...And much much weirder....
Wheeler, in 1978, proposed a thought experiment, the "delayed choice/ quantum eraser"... it was many years before the experiment could actually be done.

Start with the double slit experiment... we all know that if you shoot a beam of photons at a double slit, you get an interference pattern on a screen placed on the other side of the slits. Even more interesting, if you turn down the light intensity so that only one photon at a time is sent through, you will still get that interference effect. Each individual photon must be passing through both slits to interfere with itself. You can say to yourself 'well, yes,there are individual photons, but we also know that light is a wave so sure it is weird, but not that weird..."

Now you repeat the experiment with electrons, or Protons, or neutrons... you still get an interference pattern, even if you send the particles through one at a time.

Ok, you say, that's really weird, but it seems to indicate that matter, just like light is both a particle and a wave.

You don't believe matter can be a wave...you decide to be clever... "Aha, I will design an experiment where I measure wwhich slit the electron goes through" so you set up the experiment again, you put a sensitive detector at one or both of the slits to determine which slit the electron goes through.... and the interference pattern goes away...you simply get two stripes created by the electron PARTICLE going through one slit or the other.

To double check, you turn off the detectors at the slits, the interference pattern reappears. It seems the act of observation forces the electron to choose to be a particle.

So you are forced to accept that matter is both a particle and a wave, and the act of observation collapses the wavefunction and forces the electron to be a particle. No matter how you design the detector at the slit, no matter how little it might influence the electron, the very act of measurement forces the electron to be a particle, simply turn off the detector at the slit, and it suddenly becomes a wave.

This was known long before Wheeler's thought experiment... it is counter-intuitive to our classical understanding of reality, but it is real and is the result of quantum mechanics.

Here is where Wheeler decided to try and trick the universe..."what happens if we design an experiment where we measure which slit the photon, or electron goes through, but we ensure that the decision to measure which slit it went through happens AFTER the particle or wave would hit the screen? There is no way that the pattern at the screen could be influenced by the measurement... what happens then?"

It was a long time before the experiment could be done, but lo and behold, if the detection of which slit it went through is made - even if that decision to detect happens after the light or electron would hit the screen the interference pattern disappears.

This experiment has been done many times with many variations to eliminate possible loopholes, the results are the same. It is as if a measurement in the future can force the electron to be a particle or a wave IN THE PAST. Wheeler predicted this would be the case, and years later he was proven to be correct.

But he didn't stop there, all these experiments have been done in the small confines of a lab, but the same result should apply on the cosmic scale.

Take a quasar 10 billion light years away... let's say between us and the quasar is a galaxy cluster 2 billion light years away gravitationally lenses the quasar such that it creates two images of the quasar- astronomy has found MANY such cases of gravitational lenses. This double image is effectively our double slit on a cosmic scale, light from the quasar can take two possible paths to get to us...

If we set up an experiment to determine which path a photon took around the galaxy cluster 2 billion years ago we are effectively forcing the photon to be a particle instead of a wave 2 billion years before we even decided to do the experiment. When the light passes around the galaxy cluster, it has no idea that which path it took would be measured, so it should take both paths as a wave. But somehow, our decision 2 billion years later forces it to behave instead as a particle.

This retrocausality is counter-intuitive in the extreme, it seems to violate Einstein's theory of relativity, but it is reality. The quasar experiment has yet to be done, it would be EXTREMELY challenging... but quantum mechanics and the experiments in the lab assure us the results will be the same...

The act of observation can affect the past... be it nanoseconds in the past in the lab, or billions of years in the past on cosmic time scales.

This is reality... this is physics....what it ultimately means, for now, is philosophy.