Is the H.U.D.F. view in excess of 13 bly's. or not.

  • Thread starter Peter Watkins
  • Start date
In summary, N.A.S.A. has stated that the Hubble Ultra Deep Field view takes us within 800 million years of the Big Bang, with the possibility of seeing objects within 400 million years, indicating that the most distant objects seen in the HUDF view are at a distance of approximately 13 billion light years from us. This suggests that we are looking at this region as it was over 13 billion years ago when the light from these objects first began its journey towards us.
  • #1
Peter Watkins
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Regardless of whether the universe expanded by swelling, ballistic motion, expanding space, vacuum energy or reversed gravity, is it the case that the most distant objects seen in the Hubble Ultra Deep field view, (hubblesite.org), are at a distance in excess of 13 billion light years from us, as stated by N.A.S.A.? If so, are we looking at this region as it was something over 13 billion years ago?
 
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  • #2
Peter Watkins said:
Regardless of whether the universe expanded by swelling, ballistic motion, expanding space, vacuum energy or reversed gravity,

You cannot disregard all of these things to measure the distance to, or the age of the light emitted by, the galaxies in the HUDF using redshift alone which, since you haven't given a direct link to any article, I can only assume is what is used. Therefore, you cannot answer these questions

Peter Watkins said:
is it the case that the most distant objects seen in the Hubble Ultra Deep field view, (hubblesite.org), are at a distance in excess of 13 billion light years from us, as stated by N.A.S.A.? If so, are we looking at this region as it was something over 13 billion years ago?

with your constraints.
 
  • #3
Peter Watkins said:
...is it the case that the most distant objects seen in the Hubble Ultra Deep field view, (hubblesite.org), are at a distance in excess of 13 billion light years from us, as stated by N.A.S.A.?...

First off, I think Matt's replies are right on target.

Just to mention one point, we would need a link to exactly what you are quoting simply to tell what kind of distance they mean. There's light travel time. That often gets used as a measure of distance in popular science journalism and outreach writing for wide audience. Treating light travel time as a measure of distance is somewhat of a concession to the audience.
It is not the distance measure you'd normally find used in a journal article.

Maybe you would like to try an online calculator that converts travel time to redshift (readily convertible to comoving distance)
http://www.astro.ucla.edu/~wright/DlttCalc.html
It's easy, just put in 13 billion years and you get that z=7.87 and that the actual present-day distance is 29.7 billion lightyears.
(press the "general" button, he already has standard model parameters put in as the default.)

===============================
I've been assuming that when you mentioned 13 billion, that was light travel time. If the article actually said that some object in the picture was currently at a distance of 13 billion lightyears (that would be the today distance, the comoving distance) then that means the light travel time would be considerably less. this calculator can help us find out:

Put in a light travel time of 8.8----8.8 billion years---and again press "general". It will tell you that the today distance is 13.1 billion lightyears.
And the redshift is z = 1.27. So if we see a galaxy with redshift 1.27 and the light has taken 8.8 billion years to get here, that means that the present distance to the galaxy is about 13 billion lightyears.

Ask more questions if any of this is puzzling.
 
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  • #4
I'm sorry, my brain is going. What I meant to ask is whether those objects were at a distance of some 13 bly's. at the time that the light from them that is reaching us now, left there? I realize that expansion, or collapse, has continued during the intervening years. N.A.S.A. states that the H.U.D.F. takes us to within 800million years of the big bang, with a possibility, (at that time), of seeing objects that are within 400million years, hence the 13bly question.
You imply that light years as a distance measure is a sop to the masses. We've always been told that we see the object as it was at the time that the light left. Which is logical. If the light traveled for ten years, then surely we see it as it was ten years earlier, where it was ten years earlier, and at a distance of 10 light years.
 
  • #5
Peter Watkins said:
You imply that light years as a distance measure is a sop to the masses...
:biggrin: I hope not, Peter! I use lightyears as a preferred distance unit myself, and it's not a concession to anything or anybody!

In cosmology, expansion effects are important, so light travel time is not convenient as a measure of distance. It doesn't work in the Hubble law, for example (a proportion relating distance and the rate distance is increasing.)

The distance measure that works in the Hubble law is called the comoving distance. It is the actual distance measured today as it would be determined by a network of observers at rest with respect to the expansion process (for practical purposes "comoving" observers are those at rest wrt the CMB). You can think of it as the instantaneous today distance to the object.

It is not proportional to the light travel time. There is no simple correspondence. Light travel time is a very clumsy measure of distance, because distances have expanded at widely differing rates in the past. The light travel time is influenced by the whole history of expansion that went on while the light was in transit. So it isn't a good intuitive geometric ruler. Instead people commonly use the today distance----or the corresponding proper distance at some specified moment back then.
 
