# Understanding the role of infinity into the Multiverse.

## Main Question or Discussion Point

Hi there,

I have no mathamatics background or never attended ant classes of Cosmology. So please if you can answer this question please do so with out any Math :D please bare with me, English is not my native tongue.

This is my question:

according to some scientist the (visible) Universe is flat which could indicate an infinite universe. ( no end just goes on to infinity) Now with the theory of String which indicates that we might have a hyper space or Multiverse. Wouldn't that mean for our universe to be in a multiverse/Hyperspace. That our universe wouldnt be infinite in size, dont you need some space between the universes?

Maybe i should stop watching science shows.
Thank you.

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fzero
Homework Helper
Gold Member
It's a good question. The answer comes down to what we define as a universe within the multiverse picture http://en.wikipedia.org/wiki/Multiverse#Tegmark.27s_classification. In the cosmological setting, the notion of the "observable universe" is important.

Because of the finite speed of light, given the age of our universe, there is a maximum distance that light could have traveled since the big bang. The sphere whose radius takes the value of that maximum distance is known as a cosmological horizon. Our observable universe is the space contained within this cosmological horizon.

Events or objects that take place outside of the horizon cannot have been detected by us at the present time. The technical term for this is that those events are "out of causal contact" with us. We cannot influence those events by cause and effect and vice versa. We are completely blind to anything that goes on beyond the horizon. In particular, the physical constants that determine, for example, the relevant strength of electromagnetism to gravity, could be different in regions beyond the horizon. Events beyond the horizon could not influence the measurements of the fundamental constants that we make here on Earth.

We could call the larger, perhaps infinite, space containing our universe the multiverse. Other regions, completely beyond our horizon, within the multiverse would have their own cosmological horizons which can be used to define them as other universes. We cannot detect or otherwise interact with these universes because of our horizon. In this way, we do in fact have a notion of space between universes.