[quote]swoleupinya wrote:
[quote]DoubleDuce wrote:
[quote]Fezzik wrote:
[quote]swoleupinya wrote:
This is a useful definition of time for our every day dealings, but like I said it is not definitively how time is treated or viewed in terms of its effect on the physical world.
No. There are definitely things/events that will never be observable to us, not even given an infinite amount of time to attempt to observe them. The universe is expanding in all directions at increasing speeds. In order for us to be able to observe all things eventually, the universe would need to only be expanding away from us. However, we are part of that expansion.
if an object is moving away from us at more than half the speed of light, and we are moving away from that same object at more than half the speed of light… then, light will never overcome the distance between the two. Or, something like that… I can’t remember exactly what divisor of the speed of light defines this phenomenon… there is also a distance component.
The pace of time may not be absolute, but the direction of time creates absolute terms. The direction of time may in fact differ in various regions of the universe, or in differing universes in a multiverse scenario. However, the directional nature of time sets up defined behaviors/phenomena which determine how other forces (gravity, electromagnetism, etc…) behave.
Time and other forces like gravity do have relative qualities, but this does not mean that they are irrelevant or imaginary. It means that they effect the physical world relative to other forces.
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The speed of light in a vacuum is constant relative to EVERY inertial reference frame. So imagine 2 spaceships take of from earth each going .9c in opposite directions. Relative to earth they are going .9c, but because the speed of light is constant, the spaceships would still be visible to eachother. Light would leave spaceship A at c and get to spaceship B at c. Their speed relative to eachother changes to uphold the constant speed of light so it isn’t .9c+.9c=1.8c, it is roughly .99c. This is special relativity and time dilation (time slows down as relative speeds increase).[/quote]
Yeah, this was my understanding when I studied modern physics some years back. I was wondering if there was something relating to the expansion of space itself that could pseudo violate this and 2 objects could not observe each other. There is no way I know of currently that massed bodies can move apart in a way that prevents eventual viewing. Hence why I asked if he had something to read.[/quote]
Well, since nobody seems to have bothered to read the link I posted, here is the pertinent section:
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Some parts of the Universe may simply be too far away for the light emitted from there at any moment since the Big Bang to have had enough time to reach Earth at present, so these portions of the Universe would currently lie outside the observable universe. In the future the light from distant galaxies will have had more time to travel, so some regions not currently observable will become observable in the future. However, due to Hubble’s law regions sufficiently distant from us are expanding away from us much faster than the speed of light (special relativity prevents nearby objects in the same local region from moving faster than the speed of light with respect to each other, but there is no such constraint for distant objects when the space between them is expanding; see Comoving distance#Uses of the proper distance for a discussion), and the expansion rate appears to be accelerating due to dark energy. Assuming dark energy remains constant (an unchanging cosmological constant), so that the expansion rate of the universe continues to accelerate, there is a “future visibility limit” beyond which objects will never enter our observable universe at any time in the infinite future, because light emitted by objects outside that limit can never reach points that are expanding away from us at less than the speed of light (a subtlety here is that because the Hubble parameter is decreasing with time, there can be cases where a galaxy that is receding from us just a bit faster than light does manage to emit a signal which reaches us eventually[6][5]). This future visibility limit is calculated to be at a comoving distance of 19 billion parsecs (62 billion light years), which implies the number of galaxies that we can ever theoretically observe in the infinite future (leaving aside the issue that some may be impossible to observe in practice due to redshift, as discussed in the following paragraph) is only larger than the number currently observable by a factor of 2.36.[1]
Though in principle more galaxies will become observable in the future, in practice an increasing number of galaxies will become extremely redshifted due to ongoing expansion, so much so that they will seem to disappear from view and become invisible.[7][8][9] An additional subtlety is that a galaxy at a given comoving distance is defined to lie within the “observable universe” if we can receive signals emitted by the galaxy at any age in its past history (say, a signal sent from the galaxy only 500 million years after the Big Bang), but because of the universe’s expansion, there may be some later age at which a signal sent from the same galaxy will never be able to reach us at any point in the infinite future (so for example we might never see what the galaxy looked like 10 billion years after the Big Bang),[10] even though it remains at the same comoving distance (comoving distance is defined to be constant with time, unlike proper distance which is used to define recession velocity due to the expansion of space) which is less than the comoving radius of the observable universe. This fact can be used to define a type of cosmological event horizon whose distance from us changes over time; for example, the current distance to this horizon is about 16 billion light years, meaning that a signal from an event happening at present would eventually be able to reach us in the future if the event was less than 16 billion light years away, but the signal would never reach us if the event was more than 16 billion light years away.[5]
Both popular and professional research articles in cosmology often use the term “Universe” to mean “observable universe”. This can be justified on the grounds that we can never know anything by direct experimentation about any part of the Universe that is causally disconnected from us, although many credible theories require a total Universe much larger than the observable universe. No evidence exists to suggest that the boundary of the observable universe corresponds precisely to the physical boundary of the universe (if such a boundary exists); this is exceedingly unlikely in that it would imply that Earth is exactly at the center of the Universe, in violation of the Copernican principle. It is likely that the galaxies within our visible universe represent only a minuscule fraction of the galaxies in the Universe. According to the theory of cosmic inflation and its founder, Alan Guth, if it is assumed that inflation began about 10â??37 seconds after the Big Bang, then with the plausible assumption that the size of the Universe at this time was approximately equal to the speed of light times its age, that would suggest that at present the entire Universe’s size is at least 1023 times larger than the size of the observable Universe.[11]
It is also possible that the Universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated the Universe. It is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different. A 2004 paper[12] claims to establish a lower bound of 24 gigaparsecs (78 billion light-years) on the diameter of the whole Universe, meaning the smallest possible diameter for the whole universe would be only slightly smaller than the observable universe (and this is only a lower bound, so the whole universe could be much larger, even infinite). This value is based on matching-circle analysis of the WMAP data. Recently, this approach has been criticized.[13]
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Ok that makes sense… this relies on general relativity which is a whole 'nother beast. I basically don’t understand anything when it comes to that.
He was not reasoning out a proof. he was reasoning out a plausibility. [/quote]