The effects of cosmological expansion on the viewability of our universe is discussed. Theoretical considerations of observed cosmological expansion offer an attractive alternative to the Big Bang explanation of the universal cosmic background radiation field.

This concept was originally developed by Professor S. Warren Carey, of the University of Tasmania. Carey used the term 'Olber's Window' when referring to this effect. The term 'Optical bubble' is used within this discussion.

Carey's concept is elucidated and extended implications of this concept are discussed. The veracity and relevance of the Optical Bubble concept to recent cosmological observations and developments are also discussed.

Accelerating expansion in a large-scale isotropic cosmos.

The optical bubble is the region of our extended cosmos, that it is physically possible to observe from a near Earth observer's location in space-time. There exists a poorly understood absolute limit to the radius of this observable area--a radial distance beyond which we have no conceivable prospect of observing any radiating object.

This 'optical bubble' concept was first put forward over a decade ago (see Carey, 1988,  and particularly 1996).  This concept represents an elegant, satisfying, and naturally emerging alternative to the current 'Big-Bang' explanation of the observed cosmic background microwave radiation (C.B.R.).
 

Fig. 1  The effect of cosmological expansion on a large-scale isotropic cosmos. A viewable optical bubble always exists in an expanding cosmos, irrespective of the finite or infinite nature of the cosmos. Only a shrinking cosmos can have no optical bubble, though high densities of intervening matter may limit viewability within a shrinking cosmos.

Cosmic Background Radiation and the Big Bang

The cosmic background radiation is a pervasive long wavelength microwave radiation which permeates all space-time and is observed to originate from every direction at approximately the same energy/temperature. This microwave background radiation is currently popularly interpreted to represent a remnant after-glow from an ~15 billion year old 'big bang' (currently considered to be ~12.6 billion years ago) from which our universe began.

Alternatively, the optical bubble concept discussed here, indicates that the 1960’s Cosmic Background Radiation interpretation problem, and the popularly adopted big bang explanation of it, may be the result of misunderstanding of the nature and scale of cosmological expansion.

Recent research (Lawrence Berkeley National Laboratory - Supernova Cosmology Project) has revealed compelling evidence that, not only is the universe expanding, it is expanding at an accelerating rate. No observation or model has yet emerged to clearly explain how cosmological expansion could accelerate. Results from a number of research groups indicate that that the universe will very likely expand forever due to the lack of sufficient mass to trigger gravitational collapse.

This anomalous expansion acceleration is the opposite of what the Big Bang predicts. Because of this, many theorists now speculate on a previously unrecognized form of matter which might provide the required mass to slow or 'flatten' the universe's expansion. Even if sufficient mass is identified to 'close' our universe, the expansion rate should be slowing now due to gravitational attraction.  Recent observations of distant Type 1a supernova, show that even the expected slowing from gravitational attraction is not occurring, nor is it 'coasting-along' as within a static 'flat' universe--it is clearly accelerating and that is most unexpected. No cosmological paradigm expected this to be occurring.

Many theorists now consider that the cosmological constant, posited by Einstein, dominates all matter within our universe and that its effect negates gravitational attraction over cosmological distances. This cosmological effect is a repulsive force which defeats long-range gravitational attraction. Such a long-range universal repulsion has been quantitatively enunciated and predicted by Carey (1976, 1988, 1996) as an effect which always accompanies the large-scale isotropic distribution of mass throughout the cosmos.

This new understanding of an accelerating universal expansion has lead to great theoretical uncertainty where previously high confidence in a big-bang/inflation model had dominated. The standard cosmological model of the last 15 years is now invalidated by recent observations, and this is triggering a revolution in cosmological thinking. This revolution is bringing into question the theoretical foundations of the past 35 years. The Big Bang explanation was generally adopted during the mid 1960's as the popular scientific explanation for the origin of our universe and also to explain the observed ~ 2.7^o K universal Cosmic-Microwave-Background-Radiation field.

