| Topic: |
Science > Physics |
| User: |
"nyathancha" |
| Date: |
03 Nov 2003 10:07:52 PM |
| Object: |
Simple question |
Hi, I have a very simple, layman question for all you astrophysics gurus out
there.
From what I understand, the big bang created not just mass, but space and
time. before the big bang there wasn't even the 3 dimensional space that we
know and it came into existence after the big bang. And we know about big
bang, from the universal background microwave radiation. From what I
understand about UBM, the light or energy release during the big bang
travelled faster than the rate at which the universe was expanding, so the
microwave radiation is trapped and reflects around in the known universe.
(although I could be completely and fundamentally mistaken about the concept
of UBM).
So my question is, doesn't this indicate that the universe is finite? I
mean, if we accept the fact (or theory) that the universe is expanding, then
doesn't that immediately and inductively suggest that the universe is finite
and has an edge (or end). How could something that is infinite expand? and
doesn't the UBM prove that there is an end or edge to the universe as well?
If not, where is the radiation coming from. Isn't the assumption of a finite
universe inherent to the UBM theory?
Please clarify. Any links, suggested readings would also be much
appreciated.
-------------------
Engineer. Unashmed and unrepentant
.
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| User: "keith stein" |
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| Title: Re: Simple question - simple answer |
04 Nov 2003 08:51:40 AM |
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<nyathancha> wrote in message news:3fa72933$1@news.qut.edu.au...
Hi, I have a very simple, layman question for all you astrophysics gurus
out
there.
From what I understand, the big bang created not just mass, but space and
time. before the big bang there wasn't even the 3 dimensional space that
we
know and it came into existence after the big bang. And we know about big
bang, from the universal background microwave radiation. From what I
understand about UBM, the light or energy release during the big bang
travelled faster than the rate at which the universe was expanding, so the
microwave radiation is trapped and reflects around in the known universe.
(although I could be completely and fundamentally mistaken about the
concept
of UBM).
So my question is, doesn't this indicate that the universe is finite? I
mean, if we accept the fact (or theory) that the universe is expanding,
then
doesn't that immediately and inductively suggest that the universe is
finite
and has an edge (or end). How could something that is infinite expand? and
doesn't the UBM prove that there is an end or edge to the universe as
well?
If not, where is the radiation coming from. Isn't the assumption of a
finite
universe inherent to the UBM theory?
Please clarify. Any links, suggested readings would also be much
appreciated.
I suggest you read this little old essay of mine Mr. Nyathancha
THE BIG BANG MYTH
In the year 1600 a.d. a 52 year old Italian monk by the name
of Giordano Bruno was burnt at the stake. His heresy was to teach
that our Sun was just another star, in an infinite space. His last
words are reported to have been "Today you burn me, but in the
future all men will believe as I believe".
Fourty two years into the future Isaac Newton was born.
After a further forty two journeys of planet Earth around the sun
Isaac Newton published the Universal Theory of Gravitation. In
this he postulated that all bodies attract each other with a force
which is proportional the product of their masses, and inversely
proportional to the square of the distance between them. From this
Newton was able to give a complete account of the motion of
heavenly bodies and terrestrial apples.
An obvious objection to Newton's theory of Gravitation is
that if all bodies attract each other, how is it that all the
matter in the universe has not gathered together in one place?
Newton considered that this objection could be overcome if space
was infinite. In a letter to Richard Bently written in 1692 he
writes "..... if matter was evenly disposed throughout an infinite
space it would never convene into one mass; but some of it would
convene into one mass and some into another, so as to make an
infinite number of great masses scattered at great distances from
one another throughout all that infinite space."
Some hundred and thirty years later (1826) a serious
difficulty with Newton's "infinite space" was raised by Heinrich
Olbers. Olbers considered space divided up into spherical shells
of equal thickness, each centered on the earth. The volume of each
shell,and hence the number of stars it should contain, would
increase with the square of its radius. The light from any one
star should however decrease with the square of the radius. The
two effects therefore cancel, and the amount of starlight received
at the earth from each shell should be the same. If space is
truly infinite there would of course be an infinite number of such
shells, and we should expect to see an immense blaze of light
spread all over the sky. This became known as Olbers' Paradox,
and it was not resolved for another hundred years.
