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Selrahc
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 Posted: Wed Aug 18, 2010 1:26 pm Post subject: |
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| Noko_112 wrote: | | AhMunRa wrote: | | Ah but with blackholes consuming whole galaxies, growing larger with what they consume, wouldn't a blackhole eventually consume everything? If this were to happen the result could end up being the next "Big Bang". |
A new theory has arises-ed that there might be more of an black star than an hole (thus is has no singularity and might turn into a supernova a lot easier), but there is still many problem to be solved with both theory's |
So if we went into a black star we wouldnt die because it dosent have an event horizon?
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Ricardo
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| Posted: Wed Aug 18, 2010 3:56 pm Post subject: |
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| Noko_112 wrote: | | AhMunRa wrote: | | Ah but with blackholes consuming whole galaxies, growing larger with what they consume, wouldn't a blackhole eventually consume everything? If this were to happen the result could end up being the next "Big Bang". |
A new theory has arises-ed that there might be more of an black star than an hole (thus is has no singularity and might turn into a supernova a lot easier), but there is still many problem to be solved with both theory's |
Did I hear black star?
I actually lean towards the black hole consumes everything thus big bang reoccurs theory.
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AhMunRa
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| Posted: Wed Aug 18, 2010 4:34 pm Post subject: |
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It would explain the original forces behind the supposed big bang theory.
Energy is what makes everything what it is. Even blackholes though light doesn't escape let gamma burst radiation escape, though it doesn't really escape it's more ejected from both sides of the event horizon.
Here's one to think about next time you are sitting on the potty.
If one massive blackhole consumed the entire universe and had nothing left to consume, would it consume itself?
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<Wiccaan> Bah that was supposed to say 'not saying its dead' lol. Fixing >.> |
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Ricardo
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| Posted: Wed Aug 18, 2010 4:43 pm Post subject: |
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| AhMunRa wrote: | It would explain the original forces behind the supposed big bang theory.
Energy is what makes everything what it is. Even blackholes though light doesn't escape let gamma burst radiation escape, though it doesn't really escape it's more ejected from both sides of the event horizon.
Here's one to think about next time you are sitting on the potty.
If one massive blackhole consumed the entire universe and had nothing left to consume, would it consume itself? |
It would collapse on itself and explode.
Or at least I think it should.
Cause of all the vacuum?
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AhMunRa
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| Posted: Wed Aug 18, 2010 5:43 pm Post subject: |
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I have not clue, it's already imploded.
I don't even pretend to understand quantum physics or astral physics.
Interesting thought though.
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<Wiccaan> Bah that was supposed to say 'not saying its dead' lol. Fixing >.> |
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Ricardo
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| Posted: Wed Aug 18, 2010 8:45 pm Post subject: |
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| AhMunRa wrote: | I have not clue, it's already imploded.
I don't even pretend to understand quantum physics or astral physics.
Interesting thought though. |
Yeah me either actually
The lectures tell a lot but don't answer some questions
So is vacuum, empty space something that's been there before the big bang?
etc. etc.
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Elaborate
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| Posted: Sun Aug 22, 2010 5:18 pm Post subject: |
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It's a theory. Not 100% Proven.
The universe is expanding and a rapid rate, What we do not yet know of the certain speeds because it's forever going. Take the Universe as a balloon what keeps expanding, and can never pop. But imagine that the balloon has no centre (Like the universe). Therefore the Universe cannot collapse on itself in theory, it may be a vacuum but there is no centre. Most end of the universe theories have been denied, but remember they are only theories. Not truth, It's only the human minds description on the universe. The universe could change at any moment, there's things we haven't yet unlocked about the universe. As time goes on, we will learn. But what's time? Another word used by man.
Let's put it at this, the Universe is forever expanding; apart from that. We know that it just keeps expanding and cannot stop or slow down; because there is a theory that nothing can stop at the speed of light, but apparently the universe expands faster than light itself.
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XaLeX
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| Posted: Sun Aug 22, 2010 5:44 pm Post subject: Re: End of the universe and how lucky we are. |
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| Dialgar wrote: | | There are two main ways the universe can end, either gravity becomes too strong and pulls everything back into a singularity and then the big bang reoccurs |
well, maybe. | Dialgar wrote: | | OR things get so far apart that there is no/very little heat and everything freeze. |
sounds and smells like a huge bullshit. no offense intended, obviously.
Anyway, are you feeling philosophical tonight? You shouldn't. The answer to life, the universe and everything is 42. Now get back to cheating. 
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Ricardo
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| Posted: Sun Aug 22, 2010 6:31 pm Post subject: |
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| Elaborate wrote: | It's a theory. Not 100% Proven.
The universe is expanding and a rapid rate, What we do not yet know of the certain speeds because it's forever going. Take the Universe as a balloon what keeps expanding, and can never pop. But imagine that the balloon has no centre (Like the universe). Therefore the Universe cannot collapse on itself in theory, it may be a vacuum but there is no centre. Most end of the universe theories have been denied, but remember they are only theories. Not truth, It's only the human minds description on the universe. The universe could change at any moment, there's things we haven't yet unlocked about the universe. As time goes on, we will learn. But what's time? Another word used by man.
