a dent in a tin can

[YT2095]

after reading some of the thread about gravity and the edge of the universe etc...

a thought occured to me when I made a post that gravitity only reduces over distance but never actualy becomes Zero, there`s some that beleive the universe has an "edge" like a border.

wouldn`t these 2 ideas be in conflict at all?

 

I`m sure we all remember the old demonstration about Curved space where a large ball is placed in the middle of a rubber sheet, and then a smaller ball that would ordinarily pass along the sheet in a straight line spirals gradualy towards the large oject or takes a curved path.

now bearing this in mind, if the sheet were infinately large even at the very edge there would still be a pull downwards, if we hit a tin can with a projectile the whole can distorts in much the same way, there`s no escaping this.

 

so I`m thinking now that there couldn`t possibly be an Edge to the universe exactly because gravity carries on for ever.

 

does this idea sound about right or my thinking flawed or I`m possibly overlooking something?

[Severian]

I am not seeing what this has to do with a tin can??

 

But the idea that the universe has an 'edge' is only popular among airmchair scientists. The accepted view among physicsists/cosmologists is that the universe keeps going on forever. If it just stopped you would be violating lorentz invariance. The idea that it had a periodic boundary condidtion (ie. if you travel far enough you would come back to where you started) is self-consistant but is disfavoured by experimental data.

[YT2095]

the tin can like the rubber sheet, when influenced at a point will deform all parts of it no matter how small or what shape, a cylindrical tin can or a flat rubber sheet.

I sort of envisage the "edge" of the universe as just a "Thinning out" of what we know, but never actualy becoming Nothing or Zero.

[Snake_Arts]

There is no edge to the universe because as we know space curves due to gravity. Therefore two cases are present, if the universe keeps on expanding forever then this means the universe is infinite in size and does not have an end. Secondly, the big crunch theory, well if this is so then the universe is also infinite in size and also does not have an end due also to gravity. think of the earth for instance, it is round therfore does not have an edge. You cannot 'fall off' the earth as there is no edge. Think of the universe in the same way, either theories introduce the idea that this is also the case, due to the bending of space there cannot possilbly be an edge. Thanks to einstein we know the effect of gravity upon space, we must assume the universe holds the same effect therefore how could we say where the 'edge' was. There is no edge in the universe as there is no edge upon the earth.

 

 

 

The secret to creativity is knowing how to hide

your sources.

- Albert Einstein

[[Tycho?]]

I dont think I've ever heard anybody with any credintials say the universe has any kind of edge. While it might be finite in extent, you wouldn't ever come come to a wall where the universe ends, you'd just be looping back around.

 

But when talking about the entire universe and these sort of things, its best to take any opinion with a grain of salt. The best scientists in the world dont have anything but educated guesses on these sort of questions.

[Severian]

Snake_Arts: You are a wee bit out of date. This was the view a few years ago, but more recent data suggests that the universe need not be the same in the time direction as the space direction, so it could be spatially closed, but never come to a big crunch.

 

In fact the data points to the universe being spatially flat, but the expansion seems to be accelerating! This last observation is not understood and was a big surprise because the question had always been 'How fast is it decellerating?'. No-one expected an acceleration.

[Snake_Arts]

"Current indications from the cosmic microwave background are that the universe is spatially flat. That implies that the sum of all of the energy (density) in the universe equals the critical density, i.e. the total Omega is 1. This is quite interesting because as the Universe expands the value of Omega changes. In fact the value 1 is unstable, and the Universe would prefer to evolve towards one of the two natural values: 0, if the expands forever further apart until the Universe is almost totally empty ; and infinity, if the matter recollapses to a state of higher and higher density. Then the observation that Omega is fairly close to 1 today, means that it must have been even closer to 1 in the past. It is unsatisfying to believe that we just happen to live at the time when Omega is just starting to depart from 1 by a small factor. It is much more appealing to consider that we do not live at a special epoch, so that Omega is still close to 1 today. But then we need to explain why Omega started out very close to 1 in the early universe. The theory of inflation provides just such a justification - most versions of inflation predict that the early Universe was driven extremely close to flat, and that it is still very close to flat today. If this is so, then at least 90% the energy of the Universe is dark! Note that although the universe may be flat, that does not mean that matter makes up the crtical density. In addition to dark matter there is dark energy, e.g. a cosmological constant, that needs to be included in the accounting." if you would have read all postings you would have seen i touched upon this subject