In the 1920's the American astronomer Edwin Hubble was
conducting the first systematic investigation into our neighboring
galaxies. Using a spectrometer to analyse the light emitted from
galaxies, Hubble was able to identify various elements present on
different galaxies. Hubble also noticed that the characteristic
line spectra of the elements were shifted somewhat from those
obtained in terrestrial measurements on the same elements. These
shifts were found to be usually to the red end of the spectrum,
and increased in magnitude with increasing distance from the
emitting galaxy.
Whatever the interpretation of the observed 'red shifts', it
should be noted that Hubble's observation leads to a satisfactory
resolution of Olbers' Paradox. A shift to the red end of the
spectrum corresponds to a decrease in the energy carried by the
light. The successive shells as proposed in Olbers treatment would
not therefore contribute equal amounts of energy, but rather each
would contribute decreasing energy as the distance from the earth
increased.
At the time when Hubble was studying galaxies, there was only
one known phenomena which could explain the sort of shifts in the
frequency which Hubble observed. This was the well understood
'Doppler Effect', which occurs with all wave phenomena when the
source is travelling with a velocity relative to the observer. If
the source is travelling away from the observer, measured
frequencies will be decreased, i.e. shifted to the red end of the
spectrum in just the way observed in Hubble's measurements.
Assuming therefore that the measured shifts in frequency were due
to the 'Doppler Effect',Hubble concluded that most of the galaxies
were rushing away from us, and further that the speed of recession
is directly proportional to the distance. (The distance to a
galaxy was not easy to measure, but could be estimated from
apparent brightness.)
If one accepts the velocity distribution of galaxies proposed
by Hubble in 1929, then one is led inevitably to the "Big Bang".
Projecting the position of the galaxies backwards in time, we find
that all the galaxies appear to have set out from one point in
space some 15 billion years ago. (Actually Hubble's data yielded a
value of only about 1 billion years, an embarrassingly short time
as some rocks in the earths crust are thought to be older than
this, but revision of Hubble's distance measurements by later
astronomers have led to the more acceptable value given here).
In 1994 the Big Bang theory is virtually dogma. Cosmologists
work with particle physicists and mathematicians to develop
theories of the evolution of the universe from the first instant
of creation to the present day. The flavour of these exotic
theories may be gleaned from the following extract from Riordan
and Schramm's book -"The Shadows of Creation"
'At the very beginning of time, the hypothetical Theory of
Everything breaks down into gravity and the GUT's force. This
transition comes at about 10^-43 second, when the temperature is a
truly blistering 10^55 degrees - corresponding to an average
particle energy of 10^19 GeV. In other words, every particle has
the kinetic energy of a Lear jet! Next come the GUT's phase
transition at about 10^-34 second, and following that is the
electroweak transition about 10^-12 second later. By this time
the temperature has fallen to a mere 10^15 degrees, or a few
billion electron volts per particle. Finally, at about 1
microsecond after creation, the hot plasma of quarks and gluons
freezes into a sea of protons and neutrons that shortly thereafter
enters the era of nucleosynthesis.'
The big bang theory is not of course man's first attempt at
determining the age of the universe. In 1654 for example the
Irish divine James Ussher determined that creation had occurred at
9 a.m. on Tuesday, 26th October, 4004 B.C. In my opinion
contemporary estimates based on Big Bang theory are unlikely to
prove any more durable than that proposed by the Rev. Ussher on
the basis of biblical chronology.
Looking out from planet Earth we are privileged not just with
a view of the immensity of space, but also with the immensity of
time. Due to the finite velocity of light, we know that as we
look further out in space so we are looking further back in time.
A telescope is therefore a sort of time machine with which we can
view the history of the universe. If the universe is evolving as
proposed in Big Bang theory, then the evidence for it should be
directly observable in our telescopes. For example if the density
of the universe is decreasing with time, then we should expect to
see density increase as we look further out into space.
Similarly, as the universe is fueled by Hydrogen, we might expect
to see the proportion of Hydrogen in the cosmos appear to
increase as we look out from the earth. Nowhere have I read that
either of these trends is actually found. On the contrary, most
astronomers comment on the uniformity of the observed cosmos.
