That explanation is not based on physics. Gravity is an acceleration: the rate of distance per time squared. The only way an object can accelerate is by a force acting upon it such as gravity.
An object moving through space at a constant velocity has no acceleration. Therefore no force is acting upon it. To change its velocity, there must be an acceleration. To get that acceleration, a force must act upon the moving object.
The velocity at which the universe is expanding is increasing. That means there is an increase in acceleration. That increase can only come about due to a force.
I thought Einstein’s General Theory of Relativity proposed that gravity isn’t a force but a distortion of space-time caused by the mass of an object that resides in space-time.
I thought Einstein’s General Theory of Relativity proposed that gravity isn’t a force but a distortion of space-time caused by the mass of an object that resides in space-time.
You are assuming that the expansion of the universe consists in matter moving further apart in pre-existing empty space.
Rather it consists in the volume of space increasing over time. It’s hard to imagine it with space being three-dimensional, but down a dimension, space should be thought of not as 3-dimensional analog of an infinite plane, but of a closed surface (for simplicity, the surface of a sphere, say), which is increasing in area (volume in the 3D case) over time (like a balloon being blown up). What you say about accelerations and forces is about dynamics of matter within space (on the surface of the sphere in the dimension reduced analog) not about the dynamics of space itself.
An object moving through space at a constant velocity has no acceleration. Therefore no force is acting upon it. To change its velocity, there must be an acceleration. To get that acceleration, a force must act upon the moving object.
The velocity at which the universe is expanding is increasing. That means there is an increase in acceleration. That increase can only come about due to a force.
Thank you. That's probably the most clear and concise explanation I've seen on the subject. You must be a good teacher, 'cause I don't feel so dumb as reading the rest of these posts. Wasn't it Lord Kelvin who said physics should be clear enough to be explained to a barmaid, or some such thing?