Vacuum exerts a net zero force, or i guess pressure? on what's inside it, right? So if the universe is expanding at an accelerating rate, is the vacuum of outer space is growing? Like space is geometrically flat but expanding under an outward time curve, so vacuum is what's increasing first as it expands.

Does that mean that gravity is the shift in the net force away from zero when an object is close to a much bigger object? In the sense that at some distance, the net force of the expanding vacuum on the smaller object will degrade in the direction of the bigger object, or rather that force will be stronger from every direction except towards the bigger one.

But the stuff I've read discusses gravity as a wave, particle, or fundamental force. Am I getting this totally wrong or are those different ways of conceptualizing it relative to other things?

If the vacuum is growing, it's exerting a force, right? Is that causing energy to just spring into existence? I've been trying to understand what zero-point energy and dark energy are-- is that related to that at all?

Thanks, I know these are pretty clumsy questions, and I may have some concepts tangled up real bad.


You got some parts right:

  • As the universe expands, more vacuum is created. So if you think about it, the more the universe expands the more vacuum there is. That actually lines up with another quantity in our currently accepted model of galaxy formation and evolution: the cosmological constant $\Lambda$ (dark energy), that is why some believe that $\Lambda$ represents vacuum. However, a closer look into the problem leads to huge discrepancies between what we observe and what we expect.

    That's is where the so-called zero point energy comes into play, it$^{[1]}$ "represents the difference between the lowest possible energy that a quantum mechanical system may have, and the classical minimum energy of the system". The problem is that we can actually measure the energy content of the universe in the form of $\Lambda$ and when we compare these two results the difference are of 100 orders of magnitude$^{[2]}$

  • When galaxies expands, the gravitational force between two pair of objects separated by a distance $d$ decreases, that is because the force changes as $\sim 1 / d^2$, so if the universe expands by a factor of $2$ the force decreases by a factor of $4$. There's a caveat here, however, objects move and they can be bound gravitationally bound. To give you an example, M31 is reasonably far away from us $\sim 1$ Mpc, and still, even as the universe expands, it moves towards us$^{[2]}$

  • Gravitational waves respond to a different phenomenon. Gravity intrinsically dictates the way in which space-time behaves. As such, if something affects the gravitational field of an object, the space-time metric is also affected and that perturbation can travel in the form of waves.

$^{[1]}$ https://en.wikipedia.org/wiki/Zero-point_energy
$^{[2]}$ Everything You Always Wanted To Know About The Cosmological Constant Problem
$^{[3]}$ The M31 Velocity Vector. II. Radial Orbit Towards the Milky Way and Implied Local Group Mass

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  • $\begingroup$ Thanks! Is it possible that the huge discrepancy there is just that the closer we measure to the "grain" of spacetime, the more we're detecting all potential energy in the entire universe? Like,if it's granular, general relativity sees the energy in the system as we experience it, and quantum physics sees ALL the energy that has EVER been poured into(?) the system from the beginning of time til the moment it's measured? Have they ruled that out yet? $\endgroup$ – Matt Judge Dec 3 '18 at 22:56

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