  • #6
N.A.S.A. states that the H.U.D.F. takes us to within 800million years of the big bang,..

Matt O. and I both suggested you to give the link. It's easy to misinterpret what one reads or to overlook some key detail. For that reason it's safer and more efficient to give links so we can all be looking at the same page. We are all less likely to make mistakes then.

Assuming your paraphrase is right, though, the light travel time from the most distant object in the picture should be roughly 13.0 billion years.
(Because the age of expansion is about 13.8, the deepfield view goes back to 0.8, so the difference is 13.0.)

Look back at post #3 which says how far away those objects are. Their distance today is 29.7 billion lightyears. And their redshift is z = 7.87.

Peter Watkins said:
... What I meant to ask is whether those objects were at a distance of some 13 bly's. at the time that the light from them that is reaching us now, left there? I realize that expansion, or collapse, has continued during the intervening years.

The answer to your question is NO. You are talking about the most distant objects in the field, which emitted the light when expansion was only 0.8 billion years old, and whose light has taken 13.0 billion years in transit.
You want to know how far those objects were back then.

For that, go to Wright's usual cosmo calculator
http://www.astro.ucla.edu/~wright/CosmoCalc.html
and put in the redshift z = 7.87
You will get that the angular size distance (essentially the distance back then when the light was emitted) is 3.35 billion lightyears. We can round it off to 3.3 so as not to seem too precise.

========================
Actually a quicker way to get the same answer---3.35 billion lightyears---is just a one-stop trip to this calculator:
http://www.astro.ucla.edu/~wright/DlttCalc.html
where you put in 13 for the travel time and press general and it tells you that the angularsize distance is 3.35 billion lightyears.
Sorry, I took the long way round because I didn't register at first that what you wanted was the distance from us back then when the light was emitted---or rather the distance of that object from the matter that eventually became the solar system and us.
========================

Another calculator you might like to try
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html
On the left there are boxes for matter density, cosmological constant, Hubble rate, and redshift.
Type in .27, .73, 71, and 7.87, and press calculate.

It will tell you light travel time 13 billion years, distance then 3.3 billion lightyears, distance now 29.7 billion lightyears. It will also tell you recession speeds then and now.
 
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  • #7
Thank you for your replies. I have no particular interest in where these galaxies are today, it is where they were then that is of interest. In reply #6 Marcus concedes that that the distance from where we are now to the position that the light emanated from, is indeed some 13 bly's. Which takes me to a separate question posted earlier regarding the size of the early universe. If the light that can be seen to have come from two galaxies, each were in the opposite direction from the other, and each were at a distance of 12bly's from where we now are at the time that the light departed, then that can only mean that 12by's ago, the, (visible to us), universe had a spread of 24bly's. How is this possible in a universe that is "only" 13.7 by's old?
Also, in your email reply you state that light travel time is influenced by a whole history of varying rates of expansion expansion whilst the light was in transit. Elsewhere I also read of "tired" light or light that is losing it's energy. Does this mean that light speed is inconstant and that Einstein was wrong regarding the constancy of light speed in a vacuum?
 
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  • #8
Marcus, any response to the above reply?
 
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  • #9
Your reply to Marcus said:
Peter Watkins said:
In reply #6 Marcus concedes that that the distance from where we are now to the position that the light emanated from, is indeed some 13 bly's.

If Marcus will pardon the interference, he did not say what you stated, but rather that the light travel time was some 13 by. Light travel time has little to do with the distance that those objects were from us when the light left them. The cosmo calculators give their "then distance" from us as 3.34 bly. The cosmos has expanded in the meantime, hence light took quite a bit longer...
 
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  • #10
Hi Jorrie! Glad to see you. Don't you have your own cosmo calculator at your website, or am I mistaking?
And/or some cosmo tutorial pages?
If you do, how about posting a link (or PM if you prefer)?

I was awfully busy yesterday and didn't see PeterW's post. Glad you jumped in. Don't ever stand on ceremony in a case like that:cool:
 
  • #11
marcus said:
Don't you have your own cosmo calculator at your website, or am I mistaking?
And/or some cosmo tutorial pages?

Hi Marcus. No, I have only spreadsheet versions, but in a minor way I "collaborated" with http://www.geocities.com/alschairn/cc_e.htm". It does particularly well up to (hypothetically) high redshifts of about one million or so. IMO, The Wright and Morgan calculators are equally good (and simpler to understand) for real measured redshifts up to ~1100, where radiation density plays a minor role.

As for a tutorial - well, no, not quite. Methinks your "https://www.physicsforums.com/showthread.php?t=261161"" thread does an excellent job! It has become a bit long and unwieldy, so perhaps a separate thread to summarize the salient points may be a good idea.

