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Offline Mindspace

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Is there a cosmological constant?
« on: 12/01/2010 01:24:58 »
Is there a cosmological constant? By which I mean an expanse of space free from matter, forces and curvature where time or space/time can flow unhindered at its natural rate.

I understand the measure of time to be observationally relative and affected by mass, motion and energy and wonder if it's possible, theoretically or otherwise, that there is a natural state of being, in terms of space, by which all else can be measured?

I suppose this question relates to 'what is space?' as it would appear, logically at least, that in order for there to be curvature of space there must exist a space to curve. Is space itself the constant and the observed phenomena of distortion of space/time merely localized events?



 



 

Offline Mindspace

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Is there a cosmological constant?
« Reply #1 on: 12/01/2010 16:35:54 »
No replies? Reading through the forum you all seem a friendly and interesting bunch of people. Strange! I can't imagine my limited understandings of physics would deter people from offering explanations.

So! Is there such a thing as the cosmological constant?


When people talk of space and time being inextricably linked, how precisely is that being defined? Space can be considered to be existant, even if it exists as non-existence, but time as an existant entity? The past exists no more than the future does and we have only a succession of moments of now.

How is time slowed or speeded up? Our measure of time is the observation of the rate at which certain atoms vibrate and the slowing of that rate close to a massive object is merely that; the slowing of the rate of vibrations of an atom. The universe carries on regardless presenting it's succession of moments of now and the atom exists within that same framework of moments of now only at a reduced rate of vibration.

The analogy of the space-travelling twin leaving his sibling behind on Earth and traveling at a significant fraction of the speed of light, for a year, who returns to find thousands of years have passed on Earth seems flawed. The lightspeed traveler has traveled and existed for the same number of years as have passed on Earth
only his perception of it was different due to the slowing of the vibration of atoms in himself and his spaceship. Time didn't slow down, only his perception of it locally. The succession of moments of now carried on regardless.
 
If time seems to be an abstract human invention then is it possible that space itself is the constant that suffers distortion locally in proximity to massive objects? 

 

Offline LeeE

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Is there a cosmological constant?
« Reply #2 on: 12/01/2010 16:45:38 »
Umm...  No,there does not seem to be a region of space-time within our universe where there is no energy.  If there was such a region of 100% space-time void then the universe could not be observed from within it, for observation of the universe would require energy from the universe to be detected within the region, with the result that the region would no longer be a void.

I think all of your other questions have been discussed in other threads; try having a look through some of them.
 

Offline Mindspace

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Is there a cosmological constant?
« Reply #3 on: 12/01/2010 17:03:34 »
Will have a look through them.

If the void was free from all forces except light (which would simply pass through it anyway) then space and time would be constant and the rest of the universe observable.
 

Offline graham.d

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Is there a cosmological constant?
« Reply #4 on: 12/01/2010 17:34:44 »
The lack of replies maybe to do with your original post being at 1:24am (uk time) and then some people being busy at work (even if sometimes skiving off occasionally to look at NS. :-)

As far as is known, observations seem to indicate a positive value for the cosmological constant. The model used for the universe, which stacks up with observation, would have the universe homogenous and isotropic. With such a model it is assumed that the cosmological constant is generally applicable throughout.

Space and time are indeed linked according to the generally accepted ideas. The universe is 4 dimensional (on a large scale) and probably with many other dimensions on a small scale. It gets hard to understand the ramifications or to visualise the effects as these no longer track with how things behave in our everyday life.

You mention the twin paradox. This effect only depends on the concepts of special relativity and is much easier to understand than general relativity and its impact in cosmology. I posted a reference to a good website (at least I thought it good) that explains some of this stuff without the mathematics getting too deep. I'll post it again here:

http://www.eftaylor.com/download.html#general_relativity

The sections of special relativity should explain the twin paradox though I have not looked at them. The GR stuff on curved space is the best not-so-mathematical explanation I have seen.
 

Offline yor_on

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Is there a cosmological constant?
« Reply #5 on: 16/01/2010 13:48:57 »
"Is there a cosmological constant? By which I mean an expanse of space free from matter, forces and curvature where time or space/time can flow unhindered at its natural rate."

You make some assumptions here :) So I will make some others.

Time can mean two (or more) things. in QM you will find definitions where time seems to go both ways, backward and forward. Up here (macroscopically) time goes one way as far as we have observed, yet. That way we call 'times arrow'.

Thats one, now comes the second assumption of mine. If we have space due to mass and in a way then also to the concept of energy, as f.ex. the Big Bang as well as the inflationary period seems to indicate. And mass, acceleration and motion is what changes both our definition of time as well as distance then what would an expanse of only pure 'space' be?

Would it even exist?

There wouldn't be any arrow to such a place. And without an arrow there wouldn't be any distance as distance = 'length' as measured in time (times arrow).

So to me it seems hard to imagine. It seems as most of our definitions exist only macroscopically, from distance to times arrow. Here we have them and they works very well but as you move away further 'down' in size things become fuzzy.

 

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Is there a cosmological constant?
« Reply #5 on: 16/01/2010 13:48:57 »

 

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