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Inflation April 2, 2012

Posted by CosmicThespian in Word of the week.
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Article has moved: the astronomy word of the week is “inflation”.

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1. Steve Nerlich (@cheapastro) - April 8, 2012

Problem with this statement:

If there is a galaxy sitting 13.8 billion light years away, then there hasn’t been enough time since the Universe was formed for the light to reach us yet!

Well we can’t receive light that it is more than 13.7 billions year old. But remember the observable universe has a radius of 46 billion light years. I don’t think you are considering expansion in the above statement. It’s quite possible for us to have received light (emitted in the past) from an object that is now 13.8 billion light years away

cosmicthespian - April 10, 2012

Steve, thanks for your comments. You are correct that such a galaxy would be 46 billion light years away – that’s the problem with using “light travel time” as a distance in an expanding universe. I worded that badly — it should probably say “if it takes light 13.8 bly to reach us, then there hasn’t been enough time…” or something like that. Didn’t want to go off on a “light travel time” vs “proper distance” tangent here. You’ll be happy to know I actually cover this in next week’s post on “light-years”!

On the second point regarding evolution of curavature — I’m not sure. You might be right…it’s been a while since my cosmology course. I think the main point still stands though without getting overly bogged down in details. The post was getting too long as it is (and this is after cutting it down from nearly twice its final length!).

Thanks for some fact checking! I’ll add in some footnotes to your comments for clarification.

2. Steve Nerlich (@cheapastro) - April 8, 2012

And problem with this statement too:

Inflation means the Universe could have any shape right after the Big Bang but that curved space would get smoothed out in less than an eyeblink leaving a Universe that is uniformly flat.

This is only true up to point. If the universe continues to expand, it should not be possible for it to remain flat due to declining energy density – it should go saddle-shaped. Hence the need for ‘dark energy’ to maintain the universe’s density (and geometry) in the face of ongoing expansion.


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