-J
 
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  • #12
Thank you gentlemen. As it is unlikely that any PF contributor would raise his head above the parapet, tread on the hallowed ground that is Einstein, and state that the speed of light in a vacuum is not constant, Can I safely assume that the light from the galaxies, as configured in box #7 above, each had a travel time of 12 by's in order to reach here, now, at this place that we currently occupy, in 2009, and that 12 by's of light travel time translates into 12 bly's of distance? And that this in turn means that that particular piece of the universe had a spread of 24 bly's when the universe was approx 1.7 by's old?
Just checking out your balloon analogy, (Marcus), and I do realize that the space between ourselves the aforementiond galaxies has increased, or expanded, since the light left them.
 
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  • #13
Peter Watkins said:
Can I safely assume that ...12 by's of light travel time translates into 12 bly's of distance?

Nope. Sorry Peter you are still confused. Because light has a constant instantaneous local speed, there is no simple way to translate a large scale travel time into a large scale distance between sender and receiver.

Obviously, because after the light has traveled between two points along its way, the distance between those two can increase. So the light will be further from its source than it could have traveled on its own (without the help of distance expansion.)

So you cannot simply translate 12 billionyears of travel time into 12 billionyears of distance from source.

You should watch the balloon model animated film
You will see photons of light (pictured as little wigglers) traveling across the face of the balloon always at the same speed of about 1 millimeter per second. And if you pay close attention you will see that due to expansion each little wiggler manages to get much farther away from its source than it would be able to on its own, unaided by the changing geometry.

Google "wright balloon model" and see if it helps you think along slightly different lines.

Here
http://www.astro.ucla.edu/~wright/Balloon2.html

Try not to think only with words, because our ordinary language has the assumption of static geometry built into the words themselves. In nature, geometry is not static, so the words themselves can obstruct assimilation.

The white spiral whirlygigs are galaxies and the wrigglers that gradually lengthen wavelength and change color are photons.
 
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  • #14
marcus said:
Nope. Sorry Peter you are still confused...
Try not to think only with words, because our ordinary language has the assumption of static geometry built into the words themselves. In nature, geometry is not static, so the words themselves can obstruct assimilation...

Yes, this is a great source of confusion. Well put, Marcus.

In my opinion the frequent use of the words "is" and "are" by all and sundry also confuses, because cosmologists use them having, in the back of their minds, (and with a great deal of observational justification!) an Einsteinian-based, General Relativistic MODEL of the universe, that the calculators Marcus has referred express.

Wheras you, Peter, probably have your own rather different ideas about "distance" in the back of your mind, based on everyday experiences with rulers, radar and perspective.

But, on the scale of the universe, "distance" is a fanciful concept impossible for us to actually measure. For example even the "network of users" referred to by Marcus earlier is a purely imaginary idea, impossible to actually implement, but useful in that it allows us to project our local ideas of "distance" (rather dangerously, I think) onto the cosmic scene.

Astronomers have a better practice. They don't talk much about distances, light years etc, but just classify far-away objects with the measurable quantity z, which tells how big their redshift is. This can be related by well-established theory and modelling to make quantitative the the concept of remoteness.

Another confusing feature of the universe is that it is in practice impossible to be sure when far-apart events occur "now", or are even separated by a defined time. Cosmologists define a model-dependent "universal time" to do this, which as far as I can figure out could in practice best be measured locally (to modest accuracy relative to cosmic time-spans) only from the temperature of the locally observed cosmic background radiation, making (quite reasonable) assumptions about the origin of this radiation.
 
  • #15
oldman said:
... "universal time" to do this, which as far as I can figure out could in practice best be measured locally (to modest accuracy relative to cosmic time-spans) only from the temperature of the locally observed cosmic background radiation, making (quite reasonable) assumptions about the origin of this radiation.
Yes, that is an excellent way to observe the universal time! Each person in the cosmos is given a free standard time-piece, all the clocks having been started at the same moment (about 380,000 years into the expansion) when the medium filling space cooled enough to become transparent.
It's very democratic----one standard issue clock, pre-set and free of charge. :biggrin:
Just provide your own thermometer.===============
notice however that the deeper you are in a gravity well, the hotter the CMB becomes as it falls in. So your clock runs slower. People outside the well see a cooler therefore older universe. You see a hotter therefore younger. It's just a small correction. Something a time specialist could probably explain how to adjust for :biggrin:
===============

oldman said:
classify far-away objects with the measurable quantity z, which tells how big their redshift is. This can be related by well-established theory and modelling to make quantitative the the concept of remoteness.

Remoteness, that is the distance I was talking about. In other words distance can be calculated from redshift z by well-established theory and modeling. Making a definite idea of distance (the distance basic to stating and applying Hubble law) quantitative, as you say.