Let's put it at this, the Universe is forever expanding; apart from that. We know that it just keeps expanding and cannot stop or slow down; because there is a theory that nothing can stop at the speed of light, but apparently the universe expands faster than light itself. |
O shit the universe is expanding faster than light? sweet.
Didn't know that.
I still liked the Black star theory.
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elpacco
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| Posted: Sun Aug 22, 2010 7:45 pm Post subject: |
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| Noko_112 wrote: | | AhMunRa wrote: | | Ah but with blackholes consuming whole galaxies, growing larger with what they consume, wouldn't a blackhole eventually consume everything? If this were to happen the result could end up being the next "Big Bang". |
A new theory has arises-ed that there might be more of an black star than an hole (thus is has no singularity and might turn into a supernova a lot easier), but there is still many problem to be solved with both theory's |
Black holes don't turn into supernovas buddy, supernovas turn into black holes.
| Elaborate wrote: | It's a theory. Not 100% Proven.
The universe is expanding and a rapid rate, What we do not yet know of the certain speeds because it's forever going. Take the Universe as a balloon what keeps expanding, and can never pop. But imagine that the balloon has no centre (Like the universe). Therefore the Universe cannot collapse on itself in theory, it may be a vacuum but there is no centre. Most end of the universe theories have been denied, but remember they are only theories. Not truth, It's only the human minds description on the universe. The universe could change at any moment, there's things we haven't yet unlocked about the universe. As time goes on, we will learn. But what's time? Another word used by man.
Let's put it at this, the Universe is forever expanding; apart from that. We know that it just keeps expanding and cannot stop or slow down; because there is a theory that nothing can stop at the speed of light, but apparently the universe expands faster than light itself. |
If the universe were expanding faster than the speed of light, we wouldn't be able to see any stars.
So no, you're wrong.
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| FangBanger wrote: | | What is the best way for a lv19 Soldier to solo Sledge on Borderlands? |
Shoot him. |
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Farr.
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| Posted: Sun Aug 22, 2010 10:37 pm Post subject: |
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| it's also possible for 2 black holes to collide into each other to form an even larger black hole
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Elaborate
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| Posted: Mon Aug 23, 2010 4:49 am Post subject: |
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| elpacco wrote: | | Noko_112 wrote: | | AhMunRa wrote: | | Ah but with blackholes consuming whole galaxies, growing larger with what they consume, wouldn't a blackhole eventually consume everything? If this were to happen the result could end up being the next "Big Bang". |
A new theory has arises-ed that there might be more of an black star than an hole (thus is has no singularity and might turn into a supernova a lot easier), but there is still many problem to be solved with both theory's |
Black holes don't turn into supernovas buddy, supernovas turn into black holes.
| Elaborate wrote: | It's a theory. Not 100% Proven.
The universe is expanding and a rapid rate, What we do not yet know of the certain speeds because it's forever going. Take the Universe as a balloon what keeps expanding, and can never pop. But imagine that the balloon has no centre (Like the universe). Therefore the Universe cannot collapse on itself in theory, it may be a vacuum but there is no centre. Most end of the universe theories have been denied, but remember they are only theories. Not truth, It's only the human minds description on the universe. The universe could change at any moment, there's things we haven't yet unlocked about the universe. As time goes on, we will learn. But what's time? Another word used by man.
Let's put it at this, the Universe is forever expanding; apart from that. We know that it just keeps expanding and cannot stop or slow down; because there is a theory that nothing can stop at the speed of light, but apparently the universe expands faster than light itself. |
If the universe were expanding faster than the speed of light, we wouldn't be able to see any stars.
So no, you're wrong. |
Sorry buddy, Thing your wrong. Check-mate.
Some of the misunderstandings surrounding this topic might come from confusion over what is meant by the universe "expanding faster than the speed of light." However, for the simplest interpretation of your question, the answer is that the universe does expand faster than the speed of light, and, perhaps more surprisingly, some of the galaxies we can see right now are currently moving away from us faster than the speed of light! As a consequence of their great speeds, these galaxies will likely not be visible to us forever; some of them are right now emitting their last bit of light that will ever be able to make it all the way across space and reach us (billions of years from now). After that, we will observe them to freeze and fade, never to be heard from again.
As for your specific question of what was happening during the period of rapid expansion (or "inflation") that was thought to mark the early universe, I have to admit that I'm a little less clear on that. However, the basic idea of the theory of inflation is that the part of the universe which we can see (the "visible universe") is only a tiny part of the universe as a whole, and that the universe underwent exponential growth during the inflationary era. Therefore, there certainly would have been points which moved faster than the speed of light with respect to each other during inflation. Whether any points within our visible universe moved faster than light with respect to each other is something I'm less clear on, but I'll work on learning more about this specific point and update this if I find anything!
