We live in a bubble. Seriously.

[Rath]

tarheel91 said:

Fayceless said:

tarheel91 said:
Am I going to be the only one to own up to the fact that the void thing went WAY over my head. I'm in AP Physics C, and I'm dumbfounded. I don't see how a void would make the distance increase over time. I'm not saying they're wrong; I just don't get it.

 

It's not so much a void of matter, as it is a less dense area of the universe.  If we do live in a less dense area of the universe, then all of our calculations that show that the universe is accelerating could be wrong.

Under the current assumptions, the matter in the universe is distributed fairly evenly.  Therefore,  there is very little difference in space-time as you travel across.  We compare distant object with nearby objects in order to learn about them.  However, as matter warps space-time, if we do live in a bubble of less density, then we would have to take into account the variation in space-time.

So, if distant objects are indeed in higher density parts of the universe, then our comparisons of those objects to nearby objects are flawed.  Light is affected by space time, as I'm sure you know. Since the light would have to travel through higher density matter, it would be more affected by space-time, and it would appear that things are moving faster than they really are.  Everything would be distorted as it moved further away, appearing to speed up even if it really isn't.

We measure the universe in large part by studying type Ia supernovae.  As mentioned in the article, they are always approximately the same brightness, they would all be the same if you saw them all from the same distance.  We measure distance of a type Ia supernova by measuring the amount of light that reaches earth.  We measure the speed at which something is moving by measuring redshift or blue shift.  As an object moves closer to us, the light appears more blue, if it is moving away, it grows more red. It's the doppler effect with light.  However, if the light travels through a different density of space-time, then our measurements are off.

I really hope I'm making sense here.  Just ask me if something doesn't make sense, I'll try again.

I get that space is distorted by space time, and that a less dense area would alter it.  However, shouldn't it be altering it in constant way throughout all eternity?  Maybe everything's in a different spot, but I don't see how position can constantly change as a result of a constant amount of less density.  Glass can bend (sort of) light, but it doesn't make it looks like things are moving, it just makes the object emitting or reflecting the light look like it's somewhere it's not.

@Vlad: I took AP Physics B last year.  I aced the class and got a 5 on the AP.  Is the calculus portion of Physics C that much worse?  I'm 1/5 through the year and all it is is a repeat of Physics B so far.  I recognize that the stuff we're talking about is well beyond Physics C, but I just included it to show I did have some form of a physics foundation.

 

What if you imagine looking through a lense that makes objects appear more distant than they are. At close distances the difference between actual distance and perceived distance would be small and the difference would increase the further the object was away from you. Thus an object moving away from you would appear to be moving away at a higher speed than it really was. I believe thats the kind of distortion we're talking about here.