Will someone please explain to me in (laymans terms) why with all the billions and billions of stars in the universe, the sky at night between the stars is still jet black. Of course I know nothing at all about the universe, but it would seem to me with all those stars out there emitting light, that the universe would be very bright instead of dark. Is it because the universe is so large and distances are so great that the light becomes so diffused and scattered, that by the time it reaches us, only faint glimmers of light can be seen? I know this is a dumb question but it is something that has always bugged me. Thanks for your responses Tom Hix
Olbers asked a question about a stable infinite universe filled with stars. No one has given proof that the universe is indeed infinite. It might be. It might not be. Hundreds of billions of galaxies times hundreds of billions of stars in each galaxy gives an incredibly large number, but not infinite :-)
We respectfully request that you take us to Eden -- Doctor Sevrin :-)
Tom Hix writes: >Will someone please explain to me in (laymans terms) why with all the >billions and billions of stars in the universe, the sky at night between >the stars is still jet black. ... >I know this is a >dumb question but it is something that has always bugged me.
Actually, this is a fairly profound question in astronomy -- and it even has a name: Olber's Paradox. If you'd been born two hundred years earlier, it could well have been called Hix's Paradox.
Being bugged by a problem and diligently seeking out an honest answer is all there really is to science. As to the currently accepted answer to yours and Olber's question, please see:
> Will someone please explain to me in (laymans terms) why with all the > billions and billions of stars in the universe, the sky at night between > the stars is still jet black. Of course I know nothing at all about the > universe, but it would seem to me with all those stars out there > emitting light, that the universe would be very bright instead of dark. > Is it because the universe is so large and distances are so great that > the light becomes so diffused and scattered, that by the time it > reaches us, only faint glimmers of light can be seen? I know this is a > dumb question but it is something that has always bugged me. > Thanks for your responses > Tom Hix
The short answer is two-fold: 1) The expansion of the universe redshifts light coming from objects at greater and greater distances from us, moving it into wavelength bands we cannot see, and 2) the universe is finite in age, so that there has been insufficient time for light to travel to us for objects at distances greater than about 12 to 13 billion lightyears. The latter is more to the point than the former.
More formally, from Ned Wright's Cosmology FAQ, linked from
If the Universe were infinitely old, and infinite in extent, and stars could shine forever, then every direction you looked would eventually end on the surface of a star, and the whole sky would be as bright as the surface of the Sun. This is known as Olbers' Paradox after Heinrich Wilhelm Olbers [1757-1840] who wrote about it in 1823-1826 but it was also discussed earlier. Absorption by interstellar dust does not circumvent this paradox, since dust reradiates whatever radiation it absorbs within a few minutes, which is much less than the age of the Universe. However, the Universe is not infinitely old, and the expansion of the Universe reduces the accumulated energy radiated by distant stars. Either one of these effects acting alone would solve Olbers' Paradox, but they both act at once.
-- J. Scott Miller, Program Coordinator Scott.Mil...@louisville.edu Gheens Science Center and Rauch Planetarium http://www.louisville.edu/planetarium University of Louisville
>> Will someone please explain to me in (laymans terms) why with all the >> billions and billions of stars in the universe, the sky at night between >> the stars is still jet black.
"J. Scott Miller" <Scott.Mil...@louisville.edu> writes:
>The short answer is two-fold: 1) The expansion of the universe redshifts >light coming from objects at greater and greater distances from us, moving it >into wavelength bands we cannot see, and 2) the universe is finite in age, so >that there has been insufficient time for light to travel to us for objects at >distances greater than about 12 to 13 billion lightyears. The latter is more >to the point than the former.
And me, I add,
As an observer, I have to put in a word for (3) clouds of interstellar gas and dust intervene along our lines of sight, so that at some point, light from distant stars is absorbed or redirected by this material. (Of course, that material may well re-emit light of its own, but that is often in other wavelength bands, invisible to the eye - see (1) above.) Without all this interstellar equivalent of what you find under your couch, we'd see a great deal more light. Not an *infinite* amount, as per (1) and (2) above, but more than we have now. This is particularly the case for our own Galaxy - take a look at your favorite picture of the Milky Way, and note the big dark streaks. Those are caused by said interstellar crud, blocking out the light from the lots and lots and lots of stars that are right in our own neighborhood (relative to the expanse of the entire universe, anyhow). If you hear someone kvetching about "obscuration," that's what they're upset about.
