# Thread: Speed of light variable over time?

1. ## Speed of light variable over time?

This may be a stupid question, but here goes.

From my understanding, the universe (space-time) has expanded rapidly since the big bang. If the universe is considered a closed system then as it expands it does not gain any more energy than it had to start with.

My question is regarding the vacuum energy. If the universe is expanding, wouldn't the vacuum energy be stretched over a larger area, and thus be consistently declining over time? If this is true, could fluctuations in the vacuum energy have impacted the speed of light over the history of the universe?

edit: here's a follow up thought. it is theorized that light can go faster than c in a casimir vacuum, but what would the effect be on mass? obviously it would no longer be a vacuum at that point, but are there any thoughts on what would a lower vacuum energy mean for massive particles?

2. Ok.. since I got nothing from my fishing expedition post, I did some googling and found this...

http://arxiv.org/PS_cache/astro-ph/pdf/0605/0605173.pdf

While I can't claim to follow the whole thing, at least it is comforting that minds better than mine are toying with similar ideas.

3. My question is regarding the vacuum energy. If the universe is expanding, wouldn't the vacuum energy be stretched over a larger area, and thus be consistently declining over time? If this is true, could fluctuations in the vacuum energy have impacted the speed of light over the history of the universe?
No, conservation of energy still applies. If the universe is expanding, no energy added to it, then there is just more vacuum, null space. We got into this topic in the general science forum with the perpetual motion device. More vacuum space equals more free roam area for particles. Therefore, more mass. Energy = mass still applies but is proportional to the pressures exerted by the universe.

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