How far can we see?

[modest]

Originally Posted by sman

So this particular galaxy has put 16.4 billion light years between us in 15 billion years? This kinda throws up a flag for me.

Sorry, I didn't see this question before. Yes, you're spot on. In fact, the furthest thing we can see is the cosmic microwave background which is *currently* about 46 billion lightyears from us (that is to say, the comoving distance between us and it is 46 billion lightyears).

This means, as you correctly infer, that the hot condensed plasma which eventually become the milky way and the hot condensed plasma which eventually became some other galaxy put 46 billion lightyears between each other in 13.6 billion years. This also means it is currently expanding away from us at faster than the speed of light.

The question is: how can we see something that is expanding away from us at faster than the speed of light? In fact, we cannot; we are not seeing the thing that is expanding away from us at that speed. We are *not* seeing the galaxy as it exists today—nor can we. We see it as it existed in the very young universe. Back when the light was emitted it was not expanding away from us as fast as it is today.

Galaxies which have a light travel time distance less than 13.7 billion lightyears with a comoving distance greater than 13.7 billion lightyears started out inside our cosmic horizon but have subsequently moved out of our horizon. So we can't see how they exist today—nor will we ever be able to no matter how long we wait. We can only see how they used to be when they were inside our past light cone.

~modest

[mentor]

don`t forget that at the very start the Universe was expanding faster than light (universes are allowed to do this, its things inside em that can`t go FTL), so a HUGE chunk of the Universe is so far away that we can`t see it and never could, even with a "SuperHubble", the chunk we CAN see is comparable in size (so I read once) to about the size of a grain of sand in the Superbowl stadium.

I`m from England so I don`t actually know how big the Superbowl stadium is, but assuming it`s bigger than a football stadium, thats one BIG universe, you just need some advanced technology to get to it, like a wormhole generator or a quantum transporter of some sort, since it`s recession velocity is still faster than light (and still accelerating by recent accounts) , so going via normal space won`t cut it.

afaik the current furthest object has a recession velocity of 0.84C, so thats over 4/5ths of the way back to creation (and IF the Universes expansion IS still accelerating then that object got beyond our reachable range a LONG time ago and is now (from our viewpoint) traveling faster than light.

[Michael Mooney]

According to the theory of space expanding faster than light (as per inflation cosmology), what is it exactly that is supposed to be expanding? If space is not simply empty volume*, what then is it supposed to be? (Of course it is not empty where "stuff" exists *in space*.
This is half the "what is spacetime?" question, and it has never been answered either after over 80 original pages of that (now closed) thread.
Michael

[arkain101]

Question: How is trick of perspective explained away? Is this consideration possible or fallacy.


From a guess, I am going to say that this (what I am going to share below) is almost certainly put under consideration. With that said, what I AM interested in, is what explanations are available to explain it.

In special relativity, it is said that when an object is traveling at relativistic speeds, distance shrinks in the direction of motion. However, I propose the slight flaw in that statement. Direction "OVERALL" is arbitrary(I believe that is the right word to use). In such a way that; anything moving towards you is considered the direction you are traveling. Therefore, direction of travel can exist relatively speaking more than one direction. However, you can only specify one singular direction for a result to make sense. Therefore, velocity must be applied to "the surroundings" as opposed to the observer, because logically, an observer can't travel two directions at the same time.

Now, in a distance past, a very distant past, near the beginning of the universe; we could suggest that, the beginning of the universe, things were in a very very rapid inward velocity.

This naturally gives us the image from an external universe view of a very very very large universe collapsing inwards. To keep track of "perspectives" we will call this: The Perspective of separation. (PS) . This perspective is the imaginary kind, how we see the world naturally.

However, this natural intuitive perspective "PS", is false in the following sense: According to the accuracy of Special relativity, if a universe was collapsing inwards very close to the velocity of C, such that space is shrunk from any direction of observation. Then, it would infact be that relative to an participating observer the universe would be INCREDIBLY SMALL, NOT INCREDIBLE LARGE. At this point in time where velocity is highest space is literally shrunk. We can call this perspective: The perspective of a participant" (PP). This perspective is the realistic kind, how we are actually forced to observe anything.

In this collapsing model, we actually have to stop thinking of the universe as "collapsing", because the beginning of the space and time, the instant of creation would be equivalent to an inward velocity to become LESS than C, so that space and time could be greater than 0.

In respect to PP, the center of the universe is any location of observation. As this instant of creation occurs, it must be considered that the universe is to begin decelerating.