The detection of the 2.73 K background radiation is often
claimed as a success for the Big Bang theory, but if this
radiation comes from the edge of the observable universe, 15
billion light years away, then it must have set out from there
15 billion years ago. In other words the radius of the universe
was 15 billion light years at the very time that the universe was
supposed to be compressed to a singularity.
On the subject of the background radiation Riordan and
Schramm write the following:-
'It was the detection of this radiation in 1964 that set the
stage for modern Big Bang cosmology.... When the Universe was
still a hot plasma at the 100,000 year mark, its temperature was
roughly the same as the surface of the Sun today. As a single
continuous body at this one temperature, it radiated profusely in
the same range of optical wavelengths. Just before escaping from
matter, this radiation was predominantly composed of visible and
shorter wavelength ultraviolet light. After breaking free,
however, the radiation could not leave the Universe, which
contains everything that exists. The remnants of this radiation
therefore must still be around today.'
It is not obvious why Big Bang cosmology should attribute the
background radiation to an original temperature only a few
thousand degrees, rather than the 'blistering 10^55 degrees'
mentioned earlier. However if the background radiation actually
does come from very distant stars then the connection with a
temperature 'roughly the same as the surface of the Sun', would be
readily understandable. It seems to me therefore, that the
background radiation is more naturally explained as the remnant of
Olbers' radiation, rather than as a remnant of the Big Bang.
Yet another difficulty for advocates of the Big Bang comes
from our ability to measure our velocity relative to the
background radiation. Measurements of the "dipole variation" made
in 1991 indicate that the Milky Way is moving through the
background radiation with a velocity of 600 kilometers per second.
Although this may appear a large velocity, it is negligible
compared to the speed of light(i.e.300,000 kilometers per second).
If the measured red shifts are due to the Doppler Effect ,then
most galaxies have velocities which are an appreciable fraction of
the speed of light relative to us. If the background radiation is
uniform, then the galaxies must also have high velocities through
the background radiation. Thus our own galaxy would be in a
privileged position i.e. almost stationary at the center of the
Universe. Such a proposition, while not impossible, is highly
improbable and has been rejected by all serious cosmologists since
the ill fated Giordano Bruno.
If the systematic red shifts first announced by Hubble in
1929 are not due to the Doppler Effect then they must be caused by
some other phenomenon. In 1960 Pound and Rebka performed
experiments which demonstrated that the measured frequency of
electromagnetic radiation decreases as the detector is moved up
through a gravitational field. The similarity of gravitational
frequency shifts and Doppler shifts is nicely illustrated in these
experiments, because their experiments involved compensating the
gravitation shift with an exactly equivalent Doppler shift,
produced by moving the emitter relative to the receiver. These
experiments confirmed Einstein's prediction that the fractional
change in frequency is equal to the change in gravitational
potential divided by the square of the velocity of light.
The gravitational potential at the center of a sphere of
radius R and density d is equal to -2PiGdR^2 ,where G is Newton's
Gravitational Constant ( = 6.67 * 10^-11 mks units). (The
gravitation potential is obtained by integrating the work done in
taking unit mass from the center of the sphere to infinity.) Now
the radius of the Universe is about 15 billion light years ( = 1.5
* 10^26 m) and the density is about 10^-26 kilograms per cubic
meter. Substituting these values in the expression for the
gravitational potential we find that the gravitational potential
at the center of our Universe is almost exactly equal to the
square of the velocity of light ( = 9 * 10^16 m^2/s^2). Therefore
the fraction change in frequency which could be induced by the
gravitational effects of our universe is almost exactly equal to
unity.
In order to use gravitational red shifts to explain the
Hubble red shifts it is necessary to assume that every galaxy
emmits light as if it were at the center of the universe. On this
assumption the gravitational frequency shifts would always be to
the red end, and the maximum red shift (for a sphere of the size
and density of our universe) would be exactly 100% as observed.
I would assume that the 15 billion light year figure for the
radius of the universe is in fact only a limit on the observable
universe, and there is no reason to assume that space is not
infinite, as proposed by Newton in 1692.
keith stein
.
