Hydrogen Cloud Separation as Direct Evidence of the Dynamics of the Universe
| Scientific Paper | |
|---|---|
| Title | Hydrogen Cloud Separation as Direct Evidence of the Dynamics of the Universe |
| Read in full | Link to paper |
| Author(s) | Lyndon E Ashmore |
| Keywords | expanding universe, static universe, hubble constant, age of universe, temperature of universe |
| Published | 2008 |
| No. of pages | 11 |
Read the full paper here
Abstract
Despite the idea of an expanding universe having been around for nearly one hundred years there is still no conclusive, direct evidence for expansion. This paper examines the Lyman Alpha forest in order to determine the average temperature and the average separation of Hydrogen clouds over the aging of the universe. A review of the literature shows that the clouds did once become further and further apart (showing expansion?) but are now evenly spaced (an indication of a static universe?). Doppler parameters give an indication of the temperature and/or the degree of disturbance of the clouds and the evidence is that the temperature or degree of disturbance is increasing rather than decreasing as required by an expanding universe. Whilst these results do not support any cosmology individually, they do support one where the universe expanded in the past but that expansion has now been arrested and the universe is now static. A separate mechanism for redshift would be required to explain why, in this scenario, the Hydrogen Clouds are evenly spaced in the local universe - but have differing redshifts. High z hydrogen cloud separation can be used to give an independent estimate on the lower limit of the age of the universe in an expanding model and it is found that the age must be far greater than the presently accepted value of 13.8 billion years - if the H1 clouds are to achieve their present separations without some mechanism other than inflation being involved.
Overview
Ashmore's paper is an observational argument rather than a theoretical one. It takes two quantities that mainstream quasar-absorption work has been measuring for decades — the line density dN/dz of the Lyman-alpha forest, and the Doppler parameter b of the individual absorption lines — and reads them as a direct record of how the intergalactic medium has moved and heated over cosmic time. The reciprocal of the line density, dz/dN, is taken as the average spacing between hydrogen clouds; the Doppler parameter is taken as an upper limit on their temperature. The paper's claim is that neither quantity behaves as an adiabatically expanding universe requires: the spacing has stopped growing, and the temperature is if anything rising towards the present.
Ashmore is explicit that the data do not support any single existing cosmology. What he proposes instead is a compromise: the Big Bang happened, the elements formed as the mainstream describes, the universe expanded — but its density was exactly the critical density, so expansion has since been arrested and the local universe is now static. In that picture the time dilation seen in high-z supernova light curves is preserved, because the universe really was expanding when that light was emitted; but the redshifts of the nearby, evenly-spaced clouds must then come from some other mechanism, for which he points to tired light and cites his own work in Galilean Electrodynamics. The departure from the standard account is therefore not a rejection of expansion in principle, but a denial that it is still happening, and a denial that present-day redshift measures it.
The argument
Line counting as a dynamical record
Quasar spectra carry a comb of absorption lines imprinted by every pocket of gas along the line of sight. The Lyman-alpha forest lines mark clouds — or at least regions of higher density — of neutral hydrogen. Because redshift stands for both distance and epoch, Ashmore treats the line list as "the black dots on a high school Physics ticker timer tape", a strip recording of the motion of the intervening medium. The cosmological principle then supplies the interpretive rule: at any single epoch the clouds should on average be evenly spaced, so any change in spacing with redshift is a change with time.
The three cases are stated plainly. In a static universe the line density is the same at all redshifts. In a contracting universe the lines crowd together with time, so dN/dz falls as z rises. In an expanding universe the clouds draw apart with time, so dN/dz rises with z. The customary parameterisation is
- dN/dz = (dN/dz)0 (1 + z)γ
with γ a constant and (dN/dz)0 the line density at zero redshift.
What the literature shows
At high redshift the evolution is steep. From 34 QSOs with z > 2.6, Bechtold (1994) found γ = 1.89 ± 0.28 and concluded there must be intrinsic evolution in the number density of absorbers; comparable values were reported by several other groups. Because the clouds appeared to be vanishing faster than expansion alone would explain, two further mechanisms were invoked: thinning by galaxy formation, and ionisation of the neutral hydrogen by quasar ultraviolet radiation, both of which reduce the number density or the collision cross-section.
At low redshift the picture reverses. Weymann et al. (1998), with 63 QSOs and 987 Lyman-alpha lines over 0.0 < z < 1.5, found far more lines per unit redshift than a simple extrapolation of the high-z line predicted, and an evolution that was almost flat, γ ≈ 0.1–0.3. Ashmore assembles the later confirmations: Janknecht et al. (2006) found the evolution over 0.5 < z ≤ 1.9 "is decelerated in the explored redshift range and turns into a flat evolution for z → 0"; Lehner et al. (2007) found "no redshift evolution of dN/dz between z > 0 and z ≤ 0.4"; and Kirkman et al. (2007), working from the flux decrement rather than line counting across 74 QSOs to z = 1.6, found "no change in the number of lines per unit redshift". Ashmore's reading is that clouds with different redshifts nevertheless remain evenly spaced, over a range that "includes most of the supernovae used to show time dilation and hence expansion".
