ÿþ<html> <body> <h1>Lightweight overview  Zero Point Energy or  Quantum Foam </h1> Version : 0.9<br> Date : 15/03/2010<br> By : Albert van der Sel<br> Type of doc : just an attempt to decribe the subject in a few simple words. But, I am not sure if it is going to be any good.<br> <hr/> <br> <B>Contents:</B><br> <br> 1. Heisenberg and Quantum Foam<br> 2. The Dirac equation and the  Dirac sea <br> 3. Other current theoretical idea s (or problems)<br> 4. Vacuum polarization and related<br> 5. Higgs and the Vacuum<br> 6. Are practical ZPE applications possible?<br> <br> One fascinating phenomenon in physics, is the  Zero Point Energy , or  Vacuum fluctuations or  Quantum Foam .<br> <br> This is related to the following intruiging question: Is "empty space" really just empty, or is it a sort of bubbling ocean<br> with the creation and destruction of virtual matter? Let s take a look at this question, from a few different angles.<br> <br> <h2>1. Heisenberg and Quantum Foam:</h2> <br> <p> <table border="0" width="100%" cellpadding="10"> <tr> <td width="20%" valign="top"> <img src="fig1.jpg"> </td> <td width="50%" valign="top"> If we were able to  zoom in deep enough into the space-time fabric, we might observe a wild  sea <br> of particle creation and destruction.<br> The trick is, that the overall  net result stays zero. That is, on a somewhat<br> larger scale, the fluctuations tends to  cancel out .<br> Only at extreme brief moments, particles exists.<br> This is the creation of particle-antiparticle pairs, or virtual particles.<br> <br> Quantum fluctuations produce a foam of erupting and collapsing,<br> virtual particles, which on the leftside figure, is visualized as a topographic distortion<br> of the fabric of space time.<br> <br> There is a relation of this to one of the Heisenberg uncertainty principles, which<br> states that ”E.”t e" h/2, meaning that energy and time considered together "at close inspection",<br> are intrinsically  fuzzy . But the equation itself, implies a Energy and time relation<br> in the absolute vacuum, where the Energy  in any timeframe just cannot be  0 ,<br> because that would violate the equation.<br> So, if you think that Quantum Theory is any good, it's hard to escape from Vacuum energy.<br> <br> The effect should apply to all fields, but since the Electromagnetic field is so strong, the<br> virtual particle pairs in question are commonly considered to be electron/positron pairs.<br> <br> There are quite a few experimental results that points in the direction that the fluctuations<br> are a real property of the vacuum. For example, the famous Casimir effect seems to be<br> a direct result of this phenomenon. See the main page for links describing the Casimir effect.<br> <br> Besides this, many modern theoretical studies have linked this phenomenon to the<br> accelerating expansion of the universe, to  dark energy , and the cosmological constant ›.<br> </td> </tr> </table> </p> <h2>2. The Dirac equation and the  Dirac sea :</h2> <br> <table border="0" width="100%" cellpadding="10"> <tr> <td width="20%" valign="top"> <img src="fig2.jpg"> </td> <td width="70%" valign="top"> In relativistic quantum mechanics, Dirac's equation permits both positive <u>and</u> negative energy states.<br> This is indeed a fact that cannot be ignored.<br> To prevent the fact that positive energy particles directly radiates away energy,<br> Dirac further proposed that all negative states are already occupied, thereby creating a "sea" of negative<br> particles or states. If a negative energy electron is promoted to a positive energy state,<br> the "hole" is perceived as a positron.<br> This prediction of the positron, was (as we all know) succesfully confirmed later<br> <br> Although the Dirac s  sea of filled negative energy states, satisfied the equation, it certainly didn t satisfy all other physicists at that time.<br> <br> And today's interpretations varies quite a lot. It depends on what sort of physicist you are talking to.<br> For example, it seems rather convincing to have a "fermion" sea (half spin like leptons), while it does not<br> seem to account good "enough" for bosons (whole spin).<br> Actually, it's rather the bosons which can all occupy the "same state", while fermions will obey Pauli's<br> exclusion principle. That's why in the Dirac sea, all states are occupied.<br> <br> Anyway, the Dirac sea still remains a fascinating and valid interpretation for the vacuum.<br> Some "lattice like" interpretations (varying in some aspects) from the Dirac sea have emerged,<br> and may, at least, be considered as candidate scientific theories. </td> </tr> </table> <br> <h2>3. Some other current theoretical idea s:</h2> <b>3.1 Photon interaction with the "vacuum"</b><br> <br> Suppose we have a photon travelling through the "vacuum". Now, since the vacuum has fluctuations,<br> there is a good chance the photon will interact with such a electron/positron fluctuation from the vacuum.<br> What will happen?<br> After interaction, a new photon might result, on it's way to the next interaction.<br> What does it mean? Suppose there was no Dirac sea, or Fermion sea, would then light travel faster?<br> One thing is for sure. What we see as the "true photon", is the net result of the bare photon with<br> all vacuum interactions <I>already accounted for.</I><br> It won't conflict with Einstein, because the speed of light is constant all moving frames of reference,<br> withouth that Einstein is actually specifying a specific number.<br> There is a serious argument, that when the speed of light is measured in a sort of Casimir cavity, it will be<br> a very tiny bit faster than it travels outside. This is compliant with our idea of the vacuum, because within<br> the Casimir cavity, the number of waves is lower (just as what is the regular explanation of the Casimir effect).