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| User: "Greg Neill" |
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| Title: Re: Simple question |
04 Nov 2003 08:55:39 AM |
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<nyathancha> wrote in message news:3fa72933$1@news.qut.edu.au...
Hi, I have a very simple, layman question for all you astrophysics gurus
out
there.
From what I understand, the big bang created not just mass, but space and
time. before the big bang there wasn't even the 3 dimensional space that
we
know and it came into existence after the big bang. And we know about big
bang, from the universal background microwave radiation. From what I
understand about UBM, the light or energy release during the big bang
travelled faster than the rate at which the universe was expanding, so the
microwave radiation is trapped and reflects around in the known universe.
(although I could be completely and fundamentally mistaken about the
concept
of UBM).
Actually, space expanded much faster than light. But the
radiation that is the Cosmic Microwave Background Radiation
(CMBR, your UBM) was created along with space, everywhere,
at the instant of creation. So what we're seeing is the
radiation coming from all directions.
So my question is, doesn't this indicate that the universe is finite? I
mean, if we accept the fact (or theory) that the universe is expanding,
then
doesn't that immediately and inductively suggest that the universe is
finite
and has an edge (or end). How could something that is infinite expand? and
doesn't the UBM prove that there is an end or edge to the universe as
well?
If not, where is the radiation coming from. Isn't the assumption of a
finite
universe inherent to the UBM theory?
If the universe has a finite age (i.e. a beginning as in the
Big Bang theory) and it has a strictly Euclidean geometry,
that it would be finite but expanding and would have a
growing (but unreachable) boundary. Or, the topology may be
such that it is closed but unbounded (like the surface of a
sphere), or open and unbounded. It may be embedded in a higher
dimensions and have who-knows-what shape.
You might want to search out Ned Wright's Cosmology
Tutorial on the web.
.
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| User: "nyathancha" |
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| Title: Re: Simple question |
04 Nov 2003 07:02:49 PM |
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Actually, space expanded much faster than light. But the
radiation that is the Cosmic Microwave Background Radiation
(CMBR, your UBM) was created along with space, everywhere,
at the instant of creation. So what we're seeing is the
radiation coming from all directions.
Hmmm... this is the aspect of CMBR or UBM that still confuses me a bit.
Assuming space expanded faster than light, so we don't have to worry about
light reaching the end of the universe and not having anywhere to go.
although if i am not mistaken thats what keith stein's article seems to
imply "After breaking free, however, the radiation could not leave the
Universe, which contains everything that exists.", this is something i heard
a lot in connection with CMBR, that light "had nowhere to go", which i
thought was the explanation for the CMBR.
But anyway, if we accept for now that space did expand faster than light, as
you say, then how does radiation come from "all directions"? wouldn't we
only see the radiation from the direction where the big bang happened? the
essential "center" of the universe? How can we measure any radiation thats
already passed us (in our shadow so to speak). The picture I have in my mind
is an expanding sphere. The earth (or the position where the earth would be)
is a small marble inside the sphere. In your version, there is radiation,
which is another sphere inside this sphere which is also expanding. so the
outer sphere is space and the inner sphere is radiation and the earth is a
marble inside this inner sphere. so if the inner sphere is expanding "in the
direction" of the outer sphere, how can we measure the radiation thats
between us and the edge of the sphere?
.
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| User: "Greg Neill" |
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| Title: Re: Simple question |
04 Nov 2003 09:47:00 PM |
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<nyathancha> wrote in message news:3fa84c39$1@news.qut.edu.au...
Hmmm... this is the aspect of CMBR or UBM that still confuses me a bit.
Assuming space expanded faster than light, so we don't have to worry about
light reaching the end of the universe and not having anywhere to go.
although if i am not mistaken thats what keith stein's article seems to
imply "After breaking free, however, the radiation could not leave the
Universe, which contains everything that exists.", this is something i heard
a lot in connection with CMBR, that light "had nowhere to go", which i
thought was the explanation for the CMBR.
