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RE: The Solar System is Special - 9/5/2008 3:33:48 PM
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essentialsaltes
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quote:
ORIGINAL: DanJames
Out of curiosity, what is happening with the space between stars in galaxies? If space is expanding everywhere, then there should be a constant increase of space between stars in galaxies, not just an increase in distance between galaxies. Is gravity holding them together?
This is another point of great confusion, even to me. I've seen shouting matches over this. But yes, gravity is holding galaxies together, and electrical forces are holding atoms together (the atoms aren't expanding either). The laws of orbits and gravity tells the planets and stars where to go, since they are bound to the center of attraction. The presence of matter and its binding interactions are stronger than the overall average curvature of the universe.
But distant galaxies are not gravitationally bound to each other, and the long intergalactic distances makes the overall, average curvature of the universe apparent in the (mostly) empty space between them.
_____________________________
"My object in all arguments is not to make any preconceived opinion of mine seem right, but merely to discover and establish the truth, whatever the truth may be."
-- HP Lovecraft, letter to Robert E. Howard 7/27-28/34
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RE: The Solar System is Special - 9/5/2008 3:58:55 PM
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DanJames
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quote:
ORIGINAL: essentialsaltes
quote:
ORIGINAL: DanJames
Out of curiosity, what is happening with the space between stars in galaxies? If space is expanding everywhere, then there should be a constant increase of space between stars in galaxies, not just an increase in distance between galaxies. Is gravity holding them together?
This is another point of great confusion, even to me. I've seen shouting matches over this. But yes, gravity is holding galaxies together, and electrical forces are holding atoms together (the atoms aren't expanding either). The laws of orbits and gravity tells the planets and stars where to go, since they are bound to the center of attraction. The presence of matter and its binding interactions are stronger than the overall average curvature of the universe.
But distant galaxies are not gravitationally bound to each other, and the long intergalactic distances makes the overall, average curvature of the universe apparent in the (mostly) empty space between them.
So the strong force, electromagnetic force, and gravity are strong enough to overcome the expansion of space. Do astrophysicists account for the expansion of space when they do their formulas? If space is expanding everywhere, then two stars in a galaxy are both attracted to each other due to gravity, and "repelled" so to speak by the expansion of space. Can two stars reach equilibrium such that they are attracted and moved by space at the same rate? If the earth were made of cotton balls would the expansion of space rip the earth apart? Is this the kind of stuff that is asked in the shouting matches?
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RE: The Solar System is Special - 9/5/2008 4:22:07 PM
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Veritas
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quote:
ORIGINAL: DanJames
So the strong force, electromagnetic force, and gravity are strong enough to overcome the expansion of space.
When the forces act on distances on the size of galaxies and smaller, yes. On much larger scales, no.
quote:
Do astrophysicists account for the expansion of space when they do their formulas? If space is expanding everywhere, then two stars in a galaxy are both attracted to each other due to gravity, and "repelled" so to speak by the expansion of space. Can two stars reach equilibrium such that they are attracted and moved by space at the same rate?
There would be a distance where the gravitational attraction would exactly balance the recession due to the exapansion of space, but this would not be a stable point. The stars would either slowly fall into each other or begin to drift apart.
quote:
If the earth were made of cotton balls would the expansion of space rip the earth apart? Is this the kind of stuff that is asked in the shouting matches?
The expansion of space is not enough to tear a galaxy apart. The effect on the solar system is waaay too small to measure. If the earth were made of cotton balls, the gravity would still exert a much greater effect than the expansion. Expansion only noticeable over very large distances.
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RE: The Solar System is Special - 9/5/2008 4:38:25 PM
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essentialsaltes
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quote:
ORIGINAL: DanJames
So the strong force, electromagnetic force, and gravity are strong enough to overcome the expansion of space. Do astrophysicists account for the expansion of space when they do their formulas? If space is expanding everywhere, then two stars in a galaxy are both attracted to each other due to gravity, and "repelled" so to speak by the expansion of space. Can two stars reach equilibrium such that they are attracted and moved by space at the same rate? If the earth were made of cotton balls would the expansion of space rip the earth apart? Is this the kind of stuff that is asked in the shouting matches?
I don't think astronomy of stars in galaxies requires any consideration of the universal expansion.
