We have known for some time that our universe is expanding and in recent years have discovered that it is happeningsignificantly fasterthan we expected.

But despite significant innovations in telescope and satellite technology, much of what is out there in the cosmos is believed to be beyond our line of sight -- beyond the "observable universe," as it's called.

It also means we don't know for sure what shape the universe as a whole will take - whether it's a closed cosmic "donut," a flat plane expanding like an endless sheet of paper, or a giant sphere in a state of perpetual motion Extension.

This has got scientists wondering about the farthest reaches of space and what they look like. What do you think about the fate of the universe? Will it stretch forever?

We asked five of them - and it seems the jury is still out.

*Space experts often refer to the donut-like torus shape, which has no edges or corners. The torus is important as a mathematical object.WikiCommons*

### Here are their detailed answers:

### Anna Moore, astronomer - maybe

The short answer is we don't know. We know that the observable universe - the part we can visibly see and measure - began with the Big Bang about 13.8 billion years ago. So we know that the age of the universe is finite, at least since the Big Bang. But the universe is getting bigger. It has been spreading in all directions since the Big Bang and is continuing to do so (and lately it has been accelerating).

Remnants of the Big Bang radiation that we "cosmic microwave background' represents the earliest picture of the universe, when it was smaller, hotter and denser. We can take pictures from this early period to understand the shape (or geometry) of the universe at the largest scale. Knowing this is important in order to know whether the universe is infinite or finite.

Measurements made by satellites have indicated a flat geometry for the universe. In a flat universe, two beams of light shot side by side through space stay parallel forever and will never cross or drift apart. In this sense, we can still think of a cylindrical or toroidal universe as "flat".

Current measurements are not accurate enough to know whether the flat geometry of the universe is represented by a piece of paper, a cylinder, a torus, or some other shape that allows two rays of light to pass parallel. An infinite universe could have a geometry that is completely flat as a piece of paper. Such a universe would go on forever and contain all possibilities - including endless versions of ourselves. On the other hand, a donut-shaped universe would have to be finite since it's closed. But at the moment we do not yet know the shape of the universe and therefore its size.

### Sara Webb, Astrophysiker's—and

I think so. We know that the universe began with the Big Bang. And according to our observations, this beginning did not take place in any area. No matter where you are in the universe (in this galaxy or one far, far away), space seems to expand in all directions, with you at the center. Now we calculate that the universe is approximately 13.8 billion years old, which means space has had that much time to expand. So logically we would expect space to be 13.8 billion light years across, right?

But the size of the observable universe is actually 46 billion light-years, meaning that the very first light we can see emitted (380,000 years after the Big Bang) came from a distance that is now 46 billion light-years away. This is due to something called "rapid inflation" (more on that later). However, there is no reason to assume that the edge of the observable universe is the edge of the actual universe.

We tend to think of things as 3D shapes: a sphere, a cube, a cone. We could think of the universe as a sphere expanding indefinitely and infinitely. Or it could curve and bend in a way that could make it oneclosed system(like a donut) where if you traveled in a straight line long enough you would eventually end up back where you started: space would be finite.

But I'm leaning towards another possibility, which takes into account rapid post-Big Bang inflation. There is a theory that this inflation is in factperpetual inflation, meaning it always occurs at one point or another in the universe - making the universe infinite. This begins to delve into the intriguing idea of quantum fluctuations andeven multiverse. And as the sci-fi lover that I am, how could I not want this to be true?

### Ask Hill, Astronomer – ja

There is a limit to how much of the universe we can see. The observable universe is finite in that it has not existed forever. It stretches 46 billion light-years in all directions from us. (While our universe is 13.8 billion years old, the observable universe is getting longer as the universe is expanding).

The observable universe is centered on us. An alien in a galaxy far, far away would have its own observable universe. While there might be some overlap, they would inevitably see regions that we cannot see. Therefore it is not possible to see if the universe is finite because we cannot see everything. Instead, we can approach this question by examining the shape of the universe. While we don't know the shape of all of space, we do know that our portion of space is flat. This means that two rockets flying parallel with cruise control will always remain parallel. Since space is not curved, they will never meet or drift apart.

A flat universe could be infinite: imagine a 2D piece of paper that expands indefinitely. But it could also be finite: imagine taking a piece of paper, making a cylinder and connecting the ends to get a torus (donut) shape. Therein lies the problem.

Additionally, there are many ways the universe could be curved, but instead we live in a region of flat space. This is a very specific condition and we use a theory called "inflation" to explain it. Inflation is the idea that very early on, for a brief moment, the universe expanded rapidly, smoothing out all the kinks and curves in our part of space. After inflation, the universe grew into what we see today. But it's possible that inflation didn't just seed our universe. It may have happened elsewhere and is still happening. How big could that make the entire universe or multiverse? It opens up such possibilities that I think it's easier to imagine an infinite universe than a finite one.

### Sam Baron, philosopher of science - no

There's a tempting line of reasoning that suggests space must be infinite, but I think it's wrong. It goes like this: If space is finite, then it would have an advantage. But imagine getting into your spaceship and flying into the vastness of the universe. It seems inconceivable that you would find an edge. What would the rim look like anyway? Surely space must go on forever.

But there is another way that space can be finite. It could be a torus that is spatially finite but edge-free, like aCosmic Donut. If the universe is ring-shaped, then there is a very natural scientific test that would show whether it is finite.

Imagine directing a beam of light at a very distant reflective surface. If the surface is uneven, the light will be reflected in multiple directions. If the universe is a donut, the reflected rays bouncing back gradually curve with the shape of the universe and eventually wrap back on themselves and intersect(diagram here). That can only happen if the universe is finite, mind you. In an infinite universe, the rays would go on forever.

Now imagine you are standing at the point where the rays of light intersect. If you turn sideways, you will see the object that reflected the beam. If you turn to the other side you will see the same object but from a different angle. So if the reflecting object was a distant planet, you would see the same planet twice. Scientists have already started looking for ithall of mirrorsEffect in the faint glow left over from the Big Bang. It would prove not only the size but also the shape of the cosmos. While nothing conclusive has been found yet, who knows what we might discover if we keep looking!

### Kevin Orrman-Rossiter, historian of science - no

By "infinite" we usually mean something that is limitless or endless. My position is that space is finite. To demonstrate this, however, let's propose for a moment that space is infinite. Put simply, if that were the case and I set off in a spaceship in any direction, I would never reach a limit. But there's a problem with this experiment: I'd have to travel indefinitely to make sure there wasn't a "just a little bit further out" limit. It doesn't matter what speed I drive. My proof journey would have to be infinite to prove my hypothesis that space is infinite. Well, not many grant agencies will fund such an experiment.

This underscores that in order to provide evidence, we must do so through observation rather than direct experimentation. above thatpast centurywe have learned a lot about our universe through observation. We know that space, the universe, began about 13.8 billion years ago. We know from observations that it's expanding, and we've discovered the cosmic microwave background, which is thought to be leftover radiation from the Big Bang. Space as we see it today is a slowly expanding web of galaxies.

A key question in cosmology is whether this expansion will continue, change pace, or reverse. To answer this, the properties of dark matter and dark energy must be understood.

The interesting point is, no matter what model of the universe (and important pieces are missing here), current cosmological thinking is that there will be an end and the universe won't last forever. It has a finite existence in time, and so, to get back to the beginning of my argument, I would suggest that my spaceship journey eventually comes to an end.

*This article is republished fromThe conversationunder a Creative Commons license. read thisoriginal article.*