But anyway, if we accept for now that space did expand faster than light, as
you say, then how does radiation come from "all directions"? wouldn't we
only see the radiation from the direction where the big bang happened? the
essential "center" of the universe? How can we measure any radiation thats
already passed us (in our shadow so to speak). The picture I have in my mind
is an expanding sphere. The earth (or the position where the earth would be)
is a small marble inside the sphere. In your version, there is radiation,
which is another sphere inside this sphere which is also expanding. so the
outer sphere is space and the inner sphere is radiation and the earth is a
marble inside this inner sphere. so if the inner sphere is expanding "in the
direction" of the outer sphere, how can we measure the radiation thats
between us and the edge of the sphere?
The big bang was not an explosion inside a pre-existing
space. So your concept of "essential "center"" is not
right. The big bang created all matter and all space,
all at once, everywhere. It's just that "everywhere"
at the beginning occupied a much smaller volume than it
does now. So the radiation that is the CMBR was created
and eventually released (disentangled from the particle
soup) everywhere at once. When space expanded, it carried
along the radiation with it -- even though the expansion
was at a rate faster than light, the light embedded in
space was carried along with its local patch of space.
So the early universe was literally filled with light, and
it is this light, still travelling to us from remote
regions, that we see as the CMBR. Note that it is greatly
red-shifted in frequency from when it was originally
released. This is due to its wavelength having stretched
as the space it has travelled through stretched.
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| User: "nyathancha" |
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| Title: Re: Simple question |
07 Nov 2003 02:29:57 AM |
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The big bang was not an explosion inside a pre-existing
space. So your concept of "essential "center"" is not
right. The big bang created all matter and all space,
all at once, everywhere. It's just that "everywhere"
at the beginning occupied a much smaller volume than it
does now.
Ok, that makes it much more clear. Yeah, I knew that big bang created both
space and matter, as I wrote in my original post, but the missing piece of
information was this line "When space expanded, it carried along the
radiation with it ". that was the missing piece of the puzzle that finally
made the penny drop. The updated analogy I now have in my head is that of a
single expanding sphere (instead of two). its just that one of the old
spheres (the inner one, radiation) is "embedded" so to speak in the outer
sphere. its not independent of it.
Now I have another question, or should I say objection, raised in kieth
stein's article, in a different branch of this thread. And that is, "what
point in time do we take as a reference for the initial radiation?".
Basically, how long after the big bang do we assume the CMBR we are
observing today was released. If I understood his article correctly, we seem
to be assuming that around the 100,000 year mark the radiation broke free of
the matter. But why do we choose this mark (and subsequently the temprature
at this mark) instead of some other time (and some other temprature/
radiation wavelength)?
If we assume as you said that ""everywhere" at the beginning occupied a
much smaller volume than it does now.", then we could go all the way back to
10^-54 (or any arbitrary number) seconds into the big bang when the energies
in the universe were extremely intense and hence the wavelength was much
smaller (?).
or is this because since space is expanding faster than the speed of light,
the frequencies present at the earlier time period have been carried to a
farther distance than the frequencies present in the later time periods?
does this mean as time goes by, we will see a change in the observed
frequencies of the CMBR as the radiation from the farther reaches of the
universe (and earlier times of the big bang) reach us?
PS: Keith Steins article also seems to imply that the universe did NOT
expand faster than the speed of light. He quotes Riordan and Schramm as
"After breaking free, however, the radiation could not leave the Universe,
which contains everything that exists.". Is he wrong or am I missing
something or mis-interpreting the article completely. I would appreciate if
anyone, including Mr.Stein, could clarify this.
.
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| User: "Greg Neill" |
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| Title: Re: Simple question |
07 Nov 2003 06:56:08 AM |
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<nyathancha> wrote in message news:3fab5805$1@news.qut.edu.au...
Now I have another question, or should I say objection, raised in kieth
stein's article, in a different branch of this thread. And that is, "what
point in time do we take as a reference for the initial radiation?".
Basically, how long after the big bang do we assume the CMBR we are
observing today was released. If I understood his article correctly, we seem
to be assuming that around the 100,000 year mark the radiation broke free of
the matter. But why do we choose this mark (and subsequently the temprature
at this mark) instead of some other time (and some other temprature/
radiation wavelength)?
