in last post I was talking about the experiment that proved that light is wave, it is creating interference in the double slit experiment instead of two lines which one would assume if it was behaving as a particle. (You can imagine bullets instead of particles).
So I found out that the particle part of light is bit more complicated so I wont try to explain it so much in the PRO sense but rather in few words, if you are more interested check out this page: 1)
With this theory that light is just a wave there were finally find some problems.
If you would very accurately measure light on some spot and this light would be dimmer and dimmer, you should get dimmer and dimmer picture. But at one point there were just dots!
As you might understand this was quite confusing. Wave should not make pattern like this.
Soon it was found out that when you measure brightness you can find bumps that should not be there if light would be wave, rather it should be quite uniform.
Finally what was concluded from this is that light behaves both as wave and particle, the attribute is called particle-wave duality.
What was also found at this time (something like beginning of 20th century) is that light comes in quantas. This has very interesting effect. If you would walk away from candle and would be able to distinquish individual photons at one point the candle would not shine less and less because at one point there will be only one quantum coming to you and quantum is not divisible so it would start to disappear more and more often but it would always shine. More detail here:
It was also found that not only photon but also other subatomical particles behave like waves and particles. In 20th century it was tested with electrons and sure! They also made this interference pattern on detector.
PS: This is my 200th post!