How can we know if there is a limit to the universe?

No boundary to the Universe has been found so far. The Universe may be infinite in size, or not. This is an open question. There are several ideas about how the Universe works. The evidence so far suggests that the Universe is flat, and there is no curvature unless it turns out that there's curvature very, very far away. It's certainly flat to any distance that we could reach, for example with a flash light, or light that is coming to us.

Well, ..., Here's why the Universe is finite:

It started off with finite mass and energy. It neither creates new mass or destroys the old mass. Nor does it create or destroy energy. Even though it is currently expanding that expansion will one day stop and the universe will come to an end. The universe held no control over it's inception and creation, has no control over it's current state and cannot control it's future demise. In fact the Universe is running out of time.

I know it's an unpopular concept to grasp bu the universe is finite in energy, mass, and life cycle and that's all there is to it. See the links below:

Now the edge of the current universe is difficult at best to describe. First none one has ever observed it and it's unlikely that we ever will. There is a 300,000 light year thick bow shock of big bag that we'll never be able to peer through blocking the edge of the universe in all directions. My friends who are cosmologists tell me that the edge is a 9th dimensional structure that, you as a 3 dimensional being could never traverse. Think of it like this, it would be like your shadow suddenly picking itself up off the curb, standing up vertically and walking away as you stood still and watched it. Of course that's impossible, it's a 2 dimensional entity tied to a 3 dimensional structure. In the same way you could never traverse the edge of the universe as you are 3 dimensional structure defined and bound by a 9th dimensional structure. Comparatively speaking you're just part of the Universe's shadow!

Source

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http://en.wikipedia.org/wiki/Heat_death_of_the_uni...

http://en.wikipedia.org/wiki/Olbers'_paradox

Although our view of the universe is limited, our imaginations are not. Astronomers have indirect evidence that the universe of galaxies extends far beyond the region we can see. But no one knows if the whole universe is infinitely large ( large beyond limit ).

According to the leading theories, other parts of the universe may look very different from our own ; may even have different laws of nature.

We may never be able to find out for sure. But it is possible that clues to the answer lie in plain view, just waiting to be discovered .

NASA’s LISA mission will look for ripples in the fabric of space, predicted by Albert Einstein.

Such clues may help refine theories about what the rest of the universe is like.

Even if there is, I don't think we'll be seeing it anytime soon.

Even now they are still discovering new planets; light is still travelling to and fro the universe, and it's taking a long time because of how big the expanse is. So therefore, even if there were, we wouldn't be able to prove it with solid evidence because we can't exactly see it.