The existence of parallel universe is proved somehow by thought experiment. Imaginary situation is set and then someone would ask and answer the question. But I would like to know when answering the questions, are the answers simply judged by the physics knowledge and guesses of the one who asks the questions? As there is always limitation on the physics knowledge.

Then there is a problem, in real world, we can never prove the imaginary situation by real experiment. Then thought experiment is just like stories make up by physicists even though the sayings may be sensible, is it?

Physics is built of "models." These models help us describe physical phenomena, always employing the use of Mathematics to quantify it. A thought experiment is one in which a new model is tested based on how much sense it makes in comparison with what we already know. The only use of the "results" of a thought experiment is to make a prediction that can be tested by research. You could probably describe the theoretical process of producing a hypothesis (as opposed to using experimental data to do so) entirely as thought experiments.

But make no mistake: any results of a thought experiment really need to be backed by experimental data before it can be accepted as a real result. (Though many Physicists will talk about their theoretical results as being real even though there is no proof. This bad habit is particularly common among particle Physicists.)

-Dan

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"I must not fear. Fear is the mind killer. Fear is the little death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain." - The Litany Against Fear, "Dune" by Frank Herbert

Hi all!
I've just visited this forum. Happy to get acquainted with you. Thanks.

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Where did you get that idea from?

The idea came from an article of Wikipedia if I remember correctly

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Going to face the Hong Kong Advanced-Level Examination which is believed to be the most difficult AL exams in the world this year. I hope good results can be achieved.

I know where there idea came from. I was asking where he got the idea that it's been proved. It is merely speculation/an hypothesis at this point.