To answer the broader question in detail, we need to specify what we mean by the universe "expanding faster than the speed of light." The universe is not a collection of galaxies sitting in space, all moving away from a central point. Instead, a more appropriate analogy is to think of the universe as a giant blob of dough with raisins spread throughout it (the raisins represent galaxies; the dough represents space). When the dough is placed in an oven, it begins to expand, or, more accurately, to stretch, keeping the same proportions as it had before but with all the distances between galaxies getting bigger as time goes on.
The bottom line is that different pairs of galaxies are moving at different speeds with respect to each other; the further the galaxies are, the faster they move apart. So when we ask whether the universe is "expanding faster than the speed of light," I am going to interpret that to mean, "Are there any two galaxies in the universe which are moving faster than the speed of light with respect to each other?"
So how do we measure this? As discussed in a previous question, the universe's expansion is determined by something called the Hubble constant, which is approximately equal to 71, measured in the technically useful but conceptually confusing units of "kilometers per second per megaparsec." In more sensible units, the Hubble constant is approximately equal to 0.007% per million years -- what it means is that every million years, all the distances in the universe stretch by 0.007%. (This interpretation assumes that the Hubble "constant" actually stays constant over those million years, which it doesn't, but given that a million years is extremely short on cosmic timescales, this is a pretty good approximation. It also assumes that when we talk about the "distance" between two galaxies, we are referring to the distance between them right now -- that is, the distance we would measure if we somehow "pressed the freeze-frame button" on the universe, thereby stopping the expansion, and then extended a really long tape measure between the two galaxies and read off the distance. There are many other distances that can be defined in cosmology, but this is the most useful one for the current question.)
If we use the definition of distance given above (and only if we use this definition and no other), then the Hubble constant tells us that for every megaparsec of distance between two galaxies, the apparent speed at which the galaxies move apart from each other is greater by 71 kilometers per second. Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers).
So we have reduced the original question to a much simpler one: Are there any two galaxies in the entire universe whose distance (as defined above) is greater than 4,200 megaparsecs?
Well, we could just answer this question by "cheating": Since current cosmological theories state that the universe is infinitely big, then there certainly are a bunch of galaxies which are more than 4,200 megaparsecs away from each other -- in fact, an infinite number of them! However, if we want to stick a bit more closely to observations, we can't really prove that the universe is infinite. In light of this, a more fair question to ask might be whether or not any galaxies in the visible universe (the part we can currently see) are moving away from us faster than the speed of light.
Surprisingly, the answer is yes! Ned Wright's Cosmology Tutorial has a calculator which allows you to compute many quantities, including distance, for different models of the universe and for galaxies at different "redshifts" from us (the redshift is an experimentally easy-to-determine property of the galaxy's light that tells us how much the universe has stretched between the time the light was emitted and the time it was received). Using the best observationally-determined values for the universe's rate of expansion, acceleration and other parameters (which are the default inputs for the calculator), I found that if you use a value of around 1.4 for z (the redshift), you get the required distance of 4,200 megaparsecs. Therefore, any galaxy with a redshift greater than 1.4 is currently moving away from us faster than the speed of light.
Can we see these galaxies? Yes, we certainly can! Bright galaxies are regularly detected out to redshifts of a few; a redshift of 1.4 isn't really that much. For example, here are some pictures of quasars (galaxies with extremely active black holes in their centers) with redshifts around 5. We can even see light (although not individual objects) all the way back to a redshift of 1000 or so. (This light is referred to as the Cosmic Microwave Background and was emitted around 380,000 years after the Big Bang, right after the Universe had cooled down enough for light to get through all the intervening matter.) Meanwhile, the numbers spit out by the calculator tell us that for a galaxy with a redshift of 1.4, the light we are currently seeing from this galaxy was emitted around 4.6 billion years after the Big Bang, when the Universe was already quite well-developed.
You might be wondering how we could possibly see a galaxy that is moving away from us faster than the speed of light! The answer is that the motion of the galaxy now has no effect whatsoever on the light that it emitted billions of years ago. The light doesn't care what the galaxy is doing; it just cares about the stretching of space between its current location and us. So we can easily imagine a situation where the galaxy was not moving faster than the speed of light at the moment the light was emitted; therefore, the light was able to "outrun" the expansion of space and move towards us, while the galaxy moved away from us as the universe expanded. Keeping in mind what we learned above -- that farther objects recede faster in a proportionally stretching universe -- we can immediately see that right after the light is emitted, the galaxy is moving away from us faster than the point at which the light is located, and that this disparity will only increase as time goes on and the galaxy and light separate even more. Therefore, we can easily have a situation where the galaxy keeps on moving away faster and faster, eventually reaching or exceeding the speed of light relative to us, while the light which it emitted billions of years ago leisurely coasts on, never having to move across a region of space that was stretching faster than the speed of light, and therefore reaches us eventually.
You might also be wondering how a galaxy is ever able to surpass the speed of light barrier in the first place; for that, see our answer to a previous question.
