As the turn of the next century
approaches, we again find an established science in trouble trying
to explain the behavior of the natural world. This time the problem
is in cosmology, the study of the structure and "evolution"
of the universe as revealed by its largest physical systems, galaxies
and clusters of galaxies. A growing body of observations suggests
that one of the most fundamental assumptions of cosmology is wrong.
Most galaxies' spectral lines are shifted toward the red, or longer
wavelength, end of the spectrum.
Edwin Hubble showed in 1929 that the more distant the galaxy,
the larger this "redshift." Astronomers traditionally
have interpreted the redshift as a Doppler shift induced as the
galaxies recede from us within an expanding universe. For that
reason, the redshift is usually expressed as a velocity in kilometers
per second.
One of the first indications that there might be a problem with
this picture came in the early 1970's. William G. Tifft, University
of Arizona noticed a curious and unexpected relationship between
a galaxy's morphological classification (Hubble type), brightness,
and red shift. The galaxies in the Coma Cluster, for example,
seemed to arrange themselves along sloping bands in a redshift
v.s. brightness diagram. Moreover, the spirals tended to have
higher redshifts than elliptical galaxies. Clusters other than
Coma exhibited the same strange relationships.
By far the most intriguing result of these initial studies was
the suggestion that galaxy redshifts take on preferred or "quantized"
values. First revealed in the Coma Cluster redshift vs. brightness
diagram, it appeared as if redshifts were in some way analogous
to the energy levels within atoms.
These discoveries led to the suspicion that a galaxy's redshift
may not be related to its Hubble velocity alone. If the redshift
is entirely or partially non-Doppler (that is, not due to cosmic
expansion), then it could be an intrinsic property of a galaxy,
as basic a characteristic as its mass or luminosity. If so, might
it truly be quantized?
Clearly, new and independent data were needed to carry this investigation
further. The next step involved examining the rotation curves
of individual spiral galaxies. Such curves indicate how the rotational
velocity of the material in the galaxy's disk varies with distance
from the center.
Several well-studied galaxies, including M51 and NGC 2903, exhibited
two distinct redshifts. Velocity breaks, or discontinuities, occurred
at the nuclei of these galaxies. Even more fascinating was the
observation that the jump in redshift between the spiral arms
always tended to be around 72 kilometers per second, no matter
which galaxy was considered. Later studies indicated that velocity
breaks could also occur at intervals that were 1/2, 1/3, or 1/6
of the original 72 km per second value.
At first glance it might seem that a 72 km per second discontinuity
should have been obvious much earlier, but such was not the case.
The accuracy of the data then available was insufficient to show
the effect clearly. More importantly, there was no reason to expect
such behavior, and therefore no reason to look for it. But once
the concept was defined, the ground work was laid for further
investigations.
The first papers in which this startling new evidence was presented
were not warmly embraced by the astronomical community. Indeed,
an article in the Astrophysical Journal carried a
rare note from the editor pointing out that the referees "neither
could find obvious errors with the analysis nor felt that they
could enthusiastically endorse publication." Recognizing
the far-reaching cosmological implications of the single-galaxy
results, and undaunted by criticism from those still favoring
the conventional view, the analysis was extended to pairs of galaxies.
Two galaxies physically associated with one another offer the
ideal test for redshift quantization; they represent the simplest
possible system. According to conventional dynamics, the two objects
are in orbital motion about each other. Therefore, any difference
in redshift between the galaxies in a pair should merely reflect
the difference in their orbital velocities along the same line
of sight. If we observe many pairs covering a wide range of viewing
angles and orbital geometries, the expected distribution of redshift
differences should be a smooth curve. In other words, if redshift
is solely a Doppler effect, then the differences between the measured
values for members of pairs should show no jumps.
But this is not the situation at all. In various analyses the
differences in redshift between pairs of galaxies tend to be quantized
rather than continuously distributed. The redshift differences
bunch up near multiples of 72 km per second. Initial tests of
this result were carried out using available visible-light spectra,
but these data were not sufficiently accurate to confirm the discovery
with confidence. All that changed in 1980 when Steven Peterson,
using telescopes at the National Radio Astronomy Observatory and
Arecibo, published a radio survey of binary galaxies made in the
21-cm emission of neutral hydrogen.
Wavelength shifts can be pegged much more precisely for the 21-cm
line than for lines in the visible portion of the spectrum. Specifically,
redshifts at 21 cm can be measured with an accuracy better than
the 20 km per second required to detect clearly a 72 km per second
periodicity.
Red shift differences between pairs group around 72, 144, and
216 km per second. Probability theory tells us that there are
only a few chances in a thousand that such clumping is accidental.
