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Don, you have talked about the idea of a outward force to produce the expansion of the universe on your own blog, and I'll leave it to others who want to pick up that discussion there. I argue that you have fallen into an Aristotelian trap. As I recall your description on your blog, you seem to be envisioning an invisible heaven to which all normal matter is drawn by a divine force.

As Galileo correctly asserted and Newton formalized in his first law, there is no need for any outside force to cause the outward motion of the galaxies (though neither knew about galaxies in particular). Inertia is sufficient, assuming that the Big Bang theory is a valid initial event. I discuss this a bit in the cosmology sections of Physics Decade by Decade.

The issue here is the apparent acceleration of the expansion, rather than the deceleration that would be expected due to gravitational attraction among the galaxies.

The article cited argues that the acceleration may be an illusion due to our being in an unusually galactically-sparse region of the universe. The authors claim, as you do, that there is no need for dark energy. But they claim it is because there is no acceleration.

Another (and more common) explanation for the acceleration is the Cosmological Constant of General Relativity.

Fred Bortz -- Science and technology books for young readers (www.fredbortz.com) and Science book reviews (www.scienceshelf.com)