Question Why is the horizon of the observable universe?

Apr 1, 2022
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Is it because we see back in time to before stars formed and thus there is no more stars beyond that point?

or is it because space is expanding at the hubble constant and when you reach the horizon space expands at the speed of light so we cannot see past it?
 
Is it because we see back in time to before stars formed and thus there is no more stars beyond that point?

or is it because space is expanding at the hubble constant and when you reach the horizon space expands at the speed of light so we cannot see past it?
As we look farther and farther away, the light becomes more and more red shifted due to expansion of space. At a red shift of 3000, which puts visible light at 145 MHz, which is a temperature of 3K, we are seeing as far back as we can. We cannot see any farther back using EM waves.
 
There are two ways to detect weaker than visible, visible light. One is with collected area and one is with collected time.

Using one or both, one will eventually detect white starlight in any direction. At any point. If the inverse square law was not at play, you couldn't find a shadow in this cosmos.

We will detect much older light and greater distances in the future. But not now. For we misunderstand light. And the shift of it.

EM emission blinks. And the only thing that changes with emitter movement is the off time of the blink. Only the off time shifts. The on time is constant for life of emission. Unless the detector is moving. Then the on time and the off time shift the same amount.

A wave needs a media to vibrate thru. Light has no such need. It's not a vibration. It blinks. It doesn't buzz.
 
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Is it because we see back in time to before stars formed and thus there is no more stars beyond that point?

or is it because space is expanding at the hubble constant and when you reach the horizon space expands at the speed of light so we cannot see past it?
Taken from "From a drop of water...." #414:

"....
I've constantly denied it in the past (pardon the pun) but I grow to realize that some things may not exist until they are "observed" to exist. That "observation" is a real, though subjectively relative, physic.

One of those things is "coordinate 'point' SPACETIME" (past histories past light (t=+1) -->|<-- (t=-1) future histories future light cone). What is observed to be a past history in the past light cone (t=+1) of coordinate 'point' SPACETIME to one observer somewhere is a future history [as yet to be observed] in the future light cone (t=-1) of coordinate 'point' SPACETIME to some other observer somewhere else. My big mistake is thinking everyone can see and think multi-dimensionally, including myself upon occasion (my dismissing "Some things may not exist (for some) until they are observed to exist").
...."
 
The Earth's horizon is obvious and easy to picture. But can you picture a super-positioned collapsed cosmological constant (/\) P/BB Horizon Mirror (t=*1*) of infinities (a working 'Horizon' of endless beginnings rounding)? Infinities you cannot possibly observe as such? Similar to Earth's horizon, a processionary and recessionary Horizon? If you were an immortal traveler who could travel, self-powered and constantly accelerating, forever the infinite vistas of infinities of universe(s), but never being fixed anywhere but dead centering that horizon, that Horizon Mirror, accelerating in expansion and evolution to you and at once away from you the traveler traveling horizon to horizon, could you see it? Could you picture it?.
 
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Jan 2, 2024
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or is it because space is expanding at the Hubble constant and when you reach the horizon space expands at the speed of light so we cannot see past it
Yes, this is correct. The horizon is expanding relative to us) at the speed of light.

You may find it interesting to note that the observable universe is unique to our gravitationally bound Galaxy/area i.e. a place a few billion light years away will have a different horizon ( expanding also at c).

You also asked if looking back to the past was a "horizon". What you didn't use was the phrase "Event Horizon". This phrase is usually associated with Black Holes. It defines a region from which light cannot escape to reach us.

The Horizon to which you refer above is also described (e.g. by Stephen Hawking) as an Event Horizon because light cannot reach us (it would need to exceed 'c' to overcome the outward expansion of our observable universe - as you surmise). Accordingly, we are unable to see beyond a certain distance - to the point at which the universe horizon is receding at 'c'

I suppose that if you were to travel at a significant fraction of the speed of light ('c') then any part of the universe that was previously beyond the horizon ( in the direction of travel) would then become within it!

As billslugg said earlier the further you look the further to the past you observe, however, { "WARNING" the following is my own speculation and should be treated with kid gloves} this is not a view toward the Big Bang origin of the universe but is simply a view along the circumference of a sphere (a hypersphere). Note the BB origin would be the centre of the hypersphere BALL.

If we consolidate the above comments we can make a prediction: If we were able to accelerate a camera sufficiently to region escape velocity such that we could see beyond our current horizon then we would be able to observe even more galaxies - well past any supposed BB date
 
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I believe you are correct. When traveling fast, what is ahead is blue shifted. The cosmic horizon occurs because what we see is red shifted out of visibility. The two should be additive, causing the forward horizon to recede. Conversely, the horizon out the back window would come closer.
 
Odd how few people, how very, very, few people, realize where the 0-point-center of universe(s) -- centered in horizon (also Hawking's "Grand Central Station" of Universe with its centered frozen time clock) -- is! Horizon to horizon, to horizon, to horizon (to infinity)... and never once leaving 0-point center of universe(s) in horizon . . . never once allowed by the collapsed cosmological constant (/\) of Mirror P/BB Horizon (t=*1*) to leave 0-point-center!
 
Apr 1, 2022
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I believe you are correct. When traveling fast, what is ahead is blue shifted. The cosmic horizon occurs because what we see is red shifted out of visibility. The two should be additive, causing the forward horizon to recede. Conversely, the horizon out the back window would come closer.
perhaps we could we peer into a black hole with a fast enough craft by the same means of additive shift.
 
perhaps we could we peer into a black hole with a fast enough craft by the same means of additive shift.
Yes, an observer on a fast craft would see a receding event horizon, slightly closer to the BH than we would see from Earth. Everybody sees a slightly different event horizon depending on our velocity relative to it. However, the event horizon is always there. Every observer sees one ahead of them. Daisy chaining observers to get a glimpse of the central singularity won't work because what you gain by going fast you lose in your ability to communicate outward.
 
