What are the drawbacks of the tidal theory?

The concept of tidal theory does not refer to a single, unified scientific explanation, but rather a collection of hypotheses across astrophysics and geology attempting to explain phenomena driven by differential gravitational forces. While modern science readily accepts the Newtonian gravitational foundation for ocean tides, the historical record, and even contemporary application in complex systems, reveals significant conceptual and quantitative drawbacks associated with purely tidal explanations. Examining the failures and limitations of these theories—from the attempts to explain the Earth’s origin to the intricacies of celestial mechanics—provides a clearer picture of where purely tidal models fall short.

# Galilean Misstep

Perhaps the most famous, yet most demonstrably flawed, application of a tidal-like concept comes from Galileo Galilei’s explanation for the ebb and flow of the ocean. In a move later deemed one of his worst scientific arguments, Galileo emphatically rejected the correct, lunisolar theory—which attributed tides to the gravitational influence of the Moon and Sun—dismissing it as “childish” and “occult”.

Galileo’s theory attempted to attribute the tides solely to the Earth’s combination of rotation on its axis and its revolution around the Sun. He visualized this using a torus (a ring or donut shape) filled halfway with water, representing the ocean around the globe. When this ring is spun on its midpoint (Earth’s rotation), the water stays level due to symmetry. However, when this spinning ring is also moved along a circular path (Earth’s orbit around the Sun), asymmetry arises. One part of the ring is boosted by the orbital motion, while the other is slowed down or opposed. The faster water piles up on the slower water, creating a high tide, and leaving a low tide behind it.

The immediate, glaring drawback was that this mechanism predicted an interval of twelve hours between high and low water, corresponding to the Earth’s full rotation cycle relative to the Sun in his model. In contrast, the universally observed reality is that high and low water occur roughly six hours apart, accounting for two high and two low tides in a 24-hour period. Galileo was so certain of his model that he attempted to dismiss the six-hour interval as coincidental or specific only to the Mediterranean Sea, even citing false data suggesting Lisbon experienced twelve-hour tides.

A second critical failure within this historical model related to seasonality. Based on his reasoning involving the inclination of the Earth’s axis, Galileo’s theory implied that tidal effects should be maximal in the summer and winter months. Observationally, however, the most extreme tides are known to occur during the spring and fall, precisely when the solar influence is structurally maximized due to the alignment of the Sun, Earth, and Moon.

The most fundamental challenge to Galileo’s tidal mechanics, however, lay in its inconsistency with his own espoused principle of relativity—the idea that experiments within a uniformly moving system cannot reveal that system's absolute motion. If his torus model worked as claimed, a scientist on a ship moving in a straight line could detect that motion by observing the resulting water sloshing within a container. Since motion relative to the Earth itself, and relative to the water, is what matters for fluid dynamics, Galileo’s model, which relied on the absolute inequality of speed stemming from the Earth’s orbit, could not hold up against his own philosophical underpinnings. Contemporaries quickly pointed out that his model failed to produce the necessary relative inequality of speed within the water body itself that is required to generate tides.

# Formation Hypotheses Overthrown

Moving from the explanation of daily tides to the origin of the solar system, the “Tidal Hypothesis,” proposed primarily by Sir James Jeans in 1919 and later modified by Harold Jeffreys, also crumbled under the weight of its own theoretical shortcomings. This theory suggested that the planets formed from a massive cigar-shaped filament of incandescent gaseous matter ejected from the primitive Sun following a close gravitational encounter with a much larger, passing “intruding star”.

The first major strike against this model was one of cosmic probability. In a universe where stars are immensely distant, the necessary close approach between the Sun and this hypothetical rogue star was deemed statistically improbable by critics like B. Levin. Furthermore, Jeans never accounted for the ultimate fate or location of this crucial intruding star, leaving a massive explanatory hole in the narrative.

Beyond probability, physical and compositional discrepancies proved fatal. Mathematical analysis performed by N.N. Parisky demonstrated that the resulting structure of the ejected filament could not mathematically account for the actual distances separating the planets in our current solar system. A more damning chemical argument was the composition mismatch: the resulting planets were found to be composed largely of elements with higher atomic weights, whereas the Sun, the supposed source material, is overwhelmingly composed of light elements like hydrogen and helium. The tidal hypothesis offered no credible mechanism to explain this significant compositional sorting during ejection and condensation.

Finally, the hypothesis failed on dynamical grounds. Jeans could not explain how the ejected, incandescent gaseous matter actually condensed into solid or liquid planetary bodies, nor could he adequately describe the mechanism by which the planets acquired their orbital and rotational angular momentum from the resulting filament. Jeffreys attempted modifications in 1929, suggesting the intruding star collided with a companion star first, but even he eventually conceded that his updated version required significant revisions and was flawed in several areas. The failure of this model paved the way for the Nebular Hypothesis, which better explains the distribution of angular momentum via a collapsing disk structure, highlighting that a theory which cannot account for the conservation of angular momentum will inevitably fail.

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# Analytical Obstacles in Modern Tidal Mechanics

Even when dealing with the accepted gravitational framework—which explains oceanic tides via the differential pull of the Moon and Sun—applying tidal theory to complex, multi-body systems or to interior planetary dynamics reveals inherent drawbacks related to unknown parameters and the nature of energy dissipation.

