Has the Universe Quit expanding?

[budcamp]

We know the universe was expanding, but I belive it has stopped and is now contracting. Does anyone else have any thoughts on this?

Why do you think so?

[K6-III]

Why do you believe that it has stopped expanding?

[budcamp]

Well I looked at the characteristics of an expending universe and what one should find if it had quit expanding and started to collapse. I think that we are exhibiting condition of collapse right now.

How could we see if it had started to collapse? What are the outward manifestations of a collapsing universe? They are either elemental, or I am dumber than I think I am. Actually, both those things may be true.

I want to see what other people think. I hear no one talking about the collapse of the universe, but I have heard several people speak of what conditions would let us know it was happening. And others speaking of those conditions as already exiting but discussing that in a different context.

Does any one know how to tell if we are contracting or not?

[K6-III]

Shouldn't be too hard to look for blue shift...

[budcamp]

Where would you look, and what would it mean?

[timeshifter]

Well, if the universe really is contracting all around us, couldn't we lookanywhere for a blue shift?

[budcamp]

No! If that was the case, everyone would be saying we are no longer expanding. It's a little more compilcated than that.

[irizarry]

It has been proved by Hubble that galaxies in the universe are not static and are all receding (moving away) from our galaxy. It has also been determined that the farther away a galaxy is the faster it is moving (greater velocity of recession). These properties have been consolidated into the formula

v = H(0)r
Where
V = velocity of the receding galaxy
r = is the radial range to that galaxy
H(0) = Hubble’s constant

The spectral lines emitted by a galaxy is the physical property used to determine its velocity. And it is the Doppler redshift that ultimately gives the velocity. Again this property has been consolidated into the formula

lambda (0)/lambda(e) = 1 + s

where

lambda(0) = the wave length at which the spectral line is
observed
lambda(e) = the emitted wavelength of the spectral line
s = the redshift

both sides of the equation are unitless.

Recession velocities can be measured very accurately, however distances (as in r above) can not. There is also another constraint. The distribution of galaxies must be isotropic and expand uniformly. The problem here is - Does this mean that there must be uniform distribution locally (there are clumps of matter in local surveys that do not reflect uniform distributions)? Also there are two camps on what the value for H(0) should be and it has caused considerable debate. H(0) is either

45 – 60 km s^(-1)Mpc^(-1) or
75 – 100 km s^(-1)Mpc^(-1).

Again physical properties of the galaxies are very difficult to measure at great distances. The added constraint is that physical properties act the same locally as they do at great distances. Recent observations do not show a decrease in Hubble’s constant. Then again since it can’t be measured accurately any slight decrease would probably be attributed to systematic errors. Also in the standard cosmological model it is assumed (based on the Big Bang) that the universe’s expansion rate (Hubble’s constant) must have been greater at an earlier time and it is modified to indicate the decelerating effect of gravity. The assumption here is that gravity a long distance force has no limit. There are some other interesting effects such as the universe expands it also cools down. We are also in the matter epoch of the universe (that is the period of time were mater is condensating). If matter condensates and the universe cools then there are possibilities of new forces forming that have never existed before (maybe the 5th force, or the Lambda force, or the recently theorized Repulsion force).

So to answer your question, and a GREAT one, my opinion, we wouldn’t know if the expansion was slowing down if it were subtle but might if it were dramatic-then again new forming forces might actually hide this initially.

There is nothing like a straight forward confusing answer to nail down your thoughts!

Irizarry

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[budcamp]

Lets say that expansion stopped between 10 and 100 million years ago. How would we know that.



A different point. The speed of light is an absolute limit through space. However space can expand faster than the speed of light. Therefore galaxies can be moveing away from each other at faster than the speed of light.

[K6-III]

That expansion would have to be a continuous process that could be demonstrated today by measuring the acceleration of expansion.

Seeing as said acceleration is positive, it makes no sense for rate of expansion to have slowed...

[budcamp]

The Hubbell deep field showed us the universe out to about 15 billion light years. At that time, the far galaxies were red-shifted from us at the over 90% of the speed of light. Remember that when we look at these far galaxies we are seeing the universe 10 billion years before our solar system started to form.