Special Relativity; a working accurate theory in our point and time and "PERSPECTIVE ON THE UNIVERSE"; SR's relativistic equations would suggest that as the universe slows down, space would expand in the direction of travel. Geometrically speaking, the direction of travel is equal to all directions. This translates into saying the universe beings to expand in every direction.

Another way of phrasing this expansion of space-time, or slowing down of collapse; in respect to our physics is; The potential energy of the universe, or the Total energy of the universe decreased.

That is, if at the beginning of the universe's total energy was equal to velocity C, with distance 0 etc, then a decrease in Total energy, equates, space-time expansion.

(Before the expansions of space-time, was Time (t), unknown, singularity, where mass is both impossible and excluded, "i couldnt begin to guess physics of a singularity" other than, a state of velocity C)

As this expansion occurs, one could also calculate that the Potential energy of the universe as one entity, decreases proportionally. That is, the rate at which the universe slows down increases per unit exponentially. That is, the deceleration of the universe, produces an acceleration of space-time.

As such, The act of a universe decreasing from velocity C produces space-time value, and exponential expansion in all directions.

In respect to physics, a prediction or expectation is that the; If this were "TRUE" one could calculate the EXACT age of the universe by taking in the account of the current stage off acceleration, the initial velocity (C), and the current velocity of expansion.

Furthermore, one could predict, that the accelerating universe will eventually stop, as relativistic speeds reduce.


So ALL of the above is a consideration. A specific consideration that I will call "TRICK of Perspective".


I ask, How is this consideration explained away as invalid data and theory?

[modest]

Originally Posted by Michael Mooney

According to the theory of space expanding faster than light (as per inflation cosmology), what is it exactly that is supposed to be expanding?

On cosmic scales everything is expanding away from everything else. The simplest way to express such a thing is to put everything on a metric (or a grid, if you like), and to scale the metric. This accomplishes something very specific which I will describe.

If you consider a galaxy such as the Milky Way and measure the speed at which other galaxies are moving away from it then the further the galaxies are, the faster they will be moving away. That is a physical law of astronomy known as Hubble's law.

It is sensible to assume that our position in the universe is not special so that any other galaxy out there also has galaxies receding from it in such a way that the recession velocity increases with distance. An easy way to show this (to model it) is to use a rubber sheet (think of a piece of paper made of rubber). You can mark a bunch of dots on the sheet representing galaxies.

If you have 4 people each grab a corner of the sheet and stretch it apart then you have effectively modeled the manner in which galaxies move away from one another. One of those dots on the rubber sheet has every other dot moving away from it and the further the other dots are from it, the faster they move away. This is true for any dot.

The expansion of the universe is very similar. Saying "space is expanding faster than the speed of light" means that the distance between two objects on the metric is increasing faster than c. This is an inevitable conclusion given two things:

1. The further away one galaxy is from another the greater the rate at which their distance increases.
2. The universe is infinite in size.

You're probably wondering what difference it makes if we say something is moving through space or if we say space is expanding between things. And, it indeed does make a difference which can only be revealed by measuring and understanding the apparent motion of cosmic objects. To give one example, if an object is moving away from us *through space* then we expect it to exhibit a redshift which can be calculated with and is due to special relativistic Doppler shift. If, however, space is expanding SR doppler shift will not give the correct redshift results. Cosmological redshift must be used. Wiki summarizes the difference:

Hubble's law of the correlation between redshifts and distances is required by models of cosmology derived from general relativity that have a metric expansion of space. As a result, photons propagating through the expanding space are stretched, creating the cosmological redshift. This differs from the Doppler effect redshifts described above because the velocity boost (i.e. the Lorentz transformation) between the source and observer is not due to classical momentum and energy transfer, but instead the photons increase in wavelength and redshift as the space through which they are traveling expands. The observational consequences of this effect can be derived using the equations from general relativity that describe a homogeneous and isotropic universe.

Redshift - Wikipedia, the free encyclopedia

That quote references "the metric expansion of space" which is a good article at wikipedia. If you want to get a good understanding of just what astrophysicists mean by expanding space then that would be a good place to start.

I should probably also note that cosmic inflation which you mention is not any more fundamentally superluminal expansion than the expansion of space today. This is a common misconception which is addressed here:

Inflation is sometimes described as “superluminal expansion” [App. B: 22–23]. This is misleading because any expansion described by Hubble’s law has superluminal expansion for sufficiently distant objects. Even during inflation, objects within the Hubble sphere (D < c/H) recede at less than the speed of light, while objects beyond the Hubble sphere (D > c/H) recede faster than the speed of light. This is identical to the situation during non-inflationary expansion, except the Hubble constant during inflation was much larger than subsequent values.

Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe (page 6)

Originally Posted by Michael Mooney

If space is not simply empty volume*, what then is it supposed to be?

I don't think "volume" is that bad of a word to substitute for "space" in the setting of astronomy and cosmology. We could say that the volume between galaxies increases over time rather than saying the space between them increases. We would also say that the rate at which volume expands is proportional to the volume itself much in the way we would say the expansion of space between objects is proportional to the distance between them.

~modest

[Pluto]

G'day Modest

You said

On cosmic scales everything is expanding away from everything else. The simplest way to express such a thing is to put everything on a metric (or a grid, if you like), and to scale the metric. This accomplishes something very specific which I will describe.

If you consider a galaxy such as the Milky Way and measure the speed at which other galaxies are moving away from it then the further the galaxies are, the faster they will be moving away. That is a physical law of astronomy known as Hubble's law.

I understand what you say and yet when I look at images near and far 13,2 Gyrs I see galaxies mature and young, various forms from spiral to elliptical and so on as we see them close. In addition the images show a clustering effect proven by galaxies merging and clustering into a super cluster of clusters of galaxies.

I may have posted thes links before.
These are for the people who have not read them and may express their own opinion on them.

There are a number of papers that are of interest.


[0806.4481] Hubble's Cosmology: From a Finite Expanding Universe to a Static Endless Universe
Hubble's Cosmology: From a Finite Expanding Universe to a Static Endless Universe
[0806.4481] Hubble's Cosmology: From a Finite Expanding Universe to a Static Endless Universe

[0810.0153] Expanding Space: The Root of Conceptual Problems of the Cosmological Physics
Expanding Space: The Root of Conceptual Problems of the Cosmological Physics
[0810.0153] Expanding Space: The Root of Conceptual Problems of the Cosmological Physics

[0811.3968] The origin of redshift asymmetries: How LambdaCDM explains anomalous redshift
The origin of redshift asymmetries: How LambdaCDM explains anomalous redshift
[0811.3968] The origin of redshift asymmetries: How LambdaCDM explains anomalous redshift

On The Origin Of The Highest Redshift Gamma-Ray Burst GRB 080913
[0812.2470] On The Origin Of The Highest Redshift Gamma-Ray Burst GRB 080913
Authors: Krzysztof Belczynski, Dieter H. Hartmann, Chris L. Fryer, Daniel E. Holz, Brian O'Shea
(Submitted on 12 Dec 2008)
[0812.2470] On The Origin Of The Highest Redshift Gamma-Ray Burst GRB 080913

Could these papers be wrong or is the Big Bang theory in question.

[modest]

Pluto, I've answered your post here: Re: Origin of the Universe,,,,Bang or no Bang

~modest

[Michael Mooney]

Modest

]On cosmic scales everything is expanding away from everything else. The simplest way to express such a thing is to put everything on a metric (or a grid, if you like), and to scale the metric. This accomplishes something very specific which I will describe.

If you consider a galaxy such as the Milky Way and measure the speed at which other galaxies are moving away from it then the further the galaxies are, the faster they will be moving away. That is a physical law of astronomy known as Hubble's law.

It is sensible to assume that our position in the universe is not special so that any other galaxy out there also has galaxies receding from it in such a way that the recession velocity increases with distance. An easy way to show this (to model it) is to use a rubber sheet (think of a piece of paper made of rubber). You can mark a bunch of dots on the sheet representing galaxies.

Maybe you are not yet familiar with how i see the cosmos, as re-stated yet again in post #26 of the "Bang/Crunch Revisited" thread, as follows:

Our cosmic event horizon is just a small bubble of visibility *within* the thickness of the "rubber" of the good old cosmic expanding balloon. This mini-cosmos within the maxi-cosmos, the Whole Balloon, is cycling through bangs and crunches even as the whole balloon keeps expanding.... *Yes*... out into the infinity of space.
...
Anyway, we can't even "see out of the rubber" (the visible cosmos) let alone see the *yes* empty space within or beyond the bubble.

Modest:

If you have 4 people each grab a corner of the sheet and stretch it apart then you have effectively modeled the manner in which galaxies move away from one another. One of those dots on the rubber sheet has every other dot moving away from it and the further the other dots are from it, the faster they move away. This is true for any dot.