The big-bang was adopted as the default paradigm in the 1960's, principally because it seemed to be the only model which offered an elegant and convincing explanation for the newly identified cosmic background radiation. It therefore won a paradigm shoot-out with the only other viable model on offer at the time--the Steady-State cosmological model.
 

The Optical Bubble and the C.B.R.

As will become clear within this document, the C.B.R. does not require a big-bang explanation. Furthermore, the optical bubble concept discussed here potentially applies to both an adjusted big-bang cosmology and also, to a derivative of the Quasi-Steady-State cosmology.

The absolute limit to optical visibility within our cosmos is primarily imposed by these two factors:

• The speed-of-light--considered to be a universal constant;

• And, Relative recession velocities (relative to an observer) of large-scale radiative matter as it recedes from the observer due to the accelerating universal expansion.

i.e.

The object's relative recession velocity away from the observer increases according to the object's distance from the observer. This relationship does not alter as the cosmos expands, regardless of how far away the object is from the observer--the object will always recede faster as the distance from the observer increases.

At more than 10 billion light years distance from the observer, the relative recession velocity away from the observer becomes very high and this is reflected by increasing Doppler-shift of the observed photon wavelengths received from these very distant and rapidly receding objects.

As the radial distance to the objects continues to grow, the statistical spread of relative recession velocities for these objects continues to increase, eventually increasing to a recession velocity approaching the speed-of-light.

The resulting extreme Doppler-shift of photon wavelengths from these rapidly receding objects causes the wavelengths to become stretched out (i.e. skewing to longer wavelengths with increasing distance from the observer's location). Very distant, unresolved objects (implying a very high recession velocity), are detected as extremely Doppler shifted photons, which extend from the visible, infra-red, radio/microwave regions of the electromagnetic spectrum as the distance to the observer increases.

i.e.

Because of this expansion induced Doppler stretching of light waves, the observed apparent long wavelength photons may originally have been emitted as ultra-violet light, X-rays or gamma-rays--emitted from an object moving away from the observer at close to the speed of light. Due to simple redshift, its wavelength would become effectively infinite, and hence its energy would be zero, as according to Planck's equation relating to the energy of a photon and its wavelength.

Clearly, the real source of the Cosmic Background Radiation is not necessarily due to a big bang. It is very likely that the C.B.R. results from an entirely predictable extreme doppler stretching of photons as their relative recession velocities away from the observer approaches the speed-of-light.

As the radial distance to an object is further increased, the relative recession velocity eventually exceeds the speed-of-light (measured relative to the observer). Because of this superluminal relative motion, it is absolutely impossible to observe any light emitting object beyond this radial distance from the observer, where relative superluminal recession velocities begin. The light can no longer reach the observer because the expansion of space-time has now exceeded the speed of light at this distance and the emitting object has, for all intents and purposes, permanently exited the observers personal unique universe!  Therefore, we can only observe radiating objects within our own local optical bubble (hence, the term 'Olber's Window' as used by Carey), as all the objects inside the observer's bubble recede at a velocity below the relative speed-of-light.

• Every object with a sub light speed recession velocity is within our viewable optical bubble--our knowable and observable universe.

• The radial distance, where relative recession velocities exceed the relative speed of light, is referred to in this discussion as the optical extinction boundary (~15 billion light years radial distance from Earth).

This astonishing C.B.R. isotropy presents serious difficulties for big-bang cosmologists, because it is difficult to imagine how large-scale galaxy formation, clumping and clustering, could occur in the way observed if this clustering was produced by the same event which produced the C.B.R.s' extraordinary homogeneity and isotropic flatness. The cosmological theory of inflation, initially controlled by quantum scale effects, has been put forward to explain the disconnect between galaxy clustering (local anisotropy) and the observed large-scale isotropic C.B.R.  The inflation cosmology is now also under pressure from the recent observations that the expansion rate is accelerating. Some quantum inflationists theorize that the cosmos is beginning a new phase of inflation--it is quite difficult to envision how this could occur, but can not be ruled out yet.