The fact that galaxies we see now are moving away from us faster than the speed of light has some bleak consequences, however. Astronomers now have strong evidence that we live in an "accelerating universe," which means that the speed of each individual galaxy with respect to us will increase as time goes on. If we assume that this acceleration continues indefinitely, then galaxies which are currently moving away from us faster than the speed of light will always be moving away from us faster than the speed of light and will eventually reach a point where the space between us and them is stretching so rapidly that any light they emit after that point will never be able to reach us. As time goes by (billions of years in the future), we will see these galaxies freeze and fade, never to be heard from again. Furthermore, as more and more galaxies accelerate past the speed of light, any light that they emit after a certain point will also not be able to reach us, and they too will freeze and fade. Eventually, we will be left with a universe that is mostly invisible, with only the light from a few, very nearby galaxies (whose motions are strongly affected by local gravitational interaction) to keep us company. For more details, here is a technical paper on this topic.
Which galaxies are currently "saying their last goodbyes?" That is, if we imagine that there are aliens living in these galaxies who hope to make contact with us, which galaxies are running up against their deadline right at this moment? A reasonable guess would be that the galaxies which are currently moving at the speed of light with respect to us (at a distance of 4,200 megaparsecs and redshift of 1.4, as discussed above) are at the "critical point" where any light they emit after now will never be able to reach us. Roughly speaking, this is correct, but a detailed calculation (such as the one contained in this paper) shows that for the simplest viable model of the universe's acceleration, it is actually galaxies at a distance of 4,740 megaparsecs and redshift of 1.69 that are just now reaching the critical point, while galaxies at a redshift of 1.4 are still emitting light that will eventually reach us.
The difference is due to a rather subtle fact: Even though the universe is "accelerating" in the sense that each galaxy moves faster as time goes on, the Hubble constant is actually decreasing with time -- in other words, the rate at which space is expanding, measured at a point which is at a fixed distance from us, gets smaller as time goes on. If we keep our eyes on an individual galaxy as it moves away from us, we will see it accelerate, but if we keep our eyes on a fixed point in space and watch many different galaxies go past that point, each galaxy's speed will be slower than the one before it. (As a very rough analogy, the universe behaves like a river with rapids. If you put a boat in the river and allow it to be carried by the flow, it will accelerate as it moves downstream and enters the rapids. But if you sit on the bank and measure the speed of the water at one location, it changes based on an entirely different set of factors -- for example, the rate at which the supply of water from upstream is changing. It is possible for the water speed at your location to decrease with time, even though each boat that you release accelerates as it heads into the rapids.) Because of this effect, if light is able to "swim against the tide" and remain at a roughly constant distance with respect to us (as would happen if it is emitted from a galaxy moving away from us at the speed of light), then as time goes on and the Hubble constant decreases, it will eventually be able to gain ground, "swim upstream" and traverse the necessary distance of space to reach us.
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Ricardo
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| Posted: Mon Aug 23, 2010 9:16 am Post subject: |
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| Elaborate wrote: | | elpacco wrote: | | Noko_112 wrote: | | AhMunRa wrote: | | Ah but with blackholes consuming whole galaxies, growing larger with what they consume, wouldn't a blackhole eventually consume everything? If this were to happen the result could end up being the next "Big Bang". |
A new theory has arises-ed that there might be more of an black star than an hole (thus is has no singularity and might turn into a supernova a lot easier), but there is still many problem to be solved with both theory's |
Black holes don't turn into supernovas buddy, supernovas turn into black holes.
| Elaborate wrote: | It's a theory. Not 100% Proven.
The universe is expanding and a rapid rate, What we do not yet know of the certain speeds because it's forever going. Take the Universe as a balloon what keeps expanding, and can never pop. But imagine that the balloon has no centre (Like the universe). Therefore the Universe cannot collapse on itself in theory, it may be a vacuum but there is no centre. Most end of the universe theories have been denied, but remember they are only theories. Not truth, It's only the human minds description on the universe. The universe could change at any moment, there's things we haven't yet unlocked about the universe. As time goes on, we will learn. But what's time? Another word used by man.
Let's put it at this, the Universe is forever expanding; apart from that. We know that it just keeps expanding and cannot stop or slow down; because there is a theory that nothing can stop at the speed of light, but apparently the universe expands faster than light itself. |
If the universe were expanding faster than the speed of light, we wouldn't be able to see any stars.
So no, you're wrong. |
Sorry buddy, Thing your wrong. Check-mate.
Some of the misunderstandings surrounding this topic might come from confusion over what is meant by the universe "expanding faster than the speed of light." However, for the simplest interpretation of your question, the answer is that the universe does expand faster than the speed of light, and, perhaps more surprisingly, some of the galaxies we can see right now are currently moving away from us faster than the speed of light! As a consequence of their great speeds, these galaxies will likely not be visible to us forever; some of them are right now emitting their last bit of light that will ever be able to make it all the way across space and reach us (billions of years from now). After that, we will observe them to freeze and fade, never to be heard from again.
