I Cosmological scale and the pressure of light....

[AshPowers]

TL;DR Summary

Expansion theory.

One of the things I have yet to come across in the explanation for the expansion of the universe is the effect of light...

Most all of the matter we observe out there are stars - fusing nuclei and radiating EM energy in incomprehensible quantities... And this has been happening since the dawn of time, right? We can only see very small fragments of that emitted light that make it's way to us.. But how much energy is being emitted? How much has been emitted?

If I am not mistaken, for the most part, by and far, these stars are just churning out the conversion of mass into energy. Everywhere you look, the dominating change that occurs everywhere is the conversion of mass into energy. Sure, fusion creates more complex forms of matter, supernovae make all the stuff more complex than iron which, yes, is an endothermic process, however, requires all of the mass->energy fusions of lighter nuclei to run it's course until G kicks into make all the heavier stuff... Even at the chemical level, entropy prevails...

SO, Kepler recognized way back when that EM radiation exerts a pressure on matter - a force that pushes..

Following that logic, at cosmological scales, can this EM pressure be responsible for the observed expansion of the universe? In whole? In part? How is this phenomenon integrated into the model?

 

[Orodruin]

Summary: Expansion theory.

And this has been happening since the dawn of time, right?

Not right. It took quite some time for the first stars to form.

Summary: Expansion theory.

these stars are just churning out the conversion of mass into energy.

In essence mass is a form of energy so nothing is being converted ”to energy”. Also, energy is not conserved in cosmology (apart from locally).

Summary: Expansion theory.

Following that logic, at cosmological scales, can this EM pressure be responsible for the observed expansion of the universe?

Not in the way you are likely imagining. The radiation pressure does influence the evolution of the Universe, but it is homogeneous and isotropic. The effects of radiation pressure have also been negligible more or less since matter-radiation equality, which occurred before stars were born.

 

[AshPowers]

1) Well, yes, it took some time to cool down and stars to star fusing, but there was still an expansion pressure energy from time 0.

2) Yes, mass is energy in a localized form, however, mass and energy do not have the same properties. In context to the OP, mass produces attractive forces upon other mass through gravitation. EM energy has a gravitational effect as well, but, it also has a radiation pressure it exerts as a pushing force.

3) Just how much EM energy is "out there" within the entire cosmos? Once emitted, it doesn't just disappear, or fade out over time, right? All of that EM energy is still within the cosmos, right? What kind of effect does all of that EM energy have on space? How can it be homogenously distributed everywhere? Was EM energy ALWAYS being produced at the same rate, everywhere, at the same time, forever?

 

[phinds]

3) Just how much EM energy is "out there" within the entire cosmos? Once emitted, it doesn't just disappear, or fade out over time, right? All of that EM energy is still within the cosmos, right? What kind of effect does all of that EM energy have on space?

Since it's the same in all directions, none. Also, "space" is just geometry. It is NOT, as pop-science would have you believe, something that can be stretched or bent. Things just move apart ("metric expansion") and move on geodesics (the "bending"). Also I suggest the link in my signature.

 

[Orodruin]

Yes, mass is energy in a localized form, however, mass and energy do not have the same properties.

This is wrong.

EM energy has a gravitational effect as well, but, it also has a radiation pressure it exerts as a pushing force.

This is wrong too. In fact, the accelerated expansion of the universe is hypothetically driven by dark energy, which would have a negative pressure.

3) Just how much EM energy is "out there" within the entire cosmos? Once emitted, it doesn't just disappear, or fade out over time, right?

Wrong. Energy conservation requires time translation invariance. An expanding universe is not invariant under time translations.

 

[phinds]

Just how much EM energy is "out there" within the entire cosmos? Once emitted, it doesn't just disappear, or fade out over time, right?

Wrong. It does.

To expand/restate what Orodruin has already pointed out, energy conservation is not a universal law, it is a local law. See: Sean Carroll on "Energy is not conserved"
http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/

 

[Bandersnatch]

SO, Kepler recognized way back when that EM radiation exerts a pressure on matter - a force that pushes..

Following that logic, at cosmological scales, can this EM pressure be responsible for the observed expansion of the universe? In whole? In part? How is this phenomenon integrated into the model?

This might have not come across very clearly in the responses so far, so let me clarify: The effect of radiation is included in the equations governing the expansion of the universe and it causes deceleration of the expansion - similar to matter.
This is because in general relativity pressure (just as energy) is a source of gravity, and it is the global effect of gravity that determines how the universe as a whole evolves.
The more mundane effect of radiation pressure transferring momentum that you talk about here is irrelevant as, on average, for any photon hitting a body from one side, there's another hitting it from the opposite side. Furthermore, the universe is sparse enough that the vast majority of photons ever emitted could have traveled for the entire history of the universe (ever since recombination) without ever interacting with anything - which is necessary for momentum transfer.

You can find more about how the radiation is integrated into the cosmological equations by looking up the 'FLRW metric' and the 'cosmological equation of state'. Depending on your background, picking up a textbook first might be recommended.