Expanding Space Questions

[Jeremy Mallin]

New here. A physics school teacher recommended this forum on Twitter.

 

In the last century astronomers and cosmologists have put forward evidence that space itself is expanding -- not just that matter is moving away from other matter, but that the space itself in between is expanding.

 

Questions: (1) If space itself is expanding, is that expansion homogenous with respect to all four dimensions, x, y, z and t? In other words, is that expansion uniform throughout the universe? What does observation and evidence suggest?

 

(2) Is the expansion of space necessarily the same at all scales? Should the same effects of expansion observed on a grand cosmological scale also be theoretically observable at very small scales (Planck and above)? Why or why not?

 

(3) Which precise definition of space is generrally used when trying to explain the expansion of space, especially expansion greater than light speed? I realize that many physicists have gone back and forth about what space actually is.

 

---

 

Because I'm new here I'll tell a bit about my background. I'm a mechanical engineer and an artist. I've worked professionally in both fields. I've read many books on theoretical physics and cosmology by authors including Brian Greene, Albert Einstein, Stephen Hawking and Lisa Randall. Beyond engineering school requirements, I have not taken any advanced or theoretical physics courses.

 

Recommendations for other authors to read are greatly appreciated as well.

Edited December 26, 2012 by Jeremy Mallin

[mathematic]

http://www.atlasoftheuniverse.com/bigbang.html

 

Above is a good place to start. Google "expansion of the universe" to get more.

[Anubis-UK]

Its not only expanding but isnt it expanding faster and faster because of Dark Energy?

New myself only here through interest! long past studying

[alpha2cen]

(3) Which precise definition of space is generrally used when trying to explain the expansion of space, especially expansion greater than light speed? I realize that many physicists have gone back and forth about what space actually is.

These are the calculated results from the expansion models.

 

1) At the beginning from the some area, i.e., Inflation and expansion.

a) Constant accelerated expansion

http://blogs.scienceforums.net/alpha2cen/2012/12/13/constant-accelerating-universe-mathematical-solution-for-the-telescope-observer/

b) Constant speed expansion

http://blogs.scienceforums.net/alpha2cen/2012/12/18/constant-speed-expanding-universe-calculated-results/

 

2) At the beginning from the one point

a) Constant accelerated expansion

http://blogs.scienceforums.net/alpha2cen/2012/12/16/one-point-accelerating-universe-calculated-results/

b) Constant speed expansion

http://blogs.scienceforums.net/alpha2cen/2012/12/16/one-point-accelerating-universe-calculated-results/

 

Calculated expansion style; from the redshift data and the space expansion model

http://blogs.scienceforums.net/alpha2cen/2012/12/24/space-expansion-model-universe-expansion-graph/

 

The steady state Universe model was also calculated.

http://www.scienceforums.net/topic/71791-light-interaction;-calculated-results-about-the-steady-state-universe/#entry720407

 

Decelerated speed expansion cases are not calculated yet.

Edited December 26, 2012 by alpha2cen

[Iggy]

New here. A physics school teacher recommended this forum on Twitter.

 

In the last century astronomers and cosmologists have put forward evidence that space itself is expanding -- not just that matter is moving away from other matter, but that the space itself in between is expanding.

 

Expanding space is another way of saying that everything is moving away from everything else. It is mostly a distinction without a difference.

 

 

Questions: (1) If space itself is expanding, is that expansion homogenous with respect to all four dimensions, x, y, z and t? In other words, is that expansion uniform throughout the universe? What does observation and evidence suggest?

 

Spatial expansion is homogenous. The rate of expansion changes over time so you couldn't really say that expansion is homogenous with respect to time.

 

(2) Is the expansion of space necessarily the same at all scales? Should the same effects of expansion observed on a grand cosmological scale also be theoretically observable at very small scales (Planck and above)? Why or why not?

 

In multiple respects, it is not the same at all scales. Eddington put it very well in something he wrote:

 

When we assert that the universe expands, what is our

standard of constancy? There is no particular subtlety about

the answer; the expansion is relative to the standards that

we ordinarily employ. It is relative to the standard metre

bar, for example, or to the wave-length of cadmium light

which is often suggested as a more ideal standard, or to any

of the linear dimensions associated with atoms, electrons, etc.

which are regarded as "natural constants" in atomic physics.

But if the universe is expanding relatively to these standards,

all these standards are shrinking relatively to the universe.

The theory of the expanding universe is also the theory of the

shrinking atom.

A. Eddington, 1935

 

In other words, the little things don't expand with large intergalactic distances.

 

(3) Which precise definition of space is generrally used when trying to explain the expansion of space, especially expansion greater than light speed? I realize that many physicists have gone back and forth about what space actually is.

 

Space is what a ruler measures. The cosmos expands because the distance between galaxies as measured by something like a series of meter sticks increases over time. The further away the two galaxeis which are being measured, the rate at which the measured distance increaes over time.

Edited December 26, 2012 by Iggy

[Jeremy Mallin]

I want to thank everyone who posted a reply for your answers, mathematic, Anubis-UK, Alpha2cen and Iggy.

 

Your answers helped me a lot, especially the reference links and the Eddington quote. The more I learn, the more questions I have, but I suppose that is a good thing.

 

One thing I don't understand from a theoretical point-of-view (Iggy and Eddington make it perfectly clear from an empirical point-of-view) is why "the little things don't expand with large intergalactic distance". If no one minds another question... Is this a question that there are any good answers for or is it still in the hypothesis stage? Is one of the ideas something to do with forces that act with different strengths at different scales? or do physicists thing curvature of space (due to mass or dark matter, dark energy, whatever else) has something to do with different expansion at different scales?

 

I appologize if the reference links above already address some of these questions. I will check out the links too.

 

Thanks again.

[StringJunky]

One thing I don't understand from a theoretical point-of-view (Iggy and Eddington make it perfectly clear from an empirical point-of-view) is why "the little things don't expand with large intergalactic distance".

 

Up to the size of Superclusters, like the Virgo Supercluster we are in, gravity overwhelms the Metric Expansion of Space so all the objects you see in the following image aren't influenced by it within its confines ....we are in the that bit in the centre, the Local Group.

 

http://en.wikipedia.org/wiki/Virgo_Supercluster