why are a bunch of scientists lately have a theory that the universe is expanding?

Question

im not saying that it isnt, but im just curious about how something thats suppose to be infinite, can begin to expand

Answer 1

I think it's because it's evident that the galaxies are getting farther apart. This makes them think that the universe is expanding, and that a very long time ago the whole universe was infinitely dense and infinitely small. I just read something about this today, so I'm not sure if this is the full answer...

Edit: And are you sure the universe is considered infinite? Cause if so, that's extremely confusing haha.

Answer 2

That is a good question, though it is not just lately.

The theory that the universe is expanding started with Edwin Hubble, who noticed that in photographs he was taking of galaxies, the light from those galaxies was RedShifted, that is, they were traveling away from him!

To understand this, you must undertand that light behaves as a wave, sort of like sound. When a car flies past blasting its horn, you hear the pitch change as it goes by. This is because as the car approaches, the sound waves are compressed, making them higher in pitch. As the car goes by the sound waves are get longer, and as the car is heading away from you the pitch drops.

The same thing happens with light. If something is headed toward you at a very high speed, the light from it has a compressed wavelength, making it appear more blue (it is shifted to the blue end of the spectrum, or blue shifted) and when going away, the light is redshifted.

Hubble realized that when he looked at lots of different galaxies, there was a lot of red shifting going on, and not much blue shifting at all, in fact, only a couple of galaxies were blueshifted! The galaxies all being redshifted could only mean that they were all heading away from us.

Naturally, since galaxies are collections of billions of stars, are VERY far away, and the Milky way is NOT the center of the universe, the only way to explain this observation was that the universe was EXPANDING.

Worse, it seems that the further away a galaxy is, the faster it tears outta here. The universe appears not only to be expanding, but the expansion seems to be accelerating!

Going in reverse, one can easily extrapolate that if the universe is expanging, it must have started somewhere. But where?

All the galaxies seem to be moving away from us, with uniform speeds when they are at the same distance. Common sense would tell us that the universe started right here, wouldn't it? If everything seemed to move away from us? No, not quite. Think about a balloon with a bunch of dots drawn on it. The dots are galaxies. Now inflate the balloon. They all move away from each other--that is how the universe is expanding.

Trying to get one's head around all of this can take a little time. Here is a link to a site that goes into it all more.

Answer 3

They are saying this because for the same reason that I just answered another question on the same subject. An expansion would depend on the ratio of the density of the Universe to the critical density. If the density is higher than the critical density the Universe will recollapse in a Big Crunch. But current data suggest that the density is less than or equal to the critical density so the Universe will expand forever. AND.. that appears to be what they are relying on.. the same idea

Answer 4

Not lately.
I was reading Sir Arthur Eddington already old books on the expansion of the universe already in the 1950's.
The universe may not be infinite but unlimited, such as the surface of a sphere, expanding away from the center of the Big Bang.

Answer 5

Because the universe isn't static. Throughout history, the universe expands or decompresses.

The universe is FINITE not infinite.

Answer 6

I don't think they think it's infinate anymore. That would mean it couldn't expand, and (most) scientists aren't stupid.

There are gobs of theories about what the universe really is, and those all play into it, and the whole thing kind of makes sense to me.

Answer 7

Well the only universe that we know about is the furthest stellar object that we can see. That object is blue shifting, which means its moving away from us. One can only naturally assume that (assuming the BB theory is correct) the universe is expanding.

Answer 8

They are not only saying it is expanding, they say the expansion is accelerating. Nobody knows why. They determined this by measuring the brightness of supernova at varying distances.

Answer 9

Not lately.

Not infinite.

Answer 10

They have said that for a very long time.