Apologetic value of the acceleration of the expansion of the universe

Johannes.Ar

Member
Oct 13, 2019
10
2
Buenos Aires
Visit site
✟15,495.00
Country
Argentina
Faith
Catholic
Marital Status
Single
Most of you probably know that astrophysical observations of vastly different kinds have consistently shown since 1998 that the expansion of the universe is accelerating, actually that it has been accelerating since a time roughly midway between now and "big bang". I want to point out that this already established fact has apologetic value for monotheistic faiths holding creation ex nihilo. This is so because there are several plausible mechanisms whereby a contracting universe would not contract all the way into a singularity, i.e. a state of truly infinite density, but at some maximum density would "bounce" and start to expand. Therefore, in principle it is possible that the universe would undergo a cycle of indefinite duration (both from an infinite past and into an infinite future) consisting of the phases:

... big bounce - decelerated expansion - stop at max size - accelerated contraction - big bounce ...

Since such a cyclic universe would fit neatly the cyclic cosmologies of hinduism and buddhism, it is very good that the expansion of the universe is accelerating, as it invalidates this case. The reason of this invalidation is quite simple: let us assume that the universe indeed undergoes cycles. On the other hand, we know that the present cycle will not stop its expansion and then turn into contraction, but rather will expand forever and moreover in an accelerated way. Now, what could have changed between the previous cycles, in which the universe expanded to a maximum size/minimum density and then started to contract, and the present cycle? The only logical answer is that nothing could have changed, there were just no previous cycles.
 

SkyWriting

The Librarian
Supporter
Jan 10, 2010
37,279
8,499
Milwaukee
✟410,918.00
Country
United States
Faith
Non-Denom
Marital Status
Married
Politics
US-Others
Most of you probably know that astrophysical observations of vastly different kinds have consistently shown since 1998 that the expansion of the universe is accelerating, actually that it has been accelerating since a time roughly midway between now and "big bang". I want to point out that this already established fact has apologetic value for monotheistic faiths holding creation ex nihilo. This is so because there are several plausible mechanisms whereby a contracting universe would not contract all the way into a singularity, i.e. a state of truly infinite density, but at some maximum density would "bounce" and start to expand. Therefore, in principle it is possible that the universe would undergo a cycle of indefinite duration (both from an infinite past and into an infinite future) consisting of the phases:

... big bounce - decelerated expansion - stop at max size - accelerated contraction - big bounce ...

Since such a cyclic universe would fit neatly the cyclic cosmologies of hinduism and buddhism, it is very good that the expansion of the universe is accelerating, as it invalidates this case. The reason of this invalidation is quite simple: let us assume that the universe indeed undergoes cycles. On the other hand, we know that the present cycle will not stop its expansion and then turn into contraction, but rather will expand forever and moreover in an accelerated way. Now, what could have changed between the previous cycles, in which the universe expanded to a maximum size/minimum density and then started to contract, and the present cycle? The only logical answer is that nothing could have changed, there were just no previous cycles.

Our conclusions are wrong, or there were no previous cycles.
Either one.
 
Upvote 0

FrumiousBandersnatch

Well-Known Member
Mar 20, 2009
15,258
8,056
✟326,229.00
Faith
Atheist
... we know that the present cycle will not stop its expansion and then turn into contraction, but rather will expand forever and moreover in an accelerated way.
But we don't know that.

It's tautologically obvious that if the expansion continues indefinitely, there will be no contraction, but since cyclic cosmologies are predicated on the expansion not continuing indefinitely, the fact that expansion is currently occurring doesn't, of itself, invalidate them.
 
Upvote 0

Occams Barber

Newbie
Supporter
Aug 8, 2012
6,287
7,421
75
Northern NSW
✟981,569.00
Country
Australia
Faith
Atheist
Marital Status
Divorced
Since such a cyclic universe would fit neatly the cyclic cosmologies of hinduism and buddhism, it is very good that the expansion of the universe is accelerating, as it invalidates this case.
An acceleration phase is a necessary part of an expansion/contraction cycle. To go from rest (i.e., maximum contraction) to a given speed (i.e., a given rate of expansion) is impossible without an acceleration phase.

