Quantum mechanics and gender of unborn baby Having a debate with my other half here, I'm currently pregnant and we have not had any scans or tests to determine gender of the baby. 
I'm seeing this as similar to a Schroedinger's cat experiment in that my baby is both male and female until it is determined either way. However my partner believes that it is unequivocally fixed because the sperm and egg determined the gender, the fact that it has not yet been observed is irrelevant. 
I know that this is all mainly theory but I wanted to get a physicist's opinion. How determined is my baby's gender right now? 
 A: I would just like to emphasise what Conifold pointed out, which is that your baby's gender was determined at the time of fertilisation. This is the absolute key in understanding the difference between quantum superposition and, in this case, your baby's gender. It's not even to do with how many particles a system contains. 
When Conifold said "uncertain", what was meant was that it wasn't just our lack of knowledge, but the cat really has no determined state. It is neither alive, nor dead. But your baby clearly already has a fixed gender - if we imagine having identical copies of the same egg and the same sperm that forms your baby, no matter how many times we perform the experiment, the outcome will be the same. However, if we do the Schrodinger cat experiment numerous times, sometimes the cat will be dead when we look, and sometimes alive.
A: Schroedinger's Cat is a thought experiment and an analogy used to explain superposition and indeterminacy. Instead of a cat you should actually understand a quantum system. This system is under the rules of Quantum Mechanics and in the thought experiment it is in a superposition of two states (live and dead, up and down, whatever, those are just labels). Once you measure the system (open the box) you project the superposed state into one of its components (live or dead).
Now it comes to the question: Is a fetus, or even a zygote, a quantum mechanical system? It is definitely small but yet too big to show effects originated from state superposition. Otherwise one would detect a interference pattern in a double slit experiment made out of cells. This has never been observed. The largest structure showing such a quantum mechanical effect is a structure called bucky-ball which is made out of 60 atoms. On the other hand, a single cell has approximately $10^{14}$ atoms. That is too much to show quantum effects. So the zygote is not in a superposition of states (male and female) and the baby genre's is determined right after the fecundation.
