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If our universe is inflating, which means it is getting bigger and bigger in size, and every thing it consists of is also enlarging, in a special way such that the mass of the universe remains constant and only the volume changes.

In that case, how will we observe the changes in the physical layout of the universe? In particular, are these guesses correct?

  1. We will observe that the speed of light is decreasing, as light usually travels $3*10^8$m, in a second, but now since the universe is inflating, it will travel something lesser then that for instance $1.5*10^8$

  2. As far as observation is considered, I dont think we will see any changes, since the retina of our eyes would then also have enlarged,

  3. As far as physics of the universe is considered I think the planets will keep to their orbits as their mass has not changed a bit and they maintain same distance with other celestial bodies as they used to,

David Z
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Tomarinator
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1 Answers1

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See spacetime expansion and universe expansion?, which addresses some of your questions. In particular the planetary orbits won't change because on the scale of the solar system the gravitational force between the planets far outweighs the expansion of the universe. The retinas in our eyes also don't expand, again because the intermolecular forces holding them together are far stronger than the forces caused by the expansion.

Actually a quick note on terminology: the term "inflation" applies only to an initial rapid expansion of the universe shortly after the Big Bang. The term used for the current growth of the universe is simple "expansion".

To answer the first part of your question, the speed of light is (locally) constant i.e. it's 3 x 10$^8ms^{-1}$ and doesn't change as the universe expands. On very large scales, i.e. gravity cluster scales, the expansion does overcame gravity so on large scales we see the expansion as the red shifts of distant galaxies.

The matter in the universe remains (approximately) constant, however an important contribution to the total energy of the universe is dark energy. Unlike mass, dark energy is a property of spacetime so it increases at the same rate as the universe expands. That means in the future, as matter is diluted by the exansion the universe will increasingly be dominated by dark energy.

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John Rennie
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