Since then, they have had 15 billion years to continue accelerating or to slow down. If we assume they continued to expand at the last rate seen, They can never be seen again, because they are receding from us at way over the speed of light. They are now at least 30 billion light-years away from us.

THAT BEING THE CASE:


Let's assume that somewhere around 5 billion years ago, slowing started, and 100 million years ago expansion stopped and the collapse started. How would the model of the universe change from that of a continuously expanding model?

BOTH MODELS CAN NOT BE IDENTICAL, SO WHAT WOULD BE THE DIFFERENCES BETWEEN THEM???

[PhysBrain]

Another way of measuring cosmological motion is with respect to the Cosmic Microwave Background (CMB) radiation. The CMB is a residual field of electromagnetic radiation left over from the time when the universe was a dense hot ball of plasma. As the universe expanded though, this radiation has steadily cooled off, much like an expanding gas. However, some residual radiation is still measureable today as low level electomagnetic field which permeates all points in space. If one were to treat the universe as a blackbody [1], one could assign a temperature of about 2.7 Kelvin, with the peak frequency in microwave region of the electomagnetic spectrum. If the universe were to begin to collapse, then the temperature of the universe would begin to increase again.

More importantly, one can roughly judge our motion in the universe using the CMB as a reference frame. Since the CMB should be fairly uniform at all points in space, then the universe should be observed to be the same temperature in all directions. However, there is an almost perfect dipole effect super imposed on the CMB. This means that roughly half of the sky looks slightly warmer than it should, and the other half looks slightly cooler. This dipole is induced by doppler shift due to our motion with respect to the CMB. Our galaxy, and the local group of galaxies, are all moving at about 600 km/s with respect to the CMB [2].

If one takes this relative motion into account along with the doppler [3] red-shift measured for distant galaxies, then one can pretty accurately conclude that everything is continuing to expand away from each other.

As an interesting side-note, the only extra-galactic body which is not red-shifted is the Andromeda galaxy at about 2.9 million light years distant. Andromeda is actually moving towards us, and is blue shifted very slightly. This is thought to be due to the overall movement of the local group. That is to say that our galaxy and the Andromeda galaxy are moving (with respect to the CMB) towards the same region of space, and not directly towards each other.

[1] http://hea-www.harvard.edu/~efortin/thesis/html/Black_body.shtml
[2] http://www.noao.edu/noao/noaonews/sep99/node3.html
[3] http://hea-www.harvard.edu/~efortin/thesis/html/Doppler.shtml

[budcamp]

Most of what is being used to check the expansion (red shift, COBE, etc.), is ancient history. I'm only talking about the last 100 million years. We can not investigate that time period by looking a billion years plus into the past.

We have to check the space within 100 million light years. What is happening within that area of our space?

[Grant Nockolds]

Budcamp I must congratulate you this one... I for one have never considered the fact that all the data we collect and collate that says our universe is expanding is millions and millions if not billions of years old.

It is a very real possibility that we are in fact contracting...

The only point of fact that I believe tends towards the likelihood that we are still expanding is that the data says the universe is still expanding at an "Increasing Rate". Therefore as recent as we can ever get it; the universe has not even begun to slow down, never lone stop altogether and then eventually contract.

Still though you may be right and the Andromeda Galaxies blue-shift adds a nice tit-bit of titallation to the whole concept...!

[budcamp]

I have tried to organize my thoughts on this subject a
bit better. See if this is easier to grasp.

The Contraction Of The Universe.

Cosmologists generally agree that if there is enough
matter in the Universe it will expand for awhile and
then contract. This is the closed Universe model.
Gravity will slowly gain control of all matter. When
it has, the universe will start to contract. How would
that model progress?

This contraction would first be noticed in the home
galaxy. Then the local group would start to move
together. In the beginning of the Local Group’s
contraction the Virgo Cluster would still be expanding,
though at a reduced rate.

In another few million years or so, the Virgo Cluster
would start to move together, but the Virgo
Super-Cluster would still be expanding, though at a
reduced rate. Of course in real time the entire
Universe stopped concurrently (or thereabouts), but
because of the look back into time we can only observe
the contraction within the number of light years since
the contraction began. Before that time, it was still
expanding.

