how do we no the universe is expanding?

Question

if we have never seen the edge of the universe. how do we know its moving?

Answer 1

everything in the universe tries to equally distribute itself.

it's not expanding it is distributing itself across space. dont believe everything you hear. expand is to increase, increase means add. nothing is being added to the universe. the law of conservation of energy states that energy is not created or destroyed but changes form.

Answer 2

All the galaxies in the universe are moving away from each other generally. Some close to each other might be moving closer. Red shift, Doppler effect as stated in other answers is correct.
One answer had a misconception - the universe is not expanding into anything. The universe contains all of space. There is no edge. Think of ants walking on a balloon that is being blown up. The ants are getting further from each other, but they could walk forever and not get to an edge.
We can almost see the beginning of the universe 13.5 billion years ago, but we see the same view everywhere we look. The ants would see the same view no matter which way they looked.

Answer 3

Nice question. The universe is known to be expanding because of the distance between galaxies. Its increasing and galaxies are moving apart. Simple analogy would be.....take a balloon, blow some air and then mark big dots with a marker. Then blow more air into it and see what happens. The distance between the dots (on the surface of balloon) will have increased since the balloon has expanded. Same thing with space.
Ofcourse, scientists are still debating about different questions that arise with this expansion theory such as....what is the universe expanding into? is it enclosed in another entity?, is it finite?, is it infinite? would it expand forever? and the list of questions are never ending and are extremely interesting.

Answer 4

While Roy was partially correct, there is a bit more to it.

The Red Shift is caused by the velocity of an object and the Doppler Effect. As an object moves away from us, the light is drawn out and the wavelengths become longer, shifting to red. Conversely, if it is moving toward us, the wavelengths become shorter and it shifts towards blue.

Using this guide, scientist have noticed that everything (outside our neighborhood) is moving away from us. The only explanation is that the universe itself is expanding.

Answer 5

By what is called the Red Shift. Basically, as light moves further and further away from the observer, the spectrum shifts toward the color red.

Recognizing that some of the light that we can see through a telescope is billions of years old..We can compare that to light that is not quite so old..And determine the universe is expanding. As evidenced by The Red Shift.

Answer 6

Just a quick addition to the answers already put up...
The red-shift answers are basically correct...but they wouldn't mean anything unless we knew the distance to the galaxies we see moving away from us in all directions. We know the distance to thousands of galaxies now from studying both cepheid stars in them (variable stars with a very precise period to absolute magnitude ratio), and from studying Type IIa supernovae we see in those galaxies. Using the distance we can very accurately compare the red shift in their spectra to the distance, and sure enough -- the further a galaxy is from us, the faster it's moving away from us.

Also, *NOT* everything is moving away from us. In our local neighborhood of galaxies, gravity is moving some things faster than space is expanding...for example, the Andromeda galaxy (one of the "local group" of galaxies of which our Milky Way is a member) is moving *TOWARDS* us at a pretty good clip -- our galaxy is going to collide with it in around 2 billion years. But don't worry, galaxy collisions are mostly gravitational interactions, there aren't really any collisions of stars or planets involved. The two galaxies will spend a few million years doing an interesting gravitational dance, after which they'll be one larger galaxy. Our solar system will probably not be affected at all.

Answer 7

This is still a theory, as long as its expanding, that means there is some other space that the universe using to keep expanding, then for how far? then after? when that space "if any" will be filled? these are all theories but its very interesting, I believe the science still needs hundreds of years to prove a lot of outstanding issues!

Answer 8

We know because everything is generally moving away form one common point in the universe.

Answer 9

Because everything is getting further away from us in all directions.

Everything started out in the middle (Big Bang theory). And then exploded out in all directions. We are in the middle of a slow motion explosion but its only slowmotion from our point of view. Imagine a hand grenade going off in slow motion. Boom. Shrapenal flies outwards in every direction. We are a piece of shrapenal orbiting a bigger bit. Some bits flew off faster and some slower. So from out point of view the stuff going faster than us is moving away from us but in actual fact we're flying and they're flying just a bit faster. Similarly the stuff flying slower than us gets left behind so from our point of view its getting further away from us but its just moving slower than us is all. But because we have no refernce it looks like we're stationary but really we're zooming through space clinging to the orbit and warmth of a star flying outwards into infinity and darkness. Until gravity pulls us all back to the middle again that is...

Answer 10

Because things are moving away from us in all directions, as indicated by the red-shift.