The closest answer to a full answer but also remember that you have a threshold to overcome to be able to see any light. The eye seems to have a +ACI-exposure time+ACI- of about 1/15th of a second or so anything that doesn't trip the eye's sensors in that time period aren't seen and if it happens occasionally, then the brain considers it noise in the system and ignores it. You also see a star and your eye adjusts to that as the white and thus the darker area around the star ends up being black due to the relative lack of light. It's all relative in a way. Have Fun and Keep Looking Up. Bob May
Aas for the comment thatspace is empty and light just has no reflection, I have been told that space is actually very full, with solar wind particals and other like things. I will concurr that space is black because it just appears black to the human eye because the human eye only picks up a very small part of the colar spectrum. Once you get into things like x-rays, infra rays, radiation, space actually turns into a multitude of colors.
I talk, talk.. I talk to you -- In the night, in your dreams, of love so
true. (Real McCoy)
> > Will someone please explain to me in (laymans terms) why with all the > > billions and billions of stars in the universe, the sky at night between > > the stars is still jet black. Of course I know nothing at all about the > > universe, but it would seem to me with all those stars out there > > emitting light, that the universe would be very bright instead of dark. > > Is it because the universe is so large and distances are so great that > > the light becomes so diffused and scattered, that by the time it > > reaches us, only faint glimmers of light can be seen? I know this is a > > dumb question but it is something that has always bugged me. > > Thanks for your responses > > Tom Hix
> The short answer is two-fold: 1) The expansion of the universe redshifts > light coming from objects at greater and greater distances from us, moving it > into wavelength bands we cannot see, and 2) the universe is finite in age, so > that there has been insufficient time for light to travel to us for objects at > distances greater than about 12 to 13 billion lightyears. The latter is more > to the point than the former.
1. is irrelevant. The redshift also shifts UV, X and gamma wavelengths to visible light. 2. is the true explanation.
Gavin
>snip > -- > J. Scott Miller, Program Coordinator Scott.Mil...@louisville.edu > Gheens Science Center and Rauch Planetarium > http://www.louisville.edu/planetarium > University of Louisville
-- Dr.Gavin Tabor email : ga...@ic.ac.uk home page : monet.me.ic.ac.uk/people/gavin/gavin.html Department of Mechanical Engineering, Imperial College, London SW7 2BY
> J. Scott Miller wrote: > > The short answer is two-fold: 1) The expansion of the universe > > redshifts light coming from objects at greater and greater distances > > from us, moving it into wavelength bands we cannot see, and 2) the > > universe is finite in age, so that there has been insufficient time > > for light to travel to us for objects at distances greater than > > about 12 to 13 billion lightyears. The latter is more to the point > > than the former.
> 1. is irrelevant. The redshift also shifts UV, X and gamma wavelengths > to visible light. 2. is the true explanation.
> Gavin
Then let me elaborate. 1. is relevant because the expansion of the universe, and the redshift that occurs, causes a diminishing of the energy of the photons emitted from the surface of the object, regardless of the energy at which it was emitted. Calculations show that this effect alone can account for a dimming of the background by a factor of two.
Thus, it is not the sole solution, but contributes to the whole.
(reference: Jay Pasachoff, "Astronomy: From the Earth to the Universe") -- J. Scott Miller, Program Coordinator Scott.Mil...@louisville.edu Gheens Science Center and Rauch Planetarium http://www.louisville.edu/planetarium University of Louisville
> > > The short answer is two-fold: 1) The expansion of the universe > > > redshifts light coming from objects at greater and greater distances > > > from us, moving it into wavelength bands we cannot see, and 2) the > > > universe is finite in age, so that there has been insufficient time > > > for light to travel to us for objects at distances greater than > > > about 12 to 13 billion lightyears. The latter is more to the point > > > than the former.
> > 1. is irrelevant. The redshift also shifts UV, X and gamma wavelengths > > to visible light. 2. is the true explanation.
> > Gavin
> Then let me elaborate. 1. is relevant because the expansion of the universe, > and the redshift that occurs, causes a diminishing of the energy of the > photons emitted from the surface of the object, regardless of the energy at > which it was emitted. Calculations show that this effect alone can account > for a dimming of the background by a factor of two.
> Thus, it is not the sole solution, but contributes to the whole.
> (reference: Jay Pasachoff, "Astronomy: From the Earth to the Universe") > -- > J. Scott Miller, Program Coordinator Scott.Mil...@louisville.edu > Gheens Science Center and Rauch Planetarium > http://www.louisville.edu/planetarium > University of Louisville
The redshift IS irrelevant. If you converted every galaxy redshift into a blueshift of the same magnitude, the night sky would still be dark. An entire book has been written about Olbers' paradox and discusses wrong solutions (redshift, interstellar absorption, inability to perceive faint light, etc.) as well as the two correct solutions (finite age of the universe, lack of energy in the universe): DARKNESS AT NIGHT by Edward Harrison.