In other words if the universe came to a dead stop 100
million years ago, what would we see now? Well, we
should see our own Galaxy perhaps having a slight
contraction. Our local group should be generally
trending toward blue shift, though the proper motions
of the bodies would ameliorate this to some degree.
Our cluster would be a trifle into the blue. Our
super-cluster would be red shifted but decreasingly so.

This is exactly the condition we find today. Our home
galaxy is not expanding. In our local group: the
Magellanic clouds are in the process of merging into
the Milky Way, as are M42, M44, and M45 among a number
of others.

The Andromeda Galaxy is closing on us, while also
merging with M32, M33, and M110 amongst others. The
entire local group is moving toward the Virgo Cluster.
Which is moving toward the Virgo Super-Cluster. Which
seems to be moving toward an area called the Great
Attractor.

This meets all of the conditions for contraction of the
closed model of the Universe. Why then would we still
think that the universe is continuing to expand? It
seems to me the reason for this is that it is less than
100 years since we found out there was any expansion.
It was quite a shoocking discovery since everyone at
that time thought the universe was stable. Even
Einstein!

Since we were not around when the Milky Way was
expanding, we didn’t notice it stopping. The same
applies to the local group! We didn’t see it expanding
so we think it was always gravity bound. We have never
really dealt with the question of “Why isn’t space
expanding between us and the other galaxies in the
local cluster?” We just said they are gravity bound
and let it go at that. Gravity bound is one of the
first characteristics of a contracting Universe.

Occam’s razor say’s the simplest explanation that fits
all of the facts is probably the correct one. I would
sure like to hear another explanation that fits the
facts, or to have my facts challenged. If I am barking
up the wrong tree please let me know.

Bud

[irizarry]

I have never heard of a cosmological model that suggests that local deceleration events would be indicators, or used as a gage to determine universal de-expansion. In fact a given quantity of matter with no other influence other than gravitational attraction will attempt to compact. In an ever-expanding world sheet congregating matter in local clumps is OK. It is to be expected, since the space between points are expanding the local spherical volumes have changing mass densities. The Milky Way is not the only galaxy that will experience collisions or have experienced collisions in the past (consider the Tadpole Galaxy-theorized to be a remnant of a prior collision). The Great Attractor is not an indicator that the Universe is virtually heading for the Big Crunch (it may be but not based on the Great Attractor). This is really what the whole debate is about. What indicator, tools, or variable are available to make a scientific conclusion one way or the other? We use light because we have access to light from the far reaches of our Universe. However precision becomes critical and this is where we set. If I saw one of Saturn’s moons fall into Saturn itself it would not be a sign that Universal collapse is eminent. It would only mean local conditions warranted an increase in Saturn’s mass. Gravity is a central acting force. In the case of the Universe -Where would the center be? Would it be US just because we saw some local clumping? Note: The Big Bang did not originate from a central point! It occurred everywhere at once. It is inappropriately modeled as some kind of expanding balloon with white dots painted on, which is used to illustrate the expansion between galaxies. I do not know for sure but I would imagine the Big Crunch could be the reciprocal effect. Where matter compacts everywhere at once. The Great Attractor is just what its name implies-“one hell of gravitational central point”. It does pose other questions-are there other “great attractors”?. If there are, what does this imply? Additionally, colliding galaxies may not be the form of mass condensation that would be observed in the Universe at Big Crunch time. I will admit that the “growing Virgo Cluster” argument is a most attractive way to connect the dots when viewing local events.

Irizarry

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[budcamp]

Grant:

The acceleration you are talking about was detected by observing super novea that are five billion light years away. I will agree that five billion years ago the universe was expanding. What I am talking about only started 100 million years ago, so data that is five billion years old is not of much use.

[irizarry]

Do you think that in a 100 million years the Universe has coasted to a stop and then began contracting? Its sort of like worrying about the very instant the light was turned on in the kitchen. Was that 9:17:23 or 9:17:23.1. One might say the time frame to meaure a Universal event as this might be to short for an indicator or the change should be instantaneous. Don't get me wrong-You still have a good question!