The original emitted wavelengths of a given photon, does not affect its radial extinction distance from the observer, as this is controlled by the recession velocity of the emitting object relative to the observer (and the speed-of-light, which hopefully is a actual 'universal constant'). Consequently, every point in the universe has it's own unique optical bubble or 'window' on the viewable universe (Carey, 1988 - called this observer's optical bubble, 'Olber's Window'). The radius to the optical extinction boundary will be the same for all optical bubbles regardless of where the observer is located within the cosmos--but only if light is truly universally constant and the accelerating expansion rate is also 'constant' across the entire cosmos.

What this effectively means, is that Earth's 'observable universe' is bounded by the optical extinction radius (~15 billion light years).  If we could determine the precise distance to this boundary we would have a master reference frame for measurements of 'our universe'. I am differentiating the word Universe from the word Cosmos here.  The 'Universe' is our viewable area within the greater cosmos, which exists outside of our optical extinction boundary (as per the definitions proposed by Carey).

Furthermore, if gravity propagates at the speed of light (this is unknown), the Earth would only be directly affected in gravitational terms, by mass within our unique optical bubble.  In which case, once matter exits the Earth observer's optical extinction boundary, the mass and it's associated gravitation, has effectively exited our personal universe. Therefore, the optical bubble boundary (C.B.R.) may also be a gravity extinction boundary for Earth observers.  However, mass beyond this proposed combined photon/graviton extinction boundary, can and will continue to affect matter inside the optical extinction boundary.
 

Figure 2. Shows the potential effect of external optical bubble mass and energy upon objects within our optical bubble. Point A represents an observer's location at the centre of the left-hand optical bubble. Point B represents a large radiative astronomical object that is clearly visible to the observer at point A. Point B's unique optical bubble radius is also displayed on the right-hand side. Point C, is outside the optical bubble of the observer located at point A, but it is well within the observation bubble (or sphere of influence) of B. What this implies, is that the gravitational mass and radiative energy of C will directly impinge on  B (which is inside A's bubble), but it can never directly reach A. The observer at point A can study B and detect the subtle effect upon B, produced by the unobservable existence of C. Therefore, the total mass and energy budget that directly, and also indirectly controlling the behaviour of matter and energy within Earth's optical bubble, extends well beyond the optical extinction boundary. Therefore, there may be much more matter affecting our local optical bubble than the matter and energy contained within it's ~15 billion light year radius. The inverse squares law indicates that this unseen 'affecting matter', may be more than double the total of the mass and energy contained within our local optical bubble.

One further point, the C.B.R. is not equivalent to the optical extinction boundary.  The C.B.R. sphere is closer to the observer and is the last cosmological feature observable before the optical extinction boundary radius. The extinction boundary itself is of course 'non-viewable', because it is the very point at which superluminal velocities dominate, so light can no longer travel back toward the observer. The C.B.R.s' distance from the observer indicates the near proximity to the extinction radius immediately beyond the CBR.

Several readers may have realized that this concept also predicts an INFRA-RED CBR field which should exist at a closer radial distance from the observer than the ~2.7K MICROWAVE CBR.  The good news is such a universal infra-red background radiation has recently been discovered by the Diffuse-Infrared-Background-Experiment, aboard NASA's Cosmic Background Explorer (COBE).  See the following links for details:

DIRBE detects Cosmic Infrared Background, January 9th 1998:
Astronomers Discover an Infrared Background Glow in the Universe

COBE's Infrared View Of The Universe:
Three pictures of the full sky as seen in infrared light.