In 1982 an updated study of radio pairs and a review of close
visible pairs demonstrated this same periodic pattern at similarly
high significance levels.
Radio astronomers have examined groups of galaxies as well as
pairs. There is no reason why the quantization should not apply
to larger collections of galaxies, so redshift differentials within
small groups were collected and analyzed. Again a strongly periodic
pattern was confirmed.
The tests described so far have been limited to small physical
systems; each group or pair occupies only a tiny region of the
sky. Such tests say nothing about the properties of redshifts
over the entire sky. Experiments on a very large scale are certainly
possible, but they are much more difficult to carry out.
One complication arises from having to measure galaxy redshifts
from a moving platform. The motion of the solar system, assuming
a doppler interpretation, adds a real component to every redshift.
When objects lie close together in the sky, as with pairs and
groups, this solar motion cancels out when one redshift is subtracted
from another, but when galaxies from different regions of the
sky are compared, such a simple adjustment can no longer be made.
Nor can we apply the difference technique; when more than a few
galaxies are involved, there are simply too many combinations.
Instead we must perform a statistical test using redshifts themselves.
As these first all-sky redshift studies began, there was no assurance
that the quantization rules already discovered for pairs and groups
would apply across the universe. After all, galaxies that were
physically related were no longer being compared. Once again it
was necessary to begin with the simplest available systems. A
small sample of dwarf irregular galaxies spread around the sky
was selected.
Dwarf irregular galaxies are low-mass systems that have a significant
fraction of their mass tied up in neutral hydrogen gas. They have
little organized internal or rotational motion and so present
few complications in the interpretation of their redshifts. In
these modest collections of stars we might expect any underlying
quantum rules to be the least complex. Early 20th century physicists
chose a similar approach when they began their studies of atomic
structure; they first looked at hydrogen, the simplest atom.
The analysis of dwarf irregulars was revised and improved when
an extensive 21-cm redshift survey of dwarf galaxies was published
by J. Richard Fisher and R. Brent Tully. Once the velocity of
the solar system was accounted for, the irregulars in the Fisher-Tully
Catalogue displayed an extraordinary clumping of redshifts. Instead
of spreading smoothly over a range of values, the redshifts appeared
to fall into discrete bins separated by intervals of 24 km per
second, just 1/3 of the original 72 km per second interval. The
Fisher-Tully redshifts are accurate to about 5 km per second.
At this small level of uncertainty the likelihood that such clumping
would randomly occur is just a few parts in 100,000.
Large-scale redshift quantization needed to be confirmed by analyzing
redshifts of an entirely different class of objects. Galaxies
in the Fisher-Tully catalogue that showed large amounts of rotation
and interval motion (the opposite extreme from the dwarf irregulars)
were studied.
Remarkably, using the same solar-motion correction as before,
the galaxies' redshifts again bunched around certain specific
values. But this time the favored redshifts were separated by
exactly 1/2 of the basic 72 km per second interval. This is clearly
evident. Even allowing for this change to a 36 km per second interval,
the chance of accidentally producing such a preference is less
than 4 in 1000. It is therefore concluded that at least some classes
of galaxy redshifts are quantized in steps that are simple fractions
of 72 km per second.
Current cosmological models cannot explain this grouping of galaxy
redshifts around discrete values across the breadth of the universe.
As further data are amassed the discrepancies from the conventional
picture will only worsen. If so, dramatic changes in our concepts
of large-scale gravitation, the origin and "evolution"
of galaxies, and the entire formulation of cosmology would be
required.
Several ways can be conceived to explain this quantization. As
noted earlier, a galaxy's redshift may not be a Doppler shift,
it is the currently commonly accepted interpretation of the red
shift, but there can be and are other interpretations. A galaxy's
redshift may be a fundamental property of the galaxy. Each may
have a specific state governed by laws, analogues to those in
quantum mechanics that specify which energy states atoms may occupy.
Since there is relatively little blurring on the quantization
between galaxies, any real motions would have to be small in this
model. Galaxies would not more away from one another; the universe
would be static instead of expanding.
This model obviously has implications for our understanding of
redshift patterns within and among galaxies. In particular it
may solve the so-called "missing mass" problem. Conventional
analysis of cluster dynamics suggest that there is not enough
luminous matter to gravitationally bind moving galaxies to the
system.
Reference: "Quantized Galaxy Redshifts" by William G. Tifft & W. John Cocke, University of Arizona, Sky & Telescope Magazine, Jan. 1987, pgs.19-21
November 19, 1998
Back to the Velocity of Light pages
To Lambert Dolphin's Library