Hi members!
The universe supposedly has no boundaries and is expanding,so with respect to us,
it can be considered infinite.Why then can we see stars and other celestial bodies
distinctly and not the uniform illumination of the night sky?I mean, if the universe IS infinite,then there would be an infinite number of stars, galaxies,nebulae,etc and we'd definitely end up looking at some bright object irrespective of the direction in space with respect to the Earth.I request some advanced member to clear this (silly?) doubt...
PS:I DO NOT expect Zephir to post any of his 'professional' stuff.I've had enough of all those 'advanced' posts of his...
There are a few reasons you can consider.
1. The biggest one is that we can see only a finite distance into the universe. If the universe is a few billion years old (I can't remember the exact number, maybe 35 billion, or so), then we can only see things within 35 billion light years.
2. Because of the way the universe is expanding, things are moving away from us at a rate proportional to their distance (or the square? I'm not sure). Either way, this means that objects a sufficient distance away from us are effectively moving away from us at a rate faster than the speed of light (note, this does not violate relativity, as there is no actual relative motion, rather the distance between us is increasing). Anything beyond this critical distance we will not be able to see, no matter how long we wait for the light to travel.
3. Because of the low average density of space. Even if the universe were infinite (which it isn't), and we could guarantee that in any direction we would be for sure looking at some bright object, the chances of that object being within a reasonable distance is very small, and as such the intensity of the light from most of the space will be so low as to be imperceptible, except for the (relatively) few points where there are stars within a few million light years or so. Add to that dust absorption, random quantum activity, quantization of light, etc. and for anything beyond a certain distance the light may not reach us at all.
1. The biggest one is that we can see only a finite distance into the universe. If the universe is a few billion years old (I can't remember the exact number, maybe 35 billion, or so), then we can only see things within 35 billion light years.
2. Because of the way the universe is expanding, things are moving away from us at a rate proportional to their distance (or the square? I'm not sure). Either way, this means that objects a sufficient distance away from us are effectively moving away from us at a rate faster than the speed of light (note, this does not violate relativity, as there is no actual relative motion, rather the distance between us is increasing). Anything beyond this critical distance we will not be able to see, no matter how long we wait for the light to travel.
3. Because of the low average density of space. Even if the universe were infinite (which it isn't), and we could guarantee that in any direction we would be for sure looking at some bright object, the chances of that object being within a reasonable distance is very small, and as such the intensity of the light from most of the space will be so low as to be imperceptible, except for the (relatively) few points where there are stars within a few million light years or so. Add to that dust absorption, random quantum activity, quantization of light, etc. and for anything beyond a certain distance the light may not reach us at all.
Have you considered that our 'eyes' have not evolved to detect certain aspects? The wave-form may well exist at a frequency we have not yet evolved to detect, with eyes. This is why we need 'ears' for the detection of different frequencies.
We certainly have not evolved to detect things moving at the speed of light, but only visibly detect the 'light' when it collides with something else, thus, of course, 'slowing' it down (transforming it into 'colour'/visible spectrum?).
We certainly have not evolved to detect things moving at the speed of light, but only visibly detect the 'light' when it collides with something else, thus, of course, 'slowing' it down (transforming it into 'colour'/visible spectrum?).
QUOTE (mandible+Dec 21 2007, 06:47 PM)
Have you considered that our 'eyes' have not evolved to detect certain aspects? The wave-form may well exist at a frequency we have not yet evolved to detect, with eyes. This is why we need 'ears' for the detection of different frequencies.
While we've disagreed before, this part is right on the money, if a bit uniformed.
Check this out, mandible. It's pretty much exactly the phenomenon you were referring to.
Wikipedia - Cosmic Background Radiation
Once again, you're pretty much describing what happens when we perceive light.
Check this out:
HowStuffWorks - Visible Light
While we've disagreed before, this part is right on the money, if a bit uniformed.
Check this out, mandible. It's pretty much exactly the phenomenon you were referring to.
Wikipedia - Cosmic Background Radiation
QUOTE
We certainly have not evolved to detect things moving at the speed of light, but only visibly detect the 'light' when it collides with something else, thus, of course, 'slowing' it down (transforming it into 'colour'/visible spectrum?).
Once again, you're pretty much describing what happens when we perceive light.
Check this out:
HowStuffWorks - Visible Light
QUOTE
While we've disagreed before, this part is right on the money, if a bit uniformed.
Check this out, mandible. It's pretty much exactly the phenomenon you were referring to.
Wikipedia - Cosmic Background Radiation
Check this out, mandible. It's pretty much exactly the phenomenon you were referring to.
Wikipedia - Cosmic Background Radiation
BDW, I think we're all here for the same reason, actually. Even though people are kind of resisting it, knowledge is seeping through all the time!