As for your specific question of what was happening during the period of rapid expansion (or "inflation") that was thought to mark the early universe, I have to admit that I'm a little less clear on that. However, the basic idea of the theory of inflation is that the part of the universe which we can see (the "visible universe") is only a tiny part of the universe as a whole, and that the universe underwent exponential growth during the inflationary era. Therefore, there certainly would have been points which moved faster than the speed of light with respect to each other during inflation. Whether any points within our visible universe moved faster than light with respect to each other is something I'm less clear on, but I'll work on learning more about this specific point and update this if I find anything!
To answer the broader question in detail, we need to specify what we mean by the universe "expanding faster than the speed of light." The universe is not a collection of galaxies sitting in space, all moving away from a central point. Instead, a more appropriate analogy is to think of the universe as a giant blob of dough with raisins spread throughout it (the raisins represent galaxies; the dough represents space). When the dough is placed in an oven, it begins to expand, or, more accurately, to stretch, keeping the same proportions as it had before but with all the distances between galaxies getting bigger as time goes on.
The bottom line is that different pairs of galaxies are moving at different speeds with respect to each other; the further the galaxies are, the faster they move apart. So when we ask whether the universe is "expanding faster than the speed of light," I am going to interpret that to mean, "Are there any two galaxies in the universe which are moving faster than the speed of light with respect to each other?"
So how do we measure this? As discussed in a previous question, the universe's expansion is determined by something called the Hubble constant, which is approximately equal to 71, measured in the technically useful but conceptually confusing units of "kilometers per second per megaparsec." In more sensible units, the Hubble constant is approximately equal to 0.007% per million years -- what it means is that every million years, all the distances in the universe stretch by 0.007%. (This interpretation assumes that the Hubble "constant" actually stays constant over those million years, which it doesn't, but given that a million years is extremely short on cosmic timescales, this is a pretty good approximation. It also assumes that when we talk about the "distance" between two galaxies, we are referring to the distance between them right now -- that is, the distance we would measure if we somehow "pressed the freeze-frame button" on the universe, thereby stopping the expansion, and then extended a really long tape measure between the two galaxies and read off the distance. There are many other distances that can be defined in cosmology, but this is the most useful one for the current question.)
If we use the definition of distance given above (and only if we use this definition and no other), then the Hubble constant tells us that for every megaparsec of distance between two galaxies, the apparent speed at which the galaxies move apart from each other is greater by 71 kilometers per second. Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers).
So we have reduced the original question to a much simpler one: Are there any two galaxies in the entire universe whose distance (as defined above) is greater than 4,200 megaparsecs?
Well, we could just answer this question by "cheating": Since current cosmological theories state that the universe is infinitely big, then there certainly are a bunch of galaxies which are more than 4,200 megaparsecs away from each other -- in fact, an infinite number of them! However, if we want to stick a bit more closely to observations, we can't really prove that the universe is infinite. In light of this, a more fair question to ask might be whether or not any galaxies in the visible universe (the part we can currently see) are moving away from us faster than the speed of light.
Surprisingly, the answer is yes! Ned Wright's Cosmology Tutorial has a calculator which allows you to compute many quantities, including distance, for different models of the universe and for galaxies at different "redshifts" from us (the redshift is an experimentally easy-to-determine property of the galaxy's light that tells us how much the universe has stretched between the time the light was emitted and the time it was received). Using the best observationally-determined values for the universe's rate of expansion, acceleration and other parameters (which are the default inputs for the calculator), I found that if you use a value of around 1.4 for z (the redshift), you get the required distance of 4,200 megaparsecs. Therefore, any galaxy with a redshift greater than 1.4 is currently moving away from us faster than the speed of light.
Can we see these galaxies? Yes, we certainly can! Bright galaxies are regularly detected out to redshifts of a few; a redshift of 1.4 isn't really that much. For example, here are some pictures of quasars (galaxies with extremely active black holes in their centers) with redshifts around 5. We can even see light (although not individual objects) all the way back to a redshift of 1000 or so. (This light is referred to as the Cosmic Microwave Background and was emitted around 380,000 years after the Big Bang, right after the Universe had cooled down enough for light to get through all the intervening matter.) Meanwhile, the numbers spit out by the calculator tell us that for a galaxy with a redshift of 1.4, the light we are currently seeing from this galaxy was emitted around 4.6 billion years after the Big Bang, when the Universe was already quite well-developed.
You might be wondering how we could possibly see a galaxy that is moving away from us faster than the speed of light! The answer is that the motion of the galaxy now has no effect whatsoever on the light that it emitted billions of years ago. The light doesn't care what the galaxy is doing; it just cares about the stretching of space between its current location and us. So we can easily imagine a situation where the galaxy was not moving faster than the speed of light at the moment the light was emitted; therefore, the light was able to "outrun" the expansion of space and move towards us, while the galaxy moved away from us as the universe expanded. Keeping in mind what we learned above -- that farther objects recede faster in a proportionally stretching universe -- we can immediately see that right after the light is emitted, the galaxy is moving away from us faster than the point at which the light is located, and that this disparity will only increase as time goes on and the galaxy and light separate even more. Therefore, we can easily have a situation where the galaxy keeps on moving away faster and faster, eventually reaching or exceeding the speed of light relative to us, while the light which it emitted billions of years ago leisurely coasts on, never having to move across a region of space that was stretching faster than the speed of light, and therefore reaches us eventually.
