Here's an idea I thought about; more of a thought experiment than anything:
The universe is essentially the same as the universe 14 billion years ago, just stretched. However, all matter stretches with the universe, so it doesn't seem like anything is stretching at all to us. Even atoms "stretch". There is no new universe "material" being "added" constantly; the universe is just stretching really fast.
Does this violate any physics principle, a.k.a. is there a simple way to disprove this?
The size of atoms is determined by the strength of the electromagnetic force, the mass of the electron and some other constants like the value of Planck's constant. If the size of atoms was changing it means that one or more of these constants must be changing.
The trouble is that these fundamental constants crop up all over the place in physics, and if they were changing it would affect all sorts of other things and we would certainly have noticed. That means we can rule out your suggestion.
In your model, of everything stretching, there would be no way to observe any stretch. We would live in static dimensions as far as we are concerned.
It is our observations of the way the stars, galaxies and clusters of galaxies behave that has led to the idea of an expanding universe :
Hubble inferred the recession velocity of the objects from their redshifts, many of which were earlier measured and related to velocity by Vesto Slipher in 1917.[12]
It was General Relativity that gave the mathematics to explain these observations. Inherent in this interpretation is that the stars, galaxies and clusters of galaxies are not measurably expanding.
In his/her comment @userLTK states the true reason:
The tiny (on that scale) dark energy force wouldn't cause atoms to expand any more than gravity causes atoms to collapse.
In general relativity it is the cosmological constant that generates this dark energy for the expansion of the universe. Its value has been explored from observations and its effect is very small, within the planetary system for example, and limits are extracted for this.. It is immaterial when it comes to the other three forces which are much stronger than the gravitational forces.
So your idea violates observations.