The simplest model of the expansion of the universe is based on a homogeneous matter distribution. And this gives equal expansion everywhere in the space.
Now, the universe isn't homogeneous. From our standpoint, it's pretty lumpy. Galaxies here and there, and giant voids of nothing in between. But if you take the loooooong giant-scale view, it starts to look homogeneous as the galaxies dwindle into something like atoms in a gas that are randomly distributed, but still have an average density that doesn't fluctuate too much. On that scale, the expansion model works well and provides explanations of the large scale expansion of the universe. When we look at two 'nearby' galaxies, the model breaks down badly. It's not homogeneous - there's a lot of matter, then a lot of nothing, then a whole lot of matter again. The real solution to the general relativity equations near all these lumps has to look a lot different from that smoothly expanding model. We know that general relativity for 'ordinary' cases reduces to Newton's theory, just as relativity reduces to Newtonian mechanics for objects not moving near the speed of light. Stars moving around a galaxy are 'ordinary' cases, so the solution must look a lot like ordinary orbits. 'Ordinary' orbital solutions do not involve the expansion of space itself.
So if one could really write down a correct solution to the equations, I expect you'd find that there's lots of expanding space, but it's dotted by little flaws (galaxies) that have no expansion of space. This is why the pennies taped to balloons, or raisins in dough analogies are good. The balloon-y or dough-y material has all the expansion, while the penny-galaxies and raisin-galaxies do not expand.
_____________________________
"My object in all arguments is not to make any preconceived opinion of mine seem right, but merely to discover and establish the truth, whatever the truth may be."
-- HP Lovecraft, letter to Robert E. Howard 7/27-28/34
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RE: The Solar System is Special - 9/6/2008 8:25:07 AM
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EcclesFruitcake
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quote:
So the strong force, electromagnetic force, and gravity are strong enough to overcome the expansion of space. Do astrophysicists account for the expansion of space when they do their formulas? If space is expanding everywhere, then two stars in a galaxy are both attracted to each other due to gravity, and "repelled" so to speak by the expansion of space. Can two stars reach equilibrium such that they are attracted and moved by space at the same rate? If the earth were made of cotton balls would the expansion of space rip the earth apart? Is this the kind of stuff that is asked in the shouting matches?
Every day for every 5,000,000,000,000km of space there is an expansion of about 1km. (Or 72km/s/Mpc)
The further an object is the harder it is to overcome the expansion. Although even at 2.5 million light years away the closest galaxy to the Milky Way, Andromeda, is actually getting closer to us (300km/s) and so is blue shifted (1 light year is about 9,500,000,000,000km).
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RE: The Solar System is Special - 9/6/2008 1:46:15 PM
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GHitch
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ok guys, I appreciate the clarifications but still have some problems.
I had realized that the balloon analogy falters in it's 2D aspect but still helps the imagination to visualize the phenomenon.
But what I can't see is infinite space without infinite time. Or, to divide it into 2 separate issues - infinite space or finite time.
Both seem to carry inherent inconsistencies to me. But space is the thing so...
If space is infinite how is it expanding? Expanding into what? How can that which is infinite expand? Infinity doesn't 'grow'. Otherwise it grows where? Buzz Lightyear's, "infinity and beyond", is an oxymoron. Right? After all nothing can be greater than infinity or beyond infinite.
Or is infinity a mere mathematical concept with no physical reality? Like a mathematical point.
Again, if the universe had a beginning and space is expanding, how can it be infinite?
Another question - if space is expanding, is time also expanding?
_____________________________
"The notion that not only the biopolymer but the operating program of a living cell could be arrived at by chance in a primordial organic soup here on the Earth is evidently nonsense of a high order." Sir F. Hoyle
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RE: The Solar System is Special - 9/6/2008 2:11:27 PM
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DanJames
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Thanks Veritas, ES, and EFC for your answers. And thanks for being good sports, especially Veritas for answering my cotton ball question. ES, it looks like you're saying that expanding space is greater in the absence of gravitational systems which do not expand or expand much less.
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RE: The Solar System is Special - 9/6/2008 3:21:56 PM
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essentialsaltes
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quote:
ORIGINAL: DanJames
ES, it looks like you're saying that expanding space is greater in the absence of gravitational systems which do not expand or expand much less.
