PDA

View Full Version : Questions for Ep.78



Steve Limpus
2008-Feb-29, 12:24 AM
Pamela asked for some questions for next week's show. I think I know the shape of the universe that Pamela will cite to explain the parallel lasers zapping her up the back of her head (and I don't want to give away the surprise for anyone else) but I would be very interested to hear the evidence for that particular shape.

Also, I've heard Pamela refer to our observable universe being 3-4% of the entire universe, but try as I might I've not come across the reasoning behind this estimate.

Thirdly, I'd love to hear about co-moving distances in the expanding universe, and the hubble horizon.

dcl
2008-Apr-24, 02:56 AM
As for Dr. Gay's statements regarding the shape of the Universe, I believe she is mistaken. For my views regarding the shape of the Universe, see my thread entitled "The Shape of the Universe".

Co-moving distances are distances that would be fixed if the Unierse were not expanding. Suppose that the distance between some pair of galaxies would not be changing if the Universe were not expandinig. Actually, that distance IS increasing because the Universe is expanding. Those galaxies are said to be co-moving in terms of expansion of the Universe.

johnskytalker
2009-Dec-05, 11:44 AM
I woke this morning to the sound of Ep 78 playing in the bedroom; my wife had constructed a podcast playlist to help her sleep and this was the one playing when I woke. Pamela was saying that if something like the amount of matter in the universe were different by only one part in 467 sextillion we would be living in a completely different universe, which implies that there is some physics going on we don't yet understand.

Now Ep 78 was a while ago, but not so long even by the scale of human civilization, so maybe we've learned something since then. But the statement prompted a question for me:

What if the constants aren't "fine tuned"? (See, I think we still use creationist/ID terminology, and to disadvantage, perhaps.) What if the constants we observe are just what they are now, and sort of like the way three phases of water coexist in equilibrium at a specific temperature and pressure, our experience of the universe is at a cosmic "triple point"? The constants would appear to be "fine tuned" in that case, but (presumably) only by an observer who only happened to exist because the universe was currently at that "triple point".

I'm an electrical engineer, not an astrophysicist. I'm not even a physicist. So maybe I'm just displaying my enormous ignorance. But I love to learn, and like science a lot (and am incidentally grateful that I no longer have to be amazed that "God" thought all this up and fine tuned it just this way because that's the way it needed to be for life to exist, etc.).

Middenrat
2009-Dec-05, 05:17 PM
...

Also, I've heard Pamela refer to our observable universe being 3-4% of the entire universe, but try as I might I've not come across the reasoning behind this estimate.

...

I'm not the expert you're waiting on to answer this, but the rest of the universe has already receded out of sight (beyond the Hubble Horizon) during the era of rapid expansion following the Big Bang, far in excess of the speed of light, so we can never receive any information about those regions.

Dro2
2009-Dec-07, 11:10 PM
I'm not the expert you're waiting on to answer this, but the rest of the universe has already receded out of sight (beyond the Hubble Horizon) during the era of rapid expansion following the Big Bang, far in excess of the speed of light, so we can never receive any information about those regions.

I was under the impression that Hubble could see 10+/- lights years. This seems quite a bit more than 4% Did I miss something possibly?

Or do you/Pamela mean we only see 4% because the rest just isnt bright enough to be seen?

Middenrat
2009-Dec-08, 01:29 AM
I was under the impression that Hubble could see 10+/- lights years. This seems quite a bit more than 4% Did I miss something possibly?

Or do you/Pamela mean we only see 4% because the rest just isnt bright enough to be seen?
I should maybe listen to #78 before I put my foot in my mouth, but we're having a conversation here so I'll just trust to a Cosmologist to put me right...
I guess you mean 10 billion light years referring to HST's resolution, and while that is indeed greater than 4% of our Universe's age according to BBTheory, it cannot resolve images from the 96% of the Universe which has receded from view and continues to recede faster than the speed of light. The intervening expansion of space, giving us ever-increasing redshift with distance, is happening so fast that the light (or any information) will never catch us up. Therefore it is invisible.