It is common nowadays to say space, time, gravity, mass, energy – all that we consider components with which we ‘construct’ or model our reality – are interlinked inextricably, none being entirely independent of the other.
Time, as a late good friend would say, is simply a measure of motion…and thus is not an independent dimension. But since motion is finite, dependent upon mass and energy, and observable, so is time – it is linked to the other aspects and reflects changes in state. Observations of time are evidently relative (as Einstein hypothesized with amazing insight) and time and space are related simply by a constant – the speed of light – which is another measure of how soon the presence of any aspect (such as mass or energy) can be detected. Gravity is another manifestation of such presence as well, and shares the same ‘speed’ as light…and when mass is speeding along, time (or any measurement of it) changes relatively so as to remain consistent. Or when gravity changes, so does time.
When mass is present, we hypothesize a force, of gravitational attraction; such insight is attributed to another scientific giant, Newton. Yet, no physical explanation was ever convincingly (or conclusively) attached to gravity…what it it that attracts any matter to any other? Or is it something else? Einstein therefore was fond of saying “Objects are not in space, they are spatially extended.” And he called gravity not a force, but a curvature of spacetime (coined as a single word) that varied according to variations in other aspects interacting. Therefore, an apple falls into the gravity ‘well’ directly, vertically, while a speeding bullet traces a long parabolic path. And hence he hypothesized that speeding light must bend too – which we have indeed verified in eclipses and gravitational lensing. But that would also imply that gravity may bend, perhaps, and demonstrate wave-like characteristics…yet this aspect remains unclear, unverified. Nevertheless, it is clear that mass affects what we think of as ‘space’ around it. So does energy, for mass and energy are also inter-convertible through the square of the spacetime constant.
I observed a curious thing today as I cut a small plastic bag enclosing some spicy flour. As I inserted the triangular cut portion into the empty bag, to recycle the plastic, the small bit jumped back out of the opening and stuck to my hand. The few electrostatic charges on the triangular piece, induced by the cut and handling, were far stronger than gravity. You can see this after brushing hair with a plastic comb and observe little pieces of paper jumping up to the comb if you wave the comb above them. Electrostatic forces are evidently many orders of magnitude greater than gravity. Magnetic forces too are similarly far stronger – magnetic levitation is a reality. It is perhaps a reasonable assumption, therefore, as in the Hollywood movie – Interstellar – out recently, that we will overcome the problem of gravity soon…