# Does generation of a single photon distort equilibrium in the universe?

#### Trakhtenberg

Entangled particles, like photons, need to be in opposite states/spins to maintain equilibrium in the universe. So, if a laser generates just one photon which is measured and confers to a spin state, is the equilibrium distorted since a paired photon was not generated to undertake an opposite state to balance? Or, when one photon is generated, second must have been generated too? In other words, impossible to generate just a single photon?

#### Woody

I think you are a bit confused about entanglement (but then isn't everybody)
The paired spin state is just one of many entanglement options.
It is commonly used in experiments because it is (relatively) easy to create and detect.

studiot

#### studiot

Just to repeat what I have said in your other entanglement thread and Woody has stat4ed here.

There are many degrees (options) of entanglement.

But since the Universe is not in equilibrium, there is no equilibrium to disturb by coherence / decoherence processes.

donglebox

#### benit13

There are two main ways in nature to create photons:

1. Orbital electron de-excitation; and
2. Pair production

Both of these involve (electromagnetic) $$\displaystyle interactions$$, in which quantum numbers are conserved. Photons have no spin quantum number (s=0), but they do have spin angular momentum (m $$\displaystyle \neq$$ 0, but usually m=1). In the case of orbital electron de-excitation, the orbital electron yields a unit of angular momentum to the photon. In the case of pair production, two photons are created and the other photon has the opposite angular momentum quantum number.