But I don't agree with your tone. Cepheid distance to the Virgo Cluster is not "fanciful" even tho not practical to measure by radar. All measures of distance outside the solar system involve some type of inference. They are all steps on the astronomers ladder of distance definitions. It serves little purpose to call them "fanciful."

I hope you are not intentionally giving the impression that because astronomers make use of redshift they do not use distance. Redshift is directly measured and used in galaxy catalogs---it is a useful auxilliary, but it does not replace distance at the equation level or in any fundamental sense. Astronomers constantly make essential use of several interrelated distance concepts---brightness distance, angular size distance, proper distance and so on.
 
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  • #16
oldman said:
Astronomers have a better practice. They don't talk much about distances,..



You shock me, oldman. A central effort throughout the last century was determining how far away things were. Distance has been a major obsession of astronomers. Constructing the successive rungs of the distance ladder. Determining various standard candles.

Great ingenuity has gone into this. What you say is categorically false. It would be more accurate to say that a good many of them talk almost non-stop about distance.

Off course the catalogs list redshift---that is directly measured.
But the differential equations and the formulas do not for the most part work with redshift.
The physical reasoning does not. Redshift is what you catalog and classify with, and you whip out your calculator and covert it, as needed, to the distance you need to think with, and model physics with.
 
  • #17
oldman said:
Astronomers have a better practice. They don't talk much about distances, light years etc, but just classify far-away objects with the measurable quantity z, which tells how big their redshift is.

marcus said:
You shock me, oldman. A central effort throughout the last century was determining how far away things were. Distance has been a major obsession of astronomers.

Marcus, I'm not quite as shocked as you are: we old folks have learned to accept that one of the few things we can trust from the astronomers is the redshift - at least it is very directly measured. The distance conversions are mostly model and parameter (H_0, Omega) dependent and we have seen soooo many model/parameter revisions.:wink: Lambda-CDM is most likely not the final model...

That said, the large scale distances that we have today cannot be very far out - there are some corroborating evidence from independent measurements, as you hinted.

-J
 
  • #18
marcus said:
You shock me, oldman. A central effort throughout the last century was determining how far away things were. Distance has been a major obsession of astronomers. Constructing the successive rungs of the distance ladder. Determining various standard candles.

Great ingenuity has gone into this. What you say is categorically false. It would be more accurate to say that a good many of them talk almost non-stop about distance.

Off course the catalogs list redshift---that is directly measured.
But the differential equations and the formulas do not for the most part work with redshift.
The physical reasoning does not. Redshift is what you catalog and classify with, and you whip out your calculator and covert it, as needed, to the distance you need to think with, and model physics with.

Actually, on re-reading what I said, I shock myself. Especially since I am the son of an astronomer who spent a large proportion of his working life making parallax observations to support his family, including me! But ungrateful child I am not.

Yes, of course what you say is correct.

Nevertheless on the scale under discussion here, the cosmological scale, which I had in mind as I wrote and thought about modern astronomers who use satellite observatories, there is always a screen of theory between the observation of redshift and distances in SI units, light years or light-travel times. Sometimes quite sophisticated theory, even if calculators handle it easily.

As you say, you whip out a calculator or use a web calculator. And also plot redshift against distance measured by a ladder of indirect deductions (which always starts with non-GR parallax measurements) to deduce the Hubble law. But distance, GR teaches us, is a difficult and dynamic concept. Better here, I believe, to stick to an operational approach in matters didactic and talk of redshift plain and simple, and also to stress that cosmological NOW is just as difficult a concept as a bunch of distances that morph. It should be treated carefully .
 
  • #19
I think we need to be careful here to distinguish between theory dependence and mere coordinate dependence.

1) Theory dependence: It is recognised that the interpretation of a lot of observations depend on the theory they are supporting. This is sometimes used as a criticism of the theory, but it shouldn't be. This is the way science works, you make a theoretical model which predicts what the observations should be and then you compare this with what is actually observed

2) Coordinate dependence. Anyone who has taken a course in GR should know that it allows you a lot of freedom in choice of coordinates. This isn't a problem if you do calculations using GR, but it tends to be a problem in popular accounts of cosmology, where readers tend to have an intuitive idea of what 'distance' or 'now' means and think that this extends to the farthest reaches of the universe
 
  • #20
Now with the helpful contributions of Jorrie and chronon we have the makings of an implicit balanced consensus and I basically agree with the general drift of Oldman's posts and what I imagine to be the collective sense.

Oldman it's illuminating to learn your father was an astronomer. You have a sophisticated view of cosmology and it's measurements, and I think we understand you better with that bit of background.
 