Irizarry

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[budcamp]

You didn't get the concept Irizarry. The reason for the 100 million years is that somewhere around 100 million light years is where the contraction can be observed. When we look out farther than that everything is red shifted, but closer than that, we start to see blue shift.

If you are familiar with the three basic models of universal expansion, you know they are open universe, closed universe and flat universe. What I am talking about is the closed universe model. My basic question was: if that model was already active, how would we know it. Just think about that one point for a moment. Don't worry about are we contracting or are we not, just think about how we could know we were contracting.

We would only be able to know by observing the universe within the time frame since the expansion started to reverse direction. I estimate that time frame to be somewhere around 100 million years. It may have started to slow down around 2 to 5 billion years ago, give or take a few billion years. The time frame is only important since people want to discuss the Hubble constant and other things that deal with space billions of years ago.

IF SOMETHING HAPPENS TODAY, YOU CAN’T CHECK LAST WEEK’S NEWSPAPERS TO FIND OUT ABOUT IT. Everything older than let’s say 100 million years, is old news and can’t be used to determine if we are contracting. If we are contracting how would you know it Irizarry? Don't worry about are we contracting, just how would we know if we were.

If I am correct, then we would also see this contraction within other groups of galaxies, and clusters. It is not just our part of space that is contracting. But, these other groups and clusters would still be receeding from us even though they are merging with each other.


__________________

[irizarry]

Science has given us several possible outcomes to the fate of the universe. They are (1) an eternally expanding universe (Open), (2) an expanding universe that eventually recollapses (closed) (3) an expanding universe who’s expansion rate approaches zero asymptotically at infinity (flat). The Standard model says we are a factor of 10 from the flat universe. What is science’s proof of this? They are (1) the interpretation given us by Hubble’s Constant, (2) Verification given by the Cosmological Microwave Background Radiation (as mentioned before by PhysBrain), and (3) the abundance of Helium in the Universe. Other theoretical indicators (that do not get tested directly) are the cosmological constant and scale factor. There is one other possible outcome based on Grand Unification Theory that suggests that matter will eventually evaporate into a gas of electrons, neutrinos, positrons, and photons possibly giving rise to another Big Bang on the assumption the universe does dot collapse first. This outcome is on the order of 10^30 years. Finally an additional effect is contributed to expansion and that is the solution given to Olber’s Paradox. Olber’s Paradox says that since we could see at least one star or bright object in the sky at every possible coordinate location the night sky should be as bright as the sun. The solution to this was that since the universe is expanding and many objects receding from us many of these objects have their light red shifted out of the visible spectrum thus dulling the brilliance the night sky could have.

Revisiting the three (3) verification values above (Hubble’s Constant, CMB, and Helium abundance), I do not know the smallest response time for each of these indicators. Consider the CMB now at 3K. How long would it take for appreciable change in this value to be noticed (or any of the other values). Maybe, these indicators have a response time of less than 100 million years.

These are the standards available to us right now. Lets take a look at the more speculative stuff. Since we are interested in a decelerating universe this would leave us only the flat and closed universe options. As a footnote: there is an excellent mathematical description of a decelerating universe in Paul Davies book The New Physics, page 58. (I was looking at the 1994 reprint of the 1989 copyrighted version by Cambridge University Press). Based on the following premise: the physics here is the same as physics say 100 million light years away or at the far reaches of the universe.
If that were not true then it would be another definition for “magic” which some authors have used in their science fiction novels. That is the statistical outcome for a certain natural phenomena was different than that that we expierence. Makes great theme material for science fiction but wont help us here.

In my speculation I have cataloged several possible scenarios tabulated below:

(1) Indicators used for the expansion in the Big Bang Flat universe model would be the recipricol for Big Crunch after full stop.
(2) Deceleration does not have to be the recepricol of acceleration in an expanding Flat universe model.
(3) At deceleration some indicators would be independent of indicators used for acceleration.
(4) No indicators will be available initially at all at deceleration
(5) Olber’s Paradox gets revisited.

