For upwards of 100 years...

...our knowledge of the cosmos has been vastly expanded in no small part due to the contributions of Albert Einstein and Edwin Hubble. Their work on relativity and deep space observations have taken us from a universe whose extent was believed to be only as far as the edge of our Milky Way to the realization that we are within a seemingly infinite expanse containing more galaxies than we can count.

As our knowledge has expanded, our scientific beliefs have naturally shifted in response. But as new theories have been scaffolded atop the foundations laid by these greats, we collectively neglect to revisit those theories with our modern knowledge while considering the context in which the authors first wrote them. To correct incongruencies between established beliefs and new observations, we seem to favor fantastic rationalizations that promise to patch the outmoded assumptions of a century ago.

Instead of this patchwork process, would comparing the differences between the scientific beliefs during the Progressive era and the seemingly contrary evidence we have today reveal any biases that have not been directly addressed? Even if the mathematical theory remains the same, might the description of the mechanism behind it be different given what we know now?

It is a little-referenced truth that both Einstein and Hubble shared the majority opinion of their time that the universe had no beginning. Their preferred presumption had always been that the cosmos and the contents therein are persistent. This seems counterintuitive from our frame of reference today considering Hubble flow and relativity are often cited as direct theoretical contributors to the Big Bang finite time model. But despite being named dropped in seemingly every paper on the subject (guilty!), they were always reluctant to outwardly agree to the premise even when demanded by their own theories.(1,2)

Edwin Hubble is acknowledged as the first scientist to recognize that some of what we had assumed were stars within our lone galaxy were in fact distant galaxies in their own right.(3) Collaterally, he correlated through light spectrography that the difference between observed and expected light frequencies was proportional to that galaxy’s distance from us. Considering the Doppler effect to be the only sensible cause for that shift in wavelength, he concluded that the evidence suggested an apparent acceleration of distant galaxies away from our own. Such drastic cosmic motion seemed to be in conflict with his personal belief and it required a new and unique physical property of space to accommodate it, but Hubble flow has since become the dominant cosmic model.

Einstein apparently suffered from a similar existential crisis recognizing that his relativity theory implied gravitational collapse without the aid of an outward force.(4) In a permanent universe, especially one consisting of a single galaxy, there is nothing to compel the steady state he desired. Having struggled for years with an arbitrary cosmological constant, his continued discussions with Alexander Friedmann and Georges Lemaître ultimately led to his acquiescence to the metric expansion description of his contemporaries.(5) Seemingly content that the question was settled, he elected to pursue other topics which included debating the apparent disparities between emerging quantum mechanics and his own brainchild of relativity.(6)

Their conclusions fueled considerable scientific progress in the following years. But as the middle of the century approached, new observations resulted in exceptions to metric expansion and relativity akin to the mercurian problem Einstein showed a solution for decades prior. Instead of addressing the shortcomings of their models, these notable deviations have been leveraged to substantiate the hypotheses of increasingly more exotic solutions. For example, the continuing search for definitive evidence of a dark matter or dark energy contributor to serendipitously account for deviations from Hubble’s predictions have yet to mature from divergent mathematical models to confirmed observation. Furthermore a growing divide between a strict adherence to relativity and quantum mechanics betrays the paradox of a Minkowski model and fixed minimum quanta behavior.(7)

We are quick to take ownership of these challenges and claim they are temporally removed from the originators of these models, but this reduces their contribution to a contextless group of symbols on a whiteboard. To sincerely incorporate what was their life’s work, we need to consider the limits to the information they had available.

It was after the passing of Hubble and Einstein that many of the observations which directly supported a finite time universe model were made. Most notably, the cosmic microwave background (CMB) is recognized as evidence that all we know to exist had a beginning. This ancient signal represents the limits of observation while implying that there is more to the universe beyond it. Attributed to the recombination epoch after the Big Bang(8), it is a foundational piece of cosmic origin theories, and necessitates an even distribution and simultaneity to the conversion of primordial cosmic energies.

