Say I present my friend a box. The box contains a coin. I ask my friend whether the coin is heads or tails. Unable to see what’s inside, she answers she could only give a set of probabilities: 50% heads, 50% tails. It is only when I open the box that she finally knows for sure the state of the coin.
Physicists can generate a wave function that gives sets of probabilities regarding the position and velocity of a subatomic particle. However, upon observation, this wave function collapses to just one outcome.
I want to know why this is a frustrating problem for physicists. If they observe a subatomic particle, and they get a definite answer, isn’t that a good thing? Doesn’t that mean they figured out that electron’s position or velocity accurately? I thought that’s what probability means: the likeliness that something is at a particular place. It doesn’t mean that it will certainly be there.
I’m just puzzled about why this seems such a big deal among physicists.
In: Physics
Because wave function collapse is not our knowledge (well, depending on interpretation). It’s when the universe seems to decide to treat it as one case but not others in the cascading link of entanglement.
Let’s go back to your box example. Why are you special? Someone else could have snuck a peak before you. Someone could have an xray machine. Why does the collapse wait for you? Unless we throw a shared reality out the window, it shouldn’t. And why humans? Is an ant inside the box count? How about a camera and a image recognition AI? How about just a random photon hitting it?
Now, the coin you can answer with deterministic realism. It was always that way, of course anyone person knowing didn’t matter, nor does light hitting it.
Now, a quantum object impacted by interaction and inherently probabilistic (to our knowledge)? You can’t do that. At some point some sort of interaction does something. We just don’t know the details of what or how this occurs, we just know we get a clear result and the universe seems to settle on this with no large scale macroscopic quantum effects.
The issue isn’t that you lack information like in your example. You change the outcome by measuring it.
Before you measure a particle it truly “hasn’t decided” wich side of the wave function it is on. We can prove that with the bell inequality wich disproves that the state existed before you measure it through statistics.
In your box example you could figure out wich position the coin is in by tracking previous information, like wich face was the coin put into the box, and did someone move the box. For quantum physics this information only starts existing when the wave function collapses.
This is weird because it only works when one of two very fundamental principles are violated. Either the world isn’t deterministic (same action doesn’t always lead to the same outcome) or the world isn’t local (information of your particle depends on other particles very far away). Both of these are basic blocks of how we originally understood the world, and now we know at least one of them must be wrong.
Radiation decay is a great example. There should only be half of the material after one half life, but depending on measuring it, you can have three outcomes: more than half, exactly half, or less than half. Also, your measurement device could be broken.
The beauty of physics is that no one is technically wrong, but just doesn’t have measured (observed) record of their theories. It’s the mathematicians who deal is absolutes and are no fun.
Latest Answers