Note: Since the Big Crunch closed universe model is a continuation of the deceleration event then I’ll look at deceleration only.

Item 1 above: looks like a strong possibility. We would see a change in the Hubble Constant, CBR, abundance of He at the proper response time (possibly less than 100 million years).

Item 2 above: The universe may shout its decelerating in a totally different way. It will be a surprise we have to wait for.

Item 3 above: Similar to item 2 except these indicators would be difficult to measure or act so different at deceleration than they do when accelerating. Example: is there a latent heat to the universe were by deceleration has no effect on the universe cooling down any further or actually the latent heat gets to catch up with the universe and things get warmer? Do these things have a 100 million year price tag on them!

Item4 above: No indicators means we are blind to the universe-a very sad outcome irregardless if it were 100 million years or 85 days.

Item 5 above: From the solution of Olber’s paradox deceleration would mean many objects that were red shifted out of visible light would begin to shine brighter in the visible spectrum and the night sky would slowly grow brighter. Are there objects in this category that are less than 100 million light years away? This includes gas matter that is not visible now. I think these events would show up in less than 100 million LY.

I would hope that the condition of the universe is actually written in the fabric of space time. Then we could simply go to a particle accelerator here on Earth and read the latest vital signs of Universe when ever we wanted to. Returning to Olber’s Paradox since no one has noticed an increase in the intensity of light in the night sky I would say this is an indicator the kitchen light is still off.

Irizarry

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[irizarry]

After reading this question about a decelerating or collapsing Universe I have been constantly thinking about all the solutions given in this forum. I thought why is it when you look something up no one gives you an answer to your exact question and many times they don’t even get close. Although Budcamp’s question is very interesting to me I was wondering if it was interesting to the pros! (those guys who are lucky enough to get paid just to think about this stuff). Have they addressed this question in detail. To my joy I picked up “The Nature of Space and Time” (Princeton University Press: 8th printing 2000) by Stephen Hawkings and Roger Penrose my all time favorite tag team. I will not pretend to understand this book cover to cover. The two authors basically have the same discussion we have had and with opposing positions. Cool-I feel like I’m on the leading edge of science! There preferences are mentioned through out the book but summarized on pg 119 sort of. They did a great job making rather complicated explanations understandable to the layman such as myself. Unfortunately if there are measurement techniques for the state of the universe I missed it. I’m still reading it-rather attempting to suck up ideas that I think I understand-I could be lying to myself.

Irizarry
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[budcamp]

Another great answer irizarry!

There are a lot of points in your reply. Let’s see if I can deal with them in some sort of organized manner.

First Olber’s Paradox. The paradox came about because in Olber’s time it was belived that the universe was infinitely old and there were an infinite number of stars. The reason the sky is black is because we look back into a time when there were no stars. Another factor is that stars burn out, so when one looks out into space instead of a point of light there might just be a dust cloud or a dark neutron star. Even in a contracting universe the sky would still remain black until the final stage of the contraction. The kitchen light will stay off for another few billion years. Even if the sky had gotten brighter in the last few hundred years, light pollution would probably keep us from noticing it.

I am not sure what the relevance of an abundance of helium would be, so if you could explain that to me I would appreciate it.

The Hubble constant also really has little to do with the establishment of contraction. We are still trying to figure out just what is the exact numeric value of the constant. For galaxies within our group or cluster it would not have any real value. It is more useful for galaxies that are billions of light years away.

I think that the compression of the universe will increase its heat. Though I see a couple of problems in using that change to detect if the universe is contracting or expanding. How would we find out if the temperature of the universe is increasing? How do we measure its current temperature? How do we tell what the temperature was millions (not billions) of years ago years? I don’t have a clue! Any answers will be appreciated.

I have ordered “The Nature of Space and Time” & “The New Physics”. I am looking forward to reading them. Hawkings and Penrose are favorites of mine also. I have never read anything by Paul Davies, but he has some great titles.

I am still trying to get a handle on the CMB and how it would be affected by the contraction. I will try to discuss it by next week.

[irizarry]

Bud camp

I am certainly glad your not my professor in college you give tough homework!

