One needn't have studied physics much to have heard of the notorious quantum physics thought experiment, schrödinger's cat.
It's simple, really, and goes like this:

Put a cat in a sealed container with a special device. The device consists of a bit of radioactive material, a Geiger counter, and a cyanide delivery system. when the material decays and emits an alpha particle, a switch engages the cyanide delivery and kills the cat.

Now, during the hour of running the experiment, the material might decay, and it might not. So the cat might still be alive, or it might be dead. There's no way to know without opening the container.

The Copenhagen Interpretation, put forward by Niels Bohr, states that the cat exists in both states, until the waveform collapses into one state or the other, upon observation by the researcher. So without taking a look, the cat is both alive, and it's dead. Only upon verifying the state of the cat is the state of the cat determined.
Personally, I have a problem with physicists going around so cavalierly dealing with cats - so I have insisted that they try a different approach, and this is it:

Guys, you have to use a bitter grapefruit instead of a cat. And instead of a machine that kills a cat after being impinged upon by an alpha particle, install a machine that will make a grapefruit amazingly much sweeter. Okay?

So there's your new thought experiment: is the grapefruit bitter, or is it sweet? Has the material decayed, or is it merely poised to decay?

And what else is for breakfast?