# Does red-shifted light cause expansion of space?

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Red shift is a result of the expanding universe, not the cause of it. Basic Doppler wave mechanics. Must keep the cart and horse in the right order. Question is did the original singularity have infinite energy? This is possible mathematically (1/zero). If it did, the universe will never cease to expand.

phinds
Gold Member
Red shift is a result of the expanding universe, not the cause of it. Basic Doppler wave mechanics. Must keep the cart and horse in the right order. Question is did the original singularity have infinite energy? This is possible mathematically (1/zero). If it did, the universe will never cease to expand.
That is not a necessary condition. Given that "dark energy" is constantly being created, it will continue to expand regardless of the initial conditions.

@phinds - Never thought of that.

Orodruin
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If inflation is correct there might never have been an initial singularity.

PeterDonis
Mentor
Basic Doppler wave mechanics.
Which assumes flat spacetime, but the spacetime of the universe as a whole is not flat. So your assertion does not explain why, as you put it, "redshift is the result of an expanding universe".

did the original singularity have infinite energy? This is possible mathematically (1/zero). If it did, the universe will never cease to expand
This is not correct as an assertion about possible mathematical models that are consistent with the Einstein Field Equation. One such model is a closed universe that recollapses; it has both an initial and a final singularity, and both have "infinite energy" by your definition.

As far as our actual universe is concerned, AFAIK nobody really believes there was an "initial singularity" with infinite energy; what is believed is that the classical GR model breaks down when spacetime curvature becomes large enough, and we need some other theory (the most likely candidate is a theory of quantum gravity) to tell us what happens in that regime. So the "initial singularity" in the mathematical models based on classical GR is an artifact of the model, not a claim about our actual universe.