# Does the Copenhagen interpretation say that a tree only has definite mass after I look at it?

Assume that the Copenhagen interpretation holds. Imagine a Universe, a nearly identical copy of our Universe, that contains only our Earth and me (i.e., I'm the lone conscious being and the lone self-conscious being on Earth and in the Universe, though plants, trash, mountains, etc., still exist on Earth).

As I wander about Earth's surface, I come across different bound states of particles: trees, plants, etc., with x, y, etc., definite aspects. For example, a tree I am beholding has, I determine, a mass of 1,349,080 grams (let's imagine that I can precisely determine the tree's mass in grams somehow).

Is it correct to interpret the Copenhagen interpretation as saying that the mass in grams of the tree was simply indeterminate before I saw the tree and measured its mass?

If not, why not?

• This may be more at home on Philosiphy SE Commented Aug 30, 2016 at 13:36
• I don't think so. I am simply asking about the accuracy of my picture of what the Copenhagen interpretation entails. Commented Aug 30, 2016 at 13:38
• And is the moon there if you don't look at it ;)
– Paul
Commented Aug 30, 2016 at 14:31
• In the Copenhagen interpretation conscience is unnecessary, which means it doesn't matter if you're the only person in the universe or if the universe is absent of life. Von Neumann's interpretation has a key role reserved for consciousness, but is wrong. Commented Aug 30, 2016 at 14:40
• The CI (1) avoids making statements about what is happening (2) except when observations take place for some indeterminate meaning of the word 'observation'. So the answer to your question is the CI says nothing about the tree before observation and can't give any account of when it does say something about the tree. Commented Aug 30, 2016 at 18:04

No. The Copenhagen interpretation postulates that there are two types of evolution of physical systems depending on the circumstances:

1. Quantum evolution according to Schodinger's equation if the system S is isolated
2. Wave function collapse if the system S undergoes an ideal measurement by a macroscopic measuring device

The example you give of the tree, therefore, is outside the scope of the Copenhagen Interpretation for various reasons, most notably that it is not an isolated system before you measure it.

Attempts to precisely model measurement apparatus as a quantum statistical system have given insight from within quantum theory itself to the domain of applicability of the Copenhagen Interpretation, thus absorbing the Copenhagen Interpretation into a broader Statistical Interpretation as a special case.

The reference previously recommended by members of Physics SE for this is Allahverdyan, Balian, Nieuwenhuizen : Understanding quantum measurement from the solution of dynamical models

No. The Copenhagen interpretation implicitly assumes that there's some dividing line between the big classical world, which has one reality, and the tiny quantum world. The whole point of Shcödinger's cat was to highlight the arbitrariness of that dividing line, so it has a weakness, and we do not yet have conclusive experiments to fix the problem, as far as I know.

As there is no quantum description of gravity, your question cannot be answered within accepted theoretical frameworks that are provided today.

If you were asking about other properties, like position, momentum etc. then you would "collapse" the quantum system upon measuring that observable. But is a tree a proper quantum system? I doubt that. Any theoretical uncertainty in those (quantum) observables will be neglactably small, compared to the inaccuracy of your (classical) measurement.

• So if I were asking not about the mass in grams of the tree but rather about the position-cum-momentum of the tree's particles, then the answer would be 'Yes, the position-cum-momentum of the tree's particles had been indeterminate before you came across the tree and measured the position-cum-momentum of the tree's particles'? Commented Aug 30, 2016 at 14:29