Do NOT trust astronomy textbooks. A 1987 study (Wesson, Valle, and Stabell; ApJ 317, 601) found that 7 out of 10 astronomy textbooks explained Olbers' paradox incorrectly: "Of 10 books, only three have a discussion that may loosely be termed right (Berry 1976; Harrison 1981; Kaufmann 1985). Another five are either confused or ambiguous (Landsberg and Evans 1977; Silk 1980; Raine 1981; Friedlander 1985; Hartmann 1985). And two can only be termed wrong (Mitton 1977; Zeilik 1982)."
Historically, the reason that many people still believe the redshift explains the dark night sky is because Olbers' paradox was rediscovered in the 1950s--by steady state cosmologists. In the steady state cosmology, the redshift DOES explain the dark night sky. But it is NOT the solution in the big bang cosmology.
Nice wrote: > The redshift IS irrelevant. If you converted every galaxy redshift into a > blueshift of the same magnitude, the night sky would still be dark. An > entire book has been written about Olbers' paradox and discusses wrong > solutions (redshift, interstellar absorption, inability to perceive faint > light, etc.) as well as the two correct solutions (finite age of the > universe, lack of energy in the universe): DARKNESS AT NIGHT by Edward > Harrison.
So, just for arguement sake, this reference is to be believed while that of other astronomers is not.
> Do NOT trust astronomy textbooks. A 1987 study (Wesson, Valle, and > Stabell; ApJ 317, 601) found that 7 out of 10 astronomy textbooks > explained Olbers' paradox incorrectly: "Of 10 books, only three have a > discussion that may loosely be termed right (Berry 1976; Harrison 1981; > Kaufmann 1985). Another five are either confused or ambiguous (Landsberg > and Evans 1977; Silk 1980; Raine 1981; Friedlander 1985; Hartmann 1985). > And two can only be termed wrong (Mitton 1977; Zeilik 1982)."
But, who is to say whether the text I have is as dated as the listing above. Though I will agree that they all don't get it right, comparisons of older texts with newer versions have demonstrated corrections as needed. And, indeed, I quote from my current version of Kaufmann (Universe, 5th edition):
Besides the finite age of the universe, a second effect also contributes significantly to the darkness of the night sky - the redshift. According to the Hubble law, the greater the distance to a galaxy, the greater the redshift. When a photon is redshifted, its wavelength becomes longer and its energy - which is inversely proportional to its wavelength - decreases. Consequently, even though there are many galaxies far from the Earth, they have large redshifts and their light does not carry much energy. A galaxy nearly at the cosmic particle horizon has a nearly infinite redshift, meaniing that the light we receive from that galaxy carries practically no energy at all. This decrease in photon energy because of the expansion of the universe decreases the brilliance of remote galaxies, helping make the night sky dark.
[end quote]
So, by your listing above, Kaufmann had it substantially right in his 1985 version of his text (I believe I have that copy at home to check with) and it is not likely that he changed the above significantly in this current edition. Maybe he did, and I will mention it in a future post if I do have the text in question.
> Historically, the reason that many people still believe the redshift > explains the dark night sky is because Olbers' paradox was rediscovered in > the 1950s--by steady state cosmologists. In the steady state cosmology, > the redshift DOES explain the dark night sky. But it is NOT the solution > in the big bang cosmology.
As to the claims of the steady state theorists. Remember, it was the steady state theorists who came up with the ideas of nucleosynthesis in stars, which turned out to free the big bang models of that time from the constraint of creating heavy elements beyond lithium and berylium. So, just because the ss theorists came up with redshift/diminishing energy of photons to explain dark skies doesn't mean the idea should be dismissed.
As I stated, the redshift due to expansion only contributes some of the whole, the finite age contributes the majority. And, as to absorption, I have not seen the numbers.
-- J. Scott Miller, Program Coordinator Scott.Mil...@louisville.edu Gheens Science Center and Rauch Planetarium http://www.louisville.edu/planetarium University of Louisville
J. Scott Miller <Scott.Mil...@louisville.edu> wrote in article <375E92B5.6CA4D...@louisville.edu>...
> Nice wrote:
> > The redshift IS irrelevant. If you converted every galaxy redshift into a > > blueshift of the same magnitude, the night sky would still be dark. An > > entire book has been written about Olbers' paradox and discusses wrong > > solutions (redshift, interstellar absorption, inability to perceive faint > > light, etc.) as well as the two correct solutions (finite age of the > > universe, lack of energy in the universe): DARKNESS AT NIGHT by Edward > > Harrison.
