The discussion centers on the concept of an infinite universe and its expansion, highlighting the distinction between the observable universe and the entirety of the infinite universe. Participants emphasize that while the universe is infinite, the distances between objects within it can expand uniformly over time, as described by the metric expansion of space. The analogy of the Hilbert Hotel is used to illustrate how infinity can accommodate expansion without contradiction. The conversation also critiques misconceptions prevalent in popular science regarding these concepts.
PREREQUISITESCosmologists, astrophysicists, students of physics, and anyone interested in the philosophical implications of an infinite universe and its expansion.
Any two things that are a distance ##x## apart are a distance ##x\times (1+\delta)## apart at some later time, where ##\delta## is independent of the distance ##x## and the position of either thing but (in general) not the time. That's a uniform expansion, whether you can see the end of it or not, or even if there's not an end.Michael Ray Mooney said:being everything everywhere, how is it possible for infinity to expand?
Then you've been reading popsci, which is often sloppy about that distinction. Professional discourse has no such confusion.Michael Ray Mooney said:In all my research I find confusion among cosmologists about the important distinction between the part of the universe we cqn see and the whole infinite universe.
Here's an introduction to the metric expansion of space. In general, from a geometric point of view, the spatial distances between points in space can vary over time, whether the space is finite or infinite.Michael Ray Mooney said:Considering the growing consensus that the universe is infinite, being everything everywhere, how is it possible for infinity to expand? In all my research I find confusion among cosmologists about the important distinction between the part of the universe we cqn see and the whole infinite universe.
Is that when Hilbert refurbished his infinite hotel and made all the rooms bigger? The infinite hotel expansion!phinds said:Google the Hilbert Hotel
Wasn't that the Eagles' biggest hit?phinds said:Google the Hilbert Hotel
I';m familiar, but as a mathmatical thought experiment it doesn't address the concept of of an endless universe, (No end or boundary in any direction.)phinds said:Google the Hilbert Hotel
No? I think that it does. It explains how infinity is endless. It's the Hilbert Hotel in all directions.Michael Ray Mooney said:I';m familiar, but as a mathmatical thought experiment it doesn't address the concept of of an endless universe, (No end or boundary in any direction.)
What part of the concept of an infinite universe are you having trouble with? I already explained what's meant by expansion, and PeroK provided a link to further detail.Michael Ray Mooney said:I';m familiar, but as a mathmatical thought experiment it doesn't address the concept of of an endless universe, (No end or boundary in any direction.)
That doesn't address the issue of an "expanding universe." Infinity does not expand... get bigger. We can't have it both ways... infinite and yet expanding.phinds said:No? I think that it does. It explains how infinity is endless. It's the Hilbert Hotel in all directions.
It is not about the universe itself expanding or getting bigger - it is about the things in it getting further apart.Michael Ray Mooney said:That doesn't address the issue of an "expanding universe." Infinity does not expand... get bigger. We can't have it both ways... infinite and yet expanding.
In your introduction, you said:Michael Ray Mooney said:That doesn't address the issue of an "expanding universe." Infinity does not expand... get bigger. We can't have it both ways... infinite and yet expanding.
It's hard to believe any of that is true, to be honest. How can you possibly have an "avid interest" in cosmology and astrophysics, yet be stumped by the fundamental concept of a spatially infinite, expanding universe?Michael Ray Mooney said:Hi everyone. I've had an avid interest in several fields of physics all my adult life, now 79. (Long retired as a psychologist.) My fields of interest include cosmology, astrophysics, relativity theory, quantum physics and philosophy of science applied to physics. I look forward to participation here.
Yes, we can. The mathematical model of a spatially infinite, expanding universe is perfectly consistent.Michael Ray Mooney said:We can't have it both ways... infinite and yet expanding.
What confusion are you talking about? You need to back this claim up with specific references.Michael Ray Mooney said:In all my research I find confusion among cosmologists about the important distinction between the part of the universe we cqn see and the whole infinite universe.