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Yousuf Khan wrote:
If the universe is expanding, and the further an object (e.g. a galaxy) is away from us, the faster it is moving away from us. Are there parts of space so far away from us that it's expanding away from us *faster* than the speed of light? You have to be careful of what you mean by "speed". It has units of distance over time, but it's not the same as speed in special relativity. With that caveat, the answer is yes. Therefore the Cosmic Microwave Background Radiation isn't the cloak that surrounds the secrets of the Big Bang, but just the curtain around a part of the universe that is now out of contact with us. The "speed" of the CMBR, in units of comoving distance over cosmological time, is much larger than the speed of light. I think it's about 3.2c. This means essentially nothing, since the speed of light has no special status when talking about cosmological recession velocities. -- Ben |
#12
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N:dlzc D:aol T:com (dlzc) wrote:
Are there parts of space so far away from us that it's expanding away from us *faster* than the speed of light? We expect so, yes. Okay great, then assuming by some discovery we find out how much of the universe is outside of our viewing range, will that affect the calculations for the age of the universe? Isn't it possible that given only what we can observe, we will always come up with a finite age for the universe, and it will always be the same age limit no matter when we do the calculation? For example if we're calculating the age of the universe to be somewhere around 15-20 billion years old now, then a 100 billion years from now another set of observers will look at what they can see in the universe at that time, and they too will come up with 15-20 billion years rather than 115-120 billion? In fact, wasn't there an observation made at one time, that some of the oldest stars seem to be older than the age of the universe itself? I'm not sure if that's been resolved or not. Therefore the Cosmic Microwave Background Radiation isn't the cloak that surrounds the secrets of the Big Bang, It is believed to be, yes. Choose a different word than "isn't"... but just the curtain around a part of the universe that is now out of contact with us. An endlessly expanding universe sure, but one that never had a beginning? It is also expected to have had a beginning. The current distribution of matter around us is not pure iron, which an inifnite Universe would produce. Nor are there iron to hydrogen conversion engines predicted or observable, with anywhere near the amounts required. Well, how do we know the distribution of matter isn't highly iron? We don't even know what dark matter is composed of yet. What if all of the stuff out in the galactic halos are long dead star cores (including neutron stars and stellar blackholes), which somehow migrate out into the halo over time? Separated out by gravity in some sort of natural galactic centrifuge. Afterall it seems like the laws of gravity are starting to undergo modifications these days as we do more detailed observations of the rest of the universe -- perhaps a galactic centrifuge is a quite logical outcome of the laws that we will eventually discover? As for an iron to hydrogen conversion engine, why do we need one? Doesn't matter just pop up out of nowhere in the vacuum? Near a blackhole its anti-particles could get swallowed while the particles would get boosted right out of the blackhole's vicinity in the jet. The new particles could go into refreshing the galactic gas clouds for new star formation. And mass and energy conservation would be preserved in the universe by the fact that every year, more parts of the universe become inaccessible to us as they go "beyond the rim". Yousuf Khan |
#13
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Yousuf Khan wrote:
Isn't it possible that given only what we can observe, we will always come up with a finite age for the universe, and it will always be the same age limit no matter when we do the calculation? For example if we're calculating the age of the universe to be somewhere around 15-20 billion years old now, then a 100 billion years from now another set of observers will look at what they can see in the universe at that time, and they too will come up with 15-20 billion years rather than 115-120 billion? We estimate the age of the universe to be about 13.7 billion years. As the universe expands faster and faster, our observable horizon will begin to shrink and we will no longer be able to "see" the early universe. No Center http://www.astro.ucla.edu/~wright/nocenter.html Also see Ned Wright's Cosmology Tutorial http://www.astro.ucla.edu/~wright/cosmolog.htm http://www.astro.ucla.edu/~wright/cosmology_faq.html WMAP: Foundations of the Big Bang theory http://map.gsfc.nasa.gov/m_uni.html WMAP: Tests of Big Bang Cosmology http://map.gsfc.nasa.gov/m_uni/uni_101bbtest.html |
#14
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Ben Rudiak-Gould wrote:
