Casimir Effect and Quantum Field Theory

What is known as the Casimir effect?

Energy fluctuations in vacuum space and antimatter

Our universe contains all sorts of stars, planets, galaxies and other heavenly matter. But do you know that almost 99.9999....% of the universe is nothing but empty space? Till 1948, it was a generally accepted idea that empty space or vacuum was utter empty. A region where there ain't any forces, interactive particles or any form of energy.

But this very idea of 'nothingness' was bought down by the Dutch physicist, Hendrik Casimir, who predicted that in quantum mechanics, the vacuum isn't really empty but instead filled with particle-antiparticle pairs that pop in and out of existence momentarily. They are also called 'virtual' particles. However, the actual phenomenon of Casimir's prediction through a direct experiment was observed only in 1997, almost 60 years after his prediction !!! The experiment was hence called the 'Casimir Effect'.

The Casimir Experiment

The experiment was quite simple but ended up having mind-blowing results. Two uncharged parallel plates are being kept very very close (a micron apart, approx. 10^-6 meters apart) in a vacuum, i.e, empty space. After some time, it's being noticed that the plates actually came closer than before, provided that it was placed in an empty region (vacuum) filled with no particles to exert force on the plates. 

When observed, it was found that virtual particles say photons, were present in the vacuum space along with their anti photon (a photon with the same magnitude but a different sign). The pressure (force) exerted on the outside region of the plates was much larger than the force exerted by the particles trapped in between these plates. This force exerted on the plates tends the plates to push inward and closer to each other. This experiment confirmed that the quantum vacuum was not empty at all.

 How do these particle pairs emerge out of nothing?

The appearance of random particle pairs is based on Heisenberg's Uncertainty Principle. You might be wondering why is a 'particle pair' showing up and not just a 'single particle'. Well, it is because of the fact that in quantum mechanics, every particle has an antiparticle. This coordinates with the conservation of energy throughout the universe. This means that throughout the universe, the total amount of energy is constant. So, for a photon to emerge out of empty space, it must have positive energy (regular energy) to be in existence even for less than a split second.

 But because the energy of the system should not be changed from its constant state, an anti photon, that carries negative energy in the same amount as that of its +ve pair, is created. So that now, when the photon and its anti photon finally annihilate (cancel out) with each other, the energy of the system is back to zero. This is not only for photons but for any particle pair, like an electron and a positron. 

However, the particle anti-particle pairs are too difficult to notice, because before catching a glimpse of these particle pairs, they will vanish from existence by annihilating each other. That's why they are called virtual particles because they are rarely detected or just too 'quirky' to be detected by particle detectors. 

Now, these 'virtual' particles that pop in and out of existence momentarily cause energy effects in the space-time fabric. These effects are called Quantum Energy Fluctuations or Vacuum Fluctuations. 

When the random particles come into existence, slight fluctuations or distortions takes place in the field. This happens because these particles have energy densities (or mass, both +ve and -ve, not proven yet) even though they are too small. So, this appearing and disappearing of particles create an energy fluctuation in space-time.

This effect was a major milestone in proving the famous Hawking Radiation and other properties of black holes and connecting thermodynamics as well. In Hawking Radiation, some of these virtual particles turn into real particles (or detected), which are emerged as radiation from the black hole. 

Further on Hawking Radiation and Evaporation of black holes.

CLICK HERE to read on Antimatter and its properties