The balloon analogy sort of confuses me.
In: Physics
They actually are moving away from us , our universe is expanding at a rapid rate more than 80 km per second. Soon there will be parts of our universe taken away from our sight never to be seen again which our future generation will have no clue it even existed.
Because we’re spinning around a black hole and getting sucked into it faster and faster, which makes the stuff further away from us seem to be moving away faster and faster
They appear to be moving away because they are; when something is moving away from us the wavelength of light gets shifted downwards, very similar to how a train whistle moving away from you sounds lower than a train whistle moving towards you. The shift isn’t noticeable at everyday speeds but at interstellar or intergalactic speeds it’s noticeable. So we can look at the light coming from other stars or galaxies and compare it to a known reference, see how much it shifted, and know how fast that is moving away from us. Or, more correctly, how fast it *was* moving away from us at the time the light was emitted.
In every direction we look, the farther away something is the faster it’s moving away. The only way that can work is if the whole universe is expanding. That’s what the balloon analogy is trying to convey. Draw a bunch of dots on a balloon then start blowing up the balloon. For *every* dot, all other dots look like they’re moving away and and the farther away they are the faster they’re moving.
They appear to be moving away because they are; when something is moving away from us the wavelength of light gets shifted downwards, very similar to how a train whistle moving away from you sounds lower than a train whistle moving towards you. The shift isn’t noticeable at everyday speeds but at interstellar or intergalactic speeds it’s noticeable. So we can look at the light coming from other stars or galaxies and compare it to a known reference, see how much it shifted, and know how fast that is moving away from us. Or, more correctly, how fast it *was* moving away from us at the time the light was emitted.
In every direction we look, the farther away something is the faster it’s moving away. The only way that can work is if the whole universe is expanding. That’s what the balloon analogy is trying to convey. Draw a bunch of dots on a balloon then start blowing up the balloon. For *every* dot, all other dots look like they’re moving away and and the farther away they are the faster they’re moving.
Space is expanding. That doesn’t mean the “edge” of the universe is simply pushing out, it literally means all of the space within the universe is expanding. The more space between two points, the more space there is to expand, and therefore the faster they will move away from each other.
That’s what the balloon analogy is meant to represent. It’s not just that the top and bottom of the balloon are pushing outwards, the whole surface of the balloon is stretching. Each atom is getting further from the others, the more atoms between any two arbitrary points the more expansion is happening. It’s just harder to translate this concept to space because there is no material stretching or atoms moving.
Imagine we have 5 people. Were all standing in a circle with our heads touching. We agree to all turn exactly 180 degrees and walk the other way exactly 10 feet. The person opposite me will be farther away than the person next to me but all will have moved away. If we go another ten feet the person next to me is further than they were but the person who was opposite me would be the furthest away. Each time we moved one more foot away the person opposite me would be moving two feet away.
You’ve got some correct answers already but I’ll try to break it down from another angle.
The balloon analogy can be a little confusing because the important part of the balloon is the *surface* of the balloon, which is two-dimensional…you’re not supposed to think about the inside of the balloon. The universe is three-dimensional, so a better analogy might be to think of a loaf of raisin bread rising in the oven. As the dough rises and the loaf gets bigger, the raisins are spread further and further apart from one another. The size of the raisins doesn’t change, and they’re not moving on their own, they’re just being carried apart by the dough.
The dough is space-time. When we say the universe is expanding, we mean that *space itself is getting larger.* It’s like there’s “more space” pouring out of every point in the universe, all the time. The galaxies within are getting pulled further and further apart by the expanding space, not under their own power but just getting carried, like the raisins.
That expansion force is (pretty much) uniform all over the universe: if space is expanding by, say, 1 cubic meter per second (just making that up), it’s expanding by 1 cubic meter per second here, and 1 cubic meter per second around the Moon, and at Alpha Centauri, and Andromeda, and everywhere else.
(By the way, the expansion force is much, much, much weaker than gravity, so we don’t notice it on anywhere near a local scale…the Andromeda Galaxy is moving *toward* our galaxy due to gravity, and it’s 2 million light-years away. We don’t notice expansion until we get well beyond that distance.)
So let’s say we have seven galaxies that start out 1 billion parsecs apart, and they look like this:
ABCDEFG
with each character space representing a billion parsecs. Let’s say that at the scale of 1 billion parsecs, the expansion force is “making more space” at the rate of 1 billion parsecs for every million years (again, making this up). Therefore, after one million years, these seven galaxies will look like this:
AxBxCxDxExFxG
Consider Galaxy D. It started out 1 billion parsecs away from Galaxy C and Galaxy E, 2 billion parsecs away from Galaxy B and Galaxy F, and so on. A million years later, now it’s 2 billion parsecs away from Galaxy C and E, 4 billion from B and F, and so on.
Another million years go by:
AxxBxxCxxDxxExxFxxG
Galaxy D is now 3 billion pc from C and E, and 6 billion from B and F.
So Galaxy C moved 3 billion pc away from Galaxy D over two million years, while Galaxy B moved 6 billion pc in the *same* amount of time. The effect of expansion is *cumulative*: the greater distance you have to measure, the more space is going to expand. Galaxy B moved away from Galaxy D twice as fast as Galaxy C did.
Look at it from Galaxy F’s perspective. From its perspective, E and G moved 3 billion over two million years, and D moved 6 billion, C moved 9, and so on. It’s seeing the same phenomenon: every galaxy is moving away from it, and the farther a galaxy is, the faster it’s moving away.
And that’s why.
What I didn’t include in this story is that the expansion force is accelerating over time, but that’s not really important to answer your particular question.
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