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Cosmo_Ken

Accelerating Expansion of the Universe?

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If it is correct that the expansion of the universe is accelerating, it seems that this would imply that the universe is not as old as previously thought?  This would lead to the conclusion that the most distant galaxies are not as far away as we previously thought, obviously they can not be older than the universe itself?  Do they have a model for the rate of expansion as a function of time post the above discovery, i.e. has it been accelerating ever since inflation?  

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2 hours ago, Cosmo_Ken said:

If it is correct that the expansion of the universe is accelerating, it seems that this would imply that the universe is not as old as previously thought?  

Can you explain why an accelerating universe implies a younger universe? And when you say not as old as 'previously thought', what age are you specifically speaking of?

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5 hours ago, Cosmo_Ken said:

If it is correct that the expansion of the universe is accelerating, it seems that this would imply that the universe is not as old as previously thought?  This would lead to the conclusion that the most distant galaxies are not as far away as we previously thought, obviously they can not be older than the universe itself?  Do they have a model for the rate of expansion as a function of time post the above discovery, i.e. has it been accelerating ever since inflation?  

Why? I fail to see your reasoning.

The universe after Inflation and the BB, has been in a deaccelerated state up until around 5 billion years ago if I recall correctly...then acceleration took hold, as the gravity of the energy/density of the mass in the universe/spacetime grew less dense, as opposed to the constant component driving the expansion...Acceleration is/was a natural occurrence. The mystery is of course what this component force we call DE is.

Edited by beecee

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My reasoning is that prior to the discovery of the accelerating expansion, the model would have had deceleration from the end of inflation until now, resulting in lower velocity of expansion as a function of time.  With the discovery of accelerating expansion, the velocity of expansion would have been increasing with time and would thus have taken less time for the universe to get to its current state (size), i.e. it must be younger than in the previous model???

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10 minutes ago, Cosmo_Ken said:

My reasoning is that prior to the discovery of the accelerating expansion, the model would have had deceleration from the end of inflation until now, resulting in lower velocity of expansion as a function of time.  With the discovery of accelerating expansion, the velocity of expansion would have been increasing with time and would thus have taken less time for the universe to get to its current state (size), i.e. it must be younger than in the previous model???

The universe has simply been decellerating for around 8.8 billion years and accelerating for the last 5 billion years. It's still 13.8 billion years old.  I still can't see any problem.

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If as you say, the universe has been accelerating for the last 5 billion years, this would result in a higher velocity of expansion profile during those 5 billion years than in the previous model, so that has to result in a difference.  The universe would take less time to get to its current size than in the old model.

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11 minutes ago, Cosmo_Ken said:

If as you say, the universe has been accelerating for the last 5 billion years, this would result in a higher velocity of expansion profile during those 5 billion years than in the previous model, so that has to result in a difference.  The universe would take less time to get to its current size than in the old model.

I would envisage that this has been taken into account. 

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As mentioned the acceleration portion occurs roughly when the universe is approx 7 Gyrs old. This is the start of the Lambda dominant era. Prior to Lambda dominant, the universe started in the radiation dominant ( BB to surface of last scattering (CMB)) followed by the matter dominant era.  Leading to our current Lambda dominant era.

 When this was discovered the age estimates were recalculated. This includes the distance measures beyond the Hubble horizon. 

Coincidentally the calculator on my signature is capable of showing the inflection crossover point for the matter dominant to the Lambda dominant. However it takes several calcs to fine tune the min max Stretch values (1/a) inverse scale factor "a".

One can also modify the datasets and see how the ratios of matter, radiation and Lambda affects expansion, Cosmological horizons, universe age, and distance measures.

If interested let me know and I will try to explain how to use the calc to show the inflection crossover point.

 

 

Edited by Mordred

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In 1965 I was in summer grammar school when I learned the age of the universe was between 15 and 20 billion years old.  Maybe the discovery of accelerated expansion, of 5 billion years ago, caused them to revise the age downward to 13.799 billion years, plus or minus 21 million years.  In what year was this discovery made and this number arrived at?

https://en.wikipedia.org/wiki/Age_of_the_universe

 

Edited by Airbrush

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On 02/09/2017 at 1:54 AM, Cosmo_Ken said:

If as you say, the universe has been accelerating for the last 5 billion years, this would result in a higher velocity of expansion profile during those 5 billion years than in the previous model, so that has to result in a difference.  The universe would take less time to get to its current size than in the old model.

That data wasn't available to earlier estimates of the age of the universe (which is why the discovery of acceleration was such a surprise).

8 hours ago, Airbrush said:

In 1965 I was in summer grammar school when I learned the age of the universe was between 15 and 20 billion years old.  Maybe the discovery of accelerated expansion, of 5 billion years ago, caused them to revise the age downward to 13.799 billion years, plus or minus 21 million years.  In what year was this discovery made and this number arrived at?

https://en.wikipedia.org/wiki/Age_of_the_universe

I think the change has been mainly driven by the increasingly accurate measurement and different sources of data.

This page has a table showing some of the estimates of the Hubble parameter (which allows the age to be derived): https://en.wikipedia.org/wiki/Hubble's_law#Observed_values

 

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1 hour ago, petrushka.googol said:

The Universe is not expanding (in the conventional sense), the space between galaxies is increasing 

What is the difference?

The phrase "expanding universe" is short-hand / analogy for "distances between things increasing by a changing scaling factor".

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On 9/2/2017 at 11:35 PM, Airbrush said:

In 1965 I was in summer grammar school when I learned the age of the universe was between 15 and 20 billion years old.  Maybe the discovery of accelerated expansion, of 5 billion years ago, caused them to revise the age downward to 13.799 billion years, plus or minus 21 million years.  In what year was this discovery made and this number arrived at?

https://en.wikipedia.org/wiki/Age_of_the_universe

 

Hard to believe they can be comfortable making that claim wrt the accuracy. I suspect they've been staring at the numbers a little too long, or Wiki is misquoting based only on their assumptions and associated perceived precision. They simply cannot be that confident in all the assumptions that is based on.

 

It wasn't that long ago they wondered why some Galaxy's appeared to be older than the Universe appeared to be.

Edited by J.C.MacSwell

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On 9/4/2017 at 0:16 PM, Strange said:

What is the difference?

The phrase "expanding universe" is short-hand / analogy for "distances between things increasing by a changing scaling factor".

The expansion of the Universe could be described as "the time evolution of space".  As an extension of this, the Universe could be described as "finite and unbounded".
 

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Umm no it cannot, to see the difference would require examining the time/dependant and time independancy of the two ds^2 line metrics. The two being commoving coordinates under the FLRW and the Schwartzchild.

In the former the coordinates evolve. (expand/contract) however under the Schwartzchild the spatial coordinates are static. 

Its extremely important not to confuse what changes under a given metric.

 

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