  • #21
Once again gentlemen, I thank you for your time and I can imagine the sense of frustration that you must feel. Am I right in assuming that what you are saying is that in addition to the light travel time that would be 12 billion years, if the universe were static, must be added the extra time that the light has taken to travel in order to cover the extra distance that the expansion of the universe has created during the duration of it's travel. If so, then presumably the same would apply to the galaxies that are seen to be 24 bly's apart as the light that is traveling between them also has had to travel extra distance, or does our distant perspective rule that out. In short, were they further apart from each other, and further away from our present position, at the time that the photons of light that we are now receiving, left their source?
 
  • #22
Peter Watkins said:
I can imagine the sense of frustration that you must feel.

Not at all, Peter! This has been a very agreeable thread so far.

Am I right in assuming that what you are saying is that in addition to the light travel time that would be 12 billion years, if the universe were static, must be added the extra time that the light has taken to travel in order to cover the extra distance that the expansion of the universe has created during the duration of it's travel.

No Peter, that way lies madness.
Nothing needs be added to travel time. It is what it is.

If so, then presumably ...

And if not, then not. And so we are done.
----------------------------------------------------------------

If I may comment, any newcomer to cosmo would be welladvised to spend quite a bit of time simply playing with Wright's calculator and watching his balloon animation. To massage his imagination. People who come to cosmo without math/phys background naturally enough tend to think almost entirely with words, in a purely and even sometimes rigidly verbal way. But cosmo is pictorial and numerical, different modes of thinking have to kick in. Wright is a worldclass cosmologist, one of a handful of leaders in the field, and he teaches the UCLA grad course in cosmo. I'm only beginning, after years of experience with this kind of thing, to realize the extent to which Wright is also a worldclass teacher and in a more general way a public educator. He has identified what a person needs, to grow his intuition. It is no accident that the balloon animation and the calculator that we use are both at his website. And other pedagogical stuff too.

So Peter here is an example you can discover and explore by playing around with Wright's calculator. We think the expansion has been going on for about 13.7 billion years.
Suppose right near the beginning there was some matter that eventually became us, and that matter sent out a photon which by some miracle didn't ever bump into anything and get scattered. (This is a thought experiment, it goes on a straight path by some fluke.)
How far away is it now?
 
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  • #23
Re thought experiment. Is that how far away from the point that it left, or how far from us where we are now? If we are both headed in the same direction, presumably we, or the matter that would become us, would be left standing as formed matter would have started out at something less than light speed and slowed due to the effect of gravity, whilst the photon would have always maintained it's initial, light speed velocity. Which brings me to a question that occurred to me when I first heard of the background radiation. It was originally stated that we are now receiving the light from the big bang as it occurred 15 billion ly's from where we are now and so it took that long to arrive here. How then, did we, as slower moving formed matter, come to be in a position to receive this light. In short, how did we get here first? And sadly, I don't know the easwer to your question. But I do believe that cosmology is not simply a mathematical science, it is also intuitive. I'm willing to bet that Copernicus did not reason out the universe mathematically, but that he took a mental leap to outside of the then known universe and visualised it. Perhaps it was proved by mathematics, but observation did the same thing. I appreciate your efforts to educate me, and I hope that you don't get too bored as I have a few more questions, particularly concerning the cmbr.
 
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  • #24
Peter Watkins said:
Re thought experiment. Is that how far away from the point that it left, or how far from us where we are now? If we are both headed in the same direction, presumably we, or the matter that would become us,...

Don't think of us, or the matter that would become us, as moving. That is a pop-sci media misconception. TV channels should lose their broadcast license if they ever present the Big Bang as an explosion, with matter flying away from a central point, out into empty space.

The standard expansion cosmo model was given the highly misleading name Big Bang by a man named Fred Hoyle who was basically hostile to the model (he had an alternative concept which lost out) and chose a deceptive name expressing his contempt. It caught on with the journalists and after a while got locked into our language.

So think of our matter as at rest, and the photon flying away. The question is, now, after 13.7 billion years, how far away is the photon? How far is it today?

You can find out by going to Wright's calculator and putting in any really large redshift z, like several thousand.

Jorrie says that he and Hellfire have calculators that are, if I understand, even more accurate than Wright's for this sort of thing. But all we need is accuracy to a few percent so Wright's will do fine.

Try z = 1000 and z = 10,000. There shouldn't be much difference.

To get Wright's calculator you simply google "wright calculator"

Which brings me to a question that occurred to me when I first heard of the background radiation. It was originally stated that we are now receiving the light from the big bang as it occurred 15 billion ly's from where we are now and so it took that long to arrive here. How then, did we, as slower moving formed matter, come to be in a position to receive this light.

The background is not light from the big bang, if you mean the start of expansion.
Pop-sci lies.
It is light from 380,000 years after the start of expansion.

The big bang did not occur 15 billion lightyears from where we are now!
Pop-sci lies and destroys people's minds. It is terrible if you were really told it did. Could they have said something else and you perhaps have misunderstood?