<br> There are some experiments done, pointing the effect to be true. But the scientific community seems still<br> somewhat divided in this area. There is for example a difference in the speed of light at the wavefront,<br> as compared to transmitting "true information" as such. Secondly, very good and convincing results seems not<br> to have been produced yet.<br> <br> <b>3.2 The accelerating universe.</b><br> <br> According to the latest insights, the universe is expanding in an accelerated rate.<br> That's an incredable phenomenon by itself ofcourse, but in relation to the modern thoughts<br> about the vacuum, we might have a "crisis". Quantum field theories predict a huge cosmological constant <br> from the energy of the quantum vacuum.<br> Now, it's fair to say that science still do not have figured out exactly what is going on.<br> One startling point is the idea that the acceleration seems to be fairly recent compared to<br> what is seen as the total age of the universe.<br> The following is somewhat speculative, but Dark energy  the unknown substance that is causing<br> the expansion of the universe to accelerate  could be due to quantum fluctuations of the vacuum.<br> That is a serious scientific consideration.<br> Indeed, my description is incredably vague, but the only purpose here is to point out that the vacuum energy and structure<br> is a serious component in modern cosmology too.<br> But the structure of the vacuum has been revised. We already had the classical concept of fluctuations, and,<br> superimposed, a new "field" has been "designed", which is called "quintessence", which will vary over space and time.<br> This then might be the driving force behind the acceleration.<br> Others argue that the "Cosmological constant" (a measure of the energy in vacuum), is driving the expansion.<br> But.. that is <I>just one</I> of the theories. Other explanations exist as well<br> <br> <br> <h2>4. Vacuum polarization and related:</h2> If the vacuum produces short-lived charched "virtual" particle-antiparticle pairs, then they would on average<br> "reposition" themselves in the presence of a field or charged particle.<br> In a way, the vacuum is in effect counteracting the field, or charged particle.<br> This effect is called "vacuum polarization". <br> Has this been observed in experiments? In several ways, yes.<br> For example, the small "Lamb" shift<br> in spectral lines of Hydrogen (and other elements), is attributed to the interaction with the vacuum.<br> Similar to the former effect, vacuum polarization is very likely to be experimentally observed in muonic atoms.<br> <br> <br> <h2>5. Higgs and the Vacuum:</h2></b> Waves and "fields" are not exactly the same. With "fields", virtual particles pop into and out of existence constantly.<br> We already have seen the photons assiociated with EM fields<br> <br> A hypothetical "Higgs" field may exists, with has associated Higgs particles. This field has a certain value in all<br> space, and "interacts" with many elementary particles, giving rise to their observed mass.<br> <br> Now, some theories propose that this Higgs field itself, may exist in a "false vacuum" state, and that<br> might be responsible (as some folks say) for the driving force behind the accelaration of the universe.<br> <br> Certainly the following is a well-know hypothesis among cosmologists: As spontaneous symmetry breaking occurred after<br> the inflationary period, the Higgs field takes on different orientations in unconnected regions of space.<br> Along the boundaries, between these differently oriented regions of space, the vacuum energy (or phase)<br> for that "region" is trapped, and a defect is formed. In effect, the universe could consist of a whole array of these "bubbles".<br> Each of those domains would have different "vacuum" conditions.<br> Interrestingly, "cosmic strings" may have formed along the domain 'walls', but that is another subject.<br> <br> Even if no separate domains were formed during the early universe, the theory is that at a certain fase,<br> Higgs rolled down the potential giving rise to a large mass to the Higgs "particle" itself ( believed to be 122-197 times<br> the mass of the proton).<br> <br> There is much to learn from Higgs, and thats one reason why the coming LHC experiments are quite exiting:<br> will the Higgs particle be found?<br> If it does get found (or even if it does not get found), that will have important conseqences for our understanding<br> of the Vacuum (and the universe as a whole).<br> <br> <h2>6. Are practical ZPE applications possible?:</h2></b> Since everything "sits" in the vacuum, and since the vacuum is interacting with "everything",<br> in a sense, everything we do or create, is already effected by the vacuum.<br> If somebody would say that the vacuum in a way effects everything, I would not immediately disagree.<br> <br> Ofcourse, what is meant by "practical applications", is the question if we can utilize the vacuum energy<br> for a <I>practical purpose</I> like energy production, or as a source for propulsion.<br> A great application would be ofcourse "clean" and cheap energy for all.<br> One other facinating application would be to use ZPE as way to propell a spacecraft.<br> Unfortunately, some theoretical studies have shown that, generally speaking, the resulting acceleration<br> is very little. But it is likely that there is still a lot to learn on optimizing materials, orientation,<br> and applying some <I>catalizing</I> substance, or energy.<br> Anyway, I would not be too surprised if a true <I>practical</I> ZPE device would be presented one of these days.<br> <br> <br> </body> </html>