The double slit experiment is one of the most famous and talked about experiment in quantum physics. It was the first pioneer experiment to decipher the nature of light and understand it.
Light is said to travel in waves just like the waves we see when we throw a stone in the water. From the point of impact on water we see waves going outwards. Light also behaves in the same way when we focus a torch on a wall. The focus area is lit up fully. But when we observe it starts behaving like a particle. In quantum physics language observing means measuring.
Now let us have an example.
Suppose there are two walls in front of you, the first wall has two large holes and the next wall is solid with no holes. You are throwing tennis balls at the first wall. Some balls will bounce back from the first wall and some balls will go through the holes and hit the second wall. If we mark the place where the balls hit the second wall we will see two strips of marks almost similar to the size of the holes.
Now we scale down the experiment to a smaller level and use a shining white light. As mentioned above there are two small slits on the first wall and the second one is solid. The light wave from the light source passes through both the slits and creates two wave patterns. Each wave pattern is created by each slit. At points where the peak of one wave meets the trough of the other they cancel each other and where the peak of one wave meets the peak of the other wave the strengthen each other (the blue color portion in the middle). Where they reinforce each other there is bright light. When ultimately it reaches the second wall it creates a stripy pattern which is called the interference pattern because the second wall is interfering and stopping the light.
When the light source is illuminated the pattern on the second wall will be like that of dots. The dots are actually not hitting the same place but the dots created by each slit are scattered. Over some time when all the points where the dots were made, gets marked then it will be seen that the dots have actually formed a pattern of stripes of alternate bright and dim color.
The dot marks are formed because when we are trying to measure it on the second wall the photons are behaving as a particle similar to the tennis ball. Before hitting the second wall it is behaving like a wave similar to that we see in water.
What might be happening.
It may be that after crossing the slits the photons are interfering with each other and therefore not hitting the came place. But when electrons are fired one after another then also they don't hit the same place but are scattered. It could be that the electron splits up before the first wall and the recombines behind the first wall to mark a single point on the second wall.
The spooky part happens when we put a detector on the two slits also( previously the detector was on the second wall). Now the pattern on the slit detectors turn to particle pattern and the wave like interference pattern disappears. It is as if when we are observing (measuring), it behaves like a particle like the tennis balls. It is just like they know that now they are being measured and therefore change there behavior.
What does the experiment tells us.
It tells us that sub atomic particles somehow have the capability to behave as a wave and also a particle. It also says that the act of observing or measuring the quantum system has a n effect on the system itself. This is the wave particle duality of quantum mechanics.
Is it possible that our body being also made up of these quantum particles behave the same way until observed?
"It is just like they know that now they are being measured and therefore change there behavior." Exactly, you made it clear for me now. If you remembered i asked the question in one of the comment: who is observer? Is it human or electron itself?. It turns out now, it is electron/sub-photon itself. If this is the case, then there is really long to way to decipher matter and light at quantum level because of these inner intelligence by sub photon.
Regarding your question asked: i think, as such is the nature of sub photon, the same applies for quantum biology to decipher it. But i guess, our body also made up of these quantum particles. That's why it's hard to grasp for scientist what happened exactly when the body is asleep (i mean what changes happened inside of it for the brain, cells etc..).