Size of universe after inflation?
RBZan...@aol.com
http://physics.stackexchange.com/questions/32917/size-of-universe-after-inflation
Having said this, Don Page has suggested a lower bound for the size of the whole universe at the end of inflation, and his answer is 10 10 10 122 10^10^10^122 cubic megaparsecs. However I think you should regard this as extremely speculative
Size of universe after inflation?
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Wikipedia states the period of inflation was from 10 −36 sec to around 10 −33 sec or 10 −32 sec after Big Bang, but it doesn't say what the size of the universe was when inflation ended. Just saw a Brian Greene show on the Multiverse and I thought I heard him say size was galactic scales when inflation ended. However I've also read size was about a basketball. Are there multiple theories with different resulting sizes? Does 'size' even mean anything in this context? | |||||
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With the proper definition of the "size" of the universe, this question does make sense. The standard model of cosmology would say that the universe is infinite which therefore does not have a "size". However, if we take into account that the big bang occurred 13.7±0.17 billion years ago we can define a meaningful size for the observable universe. You might, for example, define the size of the observable universe as the distance a photon could have traveled since the big bang. Consider, for example, a cosmic microwave background (CMB) photon that was emitted as visible light about 379,000 years after the big bang and is just now hitting our microwave detectors (the redshift is z=1089): that photon has been traveling for 13.7 billion years so it has traveled a distance of 13.7 billion light years. So you might imagine that the current radius of the observable universe is 13.7 billion light years. However, during this time the universe has been expanding, so the current position of the matter that emitted that photon will now be 46.5 billion light years away. (By now, the little 10 −5 bumps on the CMB will have condensed into galaxies and stars at that distance.) This gives a diameter of the current observable universe of 93 billion light years. Note that as time passes, the size of the observable universe will increase. In fact it will increase by significantly more than two (to convert radius to diameter) light years per year because of the continued (accelerating) expansion of the universe. Also note that we will not be able to use photons (light) to explore the universe earlier than 379,000 years after the big bang since the universe was opaque to photons at that time. However, in the future we could conceivably use neutrinos or gravitational wave telescopes to explore the earlier universe. So given a size of the current observable universe, we can ask how big was that volume at any particular time in the past. According to this paper at the end of inflation the universe's scale factor was about 10 −30 smaller than it is today, so that would give a diameter for the currently observable universe at the end of inflation of 0.88 millimeters which is approximately the size of a grain of sand (See calculation at WolframAlpha). It is believed that inflation needed to expand the universe by at least a factor of 60 e-foldings (which is a factor of e 60 ). So using WolframAlpha again we find that the diameter of the universe before inflation would have been 7.7×10 −30 meters which is only 48,000 Planck lengths. Perhaps Brian Greene was talking about the size of the observable universe at the time when the CMB photons started traveling towards us. That happened 379,000 years after the big bang at a redshift of 1098 which means the universe was about 84.6 million light years in diameter which, per WolframAlpha, is about half the diameter of the local super cluster of galaxies or about 840 times the diameter of our galaxy. | |||||||||||||||||||||
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In the simplest model of the universe, the FLRW metric, the universe is infinite and has always been infinite right back to the Big Bang. Inflation doesn't change this assumption. So it makes sense to ask, for example, how big a Planck volume became during inflation, but it doesn't make sense to ask how big the whole universe is. (Depending on what you take as the inflation scale factor a Planck volume ended up about 10 −27 m 3 and this is a lot smaller than a basketball.) Having said this, Don Page has suggested a lower bound for the size of the whole universe at the end of inflation, and his answer is 10 10 10 122 cubic megaparsecs. However I think you should regard this as extremely speculative. | |||||
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Answer to the inflation riddle is simple, it is staring everyone in the face. You can not explain the early universe in classical terms, the
size/volume whatever you want to think of before and after the
inflationary period is irrelevant. BUT Time it's self is the first dimension, a framework of sorts, in which all the other dimensions rest, it is the container, not a point, like the exponentially dividing cell when human life begins. Time is nothing more than exponential dimension |
Vic Stenger
http://physics.stackexchange.com/questions/32917/size-of-universe-after-inflation
Having said this, Don Page has suggested a lower bound for the size of the whole universe at the end of inflation, and his answer is 10 10 10 122 10^10^10^122 cubic megaparsecs. However I think you should regard this as extremely speculative
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Lawrence Crowell
On Monday, November 4, 2013 2:09:40 PM UTC-6, Bob Zannelli wrote:
http://physics.stackexchange.com/questions/32917/size-of-universe-after-inflation
Having said this, Don Page has suggested a lower bound for the size of the whole universe at the end of inflation, and his answer is
In the end the problem might be trying to ask what physics determined the exact shape of a snowflake. We have an understanding to the general symmetry of a snowflake, but we have no predictive model for determining how a particular shape comes about. The situation is similar, for the detailed configuration is something that emerges with respect to some quantum number or topological index. This means the configuration emerges by purely stochastic means as far as we can ever determine.
