Where are we

[StringJunky]

 

So our ability to see that far isn't bounded by our technology; it's bounded by the light's ability to reach us from that far away, correct? New technology isn't going to make the pole longer.

Yes, I think so. It's a limit of physics. I'm sure I'll be corrected if I'm wrong. The Hubble Limit is the edge.

Edited December 5, 2016 by StringJunky

[Phi for All]

Edit: Phi knows what I meant. This one's without the donkey.

 

Doesn't it say a lot about modern usage that the first internet image of this is with a man instead of a donkey? I often feel this way.

[AbstractDreamer]

 

That stick is too short, or string too long, or carrot too big!

 

The point is the carrot is supposed to be out of reach?

[Mordred]

Yes, I think so. It's a limit of physics. I'm sure I'll be corrected if I'm wrong. The Hubble Limit is the edge.

No the Hubble limit isn't the edge. The cosmological event horizon is.

[StringJunky]

No the Hubble limit isn't the edge. The cosmological event horizon is.

What's the difference?

[Mordred]

Hubble horizon is the distance light can reach us based upon the linear equation v=Hd. It doesn't account for the accelerating expansion.

 

https://en.m.wikipedia.org/wiki/List_of_cosmological_horizons

 

See the equations under Hubble horizon and event horizon. Particle horizon being simply c×age of universe.

 

This wiki article places it at 4.1 Gpc.

 

The cosmological event however is 14.3 Gpc. Theoretically the farthest we will ever be able to recieve a signal in the future is roughly 19 Gpc

 

https://en.m.wikipedia.org/wiki/Observable_universe

 

Think of it this way without going into too much detail. Hubble horizon was at one time the theoretical limit before we discovered the cosmological constant.

Edited December 5, 2016 by Mordred

[geordief]

Either infinite or finite but unbounded.

 

A finite and bounded universe would have a definite center.

Are there any theories that posit the universe as being finite and bounded?

 

What implications might there be?

[StringJunky]

 

That stick is too short, or string too long, or carrot too big!

 

The point is the carrot is supposed to be out of reach?

It will always be the same distance however far you walk.

[AbstractDreamer]

It will always be the same distance however far you walk.

You dont need to walk anywhere, just arch your back until the RED LINE is vertical, and hold your arms above your head.

Or just swing the carrot until you can grab it.

 

What's the difference?

 

I'm going to get this wrong but here's my go:

 

The Hubble limit is our particle horizon or "observable" universe. Its actually not calculated by the distance to the furthest object we can see, but how far a photon emitted from us could have travelled. This is all based on the history of the universe since t=0

 

Things beyond the observable universe can be moving away at superluminal velocity, but we might be able to observe them one day if the scale factor decreases.

 

The future event horizon is much larger, its is a prediction based on the evolution of scale factor of expansion, from now until the end of time. It is the limit beyond which will never influence us, because they will always stay ahead of a photon emitted from us today. I guess this assumes that expansion will never flip into contraction.

Edited December 5, 2016 by AbstractDreamer

[StringJunky]

Hubble horizon is the distance light can reach us based upon the linear equation v=Hd. It doesn't account for the accelerating expansion.

 

https://en.m.wikipedia.org/wiki/List_of_cosmological_horizons

 

See the equations under Hubble horizon and event horizon. Particle horizon being simply c×age of universe.

 

This wiki article places it at 4.1 Gpc.

 

The cosmological event however is 14.3 Gpc. Theoretically the farthest we will ever be able to recieve a signal in the future is roughly 19 Gpc

 

https://en.m.wikipedia.org/wiki/Observable_universe

 

Think of it this way without going into too much detail. Hubble horizon was at one time the theoretical limit before we discovered the cosmological constant.

Right. Thanks. I thought just beyond the hubble was the point the recession velocity due to expansion exceeded light speed.

[Mordred]

close but not quite. We can see superluminal recessive velocity. At z=1104 we can see a recessive velocity of 3.2 c.

Right. Thanks. I thought just beyond the hubble was the point the recession velocity due to expansion exceeded light speed.

This is correct which is why its handy for us.

[AbstractDreamer]

i need more homework

[Mordred]

Your making excellent progress though. Feel proud of how much you learned in such a short time. Oh I should have mentioned earlier use the lightcone calculator in my signature. Its a valuable aid.

Edited December 5, 2016 by Mordred

[36grit]

At one time the universe was the size of a pea, and at that moment it had a finite size. It was the size of a pea. I'm not to bright, but I thought the CMB was the inner edge of the expanded pea and that we were looking at all the matter that was ever created by the original event, and that, that center was a matter of relative perspective.

But what ya'll seem to be saying is that the alien 4 billion light years away is seeing stars that exist much farther than we can see.

If that's true, then how do we know the age of the universe? After all, there maybe another alien 4 billion light years from him in the same outward direction.

[StringJunky]

At one time the universe was the size of a pea, and at that moment it had a finite size. It was the size of a pea. I'm not to bright, but I thought the CMB was the inner edge of the expanded pea and that we were looking at all the matter that was ever created by the original event, and that, that center was a matter of relative perspective.

