What is spacetime?

Answer 1

Spacetime can be looked at as a "fabric" of space and time. It is composed of the 3-dimentional space we are familiar with and by time. Answer improved: Spacetime is composed of three vector space displacement dimensions (ix +jy +kz) and one distance(time) dimension ct. This constitutes a quaternion space as defined by William Rowan Hamilton with i^2=j^2=k^2 = ijk= -1 . Quaternions provide a proper mathematical space with a point p=ct + ix +jy +kz and p^2 = ((ct)^2 -(x^2 + y^2 + z^2)) + 2ct(ix + jy + kz) Minkowski's spacetime is mathematically improper (not a divisions algebra).

Answer 2

In physics, spacetime is any mathematical model that combines space and time into a single construct called the space-time continuum. Spacetime is usually interpreted with space being three-dimensional and time playing the role of the fourth dimension. According to Euclidean space perception, the universe has three dimensions of space, and one dimension of time. By combining space and time into a single manifold, physicists have significantly simplified a large amount of physical theory, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels. http://en.wikipedia.org/wiki/Space_time

Answer 3

It is the fabric of space and time. In general, the smallest 'known' thing (quantum foam, which forms the fabric) is actually time itself in physical form (it's size is around 0.0000000001 yoctameters). For example, Earth's gravity. Since time's fabric is stretched throughout the Universe, and obviously isn't flat, the Earth puts a dent in it. Try putting a ball in a bowl and spinning the ball around the edges; that is what gravity is. So a more extreme thing, like a Black Hole, rips the fabric because it is so extremely dense with such extreme gravity. There are some really interesting theories regarding this, like traveling through time by flying through a tear in the fabric.

The Sun (Sol), for example, keeps the eight worlds in orbit because of it's dent. All of the planets are traveling at exactly the right speed to avoid hurtling into the bowl of gravity, and are kept at a constant speed, almost never moving closer.

You can look it up for deeper information if you really want to.