At about 3000K hydrogen recombination can occur; the plasma
of free electrons and protons can combine to form a neutral
gas. So this is when the universe first becomes transparent
and light can travel freely.
If we assume as you said that ""everywhere" at the beginning occupied a
much smaller volume than it does now.", then we could go all the way back to
10^-54 (or any arbitrary number) seconds into the big bang when the energies
in the universe were extremely intense and hence the wavelength was much
smaller (?).
Yes, the peak for the energy distribution among wavelengths
would be at a much higher frequency.
or is this because since space is expanding faster than the speed of light,
the frequencies present at the earlier time period have been carried to a
farther distance than the frequencies present in the later time periods?
does this mean as time goes by, we will see a change in the observed
frequencies of the CMBR as the radiation from the farther reaches of the
universe (and earlier times of the big bang) reach us?
When the radiation decoupled, all frequencies were present
everywhere with a distribution like that of a black body
of 3000K, the temperature at which the decoupling occurred.
When we look out now, we see the same light distributed like
a black body of about 2.7K. This is because all of the
wavelengths of light have stretched along with the universe
in the intervening time.
PS: Keith Steins article also seems to imply that the universe did NOT
expand faster than the speed of light. He quotes Riordan and Schramm as
"After breaking free, however, the radiation could not leave the Universe,
which contains everything that exists.". Is he wrong or am I missing
something or mis-interpreting the article completely. I would appreciate if
anyone, including Mr.Stein, could clarify this.
Mr. Stein's ideas are often at odds with the mainstream.
.
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| User: "nyathancha" |
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| Title: Re: Simple question |
11 Nov 2003 12:43:12 AM |
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At about 3000K hydrogen recombination can occur; the plasma
of free electrons and protons can combine to form a neutral
gas. So this is when the universe first becomes transparent
and light can travel freely.
Right. Gottcha....
Yes, the peak for the energy distribution among wavelengths
would be at a much higher frequency.
When the radiation decoupled, all frequencies were present
everywhere with a distribution like that of a black body
of 3000K, the temperature at which the decoupling occurred.
When we look out now, we see the same light distributed like
a black body of about 2.7K. This is because all of the
wavelengths of light have stretched along with the universe
in the intervening time.
Ok, I don't know much about black body radiation. But why 2.7K though? I
mean if the radiation decoupled at 3000K, even after a bit of red shift,
wouldn't it be closer to 3000K than 2.7K, which is a few orders of magnitude
difference? (I might be missing some concept of black body radiation here).
If I understand you correctly, and please indicate whether I do, the CMBR
actually contains the whole gamut of frequencies (including the visible
part). And the energy distribution among these frequencies is the same as
the energy distribution among the frequencies of a black body at a
temperature of 2.7K. I am assuming that this distribution has very small
energy in the visible part of the spectrum as we cannot actually see the
CMBR. Is this correct?
Also, as the universe cooled down, the energy distribution of the radiation
would change as well. So as time progresses, would we see a change in the
CMBR, as we start recieving the radiation from when the universe was hotter
and thus had the energy distribution of a hotter body (with the max being
3000K as you said). or is it that we would see energy distributions of all
possibilities from the current temprature to max of 3000K and the 2.7K is
just the energy distribution of the current radiation reaching us, from back
when the universe was actually 2.7K?
Just thought of another thing. If space is expanding faster than the speed
of light (carrying the radiation with it), how come we see any radiation at
all? wouldn't it always be carried away from us, never being able to reach
us? the picture I have in my mind is a travelator going in one direction at
a certain speed and a person standing on the travellator going the opposite
direction at a slower speed. The person would never reach the end of the
travellator.
Thank you for the prompt replies. This has been a very illuminating
discussion for me
.
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| User: "Greg Neill" |
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| Title: Re: Simple question |
11 Nov 2003 09:08:14 AM |
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<nyathancha> wrote in message news:3fb08500$1@news.qut.edu.au...
At about 3000K hydrogen recombination can occur; the plasma
of free electrons and protons can combine to form a neutral
gas. So this is when the universe first becomes transparent
and light can travel freely.
Right. Gottcha....