We are not "slower moving" if you mean moving away from some mythological point. Essentially, aside from some negligible random motion that doesn't count, we are not moving at all.
 
  • #25
'Where they are now' is rather uninteresting. We observe no object beyond redfshift ~10 at present - which is very interesting. Given the speed of light is the only meaningful 'yardstick', it is all that matters.
 
  • #26
Re "pop sci"), my understanding of the cmbr. came from, (amongst others), a NASA. web-site, the address of which escapes me, but I do recall that it the picture of a balloon being blown up. It stated that which I already understood ie., that the early universe was so hot that no matter could exist, at least not as we understand it, ie. nucleii, composed of protons and neutrons, with electrons dancing in attendance. Photons could not travel far without colliding with whatever baryons barred their progress and hence no photons, of any frequency, escaped from this inferno for between 3-400.000 years.
(This particular point raises questions. This early universe, even at it's largest, was, (relatively), tiny, ie. finite and easily measurable. Why then, is the universe now considered infinite? You, (by whom I mean all modern cosmologists), with all your tables and equations should know the size to within an inch. Also, isn't it matter that propogates photons, so from where did those within the "energy only" universe originate?)
To continue; When sufficiently cooled, those photons, of all frequency,were able to "escape", the so-called "last scattering of light". This was a "one off" event and the only way to interpret this is that they moved out and away from what constituted the entire universe and should have disappeared. The newly forming matterwould have started out at something less than light speed. So how then, can the background radiation possibly be anything to do with the early, energy only universe. It has been said that the CMB that we receive today was propogated by one layer of the matter within the early universe and that tomorrows by the next layer. But, there was no matter within the energy only universe, and besides, it disappeared after less than 1/2 a billion years.
 
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  • #27
Peter Watkins said:
... This early universe, even at it's largest, was, (relatively), tiny, ie. finite and easily measurable...

Another widespread popular misconception. Who told you this, Peter?
Astronomers including cosmologists almost all use the standard model called LCDM.
Of the two versions, spatial finite and spatial infinite, the latter is generally favored for calculations, or they fit the data to both and compare results.

So you could say that spatial infinite model is currently preferred, although finite has not been ruled out.

And of course for the preferred model the early universe has infinite volume. Basically it starts out infinite.

Popularizations, including some NASA public outreach, mislead the public by saying things like "all the galaxies that we can see would fit in a canteloupe", or telephone booth, or whatever. They fail to make clear that is not the whole universe.

Don't be misled. That does not mean astronomers think the early universe was spatially finite!
They are only saying that the finite spatial chunk of it that we can currently see is, and of course was, spatially finite.

If the full universe is spatially infinite now, then it always was. There is no inconsistency such as you describe.
To continue; When sufficiently cooled, those photons, of all frequency,were able to "escape", the so-called "last scattering of light". This was a "one off" event and the only way to interpret this is that they moved out and away from what constituted the entire universe and should have disappeared. The newly forming matterwould have started out at something less than light speed. So how then, can the background radiation possibly be anything to do with the early, energy only universe. It has been said that the CMB that we receive today was propogated by one layer of the matter within the early universe and that tomorrows by the next layer. But, there was no matter within the energy only universe, and besides, it disappeared after less than 1/2 a billion years.

This is shot through with misconceptions. Peter, I've know people that actually enjoy wallowing in the contradiction and misunderstanding about cosmology that they get either from pop-sci, or bad NASA public outreach, or anti-science Christian websites, or wherever. So you tell them "The Big Bang was not an explosion." Picturing it that way leads to a lot of contradictions and confusion. And they won't take it in! They come back the next day still tormenting themselves and their readers with the picture of the Big Bang as an explosion.

You have not yet come to grips, made contact with, what cosmologists actually say. You aren't engaging the models professionals use and how they think about the universe.

Either you enjoy a make-believe game where you cling to popular misconceptions and say "look at all the foolish things those scientists say, it doesn't make sense!" or else
at some point you have to throw out all the garbage and make a fresh start and try to make contact with real cosmology. You choose.

BTW Peter, there's a good article at the Princeton.edu astronomy department website, by a top cosmologist. The link is in my signature. It's called Misconceptions about the Big Bang. Haven't I suggested it to you before? Have you had a look?
It's written outreach-style. No math. But it is that rare outreach article that doesn't oversimplify to a misleading extent.
If you want to learn about the standard cosmo model, it's a good place to start.
 
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  • #28
The observable universe is necessarily finite. Since that is the only portion we can study, further speculation is philosophy, not science. It is therefore impossible to prove, or disprove, the universe is infinite. It is equally impossible to assert it is, or is not, the consequence of a 'creation' event. I see no way to logically escape something that resembles a 'creation' event, but that too, is philosophy, not science.
 