Yousuf Khan wrote: If the universe is expanding, and the further an object (e.g. a galaxy) is away from us, the faster it is moving away from us. Are there parts of space so far away from us that it's expanding away from us *faster* than the speed of light? You have to be careful of what you mean by "speed". It has units of distance over time, but it's not the same as speed in special relativity. With that caveat, the answer is yes. Therefore the Cosmic Microwave Background Radiation isn't the cloak that surrounds the secrets of the Big Bang, but just the curtain around a part of the universe that is now out of contact with us. The "speed" of the CMBR, in units of comoving distance over cosmological time, is much larger than the speed of light. I think it's about 3.2c. This means essentially nothing, since the speed of light has no special status when talking about cosmological recession velocities. -- Ben I'm not sure I understand: Does that mean that there are portions of the universe that we can never see because they are in effect moving away from us faster than the speed of light? I thought that was impossible--that the light just got more red-shifted at greater distances. |
#15
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"Yousuf Khan" wrote In fact, wasn't there an observation made at one time, that some of the oldest stars seem to be older than the age of the universe itself? I'm not sure if that's been resolved or not. Maybe you will find this interesting (I did): "Cosmological Redshift in a Relational Quantum Theory ....An exact formulation is possible in a closed FRW cosmology in which cosmological redshift is given by 1+z = a_0^2/a^2(t). This is consistent with observation for a universe expanding at half the currently accepted rate, twice as old, and requiring a quarter of the critical density for closure...." Rest is at: http://arxiv.org/abs/gr-qc/0508077 --Ivica |
#16
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Sam Wormley wrote:
We estimate the age of the universe to be about 13.7 billion years. As the universe expands faster and faster, our observable horizon will begin to shrink and we will no longer be able to "see" the early universe. Okay, then wouldn't we then be calling whatever we can still see to be the "early" universe? And therefore wouldn't we then be saying that the universe is always 13.7 billion years, since that's as far out into that we can see? Yousuf Khan |
#17
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Ivica Kolar wrote:
Maybe you will find this interesting (I did): "Cosmological Redshift in a Relational Quantum Theory ...An exact formulation is possible in a closed FRW cosmology in which cosmological redshift is given by 1+z = a_0^2/a^2(t). This is consistent with observation for a universe expanding at half the currently accepted rate, twice as old, and requiring a quarter of the critical density for closure...." Rest is at: http://arxiv.org/abs/gr-qc/0508077 Translate it for me, what does it mean? Yousuf Khan |
#18
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Yousuf Khan wrote:
Sam Wormley wrote: We estimate the age of the universe to be about 13.7 billion years. As the universe expands faster and faster, our observable horizon will begin to shrink and we will no longer be able to "see" the early universe. Okay, then wouldn't we then be calling whatever we can still see to be the "early" universe? And therefore wouldn't we then be saying that the universe is always 13.7 billion years, since that's as far out into that we can see? Yousuf Khan Why do you not think that in one billion years we will estimate the age of the universe to be 14.7 billion years? The restriction of observable horizon won't kick in for a while? In the near term, our observable horizon is expanding about one light-year every year. |
#19
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John Graeme wrote:
The "speed" of the CMBR, in units of comoving distance over cosmological time, is much larger than the speed of light. I think it's about 3.2c. This means essentially nothing, since the speed of light has no special status when talking about cosmological recession velocities. -- Ben I'm not sure I understand: Does that mean that there are portions of the universe that we can never see because they are in effect moving away from us faster than the speed of light? I thought that was impossible--that the light just got more red-shifted at greater distances. Yeah, the light speed limit is only the limit of matter or energy *moving* inside space. There is no such speed limit when it comes to how fast space itself grows or shrinks inside itself. I always throught of it like a bunch of boats in water, if the boats have a maximum speed of 10 knots, then there's nothing that says you can't have a 20 knot current in the water which moves them faster. Think of the boats as matter or energy, and think of the water as space. Yousuf Khan |
#20
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"Yousuf Khan" wrote in message ups.com... Sam Wormley wrote: We estimate the age of the universe to be about 13.7 billion years. As the universe expands faster and faster, our observable horizon will begin to shrink and we will no longer be able to "see" the early universe. Okay, then wouldn't we then be calling whatever we can still see to be the "early" universe? And therefore wouldn't we then be saying that the universe is always 13.7 billion years, since that's as far out into that we can see? Possibly. We can estimate the age of the universe (within obvious margins or effort) through other means though, and generally these are consistent with the age of the universe being around 12-17 billion years old. Even our saying "13.7 billion years old" is to a massive (by Human standards) margin of error - around 49 million years either way would still be "13.7 billion years." |
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