Exploring Galileo's Nightmare: Einstein's Universe

[Boballoo]

TL;DR Summary

Old documentary says something odd about gravity that I don't understand.

I was watching an old documentary called "Einstein's Universe" from the seventies with Peter Ustinov. They were at a large observatory, outside by the railing, one story above ground, testing Galileo's theory of gravity using two weights of 1 KG and .25 KG of the same shape so air does not affect either one significantly. Dropping them, they both landed at the same time as expected, but one of the astronomers there, the one who dropped the weights, said the following:

“The reason those things all move at the same rate is that objects get their moving orders​

from the same piece of space. It’s not the distant Earth, it’s the space right where they are.”​

I have never heard gravity being described like this. What exactly is meant by this statement? Is he correct? Can someone explain what is meant here in the context of physics knowledge available in the seventies?

 

[256bits]

Quote "Mass tells space-time how to curve, and spacetime tells mass how to move." John Wheeler.
That is a brief description of the general theory of relativity.

The astronomer is referencing the second part of the quote.

 

[phinds]

What exactly is meant by this statement? Is he correct?

He is talking about the fact that a gravitational field exists there whether the objects are there or not. That is, the gravitational attraction does not come into existence when the objects are dropped, it was right there all along and influences the objects whether they are released or not.

 

[PeroK]

“The reason those things all move at the same rate is that objects get their moving orders​

from the same piece of space. It’s not the distant Earth, it’s the space right where they are.”​

He could have added that "the spacetime where they are gets its shaping orders from the distant Earth".

Note that it's the shape of spacetime (not just space) that matters.

 

[tech99]

Quote "Mass tells space-time how to curve, and spacetime tells mass how to move." John Wheeler.
That is a brief description of the general theory of relativity.

The astronomer is referencing the second part of the quote.

I am not an expert in this field(!) but I seem to remember reading, maybe from Eddington, that it is a curvature of space-time that defines a mass, and not the opposite way round.

 

[PeroK]

I am not an expert in this field(!) but I seem to remember reading, maybe from Eddington, that it is a curvature of space-time that defines a mass, and not the opposite way round.

Mass (more generally the stress-energy tensor) and the curvature tensor are related by the Einstein field equations. In a sense, therefore, they both define each other.