Theoretically, before the first second had passed, the universe’s contents had been spread over a volume of at least several dozen parsecs in diameter which would dilute any propagating forces in that brief time to be insignificant. It seems reasonable to infer that particles would be causally naive to one another after cosmic inflation. Although there is continued speculation regarding the impact of relativity in these formative moments, the influence of gravity is necessarily suspended or diluted to permit the inflationary epoch.

Astronomically, intergalactic rates of propagation have only been considered when observing electromagnetic (EM) energy or neutrino detections which are known to be causally compliant with the speed of light. This is why we experience a limited observable range despite the theory that the universe is effectively much larger in volume. However, it is a more recent revelation that gravity should now be given that same consideration.

As expected of all particles and forces by relativity, it had been speculated that the spread of the effect of any perturbation to spacetime, including propagation of a gravitational field, must likewise be limited to the speed of light. Although Einstein is credited with this theory, he seemed reluctant to assign gravitational waves any material significance(9). Since he presumed that the contents of the universe were persistent, the gravitational influence of all masses would have already reached cosmic extents making the point moot. Absent compelling experiments or observations, there was little consensus between those who believed in instantaneous persistent gravitational influence and those who adhered to the strict causality limitations in relativity.

Richard Feynman, defying Einstein’s own assertions on the matter, proposed that propagating gravitation must be energetic and suggested how to prove it observationally. This led to the development of the LIGO project which in the last decade has provided the strongest evidence for energetic gravitational waves as well as confirming a speed of light propagation rate. There is now emergent research to characterize a gravitational wave background similarly to the CMB but to help us observe beyond the recombination epoch.(10)

I attempted to substitute these modern realizations into the context of scientific thought from a century ago, from the gravitational questions inspired by Mercury’s curious orbital progression to the latest research regarding quantum foam. While I gained appreciation for the forward progress across all the physical sciences, it was the discoveries I made looking backwards that interested me the most. This thought experiment led to the realization that we have built the models describing our observably finite time and effectively infinite volume universe on the paradigms of men who often promoted the opposite to be true.

This compelled me to ask: If we consider gravitational waves as a propagating energy in a finite time universe in the same way we do with electromagnetic waves, might that change interpretations of observations made over the last hundred years?

To visualize how one might consider this question, imagine a pool in which a stone is dropped. The stone represents an infant particle at the beginning of the universe, and the outbound ripple is its gravitational influence from the first second after inflation. As suggested by the CMB and the way we treat causality with EM energy, these events occur simultaneously for all the other particles that now exist. So if we drop an immeasurable quantity of pebbles evenly spaced into an infinite pond and the expanding ripples represent the initial interaction between them, we see how an individual ripple front impacts a growing area and the reciprocal effect to that individual. Despite the wavefront diminishing in intensity, the range of causally associated pebbles continues to grow at that velocity.

The very concept of a cosmic horizon and an observable universe implies that the propagation velocity of particles since the beginning of time has limited the distance we can observe, and ostensibly the distance into the universe from which you could observe our point. This is an effect we directly observe electromagnetically and have recently verified to be true gravitationally. Note that for the following illustration all sources are presumed in-phase. Although this is not necessarily the case for EM energy, gravity is strictly additive as there is no evidence for out-of-phase time dilation or other “anti-gravity” properties.

To calculate the influence of a progressive flood of new gravitational wave force from the expanding edge of the observable universe, we consider Sir Isaac Newton’s inverse square law (F=1/R^2) which describes the reduction of radiating power over distance. Originally conceived to describe gravitational force, it is the same trend for any radiated wave whether it be force through a medium or energy emitted in free space. And since the range of gravitational effect is unlimited, one can expect its impact to propagate indefinitely.

Although the outbound trend of gravitational energy from a given mass is clearly established, it is the plurality of inbound force in which we are truly interested. As the time-of-flight distance to the cosmic horizon increases linearly, the surface area of our causality frontier grows exponentially (A=4R^2). It is the combination of these two geometries (expansion of surface area and inverse square power) that result in a linear trend.