Where does it say that galaxies themselves will be ripped apart?

I'm not a big fan of wikipedia. Maybe if you found an actually published article about it.

Anyway, I remember reading an article of Krauss' and maybe reading about it in his A Universe From Nothing book as well, that our galaxy would eventually be driven so far apart from other galaxies that future humans wouldn't be able to tell there's a whole universe out there, beyond their galaxy(which we thought as well at a certain point in the past, before Hubble proved there's other galaxies out there). However, Krauss was referring to a far later date in the future than 5 billion years, if I'm not mistaken.

(February 13, 2016 at 10:25 am)Brian37 Wrote:

(February 13, 2016 at 10:09 am)Excited Penguin Wrote: That article doesn't talk about what you talk about. It talks about the implications of an infinite universe.

But my question is, don't we already know the universe to be finite because of the Big Bang? How could it possibly be infinite if it had a start?

I think you missed my point. Again, why cant it be both infinite and finite? You can literally draw a finite line on a piece of paper and have an infinite number of decimal places within that finite line.

AGAIN, although we don't know right now either way, my guess  OFF is not infinite and On is not infinite, but going from off to on back to of to on.......could be infinite.

That's not exactly infinity. That's still a finite thing you're talking about. It's only infinite mathematically(or theoretically), but not really. Real infinity would simply mean that you could go in one direction forever, without ever having to stop or going in circles.

You can't have both infinite and finite space. That's absurd. How do you even imagine such a thing?


What OFF and what ON. What the hell are you talking about.

There is a well defined notion of the spatial extent of the universe, and it is either finite or not. It could however be finite in one direction and infinite in another... All we know right now is that if it is finite, it appears to be bigger than the visible universe (otherwise it would show signatures in the CMB). If there was cosmic inflation, it is likely at least many many orders of magnitude bigger than the observable patch.

(February 13, 2016 at 10:34 am)Alex K Wrote: There is a well defined notion of the spatial extent of the universe, and it is either finite or not. It could however be finite in one direction and infinite in another...

I don't understand. How can it be infinite if it has a starting point from which it expands?

(February 13, 2016 at 10:36 am)Excited Penguin Wrote:

(February 13, 2016 at 10:34 am)Alex K Wrote: There is a well defined notion of the spatial extent of the universe, and it is either finite or not. It could however be finite in one direction and infinite in another...

I don't understand. How can it be infinite if it has a starting point from which it expands?

It doesn't have to have that, that's a common misconception. The big bang wasn't an outward explosion that necessarily started in one point. Since relativity breaks down, and inflation likely took place driven by quantum fluctuations, we cannot trace ut back to size zero anyways, and such a singularity likely never occurred.

(February 13, 2016 at 10:26 am)Alex K Wrote: Where does it say that galaxies themselves will be ripped apart?

Read the wiki article, those are the experts. I would assume that after the distances between galaxies become so great, if the expansion continues it would end  up pulling those things apart too, but again, that article explains it better than I can.