seriously how big is space?

Answer 1

Hi ross

Let's begin by asking how big is our observable universe? The size of the universe you can actually see is limited by two things:
(i) the finite age of the universe
(ii) the finite speed of light

How far away you can see things is limited to how far light can travel to reach you. If our universe is about 13 billion years old, then light can travel up to 13 billion years to reach you, hence you can "see" up to 13 billion light-years in distance (about 10^26km). (In practice you can't see all those 13 billion years back because you'll encounter a problem about 300 000 light years from the start - called the last scattering surface, this is the furthest back you can see light before the universe becomes opaque to radiation. But this is a small fraction in terms of our question here, so we'll ignore it).

You might suppose then that we live in an observable universe of radius 13 billion light years. Anything outside this distance isn't visible to us because its light hasn't had time to reach us. This is called a "Hubble volume" or "O-region" by cosmologists. However there's a further complication called the scaling factor. If you're trying to imagine how big the universe might be, it's at least certainly bigger than 13GLY* in radius. To understand why, suppose a photon is fired at you (nearly) 13 billion years ago, from a point X which is 13GLY distant. In the time that the photon is travelling from X to earth, X is moving away from earth due to the universal expansion. A measure of this movement takes into account the expansion rate with respect to time over the intervening time interval and is called a scaling factor (a). The scaling factor over that distance and time works out close to 3, so by the time the photon reaches you X is now about 3 times as far from you as it was. The radius of your universe is now about 39GLY, or 5*10^26km.

However the universe is almost certainly much much bigger than our small O-region. The most recent surveys of the microwave background indicate the universe's largest scale topology is very close to flat, which means it is very large - if not in fact infinite. Tegmark and others have recently constrained the lower limit of O-regions similar to ours to about 10000, meaning the universe is at least 780 TLY* (10^31km) across. In fact the consensus opinion is that the universe is actually infinite in size.


Hope this helps!
The Chicken


* GLY and TLY are Giga light years and Tera light years (10^9 and 10^12 light years respectively)

Answer 2

It depends on the amount of matter in the universe.

Most opinions are that the universe is infinite, however some state that it may be bent round into a giant gravity bubble, This would depend on the number of fundmental particles such as nuetrinos.

Even if it were a giant bubble it is huge, many powers of 10 of light years across.

Answer 3

It's infinite. Which gives a measure of its Creator.