I do. But my own understanding is sadly shaky for a subject that I allegedly know well, so I'm not going to start any shouting matches. So I'll stand on authority - you made me pull down Misner, Thorne and Wheeler's Gravitation. The standard joke is that this 1279 page book is massive enough to have its own measurable gravitation. From p.719:
quote:
Of all the disturbing implications of "the expansion of the universe," none is more upsetting to many a student on first encounter than the nonsense of this idea. The universe expands, the distance between one cluster of galaxies and another cluster expands, the distance between the sun and the earth expands, the length of a meter stick expands, the atom expands? Then how can it make any sense to speak of any expansion at all? Expansion relative to what? Expansion relative to nonsense! ONly later does he realize that the atom does not expands, the meter stick does not expand, the distance between sun and earth does not expand. Only distances between clusters of galaxies and greater distances are subject to the expansion. ONly at this gigantic scale of averaging does the notion of homogeneity make sense. Not so at smaller distances. ... [For mathematical detail see, e.g., Noerdlinger and Petrosian (1971).]"
That article starts by mentioning that Einstein in 1945 had shown that a solar system in a rather contrived universe would be "immune to the cosmological expansion" and goes on to discuss less and less contrived situations that suggest the same result: bound gravitation systems are 'immune' in this sense to this expansion of the universe. Distances between distant galaxies increase, but distances within the bound galaxies are fixed.
_____________________________
"My object in all arguments is not to make any preconceived opinion of mine seem right, but merely to discover and establish the truth, whatever the truth may be."
-- HP Lovecraft, letter to Robert E. Howard 7/27-28/34
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RE: The Solar System is Special - 9/6/2008 3:45:34 PM
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DanJames
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quote:
ORIGINAL: essentialsaltes
quote:
ORIGINAL: DanJames
ES, it looks like you're saying that expanding space is greater in the absence of gravitational systems which do not expand or expand much less.
I do. But my own understanding is sadly shaky for a subject that I allegedly know well, so I'm not going to start any shouting matches. So I'll stand on authority - you made me pull down Misner, Thorne and Wheeler's Gravitation. The standard joke is that this 1279 page book is massive enough to have its own measurable gravitation. From p.719:
quote:
Of all the disturbing implications of "the expansion of the universe," none is more upsetting to many a student on first encounter than the nonsense of this idea. The universe expands, the distance between one cluster of galaxies and another cluster expands, the distance between the sun and the earth expands, the length of a meter stick expands, the atom expands? Then how can it make any sense to speak of any expansion at all? Expansion relative to what? Expansion relative to nonsense! ONly later does he realize that the atom does not expands, the meter stick does not expand, the distance between sun and earth does not expand. Only distances between clusters of galaxies and greater distances are subject to the expansion. ONly at this gigantic scale of averaging does the notion of homogeneity make sense. Not so at smaller distances. ... [For mathematical detail see, e.g., Noerdlinger and Petrosian (1971).]"
That article starts by mentioning that Einstein in 1945 had shown that a solar system in a rather contrived universe would be "immune to the cosmological expansion" and goes on to discuss less and less contrived situations that suggest the same result: bound gravitation systems are 'immune' in this sense to this expansion of the universe. Distances between distant galaxies increase, but distances within the bound galaxies are fixed.
Very interesting. So based on this model of expansion, should we see other stars in our own galaxy receding? Or would we see only the Doppler effect of the motion of stars orbitting through the galaxy? I guess my question is, if the length of a meter stick does not change due to the effect of gravity on the expansion of space, then would the length of Orion's belt also not change due to the effect of gravitation on the expansion of space?
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RE: The Solar System is Special - 9/6/2008 3:57:57 PM
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essentialsaltes
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quote:
ORIGINAL: GHitch
If space is infinite how is it expanding? Expanding into what? How can that which is infinite expand? Infinity doesn't 'grow'.
Infinity is certainly a funny thing. Everyone got their mental seatbelts on? It's Essentialsaltes' Crazy Analogy Story Time.