Now, imagine yourself looking in a direction that is 180 degrees opposite the direction to our Milkyway galaxy. If you find the same cosmological objects in the same statistical distributions as observed in our optical bubble (i.e. the mass distribution within the greater cosmos is isotropic on the largest scales), the Universe is therefore an expanding Steady-State cosmos, but if the pattern you observe is substantially different, a big bang (or several) may have occurred to produce the universe. Such a big bang would be much larger than anything presently envisioned. This big bang would also have started at least 25 billion years ago--perhaps a 100 billion years, or more.

We can only see as far as the C.B.R. and because of this, we assume we are observing our entire universe and that the universe is approximately 15 billion years old. As is clear from the above, this classical view of the extent of our cosmos may be profoundly incorrect--we need to evaluate the basis of these axioms and assumptions.

There is currently no compelling evidence that the cosmos is either finite or infinite. Observations of the cosmic background radiation by new orbital instruments in the near future are expected to produce new, 'higher-resolution' maps of the C.B.R. If paired arcuate anisotropy is revealed within these new C.B.R. maps, this will result in the conclusion that the universe's geometry is that of a 3-Torus (a donut shape in other words). If the C.B.R. does not reveal such local arcuate anisotropy, determining the geometry of space-time may not be possible. (Review Article:  Is Space Finite? - by Jean Pierre Luminet, Glenn D. Starkman and Jeffrey R. Weeks., Scientific American, April 1999, p68.).

If the universe does extend beyond the optical extinction radius, we will never know whether the cosmos is finite or infinite in all four dimensions. If our optical universe is part of a greater Steady-State cosmos, mass-gravity and energy would be isotropically distributed on the largest scale. If the universe is due to one or more Big Bangs, radiative mass-gravitation should be anisotropic on the largest scale--it would vary in 4 dimensions on the largest scale according to mass-gravity and energy density.

Either way, matter and energy beyond the 15 billion light year optical bubble can never directly affect the Earth--the greater cosmos may be infinite but our unique 'universe' definitely is not (excluding the theoretical possibility of exotic 'worm-holes' etc.). It's finite boundary is defined by the rate of cosmological expansion. External non-viewable mass/energy will still significantly affect matter within our optical bubble over billions of years.  If the cosmos is steady-state, the subtle effects of invisible mass and radiation will be relatively constant and may go largely unsuspected or unnoticed.  Alternatively, if the cosmos is due to one or more vast, ancient big bang events, the effect on our optical bubble, and the mass it contains, should not be constant and large-scale anisotropy should be expected.  From current astronomical observations, this latter suggestion does not seem to characterize our viewable optical bubble.
 

Expansion Rate Effects on the Distance to the Optical Bubble Boundary

The rate of expansion directly controls the distance to the optical extinction boundary. The expansion or contraction of a cosmos alters mass-energy densities, observed average background photon wavelengths, and the radial distance to the optical extinction boundary.

i.e.

A shrinking universe can never have an optical extinction boundary, because in this case, recession velocity is not a factor so no superluminal recession boundary exists (though intervening matter density may still obscure the observer's field of view) and radiation and gravity would be truly direct and universally felt (The distinction between universe and cosmos is redundant in a shrinking cosmos). There would still be a cosmic background radiation flux but the average wavelength observed would be rising and exhibiting growing anisotropy--unless the observer were located directly at the centre of the universe's gravity well [which assumes a finite cosmos, otherwise there could never be an average 'centre-of-gravity']--a most unhealthy place to be for any observer! (due to the flux of short wavelength radiation).

i.e.

The viewable area was larger in the past but acceleration of cosmological expansion causes the optical bubble of all of the possible observing points throughout the cosmos, to reduce their radius.

Further Theoretical Considerations

If the cosmological expansion rate were exponential, the optical bubble boundary would actually be much closer to the Earth based observer than it 'appears' to be, because the recession velocity would increase exponentially with distance. If we mistakenly were to interpret an exponential cosmological expansion as ~linear, we would also interpret the visible cosmos to be significantly larger, and therefore much older, than it actually is.

