
If The Universe Is Expanding, What's It Expanding Into? - instantramen
http://io9.com/5526583/if-the-universe-is-expanding-whats-it-expanding-into
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praptak
The question contains a hidden assumption: "Everything that expands, must
expand into something else." This assumption seems obvious because everything
that we can directly observe has this property. But this does not make it
automatically true for the universe.

~~~
michael_dorfman
If it is true for matter, and the universe is the sum total of all existent
matter, why wouldn't it be true for the universe?

Put another way: "Expands into something else" is what "expands" _means._

~~~
stcredzero
When the balloon expands, its two dimensional surface are increases because
the balloon is expanding into the 3rd dimension. Why can't a universe of n
dimensions simply expand into the n+1 dimension?

Or, put in a better way - the universe humans can perceive is expanding,
without expanding into anything else we can perceive.

~~~
retube
You're reading too much into the analogy. It's merely to help understand how a
3D space can expand without having a center, and nothing else.

~~~
stcredzero
I just explained the workings of the analogy. I think you're parroting those
words without completely understanding my comment or the words themselves.

(Note, if all matter is n-dimensional, then expansion of the n-dimension space
into dimension n+1 _wouldn't_ be expansion of the Universe into anything. It
would be the expansion of an n-dimension subset into an n+1 dimension
universe.)

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ErrantX
_Don't believe the metaphors. In every science special worth its salt, you'll
see some image of a balloon being inflated._

I've always considered this metaphor really good; it's just it is badly
explained. The go to guy for decent pop physics explanations is, in my mind,
Dr Brian Cox [1] (he does some really excellent TV shows here in the UK). His
explanation with the balloon notes that while the surface area increases
(expansion of the universe) the _volume_ of the _balloon rubber_ does not. You
have to ignore the air inside and outside of the balloon as having any
importance.

Then it should become clear how the universe can "expand" without actually
expanding _into_ anything.

1\. <http://en.wikipedia.org/wiki/Brian_Cox_(physicist)>

~~~
michael_dorfman
_You have to ignore the air inside and outside of the balloon as having any
importance._

And that's the bit of mental acrobatics that makes the metaphor break down.
Which is why the advice above ("Don't believe the metaphors") is relevant.

~~~
stcredzero
If any given model of the universe involves n dimensions, why can't we simply
have it expand into the n+1 dimension? When you inflate a balloon, it's 2d
area is increasing by the balloon expanding into the 3rd dimension.

In any model of the universe as a brane of n dimension, its expansion can be
modeled as expansion in the n+1 dimension. Perhaps "universe" is a paradoxical
word that cannot have a meaning? It's hard to imagine a world of infinite
dimension.

~~~
sp332
It doesn't work. Time & space - _all_ the dimensions that exist - exist
_inside_ the universe. There is no "space" out there to expand into.

~~~
stcredzero
So you posit a universe of an infinite number of dimensions? That's nonsense.
Just because there's nothing in dimension n+1 doesn't mean it's not part of
the universe. It would also allow expansion of the n-dimension brane.

Do you know of cosmological models proposing an infinite number of spatial
dimensions?

EDIT: Note that the "expansion of the universe" is really only "expansion we
observe through telescopes." I've never heard anything about astronomical
observations concerning dimensions S, 6, or others. 3D space can easily expand
without the need for anything outside the universe, in a universe of more than
3 dimensions.

~~~
sp332
I'm saying that there are a finite number of dimensions - maybe a dozen or
less. They all exist inside the universe. "Outside" the universe, there are no
dimensions. There is no space or time. There is actually no "place" for you to
"go" outside the universe. It only makes sense to say that the universe is
expanding by measuring the space and matter in it. There is no measuring stick
outside to hold the universe up to.

~~~
stcredzero
What happened to empiricism? Where's your evidence that dimensions _other_
than the 3 we can see are _expanding_?

Waiting for the light bulb...

~~~
sp332
By "n" I thought you meant all the dimensions in the universe, not just
3+time. Like you were inventing new dimensions to expand into. So never mind
that part.

But just because the dimensions we see are expanding, doesn't mean they are
expanding into other dimensions we can't see. Here I ask you for some
empiricism - what's your evidence? To modify the balloon example, just imagine
a flat rubber sheet that is stretched to be a little bigger. No extra
dimensions necessary.

