Now, we all know that spacetime is not fundamental, because physicists are saying so. But, do we know the reason why spacetime cannot be fundamental?
This is a physics question as well as a philosophy question.
If we say that X is a fundamental ingredient of the universe, then we will have to admit that whatever will exist in it, will need X for its existence. Nothing can exist without it.
However, if there is something in the universe that does not need X for its existence, then X cannot be called a fundamental ingredient of the universe.
Now, we want to know why spacetime is not fundamental. So, we will ask this question now: Is spacetime a fundamental ingredient of the universe? And we will try to find out an answer to this question.
Our task is very simple here. We will ask just one more question here: Is there anything in the universe that does not need spacetime for its existence?
If the answer is yes, then we know for sure that spacetime is not a fundamental ingredient of the universe.
And the answer is yes here, because there is at least one entity in the universe that does not need any spacetime for its existence. That entity is light. Einstein’s special theory of relativity has shown that a photon occupies zero space for zero time because both the travel time and the travel distance become zero for light.
It is also true that we cannot do anything without light; light is so much essential for us. And the irony is that this most essential entity for us does not need any spacetime for its existence. It can do without it.
So, how can we say that spacetime is a fundamental ingredient of the universe? How can we say that it is fundamental?