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Questions about Time, Distance, and Relativity
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 (November 10, 2014 at 4:10 pm)Pickup_shonuff Wrote: Ok..few more...for now... Because over relatively short distances (relative to the amount of mass involved), gravity dominates over the relatively small but ubiquitous influence of expansion.  (November 10, 2014 at 4:10 pm)Pickup_shonuff Wrote: Ok..few more...for now...There speed toward each other has to be faster than the expansion of the space between them. No mind-blown answer on this one. Quote:Why is it that we don't actually experience the expansion of space? Is it because of the gravitational field? As in... it keep us "bounded" to this particular bodily composition, in terms of persons, planets, solar systems, galaxies, superclusters, etc.?It is too of a small scale for us to feel/see it. On the very large scale (supercluster level), all the small effects add up to something that we can observe. Plus, the forces that keep us together (gravity for the big stuff and EM for the smaller stuff) are much stronger on the smaller scales. This might not be case in the far futher. Quote:I understand Krauss to be arguing something to the effect that space must RESULT from fluctuations in the quantum gravitational field... but isn't this "quantum foam" itself an ultra-microscopic region of space? Doesn't he just mean that space can be inflated and produce matter from prior energy? I think he believes similiar to me where you can create something from nothing as long you bring along its exact opposite. That would include space. What would be the exact opposite of space? No idea. No prior energy required. The total energy of the visible universe has been measured to be very close to zero (note that we can't see all of the universe). It is believed that it is zero because that would produce a flat universe. The universe is observed to be flat. It makes sense the total energy of the universe is 0 because gravity is negative energy. The way to visulize it, consider a ball sitting on the ground. It has zero potential energy. Now, you digged a hole that it can fall into. What is its potential energy? It's negative. Similiar with gravity, a flat spacetime is the ground, the curved spacetime gives you negative energy.  RE: Questions about Time, Distance, and Relativity
November 11, 2014 at 10:18 am
(This post was last modified: November 11, 2014 at 10:27 am by Alex K.)
If you feel like doing simple maths, you can take the distance between, say your two hands stretched out, and simply multiply it by the current Hubble "constant". You then get a velocity out of it which is the velocity at which your hands would move apart due to universal expansion if they were not bound by electromagnetic forces. Youll find that it is a mind bogglingly small speed. You can then repeat the exercise with the andromeda galaxy and the milky way. You should find that now, it is a more significant relative speed which needs to be counteracted by relative motion of the galaxies themselves e.g. due to their gravitational attraction... The hardest part in the calculation is converting parsecs to meters.
(November 10, 2014 at 4:10 pm)Pickup_shonuff Wrote: Ok..few more...for now...
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
(November 10, 2014 at 4:10 pm)Pickup_shonuff Wrote: Ok..few more...for now... I don't understand how space arises in superstring theory at all. In loop gravity, you have these loop objects which themselves provide you with elementary areas and volumes. In spacetime, this network looks like a foam. Space is then what you get when many of these are connected. If course they are quantum, so the empty space which we see may not contain a sharp number of knots and loops associated with a given volume, it may be a superposition of states with arbitrary numbers of loops, I don't know. What happens upon expansion (are new ones created or do they get thinned out?) is a very good question...
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
 RE: Questions about Time, Distance, and Relativity
November 11, 2014 at 9:33 pm
(This post was last modified: November 11, 2014 at 9:34 pm by Heywood.)
(November 6, 2014 at 4:24 pm)Pickup_shonuff Wrote: Yeah, it's quite confusing... Greene writes, "Einstein proclaimed that all objects in the universe are always traveling through spacetime at one fixed speed--that of light... If an object does move through space, however, this means that some of the previous motion through time must be diverted... We now see that time slows down when an object moves relative to us because this diverts some its motion through time into motion through space. The speed of an object through space is thus merely a reflection of how much its motion through time is diverted... the maximum speed through space occurs if all of an object's motion through time is diverted to motion through space. This occurs when all of its previous light-speed motion through time is diverted to light-speed motion through space." Imagine that you are traveling in a car at exactly 60 mph. You are headed due north. In one hour you will be 60 miles further north then you were an hour ago. Suppose the road veers to the northwest. Even though you continue at 60 mph for the next hour, you won't be 60 miles further north then you were an hour ago. Why? because when your changed direction from north...to northwest the rate at which you were heading north slowed and the rate at which you were moving west increased(from 0 to say 30 mph). Some of your northward movement was diverted to westward movement. Brian Green explains it well in the Fabric of the Cosmos...illusion of time. This video from 13:40 mark on esplans it. 
Thanks Heywood. I think I'm going to pick up Fabric of the Cosmos sometime in the future because I thoroughly enjoyed The Elegant Universe (I hope it's more than a rehash though). On another note, A Universe From Nothing felt like grade school literature in comparison.
He who loves God cannot endeavour that God should love him in return - Baruch Spinoza
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