~~~
stcredzero
True, that, but we do have empirical evidence that spacetime is _not_ flat.

~~~
sp332
"Not flat" doesn't mean wrinkled into other dimensions. Again, it's just a
metaphor/visualization, not a direct representation. It's like this image:
[http://sparrow.stanford.edu/~chumakov/images/grids-
negative-...](http://sparrow.stanford.edu/~chumakov/images/grids-
negative-P.png) The 2D space has "negative curvature," but it doesn't bend
into a third dimension. It's still flat.

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AngryParsley
While the IO9 post is better than most pop-physics articles, I feel a need to
repeat myself...

Your question contains invalid assumptions. There is no analogy that gives
both a satisfying and accurate answer. You want to know about physics?
_Understand the math._ The closest you can get without differential equations
is Feynman's QED: The Strange Theory of Light and Matter

~~~
gaius
Did you see _Agora_ yet? In it the mathematician Hypatia in 4th century Egypt
(played by Rachel Weisz) makes the radical announcement that circles are not
really shapes in their own right, they're just a type of ellipse, and everyone
_wigs out_ \- everything they know about astronomy and physics will have to be
rethought. Anyway, awesome film.

~~~
AngryParsley
I watched Agora tonight. It was good. I didn't know a movie could cause me to
dislike religion even more than I already did.

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retube
The question doesn't really mean anything. Space (and time) and
attributes/characteristics/features of our universe. So there is no "outside"
(multiverse models aside). Likewise you cannot ask what was "before" the big
bang, as time only came in to existence with the big bang.

~~~
tfh
_> time only came in to existence with the big bang_

My brains segfaults imagining that there was a time where time didn't exist...

~~~
bhousel
Think of it this way: We don't have any way of measuring time that doesn't
also involve space. Whether it's pendulums, or atoms vibrating, or photons
bouncing around, any way we measure time is linked to (and relative to)
whatever space is around it. If space is being deformed by a large mass being
there, time will be affected (slowed down). Some theories of time say that
what we think of as 'time' is really just a byproduct of space.

So if space didn't exist (in any meaningful way that we would understand
today) before the big bang, time couldn't exist either.

~~~
stan_rogers
For anyone who hasn't seen it, this lecture by Bill Phillips (Nobel Laureate,
of NIST, given at the Perimeter Institute) on time, relativity, cooling and
the Bose-Einstein condensate is probably the most entertaining real science
lecture you're ever going to see:

[http://feeds.tvo.org/~r/tvobigideasVideo/~5/QOpqIcl2UDk/BI_F...](http://feeds.tvo.org/~r/tvobigideasVideo/~5/QOpqIcl2UDk/BI_Full_20080920_834096_WilliamPhillips_320x240_304k.mp4)

It's long, but it won't merit a tl;dw unless you have no curiousity,
imagination, sense of humour or innate geekiness.

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crazydiamond
So the galaxies are sitting still, the space inside it is expanding ... at
faster than the speed of light.

The way my puny layman mind can figure out ... if 2 objects move away from one
another at slightly more than half the speed of light, then one would see the
other as apparently moving away at greater than the speed of light.

Also, iirc, the expanding balloon metaphor was more to give an idea how all
points are moving away from one another, and each sees itself as the center.
It was not meant to talk of dimensions, or moving into ... (btw, thanks a lot
for the link. great read)

~~~
tydok
> 2 objects move away from one another at slightly more than half the speed of
> light, ...

IIRC, mass grows towards infinity as it approaches the speed of light. So
that's not possible if the objects have mass.

~~~
ErrantX
Which bit are you questioning - making it to half the speed of light (I
believe that is entirely possible) or the relative speed being more than the
speed of light?

If it is the latter; it's perfectly possible. Ultimately it is just
mathematics - as pointed out on Wikipedia apparent "FTL" travel is allowed by
most models.

<http://en.wikipedia.org/wiki/Faster-than-light>

~~~
tydok
The first part, making it to half the speed of light.

With massless particles is of course possible. My physics is a bit rusty so I
can't really argue on this matter :)

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baddox
"We're not actually sure whether the universe is infinitely large, or merely
very, very big, but in even supposing it is, ... "

Forget the philosophical/physics questions, what do those words even mean?

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crazydiamond
> The expanding universe is due to gravity, which means that in regions of
> high density, the dominant gravitational effects are entirely local.

Is this the conventional view. I always thought the universe was expanding as
a result of the big bang momentum. This expansion would keep going unless
there was a critical mass to pull it back. (that was the way things were when
i was a kid). Or am i misreading.

~~~
a-priori
From <http://en.wikipedia.org/wiki/Dark_energy>: "dark energy is a
hypothetical form of energy that permeates all of space and tends to increase
the rate of expansion of the universe"

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Shorel
I think it is a valid question, not because it is valid in a strict physical
sense, but because a lot of people can have the same doubts.

Carl Sagan would have provided an interesting anecdote or analogy to explain
the answer instead of ridiculing whoever ask this.

Sadly, my writing skills are way lesser than those of Sagan.

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ghjrtyh
This guy is either crap at explaining, or hasn't got a clue what he's talking
about.