# The Dissipation Unknown

In the context of tidal heating, such as that experienced by moons orbiting giant planets or the hypothetical scenario of binary planets, a major challenge surfaces: quantifying the rate at which tidal energy is converted into heat. The rate of this dissipation is a complete unknown. In practice, astrophysicists often bypass the complex mathematics—which involves numerous crude approximations and assumptions about an object's rheology (its flow properties), orbital frequency, and mass—by simply using a dissipation value that has already been observed for one of our Solar System's bodies and assuming it applies elsewhere. This reliance on analogy rather than first-principles calculation is, as one researcher noted, essentially a "massive guess".

The existence of tidal equilibrium presents a counterintuitive drawback to the heating model itself. When two bodies become tidally locked—always showing each other the same face, like the Earth and our Moon—the deformation of the surface (the tidal bulge) aligns perfectly with the line connecting the two centers. Because the bulge is static relative to the partner body, there is no longer any misalignment or ebb and flow of material across the surface. Consequently, there is no dissipation of energy, and thus no tidal heating. This shows that the very mechanism that drives orbital evolution eventually shuts itself off once equilibrium is achieved, placing a limit on the sustained effect of tidal forces.

# Challenging Gravitational Centrality

Furthermore, some critiques argue that attributing all observed periodic variations in Earth’s fluids (magma, ocean, atmosphere) solely to the gravitational interaction with the Moon and Sun overlooks the system’s internal dynamics, treating the relationship as purely external and passive. For instance, proponents of an inertial worldview argue that the most prominent tidal components—the semidiurnal (twice daily) and the spring-neap (half-monthly) cycles—are fundamentally manifestations of the Earth’s own rotational inertia and its elliptical path around the Sun, respectively, and thus have nothing to do with the Moon.

The mathematical description of the gravitational difference itself is often cited as insufficient. While Newton’s law can describe the phases of tides, the calculated magnitude of the tidal force difference ($\Delta a_g$) is often too small when compared to the Earth’s own gravitational pull to adequately explain the observed water level changes. Moreover, the standard gravitational model struggles to account for the consistent leading or lagging of tidal phases relative to the Moon’s overhead position, suggesting that the observed phenomena are only superficially synchronized with celestial bodies.

This leads to a conceptual distinction between phenomenology and fundamental cause. Gravitational theory is successful in describing the space-time phases—the superficial regularities—but fails to capture the true essence of the energy source. The fact that planets like Mars, with its moons, show complex, simultaneous atmospheric tidal peaks suggests a mechanism tied to the planet’s formation inertia rather than simple external attraction, as the number of peaks does not neatly correspond to the number of attracting moons in the gravitational framework.

# Limits in Dynamical Modeling

When applying tidal dynamics to orbital mechanics, the drawbacks manifest as complications that require extra, non-trivial terms to be added to the equations, suggesting the base Newtonian model is incomplete for high-precision, long-term predictions. While the Newtonian framework can describe an average elliptical path for the Moon around the Earth, it struggles with the observed precession of the orbit—the slow drift of the perigee (closest point) and apogee (farthest point).

The inertial model, by contrast, suggests that this orbital drift is naturally explained by a time-dependent factor ($C$) introduced into the dynamical equation, which accounts for how the overall system’s total mass-energy state ($\text{K}$) evolves over time. When this factor is non-zero ($dK/dt = C \neq 0$), the resulting equation explicitly describes an eccentric ellipse whose long axis changes over time, perfectly mirroring the observed shifting of the Moon’s perigee and apogee. The Newtonian approach requires adding these precessional effects ad hoc to the simple elliptical solution.

This difficulty in accurately modeling orbital evolution also extends to the Earth’s own orbit around the Sun, where Mercury’s well-known perihelion precession also points to the limitations of describing multi-level orbital mechanics solely through static gravitational interactions.

# A Synthesis of Failure Points

The history of tidal theory, in all its manifestations, demonstrates a pattern where initial simplicity gives way to empirical contradiction or mathematical complexity. Galileo’s failure arose from a lack of a plausible force mechanism, rejecting the correct one in favor of an explanation inconsistent with his own physical tenets. The Jeans-Jeffreys failure arose from an empirically and chemically impossible scenario—a star encounter that could not account for the final mass distribution or angular momentum structure. Modern applications reveal a third failure mode: reliance on unquantifiable rates (dissipation) and the necessity of patching simple orbital equations with extra terms to account for subtle but real orbital drifts, such as perigee precession.

If we abstract these failures, we can draw a critical conclusion about any theory relying heavily on tidal mechanisms for structure formation: any model that cannot intrinsically conserve angular momentum across all scales of accretion will fail to predict the final state of the system. The filament model of Jeans and Jeffreys, which involved material being ejected and then cooling, could not account for the organized, disk-like distribution of angular momentum seen in the solar system. When constructing a model for celestial evolution, whether it be planetary rings or entire solar systems, the constraint of momentum transfer must be an inherent part of the primary interaction, not an effect tacked on afterward to correct the geometry.

It is instructive to note how these failures force a shift in perspective. The consistent failure of purely gravitational tidal formation models to account for angular momentum required the adoption of the spinning disk concept from the Nebular Hypothesis—a concept where organized rotation is foundational, not an afterthought. In the case of Earth's tides, the failure of the purely gravitational model to account for all periodicities is driving researchers toward an inertial perspective where the inherent "energy" of formation dictates long-term, cyclical motions. The drawback, therefore, is often not that the tidal force doesn't exist, but that tidal forces alone are insufficient to be the sole or ultimate cause for the observed phenomena, whether the outcome is the architecture of a solar system or the precise timing of an ocean wave.