# If the universe is constantly expanding...
**URL:** https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149
**Category:** Great Debates
**Created:** [June 10, 2006, 1:53am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149 "2006-06-10T01:53:52Z")
**Posts on this page:** 20
**Page:** 2
### Author:  [@Aquafina](https://boards.straightdope.com/u/Aquafina)
#### Post date: [June 11, 2006, 5:44am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/21 "2006-06-11T05:44:40Z")
> [@](#):
>
> But how can anything be infinite?
It is infinite in the sense that there are parts of the universe in which lights haven’t been able to reach us.
---
### Author:  [@bup](https://boards.straightdope.com/u/bup)
#### Post date: [June 11, 2006, 12:03pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/22 "2006-06-11T12:03:10Z")
Didn’t this start in GQ? (If so), why did it get moved to GD?
---
### Author:  [@bonitahi](https://boards.straightdope.com/u/bonitahi)
#### Post date: [June 15, 2006, 7:13pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/23 "2006-06-15T19:13:02Z")
"Stephen Hawking has said that humanity is finally getting close to understanding the origin of the universe, speaking at a lecture in Hong Kong today.
The 64-year-old also said his unfulfilled ambitions, among many, were to find out what happens inside black holes, how the universe began and how the human race can survive in the next 100 years.
Above all, he joked, he wants to understand women."
---
### Author:  [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)
#### Post date: [June 15, 2006, 8:12pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/24 "2006-06-15T20:12:31Z")
> [@Der Trihs](#):
>
> An _infinite_ number of levels of infinity, as it happens.
Yes, but that’s not relevant here. In this context, “infinite” is a synonym for “unlimited”–no matter how much space you can see, there’s always more.
---
### Author:  [@bonitahi](https://boards.straightdope.com/u/bonitahi)
#### Post date: [June 15, 2006, 9:08pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/25 "2006-06-15T21:08:51Z")
Is it then correct to postulate that if one were to travel at the speed of light for an infinite period of time you would just keep on going?
Forever, and quickly? To what ends would you arrive when you got there?
I still don’t get it.
---
### Author:  [@mrklutz](https://boards.straightdope.com/u/mrklutz)
#### Post date: [June 15, 2006, 9:18pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/26 "2006-06-15T21:18:29Z")
> [@bonitahi](#):
>
> Is it then correct to postulate that if one were to travel at the speed of light for an infinite period of time you would just keep on going?
> Forever, and quickly? To what ends would you arrive when you got there?
> I still don’t get it.
You’re getting into the tricky business of mathematics involving infinity. I’m no expert, but I know enough to hurt your head worse (and yes, I think the vodka is a good idea).
Consider these two scenarios:
(a) I travel at the speed of light for an infinite period of time (as you suggested). How far have I gone? distance = speed x travel time, so I have traveled 186,000 miles per second x infinite seconds = an infinite distance
(b) I travel at a slow walking pace (2 miles an hour) for an infinite period of time. How far have I gone? 2 miles per hour x infinite hours = an infinite distance
---
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [June 15, 2006, 10:27pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/27 "2006-06-15T22:27:37Z")
> [@bonitahi](#):
>
> If the universe is constantly expanding, then is it correct to say the universe is not infinate? And never can be?
>
> My head hurts. [http://boards.straightdope.com/sdmb/newthread.php?do=newthread&f=7#](http://boards.straightdope.com/sdmb/newthread.php?do=newthread&f=7#)
> Confused
A good example of how you can make infinite things bigger would be [Hilbert’s Hotel](http://en.wikipedia.org/wiki/Hilbert's_paradox_of_the_Grand_Hotel)
---
### Author:  [@bonitahi](https://boards.straightdope.com/u/bonitahi)
#### Post date: [June 16, 2006, 12:23am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/28 "2006-06-16T00:23:49Z")
> [@mrklutz](#):
>
> You’re getting into the tricky business of mathematics involving infinity. I’m no expert, but I know enough to hurt your head worse (and yes, I think the vodka is a good idea).
>
> Consider these two scenarios:
>
> (a) I travel at the speed of light for an infinite period of time (as you suggested). How far have I gone? distance = speed x travel time, so I have traveled 186,000 miles per second x infinite seconds = an infinite distance
>
> (b) I travel at a slow walking pace (2 miles an hour) for an infinite period of time. How far have I gone? 2 miles per hour x infinite hours = an infinite distance
Whoa!
Gotta add an olive, now.
---
### Author:  [@bonitahi](https://boards.straightdope.com/u/bonitahi)
#### Post date: [June 16, 2006, 2:00am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/29 "2006-06-16T02:00:01Z")
> [@Mangetout](#):
>
> A good example of how you can make infinite things bigger would be [Hilbert’s Hotel](http://en.wikipedia.org/wiki/Hilbert's_paradox_of_the_Grand_Hotel)
Appreciated the link. Thanks.
---
### Author:  [@Malacandra](https://boards.straightdope.com/u/Malacandra)
#### Post date: [June 16, 2006, 9:57am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/30 "2006-06-16T09:57:23Z")
> [@bonitahi](#):
>
> Whoa!
> Gotta add an olive, now.
Yeah, but this is nothing difficult. Obviously there is an infinite number of positive integers. Obviously there is an infinite number of even positive integers. Obviously there are twice as many positive integers as even positive integers.
Similarly, not all integers are prime. But there are an infinite number of primes (proof, which is really easy, on request). Therefore the infinity of primes is smaller than the infinity of integers.
