In Science,  it is meaningless to ask questions or make statements that can not be measured/tested by experiments

在科学中，只有能被实验检验对错的论述，才有意义。只有答案能被实验检验对错的问题，才有意义。

I feel that a meaningful scientific question should satisfy the following condition: The different answers to the question should have different measurable consequences.

Also a meaningful scientific statement should satisfies the following condition: The statement being true or false should have different measurable consequences.

For example, "a sign shows 'stop'" is a meaningful scientific statement since it can be tested by looking at the sign. But "What does a sign show before anyone looks at it?" may not be a meaningful scientific question. (Or is it?) This kind of issue appear in the measurement theory of quantum mechanics.

How to ask a meaningful scientific question? One may first think about what might the potential answer be. Then try to design an experiment to test the validity of the answer. A scientific question is meaningful or meaningless depend on the ability to design an experiment that can test the validity of its potential answer.

Here is an example: "Is existence timeless or in time?" The potential answers are: Existence is timeless and Existence is in time. The next task is to design an experiment to test the validity of the statement "Existence is timeless" or "Existence is in time". Here I have trouble. I do not know what experiment can test the  validity of the above statement. Another commen example is "does God exist?" What is the experimental setup to test "God exits" or "God does not exist"?

Being able to design experiments to test/probe those "tough" questions will produce great scientific progresses.  One big area of scientific research is to design such kind of experiments and to make some of those used-to-be meaningless questions meaningful. (Certainly, most meaningless questions remain meaningless.)

Not having such experiments, the questions are not a meaningful scientific questions. The burden is on the person who ask the question to provide the experiment that, at least in principle, can test the validity of the potential answer.

There are many people (also known as crackpot) who make spectacular claim  about their original theories of everything. Usually, the problem with their theories is that the theories are not even wrong: The theories contain no consequences that can be tested and used to falsify the theory.