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Author Topic: phyisics question  (Read 406 times)

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Offline linggaTopic starter

phyisics question
« on: April 12, 2009, 08:53:31 PM »
this is the sciences and tech place right? so heres a physics question for you, if the universe is infinite and expanding. what is it expanding into? i'm honestly asking because i've made several attempts at understanding this.

Offline The Overlord

Re: phyisics question
« Reply #1 on: April 12, 2009, 09:21:20 PM »

That is a common notion that people make with the topic of universal inflation, because we live in an immediate environment in which everything is contained in something larger, and anything expanding is doing so within something else. What cosmologists are trying to explain and model with their theories is beyond the normal human grasp of perception, thus none of us can be blamed for making this natural conclusion.

To put this in a nutshell, it’s not just the stars, planets, galaxies, and particles in the universe that are expanding and moving away from one another….it is the void of space ITSELF that is expanding as well. The dimensions of space are inflating.

It does not need to be expanding into anything, however. This is admittedly a very abstract concept that defies logic, but there may be nothing ‘beyond’. No matter, no energy, no dimensional space, no time…literally and absolutely nothing.
« Last Edit: April 12, 2009, 09:23:34 PM by The Overlord »

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Re: phyisics question
« Reply #2 on: April 12, 2009, 11:50:32 PM »
Rudy Rucker explained this very well for me (if you are able to find it, I highly recommend his book "The Fourth Dimension".)  Think of a balloon.  Now think of minuscule creatures living within the surface of the balloon.  Now, blow up the balloon.  To the flat creatures living within the surface of the balloon, it is obviously expanding - however, their world is flat.  There is also no end to it, as they could conceivably travel forever in any direction without coming up against a wall, so they can't imagine someplace beyond it that the world is expanding 'into'.

Offline The Overlord

Re: phyisics question
« Reply #3 on: April 13, 2009, 01:51:42 AM »

The analogy of a sheet of rubber graph paper tends to work quite well also.

Under the standard models of Inflation, the fabric of space-time is stretching in every direction, carrying everything in the universe along with it, rather than objects rushing apart from one another in a largely static void.

As the sheet of graph paper keeps growing in size, the individual squares get larger with it; everything marked on the paper (planets, stars, galaxies, etc.) gets further apart. There is no unique position in the universe; an observer will see everything else rushing away from him no matter where in the universe he is.

If you can follow the balloon and graph paper abstractions this far, realize that we can't even be sure the entire universe is expanding at a uniform rate.

One of the crucial tests that cosmologists are aiming for by studying the makeup of the universe is defining its overall state. One of the big topics of debate now is that the universe is either homogenous or inhomogeneous; that is, it is either mostly the same all over, or slightly to radically different in consistency in different regions.

At present, the model of a homogenous and constantly expanding universe is the popular view; inhomogeneous cosmic makeup is still regarded as something of an unpopular view, but it has strong supporters.

What it all stems down to is dark energy. A good 60% percent of the universe or more is ‘dark energy’. It is the theoretical force that’s maintaining the observed and increasing acceleration of the universe. But ask any physicist or astronomer what dark energy is and they can’t tell you, because they don’t know what it is.

The truth is that dark energy might not even be energy in the scientific definition at all; it’s more of a metaphor. It’s something we applied an abstract term to so we can try and explain the behavior of the cosmos we’re observing.

In an inhomogeneous model, there may be distant regions of the universe that are much denser or much less dense than our own. The going theory of the inhomogeneous universe is that we’re in a low-density part of the universe. Less density means less matter in our region and less gravity to slow down expansion, relative to denser regions.

Going back to the graph paper concept; we’re in a part of the sheet where the squares are expanding faster than other parts. We are only observing our part, we can only measure its rate of expansion so we might assume everything else is expanding as quickly.

Inhomogeneous Inflation effectively does away with dark energy, because you don’t have to put anything into the equation that has the tremendous power of making the entire universe expand unchecked, as opposed to the lesser energy that would be needed to make just portions of it expand.

So mink, I realize that is a very verbose and roundabout answer to your original question, and it also goes well beyond the purpose of the question, but understanding the whole nature of the expansion and just how universal it might or might not be makes a big difference on the answer.