The Casimir effect in quantum field theory is small physical forces that arise from a quantized field. The force that acts between two parallel and close uncharged conducting plates. The effect is due to the quantum vacuum fluctuations of the electromagnetic field. Casimir effect was predicted by Hendrick Casimir, a Dutch physicist in the year 1948.
Casimir Effect can be understood with a typical example of a vacuum in space. According to modern physics, the vacuum consists of varying electromagnetic waves and it can never be eliminated. It can be compared to a vast ocean of waves that always shows its existence, and it is unstoppable. These waves always possess a package of viable wavelengths thus implying that an empty space consists of a minimum amount of energy. The energy that we can never feel, in spite of presence.
Now consider two mirrors that are placed in a vacuum facing each other. As a result, some of the waves will occupy the space between the mirrors bouncing backwards and forward. Once the mirrors are moved closer to each other the longer waves which are present, due to lack of space they may no longer fit in. This is caused when a total amount of energy that is present between the plates will be a bit less compared to the energy that is present somewhere in the vacuum.
The two mirrors are attracted to each other just as 2 objects that are held together by a stretched spring. Until the energy stored in the spring decreases, there exists a movement of two mirrors. Due to this effect, the two mirrors will be attracted to each other, and this effect is termed as the Casimir Effect.
It is one of the suggested possible cause in understanding the Casimir Effect that is based on canonical macroscopic quantum electrodynamics. There may exist a vacuum of a coupled system which detects the properties of an electromagnetic field that will give rise to force. Casimir force is characterized by a property of a coupled system wherein the synergy between the two plates is mediated by the zero-point fields.