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  • #29
Peter Watkins said:
When sufficiently cooled, those photons, of all frequency,were able to "escape", the so-called "last scattering of light". This was a "one off" event and the only way to interpret this is that they moved out and away from what constituted the entire universe and should have disappeared. The newly forming matter would have started out at something less than light speed. So how then, can the background radiation possibly be anything to do with the early, energy only universe. It has been said that the CMB that we receive today was propogated by one layer of the matter within the early universe and that tomorrows by the next layer. But, there was no matter within the energy only universe, and besides, it disappeared after less than 1/2 a billion years.

Peter, on top of what Marcus and Chronos said, the following mental picture of the CMB, using the balloon analogy, may help you. Consider the entire universe as represented by the surface of the entire balloon and the observable universe as the surface area enclosed by a smallish circle drawn on the surface of that balloon. We are obviously at the center of this circle.

Now, the event of last scattering happened across the entire surface of the balloon, with photons moving in all directions across the entire surface. What we observe as the CMB are photons coming to us from the edge of the circle that encloses us (equally from all directions). If the balloon happened to be static (not expanding), then in every second we would have observed photons coming from one light second farther from us - because the radius of the circle (the observable universe) would have grown by one light second per second. This is the simplest case of the "layers" that you referred to.

However, if the balloon is expanding, things are not that simple - the circle will get larger due the expansion. Depending upon the rate of expansion over the age of the universe, we actually observe CMB photons that originated less than one light second farther from us as every second passes. Before trying to understand this, you will have to come to grips with the best cosmological model, as Marcus suggested...
 
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  • #30
Thank you gentlemen. I sense your growing frustration and I understand it. Re casting off excess baggage; I did that and it was due to the February or March '04 issue of Scientific America. This is where I first heard of the "dark energy" notion.
The only information I used was Newtons laws on gravity, (which is the last wholly accurate statement concerning large scale movements of the universe), and the red-shift observations of the late 1920's, which was incorrectly reported as seeing that, with rare exception, galaxies in all directions moving away from us. What should have been reported was the fact that, with rare exception, galaxies in all directions are exhibiting degrees of red shift that increase with distance. It is this error in part, that has led to the current misunderstanding of the universe. As I said in my original post, this information alone is sufficient to show the structure of the universe and to predict the increase in the rate at which galaxies separate.
Separately, when, and why, was first thought that the movement described above was not ballistic, and that rather than the outward movement causing the universe to grow larger, it was the universe that is taking the galaxies outward. And isn't it the fact that the galaxies are the universe, and that the the universe is not something other than these galaxies, along with their attendant dark matter, which really isn't difficult to explain.
 
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  • #31
Peter Watkins said:
Re casting off excess baggage; I did that and it was due to the February or March '04 issue of Scientific America.

Peter I'd say you have not begun casting out popular misconceptions about cosmology until you've read the March '05 SciAm article I linked to called Misconceptions about the Big Bang, by Lineweaver. It's the princeton.edu link in my sig.

It specifically addresses the misconception of the BB as an explosion and the wacky idea of the expansion as ballistic. You evidently have not read Lineweaver. You cite something from 2004, if you give a link I will check it out and see if there are any misleading statements or dangerous oversimplifications in the 2004 article.
The only information I used was Newtons laws on gravity, (which is the last wholly accurate statement concerning large scale movements of the universe), and the red-shift observations of the late 1920's, which was incorrectly reported as seeing that, with rare exception, galaxies in all directions moving away from us.

Newton's laws are not accurate even in the solar system. They don't fit reality. GR is considerably more precise.

The Friedmann model expanding universe was already on the table by 1923, it predicted the redshift that was later observed.
The Friedmann model does not say that distant galaxies are moving away from is (that is the popularized report) it says that the distances to them are increasing.

It does not describe ballistic motion. Indeed distances to most known galaxies are increasing at rates faster than c. It wouldn't make sense to picture that as ballistic motion resulting from some fantasized 'explosion'. What we are seeing exactly fits what one expects to see from the best-tested most accurate and thoroughly tested theory of gravity we have so far (which in contrast to Newton's is a law of dynamic geometry).

Separately, when, and why, was first thought that the movement described above was not ballistic,
.

As I said the cosmo model was on the table as of 1923.

It was independently derived from 1915 General Relativity by a Russian, Alex Friedmann, and later by a Belgian, Georges LeMaître.

You ask "why". The theory does not lead one to expect ballistic motion or any sort of motion outwards from a point. There were later attempts, which failed, to interpret the data as ballistic motion. That was mainly in the 1930s and they have largely been forgotten.
From the outset, and now, over 80 years later, the redshift has been interpreted not as ballistic motion but as evidence of the dynamic changing geometry predicted by the law of gravity.