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Yes, an observer on a fast craft would see a receding event horizon, slightly closer to the BH than we would see from Earth. Everybody sees a slightly different event horizon depending on our velocity relative to it. However, the event horizon is always there. Every observer sees one ahead of them. Daisy chaining observers to get a glimpse of the central singularity won't work because what you gain by going fast you lose in your ability to communicate outward.
Bill, I don't believe -- I'm certain -- the traveler would not see recession to the front thru his windshield (so to speak). The traveler would see (would observe) an opening universe immediately to the front even if that traveler ran head into a solid wall of ground (such as the Earth's surface). There is no singularity in place.

But!

You've got me wondering, now, if possibly the traveler approaching entering a black hole has lost the distant universe horizon outside and relocated it distantly within the event horizon of the black hole as the traveler is now possibly dealing in one of Hawking's baby universes. Entering a subspace-hyperspace universe, tunneling thru the event horizon to another universe, and relative to the universe leaving if it survives whole the debris, becoming a Lilliputian in an acceleration of expanding Lilliput universe? What from the outside an observer would identify as "singularity", from the inside has now now become observed points of universe about 13 to 14-billion light years away by the traveler observer.

Looking in the rearview mirror, the traveler again observes that same horizon to be the same distance to his rear as to his front. A balance of natures to Hawking's 'Life Zone' of universe only if the traveler survived the trip transiting the extreme nature of the possible anti-Verse in event horizon superposition!

Wow, what a world the Cosmopolis probably is! I will be taking on that philosophy (that Stephen Hawking had so lamented had broken up and split out into two in a chasm that should never have happened) of philosophy and cosmology at large (to mean cosmological physics in their largest most particularly open and general aspect) soon . . . now that I've been reminded about what Hawking termed an unobservable "Cosmology of the Universe" that is in fact, and must be in fact, a "Philosophy of the Universe"!
 
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Yes, an observer on a fast craft would see a receding event horizon, slightly closer to the BH than we would see from Earth. Everybody sees a slightly different event horizon depending on our velocity relative to it. However, the event horizon is always there. Every observer sees one ahead of them. Daisy chaining observers to get a glimpse of the central singularity won't work because what you gain by going fast you lose in your ability to communicate outward.
Bill, in rereading your post, and looking at a Western sunset or sunrise landscape painting (a 4-dimensional SPACETIME landscape painted onto a 2-dimensional REALTIME canvas) on our wall while eating my supper, I realize I largely erred though I won't delete my previous post. The landscape painting does "time" as a point-singularity of distance that the landscape closes up into giving a 4-dimensional effect within the 2-dimensional window of the painting.

If I were a traveler traveling into that painting the universe would open to me near in SPACE and REALTIME while keeping that point-singularity of horizon in place far in SPACETIME. I could turn in place 360 degrees and find the same point-singularity of background horizon distancing in place, a 4-d SPACETIME landscape painted onto and/or into a 2-d 'Flatland' universe REALTIME canvas. Anyway, thanks once more for jarring my own vision and thinking, Bill.
 
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I'm not the only one thinking about what I wrote in the above post . . . though not in exactly the same way:

From 'Popular Mechanics' via MSN (couldn't find this otherwise):

"The Universe May be a Hologram, Meaning Our Reality Could Be an Illusion," by Paul Sutter:

Are we an illusion because we are home to other cellular life making each one of us up physically? We are a pyramidical life product and at the time a realized separate entity of life (our minds over our matter) than just our physical composition. There is distance in separation between.

We found out atoms weren't the distantly bottom base particles, that they are comprised of deeper more distant particles and particle groups . . . and those particles comprised of even deeper, even more distant, groups of particles (to put another way, "spooky actions at a distance"). Are atoms, because they are a specific base dimensionality yet at once not basic (a Schrodinger "is" and "is not" realization all at once), an illusion?

With distance in increasing distances between levels, layers, spaces and times, thus, physics, comes breakdowns of relativity into "entropy, disorder, chaos, always realized at a growing distance as "spooky actions at a distance!" The increasing changes always acquiring, always piling up more and more. in the ever-farther reaches, ever-increasing, distances, from the local-relative observed "observable universe." All of them, in their infinities, radially 0-point centered sphere-type observable. All of them being points (quantum entangled as their own 0-point centers of spheres) on the 'Flatland' flat-horizon surfaces of horizon observable universe spheres. Horizon to horizon, center-point to center-point, sphere to sphere, universe to universe. Relativity's breakdown to buildup, breakdown to buildup, breakdown to buildup....

Our "observable universe" in light's coordinate point SPACETIME of macrocosmic and microcosmic histories past and future is the universe that is and isn't a "hologram": That is and isn't a "reality"; that is and isn't an "illusion"!

Whew! I really got into light's coordinate point SPACETIME histories past and future light cones : "instantaneous spontaneous concurrent REALTIME" : and "emergent SPACE" (open system and opening systemic accelerating expanse) (hyperspace) (self-similar dual-level fractal zooms universe structure, center / fundamental set and reset") (warp space) (wormholes) (stargates and galactic gates . . . observable local-relative universe gates) ("Through the Looking Glass') (....).
 
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