Mr. Hilbert built himself a hotel. But it's not just any hotel - it's a hotel with an infinite number of rooms, numbered 1, 2, 3 and so on into infinity. Over Labor Day weekend, there was a convention of Shriners in town, attended by an infinite number of Shriners. They got the convention rate, so they all stayed at the Hilbert Hotel, one per room. So there were an infinite number of guests in the infinite number of rooms, and all the rooms were full.
Saturday night a travelling salesman came into the lobby. His car had broken down and he needed a place to stay for the night. Since all the rooms were full, it was a bit of a problem for Hilbert, but he felt sorry for the guy. So Hilbert asked the guest in room 1 to move into room 2, and the guest in room 2 was moved into room 3, and so on and so on. Every guest moved next door, and since there was always a room next door, everyone found a room, leaving room 1 empty for the salesman. There's always room in the Hilbert Hotel!
Later that night, the neighboring infinite hotel burned down, leaving an infinite number of members of the Benevolent and Protective Order of Elks without a place to stay. (The Elks were coincidentally having their convention the same weekend.) It was a bit of bother for his guests, but Hilbert felt sorry for the Elks, who had no place to stay. So he asked the guest in room 1 to move into room 2, room 2 moved to room 4, 3 -> 6, 4->8. And so on. Each guest moved into the room that was twice the number of his former room. Twice any number, no matter how big, is still a number, so all the old guests found new rooms. And now all the odd rooms in the hotel were empty. There are an infinite number of odd rooms, so now there was a room for each of the Elks. There's always room in the Hilbert Hotel!
Okay, that's just a silly story, but let's think about part of that last bit. When the Shriners all move to the room that's twice the number of their previous room, suddenly instead of every room being filled, every other room is filled. No rooms have been added, but suddenly the hotel is less dense. As thought the guests had 'expanded'. But the hotel didn't expand 'into' anything. No rooms were added to the building. The hotel didn't get any bigger (it's still infinite in size) but the hotel's contents have been spread out, or expanded.
I think this is roughly analogous to what happens with the universe. It doesn't expand into anything, and no extra space is added onto it. After all, you can't get any bigger than infinite. Nevertheless, the contents of the universe spread out.
quote:
Another question - if space is expanding, is time also expanding?
Certainly the rules of general relativity allow clocks to run at different rates depending on the local curvature of space time. Clocks deep in gravity wells run more slowly than clocks floating far out in space. So I expect the cosmological expansion does have some effect on time, but I can't think offhand how that would manifest or even if it makes any difference. If time started 'flowing' at twice its normal speed, clocks would still measure one second per second. We would never know the difference. But if the expansion effects are different here on earth compared to way out in interstellar space, perhaps there would be meaningful differences. I dunno.
_____________________________
"My object in all arguments is not to make any preconceived opinion of mine seem right, but merely to discover and establish the truth, whatever the truth may be."
-- HP Lovecraft, letter to Robert E. Howard 7/27-28/34
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RE: The Solar System is Special - 9/6/2008 4:02:14 PM
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essentialsaltes
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quote:
ORIGINAL: DanJames
Very interesting. So based on this model of expansion, should we see other stars in our own galaxy receding?
Nope. At least, not due to the universal expansion. As you say, we would see the 'normal' recession or approach due to any relative motion between the stars, in the Doppler shift.
quote:
I guess my question is, if the length of a meter stick does not change due to the effect of gravity on the expansion of space, then would the length of Orion's belt also not change due to the effect of gravitation on the expansion of space?
Orion's Belt shouldn't change. Only on length scales where the universe looks homogeneous will expansion occur, and that only happens at the level of distant galaxy clusters.
_____________________________
"My object in all arguments is not to make any preconceived opinion of mine seem right, but merely to discover and establish the truth, whatever the truth may be."
-- HP Lovecraft, letter to Robert E. Howard 7/27-28/34
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RE: The Solar System is Special - 9/6/2008 4:29:48 PM
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DanJames
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quote:
ORIGINAL: essentialsaltes
quote:
ORIGINAL: GHitch
If space is infinite how is it expanding? Expanding into what? How can that which is infinite expand? Infinity doesn't 'grow'.
Infinity is certainly a funny thing. Everyone got their mental seatbelts on? It's Essentialsaltes' Crazy Analogy Story Time.