> So, just for arguement sake, this reference is to be believed while that of > other astronomers is not.
Harrison's book is devoted solely to Olbers' paradox, is written by the world's expert on Olbers' paradox--a man who has studied the problem for decades--and not surprisingly has the correct solutions to Olbers' paradox. Anyone with an interest in this subject should read the book, which is readable and nontechnical. Any good library should have it.
> > Historically, the reason that many people still believe the redshift > > explains the dark night sky is because Olbers' paradox was rediscovered in > > the 1950s--by steady state cosmologists. In the steady state cosmology, > > the redshift DOES explain the dark night sky. But it is NOT the solution > > in the big bang cosmology.
> As to the claims of the steady state theorists. Remember, it was the steady > state theorists who came up with the ideas of nucleosynthesis in stars, which > turned out to free the big bang models of that time from the constraint of > creating heavy elements beyond lithium and berylium. So, just because the ss > theorists came up with redshift/diminishing energy of photons to explain dark > skies doesn't mean the idea should be dismissed.
True. I'm just explaining why, even today, many people think the redshift explains the dark night sky: because, in the steady state cosmology, it DOES explain the dark night sky. (An aside: one steady state theorist--Fred Hoyle--did indeed come up with the idea of nucleosynthesis in stars, but he says the steady state cosmology did not motivate his work.)
> As I stated, the redshift due to expansion only contributes some of the whole, > the finite age contributes the majority. And, as to absorption, I have not > seen the numbers.
The redshift is irrelevant. It only contributes a factor of two or so. You need a factor of *trillions* to explain the dark night sky. The finite age of the universe and the lack of energy in the universe explain the darkness of the night sky. The redshift does not.
>>> Will someone please explain to me in (laymans terms) why with all the >>> billions and billions of stars in the universe, the sky at night between >>> the stars is still jet black. Of course I know nothing at all about the >>> universe, but it would seem to me with all those stars out there >>> emitting light, that the universe would be very bright instead of dark. >>> Is it because the universe is so large and distances are so great that >>> the light becomes so diffused and scattered, that by the time it >>> reaches us, only faint glimmers of light can be seen? I know this is a >>> dumb question but it is something that has always bugged me. >>> Thanks for your responses >>> Tom Hix
>> The short answer is two-fold: 1) The expansion of the universe redshifts >> light coming from objects at greater and greater distances from us, moving it >> into wavelength bands we cannot see, and 2) the universe is finite in age, so >> that there has been insufficient time for light to travel to us for objects at >> distances greater than about 12 to 13 billion lightyears. The latter is more >> to the point than the former.
> 1. is irrelevant. The redshift also shifts UV, X and gamma wavelengths > to visible light.
1. is not irrelevant, since the most luminous entities in the universe - the stars - emit mostly in UV, visible light, and IR. At 12-13 billion lightyears the redshift will be large enough to shift even the UV into IR, which is invisible to our eyes. At X-ray and Gamma wavelengths, the universe is a much fainter emitter.
> 2. is the true explanation.
Both 1. and 2. are the "true explanations", and they seem to controbute about equally much to the darkness of space.
-- ---------------------------------------------------------------- Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF) Grev Turegatan 40, S-114 38 Stockholm, SWEDEN e-mail: pau...@saaf.se paul.schly...@ausys.se p...@inorbit.com WWW: http://hotel04.ausys.se/pauschhttp://welcome.to/pausch
Does the lack of enough 'dust' particles (including water vapor) to reflect light in our eyes' direction count too? Coz I thought that's the reason the whole sky is bright during daytime, instead of just a superbright dot called the Sun and all else being dark.
Curiously, many nebulae glow becoz they reflect their star's light right?
> >>> Will someone please explain to me in (laymans terms) why with all the > >>> billions and billions of stars in the universe, the sky at night between > >>> the stars is still jet black. Of course I know nothing at all about the > >>> universe, but it would seem to me with all those stars out there > >>> emitting light, that the universe would be very bright instead of dark. > >>> Is it because the universe is so large and distances are so great that > >>> the light becomes so diffused and scattered, that by the time it > >>> reaches us, only faint glimmers of light can be seen? I know this is a > >>> dumb question but it is something that has always bugged me. > >>> Thanks for your responses > >>> Tom Hix
|