The 'explosion' picture has almost exclusively been a phantom creature of the pop-sci realm. I think it is because the public has been considered incapable of accepting the idea of dynamic geometry---the idea that spacetime could be curved and therefore distances change independently of motion---and so the public has always been fed the oversimplified and essentially misleading 'explosion' picture.

Maybe in the end there will have to be a campaign of scientists, writing open letters to media people like Discovery Channel executives and producers urging them to stop the pap and get it right.
There are posts right here at Cosmo forum which could serve as horrible examples of how damaging this oversimplification has been to the public mind.
 
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  • #32
The Friedmann model did not need to predict red-shift, it was reported by Slipher in 1914. What was not known is that the nebulea that were exhibiting the red-shift, were in fact island universes, or galaxies. Lemaitre it was who first suggested that there must have been a time when all matter must have been together. The "Primeval Atom". A perceptive man. The only thing he didn't figure out was how it all came to be moving outwards, but then neither have most people. It was also predicted by a well known person that the universe was static. When expansion, or at least, movement, could no longer be denied, a surplus curvature theory was wrapped around it thus enabling a universe that could be seen to be moving, was actually going nowhere. Most of this "not expanding from anyone point" or "the universe has no limits or edge" stem from the notion that the universe is the creation of a benign God, and to question that it has a beginning, or a centre is heresy. It sounds strange today, but that's how it was.
I have at last visited your much vaunted balloon analogy and found our old friend, the loaf of raisin bread. The only difference is that the dough, which has a sufficient degree of viscosity to transport the raisins outward, has been replaced with a form of expanding space. I assume that what I was looking at was the "outside", and not a section through a spherical universe? On a different page, (I forget which one, I've clicked on so many links), was a regular arrangement of dots, each representing a galaxy. Two adjacent dots were surrounded by a halo of light. These dots then moved apart, as did all the other dots, in order to show how much further light would travel in an expanding universe. There was however, a glaring error in that as the dots moved apart, the halo of light remained concentric to the dot, it's galaxy of origin, but not it's point of origin. This point of origin should become a set of co-ordinates to signify the place of origin. If light were emitted at regular intervals, perhaps every 1/2 a billion years, there would be a series of halos, each with a different centre, by the time that the original light beam reached us.
By the way, your theory will never catch on, it's far too populist!
 
  • #33
I concur with marcus on this point.
 
  • #34
OK. I'll give up. I've worked with scientists and I know how it is; never admit that you don't know and disregard any information that contradicts your own theory. I did visit the website that Marcus recommended, (excellent in it's lack of maths), but I had read all that stuff years ago, including, I'm fairly sure, that very article. At the time of originally reading it, I thought of it as the "bypass theory" as it very neatly bypasses Einstein's law that states that the speed of light cannot be exceeded. This is a law that provides considerable difficulty for those who would construct a theory to describe the universe using only the four forces, three dimensions and ballistic motion, for all of which the evidence can be seen. As it happens, there is no need to sidestep this law as it is becoming ever more widely accepted that the Lorenz equations upon which Einstein based this law apply only to radiant, and not ballistic, motion.
This theory also bypasses the need to explain the mechanism behind the movement, saying only that the expanding universe is taking the galaxies out with itself, from which it would seem that the universe that most people think of as being composed of stars, galaxies and assorted bric-a-brac, is also being bypassed. Instead, the universe is simply expanding space and galaxies are unwitting passengers being dragged out by, and with it This is how it can be stated that galaxies are moving apart without moving!
Strangely enough, although cosmologists fiercely deny that the outward movement is ballistic, they themselves provide a theory that states positively that it is. And the same theory states positively that collapse is inevitable, although that is already self-evident.
It is, of course, the inflation theory. This states that when the universe was tiny, gravity reversed for a short while and started the expansion. This states that the energy content of gravity is greater than the inertia of the universe. This is further proven by the fact that when gravity reverted to it's more normal form of attactive energy, this headlong outward flight was halted, or at least reduced, to the level that we see today. Sceptics of this theory might point out that for inflation to work, gravity had not only to reverse but to also increase in order to overcome the inertia of what was presumably a static universe. This increased level of energy would also be needed to overcome the kinetic energy that the newly expanding universe now possessed. In order not to halt the expansion completely, gravity would then need to revert to it's original strength. So, either this whole theory, (with it's reverse, increase, revert, decrease of the strength of gravity), is nonsense, or it provided the motive power behind the expansion.

"The more bizarre a thing is, the less mysterious it usually proves to be". Sir Arthur Conan Doyle. (Sherlock Holmes).
 
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  • #35
Peter Watkins said:
I've worked with scientists and I know how it is; never admit that you don't know and disregard any information that contradicts your own theory.
Regarding this theory of yours, I wonder how much contradictory information you've disregarded...
 

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