Mr. Hilbert built himself a hotel. But it's not just any hotel - it's a hotel with an infinite number of rooms, numbered 1, 2, 3 and so on into infinity. Over Labor Day weekend, there was a convention of Shriners in town, attended by an infinite number of Shriners. They got the convention rate, so they all stayed at the Hilbert Hotel, one per room. So there were an infinite number of guests in the infinite number of rooms, and all the rooms were full.
...
difference. If time started 'flowing' at twice its normal speed, clocks would still measure one second per second. We would never know the difference. But if the expansion effects are different here on earth compared to way out in interstellar space, perhaps there would be meaningful differences. I dunno.
ES, do you feel like you understand all of this? Because I sure don't. Infinite is more of a concept than a number. Even the number of particles in the universe is thought to have a number. I can bear with the idea that I don't yet know what kind of anomaly is at edge of the universe, but I'm not sure that my little 3 pound brain should be so small that it can't grasp the idea of the expansion of the universe. Do you have another analogy?
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RE: The Solar System is Special - 9/6/2008 4:30:55 PM
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DanJames
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quote:
ORIGINAL: essentialsaltes
quote:
ORIGINAL: DanJames
Very interesting. So based on this model of expansion, should we see other stars in our own galaxy receding?
Nope. At least, not due to the universal expansion. As you say, we would see the 'normal' recession or approach due to any relative motion between the stars, in the Doppler shift.
quote:
I guess my question is, if the length of a meter stick does not change due to the effect of gravity on the expansion of space, then would the length of Orion's belt also not change due to the effect of gravitation on the expansion of space?
Orion's Belt shouldn't change. Only on length scales where the universe looks homogeneous will expansion occur, and that only happens at the level of distant galaxy clusters.
Thanks, ES. Glad I'm beginning to see this with some clarity.
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RE: The Solar System is Special - 9/6/2008 11:31:29 PM
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Veritas
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quote:
ORIGINAL: DanJames
ES, do you feel like you understand all of this? Because I sure don't. Infinite is more of a concept than a number. Even the number of particles in the universe is thought to have a number. I can bear with the idea that I don't yet know what kind of anomaly is at edge of the universe, but I'm not sure that my little 3 pound brain should be so small that it can't grasp the idea of the expansion of the universe. Do you have another analogy?
The visible universe is necessarily finite and contains a finite number of particles. But the visible universe is just a small part of the entire universe. If the universe is infinite (as is thought to be the case) and matter is evenly distributed over very large scales, then the number of particles in the universe is infinite. Current thinking is that there is no edge to the universe.
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RE: The Solar System is Special - 9/7/2008 5:50:31 PM
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DanJames
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quote:
ORIGINAL: Veritas
quote:
ORIGINAL: DanJames
ES, do you feel like you understand all of this? Because I sure don't. Infinite is more of a concept than a number. Even the number of particles in the universe is thought to have a number. I can bear with the idea that I don't yet know what kind of anomaly is at edge of the universe, but I'm not sure that my little 3 pound brain should be so small that it can't grasp the idea of the expansion of the universe. Do you have another analogy?
The visible universe is necessarily finite and contains a finite number of particles. But the visible universe is just a small part of the entire universe. If the universe is infinite (as is thought to be the case) and matter is evenly distributed over very large scales, then the number of particles in the universe is infinite. Current thinking is that there is no edge to the universe.
What makes us think that there is anything at all beyond the visible universe? Do new stars show up at what we think is outside of the edge as a result of the light getting to us? Or perhaps gravitational tug? What evidence do we have of anything outside of what we can see?
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RE: The Solar System is Special - 9/7/2008 5:56:30 PM
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Jhud
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quote:
The visible universe is necessarily finite and contains a finite number of particles. But the visible universe is just a small part of the entire universe. If the universe is infinite (as is thought to be the case) and matter is evenly distributed over very large scales, then the number of particles in the universe is infinite. Current thinking is that there is no edge to the universe.
Any references to who is thinking this 'current thinking', and how they demonstrated it?
_____________________________
Jack
It has been said that politics is the second oldest profession. I have learned that it bears a striking resemblance to the first..
