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A Baffling Physics Question That Should Make You Think (pg. 3)
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| Sushipunk |
| quote: | Originally posted by Sunsnail
3) from a distance the gravity from a black hole behaves the same as a star of equal mass |
That doesn't make sense. The gravity from a black hole is so great that even light can't escape from it. That isn't the case with a planet's gravity.
Or am I mistaken? |
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| Krypton |
| quote: | Originally posted by Sushipunk
[quote]What if there was a black hole (or something similar) that was so large and so dense that it slowed the expansion, and eventually reversed it? Is something like that possible? |
All the matter in the entire universe is not strong enough to slow down or reverse this expansion.
| quote: | | That's why the 'cyclical' theory makes more sense (to me anyway :p) |
Well, how can the cyclical theory be true if the universe's expansion isn't slowing down or reversing, but growing faster and faster? |
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| Krypton |
| quote: | Originally posted by Sunsnail
1) The universe doesn't have to have a beginning |
Big Bang Theory |
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| Sunsnail |
| quote: | Originally posted by Sushipunk
That doesn't make sense. The gravity from a black hole is so great that even light can't escape from it. That isn't the case with a planet's gravity. |
http://cosmology.berkeley.edu/Education/BHfaq.html#q6
(link is weird, look for "if the sun became a black hole")
| quote: | Originally posted by Krypton
Big Bang Theory |
not necessarily a beginning |
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| Sushipunk |
| quote: | Originally posted by Krypton
All the matter in the entire universe is not strong enough to slow down or reverse this expansion. |
If you say so. I really wouldn't know :p
| quote: | Originally posted by Krypton
Well, how can the cyclical theory be true if the universe's expansion isn't slowing down or reversing, but growing faster and faster? |
So the expansion is accelerating? What is causing that? |
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| pkcRAISTLIN |
| quote: | Originally posted by Sushipunk
What is causing that? |
well that's the question isn't it? ;) this is where dark energy or matter enters the discussion. the only answer to your question right now is we simply don't know. |
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| Krypton |
| quote: | Originally posted by Sushipunk
If you say so. I really wouldn't know :p |
Well, it's simple. The universe is expanding despite the huge amount of matter in it. So you can say that all the matter in the universe is not making the expansion slow down or reverse.
| quote: | | So the expansion is accelerating? What is causing that? |
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 a repulsive force of unknown nature, which may be a cosmological constant. Inertia dominated the expansion in the early universe, and according to the ΛCDM model the cosmological constant will dominate in the future. In the present era they contribute in roughly equal proportions.
http://en.wikipedia.org/wiki/Metric_expansion_of_space
http://en.wikipedia.org/wiki/Hubble's_Law |
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| Sushipunk |
| quote: | Originally posted by pkcRAISTLIN
well that's the question isn't it? ;) this is where dark energy or matter enters the discussion. the only answer to your question right now is we simply don't know. |
That means there's a possibility that I'm right!
No idea what I might be right about though. All this stuff is such a huge head-. I haven't thought about it much since I stopped smoking weed :stongue: |
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| SuspicionVandit |
Just think of a grenade. The particles of a grenade after the boom are traveling very very fast, eventually slowing down to resistance of the air and gravity. This is only a very few second, and this is relatively a very small bang in comparison to that needed to spark the universe.
Like I said earlier padwan, the universe may not
1) have yet reached a point where it has succumbed to its internal resistance. So we could very well have billions of more years to go before there an observation can be made that the universe has ceased its accelerated growth.
2) the bang was just so enormous that the outer most particles are traveling too fast to be affected by the gravity of particles of a different time/space. |
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| yukii |
| quote: | Originally posted by Sushipunk
All this stuff is such a huge head-. |
that's what we love :tongue2 |
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| Krypton |
| quote: | Originally posted by SuspicionVandit
Just think of a grenade. The particles of a grenade after the boom are traveling very very fast, eventually slowing down to resistance of the air and gravity. This is only a very few second, and this is relatively a very small bang in comparison to that needed to spark the universe.
Like I said earlier padwan, the universe may not
1) have yet reached a point where it has succumbed to its internal resistance. So we could very well have billions of more years to go before there an observation can be made that the universe has ceased its accelerated growth.
2) the bang was just so enormous that the outer most particles are traveling too fast to be affected by the gravity of particles of a different time/space. |
There is a problem with that. First, the grenade's blast is expanding into air, which provides friction. There is no friction in outer space. The universe is not expanding into air. So there is nothing that is going to slow down its expansion. |
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