Gravity isn’t just for keeping planets in their respective orbits; it’s a force that acts on all matter in the universe. That’s the basis of Isaac Newton’s theory of Universal Gravitation. The greater the object’s mass (and the closer it is), the greater the gravitational force on other objects around it. All of the bodies in our solar system are affected by the gravitational pull of the Sun. However, the Sun is just one of hundreds of billions of stars in our galaxy, which in turn is one of more than 100 billion galaxies – all of which have gravitational pulls. All of which also move, by the way. For example, the Sun completes one rotation around the centre of the Milky Way every 230 million years or so.
Einstein disagreed with Newton on gravity; his General Theory of Relativity stated that gravity isn’t a force at all, but a curvature in space-time (or the ‘fourth dimension’). This means that objects like the Earth are actually travelling along a straight path – because objects always seek the shortest distance between two points – but due to a curve in space-time, that straight path is spherical. There are some newer theories about gravity, but the important thing to note is that it’s ultimately what holds everything together.
Answered by Shanna Freeman, HIW contributor.