Therefore, the faster the rate of cosmological expansion with distance, the closer the optical extinction boundary will be. If exponential cosmological expansion is an actual characteristic of our cosmos, our galaxy may not be that much younger than very distant visible galaxies. Moreover, if the expansion were accelerating due to an undetermined pervasive cosmological exponential effect, either within a vast finite cosmos, or, within an infinite steady-state cosmos, the apparent shrinkage of the radial distance to the optical extinction boundary will be an 'apparent' extinction radius shrinkage--it would not be a real shrinkage of the observable space-time bubble, but merely an optical illusion produced by exponential cosmological expansion.

One commonly perceived 'problem' with this optical bubble concept is the implied superluminal relative motions which are not percieved as 'permissible' according to the General Theory of Relativity. To this I say, light exiting the observers optical bubble boundary has effectively, permanently left the observers universe, so constraints of General Relativity are not transgressed.

Also, there is a growing body of evidence that relative superluminal motions are occuring within our own galaxy. See these links below:

GRO J1655-40  "...The star, identified as GRO J1655-40, was discovered using NASA's Gamma Ray Observatory on July 27, 1994, when it underwent such a strong outburst of x-rays that it quickly became the strongest x-ray source in the sky, said Jet Propulsion Laboratory astronomer Dr. Robert Preston, a member of the observing team which began tracking the object shortly after its discovery... ..."The star exhibited some exotic behavior," Preston said, "ejecting material at 80 percent of the speed of light just like very powerful quasars..."

GRS 1915-105  "...Researchers using the Very Large Array (VLA) have discovered that a small, powerful object in our own cosmic neighborhood is shooting out material at nearly the speed of light -- a feat previously known to be performed only by the massive cores of entire galaxies. In fact, because of the direction in which the material is moving, it appears to be traveling faster than the speed of light -- a phenomenon called "superluminal motion." This is the first superluminal motion ever detected within our Galaxy..."

and,

"...During March and April of this year, Dr. Felix Mirabel of the Astrophysics Section of the Center for Studies at Saclay, France, and Dr. Luis Rodriguez of the Institute of Astronomy at the National Autonomous University in Mexico City and NRAO, observed "a remarkable ejection event" in which the object shot out material in opposite directions at 92 percent of the speed of light, or more than 171,000 miles per second. This event ejected a mass equal to one-third that of the moon with the power of 100 million suns. Such powerful ejections are well known in distant galaxies and quasars, millions and billions of light-years away, but the object Mirabel and Rodriguez observed is within our own Milky Way Galaxy, only 40,000 light-years away. The object also is much smaller and less massive than the core of a galaxy, so the scientists were quite surprised to find it capable of accelerating material to such speeds..."

What the above clearly indicates, is that these ejected stellar-jet lobes are exceeding the speed-of-light relative to each other.

i.e.  Each jet lobe achieves ~92% of c relative to the emitting star, which implies a superluminal motion of ~184% of c, when each jet lobes velocity is measured relative to the other jet!

These observations prove that the commonly perceived and accepted General Theory of Relativity's axiom that superluminal motions are not possible within our universe, has been shattered and a review of this axiom is required and the initial reasons for its positing, need to be reviewed also. Because superluminal motions are observed within our galaxy, the erroneous anti-superluminal motion axiom of General Relativity, represents no impediment whatsoever to utilisation/adoption of 'Olber's Window' concepts.
 

Which Cosmology?

The most enticing and elegant aspect of the Optical bubble/Olber's Window concept, is the way it naturally emerges from expansion observations--independent of recent and current cosmological paradigms. It can be adapted to all modern cosmological paradigms because it is 'natural' and uncontrived and also an intuitively predictable outcome of Hubble's original observation that the cosmos is expanding.

