Physics is consists of mainly particles and paradox. The double split experiment for example, shows that light can behave as both a wave and a particle, and the way that we observe it makes it one or the other.
According to the experiment, if you observe which of the two slits the light passes through, it behaves like a particle but if you observe the screen which it falls on, it behaves like a wave.
Oh, but the confusion doesn’t end just there. According to an experiment proposed by John Wheeler in 1978 and executed by scientists in 2007, observing a particle now can change what happened to another one in the past.
If you let light pass through the slit, and then observe which way it came through, it will “retroactively force it to have passed through one or the other.”
This phenomenon only affects the tiniest fraction of a second. Wheeler suggested however that light from distant stars can be observed the same way; which would alter what happened up to 1 million years ago. And they say you can’t change the past.
If this sounded too confusing, you can get a more detailed explanation here.