“What is a Parallel Universe?” asked Doris. “And, is it true that science supports the idea?” It was a tricky question and I asked for clarification.
“A friend of mine at school said that the Schrödinger’s Cat experiment proved that Parallel Universes are real. Is that true?” she asked.
I had to say no; that was a wrong statement for many reasons. “But I guess I know where did your friend get the idea from” I said. I was thinking about Hugh Everett’s interpretation of the Quantum Theory and his proposal of a «Multiverse».
“A Multiverse? What is a Multiverse?” asked Doris.
“It’s a bigger universe composed by many other universes independent from each other. That’s what scientists call «The Many-Worlds Interpretation». Any of those many other universes could be considered a Parallel Universe.”
Quantum Mechanics Theory does not prove the existence of a Parallel Universe, but because it has to include the wave function in its formulation (to explain the wave-particle duality), it allows the mathematical possibility of “Many Worlds” coexisting in the same reality – according to Everett.
“Wave function, wave-particle duality; what are you talking about?” Doris said.
I then attempted a better explanation. “But first things first” I said. “To begin with, the Schrodinger Cat does not prove anything – it was not meant to act as evidence but to illustrate some of the of problems Schrödinger saw in the (conclusions of the) Quantum mechanics theory.”
“The media has made this case bigger than it is but it’s about time people leave the poor cat alone” I told her.
On the other hand, there was one experiment held on real life (Schrodinger’s Cat experiment was only a mental one) that truly shook the world: the Double Slit experiment.
“If you are looking for the experiment that generated all the Quantum Mechanics revolution, it would be the Double Slit experiment.” I said.
The Double Slit experiment proved the wave-particle duality, which means that subatomic particles may behave sometimes like a solid body and sometimes like a wave.
“What’s so great about that?” Doris asked.
“It is enormously important, Doris. Waves and particles are two different things; it’s like if you, made of flesh and bones, could sometimes behave like if you were made of gas”.
“That would be SO cool,” she said.
As a result of this discovery, scientist tried to include this feature (the particle-wave duality) in their formulas. Three of them – Schrodinger, Heisenberg and Dirac – were successful. They three used different approaches to include the behavior of the wave (the wave function).
The problem begins when scientists used the formulas to predict the behavior of a subatomic particle because the wave function provides many alternative results (instead of one only answer), meaning that provides alternatives to one reality.
This was a huge problem because the formulas proved to work perfectly – they provide the basis for most of the modern technology gadgets we use today, as the semiconductor (that allows laptops and tables), laser applications, cellular phones, microwave ovens, and many, many more -, but…
… But we know that there is only one reality. How would scientist explain the “other realities”?
“Yes, how did they do that?” Doris asked
“The greatest physics in the world at that time – the nineteen twenties – worked together at different institutes (including the Copenhagen institute) to suggest an answer to the mystery. Albert Einstein was involved in the project, along with Bohr, Dirac, Pauli, Heisenberg, Schrödinger, and many others”.
“Did they solve it?”
“They came up with a solution which would be later known as «The Copenhagen Interpretation», which basically suggests (among other conclusions) that “the wave function collapses” allowing only one reality”.
“And why does the wave function collapse?”
“It just collapses in front of a witness”.
“Any witness,” I said. “The presence of an observer makes the subatomic particle to stop behaving like a wave and start acting like a particle. All you need is someone or something – a device – to take measurements”.
Doris remained pensive for a moment.
“That’s the weirdest thing I have ever heard,” she said. “You are trying to tell me that the particle knows that she’s being watched and prefers to be looked as particle? And that’s what the brightest men alive could come up with?”
“What if I don’t buy this wave-collapsing theory?”
“Then you could agree with Hugh Everett. As we mentioned before, in the late fifties he proposed that the wave function doesn’t collapse and that all the realities the Quantum formulas predict coexist in a Multiverse”.
In his proposal, he states that there is a very large number of universes, and all the things that could have happened in our past – and we think haven’t -, they actually happened in a parallel world.
“I am really not sure which of the two versions believe,” Doris said.