LC
meekerdb
On Nov 4, 2013, at 1:09 PM, RBZan...@aol.com wrote:
http://physics.stackexchange.com/questions/32917/size-of-universe-after-inflation
Having said this, Don Page has suggested a lower bound for the size of the whole universe at the end of inflation, and his answer is 10 10 10 122 10^10^10^122 cubic megaparsecs. However I think you should regard this as extremely speculative
Amusing that he states it in cubic Mpc. What would in be in cubic nanometers?
Brent
RBZan...@aol.com
On Nov 4, 2013, at 1:09 PM, RBZan...@aol.com wrote:
http://physics.stackexchange.com/questions/32917/size-of-universe-after-inflation
Having said this, Don Page has suggested a lower bound for the size of the whole universe at the end of inflation, and his answer is 10 10 10 122 10^10^10^122 cubic megaparsecs. However I think you should regard this as extremely speculative
Amusing that he states it in cubic Mpc. What would in be in cubic nanometers? Question for the mathematically challenged.Vic
Wikipedia states the period of inflation was from 10 −36 sec to around 10 −33 sec or 10 −32 sec after Big Bang, but it doesn't say what the size of the universe was when inflation ended. Just saw a Brian Greene show on the Multiverse and I thought I heard him say size was galactic scales when inflation ended. However I've also read size was about a basketball.
Are there multiple theories with different resulting sizes? Does 'size' even mean anything in this context?
With the proper definition of the "size" of the universe, this question does make sense. The standard model of cosmology would say that the universe is infinite which therefore does not have a "size". However, if we take into account that the big bang occurred 13.7±0.17 billion years ago we can define a meaningful size for the observable universe. You might, for example, define the size of the observable universe as the distance a photon could have traveled since the big bang.
Consider, for example, a cosmic microwave background (CMB) photon that was emitted as visible light about 379,000 years after the big bang and is just now hitting our microwave detectors (the redshift is z=1089): that photon has been traveling for 13.7 billion years so it has traveled a distance of 13.7 billion light years. So you might imagine that the current radius of the observable universe is 13.7 billion light years. However, during this time the universe has been expanding, so the current position of the matter that emitted that photon will now be 46.5 billion light years away. (By now, the little 10 −5 bumps on the CMB will have condensed into galaxies and stars at that distance.) This gives a diameter of the current observable universe of 93 billion light years. Note that as time passes, the size of the observable universe will increase. In fact it will increase by significantly more than two (to convert radius to diameter) light years per year because of the continued (accelerating) expansion of the universe. Also note that we will not be able to use photons (light) to explore the universe earlier than 379,000 years after the big bang since the universe was opaque to photons at that time. However, in the future we could conceivably use neutrinos or gravitational wave telescopes to explore the earlier universe.
So given a size of the current observable universe, we can ask how big was that volume at any particular time in the past. According to this paper at the end of inflation the universe's scale factor was about 10 −30 smaller than it is today, so that would give a diameter for the currently observable universe at the end of inflation of 0.88 millimeters which is approximately the size of a grain of sand (See calculation at WolframAlpha).
It is believed that inflation needed to expand the universe by at least a factor of 60 e-foldings (which is a factor of e 60 ). So using WolframAlpha again we find that the diameter of the universe before inflation would have been 7.7×10 −30 meters which is only 48,000 Planck lengths.
Perhaps Brian Greene was talking about the size of the observable universe at the time when the CMB photons started traveling towards us. That happened 379,000 years after the big bang at a redshift of 1098 which means the universe was about 84.6 million light years in diameter which, per WolframAlpha, is about half the diameter of the local super cluster of galaxies or about 840 times the diameter of our galaxy.
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In the simplest model of the universe, the FLRW metric, the universe is infinite and has always been infinite right back to the Big Bang. Inflation doesn't change this assumption.
So it makes sense to ask, for example, how big a Planck volume became during inflation, but it doesn't make sense to ask how big the whole universe is. (Depending on what you take as the inflation scale factor a Planck volume ended up about 10 −27 m 3 and this is a lot smaller than a basketball.)
Having said this, Don Page has suggested a lower bound for the size of the whole universe at the end of inflation, and his answer is 10 10 10 122 cubic megaparsecs. However I think you should regard this as extremely speculative.