The idea that objects in orbit are in a constant state of falling is a helpful analogy to understand the nature of orbital motion, but it's important to clarify some key concepts.
In orbital motion, an object, such as a planet, remains in a stable orbit around a central body due to the balance between its forward velocity and the gravitational pull of the central body. The object is not actually falling toward the central body, but rather continuously "falling" in the sense that its path follows a curved trajectory around the central body.
In the case of the Earth orbiting the Sun, it is not gradually falling into the Sun. The Earth's orbit is stable due to its forward velocity and the gravitational attraction between the Earth and the Sun. The Earth's motion around the Sun is in balance, resulting in a nearly circular orbit.
The conservation of angular momentum plays a crucial role in keeping the Earth in a stable orbit. The Earth's velocity is precisely balanced with the gravitational force exerted by the Sun, causing it to maintain its distance from the Sun without spiraling inward.
Given our current understanding of celestial mechanics, it is highly unlikely that the Earth will crash into the Sun in the future. However, it's worth noting that over an extremely long timescale, factors such as the gradual loss of mass by the Sun over billions of years and potential gravitational interactions with other celestial bodies could lead to changes in the Earth's orbit. But these processes occur over such vast timescales that they are not a concern for the foreseeable future.
In summary, the Earth's orbital motion around the Sun is a stable balance between forward velocity and the gravitational pull of the Sun. The Earth is not slowly falling into the Sun, and the current understanding of celestial mechanics suggests that a collision between the Earth and the Sun is highly unlikely.