Temperature from the Doppler parameter
The Doppler parameter is decomposed as b2 = bth2 + bnt2, thermal plus non-thermal broadening, so b bounds the cloud temperature from above. Collecting values from eight sources, Ashmore finds b on average smaller at low redshift than at high — implying, he argues, a medium that is becoming hotter or more disturbed with time, the opposite of adiabatic cooling. He adds a consequence for the cosmic microwave background: if the observed blackbody curve is a superposition of radiation from many epochs, each epoch must have been hotter and shorter in wavelength by exactly the right amount; a temperature history that is flat or rising cannot do that, so "the CMB must be local".
Extrapolating to a touching-cloud epoch
Taking the high-z behaviour at face value, Ashmore extrapolates Bechtold's relation backwards to ask when the clouds were in contact. With γ = 1.89 ± 0.28 and (dN/dz)0 = 9, and with H I clouds about 70 kpc across giving 6,600 clouds per unit redshift when touching, he obtains z = 31.78 with an upper uncertainty of 27.2. Pushing the same relation to an absurd limit — a cloud "separation" of 10−10 m, requiring 1.5 × 1036 clouds per unit redshift — gives z = 4.32 × 1018, with a range of 1.67 × 1016 to 7.3 × 1021. His conclusion is that in an expanding cosmology the universe must be very much older than the 13.8 billion years the Hubble constant implies, or else something other than inflation must have driven the clouds apart.
Assessment
The strength of the paper is its discipline about sources. Every number it uses is somebody else's published measurement, and the two flat-evolution results it leans on hardest — Lehner et al. and Kirkman et al., the latter using flux decrement rather than line counting and so free of the line-deblending problems that dog dN/dz — are real and are quoted accurately. The observation that the low-redshift flatness is explained in the standard picture by a near-cancellation between two unrelated processes (dilution by expansion and galaxy formation on one side, a declining UV background on the other) is a fair one; a fine balance between independent effects sustained over half the age of the universe is the kind of coincidence that deserves the scrutiny Ashmore gives it. His citation of Hartnett's finding of more local quasars than expected is a legitimate pressure point on the UV-background half of that explanation.
The arithmetic is CORRECT. Substituting into (1 + z)1.89 = 6600/9 = 733 gives 1 + z = 32.8, that is z = 31.8, exactly the paper's figure; the ±0.28 on γ propagates to roughly z = 20 to z = 59, consistent with the quoted upper bound of +27.2. The second extrapolation reproduces even better: (1 + z)1.89 = 1.5 × 1036/9 gives z = 4.33 × 1018, and the γ range gives 1.7 × 1016 to 7.5 × 1021, matching the paper's 1.67 × 1016 and 7.3 × 1021 to the precision of the rounding. What the paper does not show is the conversion behind the figure of 6,600 clouds per unit redshift. Combined with 70 kpc clouds that figure implies about 460 Mpc of distance per unit redshift, which is roughly an order of magnitude smaller than c/H0 ≈ 4,300 Mpc for H0 = 70. Using the larger distance the touching epoch moves to about z = 46 rather than z = 32. This does not damage the qualitative point, but the unstated distance scale is doing real work in a number the paper presents as a result.
The deeper difficulty is with the premise that dN/dz measures cloud separation at all. The number of absorbers per unit redshift is the product of comoving number density, absorption cross-section, and the path length dl/dz; the last of these varies with redshift in any expanding cosmology purely as geometry, with no change whatever in how the clouds are spaced. A non-evolving population already yields γ of order 0.5 to 1 in standard models, so γ = 1.89 cannot be read as "spacing scaled as (1 + z)−1.89", and γ ≈ 0 at low redshift cannot be read as "spacing constant". The paper's own recital of the literature makes the same point against it: the workers it cites attribute the high-z slope explicitly to intrinsic evolution in the number and cross-section of absorbers, not to expansion, and Ashmore then extrapolates that slope as though it were expansion when he computes the touching redshift. In the modern picture the forest is not a population of discrete conserved clouds at all but a filamentary photoionised medium whose neutral fraction tracks the ultraviolet background, which removes the object being counted.
The temperature argument has a similar shape. A rising intergalactic temperature towards low redshift does not contradict expansion, because the intergalactic medium is not adiabatic — it is photoheated by the same UV background whose decline the paper invokes elsewhere, and He II reionisation near z ≈ 3 is the standard explanation for exactly the heating trend the b-parameter data show. The CMB corollary rests on a misstatement of the standard model: the microwave background is not a superposition of radiation emitted at many epochs but light from a single surface of last scattering at z ≈ 1100, so no fine-tuned temperature history is needed to keep the blackbody spectrum perfect, and the observed COBE/FIRAS spectrum is fitted without one. Finally, the age argument does not close: z ≈ 32 corresponds to roughly 100 million years after the Big Bang in standard cosmology, which is not in tension with 13.8 billion years, and the paper never converts its redshifts into times to check. The hybrid cosmology of the conclusion — expansion exactly halted at critical density, redshift now produced by another mechanism — is also asserted rather than derived, and a universe at exactly the critical density does not stop expanding in finite time in general relativity; it decelerates asymptotically, which is not the same thing, and a truly static late universe requires either a fine-tuned cosmological constant or a departure from the field equations the paper says it is keeping.