So that I may make a respectable contribution I will do a little back reading and see what I can come up with. So I guess we will meet back here.

An aside

I always enjoyed cosmology and I do not work in that field but I consider myself a “Closet Cosmologist” and a layman in the field. Without giving up to much of other peoples personal information we closet cosmologists are in good company. Here are a few I know of:

There is a friend of mine who was a student of Penrose, he is not a paid cosmologist but does research for some government agency. I can tell you he probably is thinking about cosmology much more than his research job for the government-which by the way would stretch most people’s minds to the limit to come up with the word “interesting”. Poor B%#@%&!

Another friend of mine is a well published statistician and has a friend that lives in a sort of art colony in Vermont. Go figure! His artzy friend has no formal training in any science but actually publishes cosmology papers in a respected journal. If you got it flaunt it! He is not famous so to speak because his articles are not mainstream and tackles problems that I think no one even knows exist or feels are important right now.

I had a professor in college who is a personal hero of mine (he made many personal sacrifices in his life so that he could send perfect strangers on to grad school-one every other year!). He himself had an impressive resume of accomplishments in disease identification and the development of artificial organs and new instruments. He in turn was a close friend of a chemist who won the Nobel prize ages ago. His friend the chemist would write papers on the thermodynamics of the universe and send them to him. He in turn would give them to me-a lot good that would do. Here is renown guy outside the field ready to dabble in cosmology. This is why I like it so. From the brilliant layman to the brilliant professional you don’t know who you will run into. It’s definitely the playground of the mind.

Here is, I think an interesting story about cosmology. When I was an undergraduate I had this very eccentric math professor who taught Diffy Q. He liked to ride me a bit and was very upset that a friend of mine and I did not like to memorize things. He on the other hand would memorize the graduating lists of local colleges for the last twenty year period as an exercise. Why do people do these things? I can’t spell let alone memorize anything lengthy!. He asked us why don’t you memorize certain derivatives so you’ll spend less time on the tests. We told him ‘why memorize anything that you can derive!’ He had a fit and said he was going to work on us. This was not the kind of attention you would want from this guy. Anyway his cosmological beliefs were seldom shared with us since we were amoebas in his sea of big fish. There was one very important key point to his theories which he would of found out sooner or later anyway. One day in the hallway years after his Diffy Q class he asked me if I knew if there was a minimum mass limit for a blackhole in any of the numerous theories floating around at the time. I told he I didn’t know but knew that some theories use microscopic blackholes. Yikes! That was the wrong thing to say and he sped down the hall babbling and waving his arms like the Robinson Robot! To shake this guys world up like that (although not intentional) did bring me some pleasure - I am ashamed to admit. I had no opinion at all on the existence of microscopic blackholes and because of that I still don’t!

Unfortunately I have lost touch with most of these guys. That’s how the cosmological cookie crumbles. The Universe expanded a little more and put these people outside my region of observation.

Anyway, I’m going to do some more homework. Your not grading this are you? I look forward to our future discussions or anyone else who wants to jump in. “Come on in …. the waters fine!”

Irizarry

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[budcamp]

I got into this when I read that the universe was expanding like cake full of raisins. The space between galaxies increased and made them move away from each other. I just accepted that until I learned that some galaxies collide with each other! How was that possible if they were moving away from each other? Stuff like that bothers me. When I followed up on that aberration, I started to examine the three models of expansion and came upon the closed universe model.

When I started to examine how would we know if closed model had started to progress into the contraction stage, I was amazed that no one even seemed to think about the subject. They just say we are expanding because of the red shift of galaxies that are some 15 billions of years in the past. Or even worse that we are accelerating because of super novae observations that are 5 billions years in the past. No one seems to pay any attention to what is happening in the present or near past.

The contraction that we see in the present and less distant past is just chalked up to what has always been! I keep hearing how the local group and the Virgo cluster are gravity bound. No one knows if they have always been gravity bound or if that is a recent development. No one even mentions that. They just say that the local nature of the universe doesn’t conform to the larger scale nature of the universe.

