When they say that the universe is expanding what do they mean?

Question

Does it mean that space-time is expanding only?
or
Does it mean that space-time and matter (ie. planets, stars) are all expanding?

Note: Wikipedia folks need not reply.

Answer 1

Short & sweet:
It means that everything we can see at any
significant distance is moving away from us.
We do not see 'stars & planets` expanding
though. Gravity seems to prevent this - so far.

Answer 2

My view is unorthodox, but I believe new space is popping up everywhere, all the time, about one cubic Planck length at a time, 10^52 times per cubic meter per second. This does not expand objects, even if the new space first appears inside an object.

Answer 3

Space is a volume of a substance responsible for Gravity.
Time is a quantity that indicated the pressure status of space.
When space levels increase time increases.
As far as the observed expansion of The Universe ,its really the Galaxies that are being observed as receeding relative to the motion of the earth.
A Galaxy can contract as well as expand .And some Galaxies appear to move in a collision path,rather than moving away from each other they are approaching each other.

Answer 4

well the big bang was supposed to have created time and space, and the expansion of space has to have a speed because its impossible for it all of the sudden just be everywhere. and the matter has a speed so everything is expanding outward. from the center of the explosion. and if you want to know what its expanding into id be glad to answer that question as best as todays scientists can, its a rather interesting answer.

Answer 5

It means that space-time is expanding only.

As the space we live in expands, this _does_ act like a tiny force trying to "stretch" the atoms in our body farther apart. However, this stretching force is counteracted by the (much stronger) forces holding the atoms next to each other. So the result is that our bodies expand a tiny fraction of an inch and then stop expanding.

Answer 6

You're referring to the Big Bang theory which gave rise to our Universe. Like shrapnel, pieces of the universe (galactic clusters) are still spinning away from the initial Big Bang explosion. This "expansion" is due to the initial momentum from the cataclysmic explosion. In space, an object in motion tends to stay in motion, until something stops it. And we have evidence that galaxies have collided in the past. Hopefully, the Andromeda Galaxy, our nearest neighbor, is expanding away from us, instead of into us. Here are some famous authors on this topic:

Steven Hawking gives us a glimpse into the birth of the Universe in his book, A Brief History of Time.

Robert Jastrow, a renowned physicist describes the inevitable death of our Sun in his book, Red Giants, White Dwarfs.

This website gives the exact location of each of the moons of Jupiter: http://www.ifa.hawaii.edu/~sheppard/satellites

and this site tells us how to make an ATMOSPHERE on all the moons: http://www.atmospheres.5u.com/index.html

while this site tells you how to build a Fischer Tropsch reactor to make fuel and water:
http://www.xybex.50megs.com/custom2.html

Answer 7

Only the space between galaxies is expanding. The size of galaxies may stay the same due to it's gravitational bonds.

Answer 8

http://www.sciam.com/print_version.cfm?articleID=0009F0CA-C523-1213-852383414B7F0147

it is space-time itself that is expanding. matter is not spreading into existing space-time. matter is not expanding.

the above link does discuss this and is provided for you to read.