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Effects of a vacuum/ the expansion of the universe is accelerating

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stepson
#1
Jun30-13, 01:20 PM
P: 2
This is my 'virgin' attempt at intercourse in this venue, so please be roughly gentle.
(I.E.; this is my first post, I'm a bit slow (intellectually) but willing to learn. I tend to be somewhat playful in how I use words. I hope you will forgive me if I step outside the boundaries of appropriate decorum).
My question concerns the relationship between the effects of a vacuum and the expanding universe. Outside the event horizon of the theoretically known universe (if I'm not being too presumptuous) it would seem, to me, reasonable to suppose a void or vacuum. Would it not therefore seem reasonable to expect an accelerating expansion of said universe due to the combined effects of Newton's law of gravity within the confines of a void/vacuum?
Thank you for sharing you insights.
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Mordred
#2
Jun30-13, 10:55 PM
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there is no outside the universe, their is outside the observable universe. We do not know if the universe is finite or infinite. Expansion describes the increase of commoving distances, we can choose any 3 coordinates and trace its expansion history.

The site at my signature has a good article to help you out.

http://cosmology101.wikidot.com/redshift-and-expansion
Drakkith
#3
Jul1-13, 05:55 AM
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Quote Quote by stepson View Post
My question concerns the relationship between the effects of a vacuum and the expanding universe. Outside the event horizon of the theoretically known universe (if I'm not being too presumptuous) it would seem, to me, reasonable to suppose a void or vacuum.
Cosmologists do not believe there is an 'outside' to the universe.

Would it not therefore seem reasonable to expect an accelerating expansion of said universe due to the combined effects of Newton's law of gravity within the confines of a void/vacuum?
Thank you for sharing you insights.
I don't see how. The average density of space results in very very little pressure that would cause an expansion. The integalactic medium has something like a couple of hydrogen atoms in every cubic meter of space, so they effectively never collide with each other. Also, newtons law of gravitation is only attractive, so I don't see how it could have anything to do with an accelerating expansion. Besides, we KNOW newtons law of gravitation is wrong, as General Relativity more accurately describes the observed gravitational effects.

GeorgeDishman
#4
Jul2-13, 07:06 AM
P: 255
Effects of a vacuum/ the expansion of the universe is accelerating

Quote Quote by stepson View Post
Outside the event horizon of the theoretically known universe (if I'm not being too presumptuous) it would seem, to me, reasonable to suppose a void or vacuum.
There is no reason to presume that what lies beyond our limit of observation differs from what we see within the "observable universe". What we see is a uniform density of matter and radiation (over reasonably large scales) hence cosmologists presume the same continues beyond the observational limit. That is called the "Cosmological Principle":

http://en.wikipedia.org/wiki/Cosmological_principle
Naty1
#5
Jul4-13, 04:58 PM
P: 5,632
Hi stepson.....This forum is for discourse; intercourse may be found elsewhere. USe discretion the lords of the forum can be strict!!

My question concerns the relationship between the effects of a vacuum and the expanding universe.
Hoover, Dyson, Orek et al need not apply here.

There IS something in an 'empty' vacuum. Turns out the energy there, called dark energy, also called the cosmological constant, has a negative pressure....an expansionary effect that causes large scale distance to increase. Right now that expansion is accelerating.

A decent introduction is here:

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

In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) is equivalent to an energy density in otherwise empty space. It was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a static universe. Einstein abandoned the concept after the observation of the Hubble redshift....A positive vacuum energy density resulting from a cosmological constant implies a negative pressure, and vice versa. If the energy density is positive, the associated negative pressure will drive an accelerated expansion of the universe, as observed. (See dark energy and cosmic inflation for details.)......


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