A Question About Universe Size Again

[Mintaka]

If an aeroplane set off in one direction in our sky, it would eventually come back on itself, arrive at where it started.

 

We know this is because it is kept under the sky's roof by gravity and can't escape the atmosphere.

 

We are told the same thing about the universe, at least with the 'finite model' .

 

Like the plane, if we set off, we'd still arrive back where we started.

 

So, in a sense, the universe has a 'roof' on it, much like the earth.

 

Now, 500 years ago, we also thought the earth's "roof" was the limit of everything, that everthing spun around us.

 

Now we know that the roof is just a gravity boundary, all we have to do is use a bit more force to escape it.

 

My question is, couldn't this (and isn't it likely to be? ) just the same with the model of the universe?

 

Just because we can't escape it, just because we'd arrive back where we started, is this any more proof that the limit of the universe is like an unbreachable sealed 'container', any more than our sky is ?

[sigurdV]

I believe you may be right...Whats the point in a universe giving birth to life if its children cant escape the death of the parent?

[Turtle]

...Now we know that the roof is just a gravity boundary, all we have to do is use a bit more force to escape it.

 

My question is, couldn't this (and isn't it likely to be? ) just the same with the model of the universe?

 

Just because we can't escape it, just because we'd arrive back where we started, is this any more proof that the limit of the universe is like an unbreachable sealed 'container', any more than our sky is ?

 

a sealed container does not demand a boundary in mathematical terms, and your questions are prompted by mathematical constructs.

 

here is just one sealed container with no boundary. more at the link.

 

klein bottle @wiki

[Mintaka]

If you tipped that bottle open , would the contents pour out of that hole at the top? Are you suggesting the universe might be this shape?

 

 

 

a sealed container does not demand a boundary in mathematical terms, and your questions are prompted by mathematical constructs.

 

here is just one sealed container with no boundary. more at the link.

 

klein bottle @wiki

[Turtle]

If you tipped that bottle open , would the contents pour out of that hole at the top? Are you suggesting the universe might be this shape?

 

it depends on which way you tip it, but yes, you can pour out the contents. if you read the article i linked to there are instructions for making a model from paper. if you do this you might be able to tell me a thing or two about pouring with klein bottles.

 

so no, i am not suggesting the universe is a klein bottle nor do i know if it could be. i was giving you an example of a sealed container with no boundary per your question. your questions on the size & shape of the universe however are no less bound up in the mathematics & no less difficult to visualize in one's mind's eye. i do understand the compelling urge to visualize, but some things just can't be seen. it's nothing to get hung up on. enjoy what you can see.

 

ps here's wiki's piece on the topology of the Universe. >> shape of the universe @wiki

The shape of the universe is a matter of debate within physical cosmology over the geometry of the universe including both local geometry and global geometry. It is loosely divided into curvature and topology, even though strictly speaking, it goes beyond both. More formally, the subject in practice investigates which 3-manifold corresponds to the spatial section in comoving coordinates of the 4-dimensional space-time of the Universe.

 

The WMAP has confirmed that the universe is flat with only a 0.5% margin of error.[1] Within the Friedmann-Lemaître-Robertson-Walker (FLRW) model, the presently most popular shape of the Universe found to fit observational data according to cosmologists is the infinite flat model,[2] while other FLRW models that fit the data include the Poincaré dodecahedral space[3][4] and the Picard horn.[5]...

here's a more in-depth paper. >> Measuring the Topology of the Universe

 

Abstract

Observations of microwave background fluctuations can yield information not only about the geometry of the universe, but potentially about the topology of the universe. If the universe is negatively curved, then the characteristic scale for the topology of the universe is the curvature radius. Thus, if we are seeing the effects of the geometry of the universe, we can hope to soon see signatures of the topology of the universe. The cleanest signature of the topology of the universe is written on the microwave sky: there should be thousands of pairs of matched circles. These circles can be used to determine the precise topology and volume of the universe. Since we see hundreds of slices through the fundamental domain of the universe, we can use the microwave observations to reconstruct the initial conditions of the entire universe on the scale of a few Megaparsecs.

[CraigD]

If an aeroplane set off in one direction in our sky, it would eventually come back on itself, arrive at where it started.

 

We know this is because it is kept under the sky's roof by gravity and can't escape the atmosphere.

 

We are told the same thing about the universe, at least with the 'finite model' .

 

Like the plane, if we set off, we'd still arrive back where we started.

I think you’re confusing 2 different assertions about the universe: the first, that it contains a finite amount of mass and energy in a finite volume; the second, that it’s a hypersphere (or some other, similar hyperspherical space). The first is widely accepted. The second is the subject of much speculation and investigation, but a very tentative hypothesis. Investigating whether the universe is a hypersphere or not is an interesting and fundamentally simple endeavor – just look carefully in opposite directions, and see if you see the same thing. :)

 

Just because we can't escape it, just because we'd arrive back where we started, is this any more proof that the limit of the universe is like an unbreachable sealed 'container', any more than our sky is?

I think that whether the universe does turn out to be a hypersphere, or it doesn’t, it’s such a huge whatever-it-is that, for all practical human purposes, it can be considered limitless.

 

We’re confined to the small space we occupy – essentially the Earth’s surface and first few dozen kilometers above it, and for a very few people, the Moon – for the same reason early humans were confined to various islands or continents: we lack the technology needed to travel outside of it.

 

Humans can’t swim across ocean, so need adequate boat to span the Earth’s surface. We can’t fly unassisted, so need spacecraft to reach other planets, stars, and galaxies. So far, we’ve gotten boat (and better, aircraft) technology to about what any reasonable person could want, but have just barely gotten spacecraft technology to approach what’s needed for humans to visit a nearby planet such as Mars. Traveling to other stars is pretty conceivable, though likely will require engineering as advanced beyond our current technology as our current technology is advanced beyond stone age technology. Traveling to other galaxies would, I expect, require so long that any people undertaking it would have to be very different than what we currently consider human.

 

For more, see the wikipedia articles size of the universe and shape of the universe.

[Mintaka]

Thank you both for your detailed answers, I think you are right, we should appreciate what we can see, and make the most of what we have.

 

I was thinking about this yesterday, that really we are very lucky to be able to experience anything at all, and even see what is above our heads and feel what is below our feet,

 

, when most of "space" or the universe, is just silent , unheard and unseen.