On the other hand, we know that the present cycle will not stop its expansion and then turn into contraction, but rather will expand forever and moreover in an accelerated way.
How do you know that the Universe will 'expand forever' in an 'accelerated way'?

Now, what could have changed between the previous cycles, in which the universe expanded to a maximum size/minimum density and then started to contract, and the present cycle? The only logical answer is that nothing could have changed,
If the rate of Universal expansion is accelerating then logically it is expanding faster today than it was yesterday. For this to happen something must have changed. If a change causing expansion to go faster is possible then why is it not possible to have change moving the Universe towards contraction?
OB
 
Upvote 0

Johannes.Ar

Member
Oct 13, 2019
10
2
Buenos Aires
Visit site
✟15,495.00
Country
Argentina
Faith
Catholic
Marital Status
Single
It's tautologically obvious that if the expansion continues indefinitely, there will be no contraction, but since cyclic cosmologies are predicated on the expansion not continuing indefinitely, the fact that expansion is currently occurring doesn't, of itself, invalidate them.

General Relativity allow for three regimes of expansion of space in an universe with matter (an empty universe will expand linearly):

a. one which at some point starts to accelerate towards an exponential regime (the actual case);
b. one which keeps decelerating indefinitely but never stops, a(t) = t^(2/3);
c. one which decelerates to a stop and turns into contraction.

According to General Relativity, it is not physically possible for a universe to switch from one expansion regime to another. Since our universe is in regime a, it will always be in that regime.
 
Upvote 0

Johannes.Ar

Member
Oct 13, 2019
10
2
Buenos Aires
Visit site
✟15,495.00
Country
Argentina
Faith
Catholic
Marital Status
Single
An acceleration phase is a necessary part of an expansion/contraction cycle. To go from rest (i.e., maximum contraction) to a given speed (i.e., a given rate of expansion) is impossible without an acceleration phase.

I am not referring to an initial stage of accelerated expansion (which an inflating non-cyclic universe also has), but to a stage of accelerated expansion that starts after a stage of decelarated expansion, which is the actual case, and accurs when the expansive effect of dark energy, whose energy density is constant over time, overwhelms the contractive effect of matter, whose energy density decreases with expansion.

How do you know that the Universe will 'expand forever' in an 'accelerated way'?

From General Relativity, which is a physical theory amply confirmed by observations. See my previous response to FrumiousBandersnatch.

If the rate of Universal expansion is accelerating then logically it is expanding faster today than it was yesterday. For this to happen something must have changed. If a change causing expansion to go faster is possible then why is it not possible to have change moving the Universe towards contraction?
OB

The ongoing change that starts the accelerated phase is that which I explained in the first paragraph of this post: the change in the balance of the energy densities of dark energy (which accordings to observations is just the Einstein-foreseen cosmological constant) and matter, as the expansion of space decreases the latter. General Relativity predicts this change and at the same time rules out any other change that will turn the acceleration into contraction.
 
Upvote 0

Michael

Contributor
Supporter
Feb 5, 2002
25,145
1,721
Mt. Shasta, California
Visit site
✟298,148.00
Faith
Christian
Most of you probably know that astrophysical observations of vastly different kinds have consistently shown since 1998 that the expansion of the universe is accelerating, actually that it has been accelerating since a time roughly midway between now and "big bang". I want to point out that this already established fact has apologetic value for monotheistic faiths holding creation ex nihilo.

Um, well, that's not actually "established fact". It's certainly a fact that the "majority (consensus) cosmology model" today would presume that cosmological redshift is caused by "space expansion" and "space expansion acceleration", whereas Edwin Hubble himself actually rejected that basic premise in favor of a "tired light" cause of cosmological redshift later in his life.

