B Is the Universe really infinite?

[Chunkythunk]

I believe the universe could not possibly be infinite. I am not denying it is of extremely large scale but it still must be finite. No true infinity is found in nature but only in mathematics. why should it differ here ?

 

[russ_watters]

Infinities exist in nature, you just have to look for them in places you don't expect. But that really doesn't help any with this question. The real answer is that scientists don't know, but lack of boundaries suggests to scientists that the universe might be [spatially] infinite.
https://www.swinburne.edu.au/news/2021/08/Is-space-infinite-we-asked-5-experts/

Me personally; that feels like "want to believe". Or maybe it just makes the math easier (and I hate math too, so I get it)? So I take the opposite position: it's hard for me to believe it is infinite, so I don't.

 

[PeterDonis]

I believe the universe could not possibly be infinite.

The universe doesn't care what anyone believes. The only possible guide we have is our best current physical theories and the models we build with them. The best we can say in answer to your title question is that our best current model of the universe has it spatially infinite, but it is still possible that it is spatially finite (with the topology of a 3-sphere), just much, much larger than our observable universe.

No true infinity is found in nature

We don't know that. If spacetime is indeed a continuum, and we have no evidence that it's not, then there is a continuous infinity of points in any region.

 

[Drakkith]

No true infinity is found in nature but only in mathematics.

The number of possible positions I can move to between where I'm sitting and 1 meter to my left is infinite. The number of possible velocities my car can move at between 0 and 35 mph is infinite.
The number of possible wavelengths a light wave can be is infinite.
Shall I continue?

why should it differ here ?

For starters, we haven't seen a boundary or any other indication that the universe is finite. Not yet at least.
Second, it is actually simpler to create a model of an infinite universe than one that is finite in some circumstances. If the universe is finite, but flat, meaning that you can't travel in one direction and end up looping back on your start location, then we have to try to consider a boundary situation. What is that boundary? Do you bounce off of it if you impact it, do you disappear, or something else? Does light reflect off of it? What does gravity do around it? Is it moving? Does space expand near it? How does expansion even work in a finite, flat, bounded universe? Etc etc etc. The answers can drastically affect cosmology in different ways and we simply don't have any data to even begin to answer these questions.

A flat universe that is infinite has no boundary condition to worry about. We can simplify our models to make them easier to build and work with.

I am not denying it is of extremely large scale but it still must be finite.

There's no evidence of this.

Besides, no one is claiming with any certainty that the universe is infinite, so you're basing your opinion on fiction and not fact. We model it as infinite because it is convenient and we have no evidence to the contrary. If we see Galaxy 35899 smack into a barrier tomorrow we'll immediately update our models.

 

[strangerep]

Infinities exist in nature, you just have to look for them in places you don't expect.

Where/how have physical infinities actually been found in nature?

 

[strangerep]

The number of possible positions I can move to between where I'm sitting and 1 meter to my left is infinite. The number of possible velocities my car can move at between 0 and 35 mph is infinite.
The number of possible wavelengths a light wave can be is infinite.

Heh, what experiment(s) have you done to confirm this? I'll bet you don't have a ruler or speedometer that measures with infinitesimal precision...

 

[PeroK]

Infinities exist in nature, you just have to look for them in places you don't expect. But that really doesn't help any with this question. The real answer is that scientists don't know, but lack of boundaries suggests to scientists that the universe might be [spatially] infinite.
https://www.swinburne.edu.au/news/2021/08/Is-space-infinite-we-asked-5-experts/

Me personally; that feels like "want to believe". Or maybe it just makes the math easier (and I hate math too, so I get it)? So I take the opposite position: it's hard for me to believe it is infinite, so I don't.

It's funny that two "experts" explain why the answer is "yes" and two explain why it's "no". Only one gives the honest "I don't know" answer.

Why must they have a strong opinion about a question to which the answer is patently unknown?

 

[Drakkith]

Heh, what experiment(s) have you done to confirm this? I'll bet you don't have a ruler or speedometer that measures with infinitesimal precision...

A valid point.

 

[PeroK]

The OP's assertion rests on faulty logic. The observable universe is finite, hence the universe is finite.

 

[Ibix]

The OP's assertion rests on faulty logic. The observable universe is finite, hence the universe is finite.

Indeed. Plus a strong dose of "can't believe it could be infinite".

 

[Vanadium 50]

I believe

The universe does not care what you believe. The earlier you come to grips with this, the smoother your study of physics will be.

To answer the question, I know of no measurement that can distinguish "infinite" from "much larger than we can observe". Until there is, it really can't be addressed scientifically. Also, until there is, it really doesn't matter scientifically.

 

[Nugatory]

A number of off-topic and unnecessarily contentious posts have been removed and the thread is now closed.

As with all such closings, you can ask any mentor for a reopening if there is something more to say.