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Yes; that is exactly what I said. An excellent summation! Although I’m not sure where you got the impression that I was under the impression that the age of the universe is anything other than how long it has existed thus far.
That’s what I’ve always understood. And as everything expands away from us, more and more of it will be doing so faster than light, and will therefore actually disappear from our view forever as it moves outside our bubble of observability (which is expanding at the speed of light). Eventually, in billions of years, future astronomers will see a big empty universe and if historical records don’t survive there will be no way of ever knowing about all that stuff we can see now.
No you are not. Sheesh!
With astronomical distances, different considerations come into play, but for ordinary distances, no you are not seeing your monitor as it was in the past. Indeed, one can make just as good a case (but also ultimately wrong) that you are seeing it as it will be fractionally in the future.
I’ll just point out that if a star emits light and it is received on Earth 13.7 billion years later, then, in an expanding universe, it must’ve been closer than 13.7 billion light years when the light was emitted. The actual maths is a bit of a pain, especially as the Hubble parameter is a function of time, but it will be signifcantly less than 13.7 billion light years.
Eventually everything but our own local group of galaxies bound together will be the entire observable universe as all the other galaxies pass over the light horizon.
I assume you’re talking about the cosmological event horizon, which is not (necessarily) the same as the Hubble sphhere (the surface receding from us with a recession velcoity of c). In all of the best current models the cosmological event horizon is receding from us faster than c.
First of all, you have to understand that the interviening space is expanding at a rate which is, as far as we can tell, roughly proportional to the distance between points, such that the further twompoints are away from each other the faster they are moving apart. At the boundary of the observable universe, sometimes called the cosmic event horizon (which is, as previously mentioned, currently estimated to be about 46.5 Bly) the speed at which space is retreating from the centroid is almost c. (Note that this is true for any position in space, such that the boundary vhanges with the observer’s position and velocity.) Things outside of this boundary, like anything within the event horizon of a black hole, are forever beyond the accessible area of space-time (called the “light cone”) for the observer, and no direct observation of the amount or organization of mass and energy can be made. The extent of the non-observable universe is unknown and may well be infinite.
Stranger
Or in other words:
Link safe for work. Has audio. Of course there is one roque cosmologist in there thats just plain wrong but there is always one of those.
I think we need to clear this up, there are 3 surfaces associated with expansion:
Hubble sphere
Radius: ~13.9B ly (note that this is a little larger than the estimated age of the universe multiplied by c)
Recession velocity: c (exact)
The Hubble sphere is the surface receding from us with recession velocity c. anything beyond has a recession velocity greater than c.
Cosmolgical event horzion
Radius: ~16B ly
Recession velocity: ~1.2c (current)
The cosmological event horizon is the surface dividing events which will be able to affect us in the future. Events happening now (i.e. now in cosmological time) beyond the cosmological event horizon will not be able to affect us at any point in the future. Is not universal feature of expanding universes (though it is a feature of our universe).
Particle horizon
Radius: ~45.7B light years
Recession velocity: ~3.3c (current)
The particle horizon is the limit of our expanding universe and is the sphere containing all stars,galaxies, etc that we can see now (though obviously if they lie outisde our cosmological event horizon, but inside the particle horizon we will only ever be able to observe their past).
Not all speeds and distances are coordinate speeds and coordinate distances for the standard cooridinates.
This paper below is quite accessible and it clears a lot of the confusion that surrounds these issues.
I’m talking about the term used earlier, which was “observable universe”; and trying to understand what that term is being used in reference to. I understood it to mean the Hubble sphere (being that which is observable), but it seems that it actually refers to the cosmological event horizon.
Yes, I know. I said that. 
Actually I should clarify, if 13.7 billion years is taken to be the age of the universe then the proper distance between us and a star emitting light 13.7 billion years (not that a star could exist that early in the universe) away would vanish (i.e. go to zero) as all proper distances vanish at the big bang singularity.
If we assume the star existed a litle after the big bang, say 13.2 billion years ago (the age of the oldest known star), light emitted 13.2 billion years ago would’ve been emitted when we (or at least the spot that has the same comoving coorindates as us) had a proper distance of about 2 or 3 billion light years away from it.
That figures taken from the graph on page 3 of the paper I’ve posted above. Though due to the scale used, it’s quite difficult to read accurately for 13.2 billion years ago, so take that as a very rough figure!
That’s fair enough, though the Hubble sphere doesn’t directly relate to what you can and can’t see or what you will or what you won’t see. In fact it’s quite an arbitary surface, just dividing recession velocities into sub- and superluminal
Thanks very much for that link.
AFAIU, yes, due to the inflation theory, our light-cone bubble is a tiny spot in the surrounding super-universe. I don’t think there is a consensus among the experts on just how fast the inflation was and thus no consensus on how big this super-universe is.
Note, not not
i.e. Note: all speeds and distances are coordinate speeds and coordinate distances for the standard cooridinates.
njtt, I’m a physicist, not a physiologist, neurologist, nor psychologist, so I treat the eye as just an idealized detector, without worrying about all the complicated brain processing that goes on behind it.
Isn’t the horizon of last scattering (i.e., the CMB) the oldest thing we can see? How far away is that right now?
Toward the edge of the Hubble Sphere…where expansion equals lightspeed… frequencies/wavelengths are extremely redshifted.
Processes which generate cosmic and gamma rays redshift to visual or even radio waves, right?
The microwave cosmic background noise, when un-redshifted, reveals what processes at the dawn of time?
I believe it records the moment, about 300,000 years after the big bang, that matter and energy decoupled, and the universe became transparent. Others are better informed than I, though.