- I actually think that a little disagreement is quite healthy. After all, who is going to stand up and say they already know everything? (And if they did, what would they need to be here for?)I arrived at my current thoughts by sitting on a rock in the forest and thinking about it! -
- But then, they do say that Philosophy is the discovery of the bleedin' obvious! 
Thanks for those links, matey. Seems you're a dude after all!
QUOTE (mandible+Dec 21 2007, 07:27 PM)
I arrived at my current thoughts by sitting on a rock in the forest and thinking about it! - - But then, they do say that Philosophy is the discovery of the bleedin' obvious!
Well, that's not my preferred method of discovery, but in this particular case it seems to have served you fairly well. You seem to be interested in philosophical discussions more so than physics discussion, but I would like to recommend a few books on the subject of science that work well with a philosophical view of the world.
The Fabric of the Cosmos by Brian Greene - this book is pretty much pure science, but it's quite informative about what physics is, and helped give me and a couple friends a good idea of where physics ends and philosophy begins.
The Demon-Haunted World: Science as a Candle in the Dark by Carl Sagan - this one is a scientists look at pseudo-science, and the philosophies that enable, support and pique our interest in the subjects. One of the major subjects is the balance of credulity and skepticism, and Mr. Sagan managed to strike just the right combination when he suggested that certain pseudo-scientific claims deserve serious scientific scrutiny, as what little evidence there is to support them is actually empirical.
Both books are widely available in the science section of any chain bookstore, and neither is very expensive.
In fact, IMHO everyone on this board should read those two books. For those of us who aren't physics professional or students, they can shed much light on the subjects so often discussed here, while the few (the proud, the elite...) members who are intimately familiar with physics can get a better idea of what the interested amateur believes about physics.
- But then, they do say that Philosophy is the discovery of the bleedin' obvious! Well, that's not my preferred method of discovery, but in this particular case it seems to have served you fairly well. You seem to be interested in philosophical discussions more so than physics discussion, but I would like to recommend a few books on the subject of science that work well with a philosophical view of the world.
The Fabric of the Cosmos by Brian Greene - this book is pretty much pure science, but it's quite informative about what physics is, and helped give me and a couple friends a good idea of where physics ends and philosophy begins.
The Demon-Haunted World: Science as a Candle in the Dark by Carl Sagan - this one is a scientists look at pseudo-science, and the philosophies that enable, support and pique our interest in the subjects. One of the major subjects is the balance of credulity and skepticism, and Mr. Sagan managed to strike just the right combination when he suggested that certain pseudo-scientific claims deserve serious scientific scrutiny, as what little evidence there is to support them is actually empirical.
Both books are widely available in the science section of any chain bookstore, and neither is very expensive.
In fact, IMHO everyone on this board should read those two books. For those of us who aren't physics professional or students, they can shed much light on the subjects so often discussed here, while the few (the proud, the elite...) members who are intimately familiar with physics can get a better idea of what the interested amateur believes about physics.
Thanks for that, BDW.
The Carl Sagan sounds interesting. I will give it a go!
I actually think that all of the 'methods' of trying to understand further, when they are Honest, will arrive at similar conclusions, but they will, of course, use many differing forms of 'metaphor' to get there.
Physics, I think, attempts to use the most straightforward and obvious physical descriptions, but still describes with its own 'language' (algebra), while 'philosophy' is maybe a slightly more difficult 'language' because of its subjectiveness, and is seemingly becoming a little obscure and antiquated. However, there are 'depths' to things, and at some point there IS a meeting between the two. Philosophy seems more emotionally concerned with what we DO with this information, once we 'have' it, whereas Physics is more concerned with the straightforward, thus less emotionally biased, attainment of the facts.
Possibly, the likes of Mr. Sagan are more aware of this than us poor Mr. Average's?
For me, Psychology is possibly the 'missing link' between the two (the 'balance'?), as it is effectively a scientific study of the Human thought process, a valuable test for the correct deciphering of all this new information we are gathering.
Great info, though, so thanks again!
The Carl Sagan sounds interesting. I will give it a go!
I actually think that all of the 'methods' of trying to understand further, when they are Honest, will arrive at similar conclusions, but they will, of course, use many differing forms of 'metaphor' to get there.
Physics, I think, attempts to use the most straightforward and obvious physical descriptions, but still describes with its own 'language' (algebra), while 'philosophy' is maybe a slightly more difficult 'language' because of its subjectiveness, and is seemingly becoming a little obscure and antiquated. However, there are 'depths' to things, and at some point there IS a meeting between the two. Philosophy seems more emotionally concerned with what we DO with this information, once we 'have' it, whereas Physics is more concerned with the straightforward, thus less emotionally biased, attainment of the facts.