When nature needs to be adjusted in order to make some ones pet theory work, my first thought is usually that their theory is probably wrong. The real problem is that I usually say so! I guess that is why I was fired from almost every job I ever held. If I hadn’t run my own businesses, I would have starved instead of making more money that most of those who fired me. One never knows how things will work out in this life.

I really don’t know if the universe is contracting or not, but all of the indication I get are that it is, and I seem to be almost the only one who is even thinking about the question.


As to grades, when I did teach, I never graded anyone on their answers, only on the questions they asked.

[irizarry]

I found a brief blurp about the debate over expanding and collapsing universe in the following article:

Shermer, Michael. “Digits and Fidgets: Is the Universe
Fine-tuned for Life?, Scientific American, January 2003,
pg. 35.

This article might be of interest to those interested in extraterrestrial intelligence.

My eyes are peeled for more juicy tidbits.

Irizarry

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[irizarry]

In the discussion in this forum about the ultimate fate of the universe there is a new twist! It seems that an alternative horrific end is possible called the Big Rip. And it’s not pretty. This view is being challenged by a variation of the Big Rip with less appalling conclusions.

The agonizing chronology of the "not so slow" (in cosmological terms) disintegration of the universe if Big Crunch fails to materialize (or should I say rematerialize) can be found at the Nature Physics Portal (the http is to long to transcribe and wont copy for me) under the title “The Universe Can Surf The Big Rip” by Philip Ball. In turn the article references the original papers:

(1) Gonzalez-Diaz, P. F. You Need Not Be Afraid Of Phantom Energy, IMAFF-RCA-03-04.

(2) Caldwell, R.R, Kamionkowski, M. and Weinberg, N.N. Phantom Energy and Cosmic Doosday,

Both the article and the papers are accessable on the internet or inter-library loan. The two papers are heavy on the math but not to worry there is plenty of good text between equations. I was not aware not aware of the Big Rip was so significant until I read the articles. I also was unaware there was a spacecraft out there monitoring the acceleration of the universe and has confirmed some items talked about on this forum to high accuracies. This may change many peoples views.

Irizarry

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[budcamp]

The Hubble constant says that in the distant past the Universe was expanding very rapidly. The closer we get to the present the slower the Universe is expanding.

We generally hear the constant used to describe what happens to light shift based on how far away galaxies are from the Earth. The farther away the galaxies are, the faster they are receding and the higher their red-shift.

But the constant doesn't really deal with distance; it deals with time. If a galaxy is red-shifted is it necessarily moving away from us? Of course not! The blue-shifted light we see from Andromeda left there over two million years ago. All we know is that it was moving toward us two million years ago, not what it is doing today! Hubble deals with what was happening in the past, not with what is happening now.

The farther that we go into the past the faster the universe was expanding and the closer that we get to the present, the slower the universe is expanding. This is not theory, this is what we observe.

[cyberdyslo]

[QUOTE=irizarry]It has been proved by Hubble that galaxies in the universe are not static and are all receding (moving away) from our galaxy. It has also been determined that the farther away a galaxy is the faster it is moving (greater velocity of recession). These properties have been consolidated into the formula

v = H(0)r
Where
V = velocity of the receding galaxy
r = is the radial range to that galaxy
H(0) = Hubble’s constant

The spectral lines emitted by a galaxy is the physical property used to determine its velocity. And it is the Doppler redshift that ultimately gives the velocity. Again this property has been consolidated into the formula

lambda (0)/lambda(e) = 1 + s

where

lambda(0) = the wave length at which the spectral line is
observed
lambda(e) = the emitted wavelength of the spectral line
s = the redshift

both sides of the equation are unitless.

Recession velocities can be measured very accurately, however distances (as in r above) can not. There is also another constraint. The distribution of galaxies must be isotropic and expand uniformly. The problem here is - Does this mean that there must be uniform distribution locally (there are clumps of matter in local surveys that do not reflect uniform distributions)? Also there are two camps on what the value for H(0) should be and it has caused considerable debate. H(0) is either

45 – 60 km s^(-1)Mpc^(-1) or
75 – 100 km s^(-1)Mpc^(-1).

