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Steve101
30th January 2012 - 10:24 AM
My question is this: Does the gravitational pull of any particle actually disappear or does it get infinitely weaker with distance but not actually disappear?

If the entirety of space were empty apart from 2 hydrgen atoms, 100 milloin light years apart(or any distance for that matter), with infinite time would they eventually collide?
synthsin75
30th January 2012 - 05:18 PM
The range of gravity is considered infinite, but since it seems to propagate at the speed of light, any two objects receding from each other at c, due to the expansion of space, will not gravitationally influence each other.
Robittybob1
30th January 2012 - 06:45 PM
QUOTE (synthsin75+Jan 30 2012, 05:18 PM)
The range of gravity is considered infinite, but since it seems to propagate at the speed of light, any two objects receding from each other at c, due to the expansion of space, will not gravitationally influence each other.

If the Universe consisted of just two atoms of hydrogen would space be expanding?

I have previously calculated that if the hydrogen atoms are more than 88 mm apart they are as good as lost. Gravity between two atoms (protons) would be so small at that distance the acceleration was less than 1 Planck Length per sec^2.
synthsin75
30th January 2012 - 07:51 PM
QUOTE (Robittybob1+Jan 30 2012, 12:45 PM)
If the Universe consisted of just two atoms of hydrogen would space be expanding?

I have previously calculated that if the hydrogen atoms are more than 88 mm apart they are as good as lost. Gravity between two atoms (protons) would be so small at that distance the acceleration was less than 1 Planck Length per sec^2.

The expansion of space has not been found to require any matter at all.

Since the OP specifies infinite time, any influence at all would eventually have an effect.
Steve101
30th January 2012 - 10:07 PM
So is time not seen as infinite? Also, if its space thats expanding, not just the matter within it, that also implies that space isn't infinite. As you can probably tell, I am not well educated in physics. But it does interest me hugely.
synthsin75
31st January 2012 - 01:48 AM
Time is generally agreed to be finite into the past, and potentially infinite into the future. Of course, we cannot confirm any infinite quantity. Since space expands with time, it is considered similarly to time.
-Fairy-
31st January 2012 - 08:56 PM
QUOTE (Steve101+Jan 30 2012, 10:07 PM)
So is time not seen as infinite? Also, if its space thats expanding, not just the matter within it, that also implies that space isn't infinite. As you can probably tell, I am not well educated in physics. But it does interest me hugely.

Please, get yourself an education.
Robittybob1
31st January 2012 - 09:01 PM
QUOTE (synthsin75+Jan 30 2012, 07:51 PM)
The expansion of space has not been found to require any matter at all.

Since the OP specifies infinite time, any influence at all would eventually have an effect.

It is the matter moving away from us that makes them think space is expanding. So in someway it is matter dependent.
synthsin75
31st January 2012 - 09:25 PM
No property of matter has been found to cause spatial expansion, regardless of how we observe it. Matter has not shown to be part of the mechanism.
Steve101
31st January 2012 - 11:36 PM
QUOTE (-Fairy-+Jan 31 2012, 08:56 PM)
Please, get yourself an education.

Thank you for the insult. That post will define you from this point.
Robittybob1
1st February 2012 - 12:19 AM
QUOTE (synthsin75+Jan 31 2012, 09:25 PM)
No property of matter has been found to cause spatial expansion, regardless of how we observe it. Matter has not shown to be part of the mechanism.

QUOTE

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

Metric expansion is a key feature of Big Bang cosmology and is modeled mathematically with the FLRW metric. This model is valid in the present era only at relatively large scales (roughly the scale of galactic superclusters and above). At smaller scales matter has clumped together under the influence of gravitational attraction and these clumps do not individually expand, though they continue to recede from one another. The expansion is due partly to inertia (that is, the matter in the universe is separating because it was separating in the past) and partly to the repulsive force of dark energy, which is of a hypothetical nature, but it may be due to the the cosmological constant[citation needed]. Inertia dominated the expansion in the early universe, and according to the Lambda-CDM model (ΛCDM model) the cosmological constant will dominate in the future. In the present era they contribute in roughly equal proportions.
 


they say in that bit " The expansion is due partly to inertia (that is, the matter in the universe is separating because it was separating in the past)".

Matter may play a part?
Robittybob1
1st February 2012 - 12:23 AM
QUOTE (Steve101+Jan 31 2012, 11:36 PM)
Thank you for the insult. That post will define you from this point.

That isn’t an insult. That was just humorous advice. Wait till Granouille growls at you.
synthsin75
1st February 2012 - 12:56 AM
QUOTE (Robittybob1+Jan 31 2012, 06:19 PM)
they say in that bit " The expansion is due partly to inertia (that is, the matter in the universe is separating because it was separating in the past)".

Matter may play a part?

The inertia is hypothesized to be the contribution left over from inflation, which is just a much faster, early expansion. So the result of an earlier expansion effecting the current one.
Robittybob1
4th May 2012 - 12:40 AM
"Mysterious Dark Matter Becomes More Mysterious"
http://www.redorbit.com/news/space/1112516...ore-mysterious/
QUOTE

According to a new study, large amounts of dark matter do not surround the Sun, despite some widely accepted theories.
Source: redOrbit (http://s.tt/19v1Z)


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