Undergrad Discussion about quantum mechanics and spacetime

[docnet]

TL;DR

In the Interview called Closer To Truth: What's Real About Time? The Nobel laureate physicist David J Gross said that the metric of space time is a dynamical and quantum mechanical fluctuating object.

Robert Lawrence Kuhn:

It seems that special relativity suggests time is like gravity and electromagnetism, not built into the absolute fabric of reality like logic and causation.

David J Gross:

Yes, time is dynamical. The phenomena are dynamical and are labeled by what we call time. Including the time difference between events, what we call the metric of space time is a dynamical and indeed quantum mechanical fluctuating object. We tend to think of time as evolving. one of the strangest notions is the feeling we have of present moving, as if somehow reality consisted of the universe at a given time, observer dependent according as it may be according to Einstein, moving forward.

The interview

My Question: What did professor Gross mean when he said that the metric of spacetime is a fluctuating object? I assumed how we define time depends on the time difference between physical events, which are quantum mechanical and fluctuating. I did not know much about this topic and wanted to hear physical examples if anyone felt like explaining them.

 

[PeterDonis]

What did professor Gross mean when he said that the metric of spacetime is a fluctuating object?

He means that he believes General Relativity, the classical theory of the metric of spacetime, is not a fundamental theory; that we will need to find a theory of quantum gravity that is more fundamental, and from which GR emerges as a classical approximation the way that other classical theories (such as classical electrodynamics) emerge as approximations to underlying quantum theories.

It should be noted that we have no evidence of any quantum aspects of gravity or the metric of spacetime, so this statement by Gross is not a statement of a scientifically known fact, but a statement of his opinion. His opinion is widely shared among physicists, but it's still an opinion, not a fact.