Yes, the peak for the energy distribution among wavelengths
would be at a much higher frequency.
When the radiation decoupled, all frequencies were present
everywhere with a distribution like that of a black body
of 3000K, the temperature at which the decoupling occurred.
When we look out now, we see the same light distributed like
a black body of about 2.7K. This is because all of the
wavelengths of light have stretched along with the universe
in the intervening time.
Ok, I don't know much about black body radiation. But why 2.7K though? I
mean if the radiation decoupled at 3000K, even after a bit of red shift,
wouldn't it be closer to 3000K than 2.7K, which is a few orders of
magnitude
difference? (I might be missing some concept of black body radiation
here).
If I understand you correctly, and please indicate whether I do, the CMBR
actually contains the whole gamut of frequencies (including the visible
part). And the energy distribution among these frequencies is the same as
the energy distribution among the frequencies of a black body at a
temperature of 2.7K. I am assuming that this distribution has very small
energy in the visible part of the spectrum as we cannot actually see the
CMBR. Is this correct?
The 2.7K value just happens to be the temperature now, after
the cooling that has occurred due to expansion over the age
of the universe. It was hotter before, and will be cooler in
the future.
There is very little energy in the visible part of the spectrum.
The peak is in the microwave region.
Also, as the universe cooled down, the energy distribution of the
radiation
would change as well. So as time progresses, would we see a change in the
CMBR, as we start recieving the radiation from when the universe was
hotter
and thus had the energy distribution of a hotter body (with the max being
3000K as you said). or is it that we would see energy distributions of all
possibilities from the current temprature to max of 3000K and the 2.7K is
just the energy distribution of the current radiation reaching us, from
back
when the universe was actually 2.7K?
All freqencies comprising the 3000K black body spectrum were
stretched by the same amount, corresponding to what is called
the scale factor of the universe's size. So what we're seeing
is the radiation from the original 3000K spectrum.
Just thought of another thing. If space is expanding faster than the speed
of light (carrying the radiation with it), how come we see any radiation
at
all? wouldn't it always be carried away from us, never being able to reach
us? the picture I have in my mind is a travelator going in one direction
at
a certain speed and a person standing on the travellator going the
opposite
direction at a slower speed. The person would never reach the end of the
travellator.
The recession rate goes up with distance. Remote areas are
separating at a rate that is greater than c. These areas
we cannot see and cannot receive radiation from.
Think of the simple linear analogy of a stretching rubber
band. Mark several equally spaced points along its length
and then begin stretching the band at a uniform rate.
Marks that are next to each other will spearate more slowly
than marks that are far appart.
Thank you for the prompt replies. This has been a very illuminating
discussion for me
Cheers.
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| User: "Pettrik Steig" |
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| Title: Re: Simple question |
24 Nov 2003 01:12:08 PM |
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hi nyathancha,
think of the 2D-surface of an air-balloon as a representation of the
4D-spacetime. if you blow air in the balloon, the surface grows. that
means, the universe is expanding. the surface of the ballon hasnīt an
edge or border, but it is finite.
greets, Pettrik
nyathancha schrieb:
Hi, I have a very simple, layman question for all you astrophysics gurus out
there.
From what I understand, the big bang created not just mass, but space and
time. before the big bang there wasn't even the 3 dimensional space that we
know and it came into existence after the big bang. And we know about big
bang, from the universal background microwave radiation. From what I
understand about UBM, the light or energy release during the big bang
travelled faster than the rate at which the universe was expanding, so the
microwave radiation is trapped and reflects around in the known universe.
(although I could be completely and fundamentally mistaken about the concept
of UBM).
So my question is, doesn't this indicate that the universe is finite? I
mean, if we accept the fact (or theory) that the universe is expanding, then
doesn't that immediately and inductively suggest that the universe is finite
and has an edge (or end). How could something that is infinite expand? and
doesn't the UBM prove that there is an end or edge to the universe as well?
If not, where is the radiation coming from. Isn't the assumption of a finite
universe inherent to the UBM theory?
Please clarify. Any links, suggested readings would also be much
appreciated.
-------------------
Engineer. Unashmed and unrepentant
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