I Why Is a Flat Universe Infinite?

[mark!]

If it's flat, it must be infinite.

That's patently false.

You don't know that. Physics is an empirical science. Until the universe is shown to be finite, there remains the possibility that it is infinite.

Infinity doesn’t make any sense at all. It’s a concept made up by humans. The decimals of pi are infinite, sure, but numbers are made up by us too you know.

Ok but let me get this straight, you assume that if one would travel the universe in a certain direction, you would ALWAYS be travelling, and always observe new stars and matter around you, forever and ever? You can’t be serious.

 

[mark!]

Space =/= spacetime.

So time is something separate/additional to space, is what you’re saying?

 

[PeroK]

Infinity doesn’t make any sense at all.

There's nothing irrational about a spatially infinite universe. It's one of the main possibilities from the general theory of relativity.

Ok but let me get this straight, you assume that if one would travel the universe in a certain direction, you would ALWAYS be travelling, and always observe new stars and matter around you, forever and ever?

That's a possibility and there is no evidence to exclude it.

You can’t be serious.

The possibility of an infinite universe is at the centre of modern cosmology.

 

[PeterDonis]

Infinity doesn’t make any sense at all.

Speak for yourself. The concept of a spatially infinite universe makes perfect sense to the other posters in this thread, not to mention all of the cosmologists working on our models of the universe that have this property.

Ok but let me get this straight, you assume that if one would travel the universe in a certain direction, you would ALWAYS be travelling, and always observe new stars and matter around you, forever and ever?

Yes, that's what happens in a spatially infinite universe.

You can’t be serious.

I strongly suggest that you take the time to learn about our best current model of the universe before posting further. Your posts, and particularly statements like the one just quoted above, are very uninformed and are not adding anything of value to this discussion.

So time is something separate/additional to space, is what you’re saying?

He's saying that "space" is not the same thing as "spacetime". Which is obvious to anyone who understands what those two terms mean.

 

[mark!]

He's saying that "space" is not the same thing as "spacetime". Which is obvious to anyone who understands what those two terms mean.

So what’s the answer to my question, then?

 

[mark!]

That's a possibility.

How?

 

[PeterDonis]

So what’s the answer to my question, then?

The answer is for you to take the time to learn what our best current model of the universe actually says before posting about it further.

How?

That is what learning what our best current model of the universe actually says will tell you.

Not only are you assuming that you’re more knowledgeable than me

I don't have to assume that, since your posts have already given me plenty of evidence.

but also that this additional knowledge is relevant to even think about making an argument with regard to this topic.

Since you don't have the knowledge, how can you possibly refute such a belief if I have it?

But you don’t explain why (or if) that should be the case. I guess I just have to believe you?

No, you have to do what I've already strongly suggested that you do, twice now: learn what our best current model of the universe already says. Everyone else posting in this thread already knows that, and we are not going to hijack this thread to give you a detailed explanation when you can go find it yourself in any cosmology textbook. If you aren't sure which textbook to use, Liddle's Modern Cosmology is one that is often recommended. Or you could even look at, say, Sean Carroll's online lecture notes on GR, which have a chapter on cosmology that describes a spatially flat infinite universe and gives the basic math for it.

With all that said, you have trespassed on this discussion long enough and you are now banned from further posting in this thread. You have also earned a temporary ban from PF due to the warnings you have received. Please take the time to carefully consider the advice you have been given.