It is widely perceived by many scientists, lay people and science journalists that the steady-state cosmology was conclusively defeated by empirical evidence during the 1960's--such was not the case. What appears to have happened is that none in the steady-state proponents could offer a promising alternative C.B.R. explanation when one was desperately required to counter the big-bang interpretation of the C.B.R., but this does not mean that a steady-state explanation did not exist nor would not be identified at some latter time. Many people flocked to the big bang's C.B.R. explanation in lieu of a suitable steady-state alternative interpretation for the C.B.R.

Sir Fred Hoyle, the main proponent of the original steady state cosmology, as well as several other notable cosmology theorists, have stridently resisted the big-bang paradigm and its C.B.R. explanation. Hoyle continued to co-write papers on quasi-steady-state cosmology into the 1990’s. Many of these papers and abstracts are available through NASA’s Astronomy Abstract Service.

One of the reasons for the perceived discrediting of the steady-state model had more to do with some of its supporters than the cosmology itself.  Many of these non-scientific supporters fixated on the steady-state cosmology due to their personal philosophical or religious preferences, rather than due to scientific empiricism.  Hoyle was apparently irritated by the number of philosophers and religious individuals/groupings, who dearly hoped for the success of the Steady-State cosmology over the Big-Bang as part of an effort to resist scientific determinism, thereby preserving the desirable mystery of a vast, creative, infinite cosmos.

Hoyle, in retrospective, considered that the 'big-bangers' came to be generally perceived as more scientifically 'proper and reputable'.  This combined with the lack of an immediately forthcoming Steady-State explanation for the C.B.R., provided the boost necessary to propel the big-bang cosmology into general international scientific acceptance.  Another perceived 'problem' for the steady-state model was that it had to generate 'new matter' from the void, either within empty space between galaxies, or within galaxies, causing them to bud-off new galaxies which would grow and bud-off others, producing galactic clusters (or both mechanisms), thereby producing the 'appearance' of continuous cosmological expansion and large scale isotropy.

This is a misleading perception because generating 'new matter' out of the void is a major problem for any and all cosmological paradigms.  The big bang singularity, and what it implies is equally troublesome to the Steady-State's continuous matter generation requirements.

i.e.

"...Once upon a time, all of this energy and matter which we now see, all of the leptons and quarks that make up ordinary matter, were suddenly spontaneously generated from nothing, for no identifiable or particular reason..."  All cosmological models claim this in one form or another, so this is not an argument for or against any particular cosmological paradigm--it is an unresolved problem for all.

The big bang looks increasingly exposed at present and will remain so unless a a 'special form' of matter or energy is identified which can breath life back into this paradigm. The big bang is by no means a cosmological dead-end as a 'working model', but we should recognize that it may not survive future astronomical observations in its present weakened state.

All bets are currently off in cosmology. The emergence of an evolved quasi-steady-state derivative explanation for the cosmos can not be ruled out, although it would take some time to gain a foot-hold. The general perception that the big bang model and its C.B.R. explanation irrevocably disallowed a 'generic' steady-state cosmology, is deeply entrenched in the scientific literature and it is routinely repeated by the lay-media, and this maintains an inertia of bias against the model.

The optical bubble concept delivers a C.B.R explanation that the Steady-State model required in the 1960's, but the Steady-State cosmology still has other hurdles to address.
 

Concluding remarks

At present, no posited cosmology satisfies empirical astronomical observations. There exists no consensus from the past and present observations of the universe which specifically vindicates one cosmological paradigm over another. The optical bubble concept is flexible and applicable to all presently posited cosmologies.

Finally, the reader should consider these questions:

• If the C.B.R. does not require a big-bang explanation, what then are the compelling reasons for using the big-bang as the primary working assumption and interpretative tool within cosmology?

• Do remaining compelling reasons for subscribing to the big-bang have plausible alternative explanations within other cosmologies?

Carey, S.W., 1988. Theories of the Earth and Universe, Stanford University Press. Stanford California,  413p.

Carey, S.W., 1996. Earth, Universe, Cosmos, University of Tasmania, Tasmania Australia 245p.