Possibly, the likes of Mr. Sagan are more aware of this than us poor Mr. Average's?
For me, Psychology is possibly the 'missing link' between the two (the 'balance'?), as it is effectively a scientific study of the Human thought process, a valuable test for the correct deciphering of all this new information we are gathering.
Great info, though, so thanks again!
Hi All,
I've got a couple more authors to add to your list, BDW. Asimov is easily read and extremely prolific, but, personally, I find that John Gribbon's books cover a wide range of physics for the amateur , such as myself.
Peace,
Ron
I've got a couple more authors to add to your list, BDW. Asimov is easily read and extremely prolific, but, personally, I find that John Gribbon's books cover a wide range of physics for the amateur , such as myself.
Peace,
Ron
Ron's books carry my highest endorsements, as well.
QUOTE (Neeraja+Dec 21 2007, 02:02 AM)
The universe supposedly has no boundaries and is expanding,so with respect to us,
it can be considered infinite.Why then can we see stars and other celestial bodies
distinctly and not the uniform illumination of the night sky?I mean, if the universe IS infinite,then there would be an infinite number of stars, galaxies,nebulae,etc and we'd definitely end up looking at some bright object irrespective of the direction in space with respect to the Earth.I request some advanced member to clear this (silly?) doubt...
Nothing silly about it at all. The question has been lingering around since the time of Kepler, although Heinreich Olbers and Johann Bode popularized it in the 1820s, leading to the name Olbers' paradox. The simple answer is that the universe isn't infinite -- not infinitely old and/or not infinitely wide. Oddly enough Edgar Allen Poe was the first to suggest that our universe is not infinitely old and light has a finite speed, so light emitted past a certain distance has not yet had time to reach us.
NeoDevin was right about point 1 (the age is generally accepted as being 13.75 billion years old), and point 2 (the math gets complicated, especially if one is willing to believe in Dark Energy).
However, NeoDevin's point 3 is not correct. It doesn't matter if there is a "low average density of space" in an infinite universe. No matter which line of sight you choose you will be looking at the surface of a star. If that star happens to be particularly far away, it doesn't matter, there are an infinite number of stars behind it and an infinite numbers of stars slightly to the side of it. It will be bright. As for dust absorption, Olbers himself thought the answer to the paradox was that intervening material was absorbing the light. However, thermodynamics rears its ugly head. It was shown that the intervening material would start to heat up until the point where it glows, and thus emits as much light as it absorbs. I'm not even sure where NeoDevin was headed when mentioning "random quantum activity, quantization of light." Further explication would be nice.
There is one other effect which I hesitate to bring up, as the famous astrophysics tome "An Introduction to Modern Astrophysics" by Carroll and Ostlie claims that this effect is insignificant, but then I've seen other sources that claim it is significant. The light is being redshifted, especially for older and hence more distant stars, so what was emitted as visible light reaches us as a longer invisible wavelength. Perhaps we could have a lively debate about it.
it can be considered infinite.Why then can we see stars and other celestial bodies
distinctly and not the uniform illumination of the night sky?I mean, if the universe IS infinite,then there would be an infinite number of stars, galaxies,nebulae,etc and we'd definitely end up looking at some bright object irrespective of the direction in space with respect to the Earth.I request some advanced member to clear this (silly?) doubt...
Nothing silly about it at all. The question has been lingering around since the time of Kepler, although Heinreich Olbers and Johann Bode popularized it in the 1820s, leading to the name Olbers' paradox. The simple answer is that the universe isn't infinite -- not infinitely old and/or not infinitely wide. Oddly enough Edgar Allen Poe was the first to suggest that our universe is not infinitely old and light has a finite speed, so light emitted past a certain distance has not yet had time to reach us.
NeoDevin was right about point 1 (the age is generally accepted as being 13.75 billion years old), and point 2 (the math gets complicated, especially if one is willing to believe in Dark Energy).
However, NeoDevin's point 3 is not correct. It doesn't matter if there is a "low average density of space" in an infinite universe. No matter which line of sight you choose you will be looking at the surface of a star. If that star happens to be particularly far away, it doesn't matter, there are an infinite number of stars behind it and an infinite numbers of stars slightly to the side of it. It will be bright. As for dust absorption, Olbers himself thought the answer to the paradox was that intervening material was absorbing the light. However, thermodynamics rears its ugly head. It was shown that the intervening material would start to heat up until the point where it glows, and thus emits as much light as it absorbs. I'm not even sure where NeoDevin was headed when mentioning "random quantum activity, quantization of light." Further explication would be nice.