And so on. 🙂
---
### Author:  [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)
#### Post date: [June 16, 2006, 1:23pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/31 "2006-06-16T13:23:54Z")
> [@Malacandra](#):
>
> Yeah, but this is nothing difficult. Obviously there is an infinite number of positive integers. Obviously there is an infinite number of even positive integers. Obviously there are twice as many positive integers as even positive integers.
>
> Similarly, not all integers are prime. But there are an infinite number of primes (proof, which is really easy, on request). Therefore the infinity of primes is smaller than the infinity of integers.
>
> And so on. 🙂
You’re joking, right?
---
### Author:  [@Malacandra](https://boards.straightdope.com/u/Malacandra)
#### Post date: [June 16, 2006, 2:06pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/32 "2006-06-16T14:06:01Z")
> [@ultrafilter](#):
>
> You’re joking, right?
In what way?
---
### Author:  [@Procyon](https://boards.straightdope.com/u/Procyon)
#### Post date: [June 16, 2006, 3:00pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/33 "2006-06-16T15:00:51Z")
> [@Malacandra](#):
>
> In what way?
I am fairly certain that **ultrafilter** is referring to your statement that there are half as many even integers as there are total integers. Mathematically, it’s not true; there are exactly the same number of them. Of course, the “number” is infinity, which is why the concept is a little confusing.
The reason we can say for sure that there are the same number of integers and even integers is because we can come up with a function from the evens to the integers that is one-to-one and onto. Without going into the technical math, think of it like this: if I take all the even integers and divide them by two, the result is all integers. There is no integer that is not an even integer divided by two. So there must be the same number of elements (i.e. numbers) in each set if I can write out all the integers simply by starting with all the even integers and adding “over two.”
I hope that made some sense. I realize this has nothing to do with the actual topic, the infinite universe, but that’s how the cookie crumbles.
---
### Author:  [@Malacandra](https://boards.straightdope.com/u/Malacandra)
#### Post date: [June 16, 2006, 3:32pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/34 "2006-06-16T15:32:44Z")
Indeed. And the more it crumbles, the nearer its surface area approaches infinity. 😉
---
### Author:  [@bonitahi](https://boards.straightdope.com/u/bonitahi)
#### Post date: [June 16, 2006, 4:58pm UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/35 "2006-06-16T16:58:34Z")
> [@Malacandra](#):
>
> Indeed. And the more it crumbles, the nearer its surface area approaches infinity. 😉
Meaning, if you crumbled the cookie enough, the ultimate tiny crumbs would cover infinity?
O come on! Is that really explainable?
Or is my brain so small and limited, or just dumb?
---
### Author:  [@Strinka](https://boards.straightdope.com/u/Strinka)
#### Post date: [June 17, 2006, 12:09am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/36 "2006-06-17T00:09:01Z")
> [@bonitahi](#):
>
> Meaning, if you crumbled the cookie enough, the ultimate tiny crumbs would cover infinity?
> O come on! Is that really explainable?
> Or is my brain so small and limited, or just dumb?
No, the crumbs would have to be infinitely small, which can’t really happen in the physical world. Also, I’m not completely sure what you mean “the crumbs would cover infinity”, but it would be their surface area, not the space they take up that would be infinite.
Think about it like this: You have a cube. It has a cerain amount of surface area. Now, cut it in half. Now it has more surface area because you’ve created more surfaces. The more you do that, the more surface area you get, while retaining the same volume.
---
### Author:  [@Malacandra](https://boards.straightdope.com/u/Malacandra)
#### Post date: [June 17, 2006, 7:49am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/37 "2006-06-17T07:49:13Z")
Additionally, a crumb is not a cube or even an approximation to one - it is a nasty in-and-outy fractal surface, and the closer you look at it, the rougher it gets. And the more you take that roughness into account, the bigger the surface area.
The tiny crumbs would do a poor job of covering infinity, but that fractal surface seems to be doing a better job the bigger and better your magnifying glass. 😃
---
### Author:  [@bonitahi](https://boards.straightdope.com/u/bonitahi)
#### Post date: [June 18, 2006, 2:02am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/38 "2006-06-18T02:02:11Z")
So, are we saying that If the universe is constantly expanding, then it is correct to say the universe is not infinite at any specific point in time? Because in another minute or so the universe just got bigger, therefore at that specific point the universe was not infinite.
Just ask’n.
---
### Author:  [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)
#### Post date: [June 18, 2006, 2:29am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/39 "2006-06-18T02:29:06Z")
> [@bonitahi](#):
>
> So, are we saying that If the universe is constantly expanding, then it is correct to say the universe is not infinite at any specific point in time? Because in another minute or so the universe just got bigger, therefore at that specific point the universe was not infinite.
> Just ask’n.
Nope. Suppose the universe is infinite in size, and then expands by a foot. How big is it ? Infinite ! By 100 light years ? _Still_ infinite !
---
### Author:  [@bonitahi](https://boards.straightdope.com/u/bonitahi)
#### Post date: [June 18, 2006, 3:18am UTC](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149/40 "2006-06-18T03:18:06Z")
Confused? Who me?
If, say, " Suppose the universe is infinite in size" as you say. If then it got bigger was not it smaller by a foot or 100 light years before, as you say, it expanded, indicating it was not truly infinite at all five minutes earlier? You just thought it was?
God help us all, rather, kindly, won’t the muses be kinder to me?
Actually, I think I am getting closer.
[Previous page](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149.md?page=1)
[Next page](https://boards.straightdope.com/t/if-the-universe-is-constantly-expanding/360149.md?page=3)