The HUP states that you cannot observe both a particle’s momentum and its mass, because observing it changes one or both of those. So how can you observe something?
You need a particle that affects nothing. Let’s call it Particle A. But you have to be able to observe it. Let’s say Particle B is another particle that emits and absorbs Particle A, causing it to change in mass. But its momentum is unchangeable. So you can observe it with “normal” particles.
You can use Particle A to observe other particles without affecting them. They bounce back, and are caught by a net of Particle B. You can then observe which Particle B changed in mass, and can determine where Particle A reflected to. You can then determine the location of the particle it reflected off of based on angle and the amount of time before it returned.
Technically, the egg.
I assume that “egg” means “chicken egg”. Here’s why the egg came first:
Once upon a time, chickens were a different species. A bird of that different species laid an egg which had mutated DNA. That egg was the first chicken as we know them today. It was an egg before it was a chicken.
If the question is taken in a more metaphorical sense, it’s harder to say. Chickens were once bacteria that didn’t lay eggs. At some point there was a type of living organism that laid some egg-like thing. So you could say that the chicken came first, because there were living things before there were eggs, or even egg-like things. The first living things reproduced by splitting, not birth. Many living things still do that today, you just can’t see them.
Grammatically, the chicken came first, because it was first in that sentence. Ha ha ha, I’m so funny.