# What slowed or stopped inflation?

1. Mar 24, 2013

### abbott287

Was it gravity? Does the expansion of the universe have anything to do with the original inflation? One more. What actually is the "fabric" of space that is expanding? You always hear the balloon analogy, so what makes up the rubber of the balloon in real life? Thanks in advance for my uninformed questions. :shy:

2. Mar 24, 2013

### Drakkith

Staff Emeritus
I believe the inflaton field that drove inflation underwent a phase transition, exerting a repulsive force and starting inflation, and upon reaching its ground state the repulsive force that it generated was no longer present.

http://en.wikipedia.org/wiki/Inflaton

3. Mar 24, 2013

### phinds

As for the balloon analogy, maybe this will help you understand that there IS no "fabric"

www.phinds.com/balloonanalogy

4. Mar 24, 2013

### abbott287

That helped explain a good part of it, thank you! If there is no "material" in real life that equals the balloon however, what is it that keeps light to c going between the gravitational bound systems, while those same systems can exceed c in their movement away from one another?. I thought it was the "fabric" of space time. The "fabric" was being stretched or created between the systems, while light had to pass "through" it. Again, your time and effort explaining this is greatly appreciated.

5. Mar 24, 2013

### phinds

As I suggested in the balloon analogy discussion, I recommend that you google Metric Expansion

6. Mar 24, 2013

### Drakkith

Staff Emeritus
Replace the word "fabric" with "geometry" and you've got it. This is difficult to understand, but it is the geometry of spacetime that causes this. What this means is that as light travels across the universe, objects get further apart. Nowhere does it say that 'the fabric of spacetime itself' stretches, but the effect is similar to stretching a rubber sheet. Remember that. The effect is 'similar' to stretching a rubber sheet, yet it doesn't require that there actually be something there. That is perhaps the most confusing part. If nothing is there, what's bending, stretching, etc? Nothing. It is a product of geometry.

But what is geometry? Put simply, it is a branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space
http://en.wikipedia.org/wiki/Geometry

Normal geometry you learn in school is called Euclidean Geometry, and it is only concerned with 'flat' space. Certain rules apply here, such as the fact that all angles of a triangle must add up to equal 180 degrees. However, non-Euclidean Geometry is different. It turns out that if you have a non-Euclidean space, a triangle may not have each angle add up to 180 degrees! The common example is how the equator and two lines of longitude can form a triangle with the north pole. It's a triangle all right, it's got 3 sides and 3 angles, but all three angles add up to more than 180 degrees. http://en.wikipedia.org/wiki/File:Triangles_(spherical_geometry).jpg
http://en.wikipedia.org/wiki/Non-Euclidean_geometry

However, while the example above puts the triangle on the surface of the Earth, nothing says that a surface is required. Space itself can simply work that way, irregardless of whether or not it is made up of 'something'.

I think the main reason this is such a hard concept to grasp is that the effects of curved spacetime are not visible on our scale here on Earth. If everyone could see the effects of curved spacetime in their everyday lives there would be no question. No one asks why three angles of a triangle always add up to 180 degrees in flat space. No one thinks it's weird. It's simply accepted. Then when they hear that this geometry is wrong, they can't accept it. And that's what it boils down to. The geometry we all know and love is plain wrong. It's just accurate enough to use on our scale. (So I've been told by chronos or marcus or someone here at least)

7. Mar 24, 2013

### abbott287

I understand the triangle part perfectly. I also would not call a "bent" or curved triangle a triangle either however. It would be a bent or curved triangle! I understand that the galaxies or bound systems are what are moving away from each other, but they are moving through "space" too, correct? Now if that is empty, or if its being created, so be it, but why can they move away from each other at faster than c? What is it that is keeping light at c, and not keeping the bound systems at c? Again, I really appreciate your time in trying to get it through my thick skull.

8. Mar 24, 2013

### Drakkith

Staff Emeritus
Expansion. I don't know how else to say it. If things are very far apart, they simple recede from each other very quickly. Keep in mind that the light traveling in areas of space very far away from us is also receding greater than c. The universal speed limit does not apply to recession velocities due to expansion.

9. Mar 24, 2013

### phinds

You can call it whatever you like, but mathematicians call it a triangle.

No, not correct. If they were moving "throught" space they would be subject to the limitaion of not exceeding c.

Again, they are NOT "moving" in the sense that you mean. The distance are getting larger but nothing is moving.

10. Mar 25, 2013

### abbott287

Why? What is IT that allows them to "move" (separate) apart faster than c?

11. Mar 25, 2013

### Chronos

Its the same space, not newly created space. If you 'stretch' the coordinate system on a graph, have you created any additional coordinate space?

12. Mar 25, 2013

### Drakkith

Staff Emeritus
Geometry. Popular descriptions would say that they are riding space as it expands "beneath" them.

Both light and matter are moving through space. Light always moves at c through space. BUT, they are both also affected by expansion, by the geometry of spacetime.

The distance between them is increasing, but I wouldn't say that space is being created.

13. Mar 25, 2013

### abbott287

No, but you have stretched the paper or whatever the graph is on. So in reality, what is it you are stretching? What is that "space" made out of that is stretching?

14. Mar 25, 2013

### micky_gta

Expansion is not slowing down it is constantly increasing.
No one really knows what is the fabric of space.
We have a lot to learn, however just like in the UFO/alien domain there are a lot of guesses with no actual proof.

15. Mar 25, 2013

### Drakkith

Staff Emeritus
Nothing.

The distance between them increases. You can say more 'space' is between them, but nothing requires that space be something that is being created.

No, your belief that either something must be stretched or created is incorrect. That's the difficult part to understand. No, not understand, to believe. I believe you understand it perfectly fine, it's that you don't believe it's true, which leads you to dismiss the possibility that space isn't anything at all. Geometry itself, and by that I mean the way shapes are formed and how objects move in three dimensional space, can cause these effects.

Let me ask you this. Do you believe that something can be straight? Why? Is that not weird? Why is it like that? What if nothing could ever be straight, but only curved, is that really any weirder? What if the rules governing whether there could be straight lines or not actually changed over time? Does this require that 'something' be flexing, stretching, or similar? No. It only requires that the universe simply work that way.

Expansion is similar. To the best of our knowledge the rules that govern how objects interact with each other within space say that as the distance between them increases, they recede from each other with increasing velocity which is not limited by c. There is no answer to 'why' this is. That's simply the way it works.

16. Mar 25, 2013