Question about the universe structure?

[Hyperspace2]

question about the universe structure?

I have a question.
Does universe consist curved spacetime everywhere? ,


I believe there are plenty of flat spacetime, isn't it? . If it is so then eveywhere worm hole is not possible isn't it?

 

[bcrowell]

According to current cosmological models, the curvature of spacetime is small, nonzero, and nearly constant on large scales. On smaller scales, you have, e.g., the region near the Earth's surface, which is more highly curved.

I believe there are plenty of flat spacetime, isn't it? .

Perfectly flat? Not likely.

If it is so then eveywhere worm hole is not possible isn't it?

How does this connect logically to the rest of your post?

 

[Hyperspace2]

How does this connect logically to the rest of your post?

worm hole connects the shortest distance between two points in curved spacetime.
If majority of spacetime tends to be flat ,then we cannot drill that worm hole everywhere,isn't it ? or can we?

 

[Chalnoth]

According to current cosmological models, the curvature of spacetime is small, nonzero, and nearly constant on large scales.

Not correct. The curvature of space is extremely small on large scales. There is very significant curvature of space-time, however, which we see as the expansion of the universe.

That said, we do not expect our universe to be, on average, perfectly flat (in terms of space). Our current observations show it's flat to within about a percent or so. But there is expected to be some deviation we can't (yet) detect.

 

[Hyperspace2]

Not correct. The curvature of space is extremely small on large scales. There is very significant curvature of space-time, however, which we see as the expansion of the universe.

That said, we do not expect our universe to be, on average, perfectly flat (in terms of space). Our current observations show it's flat to within about a percent or so. But there is expected to be some deviation we can't (yet) detect.

if much percent of space was flat than , worm hole was not possible,isn't it?
Should we inspect before we make a hole.

I mean Dr Ronald L. Mallett couldnot make his wormhole in his laboratory, did he have to inspect some place to actually create wormhole.

 

[Chalnoth]

if much percent of space was flat than , worm hole was not possible,isn't it?

There are other reasons to suspect that such wormholes don't exist, but the overall spatial curvature isn't one of them.

 

[Ich]

According to current cosmological models, the curvature of spacetime is small, nonzero, and nearly constant on large scales.

Not correct. The curvature of space is extremely small on large scales. There is very significant curvature of space-time, however, which we see as the expansion of the universe.

I think that bcrowell's statement is entirely correct. Curvature of spacetime is significant, but still small (i.e. large curvature radius).

 

[Chalnoth]

I think that bcrowell's statement is entirely correct. Curvature of spacetime is significant, but still small (i.e. large curvature radius).

The point is as you go to large enough scales, the curvature radius starts to become significant compared to the scales you're considering.

I suppose there is an intermediate set of scales where the space-time curvature can be considered small, though. At least on relatively short time scales.

 

[hadsed]

,then we cannot drill that worm hole everywhere,isn't it ? or can we?

You can't drill wormholes.

So I was under the impression that measuring the curvature to be about 1% was simply our limited technology. Is it definitely known that the universe could not possibly be flat, and why/how?

 

[Chalnoth]

So I was under the impression that measuring the curvature to be about 1% was simply our limited technology. Is it definitely known that the universe could not possibly be flat, and why/how?

The first thing to point out is that the curvature is represented as a real number. This means that as long as you have physics which don't predict that the value must be some specific number, any specific number you might choose actually has zero probability of being the real value of the curvature.

Imagine, for instance, that we had initial physics that made for a probability that the curvature could be anywhere from -0.1 to 0.1 with equal probability in that range. The probability for any set of values being true is:

(# of values that match the condition)/(total # of possible values)

The problem here is that there is only one possible value that matches the condition of zero curvature, but there are actually an infinite number of potential values for the curvature between -0.1 and 0.1. In fact, there are an infinite number of potential values for the curvature between -0.00000000000001 and 0.00000000000001.

And then, when you put inflation into the mix, you recognize that the overall spatial curvature that we observe is a combination of the overall spatial curvature of the inflating patch plus a correction due to perturbations early-on during inflation. Since those perturbations are random, the curvature we measure just won't be identically zero, even if it just so happens that there is some weird physics that sets the overall curvature to zero identically.

 

[Hyperspace2]

You can't drill wormholes.

why?