You might also be wondering how a galaxy is ever able to surpass the speed of light barrier in the first place; for that, see our answer to a previous question.
The fact that galaxies we see now are moving away from us faster than the speed of light has some bleak consequences, however. Astronomers now have strong evidence that we live in an "accelerating universe," which means that the speed of each individual galaxy with respect to us will increase as time goes on. If we assume that this acceleration continues indefinitely, then galaxies which are currently moving away from us faster than the speed of light will always be moving away from us faster than the speed of light and will eventually reach a point where the space between us and them is stretching so rapidly that any light they emit after that point will never be able to reach us. As time goes by (billions of years in the future), we will see these galaxies freeze and fade, never to be heard from again. Furthermore, as more and more galaxies accelerate past the speed of light, any light that they emit after a certain point will also not be able to reach us, and they too will freeze and fade. Eventually, we will be left with a universe that is mostly invisible, with only the light from a few, very nearby galaxies (whose motions are strongly affected by local gravitational interaction) to keep us company. For more details, here is a technical paper on this topic.
Which galaxies are currently "saying their last goodbyes?" That is, if we imagine that there are aliens living in these galaxies who hope to make contact with us, which galaxies are running up against their deadline right at this moment? A reasonable guess would be that the galaxies which are currently moving at the speed of light with respect to us (at a distance of 4,200 megaparsecs and redshift of 1.4, as discussed above) are at the "critical point" where any light they emit after now will never be able to reach us. Roughly speaking, this is correct, but a detailed calculation (such as the one contained in this paper) shows that for the simplest viable model of the universe's acceleration, it is actually galaxies at a distance of 4,740 megaparsecs and redshift of 1.69 that are just now reaching the critical point, while galaxies at a redshift of 1.4 are still emitting light that will eventually reach us.
The difference is due to a rather subtle fact: Even though the universe is "accelerating" in the sense that each galaxy moves faster as time goes on, the Hubble constant is actually decreasing with time -- in other words, the rate at which space is expanding, measured at a point which is at a fixed distance from us, gets smaller as time goes on. If we keep our eyes on an individual galaxy as it moves away from us, we will see it accelerate, but if we keep our eyes on a fixed point in space and watch many different galaxies go past that point, each galaxy's speed will be slower than the one before it. (As a very rough analogy, the universe behaves like a river with rapids. If you put a boat in the river and allow it to be carried by the flow, it will accelerate as it moves downstream and enters the rapids. But if you sit on the bank and measure the speed of the water at one location, it changes based on an entirely different set of factors -- for example, the rate at which the supply of water from upstream is changing. It is possible for the water speed at your location to decrease with time, even though each boat that you release accelerates as it heads into the rapids.) Because of this effect, if light is able to "swim against the tide" and remain at a roughly constant distance with respect to us (as would happen if it is emitted from a galaxy moving away from us at the speed of light), then as time goes on and the Hubble constant decreases, it will eventually be able to gain ground, "swim upstream" and traverse the necessary distance of space to reach us. |
So basically OP gets his answer.
The universe isn't actually going to freeze but its a term because it's expanding faster than the speed of light.
also, its k elpacco.
Elaborate, 'fuck're you getting all this info from? can i get a reference?
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Elaborate
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| Posted: Mon Aug 23, 2010 2:11 pm Post subject: |
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| Ricardo wrote: | | Elaborate wrote: | | elpacco wrote: | | Noko_112 wrote: | | AhMunRa wrote: | | Ah but with blackholes consuming whole galaxies, growing larger with what they consume, wouldn't a blackhole eventually consume everything? If this were to happen the result could end up being the next "Big Bang". |
A new theory has arises-ed that there might be more of an black star than an hole (thus is has no singularity and might turn into a supernova a lot easier), but there is still many problem to be solved with both theory's |
Black holes don't turn into supernovas buddy, supernovas turn into black holes.
| Elaborate wrote: | It's a theory. Not 100% Proven.
The universe is expanding and a rapid rate, What we do not yet know of the certain speeds because it's forever going. Take the Universe as a balloon what keeps expanding, and can never pop. But imagine that the balloon has no centre (Like the universe). Therefore the Universe cannot collapse on itself in theory, it may be a vacuum but there is no centre. Most end of the universe theories have been denied, but remember they are only theories. Not truth, It's only the human minds description on the universe. The universe could change at any moment, there's things we haven't yet unlocked about the universe. As time goes on, we will learn. But what's time? Another word used by man.
