But you can take a sheet of paper [an 'infinite' sheet of paper] and you can roll it up and make a cylinder, and you can roll the cylinder again and make a torus [like the shape of a doughnut]. The surface of the torus is also spatially flat, but it is finite. So you have two possibilities for a flat Universe: one infinite, like a plane, and one finite, like a torus, which is also flat. By 'flat' we understand to be like a table, which has width. Does the Universe have width?
Flat is just a two-dimensional analogy. What we mean is that the Universe is 'Euclidean', meaning that parallel lines always run parallel, and that the angles of a triangle add up to o. Now, the two-dimensional equivalent to that is a plane, an infinite sheet of paper. On the surface of that plane you can draw parallel lines that will never meet. A curved geometry would be a sphere. If you draw parallel lines on a sphere, these lines will meet at a certain point, and if you draw a triangle its angles add up more than o.
So the surface of the sphere is not flat. It's a finite space but it's not flat, while the surface of a torus is a flat space.
Will we be able to find out if the Universe is finite or not? Even if with our Cosmic Microwave Background data we can prove that the Universe is flat, we still won't know whether it's finite or infinite. With great difficulty! We may never know it. If the Universe is finite, that means that in a two-dimensional geometry it would be like a torus. Now, think about a torus. How do stars create and release energy? What exoplanet is closest to Earth? Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter.
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Tonight's Sky — Select location. Tonight's Sky — Enter coordinates. UTC Offset:. The universe may be infinite, but we can only see a finite section of it due to the finite speed of light.
We can only see those parts from which light has had time to reach us since the beginning of the universe - which means we can in theory see a spherical universe with radius of about 47 billion light years.
If I gave you some time to think about that I'm sure that you would come up with the following conclusion - "that means that the universe must have expanded faster than the speed of light at some point", which appears to violate special relativity.
In fact that is what is thought to have happened, during a period called "inflation", and it does not violate special relativity since it is not a spatial motion, but the expansion of space itself. Back to your question: if the universe is infinite beyond our horizon, is there an infinite number of "you"s out there? I wonder if you have covered probabilities in school? If you haven't let me know if you don't understand the following.
If there is a finite probability of something happening ie. So there would be an infinite number of galaxies and planets in an infinite universe. If however there is an infinitesimal probability of something happening, then in an infinite universe there would only be a finite number for example 1 of those things.
I would argue that the probability of creating a specific person with a specific genetic make-up and way of thinking may only be infinitesimal it depends on how complex you think humans are - therefore there is only one of you! People also use this argument against the idea that there must be ET life out there in such a big universe - if the probability of life forming is infinitesimal then there could only be one life bearing planet.
I personally think that it's more likely that life forms with a finite probability than it is that a specific person forms. See an interesting article by an astronomer, Max Tegmark on this here.
It was written for a scientific audience but seems fairly readable. Karen was a graduate student at Cornell from She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK.
Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. The cosmos is only so old, and light only travels so fast. So, in the history of the universe, we haven't received light from every single galaxy.
The current width of the observable universe is about 90 billion light-years. And presumably, beyond that boundary, there's a bunch of other random stars and galaxies.
Cosmologists aren't sure if the universe is infinitely big or just extremely large. To measure the universe, astronomers instead look at its curvature. The geometric curve on large scales of the universe tells us about its overall shape.
If the universe is perfectly geometrically flat, then it can be infinite. If it's curved, like Earth's surface, then it has finite volume. Current observations and measurements of the curvature of the universe indicate that it is almost perfectly flat. You might think this means the universe is infinite. But it's not that simple.
Even in the case of a flat universe, the cosmos doesn't have to be infinitely big. Take, for example, the surface of a cylinder.
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