But what ya'll seem to be saying is that the alien 4 billion light years away is seeing stars that exist much farther than we can see.

If that's true, then how do we know the age of the universe? After all, there maybe another alien 4 billion light years from him in the same outward direction.

They can infer from reversing the rate of expansion and distances between galaxies how long ago it was that they were all physically connected into a dense mass.

[geordief]

They can infer from reversing the rate of expansion and distances between galaxies how long ago it was that they were all physically connected into a dense mass.

That is the Observable Universe,is it not?

 

Is there a claim that the Unobservable Universe was also ,by inference gathered into a small area?

 

Is it not rather that some of the Unobservable Universe (without knowing how much**) was so gathered?

 

By the way is the Universe at around the time of the Big Bang considered to be finite in size in its own terms or just from our present perspective ?

 

 

**perhaps all of it ?

Edited December 6, 2016 by geordief

[StringJunky]

That is the Observable Universe,is it not?

 

Is there a claim that the Unobservable Universe was also ,by inference gathered into a small area?

 

Is it not rather that some of the Unobservable Universe (without knowing how much**) was so gathered?

 

By the way is the Universe at around the time of the Big Bang considered to be finite in size in its own terms or just from our present perspective ?

 

 

**perhaps all of it ?

If you just look at our OU around Earth then it was small and dense but not the whole universe.

Edited December 6, 2016 by StringJunky

[geordief]

Is it possible that the expansion at around the time of the Big Bang was fueled by an outside source ?

 

Might there have been ,for example fields emanating from outside the OU that intersected?

[StringJunky]

Is it possible that the expansion at around the time of the Big Bang was fueled by an outside source ?

 

Might there have been ,for example fields emanating from outside the OU that intersected?

You are going into multiverses for which they are just an idea in some scientists heads.

[Delta1212]

At one time the universe was the size of a pea, and at that moment it had a finite size. It was the size of a pea. I'm not to bright, but I thought the CMB was the inner edge of the expanded pea and that we were looking at all the matter that was ever created by the original event, and that, that center was a matter of relative perspective.

But what ya'll seem to be saying is that the alien 4 billion light years away is seeing stars that exist much farther than we can see.

If that's true, then how do we know the age of the universe? After all, there maybe another alien 4 billion light years from him in the same outward direction.

There probably is. It's not the entire universe that was the size of a pea. It was the observable universe that was the size of a pea. The entire universe may have been much larger or even infinite in extent.

 

The CMBR is not so much the "outer shell" as it is the radiation that filled the very early universe. What we're getting now is the radiation from that early period that, thanks to expansion, had to travel 14 billion light years to reach us. And since it's limited to traveling at the speed of light, we can then determine that it took 14 billion years to get here. Which means that it has been 14 billion years since it started traveling toward us near the beginning of the Big Bang.

[geordief]

You are going into multiverses for which they are just an idea in some scientists heads.

Is there any indication as to what ratio there may be between the size of the Universe that we cannot observe and the size of the Universe that we can actually observe if we assume that this Unobservable Universe was present at the Big Bang?

[StringJunky]

Is there any indication as to what ratio there may be between the size of the Universe that we cannot observe and the size of the Universe that we can actually observe if we assume that this Unobservable Universe was present at the Big Bang?

I don't know. The OU is 96BLYS I think.

[Delta1212]

Is there any indication as to what ratio there may be between the size of the Universe that we cannot observe and the size of the Universe that we can actually observe if we assume that this Unobservable Universe was present at the Big Bang?

By definition, the unobservable universe isn't observable. There are only very limited conclusions we can draw about it from available evidence, mostly about what it is not, and even that is largely speculative because of a, by definition, lack of direct evidence about it.

 

I believe we are able to, for example, put a lower bound on how large the universe must be if it is finite in size and unbounded because it curves back around on itself and has uniform curvature throughout.

 

Local space appears to be flat to the best of our ability to measure, so any curvature must be on a lower level than we are currently capable of measuring. A bit like saying that the diameter of the Earth must be at least X because if it was less than that, the arc of the horizon would be prominent enough to be easily detectable just by looking at it.

[geordief]

By definition, the unobservable universe isn't observable. There are only very limited conclusions we can draw about it from available evidence, mostly about what it is not, and even that is largely speculative because of a, by definition, lack of direct evidence about it.

 

I believe we are able to, for example, put a lower bound on how large the universe must be if it is finite in size and unbounded because it curves back around on itself and has uniform curvature throughout.

 

Local space appears to be flat to the best of our ability to measure, so any curvature must be on a lower level than we are currently capable of measuring. A bit like saying that the diameter of the Earth must be at least X because if it was less than that, the arc of the horizon would be prominent enough to be easily detectable just by looking at it.

We have no idea what the total mass of the Universe was around the time of the Big Bang? And what the total mass of the Observable Universe is "now" ?

[imatfaal]

We have no idea what the total mass of the Universe was around the time of the Big Bang? And what the total mass of the Observable Universe is "now" ?

 

1. Would have all been energy - matter formation was later. Total mass/energy would not have changed (I think)

2. 10^53kg of normal matter