Let's put it at this, the Universe is forever expanding; apart from that. We know that it just keeps expanding and cannot stop or slow down; because there is a theory that nothing can stop at the speed of light, but apparently the universe expands faster than light itself. |
If the universe were expanding faster than the speed of light, we wouldn't be able to see any stars.
So no, you're wrong. |
Sorry buddy, Thing your wrong. Check-mate.
Some of the misunderstandings surrounding this topic might come from confusion over what is meant by the universe "expanding faster than the speed of light." However, for the simplest interpretation of your question, the answer is that the universe does expand faster than the speed of light, and, perhaps more surprisingly, some of the galaxies we can see right now are currently moving away from us faster than the speed of light! As a consequence of their great speeds, these galaxies will likely not be visible to us forever; some of them are right now emitting their last bit of light that will ever be able to make it all the way across space and reach us (billions of years from now). After that, we will observe them to freeze and fade, never to be heard from again.
As for your specific question of what was happening during the period of rapid expansion (or "inflation") that was thought to mark the early universe, I have to admit that I'm a little less clear on that. However, the basic idea of the theory of inflation is that the part of the universe which we can see (the "visible universe") is only a tiny part of the universe as a whole, and that the universe underwent exponential growth during the inflationary era. Therefore, there certainly would have been points which moved faster than the speed of light with respect to each other during inflation. Whether any points within our visible universe moved faster than light with respect to each other is something I'm less clear on, but I'll work on learning more about this specific point and update this if I find anything!
To answer the broader question in detail, we need to specify what we mean by the universe "expanding faster than the speed of light." The universe is not a collection of galaxies sitting in space, all moving away from a central point. Instead, a more appropriate analogy is to think of the universe as a giant blob of dough with raisins spread throughout it (the raisins represent galaxies; the dough represents space). When the dough is placed in an oven, it begins to expand, or, more accurately, to stretch, keeping the same proportions as it had before but with all the distances between galaxies getting bigger as time goes on.
The bottom line is that different pairs of galaxies are moving at different speeds with respect to each other; the further the galaxies are, the faster they move apart. So when we ask whether the universe is "expanding faster than the speed of light," I am going to interpret that to mean, "Are there any two galaxies in the universe which are moving faster than the speed of light with respect to each other?"
So how do we measure this? As discussed in a previous question, the universe's expansion is determined by something called the Hubble constant, which is approximately equal to 71, measured in the technically useful but conceptually confusing units of "kilometers per second per megaparsec." In more sensible units, the Hubble constant is approximately equal to 0.007% per million years -- what it means is that every million years, all the distances in the universe stretch by 0.007%. (This interpretation assumes that the Hubble "constant" actually stays constant over those million years, which it doesn't, but given that a million years is extremely short on cosmic timescales, this is a pretty good approximation. It also assumes that when we talk about the "distance" between two galaxies, we are referring to the distance between them right now -- that is, the distance we would measure if we somehow "pressed the freeze-frame button" on the universe, thereby stopping the expansion, and then extended a really long tape measure between the two galaxies and read off the distance. There are many other distances that can be defined in cosmology, but this is the most useful one for the current question.)
If we use the definition of distance given above (and only if we use this definition and no other), then the Hubble constant tells us that for every megaparsec of distance between two galaxies, the apparent speed at which the galaxies move apart from each other is greater by 71 kilometers per second. Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers).
So we have reduced the original question to a much simpler one: Are there any two galaxies in the entire universe whose distance (as defined above) is greater than 4,200 megaparsecs?
Well, we could just answer this question by "cheating": Since current cosmological theories state that the universe is infinitely big, then there certainly are a bunch of galaxies which are more than 4,200 megaparsecs away from each other -- in fact, an infinite number of them! However, if we want to stick a bit more closely to observations, we can't really prove that the universe is infinite. In light of this, a more fair question to ask might be whether or not any galaxies in the visible universe (the part we can currently see) are moving away from us faster than the speed of light.
Surprisingly, the answer is yes! Ned Wright's Cosmology Tutorial has a calculator which allows you to compute many quantities, including distance, for different models of the universe and for galaxies at different "redshifts" from us (the redshift is an experimentally easy-to-determine property of the galaxy's light that tells us how much the universe has stretched between the time the light was emitted and the time it was received). Using the best observationally-determined values for the universe's rate of expansion, acceleration and other parameters (which are the default inputs for the calculator), I found that if you use a value of around 1.4 for z (the redshift), you get the required distance of 4,200 megaparsecs. Therefore, any galaxy with a redshift greater than 1.4 is currently moving away from us faster than the speed of light.
Can we see these galaxies? Yes, we certainly can! Bright galaxies are regularly detected out to redshifts of a few; a redshift of 1.4 isn't really that much. For example, here are some pictures of quasars (galaxies with extremely active black holes in their centers) with redshifts around 5. We can even see light (although not individual objects) all the way back to a redshift of 1000 or so. (This light is referred to as the Cosmic Microwave Background and was emitted around 380,000 years after the Big Bang, right after the Universe had cooled down enough for light to get through all the intervening matter.) Meanwhile, the numbers spit out by the calculator tell us that for a galaxy with a redshift of 1.4, the light we are currently seeing from this galaxy was emitted around 4.6 billion years after the Big Bang, when the Universe was already quite well-developed.
