Avi Loeb

Now, whatever is left, the vacuum,

has no observable consequence if it's uniform throughout space and time.

If it's the same value everywhere, the only reason we feel forces is because there are differences between the vacuum at one point and another point, or any entity at one point exerts some force when the concentration of that entity is different at different locations.

So...

We wouldn't expect to discover the zero point unless we consider gravity.

Because in the case of gravity, if there is some energy to the vacuum per unit volume, that generates a gravitational force.

In fact, that is the force that appears to push the galaxies apart in the present day universe.

It's triggering the acceleration of gravity.

of the expansion.

The expansion is not at a constant speed, or it's not decelerating.

You know, you would expect if there was positive mass everywhere, matter and radiation, that the universe would decelerate.

We slow down its expansion as a function of time.

But what we are seeing now over the past half of

cosmic history is that the universe accelerated its expansion and if you extrapolate that to the future every galaxy away from our own galaxy the milky way it will be moving faster and faster as time goes on eventually exceeding the speed of light so if you had a friend that was sending you text messages from another galaxy far away eventually

These messages will not make it.

They will not be able to bridge the gap that is open between you and the friend, because the friend is accelerating from you faster than light.

One way to think about it is an expanding balloon that has ants on the surface.

So the ants walk at some speed, just like the speed of light for photons.

They propagate at some speed.

The ants can walk and visit the entire balloon as long as the balloon is not expanding too fast.