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Well, in a way I'm glad to hear that you are having difficulty with these concepts. If you found it easy, I would be sure you didn't begin to understand.
First of all, we DON'T assume that the universe is infinite. In fact, a lot of people think that the universe is finite but unbounded. I'll come to that in a minute. In principle, there are three possibilities:
1 The universe is finite;
2 The universe is finite and bounded
3 The universe is finite but unbounded.
A lot of people don't like 1 on largely philosophical grounds, because it throws up some odd implications. If the universe is really infinite, then anything which is not forbidden by the laws of physics, however improbable, happens somewhere. THat is simply the consequence of multiplying a non-zero probability by infinity. It becomes 1 - representing certainty. So somewhere there would be a planet just exactly like ours, but inhabited by the proverbial monkeys steadily typing the complete works of Shakespeare - including the ones he burned rather than publishing them. Also somewhere someone would be suffocating, because all the oxygen in the room just happened to rush into one corner of the room and stay there.
Lots of people also dislike 2, because it souds too like the Flat Earth Society, and it is hard to imagine what the edge of the universe would be like.
Which leaves 3. Imagine a 1D being in the circumference of a circle. It can go as far as it wants in either direction, but will never get to an end of the (finite) circle. Then imagine a 2D being in the surface of a sphere. It can go as far as it likes in any direction without ever coming to an edge of its (finite) world. Now tkae it to a 3D being in a finite but unbounded space. That could be you.
Now, let's talk for a moment about looking back in time. We can, and do, look back to the point in the early history of the universe when it became (because ions combined to form neutral atoms) transparent. What we see when we do that is the Cosmic Microwave Background Radiation (CMBR). Further back we can't see, because the universe is opaque.
First of all, we DON'T assume that the universe is infinite. In fact, a lot of people think that the universe is finite but unbounded. I'll come to that in a minute. In principle, there are three possibilities:
1 The universe is finite;
2 The universe is finite and bounded
3 The universe is finite but unbounded.
A lot of people don't like 1 on largely philosophical grounds, because it throws up some odd implications. If the universe is really infinite, then anything which is not forbidden by the laws of physics, however improbable, happens somewhere. THat is simply the consequence of multiplying a non-zero probability by infinity. It becomes 1 - representing certainty. So somewhere there would be a planet just exactly like ours, but inhabited by the proverbial monkeys steadily typing the complete works of Shakespeare - including the ones he burned rather than publishing them. Also somewhere someone would be suffocating, because all the oxygen in the room just happened to rush into one corner of the room and stay there.
Lots of people also dislike 2, because it souds too like the Flat Earth Society, and it is hard to imagine what the edge of the universe would be like.
Which leaves 3. Imagine a 1D being in the circumference of a circle. It can go as far as it wants in either direction, but will never get to an end of the (finite) circle. Then imagine a 2D being in the surface of a sphere. It can go as far as it likes in any direction without ever coming to an edge of its (finite) world. Now tkae it to a 3D being in a finite but unbounded space. That could be you.
Now, let's talk for a moment about looking back in time. We can, and do, look back to the point in the early history of the universe when it became (because ions combined to form neutral atoms) transparent. What we see when we do that is the Cosmic Microwave Background Radiation (CMBR). Further back we can't see, because the universe is opaque.
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