You might be wondering how we could possibly see a galaxy that is moving away from us faster than the speed of light! The answer is that the motion of the galaxy now has no effect whatsoever on the light that it emitted billions of years ago. The light doesn't care what the galaxy is doing; it just cares about the stretching of space between its current location and us. So we can easily imagine a situation where the galaxy was not moving faster than the speed of light at the moment the light was emitted; therefore, the light was able to "outrun" the expansion of space and move towards us, while the galaxy moved away from us as the universe expanded. Keeping in mind what we learned above -- that farther objects recede faster in a proportionally stretching universe -- we can immediately see that right after the light is emitted, the galaxy is moving away from us faster than the point at which the light is located, and that this disparity will only increase as time goes on and the galaxy and light separate even more. Therefore, we can easily have a situation where the galaxy keeps on moving away faster and faster, eventually reaching or exceeding the speed of light relative to us, while the light which it emitted billions of years ago leisurely coasts on, never having to move across a region of space that was stretching faster than the speed of light, and therefore reaches us eventually.
You might also be wondering how a galaxy is ever able to surpass the speed of light barrier in the first place; for that, see our answer to a previous question.
The fact that galaxies we see now are moving away from us faster than the speed of light has some bleak consequences, however. Astronomers now have strong evidence that we live in an "accelerating universe," which means that the speed of each individual galaxy with respect to us will increase as time goes on. If we assume that this acceleration continues indefinitely, then galaxies which are currently moving away from us faster than the speed of light will always be moving away from us faster than the speed of light and will eventually reach a point where the space between us and them is stretching so rapidly that any light they emit after that point will never be able to reach us. As time goes by (billions of years in the future), we will see these galaxies freeze and fade, never to be heard from again. Furthermore, as more and more galaxies accelerate past the speed of light, any light that they emit after a certain point will also not be able to reach us, and they too will freeze and fade. Eventually, we will be left with a universe that is mostly invisible, with only the light from a few, very nearby galaxies (whose motions are strongly affected by local gravitational interaction) to keep us company. For more details, here is a technical paper on this topic.
Which galaxies are currently "saying their last goodbyes?" That is, if we imagine that there are aliens living in these galaxies who hope to make contact with us, which galaxies are running up against their deadline right at this moment? A reasonable guess would be that the galaxies which are currently moving at the speed of light with respect to us (at a distance of 4,200 megaparsecs and redshift of 1.4, as discussed above) are at the "critical point" where any light they emit after now will never be able to reach us. Roughly speaking, this is correct, but a detailed calculation (such as the one contained in this paper) shows that for the simplest viable model of the universe's acceleration, it is actually galaxies at a distance of 4,740 megaparsecs and redshift of 1.69 that are just now reaching the critical point, while galaxies at a redshift of 1.4 are still emitting light that will eventually reach us.
The difference is due to a rather subtle fact: Even though the universe is "accelerating" in the sense that each galaxy moves faster as time goes on, the Hubble constant is actually decreasing with time -- in other words, the rate at which space is expanding, measured at a point which is at a fixed distance from us, gets smaller as time goes on. If we keep our eyes on an individual galaxy as it moves away from us, we will see it accelerate, but if we keep our eyes on a fixed point in space and watch many different galaxies go past that point, each galaxy's speed will be slower than the one before it. (As a very rough analogy, the universe behaves like a river with rapids. If you put a boat in the river and allow it to be carried by the flow, it will accelerate as it moves downstream and enters the rapids. But if you sit on the bank and measure the speed of the water at one location, it changes based on an entirely different set of factors -- for example, the rate at which the supply of water from upstream is changing. It is possible for the water speed at your location to decrease with time, even though each boat that you release accelerates as it heads into the rapids.) Because of this effect, if light is able to "swim against the tide" and remain at a roughly constant distance with respect to us (as would happen if it is emitted from a galaxy moving away from us at the speed of light), then as time goes on and the Hubble constant decreases, it will eventually be able to gain ground, "swim upstream" and traverse the necessary distance of space to reach us. |
So basically OP gets his answer.
The universe isn't actually going to freeze but its a term because it's expanding faster than the speed of light.
also, its k elpacco.
Elaborate, 'fuck're you getting all this info from? can i get a reference? |
I got that partly by a website. But when I was young I've always been interested in these kind of things, and I can understand most terminology on this subject (Psychics and astronomy).
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Sephiron
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| Posted: Mon Aug 23, 2010 2:44 pm Post subject: |
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If it expands and there's no energy left to create heat, then all life would cease to exist. I would think that since there is not enough energy for heat, it wouldn't have anymore energy to expand, so eventually all stars will burn out until there is absolutely nothing left. Maybe it can recycle the energy from the supernovae and use it to create a new universe? I don't know. Also, I just shat this out of my head, so don't take it too seriously.
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