As a species, we have a propensity to believe only in those things which are easily discernible to our senses. We tend to dismiss out of hand the existence of those things which are too small to be seen or not dense enough to be felt. The existence of microbes is only a fairly recent discovery, and air was once thought of in much the same way we now think of space. To primitive man air was 'nothing'. It wasn't visible. It offered little resistance to motion. It seemed to have no discernible attributes other than its inertness. They were mystified by the invisible forces of wind. Today, space seems to us to be nothing. You can't see it, taste it or feel it. Space propagates electro magnetism, but not sound. We are mystified by the invisible forces of gravity. Space doesn't appear to have any mass and it offers no measurable resistance to motion. It seems to have only one attribute - volume - which is actually VERY important. For if it wasn't for that single redeeming feature, the Universe would be a solid block of matter in a state of critical mass with nowhere to explode, and things would be really uncomfortable.
It is important to remember that most of the Universe is not material in nature and that which IS material encompasses a wide array of different components. If we allow our imaginations to be governed solely by our senses, we must conclude that space is but a single element - an inert ethereal sea devoid of properties. If we reflect on what we know and what might be possible, it could be that space is comprised of a vast spectrum of elements more numerous than those which populate the Periodic Table. And as our planet plunges through the endless sea of space, variations in the concentrations of those ethereal elements may have a subtle - but very real - effect upon our environment and our lives.
When two objects which have the property of mass approach each other, the space between them shrinks. The rate of this process is inversely proportional to the square of the distance between the masses. Did you catch that part about space shrinking? It wasn't the objects acting upon each other that caused the motion, the space between them simply compressed and motion resulted - and any transference propagated within that space (i.e. gravitational lensing of light) would certainly be altered. Mass (which is a condition that can be converted into energy) is dense. Space is immeasureably sparse. Things that come into contact with each other tend to change condition in such a way as to reduce or eliminate the differential between them. Any change in the densities of mass and space may be very small, but since mass is so much more dense, its expansion may be negligible while the shrinkage of space might be much more drastic. Could the phenomenon of gravity be this simple?
Space is a medium - a form of existence - and although its properties may be too subtle to be directly discerned by our senses and our primitive technology, the form and condition of those properties can be altered. Time is simply a measurement - the comparison of rates of change among two or more processes. Spacetime is a mathematical model that combines the attributes of both space and time into a single factor that simplifies the modeling of physics at the mega-macro and mini-micro levels. It is a scientific shorthand that adds the factor of time as a "dimension" to the three dimensions (more accurately the three axes) of space. In reality, if the properties of space are altered (made more or less dense or changing the circulation of space much like diverting currents within a sea) it would have a direct effect upon the processes occurring within it. A density change would affect the rate of propagation of those changes and altering its flow would affect the direction, sequence and even the nature of propagation. Spacetime is a convenient concept, but something is likely to be lost in the translation when you try to lump the properties of an existence and the process of change into a single continuum.
ANYTHING - material or otherwise - which has a presence within the Universe exists. Space and matter are two very different forms of physical manifestation. Space is ethereal in nature and matter is material in nature. Both exist, and the existence of an infinite expanse of space devoid of matter requires no less logical justification than would an infinite expanse of matter devoid of space.