There is one other effect which I hesitate to bring up, as the famous astrophysics tome "An Introduction to Modern Astrophysics" by Carroll and Ostlie claims that this effect is insignificant, but then I've seen other sources that claim it is significant. The light is being redshifted, especially for older and hence more distant stars, so what was emitted as visible light reaches us as a longer invisible wavelength. Perhaps we could have a lively debate about it.
Thank you, all!
...if I may opine..
We all too often speak in terms of "the" universe (the one we reside within), when in most probability "our" universe is but one of an infinite number of universes..... just as we are in one galaxy among zillions (within "our" universe).
"our" universe's expansion may actually be a contraction toward its outer limits and to its neighboring universes where cell division (big bang)occurs.
..well that's one of many ways (utterly simplified) to suppose, within our highly limited observational skills.
to add... the light on the fringes of our universe may not even travel in our direction as it is drawn only toward the intersecting gravitational forces between universe's. It could be very intense where universes intermesh.
We all too often speak in terms of "the" universe (the one we reside within), when in most probability "our" universe is but one of an infinite number of universes..... just as we are in one galaxy among zillions (within "our" universe).
"our" universe's expansion may actually be a contraction toward its outer limits and to its neighboring universes where cell division (big bang)occurs.
..well that's one of many ways (utterly simplified) to suppose, within our highly limited observational skills.
to add... the light on the fringes of our universe may not even travel in our direction as it is drawn only toward the intersecting gravitational forces between universe's. It could be very intense where universes intermesh.
Neeraja
Though it's been touched on it deserves more attention, that is the spectrum of visible light is only a tiny sliver of all the radiation we receive from space. If we could see the entire spectrum from super infrared to gamma radiation the sky would be brighter than we perceive it to be. The microwave glow(representing a few degrees above absolute zero), however, would probably be the only uniform aspect, as the universe is not a uniform density after a few million years past the Big Bang, but becomes more "clumpy" the nearer to the present you get.
As to things being too far away to see, the latest calculations seem to indicate that the furthest any two points could be apart is on the order of 46 billion light years, and they would be "traveling" away from us at about .8 the speed of light(we've seen galaxies at .6 lightspeed) and are approaching the edge of our light horizon(the point where we will never see the light leaving them "now") so, theoretically, by some calculations, possibly, we can see the whole universe right now, but not in a few billion more years. Others say we are already past that point and can never see the entire universe. Time will tell.
Also, if we lived anywhere close to the core of our own galaxy, the amount of visible light would be enough that the difference between night and day would be small, of course the radiation levels would sterilize the Earth, but what a view!!!
Grumpy
Though it's been touched on it deserves more attention, that is the spectrum of visible light is only a tiny sliver of all the radiation we receive from space. If we could see the entire spectrum from super infrared to gamma radiation the sky would be brighter than we perceive it to be. The microwave glow(representing a few degrees above absolute zero), however, would probably be the only uniform aspect, as the universe is not a uniform density after a few million years past the Big Bang, but becomes more "clumpy" the nearer to the present you get.
As to things being too far away to see, the latest calculations seem to indicate that the furthest any two points could be apart is on the order of 46 billion light years, and they would be "traveling" away from us at about .8 the speed of light(we've seen galaxies at .6 lightspeed) and are approaching the edge of our light horizon(the point where we will never see the light leaving them "now") so, theoretically, by some calculations, possibly, we can see the whole universe right now, but not in a few billion more years. Others say we are already past that point and can never see the entire universe. Time will tell.
Also, if we lived anywhere close to the core of our own galaxy, the amount of visible light would be enough that the difference between night and day would be small, of course the radiation levels would sterilize the Earth, but what a view!!!
Grumpy
QUOTE (mandible+Dec 21 2007, 11:47 PM)
Have you considered that our 'eyes' have not evolved to detect certain aspects? The wave-form may well exist at a frequency we have not yet evolved to detect, with eyes. This is why we need 'ears' for the detection of different frequencies.
We certainly have not evolved to detect things moving at the speed of light, but only visibly detect the 'light' when it collides with something else, thus, of course, 'slowing' it down (transforming it into 'colour'/visible spectrum?).
Our ears don't just detect different frquencies, they detect a very different type of wave, which is minute pressure changes in the air. If light was down at 1Khz, you still wouldn't be able to 'hear' it
When light collides with something it doesn't slow down, it just gets reflected in our direction so it enters our eyes.
We certainly have not evolved to detect things moving at the speed of light, but only visibly detect the 'light' when it collides with something else, thus, of course, 'slowing' it down (transforming it into 'colour'/visible spectrum?).
Our ears don't just detect different frquencies, they detect a very different type of wave, which is minute pressure changes in the air. If light was down at 1Khz, you still wouldn't be able to 'hear' it
When light collides with something it doesn't slow down, it just gets reflected in our direction so it enters our eyes.
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