The above is a two dimensional rubber sheet... a plane. My expanding balloon is a 3-D sphere... and the "rubber" is the "stuff" of cosmos... with a thickness containing the whole mini-sphere of visibility which is our cosmic event horizon.
So, naturally cosmos appears isotropic/homogeneous in all directions
as the whole balloon expands with our little visible cosmos as one tiny bubble in the rubber of the balloon.
Can you understand what I am saying?

The expansion of the universe is very similar. Saying "space is expanding faster than the speed of light" means that the distance between two objects on the metric is increasing faster than c. This is an inevitable conclusion given two things:[LIST=1][*]The further away one galaxy is from another the greater the rate at which their distance increases.[*]The universe is infinite in size.

Space is infinite emptiness. Cosmic "stuff" exists in specific locations within unbounded space.... reference balloon cosmology above.
Nothing... none of this cosmic "stuff" travels faster than light, and space is lack of 'things', emptiness... no-thing-ness, the *volume* in which stuff exists, and "it", being nothing, does not 'travel" or expand at all.

You're probably wondering what difference it makes if we say something is moving through space or if we say space is expanding between things. And, it indeed does make a difference which can only be revealed by measuring and understanding the apparent motion of cosmic objects. To give one example, if an object is moving away from us *through space* then we expect it to exhibit a redshift which can be calculated with and is due to special relativistic Doppler shift. If, however, space is expanding SR doppler shift will not give the correct redshift results. Cosmological redshift must be used. Wiki summarizes the difference:

I may introduce a very important criticism of all assumptions surrounding the redshift paradigm, but this is not the "place or time."
I am not "wondering" at all "what difference it makes if we say something is moving through space or if we say space is expanding between things."
It is my most profound understanding that space is empty volume in which all *observable/detectable* phenomena exist and move.
Space is emptiness. It has no properties... being the *void* in which things with properties exist. Space does not expand. Things move away from other things in space... emptiness/volume.

That quote references "the metric expansion of space" which is a good article at wikipedia. If you want to get a good understanding of just what astrophysicists mean by expanding space then that would be a good place to start.

I will study it at another time.... and get back to you on prevalent dissent on redshift as the basis for the "inevitable conclusions"... what you believe are indisputable "facts."
........

I don't think "volume" is that bad of a word to substitute for "space" in the setting of astronomy and cosmology. We could say that the volume between galaxies increases over time rather than saying the space between them increases. We would also say that the rate at which volume expands is proportional to the volume itself much in the way we would say the expansion of space between objects is proportional to the distance between them.

But the reason for more volume between objects over time is that they are simply moving away from each other as in the expanding balloon... not that "space itself" (as if it were an entity) is expanding.
This is your (and "expanding space theorists') fundamental misconception as i see it.

And don't get me started on dilating time again!

Michael

[enorbet2]

Originally Posted by Pluto

I understand what you say and yet when I look at images near and far 13,2 Gyrs I see galaxies mature and young, various forms from spiral to elliptical and so on as we see them close. In addition the images show a clustering effect proven by galaxies merging and clustering into a super cluster of clusters of galaxies.

Could these papers be wrong or is the Big Bang theory in question.

Hello Pluto
While I get it that so far the Universe seems isotropic and homogeneous when viewed on Large Scale, not to mention that the Cosmic Background Radiation is uniform to 1 part in 100,000, but are you saying you're aware of no differences in the early Universe, even at visible light frequencies?

Yes! and Yes! Those papers could be wrong AND the BBT is in question. I'm not yet saying they are wrong and, but as I've posted in other threads, the odds are still in favor of the Standard Model including BBT. Admittedly this is a revolutionary age in Astronomy and this could change rather quickly as more new data comes in. Renewed Hubble with COS, the awesome Herschel Space Telescope and the Planck telescope are but three that are underway as we speak that will likely have a profound impact on questions and answers.

BTW good to see you focusing more on redshift since it is so fundamental - if the Universe isn't expanding BBT is done. I will read the papers. Most of the links you post aren't exactly digestible in one sitting on the john (or, loo, if you prefer)

[enorbet2]

Michael
It is not a given that Space is empty since it is not yet known if it is itself discrete, especially at the Planck Scale. There are as yet deep problems correlatiing scale which seems necessary to understand why gravity is so weak let alone the full nature of the Universe. One of the major problems is formulating a theory that is background independent.

Quantizing the Universe » American Scientist

As for distance calculations this might help

http://en.wikipedia.org/wiki/Distanc...res_(cosmology)

Distance calcs may be revised sometime soon as The Planck Telescope intends to duplicate WMAP in much higher resolution. Pretty damned exciting!