- Ronald Reagan
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RE: The Solar System is Special - 9/7/2008 6:26:41 PM
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DanJames
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quote:
ORIGINAL: Jhud
quote:
The visible universe is necessarily finite and contains a finite number of particles. But the visible universe is just a small part of the entire universe. If the universe is infinite (as is thought to be the case) and matter is evenly distributed over very large scales, then the number of particles in the universe is infinite. Current thinking is that there is no edge to the universe.
Any references to who is thinking this 'current thinking', and how they demonstrated it?
Jack, you so-and-so! Where in Sam Hill have you been?! Why don't you stay out of those dag-tootin' politics forums and help out around here!!
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RE: The Solar System is Special - 9/7/2008 6:59:33 PM
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Veritas
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quote:
ORIGINAL: Jhud
quote:
The visible universe is necessarily finite and contains a finite number of particles. But the visible universe is just a small part of the entire universe. If the universe is infinite (as is thought to be the case) and matter is evenly distributed over very large scales, then the number of particles in the universe is infinite. Current thinking is that there is no edge to the universe.
Any references to who is thinking this 'current thinking', and how they demonstrated it?
How about this reference?
quote:
FROM A Brief History of Time - Stephen W. Hawking
In the first kind of Friedmann model, which expands and recollapses, space is bent in on itself, like the surface of the earth. It is therefore finite in extent. In the second kind of model, which expands forever, space is bent the other way like the surface of a saddle. So in this case space is infinite. Finally, in the third kind of Friedmann model, with just the critical rate of expansion, space is flat (and therefore is also infinite).
p. 45
As to how it is demonstrated: Obviously, we only have direct information from the visible universe, which is necessarily finite. So, an infinite universe cannot be demonstrated. OTOH, if the universe is finite, that could be demonstrated by finding the edge or observing that it curves back on itself. I know of no evidence that the universe is finite. Do you know of any such evidence?
ETA: I recall reading an article written since A Brief History of Time that said there were topologies for a boundary-less space that was flat or open. (I'll try to remember where I read it.) But those topologies were rather exotic. IIRC, the article didn't suggest that space was actually one of those topologies -- Just that you could theoretically have an open or flat finite universe. Again, if the universe is finite that could be demonstrated. An infinite universe cannot be demonstrated. I've seen no evidence to suggest that the universe is finite.
< Message edited by Veritas -- 9/7/2008 7:08:14 PM >
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RE: The Solar System is Special - 9/7/2008 8:53:33 PM
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Jhud
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quote:
Jack, you so-and-so! Where in Sam Hill have you been?! Why don't you stay out of those dag-tootin' politics forums and help out around here!!
Sorry Dan - this is the time year when a young man's fancy turns from the lab to the voting booth; but to quote a famous contemporary philosopher...I'll be back.
_____________________________
Jack
It has been said that politics is the second oldest profession. I have learned that it bears a striking resemblance to the first..
- Ronald Reagan
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RE: The Solar System is Special - 9/8/2008 12:52:18 AM
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Veritas
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quote:
ORIGINAL: DanJames
quote:
The visible universe is necessarily finite and contains a finite number of particles. But the visible universe is just a small part of the entire universe. If the universe is infinite (as is thought to be the case) and matter is evenly distributed over very large scales, then the number of particles in the universe is infinite. Current thinking is that there is no edge to the universe.
What makes us think that there is anything at all beyond the visible universe? Do new stars show up at what we think is outside of the edge as a result of the light getting to us? Or perhaps gravitational tug? What evidence do we have of anything outside of what we can see?
We have no evidence of anything beyond the visible universe. The fact that the universe looks the same in all directions and at all distances (taking into account we are looking back in time) leads us to believe things are the same everywhere. The visible universe has an edge, but only because of where we happen to be, and that edge recedes one light year every year. An observer somewhere else would have a different visible universe. We see no evidence of any sort of boundary as far as we can see. But there is no way for us to be sure.
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RE: The Solar System is Special - 9/8/2008 12:58:04 AM
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essentialsaltes
Posts: 1083
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quote:
ORIGINAL: Jhud
quote:
The visible universe is necessarily finite and contains a finite number of particles. But the visible universe is just a small part of the entire universe. If the universe is infinite (as is thought to be the case) and matter is evenly distributed over very large scales, then the number of particles in the universe is infinite. Current thinking is that there is no edge to the universe.
Any references to who is thinking this 'current thinking', and how they demonstrated it?
