Dark energy and its effect on the observable universe.

[Sorcerer]

Since the observable universe is expanding at the speed of light, (ie we can see a light second per second distance into the currently unobservable universe), yet the universes expansion is thought to be accelerating due to dark energy, does this mean we can extrapolate to a point where the size of the observable universe reaches a limit? (because the accelerated expansion makes the outer reaches of the observable universe again expand away from us faster than the speed of light)

What happens beyond this point? Do we see the universe we observed at the fringes frozen in time and this freezing of time spread back towards us as the observable universe shrinks due to the accelerated expansion outstripping the speed of light at those distances? Does this frozen image red shift?

[Strange]

Since the observable universe is expanding at the speed of light, (ie we can see a light second per second distance into the currently unobservable universe), yet the universes expansion is thought to be accelerating due to dark energy, does this mean we can extrapolate to a point where the size of the observable universe reaches a limit? (because the accelerated expansion makes the outer reaches of the observable universe again expand away from us faster than the speed of light)

 

"Speed of expansion" doesn't really make sense. Expansion is a scaling effect. The distances between two points is continuously being multiplied by a scaling factor. This means that things are (all) moving apart from one another and the speed of separation is proportional to how far apart they are (this is just simple arithmetic, nothing to do with cosmology). As a consequence there are, and always have been, points in the universe that are sufficiently far apart that their separation speed is greater than the speed of light. Rather counter-intuitively, we can see galaxies that are receding at more than the speed of light.

 

The speed of light limit only applies locally, to objects moving through space, so it doesn't apply to the expanding universe.

Edited September 1, 2015 by Strange

[swansont]

Since the observable universe is expanding at the speed of light, (ie we can see a light second per second distance into the currently unobservable universe),

 

How do we see into the unobservable universe?

 

Also since the observable universe is > 13.7 billion LY in radius (by a factor of >3), how do you reconcile this with the assertion that it's expanding at c?

[Mordred]

The expanding at greater that c is based on a misnomer.

 

Hubbles law states the greater the distance the greater the recessive velocity. This is based on seperation distance.

 

[latex]V_{rec}=H_od[/latex]

 

The rate of expansion today is 70 km/Mpc/sec.

 

So let's crunch some numbers. Take an object 5 Mpc away.

 

(70 km/Mpc)/(sec*5 Mpc)=the recessive velocity.

 

However the rate of expansion at that location is still 70 km/Mpc/sec.

[Sorcerer]

 

How do we see into the unobservable universe?

 

Also since the observable universe is > 13.7 billion LY in radius (by a factor of >3), how do you reconcile this with the assertion that it's expanding at c?

It's only true if we assumed a universe that suddenly became static I guess. Then the observable universe would expand outward at c since the light would then have the time to travel to us to be observed from points which were previously unobservable. However, now you point it out I would change that increase in the size of the observable universe (with mordreds help) to (c- V_rec)/time up to the point where V_rec = c, beyond which it is permanently unobservable.

The expanding at greater that c is based on a misnomer.

 

Hubbles law states the greater the distance the greater the recessive velocity. This is based on seperation distance.

 

[latex]V_{rec}=H_od[/latex]

 

The rate of expansion today is 70 km/Mpc/sec.

 

So let's crunch some numbers. Take an object 5 Mpc away.

 

(70 km/Mpc)/(sec*5 Mpc)=the recessive velocity.

 

However the rate of expansion at that location is still 70 km/Mpc/sec.

Hubble afaik was unaware of dark energy, how does his law appear when we factor in an accelerating expansion?

 

Are there parts of the observable universe which are coming into view which were previously outside our hubble volume? IE where V_rec > c we can never observe (change in again), because (new) light can never reach us from there, but there are points between 13.7billion light years and V_rec > c which we can observe given enough time. IE is V_rec > c where d=13.7 billion light years or is it lower than c, at which distance is V_rec > c?

 

Since the universes expansion is accelerating isn't it reasonable to assume that at some point our hubble volume will begin to shrink again as V_rec > c will tend towards a maximum and then begin to decrease in diameter?

 

If so:

 

What will the galaxies on the edge of the hubble volume then appear to do?

Will they stop in a time and red shift similar to as if they were approaching the event horizon of a black hole?

 

Then:

If we extrapolate further, at some point won't V_rec > c be shorter than the smallest distance possible between 2 fundamental fermionic particles?

Rather counter-intuitively, we can see galaxies that are receding at more than the speed of light.

 

 

 

Are these images of galaxies frozen in time and becoming more redshifted over time? How can we observe them if they weren't once receeding at less than c?

Edited September 4, 2015 by Sorcerer

[Mordred]

If you look at recessive velocities. At the Hubble sphere the recessive velocity will Start to appear greater than c. You can use the lightcone calculator in my signature to see this. For example at redshift z=1090 Cosmic event horizon the recessive velocity appears to be 3.1 c. However this is an apparent not a true velocity.

 

Hubble only knew the universe was expanding. He didn't state why.

This article written by someone I've had numerous discussions with explains it best. ( he does have a PH D in philosophy of cosmology).

 

http://tangentspace.info/docs/horizon.pdf:Inflation and the Cosmological Horizon by Brian Powell

You can find his numerous papers on arxiv as well. I still have a copy of his dissertation.

He is a member on another forum, so kept this article as low math as possible.

[Sorcerer]

Is there inverse yet parallel simarlaity where by the observation of an object approaching a black holes event horizon and an obect approaching a hubble volumes event horizon can be compared. Where one is an apparent velocity of recession caused by gravity stretching space in length away and the other is an apparent velocity of recession caused by dark energy inflating space in length away?

 

Are these inverse similarities considered in an models of the universe? For instance is there a 2 halves of a whole symmetry?

Edited September 4, 2015 by Sorcerer