Again physical properties of the galaxies are very difficult to measure at great distances. The added constraint is that physical properties act the same locally as they do at great distances. Recent observations do not show a decrease in Hubble’s constant. Then again since it can’t be measured accurately any slight decrease would probably be attributed to systematic errors. Also in the standard cosmological model it is assumed (based on the Big Bang) that the universe’s expansion rate (Hubble’s constant) must have been greater at an earlier time and it is modified to indicate the decelerating effect of gravity. The assumption here is that gravity a long distance force has no limit. There are some other interesting effects such as the universe expands it also cools down. We are also in the matter epoch of the universe (that is the period of time were mater is condensating). If matter condensates and the universe cools then there are possibilities of new forces forming that have never existed before (maybe the 5th force, or the Lambda force, or the recently theorized Repulsion force).

So to answer your question, and a GREAT one, my opinion, we wouldn’t know if the expansion was slowing down if it were subtle but might if it were dramatic-then again new forming forces might actually hide this initially.

There is nothing like a straight forward confusing answer to nail down your thoughts!

Irizarry

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l am new to the site so l would like to greet you first and by the way l am highly impressed by your contributions.
however l have a slight problem when you say if l may quote you on your first paragraph "......and are all receding(moving away)from our galaxy."
dont you think that our these galaxies should be moving away from the centre of the cosmos (where the big bang originated) and that our galaxy is not located on the centre of the cosmos in fact it is also moving away from the centr of the cosmos

[irizarry]

Welcome Cyberdyslo! I am so glad this forum is growing. To me its the hip place to be.


I was told once by a friend who is much more a cosmologist than I am ….that the Big Bang does not have a center in the Euclidian Geometry sense. Although it is true in appearance everywhere we look it appears we are at the center, this is only because we cannot see the universe in any other perspective at this point in time. It is somewhat an anthropic observation but real scientists know this is an illusion and we are not at the center of anything but our own egos. The Big Bang sprang forth all over the universe simultaneously and if there is a center to this perspective it must be in some non-Euclidian topology. Note: If your creating a universe its not built a piece at a time. The smallest piece is in fact the whole universe till you add more to it.

Irizarry

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[Yazoo]

I hope this discussion is still active.

I have to agree with you budcamp. If it is true that the expansion of the universe was uniform and if it is true that galaxies we see at closer distances are moving away from us at a slower rate than galaxies at greater distances and if it is true that the closer galaxies provide a snapshot in time nearer to the present than the further galaxies, then unless, it’s an illusion caused by some other phenomenon, those galaxies appear to slowing down or decelerating. And unless some huge force can stop the deceleration, we’ll all make like the Beatles and come together, crunch!

What I’m not sure of is at what scale or distance are these observations taking place. We can observe apparent contraction in our local group of galaxies in a 2 million light year radius. Our Milky Way galaxy is and has been gobbling up other galaxies and globular clusters for some time. It’s widely accepted the Milky Way will merge with Andromeda. Our local group is part of the 75 million light year wide Virgo super cluster. Is our local group moving toward the center of our super cluster? Anybody have a reference they can post? The Virgo super cluster is just one of many super clusters near the great attractor and most super clusters exist with a 5 billion light year radius of the great attractor. Are they all moving towards the center of the great attractor? If not, why is it called “the great attractor”? Misnomer? It is possible that the great attractor is simply the center of a large-scale structure in the universe. Our local great attractor may be one of thousands of similar great attractors in a “great attractor super cluster”! Unfortunately, we will never see them if they exist. We will be gone billions and billions of years before their light reaches us.

So where does that leave us? If deceleration is occurring, we should be able to take our red-shift observations, work backwards in time and calculate when contraction will or did start. Right?

Anyone still interested in this topic or have you already figured it out?

[André Landreau]

They can never be seen again, because they are receding from us at way over the speed of light. They are now at least 30 billion light-years away from us.

:confused:
Do you mean that Univers expands faster thant light speed ?
Or that we go in opposite direction at 45% of light speed ?
André.

[budcamp]

Matter can not move in exccess of the speed of light. However, space can expand at faster than the speed of light and cause mater in two diferent places to move apart faster than the speed of light. That is, of course, if space is still expanding.

Bud