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yajvan
21 July 2010, 01:34 PM
hariḥ oṁ
~~~~~

namasté

We are informed by astrophysicists that the universe is expanding.
The measurement, as I am informed¹, is called the Hubble constant. It suggests an expansion rate of 48 miles per second per 3.26 million light-years or 77 kilometers per second per 3.26 million light-years. This has been updated from 71 km/s/Mpc, within 5% of error, a number from 2003 so I am told.

So, my question for our esteemed scientist's on HDF and those that wish to take a stab at this question. All around me I see space, I am made of molecules and scientist say they too are ~ 90% space. Why is it I do not see some change, so differences in my surroundings or environment if the universe is expanding? In fact I am told it is the ~space~ that is expanding specifically.

One answer as I can only presume is the amount of change is very small; 48 miles over 3.26 million light years is a very small amount.
I agree if we're only talking 1 second of time. Yet note the following as I calculate 'big'.

In one day there's 86,400 seconds. That suggest, in one day, the expansion that occurred = 4,147,200 miles
In one year then the expansion would be 4,147,200 X 365 days = 1,513,728,000 miles.
I am 58 years of age , so the universe has expanded 58 X 1,513,728,000 = 87,796,224,000 miles during my life time.Now wouldn't you think I'd notice this even slightly ? that my house is a bit to the left or right then it was a few years ago :) ? Or the street I live on is now a bit further when I drive home? Or more importantly I have grown a few more millimeters and I am taller, yet none of this occurs. What then of NASA shooting for a planet , and the planet moved?

What's up with this expansion? Not to mention this expansion is suppose to be accelerating?

praṇām

source for Hubble's constant : http://www.astronomy.com/asy/default.aspx?c=a&id=4453 (http://www.astronomy.com/asy/default.aspx?c=a&id=4453)

sanjaya
21 July 2010, 04:36 PM
Ah yes, this is a common question. The answer is that the universe's expansion can be opposed by gravity. Galaxies are gravitationally bound, which is why the stars in the galaxies don't move further apart. That's why the earth doesn't move away from the Sun. With the human body or other material on earth, it has more to do with electrostatic forces between molecules. But the short answer is that gravity prevents us from expanding on this smaller scale.

yajvan
21 July 2010, 05:59 PM
hariḥ oṁ
~~~~~

namasté sanjaya,


Ah yes, this is a common question. The answer is that the universe's expansion can be opposed by gravity. Galaxies are gravitationally bound, which is why the stars in the galaxies don't move further apart. That's why the earth doesn't move away from the Sun. With the human body or other material on earth, it has more to do with electrostatic forces between molecules. But the short answer is that gravity prevents us from expanding on this smaller scale.

I have thought of gravity as the 'glue' to keep things together, yet if the universe is expanding, then what are the milestones of objects i.e. matter used to suggest this expansion takes place ? These objects have gravity exerting on them , no?

That is to suggest this expansion is uniform correct? It does not occur only in the 1100th North block of the universe but not in the 4400 South block, no? That is, there is not selective expansion. And if I looked directly into open space with not one proton or electron floating around, how can I tell space itself is expanding with out a frame of reference ( an object) ?
Any opinions and insights are welcomed.


praṇām

MahaHrada
22 July 2010, 05:41 AM
hariḥ oṁ
~~~~~

....how can I tell space itself is expanding with out a frame of reference ( an object) ?
Any opinions and insights are welcomed.


[FONT=Tahoma]praṇām

Expansion of space is a misleading term since space is not a substance that expands, the cause of this expansion/contraction is not due to space, or redshift due to a change in the photon state, but the cause is the relation between the observer and the observed and movement (=time) in curved space time continuum.

A better description of the phenomena described often as "expansion of space" would be to say "physical distances increase with time between 2 bodies at rest". (measured in respect to a cosmic fluid of uniform density)

(Contraction of space of course is only a theoretical possibility of an universe ending in a big crunch, not a practical observation)

SethDrebitko
27 July 2010, 08:26 AM
Here is a very basic way to look at it. If you have ever watched an astronaut in space blowing water droplets out into the space craft. Imagine the craft to be the universe and those droplets galaxies. Those droplets are singular things clinging together with their own glue, while their relation to the other droplets expands over time.

Another factor is the entropic nature of the universe in the short term. As stars flicker out, explode, they destroy solar systems and that effects the way things glue together.