If we were able to ‘zoom in’ deep enough into the space-time fabric, we might observe a wild “sea” of particle creation and destruction. The trick is, that the overall “net” result stays zero. That is, on a somewhat larger scale, the fluctuations tends to “cancel out”. Only at extreme brief moments, particles exists. This is the creation of particle-antiparticle pairs, or virtual particles. Quantum fluctuations produce a foam of erupting and collapsing, virtual particles, which on the leftside figure, is visualized as a topographic distortion of the fabric of space time. There is a relation of this to one of the Heisenberg uncertainty principles, which states that ΔE.Δt ≥ h/2, meaning that energy and time considered together "at close inspection", are intrinsically “fuzzy”. But the equation itself, implies a Energy and time relation in the absolute vacuum, where the Energy “in any timeframe” just cannot be ‘0’, because that would violate the equation. So, if you think that Quantum Theory is any good, it's hard to escape from Vacuum energy. The effect should apply to all fields, but since the Electromagnetic field is so strong, the virtual particle pairs in question are commonly considered to be electron/positron pairs. There are quite a few experimental results that points in the direction that the fluctuations are a real property of the vacuum. For example, the famous Casimir effect seems to be a direct result of this phenomenon. See the main page for links describing the Casimir effect. Besides this, many modern theoretical studies have linked this phenomenon to the accelerating expansion of the universe, to “dark energy”, and the cosmological constant Λ. |
In relativistic quantum mechanics, Dirac's equation permits both positive and negative energy states. This is indeed a fact that cannot be ignored. To prevent the fact that positive energy particles directly radiates away energy, Dirac further proposed that all negative states are already occupied, thereby creating a "sea" of negative particles or states. If a negative energy electron is promoted to a positive energy state, the "hole" is perceived as a positron. This prediction of the positron, was (as we all know) succesfully confirmed later Although the Dirac’s “sea” of filled negative energy states, satisfied the equation, it certainly didn’t satisfy all other physicists at that time. And today's interpretations varies quite a lot. It depends on what sort of physicist you are talking to. For example, it seems rather convincing to have a "fermion" sea (half spin like leptons), while it does not seem to account good "enough" for bosons (whole spin). Actually, it's rather the bosons which can all occupy the "same state", while fermions will obey Pauli's exclusion principle. That's why in the Dirac sea, all states are occupied. Anyway, the Dirac sea still remains a fascinating and valid interpretation for the vacuum. Some "lattice like" interpretations (varying in some aspects) from the Dirac sea have emerged, and may, at least, be considered as candidate scientific theories. |