The main 'new' result was the discovery that the expansion of the universe appears to be accelerating. This, combined with other constraints seems to offer only a flat, infinite universe, or an open, infinite universe. Closed, finite universes seem to be ruled out, although it's possible that you could think up a weird enough kind of strange new type of matter or 'dark energy' to close the universe.
Frankly, when I first heard about the accelerating expansion, I figgered the astronomers had foggy lenses on their telescopes or something, but 10 years later it hasn't gone away.
Separately from this, the inflationary model produces a flat (i.e. infinite) universe.
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"My object in all arguments is not to make any preconceived opinion of mine seem right, but merely to discover and establish the truth, whatever the truth may be."
-- HP Lovecraft, letter to Robert E. Howard 7/27-28/34
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RE: The Solar System is Special - 9/8/2008 12:25:50 PM
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DanJames
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quote:
ORIGINAL: Veritas
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ORIGINAL: DanJames
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The visible universe is necessarily finite and contains a finite number of particles. But the visible universe is just a small part of the entire universe. If the universe is infinite (as is thought to be the case) and matter is evenly distributed over very large scales, then the number of particles in the universe is infinite. Current thinking is that there is no edge to the universe.
What makes us think that there is anything at all beyond the visible universe? Do new stars show up at what we think is outside of the edge as a result of the light getting to us? Or perhaps gravitational tug? What evidence do we have of anything outside of what we can see?
We have no evidence of anything beyond the visible universe. The fact that the universe looks the same in all directions and at all distances (taking into account we are looking back in time) leads us to believe things are the same everywhere. The visible universe has an edge, but only because of where we happen to be, and that edge recedes one light year every year. An observer somewhere else would have a different visible universe. We see no evidence of any sort of boundary as far as we can see. But there is no way for us to be sure.
Thanks to everybody for helping me understand this. Do you know of any "tug" on the galaxies on the outside because of other stuff? I guess a better question would be, WOULD we see any "tug" on the outside due to other stuff.
Now for a selfish YEC sales pitch. Is it possible at all that we aren't looking back in time? I mean, is it possible that light that passes through a completely gravity-less environment is moving really-really fast, I mean like close to infinitely fast in the complete absence of gravity due to of the dilation of time?
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RE: The Solar System is Special - 9/8/2008 1:54:23 PM
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Veritas
Posts: 519
Joined: 4/19/2005
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quote:
ORIGINAL: DanJames
Thanks to everybody for helping me understand this. Do you know of any "tug" on the galaxies on the outside because of other stuff? I guess a better question would be, WOULD we see any "tug" on the outside due to other stuff.
Good question. According to Relativity, the upper limit for the propagation of information is the speed of light. If we could see a tug from beyond the visible universe, that would give us information. That means the answer is no, we cannot get any information from outside the visible universe.
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Now for a selfish YEC sales pitch. Is it possible at all that we aren't looking back in time? I mean, is it possible that light that passes through a completely gravity-less environment is moving really-really fast, I mean like close to infinitely fast in the complete absence of gravity due to of the dilation of time?
Not according to our current understanding of Relativity. The earth's gravity has only a slight effect on light. According to General Relativity, the effect of gravity cannot be distinguished from the effect of acceleration. We can cancel gravity by being in free-fall. We know how light behaves in the absence of gravity. In fact, Special Relativity deals with inertial reference frames -- SR ignores gravity.
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RE: The Solar System is Special - 9/9/2008 1:03:42 AM
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Veritas
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History has shown us that every time it was thought that we were in a privileged location for some reason or other, newer evidence showed this was not the case. I don't think there is enough evidence to say that the Solar System is special. But, for the sake of argument, let's say the Solar System is special. Now what? How is it special? What makes is special? Are there some influences that only exist here? How far do these influences extend? What is the nature of these influences? How can we observe them?
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RE: The Solar System is Special - 9/9/2008 12:44:50 PM
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GHitch
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Well, thanks for all the answers, analogies and all.
But I still feel the same questions remain open - unresolved - simply because we just don't know enough to see the solution to apparent contradictions. There's a difference between a contradiction and a paradox.
But to my mind as soon we speak of expansion we're speaking of space.
Now if I were to apply scriptur | | |
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