So let's just say right up front that 9) we have a way to maybe fix all of that. 10) Watch this. And 11) you're not going to understand this because 12) #5 up there in the first paragraph. Nobody understands it. So don't feel bad or dumb or ignorant or stupid. Because I don't understand it either, and here I am, writing about it.
Let's start with the Double Slit Experiment. Here's a picture:
You'll notice that there's a piece of wood with two slits. That's why we call this the Double Slit Experiment.
And there's a flashlight (actually a laser) and another piece of wood.
Now, if the world worked the way you think it ought to, when you turn on the flashlight, you'd get something like this:
And sometimes you do. But when the slits are narrow enough, you get something more like this:
That's because light travels in a wave, and when you shine it through two slits, the wave breaks into two waves and they interfere with each other. So that's called an Interference Pattern. It's not a big deal.
But if you use a laser and change the experiment so that you only send a photon of light through the slits at a time, like this:
this is what you ought to get:
That is, some photons go through the top slit and some go through the bottom slit. Just like you'd expect.
Except. That's not what happens. This is what you really get:
Which is an interference pattern.
That can't happen. The photons are going through one at a time. There's nothing to interfere with.
Here's where the weirdness starts.
The photons go through both slits at the same time. That means that each photon is in two places at once. And then each photon ... interferes with itself.
I told you it was weird. You should have listened.
I'm going to say that again really loudly so that you don't miss it.
THEY'RE IN TWO PLACES - TWO!!! - AT THE SAME TIME!
So now we change the experiment by putting a photon detector into the experiment. It ... detects photons. Duh. See the little black box? Photon detector. It's turned off now.
Then we turn it on. And the weirdness gets weirder. Unless you start to understand the universe in a different way:
Because when you turn the photon detector on, the photons start doing what we thought they should have done in the first place. That is, going through either the top or the bottom slit. Not both at the same time.
So what's going on? Weirdness.
The photons seem somehow to ... know ... that you're looking at them. And they change what they do.
So that you don't miss it ...
THE PHOTONS KNOW THAT YOU'RE LOOKING AT THEM!
Wait, though. That's so weird. Except that ... what's going on here is ... an Interaction. Between you and the photons. Because "looking" is an interaction.
And the whole universe may be made of just that. Interactions.
So now it all makes sense.
OK, not really. But only because we don't know how to think like that yet.
Then it gets more interesting.
We aim our photon detector towards the middle, between the two pieces of wood. Because then the photons will have already gone through both slits at the same time, and we'll figure out what it is that they are really doing.
And then we turn it on.
And the photons stop going through both slits at the same time again and start doing what they are supposed to do in a non-weirdness universe.
Which means. That the photons go through both slits at the same time, get to where you are trying to see them, see that you are trying to see them, and then they ...
..go backwards in time and change what they did. So that you can't catch them going through both slits at the same time.
Backwards in time. You read it right. That's what they do. Photons, and all little particles, can go backwards in time. You can't, even though you are made of little particles that can.
Once again, loudly.
THEY GO BACKWARDS IN TIME AND CHANGE WHAT THEY DID!
And they do this because you have Interacted with them. By looking at them, or measuring them in some way.
Your Interaction with photons, or any quantum (little tiny) particle, can cause the future to change the present, or the present to change the past, or the future to change the past.
You can't tell it how to do that. It just ... does it. Because of the Interaction.
And remember. These particles aren't really there in the way that you think they are. They are only there as a product of interactions. And the interaction starts with ...
Or some random vibration somewhere in the world. Whatever. It's still an interaction.
Still to come, you, interacting with Schroedinger's Cat backwards in time.