π‘=π‘β² π2+π‘2=1 ππ‘β+πβπ‘=0 Β
38. The Beam Splitter It follows that an incoming classical wave of complex amplitude π1 gives rise to a reflected wave π2, and a transmitted wave π3 such that: π£2=ππ£1Β Β Β ,Β Β Β π£3=π‘π£1 From these relations it follows immediately that: π£22+π£32=π‘2+π2π£12 So that the incoming energy is conserved. Β
39. The Beam Splitter Now suppose that we wish to apply a similar argument to the treatment of a quantum field. Then π£1,Β π£2,Β π£3 have to be replaced by the complex amplitude operators π1,Β π2Β ,Β π3 , which obey the commutation relations: ππ,Β ππ+=1,Β Β π=1,Β 2,Β 3 π2,Β π3+=0 Β
40. The Beam Splitter if we simply replace π£1,Β π£2,Β π£3 by the operators π1,Β π2Β ,Β π3 , we readily find that the commutation equations do not hold for π2Β ,Β π3. Instead we obtain: π2Β ,Β π3+=π2π1Β ,Β π1+=π2 π3Β ,Β π3+=π‘2π1Β ,Β π1+=π‘2 π2Β ,Β π3+=ππ‘βπ1Β ,Β π1+=ππ‘β Β
41. The Beam Splitter The reason for the discrepancy is that we have ignored the fourth beam splitter input port, which is justifiably ignored in the classical treatment because no light enter that way. However, even if no energy is flowing through the mode labeled 0, in a quantized field treatment there is a vacuum field that enters here and contributes to the two output modes.
42. The Beam Splitter Accordingly, we need to rewrite the commutation relations: π2=ππ1+π‘β²π0Β Β Β ;Β Β Β π3=π‘π1+πβ²π0 π2Β ,Β π2+=π2π1Β ,Β π1++π‘2π0Β ,Β π0+=π2+π‘2=1 π2Β ,Β π3+=ππ‘βπ1Β ,Β π1+πβ²βπ‘β²π0Β ,Β π0+=ππ‘β+πβ²βπ‘β²=0 Β
43. Science Fiction or is it? As a scientific concept, the existence of zero point energy is not controversial although the ability to harness it is. Many claims exist of ''over unity devices'' (gadgets yielding a greater output than the required input for operation) driven by zero-point energy. Zero-point energy is not a thermal reservoir, and therefore does not suffer from the thermodynamic injunction against extracting energy from a lower temperature reservoir.
44. Science Fiction or is it? In 1993 Cole and Puthoff published a thermodynamic analysis, ''Extracting energy and heat from the vacuum'' (see below), in which they concluded that ''extracting energy and heat from electromagnetic zero-point radiation via the use of the Casimir force'' is in principle possible without violating the laws of thermodynamics.
45. Science Fiction or is it? A thought experiment for a device that readily demonstrates how the Casimir force could be put to use in principle was proposed by physicist Robert Forward in 1984 . A ''vacuum fluctuation battery'' could be constructed consisting of stacked conducting plates. Applying the same polarity charge to all the plates would yield a repulsive force between plates, thereby opposing the Casimir force which is acting to push the plates together. Adjusting the electrostatic force so as to permit the Casimir force to dominate will result in adding energy to the electric field between the plates, thereby converting zero-point energy to electric energy.
46. Science Fiction or is it? In spite of the dubious nature of these claims (to date no such device has passed a rigorous, objective test), the concept of converting some amount of zero-point energy to usable energy cannot be ruled out in principle.
47. Conclusion In all the examples above (not the science fiction part of course) we see that the vacuum field plays a fundamental role and is required for internal consistency. The vacuum has certain consequences in quantum electrodynamics that have no counterpart in the classical domain and it cannot be ignored.
48. Bibliography βOptical Coherence and Quantum Opticsβ by Leonard Mandel and Emil Wolf βZero Point Energy and Zero Point Fieldβ β Calphysics Institute Zero Point Energy and Vacuum Energy β Wikipedia General Interest Articles by Matt Visser, Victoria University of Wellington