What holds us down?

Gravity or some other force?

Gravity or some other force?

The answer is going to vary based on what model you're more interested in asking about. For example, there's the Universal Acceleration concept, with the Earth being a disc accelerating ever upwards at 1G, then there's the Infinite Earth model where the Earth need not be accelerating but would still exhibit a uniform gravitational field above the surface, there's some other models that have a downward force due to a pressure referred to as denpressure, and I'm sure I'm probably forgetting a few others that have been discussed here. Did you have a particular model in mind?

Gravity or some other force?

Probably gravity.
But, can we define gravity?

What is the Infinite Earth theory? I wasn't able to find it online.

Density keeps us down. This depends on the medium we are in, we are more dense than air so we fall through air and keep falling untill we hit something that can support us. This can easily be proven with simple experiments. There is no need for a force to be Pulling or pushing anything down its literally as simple as being more dense or less dense than your surroundings.  So basically the medium determines whether something falls or rises.

Density keeps us down. This depends on the medium we are in, we are more dense than air so we fall through air and keep falling untill we hit something that can support us. This can easily be proven with simple experiments. There is no need for a force to be Pulling or pushing anything down its literally as simple as being more dense or less dense than your surroundings.  So basically the medium determines whether something falls or rises.

Density is not a vector quantity, it has no direction. So how could it cause on object to always move toward or away from the earth but never sideways?

Density keeps us down. This depends on the medium we are in, we are more dense than air so we fall through air and keep falling untill we hit something that can support us. This can easily be proven with simple experiments. There is no need for a force to be Pulling or pushing anything down its literally as simple as being more dense or less dense than your surroundings.  So basically the medium determines whether something falls or rises.

Why do objects with different weights/densities fall at the same rate? Bonus question: Why do objects with different weights/densities fall at the same rate in a vacuum?