Until Hubble found evidence of cosmological redshift, the (island galaxy) universe was assumed to be static, and potentially eternal.

Hubble Eventually Did Not Believe in Big Bang: Associated Press

Expansion/acceleration (forever) interpretations of cosmological redshift are probably more "attractive" to monotheistic faiths which teach "creation ex nihilo", which might in fact be part of the reason why that particular interpretation of the cause of cosmological redshift is more "popular" than other potential explanations for cosmological redshift which wouldn't necessarily imply or require a "creation" event, let alone a creation ex-nihilo scenario, like a big bounce concept or a static universe.

Even if you presume that the universe is expanding now, and accelerating now, it's actually not a given that acceleration will continue indefinitely either.

In short, you're making a number of various assumptions about the observation of cosmological redshift that "just so happen" to agree with your specific brand of "faith", which another individual may not automatically agree with depending on their faith (like Buddhism) or lack thereof (atheism).
 
Upvote 0

Michael

Contributor
Supporter
Feb 5, 2002
25,145
1,721
Mt. Shasta, California
Visit site
✟298,148.00
Faith
Christian
General Relativity allow for three regimes of expansion of space in an universe with matter (an empty universe will expand linearly):

With introduction of a non zero constant (not necessarily space expansion however), GR also allows for a static universe. That was Einstein's initial impetus for adding a non zero constant in fact.

a. one which at some point starts to accelerate towards an exponential regime (the actual case);
b. one which keeps decelerating indefinitely but never stops, a(t) = t^(2/3);
c. one which decelerates to a stop and turns into contraction.

According to General Relativity, it is not physically possible for a universe to switch from one expansion regime to another. Since our universe is in regime a, it will always be in that regime.

Well, even that premise is not actually 100 certain in GR. It depends on what you think "dark energy" and/or the cause of acceleration might be, and whether you believe that dark energy will continue to remain constant throughout expansion. If you don't make the assumption that dark energy will remain constant indefinitely, it's conceivably possible that the universe could expand and accelerate for awhile, but eventually slow down over time and even conceivably contract again.

You can't entirely rule out the potential for later contraction simply based on what's happened in the past.

And of course all of these ideas are predicated on one's interpretation of the exact cause of cosmological redshift. :)
 
Upvote 0

FrumiousBandersnatch

Well-Known Member
Mar 20, 2009
15,258
8,056
✟326,229.00
Faith
Atheist
General Relativity allow for three regimes of expansion of space in an universe with matter (an empty universe will expand linearly):

a. one which at some point starts to accelerate towards an exponential regime (the actual case);
b. one which keeps decelerating indefinitely but never stops, a(t) = t^(2/3);
c. one which decelerates to a stop and turns into contraction.

According to General Relativity, it is not physically possible for a universe to switch from one expansion regime to another. Since our universe is in regime a, it will always be in that regime.
That assumes that dark energy is the 'cosmological constant' (vacuum energy) . If it is a scalar 'quintessence' field, there are a variety of possible scenarios, including becoming attractive rather than repulsive, as it is time-evolving, dynamic, and spatially dependent. Last I heard, we still don't know.
 
Upvote 0

Michael

Contributor
Supporter
Feb 5, 2002
25,145
1,721
Mt. Shasta, California
Visit site
✟298,148.00
Faith
Christian
That assumes that dark energy is the 'cosmological constant' (vacuum energy) . If it is a scalar 'quintessence' field, there are a variety of possible scenarios, including becoming attractive rather than repulsive, as it is time-evolving, dynamic, and spatially dependent. Last I heard, we still don't know.

It's frankly a little weird to actually be in agreement. :)
 
Upvote 0
This site stays free and accessible to all because of donations from people like you.
Consider making a one-time or monthly donation. We appreciate your support!
- Dan Doughty and Team Christian Forums